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Rapid casting solutions: a review Munish Chhabra Department of Mechanical Engineering, Moradabad Institute of Technology, Moradabad, India, and Rupinder Singh Department of Production Engineering, Guru Nanak Dev Engineering College, Ludhiana, India Abstract Purpose – This paper seeks to review the industrial applications of state-of-the-art additive manufacturing (AM) techniques in metal casting technology. An extensive survey of concepts, techniques, approaches and suitability of various commercialised rapid casting (RC) solutions with traditional casting methods is presented. Design/methodology/approach – The tooling required for producing metal casting such as fabrication of patterns, cores and moulds with RC directly by using different approaches are presented and evaluated. Relevant case studies and examples explaining the suitability and problems of using RC solutions by various manufacturers and researchers are also presented. Findings – Latest research to optimize the current RC solutions, and new inventions in processing techniques and materials in RC performed by researchers worldwide are also discussed. The discussion regarding the benefits of RC solutions to foundrymen, and challenges to produce accurate and cost-effective RC amongst AM manufacturers concludes this paper. Research limitations/implications – The research related to this survey is limited to the applicability of RC solutions to sand casting and investment casting processes. There is practically no implication in industrial application of RC technology. Originality/value – This review presents the information regarding potential AM application – RC, which facilitates the fabrication of patterns, cores and moulds directly using the computer-aided design data. The information available in this paper serves the purpose of researchers and academicians to explore the new options in the field of RC and especially users, manufacturers and service industries to produce casting in relatively much shorter time and at low cost and even to cast complex design components which otherwise was impossible by using traditional casting processes and CNC technology. Keywords Additive manufacturing, Rapid casting solutions, Rapid investment casting, Rapid sand casting, Metalworking industry, Foundry engineering, Sand casting, Investment casting Paper type General review Abbreviations 3DP Three dimensional printing ABS Acrylonitrile-butadiene-styrene AM Additive manufacturing BPM Ballistic Particle manufacturing CAD Computer-aided design DMLS Direct metal laser sintering DSPC Direct shell production casting EARP European action on rapid prototyping EOS Electro optical system FDM Fused deposition modelling IC Investment casting IT International tolerance LENS Laser engineered net shaping LOM Laminated object manufacturing MMII Model maker II MSFC Marshal Space Flight Center PS Polystyrene RC Rapid casting RCT Rapid casting technique RIC Rapid investment casting RP&T Rapid prototyping and tooling RTV Room temperature vulcanizing SL Stereolithography SLS Selective laser sintering ZCorp ZCorporation 1. Introduction After nearly 20 years of research, development and use, the additive manufacturing (AM) industry continues to grow with the addition of new technologies, methods and applications (Wohlers, 2007). In the early development of AM technologies, the emphasis was directed towards the creation of “touch-and-feel” models to support the design (Chua et al., 1998). But, because of frequent changing requirements of manufacturing industry due to short product life cycles, fickle consumer demands, complex shaped designs, higher quality, reducing the cost and time to The current issue and full text archive of this journal is available at www.emeraldinsight.com/1355-2546.htm Rapid Prototyping Journal 17/5 (2011) 328–350 q Emerald Group Publishing Limited [ISSN 1355-2546] [DOI 10.1108/13552541111156469] The authors are thankful from the core of their hearts to Avi Cohen (Head of Medical Solutions Objet Geometries LTD), Joe Hiemenz (Stratasys, Inc.) and Ellen J. Kehoe (Senior Editor, Publications SME) for granting permissions to use figures from their sources. The authors are grateful to Management, Director General Prof. R. Yadav and HOD ME Prof. Vineet Tirth of Moradabad Institute of Technology, Moradabad for motivation and moral support. Received: 6 December 2009 Revised: 17 February 2010, 26 June 2010, 6 September 2010, 4 November 2010 Accepted: 7 November 2010 328

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Page 1: Rapid Casting

Rapid casting solutions: a reviewMunish Chhabra

Department of Mechanical Engineering, Moradabad Institute of Technology, Moradabad, India, and

Rupinder SinghDepartment of Production Engineering, Guru Nanak Dev Engineering College, Ludhiana, India

AbstractPurpose – This paper seeks to review the industrial applications of state-of-the-art additive manufacturing (AM) techniques in metal castingtechnology. An extensive survey of concepts, techniques, approaches and suitability of various commercialised rapid casting (RC) solutions withtraditional casting methods is presented.Design/methodology/approach – The tooling required for producing metal casting such as fabrication of patterns, cores and moulds with RC directlyby using different approaches are presented and evaluated. Relevant case studies and examples explaining the suitability and problems of using RCsolutions by various manufacturers and researchers are also presented.Findings – Latest research to optimize the current RC solutions, and new inventions in processing techniques and materials in RC performed byresearchers worldwide are also discussed. The discussion regarding the benefits of RC solutions to foundrymen, and challenges to produce accurate andcost-effective RC amongst AM manufacturers concludes this paper.Research limitations/implications – The research related to this survey is limited to the applicability of RC solutions to sand casting and investmentcasting processes. There is practically no implication in industrial application of RC technology.Originality/value – This review presents the information regarding potential AM application – RC, which facilitates the fabrication of patterns, coresand moulds directly using the computer-aided design data. The information available in this paper serves the purpose of researchers and academicians toexplore the new options in the field of RC and especially users, manufacturers and service industries to produce casting in relatively much shorter time andat low cost and even to cast complex design components which otherwise was impossible by using traditional casting processes and CNC technology.

Keywords Additive manufacturing, Rapid casting solutions, Rapid investment casting, Rapid sand casting, Metalworking industry,Foundry engineering, Sand casting, Investment casting

Paper type General review

Abbreviations

3DP Three dimensional printingABS Acrylonitrile-butadiene-styreneAM Additive manufacturingBPM Ballistic Particle manufacturingCAD Computer-aided designDMLS Direct metal laser sinteringDSPC Direct shell production castingEARP European action on rapid prototypingEOS Electro optical systemFDM Fused deposition modellingIC Investment castingIT International toleranceLENS Laser engineered net shapingLOM Laminated object manufacturingMMII Model maker IIMSFC Marshal Space Flight CenterPS PolystyreneRC Rapid castingRCT Rapid casting technique

RIC Rapid investment castingRP&T Rapid prototyping and toolingRTV Room temperature vulcanizingSL StereolithographySLS Selective laser sinteringZCorp ZCorporation

1. Introduction

After nearly 20 years of research, development and use, the

additive manufacturing (AM) industry continues to grow with

the addition of new technologies, methods and applications

(Wohlers, 2007). In the early development of AM

technologies, the emphasis was directed towards the

creation of “touch-and-feel” models to support the design

(Chua et al., 1998). But, because of frequent changing

requirements of manufacturing industry due to short product

life cycles, fickle consumer demands, complex shaped

designs, higher quality, reducing the cost and time to

The current issue and full text archive of this journal is available at

www.emeraldinsight.com/1355-2546.htm

Rapid Prototyping Journal

17/5 (2011) 328–350

q Emerald Group Publishing Limited [ISSN 1355-2546]

[DOI 10.1108/13552541111156469]

The authors are thankful from the core of their hearts to Avi Cohen(Head of Medical Solutions Objet Geometries LTD), Joe Hiemenz(Stratasys, Inc.) and Ellen J. Kehoe (Senior Editor, Publications SME) forgranting permissions to use figures from their sources. The authors aregrateful to Management, Director General Prof. R. Yadav and HOD MEProf. Vineet Tirth of Moradabad Institute of Technology, Moradabad formotivation and moral support.

Received: 6 December 2009Revised: 17 February 2010, 26 June 2010, 6 September 2010,4 November 2010Accepted: 7 November 2010

328

Page 2: Rapid Casting

market for new product and shorter product development

times, industry has been searching solutions for fabricating

direct metal parts since the earliest day of AM. Presently,direct metal fabrication AM technologies (also called as rapid

manufacturing) are used in a wide variety of industries, from

automotive and aerospace to electronics and dentistry(Wohlers, 2006). There are only few AM techniques

available which can manufacture metal parts directly, but

they are just the tip of the iceberg.Although, direct manufacturing of metal parts with AM is not

well developed, indirect methods have been found and shownfeasible through the combination of AM and traditional metal

casting (Detlef et al., 1999). The application of AM in metal

casting process to produce metal cast parts is regarded as rapidcasting (RC). The most important part for any casting process is

to design and produce pattern for the production of moulds intowhich to cast metal. Further, for some casting processes

(like sand casting), designing and preparation of core boxes and

gating system upon which the overall quality of casting dependsare most time consuming and costly process especially in case of

complex design castings. The use of AM technologies in the

creation of casting patterns allows a foundry to manufacture ametal part without the use of tooling for small quantities

(Rosochowski and Matuszak, 2000). In particular, patterns,

cores and cavities for metal casting can be obtained through RC(Wang et al., 1999; Bernard et al., 2003; Chua et al., 2005). The

relevance of RC techniques consists, above all, in a short timefor part availability. Traditionally, in order to produce cast

prototypes, a model and eventual cores have to be created

involving time and costs that hardly match the rules ofcompetitive market (Bassoli et al., 2007). Now, it is possible to

fabricate a complex pattern and other tooling required for

casting in a matter of hours and provide a casting in a matter ofdays.

The art of foundry is ancient, dating back to the dawn ofcivilization. It is a revolutionary change in manufacturing

industry that one of the oldest metal manufacturing

techniques, which dates back to 4000-6000 BC, is beingused with one of the most modern technology-rapid

prototyping. The first use of AM-fabricated patterns as

sacrificial patterns in traditional investment casting (IC)started in 1989 (Greenbaum and Khan, 1993). Since then all

major AM techniques have been used in different castingmethods to provide RC solution for producing metal parts.

The aim of this paper is to present valuable information

about the application of AM in investment and sand castingtechnology. A little step has been taken to collect and review

the information available about commercialised RC solutions

invented by various researchers and technocrats in order toprovide information and implementation of concurrent

engineering approach in producing prototype, pre-series andfor customized production metal casting to manufacturing

industry. In order to explain how RC solutions may be

successfully used in foundry applications, a few examples andcase studies have also been included. A list of various major

commercialised RC solutions based on different AM

processes and their suppliers is presented in Table I.

2. AM applications in IC

IC is a precision casting process which employs wax pattern assacrificial pattern to produce solid-metal parts. These

sacrificial patterns are used to create a ceramic mould by

investing refractory ceramic coatings on the patterns. Oncompletion of the coating, the expandable wax patterns areremoved at about 1408C and 200 KPa in a steam autoclave(Groover, 1996). The mould is further hardened by heating,the procedure called “firing”, and the molten metal is thenpoured while it is still hot. When the casting is solidified, themould is broken and the casting taken out during theknockout process (Jain, 2009). IC produces high quality andgeometrically complex near net shaped metal parts with tighttolerances economically in case of mass production. Theeconomic benefits of IC are limited to mass production.

