Type Of Casting Process Sand Casting Plaster Mould Casting Investment Casting Shell Molding Die Casting

Sand Casting Sand casting is the simplest method of casting aluminum. Sand is made into a mould by forming around a wooden "pattern". The pattern is removed, the sand mould assembled and molten metal pored in. The process is chosen for small production runs, for complex shape castings requiring intricate cores or for very large castings. Advantages Low equipment costs Largest size of castings possible by any casting method suited to complex shapes and cores Very low gas porosity is possible It is a versatile casting process Limitations Low casting rate 3-5mm minimum wall thickness Poor linear dimensional tolerances e.g. 4mm / m Rough surface finish Coarse grain size compared to die casting Casting weights in the range of 0.1 Kg - 100,000 Kg Approximate economical quantity range 1 - 1000 castings.

Plaster Mould Casting Permeable plaster moulds give a smooth surface finish (80~125 rms) with a finer surface detail than is obtainable with shell moulds. Castings as thin as 0.5 mm are possible. Slow solidification rates reduce internal stresses so that any casting distortion is negligible. Machining and finishing operations may be eliminated by the use of plaster moulds. Small holes may be cast to size ready for tapping. Surface finish and dimensional accuracy equates to die casting qualities. LM25 alloys are commonly cast by this process.

Investment Casting  This casting method involves producing a "wax pattern" by injecting wax or plastic into a pattern die. The pattern is attached to gating and runner systems and this assembly is dipped in a hard setting refractory slurry, which is then cured. The pattern is melted out of the mould to leave an exact cavity. The mould is heated to cure the refractory and to volatolize the remaining wax pattern material. The moulds are baked and molten metal is poured into the mould cavity. On solidification of the casting, the mould material is broken away from the castings.

Shell Moulding A shell mould consists of a sand shell, varying in thickness between 4-10 mm. The sand particles are bonded together with phenolic resins giving a permeable mould. The production of shell moulds may be automated which lends itself to medium to high production runs. The resin coated sand is placed on a hot metal pattern; this is fired in an oven to harden the shell. After cooling, the shell is removed from the pattern and is ready for use. Molten metal is then poured into the shell mould cavity and allowed to cool. The mould material is broken off the casting. Better dimensioned tolerances are possible than with sand moulding, which reduces machining costs. Fine surface finishes equal to that of permanent moulds (12~130 rms) may be obtained. and consistently reproducible thin castings with fine detail may be made. The process is more costly than sand, permanent mould or die casting.

Liquid metal is introduced in metallic molds! Die Casting Liquid metal is introduced in metallic molds! The injection of metal could be: Under influence of high hydraulic pressure with the die loaded on machine (HPDC). Under influence of low pneumatic pressure with the die loaded on machine (LPDC). Under influence of Gravity (Poured by hand) in a stationary mold, called GDC. Under influence of Gravity (Poured by hopper) in a tilted mold and subsequently straightened, called ‘Durville Process’

Why Pressure Die casting ? The decision to choose Pressure Diecasting as the preferred production method is generally driven by a requirement for high annual volume.  As the annual demand increases, the lower piece part price offered by the pressure diecasting route results in a far cheaper "Total Project Cost" than other methods of casting Aluminium. The diagram below indicates that should the volumes required be low, then the case for gravity diecasting or sand casting becomes increasingly strong, due to the low start up costs.

Types Of Die Casting High Pressure Die Casting ( HPDC) Low Pressure Die Casting (LPDC) Gravity Die Casting (GDC) Vacuum / high Vacuum Die Casting

High Pressure Die Casting Pressure die casting is a repetitive process casting identical parts by injecting Aluminum into metal moulds at pressures in the order of 1000psi. Complex machinery and expensive tooling is required for this process. Advantages Production rates may be in the order of 200 / Hr Thin wall thickness at 1 - 2.5mm The best surface finish is produced by this method Very fine grain structure is obtained The castings have high strength in the as-cast condition Good linear tolerances and repeatable properties are obtained Limitations Size of castings limited by the machine Sound, thick sections are difficult to cast Core configuration may be complex to enable disassembly Porosity may become a concern High start up costs require long production runs to reduce the overall cost Castings cannot be heat treated casting weight range 0.01 Kg - 25 Kg Approximate economical quantity range > 10,000 per annum.

Low Pressure Die Casting This is a repetitive process where identical parts are cast by injecting molten metal under low pressure into metal dies. This process requires complex machinery and is similar to high pressure die casting. Advantages Fair production rates up to 30 / Hr Thin wall thickness possible ( 2-3mm) Better linear tolerances than gravity casting surface finish improved on gravity casting, but not up to pressure die casting standards High Yields possible as runners and risers not required Reduced finishing is required Pore free castings are obtainable Sand cores may still be used to allow complex castings die costs far lower than for pressure die casting Castings are heat treatable Limitations Size of casting limited by machine size Production rates not up to pressure die casting Feeding thin sections through thick sections is not recommended casting weight range 5 Kg - 25 Kg Approximate economical quantity range >1000

Gravity Die Casting Castings are produced by poring molten metal into permanent metal moulds. (Generally made from Cast Iron). This process produces 'Chill Castings‘ Advantages Lower set up cost than Pressure Die casting Higher casting rate than sand casting Low gas porosity levels are possible Fine grain sizes may be obtained The highest quality castings with regards to mechanical integrity can be produced by this method Less finishing is required than for sand castings. Limitations Minimum wall thickness 3-5mm Linear tolerance is approximately 3 mm/m Surface finish better than sand casting The complexity of possible casting shapes is limited Casting weight range 0.1 Kg - 70 Kg Approximate economical quantity range 500 - 2500 (This may increase where sand cores are used to produce shapes impossible with pressure die casting.)

