5 Finishing Tips for Direct Metal Laser Sintering12 July 2017
The post-processing stage for parts generated using direct metal laser sintering is usually quite involved (far more than SLS prints, by way of contrast). However, with a little patience and the right techniques, a world-class result is easily achievable. In today’s tutorial, we’ll look at 5 practical tips to help you achieve the look and mechanical qualities you want for your parts.
1) Make sure your support structures have been removed cleanly
Unlike other powder bed technologies, direct metal laser sintering still requires the use of support structures. As these will be made of metal rather than plastic, nylon etc. they will require a bit more effort to remove cleanly, and may require CNC machining. Ideally, you should minimise the number of support structures during the design stage. Avoid any overhangs of less than 45° and make sure any supports that prove unavoidable will be accessible after printing, so they can easily be cut and machined.
2) Make sure your layer lines aren’t visible
Layer lines are inevitable with direct metal laser sintering, so you’ll need to remove them before any further finishing can take place. If you have optimised your part orientation to minimise any visible layers, you may be able to do this by hand, via light sanding (which may be also be necessary to remove any traces of support structures). As you do this, be sure to utilise a light touch, especially for any parts where the precise dimensions need to be maintained.
3) Explore different techniques for smoothing the surface
For a smooth, attractive surface, we would recommend media blasting or tumbling. Media blasting works by blasting the part with an abrasive material to smooth the surface, after which it is bead blasted to provide the finishing touch. This gives the part a smooth, satin finish. Tumbling is a similar process that smooths out the part’s surface by placing it in a rotating barrel filled with abrasive ceramic material. This allows multiple parts to be processed at once — potentially a huge time-saver. For functional parts, where precision must be of the highest order, you might consider specialist techniques, such as electrical discharge machining and liquid honing.
4) Don’t forget your parts’ mechanical qualities
Bear in mind that certain powders used in DMLS require additional heat treatment to achieve specific mechanical qualities. Industrial heat treatments (which typically utilise a vacuum furnace) will compensate for the inconsistent heating that takes place during printing, and ensure a part’s mechanical qualities are completely uniform. Consult your material data sheets, as these will list the part’s mechanical qualities, both before and after heat treatment. You might also consider hot isostatic pressing, to reduce the part’s porosity.
5) Take advantage of the full range of coating options
You can make use of the full range of coating materials available for metal parts with direct metal laser sintering, so don’t be afraid to be adventurous, particularly if your parts are likely to be subject to abrasive or corrosive conditions. You could even explore metal plating in materials like gold or chrome, if aesthetics are important. Before applying a coat, make sure that any leftover material has been cleaned from the part, as even if you thoroughly cleaned away the leftover powder after printing, any additional machining will create new waste material.
While there’s no doubt that the finishing process for direct metal laser sintering is more involved than other 3D printing methods, if you are patient, methodical and willing to explore the full range of options available, it will be possible to create long-lasting parts and prototypes that look great and fulfil their required function perfectly.
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