Limitations of traditional IC:. Traditional IC requires the production of metal tooling for

the injection of wax material to produce sacrificial patternswhich leads to cost justification problems for prototyping,pre-series, customized and single casting and small andmedium quantity production.

. Major part of the total lead time is consumed inproduction of metal tooling required for wax patterngeneration.

. Before committing to manufacturing, numbers of designiterations are performed by tool makers by evaluatingdifferent mould design which further incorporate anadditional cost and lead time (Beaman et al., 1997).

2.1 Rapid investment casting (RIC)

The term RIC represents the employment of RP&T techniquesin IC (Cheah et al., 2005). The cost involved in designing andfabrication of metal tooling for wax injection process can beovercome by using AM techniques to fabricate sacrificialpatterns for IC. AM also facilitates to reduce the overall leadtime involved in production of prototype casting with excellentquality. By employing AM-fabricated patterns to produce theprototypes, there is no need to commit to production tooling forsingle part or small quantity production (Chua et al., 2005). AMtechniques provide various cost effective solutions by which pre-series casting can be produced very economically. Presently,almost all commercialised AM techniques have been employedto produce IC patterns with varying success and many RCsolutions in IC are being used by various industries andresearchers.The use ofAM in IC is in three basic forms.Figure 1shows the three basic approaches used as RC solutions in RIC.

3. Direct fabrication of IC sacrificial patterns(approach1)

AM techniques have been employed to produce direct ICsacrificial patterns in wax and non-wax forms for producinginvestment cast parts.

Direct wax IC patterns

The selective laser sintering (SLS), Fused depositionmodelling (FDM), stereolithography (SL) and model makerII (MMII) systems have been found capable of producing waxpatterns, which can be used directly in IC (Dickens et al.,1995; Chua et al., 2005). The main problem of using directwax patterns is the brittleness of waxes and due to that thereare chances of damaging of these patterns while transportthem to foundry. These are also not recommended for thinwall castings.

Direct non-wax IC patterns

The non-wax patterns are having strength, durability andtoughness by which these can be used to produce thin

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

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wall castings. Non-wax patterns also allow finishing operations

for improving the surface quality of patterns which further

improve the surface quality of final casting. The problem of

ceramic shell cracking and two other main problems related to

incomplete pattern burning out and residual ash have been

observed and reported by various researchers during the use of

non-wax patterns for IC. Case study 1 explains the project

performed by tooling and casting subgroup of the European

action on rapid prototyping (EARP) to investigate the

problems associated with using AM sacrificial wax and non-

wax patterns for IC. Introduction and practical application of

major commercial RIC solutions based on direct fabrication of

IC patterns are presented in following sections.

3.1 RIC using FDM technique

The Stratasysw FDM-AM system offers a different approach

as compared to traditional IC method practiced by thousands

of IC foundries across the world. This AM technique is used

Table I Commercialised RC solutions & their application in metal casting

AM process Manufacturer RC solution and their applications in metal casting

Stereolithography (STL) 3D systems Quick Cast 1.0, Quick Cast 1.1 and QuickCast 2.0 patterns for IC

Epoxy patterns for sand casting and soft tooling

OPTOFOTM patterns for sand casting

EOS EOS-stereolithography (acrylate resin) patterns for IC

Selective laser sintering (SLS) DTM Corp.

(presently 3DSystems)

Investment casting wax, polycarbonate and TrueForm pattern for IC

Rapid tool for direct fabricating moulds for IC

TrueForm, composite nylon, polycarbonate for sand casting and soft tooling

CastForme PS patterns for IC

CRP Tech WindFormwPS patterns for IC

EOS EOSINT-S laser sintering AM to produce sand casting moulds and cores

directly from CAD solid model using polymer coated green sand

EOSINT – P IC patterns fabricating using polystyrene material

Fused deposition modelling (FDM) Stratasys Wax & ABS patterns for IC

ABS patterns and core boxes for sand casting

Laminated object manufacturing (LOM) Helisys

(Currently Cubic Tech.)

Laminated paper master patterns for sand casting and IC

Drop-on-powder deposition inkjet

printing technology(3DP)

Soligen DSPC for ceramic investment casting mould fabricated directly from CAD

solid model

ExOne ProMetal RCT to produce sand casting moulds and cores directly form CAD

files

ZCorporation Starch patterns for IC

Plaster based material patterns for sand casting

ZCaste direct metal casting process for sand casting

Drop-on-drop deposition inkjet printing technology Objet PolyJete for photopolymer resin patterns for sand casting

3D systems Thermojet for producing wax patterns directly for IC

Solidscape

(Sanders prototype)

MM II pattern for IC

Solid ground curing Cubital Wax patterns for IC

Ballistic particle manufacturing BPM Wax pattern for IC

Figure 1 Approaches used as rapid casting solutions in rapid investment casting

Rapid investment casting

RP-fabricated mouldsfor wax injection

(approach2)

Wax patterns Non wax patterns

RP-fabricated ICsacrificial patterns

(approach1)

Direct fabrication ofceramic IC shell moulds

(approach3)

Direct toolingIndirect tooling

Rapid casting solutions: a review

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Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

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Page 4: Rapid Casting

to create pattern directly from either acrylonitrile-butadiene-

styrene (ABS) or wax materials. Both wax and ABS patterns

constructed from the FDM process have proven to be suitable

for burn out from the ceramic shell with minimal modification

to the standard foundry processes (Grimm, 2003). The parts

produced by FDM-ABS have a much higher surface

definition than those produced in wax, owing to the good

powdering characteristics of the ABS, which allows final

surface finishing to be carried out[1]. The key strength of

employing FDM-fabricated pattern over MMII-fabricated

patterns includes short-built time for the process to build a

part. For the build of the benchmark model, MMII process

took more than 80 hours while the FDM process took only

16 hours (Chua et al., 2005). The use of this RIC solution is

presented as a case study in Section 3.1.1.

3.1.1 Case study: RIC using direct FDM-ABS patternsGouldsen and Blake (1998) reported the results of a program

in which six foundries had participated to evaluate the use of

ABS parts created from FDM-AM system as a substitute for

the injected wax patterns in RIC. In IC with this approach, wax

gates and vents are attached to the ABS pattern by the foundry.

The ceramic slurry is then invested on the pattern to make

ceramic shell similar to traditional IC process. Now the major

difference in this approach is that the shell is placed into a flash

fire furnace where temperatures reach upward of 1,0938C and

the pattern combusts, giving off gas possibly leaving a small

amount of ash in the hollow shell mould. The gates and vents

allow gas to escape the mould during burn out and allow

molten metal to be poured into the mould. An autoclave may

not be used, because the ABS thermoplastic does not melt at

those relatively low temperatures (approximately 3508C)

(Jain, 2009). The shells are removed from the furnace and

inspected for cracks and residual ash. If any ash remains, it is

removed by rinsing or high-pressure air. From this point on,

apart from having to reheat the moulds, there is no difference

in the process than if wax were being used.Based on the results demonstrated by all participated

foundries, the authors claimed that the patterns built from

FDM-ABS offer a number of quality advantages over patterns

made by other AM processes, namely, clean burn-out,

robustness, the ability to be handled without damage,

dimensional stability and ease of pattern preparation. One

major disadvantage with this approach is that the surface layer

and built style produces a very rough surface condition. So,

surface finish preparation of the pattern is important to

achieve the best results.Example: Hydro Quebec, an electrical power company in

Canada has been producing IC since 1997. Figure 2 shows a

set of six FDM-ABS patterns that were cast in aluminium at

Shellcast in Montreal, Canada.

3.2 RIC using MMII technique

Solidscape’s MMII system based on drop-on-drop deposition

inkjet printing technology uses two drop-on-demand inkjets to

build patterns. One inkjet is used for build material

(thermoplastic) and the other is for support material (wax).

The supports are removed by washing it away with an ATOS

solvent (Chua et al., 2005). The important feature of MMII is

that it is the highest resolution additive process having capability

to build fine castings from wax patterns using 0.0125 mm thick

layers (Wohlers, 1995a). Each layer is milled resulting in very

precise models that are especially well suited for the precision

casting of precision parts (Gebhardt, 2003). The feasibility ofemploying MMII system to fabricate sacrificial IC patterns byusing direct and indirect tooling approach is presented as casestudy in Sections 3.2.1 and 4.2, respectively.

3.2.1 Case study: RIC using MMII fabricated patternsThe feasibility of employing patterns fabricated by MMII assacrificial IC patterns to produce metal casting was studied byChua et al. (2005). The build material “protoform” is used inMMII system having the properties similar to those of thefoundry wax material. Researchers investigated two castingsolutions by using MMII-AM system. The first is by usingMMII fabricated pattern directly as sacrificial IC pattern(approach1) and second solution is an indirect tooling(approach2) involving the utilization of room temperaturevulcanizing (RTV) silicon rubber moulding with an MMII-fabricated master pattern to produce sacrificial IC-wax pattern.The researchers claimed better accuracy by employing MMII-fabricated patterns over FDM-fabricated patterns.

In the direct method, the MMII-fabricated pattern wasdirectly used as a sacrificial pattern in IC. Researchersinvestigated this approach to produce aluminium alloy IC andclaimed that:. The microstructure of MMII part was built more densely

as compared to FDM or SLS.. There was no porous structure in MMII part and no

sealing or coating was needed on the MMII part surface.. The pattern produced in this approach melted off at

relatively low temperatures with little or no residual ashleft (due to similarity between material characteristics ofMMII patterns and foundry wax).

. No sign of shell mould cracking was observed during theIC process.

. By using direct approach, there is a significant amount oftime saving and cost saving can be achieved as comparedto the conventional metal tooling method for patternproduction.

. This approach will be economical when only three to fivemodels are required and component having complicateddesign.

3.3 RIC using QuickCast 1.0 technique

A problem of ceramic shell cracking has been reported byvarious researchers while using non-wax AM patterns in IC.One example is use of SL’s acrylic patterns, which expandduring burn-out process and crack the ceramic shell duringIC. The latest method is the 3D system’s QuickCast buildstyle (consisted of triangular geometry), which eliminates95 per cent of the internal mass of a part made of epoxy resin(Rosochowski and Matuszak, 2000). The concept ofQuickCast is based on the fact that hollow structures wouldsoften at lower temperatures and collapse inwards upon itselfbefore critical stress levels are developed (Jacobs, 1993). Theidea of QuickCast is to build the pattern such that it collapsesinwards under the influence of heat, rather than expandingoutwards and cracking the ceramic shell (Yao and Leu, 1999).Using QuickCast, users can produce patterns for metalcastings in a fraction of time (Wohlers, 1995b). Aluminium,titanium, stainless steel, tool steel and copper alloys have allbeen cast successfully using IC with QuickCast patterns atFord (McMains, 1995) and QuickCast has also successfullyapplied for building tooling required for production of plasticparts, casting patterns, dies and other tooling item in Fordmotor company (Denton, 1994).

