Additive Manufacturing: A way forward transition from ... · drilling and can outperform other drill bit types. PDC drill bits were rst developed in 1970s (1). Since then, it is used

Additive Manufacturing: A way forwardtransition from Conventional to

Advanced Manufacturing Technology

Sadaqat Alia, Ahmad Majdi A Rani ∗b, c,Khurram Altaf c, Abdul Azeez d, Zeeshan Baigea, c, d, e Department of Mechanical Engineering,

Universiti Teknologi PETRONAS (UTP), Malaysiaa, b Department of Mechanical Engineering,

National University of Sciences & Technology (NUST), PakistanbCentre for Intelligent Signal & Imaging Research (CISIR),

Universiti Teknologi PETRONAS, Malaysia*Corresponding Author Email: [email protected]

March 31, 2018

Abstract

In the global world of manufacturing, researchers and in-dustries are striving continuously to improve cycle time oftheir products by minimizing wastes within the system andmaximizing their work flow. They are continuously lookinginto advanced fabrication techniques that not only providethem with improved quality at a reasonable price but alsoprovide increased flexibility in terms of design freedom with-out much needed effort. One such emerging technology isAdditive Manufacturing (AM) which is capable of produc-ing fully-dense components layer upon layer directly fromcomputer-aided-design (CAD) model as opposed to subtrac-tive manufacturing technologies. Since AM eliminates theneed of tooling, many of the current limitations of design formanufacturing (DFM) and design for assembly (DFA) areno longer applicable. AM has been in the oil and gas sector

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International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

for some time, primarily used for prototyping and designpurposes. This study focuses on the implementation of AMin the oil and gas sector motivated by the existing issuespresent in the current manufacturing methodologies. Poly-crystalline Diamond Compact (PDC) drill bit, one of themajor tools used for drilling rock formations is currentlyproduced by subtractive manufacturing method in whichsteel body is machined from premium steel grades and thenpassed through additional heat treatment processes till weget the final part. There is not much literature availableon the use of AM for manufacturing of PDC drill bit body.In this paper, current manufacturing methods of PDC drillbit body along with the problems associated with them areaddressed. Related works on improvement of drill bit bodymanufacturing and the issues associated with them are alsohighlighted. At the end of the paper, the proposed method-ology for manufacturing of PDC drill bit body through AMhas been developed which will have remarkable improve-ment in the manufacturing of the bit body.

Key Words:Additive Manufacturing; AM; CAD; DFM;DFA; PDC; drill bit.

1 Introduction

Polycrystalline Diamond Compact (PDC) drill bit is one of the ma-jor tools widely used for drilling rock formations and is consideredto be one of the most important components in oil and gas explo-ration. PDC drill bits have admirable rates of penetration duringdrilling and can outperform other drill bit types. PDC drill bitswere first developed in 1970s (1). Since then, it is used in the oiland gas sector and by 2010, 65% of the drilling operations use PDCdrill bit for drilling rock formations due to increase in its durable-ness in the past couple of years(2). A lot of research has been doneon improving the design of bit , material, cutter placement andmanufacturing process for enhanced durability and longevity(3).

Currently, PDC drill bit body is manufactured using subtractivemethod in which the final shape of PDC drill bit body is attainedby material removal process(4). The bit body is machined on CNClathes from quality steel grade and then passed through additionalheat treatment processes till we get the final desired shape(5). Dur-

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International Journal of Pure and Applied Mathematics Special Issue

ing machining process, tensile residual stresses are generated ontothe surface of the work piece that decrease the fatigue life of thepart and can lead to premature failure by increasing working tensilestresses(6).

Fig.1. PDC bit body manufacturing process(7)

PDC drill bit body is produced in two parts namely the bodysegment and the pin segment separately which are welded togetherto form a complete drill bit body(8). Since, PDC drill bits are usedin very harsh environments, the design of the bit and the joint weldneeds a lot of research and engineering improvement. It is thereforea dire desire to use an advanced manufacturing method that cansolve these issues.

Additive Manufacturing is an advanced manufacturing methodof producing functional parts. It adds and joins material layer uponlayer as opposed to subtractive manufacturing method in which thedesired shape of the part is attained by material removal from a bulkmaterial. AM has high potential to improve the shortcomings ofconventional manufacturing methods due to its unique competenceand characteristics(9). There is not much literature available onthe use of AM for the manufacturing of PDC drill bit body andmanufacturing of drill bit using AM technology is still challeng-ing. The issues identified in the current manufacturing methods ofPDC drill bit body include subtractive method for its manufactur-ing using CNC machining. It induces tensile residual stresses ontothe surface of the bit body which need to be removed before plac-ing it into function to prevent premature failure of the bit body.Since the bit is currently manufactured in two parts which are thenjoined together by welding, so Heat affected zone (HAZ) mechan-ical properties can be affected if the welding parameters are notproperly controlled.

