What is The “Lost Wax” Process?
Investment casting, or “lost wax” process, is one of the oldest known metal casting methods, in which molten metal is poured into a mould. We can trace its roots back to Ancient Egypt and China, where patterns were formed out of beeswax 5000 years ago to create jewellery or other ornamental objects. Today, we use high-technology waxes, refractory materials and a broad range of alloys.
The investment casting process offers numerous benefits:
- Allows many intricate and complex forms to be cast
- 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).
- Parts have good dimensional accuracy.
- Allows for both low and high-volume manufacturing.
- Cost of production is reduced, 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.
This type of casting also allows the production of small parts with a high level of accuracy, repeatability and integrity. 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.
How are Investment Castings Used?
Dean Group manufacture parts that can be used in a wide range of industries, from Aerospace and Military to Automotive, Energy and the general engineering sector. 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 a low cost. The resulting parts tend to be small, but investment castings weighing up to approximately 70 lbs can be created too.
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.
Steps Involved in the Investment Casting Process
- Creating the “pattern”(i.e. a replica) of the part that’s to be cast by injecting wax into a die. This process is also used for die casting. Usually, the pattern is created as one piece.
- 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(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 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.
- Breaking or cutting the cooled shell mould open to reveal the casting.
- Finishing the final part using fettling, grinding, sandblasting, heat treatment and other testing or surface finishing processes
Several Casting Processes are Available at Dean Group
We offer several investment casting techniques to meet our clients’ requirements.
The aluminium investment casting ELITE process aims to achieve good mechanical properties in castings that do not require hipping. The microstructure is tight and free from porosity and the produced parts are gas-tight with consistently high range tensile results. The process also offers thin wall section parts, fully traceable individual parts, a wide range of sizes and weights, consistency and repeatability and flexible production volumes. Our aluminium investment casting process is suitable for industries where weight, strength and casting soundness are a concern.
We also offer a premium grade investment casting process, which allows for the production of complicated shapes that would be difficult or impossible to produce using other methods; little surface finishing and only minor machining are needed. Some of the advantages of this process include short UK lead times, small to large volume runs, general cast tolerances to ISO 8062-3:2007, and a wide range of applications in several markets, such as oil and gas, automotive, aerospace and rail.
The commercial grade investment casting process offers many benefits of the premium grade investment casting such as design flexibility, good cast integrity and the ability to produce parts without draft angle consideration. However, this method is best suited to larger, less complex designed parts that may require a higher level of repeatable quality and integrity than general sand castings. In addition, the process also ensures virtually no tool wear, reduced production costs and wider cast tolerances.
We offer these processes from our factory in Manchester and through our supply partners in China.