Rapid casting solutions: a review

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Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

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3.3.1 Case study: project of EARPEARP has carried out a project to find out the problemsassociated with using AM models as sacrificial pattern for IC by

accessing the accuracy and surface finish of the models andcastings (Dickens et al., 1995). Models were manufactured bydifferent AM processes, namely, 3D systems-QuickCast 1.0,

DTM-SLS, Cubital – Solider (waxes from acrylic mould),FDM (wax models), laminated object manufacturing (LOM),

electro optical system (EOS)-SL and three foundries were usedto produce casting from a given set of models. The project wascompleted in three phases: computer-aided design (CAD)

modelling, AM model productions and IC.The CAD modellingwas performed on pro-engineer and a stereolithography (STL)

file supplied to different AM machines to produce models forIC. Some models received surface finishing to smoothing thesurface by abrasive bead blasting.

The most accurate sets of models were produced by 3Dsystems – QuickCast and from DTM Corporation’s SLS

among all AM processes.The greatest variation was observedonSL models. Three foundries were used to produce aluminium

ICs from the model received from different AM processes.

Major findings of the project. Most models did not suffer any damage during

transportation to foundries except those from FDM.. Owing to porous structure of SLS models, researchers

reported that a sealing with thin layer of wax must beemployed to SLS models before investing the shell

material. Figure 3 shows the results of casting producedby using sealed SLS model and not sealed SLS model.

. The great surprise from the results of this project was thelack of accuracy observed in various models. Models fromall the AM processes were much less accurate than

expected. The 3D system’s – QuickCast models weregenerally the most accurate and these models also

produced the most accurate castings.

3.4 RIC using QuickCast 1.1 & QuickCast 2.0

Ashley (1995) reported various problems of using patternsfabricated with QuickCast1.0 in IC. Major problem is theformation of pinholes during the removal of supports from

downward-facing surfaces, which led to the ceramic slurryentering the casting pattern’s interior. QuickCast parts often

exhibited drainage and void-ratio problems, especially in thin-curved sections. Finally, the less-than-optimal 80-per centyield of aerospace industry-acceptable castings attainable with

QuickCast 1.0 was found to be caused primarily by shell

cracking due to solid, incompletely drained patterns with low-

void ratios. To overcome these problems 3D systems

introduced QuickCast 1.1 (Jacob, 1995). This involved the

change in the geometry of build style from triangular to

square. The build style features triple up-facing and down-

facing skins 27 times stronger than they were previously,

which eliminate pinholes and sag which further improve the

surface finish. With these features QuickCast1.1 produced

lower expansion stresses on ceramic IC shells; bringing

casting yields up to 95 per cent. QuickCast 1.1 is being used

to produce castings of unprecedented quality from an AM

pattern (Wohlers, 1995b). The another development in this

process is the development of QuickCast 2.0, which is the

result of the involvement of changing the build style from

square to an “offset” hexagon. QuickCast 2.0 patterns

produce less than one-third the shell stress of QuickCast 1.1

during pattern burnout, significantly reducing the probability

of shell cracking (Hilton and Jacob, 2000).

3.5 RIC using Thermojet technique

Thermojet modeller based on the drop-on-drop deposition

inkjet printing technique (Dimitrov et al., 2008) is the ideal

wax prototyping machine. Using 3D-CAD data files in STL

format, the part to be cast can be programmed for the current

shrink and orientation. This AM technique produces patterns

by additively spraying layers of tiny wax droplets on to a

platform surface, much like an inkjet printer. These wax

patterns are used directly in IC and having ability to be

autoclaved easily. This process has been accepted widely

within the industry owing to the ease of use within the

foundry (Tromans, 2004). Thermojet from 3D systems is

capable of producing parts very quickly, whereas the Model

Maker series from Solidscape produces fine detailed parts,

but is rather slow (Hopkinson, 2002).

3.6 RIC with three dimensional printing (3DP)

technique using Zp14 pattern material

Starch-based Zp14 material is introduced by ZCorp to

produce parts which after infiltration with wax are used

extensively as patterns for IC without using moulds[2]. This

Zp14 material is used to fabricate patterns for IC by printing

on ZCorp’s 3DP machines. Then a ceramic shell is invested

on the pattern using traditional IC method and then

evacuated to obtain the cavity for pouring metal. Figure 4

shows the process stages of producing 3,16l exhaust

manifold of a racing car using this RC solution at

Figure 2 Aluminium investment casting using FDM ABS patterns

(a)Notes: (a) ABS patterns; (b) Al castingsSource: Gouldsen and Blake (1998)

(b)

Rapid casting solutions: a review

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Rapid Prototyping Journal

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University of Michigan[3]. Bassoli et al. (2007) has verifiedthe feasibility to produce thin-walled parts and evaluated thedimensional accuracy of the patterns and the parts producedby using this RC solution.

3.6.1 Case study: project of Marshal Space Flight Center (MSFC)(sponsored by NASA)Copper and Wells (2000) have evaluated the capabilities ofvarious AM processes and produced quality test hardwaregrade IC models at MSFC, a sponsored project by NASA,Washington, DC. The IC patterns of a selected propulsionhardware component, a fuel pump housing, were rapidprototyped on several AM processes. Table II shows the AMprocesses with pattern materials used to cast the selectedcomponent for this study. The shelled models were fired andcast with NASA-2, a test hardware material. Researchers havereported after this investigation that each AM processes wereof varying degrees of success and each proved a significantcost advantage over conventional manufacturing techniques.

The major findings of this research. The SLS-TrueForm model provided the most acceptable

casting followed by FDM-wax and SLS pattern built

15 times faster than FDM pattern (four hours verses

65 hours).. The least expensive model was the ZCorp pattern, which

also was the fastest to complete at 3.5 hours, and also one

of the least accurate.. Researchers recommended that the ZCorp patterns will

be more suitable for initial prototype casting, i.e. near-net-

shape castings.

Figure 3 Aluminium casting

(a)

Notes: (a) Using not sealed SLS model; (b) using sealed SLS modelSource: Dickens et al. (1995)

(b)

Figure 4 Investment casting of 316 l exhaust manifold of a racing car using Zp14 IC patterns

(a) (b)

Notes: (a) CAD model; (b) starch pattern; (c) shell moulds; (d) final casting[3]

(c) (d)

Table II AM processes with pattern materials used for MSFC project

S. no. AM process Pattern material

1 SLS Polycarbonate casting pattern material

2 SLS Trueform polyamide

3 FDM IC wax

4 LOM High performance paper

5 3DP (ZCorp) Starch (cellulose)

6 FDM ABS plastic

7 Stereolithography (SL) Epoxy 1570

8 MMII IC resins

Rapid casting solutions: a review

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3.7 RIC with SLS technique using CastForme

polystyrene pattern material

CastForme (CF) polystyrene (PS) is a polystyrene – basedmaterial developed by DTM Corp. in 1999 to fabricate ICpatterns by using SLS machines (DTM Corporation, 1999).Presently, 3D systems Corp[4] is the supplier of CF material,which acquired DTM in 2001. SLS system using CF materialis one of the fastest and most cost-effective techniques forrapid fabrication of small quantities of wax-like patterns forIC. CF is a low-ash pattern material that produces high-quality castings, even with high-reactive alloy such astitanium[5]. The pattern fabrication using this techniqueinvolves two stages: first the building of green part, and secondits infiltration with wax (Dotchev et al., 2007). The main ideabehind this two-stage process is to fabricate a pattern withproperties very close to those of conventional wax patterns,and therefore, and to be compatible with standard foundrypractices for IC. Post – processes necessary for CF patternsinclude dipping in liquefied wax to seal surface porosity and toincrease pattern strength (Cheah et al., 2005). Dotchev andSoe (2006) analyzed experimentally all stages of CF patternfabrication process and reported that the cleaning and waxinfiltration are the main leading reasons for inferior quality,part distortion and breakage. CRP Technology[6], a divisionof the Cevolini Group, is the first to use CF material forfabrication of IC patterns with DTM-SLS system for RC ofhard to cast shapes of Minardi F1 car components (uprights,suspension supports, clutch box, steering box and gear box)with the titanium alloy (Ti-6Al4V)[7]. With the combinationof SLS and CF formula, CRP saved cost and time to producecomponents having very complicated shapes and geometriesand gained freedom to investment cast parts in the alloy ofchoice (Titanium, Aluminium, Steel alloys or Super alloys)[8].Figure 5 shows the CF disposable pattern fabricated forF1upright titanium RC.

3.8 RIC with SLS technique using Windformw PS

pattern material

Windformw PS is a new PS-based material developed by CRPTechnology to fabricate IC patterns using SLS technique[9].It is particularly suited for the foundry, since the main

applications are fabrication of complex IC patterns and

casting with highly reactive alloys like titanium, in addition totypical cast alloys. Compared to other polystyrene materials

available, Windformw PS has:. improved surface quality and details reproduction; and. very low-ash content suitable for highly reactive alloys,

namely, Ti, Al, Mg, steel and Ni alloys.

4. Fabrication of moulds for producing IC-waxpatterns (approach2)

For producing large quantity of IC-wax sacrificial patterns, itis feasible to employ wax injection mould fabricated byvarious AM techniques. For mould fabrication, further two

approaches, namely, direct tooling and indirect toolingapproaches are used which are further classified as soft and

hard tooling (Chua et al., 1999). In direct tooling approach,the mould fabricated by AM techniques will not use any

intermediate steps. For improving the accuracy, strength andsurface finish of moulds, some post-processing techniques

may be used. In indirect tooling approach, AM fabricatedmaster patterns are employed to create the necessary moulds.

The materials used for fabrication of moulds in indirecttooling are polymers and silicon rubbers, which result in

relatively weaker moulds. Different direct and indirect toolingapproaches for fabrication of moulds for producing IC-wax

patterns have been reported by various researches (Chua et al.,1999; Rosochowski and Matuszak, 2000; Dickens et al., 2000;

Cheah et al., 2005).Direct tooling. In this approach, moulds fabricated on AM

machines are used for fabricating multiple wax patterns (Paland Ravi, 2007). Some pioneering processes such as direct

metal laser sintering (DMLS), Rapid Tool, ProMetal, LENSand DirectAIM have been used successfully for direct

fabrication of moulds for producing wax patterns. Thisapproach is employed in medium to high-volume production

and when reduction in time-to-market the product is majorgoal for manufacturer (Karapatis et al., 1998).

