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P.R.SRIVATHSAN

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METAL CASTING PROCESSMETAL CASTING PROCESS

Investment Casting

Vacuum Casting

Permanent-Mold Casting Slush Casting

Pressure Casting

Die Casting

Centrifugal Casting

Squeeze casting

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INVESTMENT

CASTING

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INVESTMENT CASTINGINVESTMENT CASTING

Also called lost-waxprocess

First used 4000 3000 BC

The pattern is made of wax or of a plastic by molding orrapid prototyping techniques

Term investmentderives from the fact that the pattern isinvested with the refractory material

Need careful handling because they are not strong enoughto withstand the forces involved in mold making

Wax can be recovered and reused

Introduction:

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Investment casting process

Expendable patterns

Injection molding technology

Gating system Shell building

Dewax

Preheating to 1830 F( 10000 C )

Pouring molten metal into shell Breaking of shells

Castings are cut

Sandblasting or machining

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Process parameters

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Ceramic slurry materials

Mullite (Al2O3 44-48%, SiO2 47-51%, Fe2O3 max. 1%, TiO2max. 1%).

Zircon flour.

Binders: Colloidal Silica (SiO2 25-45%, Na2O max.1% in

distilled water); sodium silicate (NaO*nSiO2*mH2O); ethyl

silicate (Si(OC2H5)4).

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Advantages and disadvantages of

investment casting

Capability to cast thin walls.

Wide variety of metals and alloys (ferrous and non-

ferrous) may be cast.

Draftis not required in the molds design.

Low material waste.

Advantages:

Excellentsurface finish. Tightdimensional tolerances.

Complex and intricate shapes may be produced.

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Disadvantages:

Individual pattern is required for each casting.

Limited casting dimensions.

Relatively high cost(tooling cost, labor cost).

Unsuitable for weights more than 5 Kg.

Precise control is needed in all stages.

Multi-step operations.

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Applications

Agricultural equipment. Automobile components, on a very large scale.

Baling and strapping equipment.

Bicycles and motorcycles.

Construction hardware and equipment.

Dentistry and dental tools.

Prosthetics. Computer hardware.

Electrical equipment , electronic hardware and radar.

Guns and armaments.

Hand tools.

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Applications

Aircraft engines, air frames, fuel systems. Aerospace, missiles, ground support systems.

Cameras.

Material handling equipment.

Oil well drilling and auxiliary equipment.

Components for compressor and pneumatic equipment.

Machine tool equipment.

Components for consumer durables.

Valves and flow control equipment.

Textile machinery parts.

Pipe fittings for plumbing applications.

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Investment Casting ProcessInvestment Casting Process

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Investment CastingInvestment Casting

One-piece mold

Dried in the air

Heated to 90 175 0C

Held inverted for 12 hrs to melt out wax The mold is then heated to 650 1150 0C for about4

hrs depending on the metal to be cast to drive off the

water of crystallization

After the metal has been poured the mold is broken up

and the cast is removed

A number of patterns can be joined to make one mold

called a tree which increases production rate

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One-piece mold - cont Small parts

The tree can be inserted on to a flask and filled withslurry investment

The investment is then placed into a chamber andevacuated to remove air bubbles

Next it is placed in a vacuum drawing machine to

produce fine detail Not a cheap process

Produces fine details

Good surface finish

Few or no finishing operations Can produce intricate parts from parts weighing 1g

35Kg

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Ex : Investment die casting examples

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Investment Casting

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Schematic illustration of investment castingSchematic illustration of investment casting

1. WAX INJECTION : Wax replicas of thedesired castings are produced byinjection molding. These replicas arecalled patterns.

2.ASSEMBLY : The patterns are attached toa central wax stick, called a sprue, toform a casting cluster or assembly.

3. SHELL BUILDING : The shell is built by immersing

the assembly in a liquid ceramic slurry and then

into a bed of extremely fine sand. Up to eight layersmay be applied in this manner.

4. DEWAX : Once the ceramic is dry, the wax is melted

out, creating a negative impression of the assembly

within the shell.

