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 FOAM LOST WAX IIIrd. GENERATION physical binding
B/ BASIC INVESTMENT CASTING PROCESS Wax pattern making Wax pattern assembly Dipping into ceramic slurry Die Wax pattern Wax pattern Gating system Ceramic coating Finished shell De-waxing Ceramic shell Metal pouring Removal of shell Casting cut-off
C/ BRIEF HISTORY OF LOST-WAX PROCESS p.n.l 0 n.l 5000 4000 3000 2000 1000 0 1000 2000 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
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 manufacture b/ Wax pattern injection c/ Pattern assembly 2. CERAMIC SHELL MANUFACTURE a/ Step-by-step shell building and drying b/ Shell de-waxing c/ Ceramic shell firing 3. METAL POURING a/ On air b/ Under vacuum 4. FINISHING OPERATIONS a/ Gating system removal b/ 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 METAL SPRAYING Master die Sand mould Plaster Low melting point alloy Low melting point alloy Sn,Bi,Pb,Cd T mel =70 C soft T mel = 138 C hard Master die GALVANIZATION Low melting point alloy Metal master pattern Ni,Cu,Fe by galvanization -By machining from solid metal blocks ( the most often used method )
1. WAX PATTERN MANUFACTURE b/ Wax pattern making WAXES USED Present waxes complex materials containing following 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 Valve Wax storage S p (piston surface) Piston pump Transport wax hose v c Injection nozzle Piston Injection cylinder with wax Master die
EQUIPMENT FOR WAX PATTERN MAKING injection machine +wax melter + conditioner
INJECTION CYCLE 1000 Speed controlled phase Pressure controlled phase 2 U (pre-set packing pressure) 3 τ E die cavity filling time τ K packing time τ N holding time τ Z cycle time (till the die opening) Pressu re [bar] NOTE: Points 1, 2, 3, 4 a 5 correspondent to the points in following picture 1a Die opening 1 1 4 5 τ E τ K τ N Time τ Z
INJECTION CYCLE Specif ic volum [cm 3 / g] 4 3 1 1a 2 1 bar 200 600 1000 1500 1 2 pressure increase in die cavity decrease of spec.volume 2 3 packing pressure slight decrease of spec.volume 3 4 pressure decrease during wax solidification constant spec. volume 4 5 wax cooling in die decrease of spec.volume (contraction) 5 NOTE: v SP = 1/ρ specific volume [cm 3 /g] ρ = 1/v SP density [g/cm 3 ] T E (wax temperature during pattern stripping from die) T M (wax temperature during injection) Temperature [ºC]
EXAMPLES OF INJECTION MACHINES
WAX PREPARATION FOR INJECTION
EXAMPLES OF WAX PATTERNS
1. MANUFACTURE OF WAX PATTERNS c/ Wax pattern assembly Wax pattern assemblies a) Horizontal placed patterns on a special gating rings Assembly Design Influenced by: -Technique of pattern assembly (glueing/welding) -Shelling technique -De-waxing technology b) Patterns straight on gating sprue -Pouring system -Casting cutting-off technique -Standartization of gating systems
2. MANUFACTURE OF CERAMIC SHELL a/ 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
SANDERS Rainfall 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. TECHNIQUES USED FOR DE_WAXING I/ By overheated steam in boilerclaves II/ By firing flash fire system CERAMIC SHELL WAX PATTERN Thermal expansion III/ By microvave heating
2. MANUFACTURE OF CERAMIC SHELL b/ Shell de-waxing Majority foundries use boilerclave system MAIN 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 REMOVAL OF IMPURITIES + NEW WAX ADDITION AUTOCLAVE BOILER TANK 16 hours IMPURITIES STORAGE TANK MASTER DIE GEAR PUMP