Indirect tooling. This approach involves fabrication of mouldfrom an AM master pattern, which is used for fabricating wax

IC patterns. Silicon rubber tooling (RTV), Epoxy resintooling, Keltool tooling and Spray metal tooling as indirect

approach for mould fabrication have been applied successfullyfor moulding wax patterns (Smith et al., 1996). All of them,

like the best-known called “Silicon rubber tooling (RTV)”, donot relate directly to AM, but are used for fabrication of

moulds by using AM master patterns. In silicon rubbertooling process, the AM master pattern is equipped with

runners put in a frame and covered with silicon rubber. Afterhardening, the solid block of silicon rubber is cut according to

the parting line and the master is removed, leaving therequired cavity. The resulting cavity is cast with wax, which

used as wax pattern in IC. Figure 6 shows the steps involvedin fabrication of IC-wax pattern using silicon rubber tooling.

Practical application of indirect tooling for mould fabricationusing FDM-ABS and MMII master patterns are presented in

Sections 4.1 and 4.2, respectively.

4.1 Case study: RIC using FDM-ABS pattern and wax

pattern moulded through RTV moulds, moulded by

FDM ABS master pattern

Lee et al. (2004) investigated the feasibility of employing

FDM process to built sacrificial IC patterns (using direct

Figure 5 CF disposable pattern (laser sintering and red wax infiltration)fabricated for F1Upright Titanium rapid casting

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and indirect approach) by using ABS material to produce metal

casting rapidly. Researchers investigated and compared the

FDM system, FDM3000 for creating direct sacrificial IC

pattern in ABS material and by producing injected wax pattern

via silicon rubber moulding (indirect tooling approach). The

study showed substantial advantages when employing ABS

models as direct IC patterns or as master patterns for producing

silicon rubber moulds to cast wax IC patterns in terms of cost

and time savings, relatively accurate final castings with

reasonable surface quality and the complete elimination of

hard tooling required in conventional IC process. The

researchers claimed that it is much more beneficial for

foundries to employ FDM-ABS-fabricated patterns in IC for

single or small quantity production of castings (,5) and to

employ the indirect approach of fabricating IC patterns via

silicon rubber moulding for medium quantity (tens of casting)

production.

4.2 Case study: RIC using wax pattern moulded through

RTV moulds fabricated with MMII master pattern

In this approach, researchers have employed an MMII-

fabricated master pattern to create RTV silicon rubber mould

(Chua et al., 2005). From the rubber mould, wax patterns

were cast and used as sacrificial pattern in IC. Researchers

claimed that this approach will be more economical to

fabricate a silicon rubber mould with MMII fabricated master

pattern and produce wax pattern from the silicon rubber

mould for IC when several tens of models are required.

5. Direct fabrication of ceramic IC shell(approach3)

This RC technique fabricates the ceramic mould (negative)

with integral cores directly from the CAD model for the IC of

metals. This technique provides a greater advantage over

traditional IC method and other RIC techniques by removing

the steps of wax pattern generation, ceramic shell production,

autoclaving and firing of mould. An introduction of

commercialised RC solution “Direct shell production

casting (DSPC)” based on this approach is given in

Section 5.1. The major advantages of this technique are:. Reduction in cost and lead time (in traditional method,

making of metal dies for production of wax pattern are

typically expensive and time consuming, with lead time

ranging from two to six months).. Less risk of damaging of shells during transportation by

preserving dimensional tolerances.

. No risk of core shifting in casting of complex shapes that

require core inserts, because shell and core are fabricated

as a single structure.. Furthermore, cores can be made hollow, leaving less

material to be leached out.. It is possible to adjust the ceramic shell thickness during

fabrication, which further helps to control the rate of heat

transfer from the casting.

5.1 Direct shell production casting

Soligen Technology Inc. (Northridge, CA) is one of the

licensees of 3DP AM technology developed at the MIT

(Cambridge, MA) and produced DSPC system in 1993[10].

By using 3DP AM technique, this system directly fabricates

the ceramic moulds (negative) with integral cores for IC of

metals. This eliminates the need for wax patterns and tooling

for cast metal parts (Wohlers, 1992). The DSPC process

utilizes the bonding approach and requires post processing

(Carrion, 1997). In this process, alumina (refractory)

powders are held together through the spraying of colloidalsilica binder with multi-jet print head. The unbound powder

is removed and the resulting shell is fired to create a rigid

ceramic mould prior to pouring the molten metal of any

castable alloy. DSPC can be used to produce parts of virtually

any shape. Diverse metals, including copper, bronze,

aluminium, cobalt chrome, stainless steel and tooling steel,

have been successfully cast in the ceramic shells produced by

this process. Metal parts can generally be produced in two to

three days (McMains, 1995). Sachs et al. (1991) reported the

use of DSPC-fabricated ceramic shells for production of

nickel super alloy casting. DSPC is used for fabrication of

prototype and small quantity of fully functional castings.Figure 7 shows a metal casting of an automotive component

produced by using DSPC process. Figure 8 shows the

orthopedic knee casting using ceramic mould made by 3DP.

6. AM applications in sand casting

Sand casting is the most widely used casting process inmanufacturing industry in which components are cast by

pouring liquid metal into the cavity of sand mould. Among

the sand casting processes, moulding is most often done with

green sand, which is a mixture of sand grains, clay, water and

other materials, which can be used for moulding and casting

processes (Heine et al., 1997). The detailed process sequence

for sand casting is shown in Figure 9 (Groover, 1996). The

basic steps involved in sand casting processes are:

Figure 6 Steps involved in fabrication of IC-wax pattern using silicon rubber tooling

(a) (b)

Notes: (a) CAD model; (b) SLA fabricated master pattern; (c) RTV mould; (d) Wax pattern for ICSource: Pal and Ravi (2007)

(c) (d)

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. preparation of the pattern;

. making the mould (ramming of sand around the pattern,

gating system for the entry of the molten metal);. core making and core setting in mould;. closing and weighting; and. pouring liquid metal into the cavity;

6.1 Rapid sand casting

Traditionally, for sand casting process, skilled workers used to

fabricate patterns and core boxes by taking design data either

from 2D drawings or from hand crafted prototypes of clay,

wood, plastic or other materials. This time consuming process

can now be performed by using a number of different AM

processes. This approach may also be referred to as rapid sand

casting process because by using AM techniques, patterns,

cores and gating system can be fabricated in a relatively short

period of time. The use of AM process has proved to be a cost

effective and time efficient approach for producing pattern,

core boxes and gating system for sand casting (Wang et al.,1999). AM helps to fabricate pattern with added cores by

disregarding internal cavities and designing core prints. LOM

is fairly popular for this application, since LOM moulds have

the feelings and look of wood, which is a traditional foundry

tooling material (Rosochwski and Matuszak, 2000). Pak and

Klosterman (1997) have documented the use of LOM AM

process to fabricate the tooling required for sand casting.

Pereira et al. (2008) have reported the advantages gained with

the application of FDM patterns in sand moulding. Many

commercialized AM techniques have been employed to

produce tooling required for sand casting with varying

success and many RC solutions in sand casting are

being used by various industries and researchers as shown

in Table I.There are mainly three approaches by which application of

AM techniques can be used in sand casting technology

(Kouznetsov, 2004). Figure 10 shows the basic approaches

used as RC solutions in rapid sand casting. By using direct

tooling approach, AM generated objects can be utilized

directly as patterns in sand moulding in case of small or

medium volume casting production as a substitution for

traditionally employed wooden patterns. The objects

fabricated by almost all AM techniques can be used as

patterns. Indirect tooling approach in sand casting can be

efficiently employed in case of large-volume production and

when great durability of pattern is required. The most

common approach is the use of AM generated model as

pattern for moulding RTV and the pouring urethane into the

mould. The resulting plastic part can be used as a pattern for

sand moulding. Third and latest approach is the use of AM

technique to direct fabrication of sand moulds (pattern less

moulds). EOS DirectCastw, ProMetal rapid casting

Figure 8 Orthopedic knee casting made of medical cobalt chrome alloyby using ceramic mold made by 3D printing[11]

Figure 9 Process sequence for sand casting

Fabricatecore boxes

Fabricatepattern

Moldcore

Preparesand

Meltingmetal

Source: Groover (1996)

Buildmold

Pourcasting

Sand

Rawmetal

Corematerial

Break outraw casting

Solidificationand cooling

Finishedcasting

degate andclean

inspection

Figure 7 Intake manifold casting produced by using DSPC[10]

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technology (RCT), and ZCast501 processes have been usedsuccessfully for direct fabrication of moulds in casting

industry.Based on these approaches, introduction of major

commercially used rapid sand casting solutions and somecase studies and examples related to them are presented in the

next sections.

7. Fabrication of sand casting patterns usingdirect tooling approach

7.1 Rapid sand casting using LOM technique

LOM is an AM process developed by Helisys Inc. (USA) and

currently, Cubic Technologies, successor to Helisys Inc., isthe exclusive manufacturer of the LOM-AM machines

(Chua et al., 2003) in which a part is built sequentiallyfrom layers of paper, plastic, metal or composite sheets, allcoated with a thermally activated adhesive (Chua, 1994;

McMains, 1995; Upcraft and Fletcher, 2003). The slices ofmaterial sheets are cut in required shape from roll of material

by using laser beam. The cutting material sheet is laid onmachine platform and bonded to the previous sheet using a

hot roller, which activates a heat sensitive adhesive. Afteraddition of all sheets, the solid part of the material is removed

from the platform. Surrounding material and material inregions of the part that are hollow must be removed in a

“Decubing” post processing step (Wang et al., 1999). LOM isallegedly five to ten times faster than other AM processes,because the laser beam need only trace the outline of each

cross section, not the entire area (Chua, 1994). LOMtechnique is widely used in fabrication of patterns for both

sand casting and IC. Castings produced by LOM patternswere found to be well within the acceptable quality range and

gave 25 per cent cost saving (Mueller and Kochen, 1999).LOM is fairly popular for sand casting, since LOM models

have the feeling and look of wood, which is a traditionalfoundry tooling material. The paper patterns of the LOMprocess also work well with IC. The paper can be burnt out

with little expansion, however, the ash residue may besubstantial (Rosochwski and Matuszak, 2000). A case study

proving time and cost savings in sand casting using LOMtechnique is presented below in Section 7.1.

7.1.1 Case studyWang et al. (1999) have investigated experimentally the specific

considerations that are relevant to using the LOM AM processto fabricate patterns and core boxes for sand casting. Authors

have also proposed that to make high-quality patterns and coreboxes for sandcasting using the LOM process, several importantissues must be considered, such as compatibility of the part

geometry, error source generation and propagation, shrinkage

considerations, and deterioration due to environmental effects

and repeated use. The process flow for fabricating the sand

casting tooling using LOM process is shown in Figure 11. The

time and cost saving in fabricating a part by using this approach

has been presented as an example given below.

