Medtech: 3D-Printed Skull Implants Get Final Touch with Surface Finishing
Using CAD software, individual cranial implants can be produced by means of additive technology. Rösler company ensures that the surfaces of the implants meet surgical requirements.
Much has already been written about the CT-scan-to-CAD method, which is used by Renishaw to produce cranial plates by means of additive technology. A relatively unknown fact so far is however that the processing times for smoothing and polishing these implants can be drastically reduced, while still delivering an exceptionally high surface quality. Rösler Oberflächentechnik has developed the technology achieving these results.
Surface Treatment of Cranial Implants Cost-Effective and Reproducible
Neurosurgeon Bartolome Oliver required implants with satin-finished, matte surfaces to match a patient's skull areas. Andy Wescott, application engineer at Renishaw, was therefore tasked with developing a cost-effective, reproducible process for the surface treatment of cranial implants. The implants were required to allow for both matt and high-gloss finish of the raw product in just one step.
The solution of this task did not require the re-invention of the wheel, but only the development of a suitable machining process using a Rösler Flow Finishing System. The high quality of printed workpieces allows for them to be machined like any other metal workpiece. In addition, Rösler has been dealing with surface treatment for about 80 years. It therefore possesses comprehensive know-how in the field of flow finishing and shot blasting of metal workpieces. Since workpieces produced in the AM process have relatively rough surfaces, Rösler can contribute their experience in the field of surface technology.
Wescott's department decided to use a Rösler centrifuge type FKS 04 to grind and polish its components. By using the new process, the skull implants, manufactured in a Renishaw AM250, require only a minimum of manual work to remove the supporting aids and smooth the surfaces with a mop wheel. Afterwards the components are put into the Rösler centrifuge. After a three-stage machining process, the parts have an extremely smooth surface. In total, manual labor could be reduced from five to under one hour.
New Process Requires Little Manual Work
Renishaw contributed its technical expertise to ensure that the new machining process delivers reproducible results. Andy Wescott explains: "We have developed a fixture that positions our workpieces at a precisely calculated angle in the flow finishing machine. Instead of moving freely in the mass of abrasive wheel, the parts are immersed in the three different types abrasives in a predetermined position. Specific surface areas must be protected from the abrasive medium. In order to achieve this, we have developed a holder that only immerses those areas in the abrasive material that need to be ground and smoothed."
Although it has not yet been possible to develop a universal surface treatment method for additive manufacturing processes, the Renishaw project demonstrates that innovative solutions are possible. Similar to the additive manufacturing process itself, surface treatment depends largely on how existing machining processes can be adapted to the individual applications.
Surface treatment of additive products is still in its infancy. But I think it is absolutely wrong to regard additive manufacturing as a self-contained manufacturing technology, "said Wescott. His recommendation: "Take a look at machining, for instance. We have been using this machining method for many years and we take for granted that appropriate deburring and anodising processes are available. As with machining, we need to develop reliable processes that match the requirements of additive manufacturing." Renishaw has found a suitable partner in Rösler Oberflächentechnik.
This article was first published by DeviceMed.
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