What is The Investment Casting Process?
Investment casting, or “lost wax” process, is one of the oldest known metal-forming methods, in which molten metal is poured into a mould. It can trace its roots back to Ancient Egypt and China; the patterns used to be formed out of beeswax 5000 years ago, when it was used to create jewellery or other ornamental objects. Now, we use high-technology waxes, refractory materials and a broad range of alloys.
This type of casting allows the production of small parts with a high level of accuracy, repeatability and integrity, and a large variety of metals and alloys can be used, including stainless steel, brass and aluminium alloys. A ceramic mould is used to create an exact duplicate of the component, and the need for secondary machining can be reduced, since the investment castings are created to shape.
Investment casting offers numerous benefits. It’s a process that allows many intricate and complex forms to be cast, and the resulting parts have smooth surfaces with no parting lines. A vast array of alloys can be used, ferrous or non-ferrous, including alloys of aluminium, bronze or magnesium, cast iron, carbon steel and stainless steel (as well as materials that can be difficult to machine), all with a good dimensional accuracy. This method allows for both low and high-volume manufacturing, and it presents a reduced cost of production, since waste is minimal and it doesn’t require too much assembly. It’s also possible to add names, logos or numbers to the parts.
The individual steps in the investment casting process include:
- Creating the “pattern” (i.e. a replica) of the part that’s to be cast by injecting wax into a die. Usually, the pattern is created as one piece. Plastic can be used instead of wax, but the reusable nature of wax (and the ease with which it melts) makes the latter more suitable.
- Compiling potentially several wax patterns into a completed assembly known as a gating system or “tree”. This form allows molten metal to flow into the mould cavity at a later stage.
- Immersing the assembly in high grade ceramic slurry (eponymously known as the investment stage).
- Building up an additional coating of coarse ceramic particles up to 10mm thick while the assembly is still wet.
- Melting the wax from the dry mould (hence the alternative name ‘lost wax casting’) to leave a thin-walled and hollow ceramic shell.
- Firing the moulds to remove any last vestiges of wax and add durability to the final mould. This can necessitate temperatures of 1000°C.
- Pouring molten metal within the still-heated moulds. A heated mould is used to instil better dimensional accuracy, with tolerances of as low as .076mm enabled. Sometimes, this stage utilises the assistance of pressure or vacuum force in addition to simple gravity
- Breaking or cutting the cooled shell mould open (using water jets, sawing, liquid nitrogen cold breaking or similar methods) to reveal the casting
- Finishing the final part using fettling, grinding, sandblasting, heat treatment and other testing or surface finishing processes
How is Investment Casting Used?
Due to its many advantages, investment casting can be used to manufacture parts such as gears, machinery components and much more. Typically, the resulting parts tend to be small, but in actual fact investment castings weighing up to approximately 70 lbs can be created. This means that here, at Dean Group, we manufacture parts that can be used in a wide range of industries, from jewellery to Aerospace, Military, Automotive and the Energy sector. The latter uses investment casting to produce turbine blades, for example. Firearms can also have components cast with this process, like triggers and hammers, and other small parts that can be produced with a high level of accuracy at low cost. 3-D printers can also create moulds to be used in investment casting, and Planetary Resources has actually used this technique to print the mould for a satellite, which was poured in ceramic to form a cast.
In short, engineers use investment casting to manufacture components for a large variety of industries, as the accuracy and repeatability of this process make it cost-effective and ideal. We ensure the parts we produce have a high degree of integrity and quality as a result, and we continuously optimise our investment casting process. Both Dean Group and all of our supply partners possess either (or sometimes both) ISO9001-2015 or TS 16949 quality accreditations, so our quality controls are as stringent as possible, which makes sure that the high quality of each casting is reliably kept throughout its lifetime.
Dean Group maintains a number of investment casting processes, including the ELITE process, which adopts a similar approach to the famous SOPHIA® casting process. We also have Premium Grade precision casting and Commercial Grade options. The latter enables a significantly lower price per piece than other casting grades, yet maintains flexibility of design, cast integrity and the option of producing parts without draft angle consideration. For further information about any of our investment casting processes, contact Dean Group today and we’ll be happy to assist you.
SOPHIA® is a trademark.