Example: casting of ballistic projectile by using LOMtechnique. Authors of this investigation have also reported an

example of casting of 25 mm ballistic projectile by using LOM-

AM technique, which was provided by Lufkin Industries, Inc. of

Lufkin, TX. The CAD design of part, match plate, pattern and

core box shown in Figure 12. The final LOM pattern and core

box together with cores and sand cast part are shown in

Figure 13. Technical tooling details are given below:. part envelope dimensions (mm): 83.68 £ 27.94 £ 27.94;. match plate dimensions (mm): 431.80 £ 304.80 £ 76.20;. core box dimensions (mm): 203.20 £ 127 £ 44.45;. LOM machine: LOM 2030;. LOM paper thickness: 0.09 mm double layered;. finish material: sanding lacquer sealer and lacquer spray;

and. application: sand casting of ductile iron.

The authors have reported a 50 per cent saving in time and

cost compared to aluminium tooling by using LOM AM

technique in sand casting. Part geometry of thin wall may not

be suitable for LOM-based rapid tooling. The authors have

also mentioned that the LOM process introduces a variety of

errors into the pattern and core-box fabrication process,

which should be carefully understood and controlled to

ensure the realization of time and cost saving.

7.2 Rapid sand casting using OPTOFORM technology

SMC Colombier Fontain Company has carried out a study

based on tooling manufacturing with a new AM process in order

to reduce “time – to – market” and the cost of the product

development in the sand casting process (Bernard et al., 2003).

The study was based on tooling manufacture by integrating

CAD softwares and a new AM process “OPTOFORM” which

is a paste polymerization process. Part designing, assembly,

filling of molten metal and the solidification simulation was

done with the CAD software to validate the sand mould. The

pattern plates and core boxes were designed with the cluster

modelling. Master patterns were manufactured with a new

rapid tooling process, which was introduced by OPTOFORM

in 1998 and which was purchased by 3D systems in 2001.This process, close to SL, brings into play material

exploitable in paste form, which allows a large-application

range. Indeed, the resin paste permits a high level of

additional material, which increases the mechanical

properties. The paste is set down into thin layers with

Figure 10 Approaches used as RC solutions in rapid sand casting

Rapid sand casting

AM-fabricated patternand core boxes

(direct tooling approach)

AM-fabricated patternand core boxes

(indirect tooling approach)

Direct fabricationof shell moulds

(Pattern less mould)

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specific scrapers, and then solidified by a laser. This process

also uses a ceramic paste to obtain parts and cores. In this

research, ceramic component and tools and alumina and

metallic parts were manufactured for the validation of the

process. A total of 500 moulds were produced and the results

were very good. The OPTOFORM process for sand casting

was validated without any problem with the small production.Researches claimed that there was 20 per cent improvement

in average time of all the operations that composed the

industrialization with the numerical channel (integration of

CAD and AM) then with the traditional techniques. But the

overall development costs were about 15 per cent more with

the numerical channel than with the traditional techniques.

This problem was due to the difficulty to realize the complex

moulding study with the CAD tools (CATIA, Pro-engineer,

etc.). SMC solved this problem by using the new user-friendly

CAD software – SolidWorks. It introduced a new outlook

on the CAD. For the parts without core, it highlights

the reduction of the design costs owing to a difference ofabout 20 per cent cheaper with the numerical channel

(AM and SolidWorks) than with the traditional techniques.By the achievements of this study, SMC has introduced a

new AM technology to manufacture the production tooling

for the sand casting process. The result proved the importancein simulation reliability due to good metallurgical results, in

spite of wall thickness reduction (to 4 mm) under the process

limits. The successful introduction of SolidWorks reduced the

part design time and CAD hourly rate. Since then, all the new

products have been designed and industrialized using the

numerical chain and design methodology in SMC.

7.3 Rapid sand casting using PolyJete technology

Objet’s patented PolyJete technology based on 3DP system

provide high resolution RC solution to sand casting process.The process provides a complete 3DP solution for virtually

any sand casting application by using Objet FullCurew

material (photopolymer resin) and Objet software (Cohen,

2008). The concept is based on the use of photopolymers as

building materials. A wide area inkjet head layer wise deposits

both build and support material. It subsequently completely

cures each layer after it is deposited with a UV flood lamp

mounted on the print head. The support material, which is

also a photopolymer, is removed by washing it away in asecondary operation (Dimitrov et al., 2008). Sand casting

facilities use Objet’s PolyJete technology to create mould

patterns (solid and split) as they offer high-resolution printing

and utilize materials that fit the requirements of this

application niche. Both solid and split patterns can have

cores inserted to complete the final part shape[12].

The Figure 14 shows the rapid sand casting of brass

component with PolyJete technology.

8. Direct fabrication of sand moulds (pattern lessmoulds)

8.1 Rapid sand casting using EOSINT-SLS machine

EOS GmbH, Munich, Germany have been marketed

EOSINT-S Laser Sintering AM machine in which sand

Figure 11 Process flow for fabricating the sand casting tooling using LOM

2D drawing ofpattern and core box

CAD solid model ofpattern and core box

Conversion of CADmodel in to. stl format

Fabrication onLOM machine

Post processing (decubing,smooth and seal)

Traditional sandcasting process

Finalcasting

Figure 12 The CAD design of part, match plate, pattern and core box

Source: Wang et al. (1999)

Figure 13 Final LOM pattern and core box together with cores andsand cast part

Source: Wang et al. (1999)

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casting moulds and cores fabricated directly from CAD solid

model using polymer-coated green sand[13]. The process is

based on the powder-based laser fusion process. Lightman

(1997) reported that this machine is a modification of EOS’

standard sintering machines, in which coated refractory sand

is used as the powder. Sand moulds and cores are produced

by using a CO2 laser that causes the sand particles to adhere

by heating and binding their coating. Moulds for complex

parts can be built quickly, and castings can be made directly

into the sand mould (Figure 15). EOS has named the process

DirectCastw (Freitag et al., 2003) which has been allowed

patent status in the USA in 2000[14]. Presently, EOS

producing two laser sintering machines such as EOSINT

S700 and EOSINT S 750, which use dual lasers to fabricate

complex moulds and cores using foundry sands EOSINT

Zircon HT and EOSINT Quartz 4.2/5.7 (Chua et al., 2003).

8.2 ProMetal RCT

ExOne (formerly Extrude Hone Corporation) has offered

three commercial 3DP machines R10, SR-2 and RCT S15

based on 3DP technique in 2005, which are used to perform

two processes, namely, ProMetal Direct Metal Printing and

ProMetal Rapid Casting [15]. Using the 3DP technology,

RCT S15 and RCT S-Max produce complex sand casting

moulds and cores directly from a CAD model without using

any physical pattern or core box. RCT tends to cast

geometrically complex shapes which are often impossible to

create by conventional means. A layer of sand (bonded with

furan resin) mixed with the hardener is spread evenly on a

machine build platform and a binding agent is then applied

using print heads at the specified areas determined by the

CAD data. The hardening agent contained in the sand

hardens the binder and creates the objects one layer at a time

from top to bottom[16]. The sand moulds and cores

fabricated with this process are poured immediately without

using secondary operation. Figure 16 shows the mould of

automotive intake manifold manufactured by this process and

the final casting. The key advantage of this RC solution is that

it provides flexibility to produce complex and pattern less

castings. Multiple and unique moulds can be produced at the

same time while reducing production costs and time to

market. Table III provides the information regarding material

being cast with these processes and their application areas.

RCT process can be used to produce prototype castings

economically and to validate mould designs. In certain

applications, it could be used to eliminate core boxes or to

produce especially intricate cores.RCT S15 is a factory-floor solution which provides

everything necessary to produce casting moulds and cores

directly form CAD files. This system includes a process

station, unloading station and a mixing unit that prepares and

stages sand for use during the process. The S15 system by

using 512 jets provides the maximum size of mould up to

1,500 £ 750 £ 700 mm and is the only system using foundry

grade materials (Wohlers, 2003). ProMetal RCT S-Max

machine is also in the market for the manufacturing of most

complex moulds and core with larger build size of

1,800 £ 1,000 £ 700 mm[17].

8.2.1 Example: use of ProMetal RCT for DiMora’s1,200 HPengine components of world’s most expensive vehicle, the NataliaSLS 2Car-designer Alfer J. DiMora has emphasized through an

article in 2007, the importance of using the RCT methods for

technically advanced engines[18]. He stated that the extreme

complexity of the 16-cylinder DiMora Volcano engine

requires the flexibility and precision that only RCT can

provide. Advanced Technology & Design Inc. president

Clifford Sands added in the same article that:

By removing the constraints of hard tooling, RCT allows extreme enginedesign to become a reality. At 14 liters displacement and producing1,200HP, the proprietary DiMora Volcano V16 is an extreme engine design.We take DiMora’s CAD data file and design the sand mould assembly whichwill be used to create this cutting-edge engine.

Figure 14 (a) 3D model printed using PolyJete technology; (b) sand casting mould; (c) the pattern is removed from the mould; and (d) final casting ofbrass component

(a) (b)

Source: Cohen (2008)

(c) (d)

Figure 15 Sand mould, sand positive, and aluminium casting producedwithin one day by using EOSINT-S laser sintering

Source: Lightman (1997)

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8.3 ZCast 501 direct metal casting

ZCast501 Direct Metal Casting is an RC solution developed

by ZCorp for sand casting of non-ferrous materials[19].

Conventionally, metal castings are produced by using sand

casting tooling, techniques and procedures as mentioned in

chart 2. Instead of utilizing this costly and time-consuming

process, the ZCast process creates the shell moulds directly

from CAD data by using 3DP-AM technology. It eliminates

the pattern creation phase of the traditional sand casting

process in a revolutionary way, resulting in a drastic reduction

of the casting lead time from weeks to days (Krouth, 2002).

ZCast provides three basic methods to fabricate moulds to

produce casting rapidly. Bak (2003) reported that the

accuracy and surface finish are consistent with sand casting

by using ZCast process. Singh (2010) reviewed the use of this

RC solution for generating prototype castings.Material. ZCast 501 powder is a plaster-ceramic composite

suitable for non-ferrous materials. Various manufacturers and

researches have been produced successful castings in

aluminium, zinc, bronze, magnesium and lead. Zb56 binder

solution and Zc5 cleaning solution is commonly used for

making moulds.

Major features:. ZCast501 mould is recommended for non-ferrous metals

with pouring temperature below 1,1008C.. The recommended shell mould wall thickness range is

minimum 13 mm and maximum 25.4 mm[20].. Before pouring, ZCast moulds must be baked in an oven

from 1808C to 2308C for between four and eight hours

(based on volume), until it is “bone” dry.. Customers cast metal into these 3DP moulds for

prototype evaluation or fully functional parts.

8.3.1 ZCast methodsDirect pour method. The process is based on 3DP using ZCast

material to fabricate a complete mould set including cores and

gating system and provides facility of casting directly bypouring molten material into the mould.