The objective of this research work is to formulate a novel man-ufacturing procedure for PDC drill bit body that eliminates mate-rial wastage incurred using subtractive manufacturing. By applyingAM technology, one piece drill bit body can be produced eliminat-ing the use of welding in the current manufacturing method. It is

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expected that this improved manufacturing method will open newdoors for improvement of PDC drill bit.

2 Background

Further information on current manufacturing practices, residualstresses generation and advanced manufacturing methodologies arepresented in this section and the advantages of AM are reviewed.

2.1 Polycrystalline Diamond Compact (PDC)drill bit

PDC drill bits are one of the most important components of the oiland gas sector and have added a great deal to the performance andeconomics of oil and gas explorations for the last couple of years.PDC drill bit was firstly developed in 1973 by General Electric andsince then, it is widely used in oil and gas sector. PDC drill bits haveoutstanding rates of penetration during drilling and can performbetter than all other bits in the right conditions. By 2010, 65% ofthe drilling operations use PDC drill bit for oil explorations anddrilling due to its durableness(2). The market usage of PDC drillbit has increased considerably in the last couple of years. The usageof PDC drill bits was only 2% worldwide as compared to roller conebits when it was firstly produced and this ratio has now increased to80% in 2011 according to the report survey(10). PDC are made bycombining successive layers of Polycrystalline Diamond (PCD) witha layer of cemented carbide liner at high temperature and pressurethat joins them together. PCD are considered to be one of the mosthard diamonds. PDC cutters are made of substrate of carbide anddiamond grit. Cobalt alloy is used as a binder and catalyst insintering process which helps in keeping the carbide and diamondintact. The PDC drill bits are manufactured in two different classesnamely the matrix-body drill bit and steel-body drill bit. Both ofthem have significant capabilities and advantages that limit anddecide its application of use. Matrix-body drill bit are made of avery hard composite material containing tungsten carbide grainsmetallurgically bonded together with a soft but tougher metallicbinder. This type of bit is capable of withstanding high compressive

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loads and is resistant to abrasion and erosion. Steel-body drill bitis made up of premium steel grades and is capable of withstandinghigh impact loads. In this study, we are focusing on the steel-bodyPDC drill bit.

PDC drill bits have outperformed other bit specially roller conebits in the last couple of years. Since its first invent in 1970s, thedevelopment of PDC bits has marked revolutionary technologicalimprovement. The cycle of improvement and growth in PDC mar-ket share has been shown in figure 2.

Fig.2. PDC bit market adoption S curve, from 1980 to projected2016(10)

2.2 Traditional Manufacturing of PDC Drillbit body

PDC drill bit is conventionally manufactured using subtractive man-ufacturing method in which the built material is machined usingconventional CNC machines to get the desired shape of the bit(4).The bit body is manufactured by using Computer Numerical Con-trol (CNC) machine which removes material from the bulk materialto give the bit desired shape and structure(11). The profile of thebit, its hydraulic design, pin section and desired structure is allachieved by machining the stock on the CNC machine. Once, thedesired shape of the bit is achieved, the PDC cutters are attachedto the pockets already machined with the help of brazing whichfirmly fits in the cutters in their appropriate place. All the bitsare produced in two parts, namely, the body section and the pinsection as shown in the figure 1 and 8. These two sections are laterjoined together by welding to get the complete drill bit body(8).

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2.3 PDC Drill bit material development

PDC drill bits are currently manufactured from premium steel gradesor a matrix of tungsten carbide powder(12). Both these types arewidely used in the industry but the properties of the material usedlimit its applications to specific purposes and loading conditions.Steel body bits are superior to matrix body bits in terms of strengthand durability(3) and are best suited for high penetration rates(12).Our study is also focused on the steel body bits due to its widelyusage and advantages. Extensive studies and research is still beingcarried out to improve the bit body base material for improved wearresistance. Therefore, a new material M2 High Speed Steel (HSS)has been addressed in this study to be used as the base material formanufacturing of PDC drill bit body. Its material properties andprocessing through AM has also been discussed in later sections.

2.4 Residual stresses generation in machining

PDC drill bit body is manufactured from premium steel grades bymachining the stock on CNC Lathe(5, 13). Residual stresses aregenerally produced in all machining processes irrespective of theprocess used(14) which have a very high impact on the strength,performance, microstructure and fatigue life of the part produced(15).The residual stresses may also produce dimensionally instable parts(16)and thus need post processing after machining in order to removethe residual stresses generated in the parts before they are subjectedto function(17).

