Making fusible mold is an important link in the production of investment casting. High quality mould is the precondition to obtain high quality casting. Mould material, pressing type and mould making process are the main factors that affect the quality of molten die.
1. Mould material
The mould material used for investment casting should have a small line shrinkage, sufficient strength and rigidity, suitable melting point, low viscosity of melting state, good fluidity, good coating property, low ash content and so on.
According to the composition and properties of the mould material, the mould material can be divided into wax base mould material, resin base mould material, filler mould material and water-soluble mould material. Among them, paraffin stearic acid mould material is easy to mould and mould release, easy to recycle and long service life, so it is widely used. However, the strength and thermal stability of paraffin stearic acid mould are poor and its shrinkage is large, so it is difficult to meet the performance requirements of high precision casting. To reduce shrinkage pattern material, prevent deformation and surface shrinkage in casting, and provide the surface quality and dimension precision, fillers can be added to the mould, this kind of material is called packing mould material and it is widely used abroad.
2. Mold making process
2.1 Fusible mold producing
Pressure pressing is commonly used in industrial models, wax base materials are injected by paste injection, resin material mostly paste. The wax model of art works uses liquid coating wax, wax brushing or pressing. In the process of mold making, the prepared wax paste is pressed into the mold to obtain the molten mold. The main parameters of mould making include injection wax temperature, injection temperature, injection pressure, holding time and starting time, which are directly affects the quality of the casting.
2.2 Assemble module
It is called module assembly to combine the repaired and inspected qualified melt die and gate rod into module. The methods of assembly include welding, bonding and mechanical assembly. The most widely used method in China is welding, which uses a low pressure welding tool or a hot blade to heat the inside gate of the mold and weld it to the gate bar. The method is simple, flexible and adaptable although it has high labor intensity and low efficiency.