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) 1000 900 800 5 ºC/min 900-1080 ºC 60 80 min 700 Teplota [ ºC] 600 500 400 5 ºC/min 575 ºC 30 min 300 200 100 0 100 ºC 30 min 0 60 120 180 240 300 360 Čas [min]
DIFFERENT TYPES OF CERAMIC MOULDS MADE BY LOST WAX PROCESS a) SOLID CERAMIC MOULD COMPACT METHOD CERAMIC SLURRY a) SOLID CERAMIC MOULD COMBINED METHOD SLURRY SAND (CEMENT) 2-3 SHELLS c) BACKFILLED SHELL d) SELF SUPPORTING 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
GRAVITY 3. METAL POURING UNDER VACUUM a/ Classical pouring b/ Roll-over pouring a/ Melting and gravity pouring under vacuum b/ Counter-gravity pouring (CLA, CLV) GRAVITY POURING POURING UNDER VACUUM VACUUM VACUUM VACUUM
POSSIBILITIES OF MOLTEN METAL FILTRATION FILTRATION POSSIBILITIES 1.STRAINER CORES 3.EXTRUDED FILTERS FILTER 2.FOAM FILTERS 4.GLASS FIBRES FILTERS
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 CASTING TECHNOLOGY where A FINAL MACHINING SHOULD BE ELIMINATED i.e. our goal is to achieve NET SHAPE CASTING to be ready for usage in AS CAST CONDITIONS complying with all DIMENSIONAL AND TOLERANCE REQUIREMENTS
The average tolerance exhibited by various casting processes (by J.Campbell)
THE FINAL CASTING S DIMENSIONS dependent on Dimensional changes during individual stages of investment casting technology INVESTMENT CASTING PROCESS PATTERN DIE DIMENSIONS FINAL CASTING DIMENSIONS
PATTERN DIE DIMENSION must comply with All subsequent dimensional changes during the process PATTERN MAKING i.e. SHELLING DE - WAXING SHELL DRYING and FIRING METAL POURING, SOLIDIFICATION and COOLING
DIMENSIONAL CHANGES DURING INVESTMENT CASTING PROCESS tolerances dimension 1 Tool cavity Dimension Dimension + tolerances tolerances 1 2 3 4 5 2 Wax pattern 3 Dried shell 4 Fired shell 5 Final casting Stage Stage of the pocesss pocesss
DIMENSIONAL ACCURACY OF INVESTMENT CASTINGS
F/ CAPABILITIES OF INVESTMENT CASTING TECHNOLOGY
EXAMPLES OF CASTINGS MADE BY LOST WAX TECHNOLOGY Aircraft 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 Investment castings for shotgun- Cr hardenable stainless steel Boeing 777 APU duct- Ti alloy Part of helicopter V-22 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 USED BY LOST WAX PROCESS
MACHINING+ WELDING +BENDING Weight 0,5 kg Material Fe alloy INVESTMENT CASTING Weight 0,2 kg Material AlSi10 Mg Dimensions 155x55x55 mm Benefit weight+ labour reduction, better part properties
1. part PLAST-2.part Al machined by milling+ screwed together Weight 0,11 kg Material: plast+ Al alloy dimensions 100x40x30 mm Investment casting Weight 0,14 kg Material AlSi10 Mg 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 Weight 0,05 kg Material Al alloy Dimensions: 55x40x40 mm INVESTMENT CASTING Weight 0,02 kg Material AlSi10 Mg 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 AGAINST PRESSURE DIE CASTING ECONOMICAL COMPARISON OF CORNER CASTING Inv.Cast. (CzCrowns) Press.Die (CzCrowns) Die price 30.000 460.000 IC(total) PD(total) 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 Weight 0,9 kg Material Fe alloy INVESTMENT CASTING Weight 0,4 kg Material AlSi7 Mg T6 Dimensions 150x80x60 mm Benefit: weight reduction and less labour during machining
Customer: Tadiran Communications 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
Customer: Wyman-Gordon Dimensions: 518 x 147 x 32 mm Title: Ramback side Material: A 357 Weight: 1,38 Kg
THANK YOU FOR YOUR ATTENTION HAVE A NICE DAY!