Investment Castings

LATEST TRENDS IN INVESTMENT CASTING TECHNOLOGY

Dr.Ing.Milan Horáček,PhD Brno University of Technology, CZ

PAPER STRUCTURE

A/ Survey of foundry technologies available for casting manufacture

B/ Basic principles of lost wax process – investment casting

C/ Brief history of the investment casting technology

D/ Description of individual investment casting process phases - wax pattern manufacture- ceramic shell manufacture- de-waxing- shell heat treatment- metal pouring- finishing operations

E/ Accuracy of investment casting technology

F/ Capabilities of modern lost wax technology (examples of castings)

A/ SURVEY OF CASTING TECHNOLOGIES USING SAND MOULDING

Ist . GENERATION - clay binders

IInd. GENERATION – chemical binding

a/ Self-hardening processes (plaster,cement,sodium silicate,resin)

b/ External hardening processes (sodium silicate, resin)

c/ Ceramic moulds (mould firing before pouring)

1. Permanent pattern 2. „Lost“ pattern

LOST WAXLOST FOAM

IIIrd. GENERATION – physical binding

B/ BASIC INVESTMENT CASTING PROCESSWax pattern making Wax pattern assembly Dipping into ceramic

slurry

Ceramic coating Finished shell De-waxing

Metal pouring Removal of shell Casting cut-off

Die

Wax pattern

Gating system

Ceramic shell

Wax pattern

C/ BRIEF HISTORY OF LOST-WAX PROCESS

Thajsko Mezopotámie Izrael Indie/S.V. Asie Anatólie Čína Egej / Řecko Etrusko Keltská S. Evropa Římané Jižní/Střední Amerika Západní Afrika Západní Evropa Renesanční Itálie

5000 4000 3000 2000 1000 0 1000 2000p.n.l – 0 – n.l

EXAMPLES OF HISTORICAL CASTINGS

gold comb casting(300g, Dniepr area, 4th cent.A.D.)

bronze head (Benin – 12th.cent.A.D.)

bronze statue of Perseus with Meduza head(Cellini, 1540)

D/ DESCRIPTION OF INDIVIDUAL PHASES OF INVESTMENT CASTING PROCESS

1. WAX PATTERN MANUFACTURE

a/ Die manufactureb/ Wax pattern injectionc/ Pattern assembly

2. CERAMIC SHELL MANUFACTURE

a/ Step-by-step shell building and dryingb/ Shell de-waxingc/ Ceramic shell firing

3. METAL POURING

a/ On airb/ Under vacuum

4. FINISHING OPERATIONS

a/ Gating system removalb/ Surface finish cleaning, blasting, etc.

1. WAX PATTERN MANUFACTURE

a/ Master die making

-Using master pattern(using low-melt point alloys, by metal spraying, by galvanization)

Master pattern

Sand mould

Plaster

Low melting point alloySn,Bi,Pb,CdTmel=70°CsoftTmel= 138°Chard

Master die

METAL SPRAYINGMaster die

Low melting point alloy

GALVANIZATIONLow melting point alloyMetal master pattern

Ni,Cu,Feby galvanization

-By machining from solid metal blocks( the most often used method )

1. WAX PATTERN MANUFACTUREb/ Wax pattern making

WAXES USED

Present waxes – complex materials containingfollowing components:

- natural waxes TYPES of WAXES- syntetic waxes- natural resins - Straight (non-filled)- syntetic resins - Filled (30% of filler)- organic fillers - Emulsified- water (by water, air)

Combination of different raw materials properties to achieve optimal wax characteristics:-melting and congealing point - ash content (‹ 0,05%)-hardness - flexibility-viscosity - surface quality-expansion/contraction - stability to oxidation-solidification rate - possibility to recycle

BASIC PRINCIPLE OF INJECTION MACHINE FOR WAX PATTERN MAKING

vc

Piston

Piston pump

Master die

Injection nozzle

Transport wax hose

Injection cylinder with wax

Valve

Sp (piston surface)

Wax storage

EQUIPMENT FOR WAX PATTERN MAKING –injection machine +wax melter + conditioner

INJECTION CYCLE

τNτK

τZ

τE

1

1a

32

4 5

U (pre-setpackingpressure)

Pressurecontrolledphase

Die opening

Speed controlled phase

Pressure

[bar]

τE …die cavity filling timeτK …packing timeτN …holding timeτZ …cycle time

(till the die opening)

