Surfaces in 3D printing

Lecture at the workshop on "Surface modification and finishing of additively manufactured components" - SurfAM3

September 2021 - The appearance of components plays an important role in 3D printing. However, not only the optics. Much more points are determined by the surface. The challenges and possible solutions for components from additive manufacturing were presented and discussed in Dresden. Fraunhofer Institute for Material and Beam Technology (IWS) and European Research Association for Thin Films (EFDS) organized the third workshop SurfAM3. Post-processing according to customer requirements.

At the workshop, PTZ presented its work with components from 3D printing. The surfaces of components made from stereolithography, laser sintering, fused filament fabrication (FFF) or laser melting (SLM) are reworked every day. Depending on the customer's requirements, the surface is removed or applied. Thanks to the further development of the machines, many generatively created component surfaces can be used very well.

Plastics process - combining design freedom with precision.

The oldest process, stereolithography, produces a very good surface out of the modern STL machines. The starting points of the support structure must be removed by grinding. The most common use as a master model for vacuum casting molds usually requires large-area grinding, as well as a filler and a painting process. Most of the stereolithography material is not too hard, it can be sanded in a filigree and function-oriented manner.

With laser sintering, the component is cleaned and used out of the SLS machine in over 90% of the buildjobs. Because of the stable material (polyamide), grinding is not advisable. If a spatula is applied beforehand, a smooth surface can be achieved. The process remains complex. With chemical smoothing, a laser sintered part can be given a smoother surface in a subsequent process. It must be considered whether the removal is compatible with the requirements for dimensional accuracy. In some cases, CNC milling might be preferred. Milling concentrates just on functional surfaces. Precision is combined with the high degree of design freedom of SLS plastic.

The situation is similar with the FDM process for plastic parts. These are also used from the 3D printer after they have been detached from the support structure. Only individual starting points or transition points from the applied filament are reworked.

Metal processes - blasting, grinding or polishing

Even if selective laser melting is a powder bed process, this is not enough to position the component in the machine (compared with laser sintering). The metallic support structure (made of the same material as the component) must be removed. Depending on the component and its alignment in the SLM system, reworking might take several hours. For visually relevant parts, e.g. for the vehicle interior, the visible area is reground or, in individual cases, even polished. For this purpose, sample parts were presented at the lecture as well as the parts with milled surfaces.

The situation is similar with 3D metal printing using the filament process (FDM / FFF). Metallic support structure and the surfaces require processing, depending on the requirements.

Experience from research and application

Most post-processing is a partial finishing of the surface. This confirms a small survey among the workshop participants. Current developments in processes focus on processing the entire surface. Usually, it is not necessary or useful. This was the subject of presentations by Siemens AG and Nehlsen BWB Flugzeug Galvanik from OHB System AG. Fraunhofer IWU, plant manufacturer Trumpf and material supplier Sindlhauser Materials GmbH contrasted what further development of machines and materials can do for future component surfaces. The requirements and influences of the components in use in medical technology, aerospace or mechanical and plant engineering were presented among others by the Medical Faculty Carl Gustav Carus (TU Dresden), Airbus Deutschland GmbH, MT Aerospace AG or VON ARDENNE GmbH. That made the workshop balanced in terms of research, development, application and exchange of experience.

About PTZ

In the PTZ-Prototypenzentrum GmbH, which was founded in 1996, 25 employees use the most modern technologies to manufacture first models, tools and small series for German and European customers, among others from the automotive industry as well as medical and device technology. Brand manufacturers such as Siemens, Bosch, Miele, Fresenius and Ducati as well as many medium-sized companies appreciate them.

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