Improving surface quality for sustainable manufacturing

Fab Lab for research and creative development

Fab Lab at Halmstad University is a creative centre with a focus on free-form production and 3D printing. At Fab Lab, the University’s researchers and students work on developing materials and manufacturing methods, often in collaboration with industry. One of the research groups working at Fab Lab is the material systems group within the research environment Rydberg Laboratory for Applied Sciences (RLAS). Amogh Vedantha Krishna is a PhD student at Halmstad University and Chalmers University of Technology, working in the material systems group with research specifically on the surface quality of products produced by AM.

“Although AM has several advantages, one of the main downsides of this technique is the surface quality. Surface defects can influence the functional performance of the manufactured parts and cause significant failures if left unchecked. The focus of my research is to improve the surface quality of products produced by AM to match the standards set by conventional manufacturing processes, for example milling, turning and injection moulding. By doing so, more industries can use AM technology in their supply chain”, says Amogh Vedantha Krishna.

Why is surface quality so critical?

It is very important to control the surface quality, especially in high-end precision applications, where the nature of the surface plays a major role in the functional performance of the part. For other application areas, where the surface does not affect the function of the part, the surface quality might not be as crucial, making AM easier to implement as a manufacturing method. One example of when the surface quality is highly important is for parts in an engine, more specific a piston and cylinder. A layered surface produced by AM can lead to high wear rate – more friction – between the piston and the cylinder, ultimately causing a failure in the engine. A too smooth surface can on the other hand also be a problem as it may not hold necessary lubricant, which can also cause high friction and engine failure.

“In this case, an engineered surface that is comparatively smooth but has some groves to hold lubricants is required. This can be achieved by improving the surface of an AM printed part after it has been created, so-called post-processing. In this way, the surface can be manufactured to maximise efficiency and functionality of the part in an engine. This is not a case that I have worked with, but it is a good example to illustrate the importance of surface quality”, says Amogh Vedantha Krishna.

The choice of post-processing method depends on the nature of the surface and material as well as on the design of the final product. Amogh Vedantha Krishnas research focuses on which post-processing method is the best possible choice to improve the surface quality of a specific product.

“I have evaluated the post-processing methods based on the cost, time, geometry and function of the polymer products specific to an AM technology called Fused Deposition Modeling (FDM). My research showed that the extra incurred costs of post-processing can be compensated by re-designing the models to reduce the manufacturing time and material usage”, says Amogh Vedantha Krishna.

Collaboration with TylöHelo

There are many other examples, besides the engine case above, where surface quality is important. Amogh Vedantha Krishna has worked together with sauna company TylöHelo to help them improve the visual appearance of AM produced parts. This was done by using post-processing methods, which significantly improved the aesthetic properties of polymer parts produced by AM technology. However, it increased the cost per part due to the additional processing steps.

“TylöHelo wanted to use AM to enable customisation. At the same time, they required quality and cost to be as good as using injection moulding (IM) as manufacturing method”, says Amogh Vedantha Krishna.

The additional costs for post-processing were reduced by using a mathematical method called Topology Optimisation for re-designing parts to reduce material usage while retaining or maximising functional performance.

“The capability of AM to produce the Topology Optimised parts compared to conventional manufacturing processes is remarkable”, says Amogh Vedantha Krishna.

By employing post-processing methods and Topology Optimisation, it was possible to come close to the quality and cost set by the IM process. This encouraged TylöHelo to set up an AM machine for manufacturing their sauna parts which were earlier produced by the conventional IM method.