Vacuum and high Vacuum Die casting The porosity sets the limit to the conventional casting Limited heat treatable Limited weldable The die can be vented with the support of a vacuum The Quality is increased with a moderate vacuum between 200 and 500 mbar

Vacuum and high Vacuum Die casting Start Evacuation High vacuum lower than 50 mbar Valve closing Intensification Dosing Turbulence-free filling Additional measures Die concept (sealing) Die spraying Melt treatment Metal dosing

Vacuum and high Vacuum Die casting Requirements to structural parts Rp0,2 120-150 Mpa Rm >180 Mpa A5 >15%

Additional advantages Vacuum and high Vacuum Die casting Additional advantages Cast parts are easily heat treatable and weld able High mechanical properties are reachable High consistency of this properties Expensive but high quality alloys can be cast economically

Vacuum and high Vacuum Die casting An entire new part spectrum for the die caster Typical vacuum die cast parts Space frame node Climate control

Advantages of Die Casting Mass Production Process Consistent quality over mass production Least dependence on human skill Higher engineering strength of materials

BUT It is an energy intensive process Continuous energy input is a PREREQUISITE!

And Energy is going to be ever COSTLIER!

Aluminum is the most widely used metal for die casting!

This is because: It responds well to mold filling It is light in weight Its thermal properties are excellent Its engineering strength is comparable with steel. It is non-corrosive hence longer functional life.

BUT At higher temperature it has: Affinity for oxygen (oxide formation) Affinity for hydrogen (causing gas porosity) Oxidation causes metal loss Porosity causes rejection Facility to control melting, holding of metal and casting parameters is essential!

Other Metals Used In Die Casting 1. Magnesium 2. Brass 3. Zinc

Initial cost of equipment to melt and hold liquid metal is high!

Investment is called for in Quality Assurance and Energy Saving Activities!

High Pressure Die Casting!

Casting parameters are best controlled by this process!

It is also the most productive process of casting with least energy consumption

Because Casting process is carried out on machine. Modern machines are equipped with strict casting parameter controls. Strength of castings, thus produced, is high. Rejection is least. Any deviation from set parameters is reported by audio signal and further production is halted. Deviation report is available on microprocessor hence quick rectification.

BUT It does not accept any collapsible mold (e.g. Sand Cores) Each machine is designed for a specific range of casting size! Larger castings cannot be made on a smaller machine size. Smaller castings can be manufactured on larger machine size using multi-cavity mold scheme. Multi-cavity mold scheme is justified for large and constant quantum off-take. Such machines are costly! Levels required of plant cleanliness and tool & machine maintenance are high.

Some facts Modern Casting Purchasers Envisage excellent capability of vendor to produce large series. Expect in-time casting delivery of goods. Presume High and Consistent Quality & Productivity Standards. Encourage only those vendors with ISO Quality Certification. ISO Quality Certification necessitates strict parameter control and Documentation thereof.

Market Prospects HPDC Castings are mainly consumed all over the world by: Automobile Industry Electrical & Electronic Industry Communication Industry (Mobile Phones, Laptop Bodies, etc.)

Export Market for the die cast products is not exploited at all by Indian Die Casting Industry!

All this for the fear and magnitude of Initial Investment!!!

Installing HPDC Capability requires Excellent marketing strategy Strong financial capability Alert Purchase Policy Accurate choice of machines Selective customer base Customers requiring large series quantities Customers with good credit rating Uninterrupted energy supply High tool design capability Equipment to closely control production parameters High maintenance standard Limited, yet skilled, manpower Strong and alert marketing personnel Efficient accounting system

Conclusion

Advantages High productivity High dimensional accuracy Good surface; polishable Near net shape High strength of the surface layer Inserts, composites casting well realizable Very economical with large quantities

Disadvantages Pore-free structure difficult to produce High investment costs Limited freedom in design Low elongation Castings only limited heat treatable and weldable Decorative coatings almost impossible

Pressure Die Casting Process is Economical When Large Quantum Production is envisaged High Quality of produce over large quantum is the requirement Machine ‘down time’ due to lack of contracts is least Machine ‘down time’ due to breakdowns is least Material purchase cost is well controlled Technical parameters are strictly adhered to.

Good luck!

ejection of die casting Conventional die casting The conventional die casting is one of the most economical casting process Dosing of metal from the top Die opening ejection of die casting Die filling real-time controlled Venting slots