Prototyping with 3D printing and investment casting

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Computer-aided design (CAD) allows us to go much further in the design process from our desks than ever, but eventually there comes a point where we have to make real parts for testing. This used to be a painful process as one-off production was time consuming and costs were high. Luckily for us, we are living in modern times.

Unless you have been living under a rock for the past few years, you will have heard of 3D printing. This additive manufacturing technique has become very widespread and has even made its way into some homes. A 3D printer manufactures a part by creating it layer by layer - a bit like laying bricks for a house, only these are tiny micron-scale bricks.

3D printing allows for intricate parts to be created with ease, even parts that cannot be produced with other techniques.  It also allows us to easily make prototype parts from our CAD models without any tooling, which would become wasted if any later modifications are required (note: modifications are always required).

There is just one problem; we need parts in metal. To fuse the deposited materials together to form a part, a 3D printer needs to heat the deposited material so that it sticks to the previously laid material; with metals, this requires a lot of heat, which not only means a high electricity bill, but also other complications (such as thermal expansion) that needs to be controlled. All this means that 3D printing metal is insanely expensive.

Fortunately, a solution is readily available, and it is a centuries old technique called investment casting. Investment casting typically works by coating a wax pattern in ceramic, then after the ceramic hardens, the wax is melted out leaving a ceramic mould ready for casting the metal part. After casting, the ceramic mould is destroyed to remove the part.

By combining the two techniques, we can 3D print a part in plastic and have it used as the pattern for investment casting - the end result is a fully functional metal part without any one-off tooling costs!

Being able to make prototype parts this way has many benefits: the process is much quicker as no tooling is required, and this also means that the one-off manufacturing cost is lower. This means we are able to test more parts, run more iterations to make improvements if necessary, and produce a much better quality end-product.

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Bernard Wong