30 January 2016

What is investment casting? | Operation procedure| Advantage | Disadvantage | Application

What is investment casting?

Investment casting is an industrial process based on lost-wax casting the oldest metal forming technique in which wax pattern is surrounded by an investment compound and then baked so that the investment is hardened to form a mould and the pattern material may be melted and run-off. 

Operation procedure for investment casting:

Step-1: Produce a master pattern.
Step-2: Create a mould. 
Step-3: Production of patterns such as heat disposable wax, plastic and polystyrene.
Step-4: Assembly of these patterns onto a gating system.
Step-5: Apply investment material or covering the pattern assembly with refractory slurry. 
Step-6: Melting the pattern assembly and remove the pattern material. 
Step-7: Burnout preheating. 
Step-8: Firing the mould to remove the last traces of the pattern material 
Step-9: Pouring.
Step-10: Knockout, cutoff and finishing.

Some important facts about investment casting:

  • Investment casting is also called precision casting.
  • It is a manufacturing process that allows the casting of extremely complex parts, with a good surface finish. 
  • Very thin sections range about 0.015in (0.4mm) can be produced by this process. 
  • Investment casting also allows for high dimensional accuracy. Tolerance is as low as 0.003in (0.076mm) have been claimed. 
  • Manufactured parts are generally small and any metal can be investment cast. 
  • Parts of the investment process may be automated. 
  • Investment casting is a complicated process and also expensive. 

Advantages of investment casting:

  • A complex shape which is difficult to produce by any other method is easily produced by this process.
  • Formation of hollow interiors in cylinders without cores.
  • Almost any metal can be cast and any intricate parts can be castable. 
  • Very close tolerance and better surface finish can be produced.
  • Dimensions should not vary because there is no parting line.
  • Controlled mechanical properties can be obtained.

Disadvantages of investment casting:

  • Investment castings require very long production cycle times as compared to other casting processes so time-consuming process. 
  • Difficult to cast objects requiring cores.
  • More expensive process because of large manual labour involved in the preparation of pattern and the mould.
  • This process is virtually infeasible for high volume manufacturing due to its high cost and long cycle times.
  • Holes cannot be smaller than 1/16 inch (1.6mm) and should be no deeper than about 1.5 times the diameter. 

For detailed information:

Read more >> Advantages and disadvantages of investment casting

Application of investment casting:

This process was used in the olden days for preparation of jewellery and surgical instruments.

Nowadays this process is used for making products like vanes and blades for the gas turbine, shuttle eyes for weaving, waveguides for radars, bolts and triggers for firearms, stainless steel valve bodies and impellers for turbochargers.