2.5 Effect of Residual stresses on Fatigue lifeof machined parts

Residual stresses are generally produced in machining of parts andvary in depth and magnitude(18). They have high impact on the fa-tigue life of engineering components(19). As shown in the figure 3,the compressive residual stresses are high enough while being closeto the surface and start decreasing as the depth is increased. At acertain specified value of depth, the residual stresses become negli-gibly very small and if the depth is increased further, it results intogeneration of tensile residual stresses. Compressive residual stresses

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prevent the nucleation of cracks and generally improve the perfor-mance and fatigue life of the component, whereas, tensile residualstresses lead to premature failure of components by increasing theservice stresses(20).

Fig.3. Residual Stresses Distribution along the Depth ofSurface(19)

2.6 Effect of welding on strength and fatiguelife of parts

PDC drill bit body is produced in two parts, the body section andthe pin section. These two sections are then joined together bywelding to get a complete drill bit body(8). Since the PDC bits aresubjected to heavy loads during drilling, the welded joints requirebeing stable structurally and mechanically to bear these loads inharsh environments. Improper welding might lead to propagationof cracks in the welded area which can lead to a severe reduction inthe strength of the parts being welded(21, 22). Heat affected zone(HAZ) mechanical properties change remarkably if proper weldingparameters are not selected(23). Since PDC drill bits are subjectedto heavy loads, improper welding can be a major factor in thefatigue life reduction of bit body. Residual stresses are generatedduring welding due to rapid heating and subsequent cooling whichadversely affect the fatigue behavior of the component leading topremature failure and crack generation(24, 25). Figure 4 shows thecrack generation in a gear due to improper welding parameters.

Fig.4. cracking in a large cast girth gear caused by improper weld

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2.7 Additive Manufacturing

Additive Manufacturing (AM) also known as 3D printing, RapidPrototyping (RP) may be defined as a process of joining materi-als to make objects from 3D model data, usually layer upon layer,as opposed to subtractive manufacturing methodologies(26). It allstarts with creating a three dimensional model of the part to beproduced in a CAD software or a 3D scan of the existing object byscanning its dimensions along with the shape with a 3D scanner.This model is then exported to the software of the AM machinewhich slices down the entire model into a number of layers de-pending upon the shape and size of the object. The AM machinethen fabricates the part layer upon layer until the entire objectis formed. AM can produce parts of any shape from very simpleshape to complex and intricate shapes that cannot be manufacturedeasily with subtractive manufacturing methods with substantiallyreduced time, cost and material wastage(27). During the last twodecades, the AM technology has progressed a lot and functionalparts can now be manufactured using AM without the need ofany tooling(28). It has been reported that products and servicesmanufactured using AM in the last 10 years are almost 30 % ofthe products produced worldwide(29). With the design freedom,AM can now produce parts that were previously not possible withsubtractive manufacturing methods. AM has reduced the supplychain management and the material wastage using AM has beenreduced drastically to 40 % in metal applications worldwide(30).A comparative summary between AM and traditional subtractivemanufacturing technologies has been given in table 1.

Table 1: Additive Manufacturing Technology vs. TraditionalManufacturing(27)

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2.8 Overview of different AM technologies

There are a number of AM technologies which use the same prin-ciple of adding material layer upon layer. They only vary in termsof material used and the way the material is deposited. AM can bedivided into two main classes namely by

i) the physical state of the material ; liquid, solid or powderbased

ii) the way the material is fused together

The classification of AM process has been shown in figure 5.

Fig.5. Classification of different AM processes

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2.9 Selective Laser Melting

Selective laser melting (SLM) is a powder-based AM technologythat produces parts from CAD model. During SLM process, suc-cessive layers of metal powder are melted and fused on top of eachother by energy of a high intensity laser beam. Consequently, al-most fully dense parts are produced using SLM that do not needany post processing and can be directly used. Normally metallicparts are produced using SLM and there is a wide range of metalpowders that can be processed using SLM. In SLM, the laser beamfocuses at specific location on the powder bed for each layer spec-ified by the CAD file. The particles lie loosely in a bed, which iscontrolled by a piston, that is lowered the same amount of the layerthickness each time a layer is finished. The laser system consistsof a laser source, a laser scanner, a powder loading unit, a buildingplate, recoater and a gas flow controller. The laser scanner movesalong the building plate by use of scanning mirrors. Different typeof laser can be used with different wavelengths to match the ab-sorption characteristics of the corresponding powder granules. Thetwo types of laser sources that are commonly used for laser melt-ing is a continuous wave CO2 laser with a wavelength of 10.6 m,which is particularly suit-able for processing ceramics. The otheris a continuous wave ytterbium fiber laser with a wavelength of1.1m, which is commonly used for processing metals. The processbegins by spreading and leveling a thin layer of metal powder us-ing the recoater blade and after height adjustment of the buildingplate with the recoater and achieving environmental conditions, thelaser exposure begins. The laser beam is directed by the scanningmirrors and delivers the power P to the powder making the firstlayer. Repeatedly the laser beam scans over new layer of powderon the previously solidified layer and makes the next layer. Thisis repeated until the part is built(31). A schematic diagram of theSLM process is shown in figure 6.

