Learn about the investment casting process and how you could apply it to your operations to improve the quality and finish of your output.
Investment casting, or vacuum induction melting and casting, has a wide range of heat treatment and advanced manufacturing applications. This is largely down to the exceptional qualities of the parts or materials it can be used to produce.
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It results in a high-quality product with excellent corrosion resistance.
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It has high dimensional accuracy.
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It delivers an excellent surface finish.
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It achieves a more effective metal utilisation or casting yield.
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The process has a high level of safety.
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Almost any metal can be cast.
Like many heat treatment processes, there are benefits to investment casting taking place in a vacuum. But what does the process actually involve? Which industries get the most use out of investment casting — and could upgrading your investment casting capabilities benefit your operations?
What is investment casting?
Investment casting is an industrial process based on ‘lost-wax casting’ principles (more on this later), which is one of the oldest metal-forming techniques. Today, it’s known as a secondary metallurgy process, which means it’s usually used to cast shapes from alloys that have already been previously melted.
It’s also a form of aftertreatment used by manufacturers to cast products with more desirable qualities. Because of this, it can be used to produce output for a variety of high-end applications and industries such as turbine blade manufacturing for industrial gas turbines. In fact, it has become an enabling technology in many of today’s top industries, including:
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aerospace and defence
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power generation
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automotive
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oil and gas
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medical/orthopaedics
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general engineering
Vacuum precision investment casting (VPIC) has demonstrated to be the best available technical solution for those applications where dimensional accuracy is required and machining is not cost-effective, or the component is required to be highly intricate with internal hollow passages to reduce weight or to provide performance cooling.
If this sounds familiar and you’d like to know more about how VPIC could benefit your operations, get in touch. VFE works in partnership with Retech, a global leader in metallurgical processing systems, for the supply, installation and aftercare of VPIC systems. Contact us today to discuss your requirements and how a VPIC system could help.
The investment casting process explained
As well as the vacuum melting furnace, investment casting requires the use of a number of standalone processes to produce wax and ceramic moulds and preheat the moulds for casting.
Following casting, machines are also needed for etching, sandblasting, cutting, or post-process heat treatment. The process steps include the following:
1. Pattern creationThe wax patterns are typically injection-moulded into a metal die and are formed as one piece. Cores may be used to form any internal features on the pattern. Several of these patterns are attached to a central wax gating system (sprue, runners, and risers), to form a tree-like assembly. The gating system forms the channels through which the molten metal will flow to the mould cavity. |
2. Mould creation
This ‘pattern tree’ is dipped into a slurry of fine ceramic particles, coated with more coarse particles, and then dried to form a ceramic shell around the patterns and gating system.
This process is repeated until the shell is thick enough to withstand the molten metal it will encounter. The shell is then placed into an autoclave and the wax is melted out, leaving a hollow ceramic shell that acts as a one-piece mould, hence the name ‘lost-wax’ casting.
Note: VFE also supplies, upgrades and delivers essential aftercare support for dewaxing autoclaves, which are an integral part of the casting plant operation.
3. PouringThe mould is preheated in a furnace to approximately 1,000°C (1,832°F) and the molten metal is poured from a crucible into the gating system of the mould, filling the mould cavity. Pouring is typically achieved by tilting the crucible, but other methods such as bottom pouring are sometimes used. |
4. Cooling
After the mould has been filled, the molten metal is allowed to cool and solidify into the shape of the final casting. Many investment casting furnaces utilise the bridgman technique which utilises a high thermal gradient and slow cooling method to produce directionally solidified or single crystal parts.
5. Casting removalAfter the molten metal has cooled, the mould can be broken and the casting removed. The ceramic mould is typically broken using water jets.Once removed, the parts are separated from the gating system by either sawing or cold breaking (using liquid nitrogen). |
6. Finishing
Often, finishing operations such as core leaching, etching, grinding or sandblasting are used to smooth the part at the gates. Vacuum heat treatment is also sometimes used to stress relieve or harden the final part.
Upgrade your operations with casting furnace capabilities
Could the superior-quality product with high corrosion resistance and an excellent finish created by the VPIC process improve the standard of your output?
Would your operations benefit from a greater metal utilisation or casting yield?
If you’re personally measured against these metrics or you’re interested in innovating to future-proof the efficiency and quality of your operations, click to find out more about our investment casting services and how you could benefit.
As well as supplying and installing VPIC systems through our partnership with Retech, we also deliver comprehensive upgrades, services and calibrations for any well-known brand of VPIC system. Get in touch with any questions you have about the process and how you could apply it — or upgrade and service existing systems — across your sites.
For more information about our investment casting products and services, click the image below to download your copy of our VPIC service sheet.