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5. CONVENTIONAL CASTING:In the conventional process, the shell is filledwith molten metal by gravity pouring. As themetal cools, the parts and gates, sprue and

pouring cup become one solid casting.

6. KNOCKOUT:When the metal has cooled and solidified, theceramic shell is broken off by vibration orwater blasting.

7. CUTOFF:

The parts are cut away from the central sprue

using a high speed friction saw.

8. FINISHED CASTINGS:

After minor finishing operations, the metal

castings--identical to the original wax patterns--

are ready for shipment to the customer.

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SHELL MOULDING

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Fig : Investment casting of an integrally cast rotor for a gas turbine. (a) Wax pattern assembly. (b)

Ceramic shell around wax pattern. (c) Wax melted out and the mold is filled under a vacuum, withmolten super alloy. (d) The cast rotor produced to net or near-net shape.

Variation of the investment-casting process

Uses same type ofwax or plastic pattern as investment casting

Patten is then dipped into fluidized bed of fine grained fused silicaand zircon flour

Pattern is then dipped into coarser grained silica to build upadditional coatings and proper thickness to withstand the thermal

shock of pouring The rest of the procedure follows the investment casting process

CERAMIC SHELL MOULDING

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Methodology

Usage of dump box

Dump box

phenol formaldehyde or furane

(2.5-4.5% of sand volume)

Catalyst(11- 14% of resin volume).(Ammonium chloride or Hexamine, a white powder.)

Thickness-10 mm

Curing

Release of shell

mould

Addition of cores to shell mould

Pouring of molten metal

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Sequence of operations

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Applications

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Applications

Cylinders and cylinder heads for air cooled I.C. engines.

Automobile transmission parts.

cast tooth bevel gears, brake beam.

track rollers for crawler tractors, transmission planet carrier.

steel eyes, gear blanks.

chain seat bracket, refrigerator valve plate.

small crank shafts.

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Advantages

Good casting detail

Dimensional accuracy

Moulds are lightweight and stored for extended periods of

time

Better flexibility in design than die-casting

Less expensive

Capital plant costs are lower than for mechanized green sand

moulding

Superior surface finish

Lower fitting costs than conventional casting

Metal yields are relatively high

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SQUEEZE CASTING

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SQUEEZE CASTING

Mold is closed in the molten metal and high pressure is

maintained until solidified.

Keeps porosity low.

Excellent heat transfer due to metal mold and highpressure.

Gases are forced to stay in solution by the pressure and

allowed to diffuse out later.

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Process variables

Melt volume

Casting temperature

Tooling temperature

Time delay Pressure levels

Pressure duration

Lubrication

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Materials:

Squeeze casting is commonly used for processing aluminum

and magnesium alloys.

This process is also used for fabrication ofreinforced metal

matrix composites where molten aluminum infiltrates a fiberreinforcing structure.

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Characteristics of squeeze casting:

low shrinkage and gas porosity;

enhanced mechanical properties because of fine grain

structure caused by rapid solidification ;

good surface quality.

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THE ENDTHE END

Types of squeeze casting

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Direct squeeze casting process

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Sequence of operations

Schematic illustrating squeeze casting process operations.

(a) Melt charge, preheat and lubricate tooling. (b) Transfer melt into die cavity. (c) Close

tooling,

solidified melt under pressure. (d) Eject casting, clean dies, charge melt stock

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Squeeze CastingSqueeze Casting

(a) Melt Metal

(b) Pour molten metal into die(c) Close die and apply pressure

(d) Eject squeeze casting and

charge melt stock andrepeat cycle

This processcombines the

advantage of

casting and

forging

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Applications

Aluminium front steering.

Knuckles.

Chassis frames.

Brackets or nodes. High capacity propellers for boat engine.

Reciprocating engine pistons ,brake rotors.

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Disadvantages of Squeeze Casting

*Squeeze Casting Process is costlier.Manufacturing

dies to accurate dimensions involves complex

processes.

*Accurate metering of molten metal is a slight difficult

problem

*Squeeze Casting Process is Un-economical for smallquantity production.

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