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Figure 6: A schematic view of the SLM process(32)

2.10 Selective Laser Melting of M2 High SpeedSteel

M2 is a tungsten-molybdenum high-speed steel (HSS) and is widelyused for general purpose cutting and non-cutting applications. Ithas a wider heat-treating range than most of the molybdenum high-speed steels, coupled with a resistance to decarburization. M2 offersan excellent combination of red hardness, toughness, and wear re-sistance. It is widely used for its high hardness of 800 HV andexcellent wear resistance(33). SLM of M2 HSS has been attemptedby researchers and the feasibility of processing M2 HSS with SLMtechnique is still challenging. SLM can be used to produce toolswith complex geometries and M2 HSS is a material from the groupof tool steels used to produce tools. It is thus an appropriate mate-rial for producing complex tools(34). SLM process parameters havebeen investigated by many researchers in an attempt to producegood quality parts with high density and retaining properties com-parable to conventionally produced M2 HSS. The M2 HSS powderis produced by the gas atomization process. Particle size is between15 to 45 m. A SEM picture of the powder shown in fig. 7 revealsthat the particles are spherical in shape as expected from the gasatomization process. This will provide excellent powder flow abil-ity that is necessary for an ideal powder layer deposition, ensuringgood part density and quality(35).

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Figure 7: SEM image of M2 HSS powder(35)

3 Related Works

The use of Additive Manufacturing for the production of PDC drillbits is still challenging and literature on the use of AM for producingdrill bits is very little. Khurram Altaf et al(4) have tried to combineAM and investment casting for prototype development of PDC drillbit body. They used the combination of Thermojet 3D printing andinvestment casting to develop the prototype. Wax patterns werecreated using AM in separate sections for minimizing the supportstructure. Then the drill bit body was casted using investmentcasting process. Due to machine printing limits, the 3D CAD modelwas divided into three parts and printed separately using Thermojet3D printing. The PDC drill bit body wax pattern was divided intothree parts and 3D printed individually.

Figure 8: Wax patterns for the top and bottom sections(4)

For the investment casting, they used TJ2000 material which isone of the classes of steel. Since, the parts were produced separately,they were welded together to form a complete drill bit body asshown in the figure 9 below. The author(4) believed that AM can bea promising technology in the manufacturing of PDC drill bit bodyand recommends more research on the material and productionprocess.

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Figure 9: Investment casted PDC bit body before and afterpainting(4)

4 Methodology

The proposed methodology of the project is shown in the figure10 which includes the manufacturing of the bit using both con-ventional and AM technology. The AM process involves properselection of raw material, SLM machine process parameters includ-ing scan speed, laser power, layer thickness, focal spot size andwavelength of the beam used. For the conventional manufacturing,proper selection of M2 rod size is of utmost significance. The flowchart of the methodology which summarizes the whole project isshown in the figure 10.

Figure 10: Methodology of the project

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5 Conclusion

At the end of this study, it is highly expected that AM will serveas the most suitable technique of producing a stress free PDC drillbit body with enhanced mechanical properties in terms of increasein strength, improved wear resistance, durability and long lasting.The oil and gas sector will be greatly influenced by this new method-ology of PDC drill bit body. M2 HSS has good wear resistancewhich will improve the life of the drill bit. The preliminary resultspresented are obtained from the similar work in the literature. Itdisplays that SLM of M2 HSS has been proven to be feasible. Partswithout cracks can be produced with an achievable density of 97%.Furthermore, parts produced directly from the SLM process havehigh average hardness values between 800 HV to 900 HV which arecomparable to conventionally produced casted parts. These conven-tionally produced M2 HSS cast parts have hardness values between750 HV to 830 HV depending on the heat treatment process(36).

Fig.11. Hardness of M2 HSS SLM parts compared toconventionally produced parts(35)

Karolien Kempen et al(36) proved in their study that crack-free M2 HSS parts with a high density can be produced by SLM.The part with the maximum density of 99.8% is produced at apreheating of 200C, a laser power of 105 W, a scan speed of 150mm/s and a hatch spacing of 126 µm. These previous results arethe source of motivation for this project and the authors believethat this project will have remarkable results in future.

Acknowledgement The authors would like to express theirgratitude to Univeristi Teknologi PETRONAS (UTP) for the fi-nancial support and facilities provided for this project.

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Documents

Additive Manufacturing: A way forward transition from ... · drilling and can outperform other drill bit types. PDC drill bits were rst developed in 1970s (1). Since then, it is used