1

1000

Time

NOTE:Points 1, 2, 3, 4 a 5 correspondent to the points in following picture

INJECTION CYCLE

TM (wax temperature during injection)TE (wax temperature during pattern stripping from die)

1 bar

600

1500

200

1000

Specific

volum[cm3/

g]

1 – 2 …pressure increase in die cavity → decrease of spec.volume2 – 3 …packing pressure →slight decrease of spec.volume3 – 4 …pressure decrease during wax solidification → constantspec. volume4 – 5 …wax cooling in die →decrease of spec.volume(contraction)

Temperature [ºC]

NOTE:vSP = 1/ρ …specific volume [cm3/g]ρ = 1/vSP …density [g/cm3]

1

1a

23

4

5

EXAMPLES OF INJECTION MACHINES

WAX PREPARATION FOR INJECTION

EXAMPLES OF WAX PATTERNS

1. MANUFACTURE OF WAX PATTERNSc/ Wax pattern assembly

b) Patterns straight on gating sprue

Wax pattern assembliesa) Horizontal placed patterns on a special

gating rings

Assembly Design Influenced by:

-Technique of pattern assembly (glueing/welding)

-Shelling technique

-De-waxing technology

-Pouring system

-Casting cutting-off technique

-Standartization of gating systems

2. MANUFACTURE OF CERAMIC SHELLa/ Shell building and drying

I/ DEGREASING OF WAX PATTERNS(removal of remaining separator from the wax pattern surface)

II/ DIPPING INTO CERAMIC SLURRY(ceramic slurry consists of filler and binder)

Filler – heat resistant ceramic flour (fused silica,molochite,zircon,..)Binder – colloidal silica sols based on alcohol (alcosols) or water (hydrosols)

III/ SHELL DRAINING

IV/ STUCCO APPLIED WITH CERAMIC GRIT( fluid or rainfall systems)

Stucco materials – silica, molochite, alumina, zircon, atd. Grain size according to the coat number :

- first 1-2 „prime coats“ fine particles –0,175-0,25 mm (CASTING SURFACE FINISH)- next 3- x „back-up coats“ coarser – 0,25-0,5 mm (MOULD GAS PERMEABILITY)

V/ SHELL DRYING(in aircondition room 2-4hours – temp. 20 °C ±1 °C , relative humidity 30-60% -according to the type of binder used, sufficient air flow)

VI/ REPEATING ( II – V)(till the needed number of coats – 8-12)

SLURRY MIXING TANKS

SANDERSRainfall Fluidized bed

ROBOTIZIED SHELLING LINES

FULLY ROBOTIZED SHELLING LINE

2. MANUFACTURE OF CERAMIC SHELL

b/ Shell de-waxing

KEY PROBLEM : different wax and shell expansion !Wax expansion bigger,therefore danger of shell cracking during de-wax process.

NECCESITY of „dilatation gap“ building on wax pattern surface –through THERMAL SHOCK – see picture bellow.

CERAMIC SHELL

WAX PATTERN

Thermal expansion

TECHNIQUES USED FOR DE_WAXING

I/ By overheated steam – in boilerclaves

II/ By firing – „flash fire“ system

III/ By microvave heating

2. MANUFACTURE OF CERAMIC SHELL

b/ Shell de-waxing

Majority foundries use boilerclave systemMAIN REASONS:-Ideal steam properties for heat transfer-Easy to collect de-waxed wax-High efficiency

Typical working parameters:-Steam temperature – 160-170°C-Working pressure – 6-8 atm-Reaching work.pressure in 4-5 s-Controlled speed of pressure drop

DE-WAXING IN BOILERCLAVE

WAX RECYCLING AFTER ITS DE-WAXING

WAX RECYCLING

AUTOCLAVE

BOILER TANK

REMOVAL OF IMPURITIES + NEW WAX ADDITION

GEAR PUMP

MASTERDIE

16 hours

IMPURITIES

STORAGE TANK

2. MANUFACTURE OF CERAMIC SHELL

c/ Shell firing

GOAL: transfer of amorphous type of SiO2 binder layer into a crystallic one +removal of volatiles matters (waxes remains)

0

100

200

300

400

500

600

700

800

900

1000

0 60 120 180 240 300 360

Čas [min]

Tepl

ota

[ ºC]

