Development of novel abrasive finishing process to achieve final net shape of complex metal additive manufactured components

5. Technical Approach: This project aims to develop novel mechanical conversion processes for finishing metal AM parts to achieve 1)surface polish finish to required standards (M1: month 6) 2)to finish AM parts to correct tolerances (M2 month 9) 3) remove internal support structures (M3: month 12)(AppendixB). CAM will design and fabricate a novel abrasive flow polishing process with pump energised reversible flow of abrasive media for multiple AM parts. Flow will be provided by an industrial sized peristaltic or pneumatic pump through a customised chamber with compartments to separate each AM part in the batch, to prevent part on part collisions whilst retaining 360 free rotation. Due to the small apertures in the AM parts currently available polishing media may have to be mixed in new combinations to achieve the desired effect. CAM will investigate timings and abrasive media in a rotational polisher to produce different finishes. CAM will investigate novel recycled glass polishing media (Vibraglaz) in a vibratory bowls to remove internal support structures. Suitable AM test pieces will be designed and built inhouse. Stepwise changes in polishing media and timings will be recorded and results measured by light (inhouse) and SEM (STFC) microscopy, photography and external surface finish evaluators. A project director will manage progress and reporting. CAM will seek external technical support through an advisory board formed from academia, equipment companies and end users. This will include members from Liverpool John Moores University and STFC. Alternative techniques have been sought, but currently there are no standard processes available that deliver specified shape or measurement for metal AM parts. Whilst liquid finishing and electro-polishing can provide a surface finish, they emphasise the uneven surface of AM parts (Appendix B). Some AM companies use CNC machining to produce final shape however this method cannot access internal surfaces of AM parts.
6. Innovation: 3RTP created the titanium AM Queen's Baton for the Commonwealth Games, they polished the external surfaces to a high mirror finish and left the inside as natural finish as an artisitic effect. This method cannot be used in many industrial processes as for food production all surfaces would be required to be finished to the same specification. Other AM companies use CNC maching to finish their AM parts, this is possible for parts with external machineable surfaces. Other AM users eg aerospace companies are pursuing finishing on more complex parts however as yet no information on these processes has been identified through literature search. CAM tests on mechancal finishing for latticework AM parts identified a need for tooling and labour, therefore potentially inefficient (AppendixB). This project is therefore innovative as it aims to develop novel finishing process that would allow internal surfaces to be polished by the manipulation of new combinations of media, and by the design of abrasive flow process over freely rotating batches of parts to deliver high specification finishes and tolerances required for certain industrial standards.No similar abrasion flow designs were found in patent searches. In addition the removal of internal build structures allows AM parts to be designed with more internal complex chambers that currently would not be employable due to the retained build support structures. These innovations would develop final part shape productionby metal AM, decrease labour and advance this technology's capabilities to deliver high specification parts and additional complexity.
7. Some Risks identified at this stage are shown in Appendix B. Identified risks include: Low Risk: The small sized abrasion media required for small apertures may not be energised sufficiently to polish metal AM parts. More energy could be supply by altering speed, direction and combination of medias. Abrasive burring of AM part edges through over exposure to media: time and type.Solution is to examine at short time intervals to identify this effect then change test parameters ie time, media type. Medium Risk: While external surfaces of metal AM parts may be polished before the internal parts leading to decreases in desired external dimensions. This may be decreased by increasing energy by the introduction of ultrasonic energy to abrasion media. Uneven polishing: may have to introduce jigs to hold parts in place and rotate parts. Project may not progress well due to inadequate record keeping and review. CAM and external advisors will monitor all experiments, collate the results and ensure that timely delivery keeps project on track. High Risk: Abrasion flow processor may not work, tubes might be worn away due to reverse flow. CAM engineers have the ability to assess problems, provide solutions and adapt strategies to achieve the desired result thus decreasing the risk that the customised processor may not physically work. However the ability of abrasive polishing to achieve final shape for metal AM parts is unknown, but preliminary tests suggest that improvements can be made .