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precision casting

Precision Casting method refers to the general name of Casting methods that use non-metallic moulds and whose dimensional accuracy is higher than that of ordinary sand mould castings, including Lost Wax Casting or Investment Casting, Plaster Mold Casting and Ceramics Mold Casting.

 

Precise casting by dewaxing

 

2-1 Features and advantages

 

(1) The maximum limit length of the casting is 700mm, and the easy length is less than 200mm.The maximum weight of the casting is about 100 kg, usually less than 10 kg.

(2) The dimensional tolerance of the casting is 20mm ±0.13mm, 100mm ±0.30mm, 200mm ±0.43mm, and the dimensional accuracy of small parts is not easy to reach within ±0.10mm.Angle tolerance of ±0.5~±2.0 degrees, casting minimum thickness of 0.5~1.5mm.The surface roughness of casting is about Rmax 4S~12S.

(3) the casting material is almost without any restrictions, such as aluminum alloy, magnesium alloy, titanium alloy, copper alloy, all kinds of steel, cobalt and nickel based heat resistant alloy, hard materials.

(4) the production of complex shape of the workpiece, good dimensional accuracy, less cutting.

(5) save material waste, and can be produced in large quantities.

 

Dewaxed precision castings are widely used in jet engines, gas turbines, steam turbines, aircraft parts, internal combustion engines, vehicles, food machinery, printing machinery, paper making machinery, compressors, valves, pumps, meters, sewing machines, weapons, business machines, and other machine parts.

 

2-2 process

 

There are two main types of dewaxing casting methods: Solid Mold and Ceramic Shell Mold, the latter being a modification of the former.

 

The solid mold method takes into account the condensation shrinkage of the wax mold, the heating expansion of the mold and the condensation shrinkage of the molten metal, and produces a mold that is similar to the final casting size.The melted wax is pasted into the mold made of metal or silica gel, the wax mold is taken out, and soaked into the slurry made by mixing the powder refractory material and binder.After dripping, spread coarse-grained refractory and allow to dry.Put into the casting frame, fill the refractory particles mixed with binder, and then dry them.The wax is then heated to melt it out and make a mold.The mold was heated at high temperature to burn off a small amount of residual wax and increase its strength, and then metal melt was injected.

 

The production of the ceramic shell mold until the wax mold is the same as that of the solid mold, except that after one dip and sand drenching (or sand floatation), the coating operation is not carried out, but repeated several times until the predetermined shell thickness is obtained.This method is widely used by dewaxing precision foundry operators at present because it has the following advantages: drying, heating, melting out of wax, high temperature heating and then pouring.

 

(1) Better dimensional stability

(2) less use of refractory materials

(3) light weight, easy to handle, make large castings

(4) The manufacturing process can be partially automated to save manpower and improve the production rate

(5) Low production cost

(6) The ceramic shell mould is thin, and the cooling rate of casting after casting is high and uniform, so its mechanical properties are better.

 

(A) Master Pattern

 

The appearance of the main model is similar to that of the final product. Consideration must be given to condensation shrinkage of the wax, heating expansion of the mold and condensation shrinkage of the casting metal.For example, when the cold shrinkage rate of the wax mold is 1.2%, the thermal expansion rate of the mold is 0.7%, and the cold shrinkage rate of the casting metal is 1.7%, the size increase rate of the main model is 2.2%. The commonly used materials are aluminum alloy, copper alloy and stainless steel.


Post time: Apr-08-2021