When designing a part, a designer often has a manufacturing ‘method’ in mind. When designing a shaft, the designer looks to design around an axis of concentricity and the method for manufacture is turning. When designing a bracket, the designer may look for ways of holding the part for milling and how to minimise milling operations.
A designer still needs to have a method for manufacture in mind for Selective Laser Melting (SLM). When designing for SLM, the designer is open to create the part as they wish. They need to consider for tool allowances because part-holding and geometry are gone. Instead of a large chunk of material to resist the loads, there can be a much more detailed structure that transfers the loads more effectively but also lightens the part and makes it look a lot better. Parts that have to be separate for conventional manufacture can now be made from one piece; we call this design freedom.
There are a few considerations to think about when designing for manufacture using SLM, the four rules are as follows:
- Reduce part volume – the part should have as little material as possible. Material volume equals cost. Get rid of material that serves no purpose. Consider hollowing the part out.
- Consider build direction – the part may need to be orientated in a specific direction to best achieve the part detail or to best resist potential deflections. Parts with some symmetry and parts that blend in changes of cross section work well. We love curves – organic blended shapes work the best. Get rid of those sharp corners!
- Allow surfaces for support – there will be some support needed to hold your part to the build plate, however this can be small. Supported surfaces will have a slightly different surface finish due to the removal of the support. Most downward facing surfaces (below 30˚ to the plate) will require additional support, try to eliminate them where possible.
- Allow for post processing – consider the critical surfaces that may require further processing. Bearing and sealing surfaces for example. Sometimes it is worth adding a little machining allowance or datums to help post processes.