575 ºC

60 – 80 min

900 - 1080 ºC

100 ºC

30 min

30 min

≈ 5 ºC/min

≈ 5 ºC/min

DIFFERENT TYPES OF CERAMIC MOULDS MADE BY LOST WAX PROCESSa) SOLID CERAMIC MOULD – COMPACT METHOD

a) SOLID CERAMIC MOULD – COMBINED METHOD

CERAMIC SLURRY

SLURRY SAND(CEMENT)

2-3 SHELLS

d) SELF SUPPORTING SHELLc) BACKFILLED SHELL

2-3 SHELLS 5-8 SHELLS

POSSIBILITIES OF USING CERAMIC CORES

Ceramic core manufacturing:

-Preparation of ceramic mass

-Forming into a needed shape

-Heat treatment

3. METAL POURING

UNDER VACUUMGRAVITY

a/ Classical pouringb/ „Roll-over“pouring

a/ Melting and gravity pouring under vacuumb/ Counter-gravity pouring (CLA , CLV)

GRAVITY POURING POURING UNDER VACUUM

VACUUM VACUUM

VACUUM

POSSIBILITIES OF MOLTEN METAL FILTRATION

FILTRATION POSSIBILITIES

1.STRAINER CORES

2.FOAM FILTERS 4.GLASS FIBRES FILTERS

3.EXTRUDED FILTERS

FILTER

4. FINISHING OPERATIONS

- casting cut-off from gating system(by vibration , cutting )

- casting surface cleaning(by blasting , grinding )

- casting heat treatment

5. CASTING QUALITY INSPECTION

- chemical composition, structure(spectrometr, metalography )

- internal casting quality(X-ray, ultrasonic )

- casting surface finish(capillar methods )

- mechanical properties(tensile strength, hardness, ductility, etc. )

- dimensional accuracy

E/ DIMENSIONAL ACCURACY OF INVESTMENT CASTINGS

INVESTMENT CASTING PROCESS(Lost wax process) is

whereCASTING TECHNOLOGY

i.e. our goal is to achieveA FINAL MACHINING SHOULDBE ELIMINATED

to be ready for usage inNET – SHAPE CASTING

complying with allAS CAST CONDITIONS

DIMENSIONAL AND TOLERANCEREQUIREMENTS

The average tolerance exhibited by various casting processes (by J.Campbell)

THE FINAL CASTING’SDIMENSIONS

Dimensional changes during individual stages of investment casting technology

dependent on

PATTERNDIE

DIMENSIONS

INVESTMENTCASTINGPROCESS

FINAL CASTING

DIMENSIONS

PATTERN DIE DIMENSIONmust comply with

All subsequent dimensional changes during the processi.e.

PATTERN MAKING

SHELLING

DE - WAXING

SHELL DRYING and FIRING

METAL POURING, SOLIDIFICATION and COOLING

DIMENSIONAL CHANGES DURING INVESTMENT CASTING PROCESS

dimensiontolerances

Dim

ensi

onD

imen

sion

+

+ tol

eran

ces

tole

rance

s

StageStage ofof thethepocessspocesss

1 2 34 5

1 Tool cavity

2 Wax pattern

3 Dried shell

4 Fired shell

5 Final casting

DIMENSIONAL ACCURACY OF INVESTMENT CASTINGS

F/ CAPABILITIES OF INVESTMENT CASTING TECHNOLOGY

EXAMPLES OF CASTINGS MADE BY LOST WAX TECHNOLOGYAircraft engine blade – equiaxed structure, directional solidification,

single crystal - superalloys Ni base, vacuum cast

Superalloys Ni base, vacuum cast-castings for power industry

Part of aircraft engine GE (Boeing 747,767) – Ti alloy

EXAMPLES OF CASTINGS MADE BY LOST WAX TECHNOLOGY

Casing of tank control system – Al alloy

Part of helicopter V-22 – Ti alloyInvestment castings for shotgun-Cr hardenable stainless steel

Boeing 777 APU duct- Ti alloy

EXAMPLES OF CASTINGS MADE BY LOST WAX TECHNOLOGY

Typical aluminium investment casting features

EXAMPLES OF CASTINGS MADE BY LOST WAX TECHNOLOGY

Investment vacuum castings for surgical implants ( knee and hip joints)- Ti6Al4V alloys , CoCrMo alloys