Shell method. This method is used to manufacture largermould than used in the direct pour method and when thegating system would require very large ZCast components.If the size of the mould exceeds the working volume of theprinter, the shell method is recommended[20]. The mouldcavity is formed by a shell of ZCast material and is held in placeby backing it with conventional sand. The gating system isconstructed in the foundry sand by using traditional foundrytooling. In this method, designer is allowed to mount ZCastpieces on a pattern board, which align them with respect to therest of the mould. The ZCast shells have to be so designed thatthey provide connections to the gating system vents and risers,and they must have features that anchor them to the backing offoundry sand. The printed mould pieces consist of cores and auniform shell that surrounds the mould cavity. A flange(containing vent holes, core prints and alignment pin) ofsimilar thickness extends out on the parting line. The mouldpieces are built in sections and aligned together on a blockingboard. The blocking board assembly is placed in a mouldingbox. Standard gating forms are provided in moulding box andfoundry sand is placed around the printed parts.

Combination method (production intent casting). In thismethod, only cores are printed with the ZCast material andused in conventional sand moulds for producing hollowcastings. The sand mould can be created with traditionalmachined pattern or AM fabricated pattern. The mainadvantage of using this method is that cores and inserts can bemade without any special tooling (e.g. core boxes) that wouldlengthen the time to produce the prototype casting.

8.3.2 Research based on ZCast processDimitrov et al. (2007) have presented the results obtained fromthe experimental studies on different RC solutions (all threemethods of ZCast and fiber glass tooling) based on 3DPtechnology in order to improve the design and manufacture offoundry equipment that is used for sand casting of prototypes infinal material. Based on this research authors have suggestedthat in cases where up to four cast components of highcomplexity are required, the ZCast-Direct pour methodprocess should be used. On the other hand, in cases, wheremore than 15 parts or higher runs are needed, or if the tools areexpected to undergo heavy handling, the production intentcasting or even the Fibreglass Tooling process is recommended.

Bassoli et al. (2007) have investigated through experimentsto verify the feasibility and evaluation of the dimensional

Figure 16 Automotive intake manifold

(a)

Notes: (a) Sand mould prepared with ProMetal RCT; (b1, b2) final casting[17]

(b1) (b2)

Table III ProMetal RCT casting materials and application areas

S. no. Material Application areas

1 Al Automotive, prototyping

2 Cu alloys Marine, bearings, fittings

3 Ferrous alloys (grey iron,

ductile iron, steel)

Automotive, general purposes

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accuracy of two RC solutions based on 3DP technology.

The first solution was IC starting from 3D-printed starch

patterns and the second solution was ZCast process for the

production of cavities for light-alloys castings. For the second

solution, a design of manufacturing analysis was performed

on the selected benchmark with SOLIDCastw software.

Starting from the CAD model of the casing, complete with

feeding runners and riser, the mould was modelled with a

wall thickness between 12 and 25 mm, minimizing the ZCast

material to limit production time and cost. Researchers

reported that the ZCast technique provided satisfactory

results, limited at present to the field of light alloys. In a

latest research, the mechanical performances of parts

produced by ZCast process were also optimized by varying

thermal treatment parameters (heat treatment by varying

temperature and time) and proved that in the heat treatment

of ZCast parts time has a negligible effect on the compressive

strength, whereas temperature has significant effect for best

mechanical response (Bassoli and Atzeni, 2009).Kaplas and Singh (2008) performed experimental study to

investigate the feasibility of decreasing the shell wall thickness

of mould from 12 to 2 mm thickness using ZCast process to

evaluate the dimensional accuracy and mechanical properties

of castings of zinc-alloy produced by this RC solution.

Dimensional tolerances and mechanical properties were

compared to verify the suitability of castings and further

results were supported by radiography analysis.Singh and Verma (2008) verified the feasibility of

decreasing the shell wall thickness of shell mould from 12 to

2 mm thickness using ZCast process in order to evaluate

the dimensional accuracy for aluminium castings. Further

consistency with the tolerance grades of the castings has been

checked as per IT grades along with mechanical properties of

the aluminium castings.Singh and Singh (2009c) investigated the feasibility of

decreasing the shell mould wall thickness using ZCast RC

solution for brass and lead alloy castings. The study suggested

that the production of sound casting for minimum wall

thickness depends upon pouring temperature and weight

density. The results suggest that for small castings below a

mass of 10 g, shell thickness can be reduced from the 12 to

0.5 mm for lead alloy and 12 to 2 mm for brass alloy castings.

Singh and Singh (2009a,b) also reported the investigation of

this process under statistically control for the best shell wall

thickness in case of low brass (2 mm) and lead (0.5 mm).Based on the results of these researches, it has been found

that it is feasible to reduce the shell wall thickness of moulds

prepared by using ZCast501 from the recommended

thickness (13 mm)[20] and to save the cost and time for

the production of various non-ferrous material castings.

The information in this regard is presented in Table IV.

The researches have proved that the investigated ZCast

solution is effective in obtaining cast technological prototypes

in short times and with low cost, with dimensional tolerances

that are completely consistent with metal casting processes.

The previous major research accessed the feasibility of

decreasing the shell wall thickness of mould obtained using

ZCast solution to evaluate the dimensional accuracy and

mechanical properties of castings of various non-ferrous

alloys. The literature is still lacking in finding the reasons or

factors for obtaining the minimum shell wall thicknesses of

mould by using ZCast solution for a particular material.An attempt has been planned by the authors of this paper to

investigate the means for generating cost effective RCs using

3DP technique[21]. To achieve this objective ZCaste Direct

Metal Casting RC solution will be used to produce shells for

casting to verify the feasibility of decreasing shell wall

thickness from 12 to 2 mm (12,11,10,9,8,7,6,5,4,3,2 mm) as

shown in Figure 17d in order to reduce the cost and time for

the production of Al, Cu and brass castings. Starting from the

identification of benchmark, component and shells have been

modelled using UNIGRAPHICS version NX5 and materials

(Al, Cu and brass alloy) have also been selected to produce

technological prototype castings at different shell wall

thicknesses using 3DP (Z Print machine, Model Z510) with

ZCast501e powder. Consistency of the tolerance grades of

the castings (IT grades) will be evaluated as per UNI EN

20286-I (1995) standards for casting process. Measurements

on a coordinate measuring machine (CMM) with GEOPAK

v2.4.R10 CMM software will be used in calculating the

dimensional tolerances of the castings. Microstructure

analysis and some important mechanical properties will

be compared to verify the suitability of the castings. Further

the dependence of optimum shell wall thickness on change in

volume of casting, pouring temperature, weight density and

heat transfer rate of molten material will also be evaluated.The specific objectives of this proposed research study

include:. effect of change in volume of casting for obtaining

optimum shell wall thickness;. effect of pouring temperature of molten metal for

obtaining optimum shell wall thickness;. effect of weight density of molten material for obtaining

optimum shell wall thickness;. effect of rate of heat transfer for obtaining optimum shell

wall thickness; and. process capability study of optimum shell wall thickness of

materials, namely, Al, Cu and brass experimentation.

Figure17 shows a pilot experiment processing steps from

CAD design of shells to final aluminium casting of benchmark

Table IV Optimum minimum shell wall thickness achieved and reduction in cost and time in comparison to recommended 13 mm thickness usingZCast501by various researches

Researches Casting material

Optimum minimum shell wall

thickness achieved

Production cost

saved (%)

Production time

saved (%)

Kaplas and Singh (2008) Zinc alloy 7 mm 41 37

Singh and Verma (2008) Aluminium alloy 5 mm 54.6 55.4

Singh and Singh (2009a) Lead alloy 0.5 mm 45.75 43

Singh and Singh (2009b) Brass alloy 2 mm 40.05 32.84

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

341

Page 15: Rapid Casting

using ZCast501 with Z510 printer based on this current

research.

9. Discussion

The survey regarding RC solutions reported in this paper does

not present a complete picture of this incredible technology.

The result from this review is that there is still considerable

room for improvement and innovation of RC solutions.

Despite the invention of various RC solutions, many factors

need to be researched out for the implementation of RC

in traditional foundry practices. These factors are: AM

materials, AM systems, accuracy, surface finish, geometry

flexibility, build time, machine building size, mechanical and

thermal properties, cost and post processing of patterns,

moulds and cores. The major deciding factor to adopt RC

solutions is the cost, because AM systems and materials are

very much expensive when compared to traditional casting

tooling. Presently, RC is economical when the component to

be cast is in the initial stages of design cycle and required in

low quantity. Furthermore, RC is also economical when there

is a need to produce geometrically complex castings and

requirement of changes in design are high. Many researchers

and manufacturers are involved worldwide into the

development of potential new AM systems and materials

used in IC and sand casting.

9.1 Direct fabrication of IC patterns

Although generation of prototype is a natural application of

AM, it is proved that any AM generated component, which

can be flash fired without damaging the ceramic shell can be

used as a substitute of wax IC pattern. Since 1989, many AM

materials have been invented to be used commercially to

produce direct pattern for IC. The main stress has been given

on finding the new materials used for fabricating non-wax IC

patterns without creating the problems of ceramic shell

cracking, incomplete pattern burning out and residual ash

after autoclaving. Although many RC solutions are available

for the production of wax patterns (namely, FDM, MMII,

Thermojet and BPM) directly, non-wax AM patterns are

more popular due to the property of durability and strength

and can be employed for casting of thin wall structure.

Further, to improve the surface quality of patterns, finishing

operation can be performed on non-wax patterns due to their

toughness property. Many AM materials used to produce

non-wax patterns having capability to counter the problems of

ceramic shell cracking, incomplete pattern burning out

and residual ash have been introduced by various

AM manufacturers. The pioneers amongst them are FDM-

ABS, CastForm PS, WindForm PS and ZCorporation’s

starch patterns. As far as ZCorporation’s starch patterns are

concerned, no residual ash appears after burnout process.

Furthermore, starch patterns also have the capability to create

high-quality castings with excellent surface finish. Bassoli et al.(2007) claimed after experimental investigation that the

feasibility of these starch patterns was proven even in the case

of thin walls. Table V presents the advantages and

disadvantages of various AM materials for producing IC

patterns. Mechanical properties and general properties of

some RIC pattern materials are presented in Tables VI and

VII, respectively.

