Lost Wax or Investment Casting Method Steps

Investment or lost-wax castings:

The Lost-wax method, sometimes, also called simply as precision-investment casting has been used for many years by jewelers and dentists. Since world-war-II, the method has been adapted to the production of small and precise, industrial fasting. Basically, the method involves the use of expendable (heat disposable) pattern unrounded with a shell of refractory material to form the casting mould.  Example: Piston making.
Cast parts are formed by putting the molten metal in the cavity. The wax pattern is melted and it is not reusable because of that the method is named "lost - wax method".

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 The steps involved in this Lost Wax Method  method are explained below:
  • Wax injection
  • Assembly
  • Shell building
  • Dewax
  • Conventional casting
  • Knockout
  • Cut-off
  • Finished castings
   (a) Wax patterns are usually made by injection molding



   (b) Multiple Patterns are assembled in central wax sprue .



(c) The assembly is immersed in a liquid ceramic slurry. After that this structure is dipped into a bed of very fine sand. More than one layer of sand may be necessary.



(d) The ceramic becomes dry. The wax is then melted. To melt all the wax ceramic is fired.


(e) Simple gravity pouring is used for filling the mould. After solidification all the parts of the ceramic structure become casting. Hollow castings can be made by pouring out the extra metal before solidification.



(f) The metal cools to room temperature and after that the ceramic structure is broken off by water blasting or by applying vibration. 



(g) The parts are separated by the high speed friction saw. Minor finishing is given to the parts. 



Advantages of Investment Casting Method:
  1. Intricate details can be cast.
  2. Undercuts and other shapes, which would not allow the withdrawal of a normal pattern, are easily obtained.
  3. The surface is very smooth and there is no parting line.
  4. High accuracy can be obtained so that much of complicated and costly machining can be eliminated.
  5. Unmachinable alloys can be cast.
  6. More than one casting can be made at a time.
  7. It can be reused.
  8. Preferred for casting weight less
Limitations of Lost Wax Casting :
  1. It is involved and thus expensive
  2. It has limitations in use of and location of holes
  3. The parts are limited in size to a few kg
Application:
  1. Parts for aerospace industry
  2. Parts for computers
  3. Parts for food and beverage
  4. Costume jewellery
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