EXAMPLES OF ALUMINIUM INVESTMENT CASTINGS

SUBSTITUTION OF ORIGINAL TECHNOLOGY USEDBY LOST WAX PROCESS

MACHINING+ WELDING+BENDING

INVESTMENT CASTING

Weight 0,5 kg Weight 0,2 kg

Material – Fe alloy Material – AlSi10 Mg

Dimensions 155x55x55 mm

Benefit – weight+ labour reduction, better part properties

1. part PLAST-2.part Al machined by milling+ screwed

together

Investment casting

Weight 0,11 kg Weight 0,14 kg

Material: plast+ Al alloy Material AlSi10 Mg

dimensions 100x40x30 mm

Benefit – labour less demanding, increased lifetime and component utility values

MACHINING -GLUEING INVESTMENT CASTING

Weight O,52 kg Weight 0,32 kg

Material – Al alloy Material: AlCu4 Ti

Dimensions 70x95x110 mm

Benefits: labour less demanding, increased component utility values

MACHINING,WELDING INVESTMENT CASTING

Weight 0,15 kg Weight 0,03 kg

Material – Fe alloy Material – AlSi10 Mg

Dimensions 40x40x40 mm

Benefits: by 30% less labour demanding, increased part utility value

MACHINING,BENDING, WELDING

INVESTMENT CASTING

Weight 0,05 kg Weight 0,02 kg

Material – Al alloy Material – AlSi10 Mg

Dimensions: 55x40x40 mm

Benefits: by 35% less labour , increased part utility value

PRESSURE DIE CASTING INVESTMENT CASTING

Weight 0,10 kg Weight 0,04 kg

Material : Zn alloy Material: AlSi10 Mg

Dimensions:60x60x25 mm

Savings: see next picture

SAND CASTING INVESTMENT CASTING

Weight 0,25 kg Weight 0,20 kg

Material – AlSi10 Mg Material – AlSi10 Mg

Dimensions: 204x100x15 mm

Savings: less labour cost and increase of component quality

SAND CASTING INVESTMENT CASTING

Weight - 4,8 kg Weight – 0,8 kg

Material - grey iron Material - AlSi7 Mg

Dimensions 240x130x40mm

Benefit: Labour costs savings

MACHINING INVESTMENT CASTING

Weight of piece for mach. 3,36 kg Weight 0,12 kg

Material – Fe alloy Material - AlSi10 Mg

Dimensions Ø 220x18 mm

Benefit: labour costs savings

SAND CASTING INVESTMENT CASTING

Weight 2,4 kg Weight 1,8 kg

Material RR 350 ( AlCu5Ni) Material RR 350 (AlCu5Ni)

Dimensions: 150x150x110 mm

Benefits: weight reduction, increase of engine power by app. 15 %

INVESTMENT CASTING AGAINSTPRESSURE DIE CASTING

• ECONOMICAL COMPARISON OF „CORNER“ CASTING

Inv.Cast. (CzCrowns)

Press.Die (CzCrowns)

IC(total) PD(total)

Die price 30.000 460.000

1.000 pcs 45.000 16.000 75.000 476.000

10.000 pcs 450.000 160.000 480.000 620.000

15.000 pcs 675.000 240.000 705.000 700.000

BREAK-EVEN POINT IS app. 15.000 pcs

In other words only over this amount of castings is PD technology more economical

AIRCRAFTS WITH „MIKRON“ ENGINES (www.parmatechnik.cz)

SAND CASTING INVESTMENT CASTING

Weight 8,7 kg (45 kg) Weight 2,7 kg

Material. Fe alloy Material:AlSi7 Mg T6

Dimensions: 260x260x100 mm

Savings: on material and labour

SAND CASTING INVESTMENT CASTING

Weight 0,9 kg Weight 0,4 kg

Material – Fe alloy Material AlSi7 Mg T6

Dimensions 150x80x60 mm

Benefit: weight reduction and less labour during machining

Customer:

TadiranCommunications

Title:

Body 9004

Dimensions:

234 x 318 x 201 mm

Material:

A 356

Weight:

3,5 Kg

Customer:

BMT

Title:

Support

Dimensions:

190 x 301 x 240 mm

Material:

A 356

Weight:

1,33 Kg

Customer:

Borcad

Title:

Rack

Dimensions:

304 x 337 x 57 mm

Material:

A356

Weight:

0,82 Kg

Customer:

Uniplet

Title:

Cover

Dimensions:

209 x 360 x 118 mm

Material:

A356

Weight:

1,25 Kg

Title:

Ramback side

Material:A 357

Customer:

Wyman-Gordon

Dimensions:

518 x 147 x 32 mm

Weight:

1,38 Kg

THANK YOU FOR YOUR ATTENTION

HAVE A NICE DAY !