Investment casting is a unique process allowing the manufacture of highly complex, detailed, and accurate metal castings. It is based on the ancient lost wax process and is vital for the manufacture of many components used in equipment that we take for granted today and as such it is crucial to the functioning of the modern world.
The lost wax process dates from around 4000 BC with origins believed to be in North Africa, Middle East & Asia for producing jewellery and sculptures.
Wax softens with heat allowing it to be easily shaped, originally patterns were made from bees wax but today the term wax applies to any substance having wax like properties and in the context of investment casting it could more accurately be described as an industrial moulding compound.
The 20th century saw the commercial development of the process in the dental industry then with WWII came the need for mass production of near finished components which led to the major industrial development of the process. Modern industrial manufacture demands ever more sophisticated castings only achievable through investment casting. Today the lost wax process influences and benefits everyone’s daily life.
Wax patterns are injected and assembled on to the wax tree or runner and gating system. The system will contain a ceramic pour cup to assist both dewax and casting. Complex patterns can contain either soluble wax cores, which will be removed prior to assembly and shelling, or ceramic cores which will remain in place until later in the process. The core is used where a cavity or air passage is required in the finished component.
Once the wax patterns are assembled onto the tree or runner and gating system the assembly is checked and dressed to remove any minor imperfections. This stage is critical as any surface defects will carry forward into the finished metal component. Blayson recommends that the assembly is now dipped in its Trisol pattern wash and etching agent to provide the optimum wax substrate before preceding to the shelling process.
A shell is now formed around the wax assembly by applying a series of ceramic coatings of gradually increasing particle size. Specifically, the wax assembly is dipped in a liquid slurry solution and then refractory stucco materials are applied which combine to form the shell coating. The shell material is then allowed to set before preceding to dewax.
The wax is now removed from the shell system using high pressure steam in the autoclave dewax process or high temperature in the flashfire dewax method. In either process the wax is collected and made available for recycling. The shell is now fired and conditioned at high temperature creating a precision casting mould ready to accept the molten metal.
Ceramic foam filters are added to the precision casting mould to improve flow of the molten metal and remove any impurities. The mould is covered with fibre insulating blankets to control cooling rates and then the molten metal can be introduced using a variety of methods from traditional hand pouring techniques to single crystal casting technology of complex alloys.
Once the metal or alloy has cooled sufficiently the shell material is removed using mechanical processes and any internal ceramic cores are later removed from the casting by dissolving in a caustic solution.
Finally, the castings are removed from the tree and are finished and inspected. The remaining metal from the runner and gating system is recycled. The process is complex and relies on precise accuracy and control at every stage to produce a finished component with the required dimensional and mechanical characteristics.
Wax patterns are injected and assembled on to the wax tree or runner and gating system. The system will contain a ceramic pour cup to assist both dewax and casting. Complex patterns can contain either soluble wax cores, which will be removed prior to assembly and shelling, or ceramic cores which will remain in place until later in the process. The core is used where a cavity or air passage is required in the finished component.
Once the wax patterns are assembled onto the tree or runner and gating system the assembly is checked and dressed to remove any minor imperfections. This stage is critical as any surface defects will carry forward into the finished metal component. Blayson recommends that the assembly is now dipped in its Trisol pattern wash and etching agent to provide the optimum wax substrate before preceding to the shelling process.
A shell is now formed around the wax assembly by applying a series of ceramic coatings of gradually increasing particle size. Specifically, the wax assembly is dipped in a liquid slurry solution and then refractory stucco materials are applied which combine to form the shell coating. The shell material is then allowed to set before preceding to dewax.
The wax is now removed from the shell system using high pressure steam in the autoclave dewax process or high temperature in the flashfire dewax method. In either process the wax is collected and made available for recycling. The shell is now fired and conditioned at high temperature creating a precision casting mould ready to accept the molten metal.
Ceramic foam filters are added to the precision casting mould to improve flow of the molten metal and remove any impurities. The mould is covered with fibre insulating blankets to control cooling rates and then the molten metal can be introduced using a variety of methods from traditional hand pouring techniques to single crystal casting technology of complex alloys.
Once the metal or alloy has cooled sufficiently the shell material is removed using mechanical processes and any internal ceramic cores are later removed from the casting by dissolving in a caustic solution.
Finally, the castings are removed from the tree and are finished and inspected. The remaining metal from the runner and gating system is recycled. The process is complex and relies on precise accuracy and control at every stage to produce a finished component with the required dimensional and mechanical characteristics.