9.2 Fabrication of mould for producing wax IC patterns

This approach utilizes direct and indirect rapid tooling

techniques to fabricate moulds for production of large

number of wax IC patterns economically and with better

accuracy. This approach further relieves the manufacturer

from the problems related to non-wax pattern and using

relatively costly direct AM wax patterns. The indirect tooling

technique is feasible and economical when usually 5-10 AM

patterns of complex shape are required in short period

(one to five weeks) which otherwise required machine tooling

Figure 17 Pilot experiment processing steps from CAD design of shells to final Al casting of benchmark using ZCast501 with Z510 printer

(a) CAD model of upper shell, component and lower shell

(b) Shells in stl. formet in machine software

(c) Printing of shells in Z510 machine

(d) Shells with different wallthicknesses (12-2mm)

(e) Shell ready for pouring (f) Shell poured withmolten metal

(g) Final casting obtainedusing Zcast process

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

342

Page 16: Rapid Casting

Table

VA

dvan

tage

san

ddi

sadv

anta

ges

ofA

Mfa

bric

ated

ICpa

tter

ns

QuickC

ast

patterns

FDM

ABS

patterns

FDM

WAX

patterns

Model

Mak

erII

patterns

TrueForm

patterns

CastForm

PS

patterns

Windform

wPS

patterns

Thermojet

patterns

Zp14patterns

Advantages

Easy

burn

out

No

risks

of

dam

agin

gdu

ring

clea

nup

proc

ess

Easy

burn

out

Easy

burn

out

Post

finis

hing

isno

t

requ

ired

Low

burn

out

tem

pera

ture

Post

curin

gis

not

requ

ired

Easy

burn

out

Bes

tsu

rfac

efin

ish

asco

mpa

red

to

othe

rno

n-w

axA

M

patt

erns

Bet

ter

surf

ace

finis

has

com

pare

d

toFD

M-w

ax

Cas

ting

tech

niqu

es

usin

gFD

M-w

ax

patt

erns

are

norm

alas

trad

ition

alw

ax

patt

erns

with

out

any

chan

ges

inth

e

conv

entio

nal

IC

proc

ess

Goo

dsu

rfac

efin

ish

Goo

dsu

rfac

efin

ish

Proc

essi

ngof

CF

patt

erns

asno

rmal

wax

patt

erns

with

out

any

chan

ges

in

conv

entio

nal

IC

proc

ess

Hig

hsu

rfac

efin

ish

Exce

llent

up-f

acin

g

surf

ace

finis

h

Due

tow

ax

mat

eria

ls,

patt

erns

can

beus

ed

dire

ctly

inIC

Low

ash

cont

ent

afte

rbu

rnou

tdu

e

toho

neyc

omb

stru

ctur

e

Patt

erns

can

be

tran

spor

ted

easi

ly

due

tohi

gh

stre

ngth

of

mat

eria

l

No

ash

cont

ents

No

supp

ort

stru

ctur

eis

requ

ired

Low

ash

cont

ent

(,0.

02%

)af

ter

burn

out

Low

ash

cont

ent

(,0.

02%

)af

ter

burn

out

No

sepa

rate

mat

eria

lre

quire

d

for

supp

ort

stru

ctur

e

Qui

ckC

ast

build

styl

epa

tter

nsar

e

succ

essf

ulin

coun

terin

gsh

ell

crac

king

durin

g

auto

clav

ing

Less

mat

eria

lis

requ

ired

to

prod

uce

patt

erns

due

toho

neyc

omb

stru

ctur

e

No

risk

ofsh

ell

crac

king

Less

chan

ces

of

shel

lcr

acki

ngdu

e

tolo

wpa

tter

n

expa

nsio

ndu

ring

the

shel

lfir

ing

Cap

able

ofbe

ing

auto

clav

ed

No

risk

ofsh

ell

crac

king

Bui

ldm

ater

ial

can

bere

cycl

ed

Enab

leto

prod

uce

cast

ing

with

high

accu

racy

Hig

hac

cura

cyas

com

pare

dto

FDM

patt

erns

Bet

ter

accu

racy

Patt

erns

prod

uced

with

tight

tole

ranc

es

Hel

pto

redu

cele

ad

time

ofca

stin

gas

com

pare

dto

trad

ition

alIC

Perf

ect

for

Al

and

stee

lca

stin

g

Suita

ble

toca

st

mat

eria

lsw

ith

diff

eren

tm

eltin

g

tem

pera

ture

rang

e

such

asA

l,M

gto

titan

ium

Cas

tw

ithal

lca

st

allo

ysan

dhi

ghly

reac

tive

allo

ys

Patt

ern

can

be

prod

uced

quic

kly

Low

prod

uctio

n

time

and

cost

(con

tinue

d)

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

343

Page 17: Rapid Casting

Table

V

QuickC

ast

patterns

FDM

ABS

patterns

FDM

WAX

patterns

Model

Mak

erII

patterns

TrueForm

patterns

CastForm

PS

patterns

Windform

wPS

patterns

Thermojet

patterns

Zp14patterns

Abi

lity

topr

oduc

e

thin

wal

lpa

tter

ns

Faci

litat

ein

cast

ing

ofhi

ghly

deta

iled

com

pone

nts

like

jew

elle

ry

Enab

leto

cast

very

thin

wal

lse

ctio

ns

Enab

leto

prod

uce

com

plex

cast

ing

with

inte

rnal

cavi

ties

havi

ngth

in

wal

lth

ickn

esse

s

Enab

leto

prod

uce

cast

ings

of

com

plex

geom

etry

Enab

leto

prod

uce

com

plex

cast

ing

with

vary

ing

thic

knes

s

Disad

vantages

Cas

ting

with

Qui

ckC

ast

patt

erns

requ

irem

ore

expe

rienc

ean

d

spec

ial

proc

essi

ng

asco

mpa

red

to

othe

rno

n-w

axA

M

patt

erns

Poor

surf

ace

finis

h

asco

mpa

red

to

wax

patt

erns

fabr

icat

edw

ith

trad

ition

alw

ax

tool

ing

proc

ess

Slow

build

spee

d

ofsy

stem

Not

suita

ble

for

titan

ium

allo

y

Dow

n-fa

cing

surf

ace

finis

his

poor

Rem

oval

of

supp

ort

mat

eria

l

requ

ires

mor

etim

e

and

spec

ial

care

Cos

tlypr

oces

sing

Furn

ace

isre

quire

d

for

auto

clav

ing

due

tohi

ghm

eltin

g

tem

pera

ture

of

AB

Sm

ater

ial

Wea

kpa

tter

ns

Tran

spor

tatio

nto

a

foun

dry

requ

ires

spec

ial

care

Supp

ort

mat

eria

lis

diff

eren

tfro

mbu

ild

mat

eria

l

Solv

ent

isre

quire

d

for

clea

ning

the

supp

ort

mat

eria

l

Take

sla

rge

cast

ing

time

asco

mpa

red

toC

Fpa

tter

nsas

it

requ

ires

tota

llydr

y

cera

mic

shel

l

befo

reau

tocl

avin

g

Patt

erns

are

frag

ile

and

can

bebr

oken

durin

gcl

eani

ng

and

wax

infil

trat

ion

stag

e

Wax

infil

trat

ion

incr

ease

s

man

ufac

turin

g

time

and

intr

oduc

esfu

rthe

r

dim

ensi

onal

erro

rs

Pres

ently

,ve

ryfe

w

indu

strie

sha

ve

expe

rienc

ed

Win

dFor

mPS

Patt

erns

are

britt

le

inna

ture

and

diffi

cult

to

tran

spor

tto

foun

dry

Diffi

cult

tore

mov

e

supp

ort

stru

ctur

e

Expe

nsiv

ebu

ild

mat

eria

l

Dim

ensi

onal

varia

nce

indu

ced

durin

gw

axdi

ppin

g

stag

e

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

344

Page 18: Rapid Casting

which take six-25 weeks to build. Furthermore, indirecttooling requires very simple processing and post processing

technique and less equipment and material cost as compared

to direct tooling technique.Direct tooling technique for mould fabrication requires post-

processing steps like infiltration, de-binding, sintering and

finishing operations to fabricate mould with high accuracy and

quality. The major constraint to use this technique to generatewax IC pattern is the lead time require for mould production.

Even though some pioneering processes such as DMLS, Rapid

Tool, ProMetal, LENS and DirectAIM have been used

successfully for direct fabrication of moulds for injection ofwax patterns, which result in relatively strong moulds and

suitable for large volume production.

9.3 Direct fabrication of IC ceramic shells

In continuation to progress made in RIC, a novel casting

solution “DSPC” is moving with a stunning pace inmanufacturing industry to facilitate direct fabrication of the

IC ceramic moulds (negative) with integral cores to produce

parts of virtually any shape and material. This techniqueprovides a greater advantage over other RIC techniques by

removing the steps of wax pattern generation, ceramic shell

production, autoclaving and firing of mould.

9.4 Sand casting

Similar to RIC, extensive worldwide research is being

undertaken by various organizations to improve the existingRC solutions for sand casting. All AM fabricated patterns

having strengths to bear the pressure of moulded sand and

ability to withstand the chemicals in the sand can be used assand casting patterns. As far as dimensional accuracy is

concerned, it is not a critical issue for rapid prototypes to be

used as concept models for visualization purpose. However,

for producing AM-fabricated patterns and core boxes for sandcasting, any error in these casting tooling will be conveyed to

the final cast components. Wang et al. (1999) mentioned in an

investigation that the LOM process introduces a variety of

errors into the pattern and core box fabrication process forsand casting and further the part geometry of thin wall may

not be suitable for LOM-based rapid tooling.A great need of RC solutions having capability of

fabricating ready to pour moulds (pattern less casting) has

been raised by the manufacturers worldwide. Presently, EOS

DirectCastw, ProMetal RCT and ZCast501 are being usedsuccessfully to produce patternless casting by producing

direct sand casting moulds and cores directly from a CAD

model. The introduction of these systems eliminated the

thousand-year-old requirement of physical patterns used tocreate sand moulds. Using this system highly complex and

intricate designed component can be cast very quickly and at

low cost, which was earlier impossible for the traditional

foundry practice. This feature also motivates foundries toproduce spare parts of any product whenever demanded by

the customer. These systems also help to make job shop type

of production economical and feasible for an industry byproducing different designed components with fast

production rate. Table VIII presents the technical features

and Table IX presents the advantages and disadvantages of

these direct sand mould RC solutions. The ProMetal’s RCTS-max machine with largest build area amongst other

available RC solution is a revolutionary invention in the

field of RC to produce large-size component of any geometryof any castable material. The EOS DirectCastw and ProMetal

RCT are also capable produce functional metal casting

in batches.Available AM materials and machines used to fabricate

patterns, moulds and cores for sand casting are being improved.

3D-printed sand used for RC is a latest development in rapid

sand casting. A recent study has been performed to investigatethe behaviour of 3D-printed sand in contact with molten metal

(at elevated temperature) in order to measure the thermal

distortions of the chemically bonded sand binder systems usedto print cores and moulds (Rebros et al., 2007).

Based on applications of various RC solutions, case studies

and examples as discussed above, the major benefits of RC tofoundrymen and challenges amongst the AM manufacturers,

researchers and developers of RC solutions are summarized

below.

9.5 The benefits of RC to foundrymen

1 Cost saving. Cost is saved due to the elimination oftraditional casting tooling required to cast prototype or low

volume production castings. The cost involved in

modifying a poor-designed component and iterationsrequired before finalization of design is also reduced by

using RC solutions. Casting tooling does not need to be

ordered until the design is finalized and frozen.

