Investment casting

Dr. Dmitri Kopeliovich

Investment (lost wax) casting is a method of precision casting complex near-net-shape details using replication of wax patterns.

• Investment casting process
• Ceramic slurry materials
• Advantages and disadvantages of investment casting

The investment casting process uses expendable patterns made of investment casting wax.

• The wax patterns are commonly prepared by injection molding technology which involves injection of wax into a prefabricated die having the same geometry of the cavity as the desired cast part.

• The wax patterns are then attached to a gating system (a set of channels through which a molten metal flows to the mold cavity).

• The next stage is the shell building - the wax assembly is immersed into refractory ceramic slurry of hardening mixtures followed by drying. This operation is repeatedly carried out resulting in formation of a solid ceramic shell of 1/4” -3/8” (6mm – 9mm) thick.

• The next stage is dewax. At this stage the assembly is heated in an autoclave where the most of the wax is melted out. This operation is followed by burning out the residual wax in a furnace.

• The mold is then preheated to 1830°F (1000°C). Now the mold is ready for filling with a molten metal.

• Casting stage is conventional operation involving pouring a molten metal into the shell through the gating system.

• After the metal has solidified and cooled to a desired temperature, the shell is broken and the castings are cut away from the gates and sprue.

• The last stage is finishing carried out by sandblasting or machining.

to top

• Mullite Al₂O₃ 44-48%, SiO₂ 47-51%, Fe₂O₃ max. 1%, TiO₂ max. 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.

to top

Advantages:

• Excellent surface finish.
• Tight dimensional tolerances.
• Complex and intricate shapes may be produced.
• Capability to cast thin walls.
• Wide variety of metals and alloys (ferrous and non-ferrous) may be cast.
• Draft is not required in the molds design.
• Low material waste.

Disadvantages:

• Individual pattern is required for each casting.
• Limited casting dimensions.
• Relatively high cost (tooling cost, labor cost).

to top

• Casting properties
• Melting furnaces
• Sand casting
• Permanent mold casting
• Die casting
• Centrifugal casting
• Squeeze casting
• Continuous casting
• Horizontal continuous casting in graphite mold
• Continuous casting in traveling mold
• Direct Chill (DC) casting
• Solidification
• Crystallization

to Metals
to Foundry technologies