Table VI Mechanical properties of RIC pattern materials

CastForm PS FDM ABS Zp14

Tensile strength 2.8 MPa 34.45 MPa (ASTM D638) 10.8-15 MPa

Elastic modulus 1,604 MPa 2,495 MPa (ASTM D638) 3,000-4,000 MPa

Elongation – .10% (%at yield) –

Impact strength ,11 J/m 107 J/m (notched Izod test) 12-13 J/m

Hardness (shore D-scale) – 78 68-74

Table VII General properties of RIC pattern materials

WindForm PS Thermojet88 CastForm PS

Density 0.43 g/cm3 (ASTM D4164) 0.846 g/cm3 0.46 g/cm3

Ash content ,0.02% (ASTM D482) 0.00-0.01% (gray wax) 0.02% (ASTM D482)

Glass transition temp 87.5oC (DSC) 85-95oC 89oC

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

345

Page 19: Rapid Casting

Table

VIII

Tech

nica

lfe

atur

esof

dire

ctsa

ndm

ould

RC

solu

tions

RCtechnology

Machine

Compan

y

Core

technology

Builden

velope

(X,Y,Z)(m

m)

Additional

supports

required

?

Building

material

Binder

Infiltration

agen

t

Layerthickn

ess

(mm)

Buildspee

d

Prices

(baseprice)

ProMetal

RCT

technique

RC

TS1

5Ex

One

Sand

3DP

(Dro

p-on

-Bed

)

1,50

750£

700

NO

Sand

Res

inN

/A0.

15-0

.415

,000

cm3/h

$1.4

mill

ion

RC

TS-

Max

1,80

1,00

700

0.28

-0.5

59,4

00-

108,

000

cm3/h

$1.3

mill

ion

ZCastdirectmetal

casting

ZPr

inte

r

310p

lus

ZC

orp

3DP

(Dro

p-on

-Bed

)

203£

254£

203

254£

356£

203

NO

ZCas

t50

1Zb

56N

/A0.

089-

0.20

32-

4la

yers

/min

2la

yers

/min

$19,

900

Spec

trum

Z510

DirectCastEO

SINTS

EOSI

NT

S750

EOS

Sand

LS

720£

380£

380

700£

380£

380

NO

Qua

rtz

4.2/

5.7

N/A

N/A

0.2

2,50

0cm

3/h

e69

0,00

0

EOSI

NT

S700

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

346

Page 20: Rapid Casting

2 Gating system optimization. The major effort involved in

foundry is to optimize gating and runner system design.

The use of AM patterns for trial run castings facilitates

the optimization of gating system before placing the orderof production tooling.

3 Concurrent engineering approach. AM facilitates theimplementation of concurrent engineering approach by

creating a communication link between designers, pattern

makers, foundry men and customer simultaneously. This

approach helps to study the problems associated withevery stage of casting a product and also to analyze

product modification options by using AM models which

result in short time to market the product.4 RC allows the foundry to cast components with complex

geometry and intricate cavity which are either too

expensive or impossible to cast by conventional castingmethods.

5 Process optimization. Before manufacturing the production

tooling, the perfect positioning of parting lines, ejectingpins and inserts can be analyzed with prototype casting

produced by using RC solution. Optimization of

moulding parameter and evaluation of mould andpattern can be conducted effectively.

6 The use of RC solutions is found more economical and

feasible in emergency especially if quantities of castingsare required before the production tool is ready.

9.6 Challenges amongst AM developers for RC

1 The claim of available RC solutions to producedimensionally accurate, smooth surface finish and

durable casting with shorter time to market needs to

be further addressed, verified and improved.2 Although RC tends to generate complex casting, some

RC solutions require additional post-processing steps

which increase the cost and lead time required to castcomponents.

3 From the above discussion, it is obvious that each RC

solution possesses its own set of qualities. The real factis that some RC solutions are in their initial

development stages, and there is no clear evidence

that the use of these RC solutions will be beneficial in

terms of cost and lead time required to produce a unit of

final metal casting.4 Development of low cost RC materials and AM

machines for small scale foundries.5 Need to familiarize the casters and pattern makers with

available RC solutions, processes, parameters and

techniques to implement RC in the traditional foundry

practices.6 Development in AM machines to reduce the build time

required to produce casting tooling.7 Fulfill the requirement of mass production of metal

casting at commercial level.8 Development of new AM material and machines to

produce casting in metals, ceramic and composites

directly.9 Solutions for problems associated with application of

non-wax patterns in IC.10 Enhancement in work volume of AM machines to

produce large-size cast components.

10. Future trends in the development of RCT andtheir application

Rapid casting has gained acceptance worldwide by the

manufacturers and is expected to become one of the

important applications of additive technology in future. RC

solutions discussed in this paper are being improved

continuously, and new casting solutions are being

developed. It is anticipated that a number of new systems

dedicated to provide casting solutions directly (without using

any intermediate step) like DSPC, ProMetal RCT and

EOSINT S will be on the market in the next few years.

An important constraint to incorporate RC in foundry is the

high cost of AM machines, building materials and

consumables. Foundry industry requires cheaper machines

with low-cost building materials and consumables to produce

patterns or direct moulds for IC and sand casting.

Table IX Advantages and disadvantages of direct sand mould RC solutions

DirectCast with EOSINT S700/750 ProMetal RCT S15/SMax ZCast501 with Zprinter501

Advantages Minimum post processing is required

Cast any type of material from Al,

Mg to high alloy steel

Same sand material is used for support

structure

Enable to build large size castings

Patternless

Ability to make high quality fully functional

castings in small series

Enable to generate cost effective prototype

castings rapidly

No post processing is required

Suitable for ferrous and nonferrous castings

No support structure is required

Larger build area for producing large moulds

Patternless

System is provided with automatic loading

and unloading conveyors

Online mixing of sand and hardener

Ready to pour moulds

Ability to cast relatively low volume part with

good degree of complexity

Geometry independent process

Support is provided by the build material itself

Suitable in office environment just like office

printer

Patternless

Z510 printer is fastest 3D colour printer

Cost effective castings can be produced in a

short time

Disadvantages Relatively large space is required to install the

system

Consume high power due to use of lasers to

sinter the sand

System is dedicated to fabrication of sand

moulds and cores only

Large space required to install the system as

compared to other two processes

Suitable only for non-ferrous castings

Suitable for small size prototype castings

Costly build material and binders used as

compared to other systems

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

347

Page 21: Rapid Casting

The worldwide ongoing research in various fields of RC

and AM will give momentum to the following developments

in RC:. New wax like materials will be invented for IC patterns

which will produce patterns with high accuracy, surface

finish and without producing ash contents and shell

cracking during autoclaving.. Invention of material to produce pattern less moulds for

sand casting for ferrous and nonferrous material having

high melting temperature.. Invention of material having high strength for production

of patterns which can produce large number of moulds for

mass production of casting.. New AM machines will be available in the market with

large working platform to produce large-size patterns and

moulds for casting of large-size components.. With the development of AM machines having features

such as fast build speed, high resolution and capability of

producing parts with thin layer thickness, the mass

production of geometrically complex casting with desired

material will be possible.

There will be a great change in the attitude of foundry men by

adopting RC solutions in their foundries. Although various

RC solutions like EOSINT – S and ProMetal RCT are

available to produce moulds and cores directly using

conventional foundry sand, invention of new AM material is

possible in future, which will enhance flowability of pouring

metal and will also help to improve the microstructure of

casting. In addition, transparent material will also be

invented, so that the proper filling of cavity can be judged

on the spot. The possibilities seem limitless. One future

application is the development of expert system and

intelligent AM systems, a combination of AM, RT, RC and

artificial intelligence. Several expert systems based on RC will

be available in market for the selection of RC solutions, AM

systems and suitable materials for the required casting. RC

industry will also move toward standardization. All these

future developments will be possible only when foundry

industry will be willing to be an active partner in the

development and use of these RC solutions.

11. Conclusion

Based on the survey presented in this paper regarding RC

solutions, a conclusion can be drawn that the RC which has

evolved from AM, extends from its infant stage and is ready

to play a mature role in achieving the goal to produce fully

functional AM products in the required material. The main

aim of this review is to present the various commercialized RC

solutions in investment and sand casting technologies. One of

the most important contributions of RC in manufacturing

industry is the facilitation of concurrent engineering approach

in design, development and production of any type of casting.

The RC solutions reviewed in this paper for both IC and sand

casting will serve the purpose of researchers, academicians,

users, manufacturers and service industries to explore the new

options and further development in the field of RC.

The various approaches and techniques explained of using

AM in investment and sand casting processes may serve the

purpose of foundrymen in different working conditions.

The paper ends with a hope that in future, RC solutions will

emerge with the capability to provide dimensionally more

accurate and better surface finish castings of any size, shape

and material with more speed and at low cost. In order to

strengthen the manufacturing capabilities, especially for

developing countries to cope up with the impatient global

customer demands, RC solutions and AM machines should

be within the financial reach for small-scale foundries.

Notes

1 Project-Innovative production machines and systems

(2006), available at: www.iproms.org/system/files/

iproms_D4.9_APM_updated_State_of_the_Art_8_8_06.

pdf2 Z Corporation ZP14 investment casting processing

guide, ZCorporation, available at: www.zcorp.com3 http://um3d.dc.umich.edu4 www.3dsystems.com/products/sls/index.asp5 Italian Formula 1 Race Team Turns to Rapid

Prototyping and Manufacturing to Create High-

Performance Titanium Parts Made from CastForm PS

Patterns PR Newswire 21 July 2000, available at: www.

thefreelibrary.com6 www.crptechnology.com7 www.crp.eu8 Racers digs speed of rapid prototyping, MetlFax,

December 2000, available at: www.allbusiness.com/

manufacturing/9 www.windform.it/sito/en/windform-ps-new-polystyrene-

based-material.html10 Soligen Technologies Inc., www.soligen.com11 www.mit.edu/, tdp12 Sand Casting Applications, available at: www.2objet.com13 www.eos-gmbh.de14 US patent issued to EOS GmbH for sand-casting

application of laser-sintering: DirectCast, 13 October

2000, available at: www.thefreelibrary.com15 www.exone.com16 RCT takes layer-by-layer approach to mold, core

production, modern casting, 1 February 2005, available

at: http://goliath.ecnext.com17 www.prometal-rct.com18 Rapid casting technology is critical to “world’s most

expensive production vehicle”, Foundry Management

and Technology, 11 October 2007, available at: www.

foundrymag.com19 www.zcorp.com20 ZCast501 Direct Metal Casting, Design Guide,

September 2004, ZCorporation, available at: www.

zcorp.com21 Three dimensional printing: shortcut to the final

product, technology transition: NSF-funded research to

market, 6 May 2002, available at: www.nsf.gov

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Corresponding author

MunishChhabra can be contacted at: [email protected]

Rapid casting solutions: a review

Munish Chhabra and Rupinder Singh

Rapid Prototyping Journal

Volume 17 · Number 5 · 2011 · 328–350

350

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