Hands-on research for knowledge-based mass finishing processes

The RWTH Aachen is one of the eleven German universities that are recognized as “universities of excellence”. When it comes to the fields of technology and natural sciences, the Aachen university is one of the most renowned academic and research institutions.  For decades the machine tool institute, one of the largest and oldest establishments at the Aachen university, has been a globally recognized beacon for future-focused research in the field of manufacturing technologies. One reason for this success has been the close cooperation between the four academic sectors “measuring technologies in manufacturing”, “quality management”, “manufacturing systems” and “manufacturing and machine tool technologies” combined with a balanced mix of basic and practical research. Marius Ohlert, project manager for grinding technologies in the field technology planning and grinding methods, that is integrated in the academic sector manufacturing technologies, comments: „Through the close cooperation with a variety of industrial companies we make sure that our research projects are based on industrial needs and that the results can be quickly transformed into practical results”.

Mass finishing as a research subject

The mass finishing technology is a widely used system for all kinds of surface refinement tasks such as deburring, edge radiusing, surface smoothing, polishing, descaling and de-rusting. Despite the importance of this technology for many industries most mass finishing processes are still based on the knowhow of experienced experts. Mr. Ohlert describes one research goal as follows: „With our basic research we want to achieve that mass finishing processes are knowledge-based, thus allowing a quicker, more efficient and goal-oriented process development. For this purpose, we study in detail the physical effects of the various mass finishing methods”. With application-oriented finishing tasks one objective is to improve already existing mass finishing processes so that the work piece quality can be improved. On the other hand, surface finishing processes must be developed for work pieces made from innovative new materials or for work pieces produced with new manufacturing technologies. For example, this is the case with fiber re-enforced ceramics, which are still under development.  For the necessary processing trials, the WZL uses its own equipment but also the comprehensive range of mass finishing machinery at the Customer Experience Center of the Rösler Oberflächentechnik GmbH. Around ten years ago the manufacturer of mass finishing equipment and consumables entered a strategic alliance with WZL machine tool institute. „With Rösler we have a partner, who is highly motivated to further develop the mass finishing technology, not only within the company but also in cooperation with us. For this purpose, we are constantly communicating with the company’s R & D department. From this information exchange about developments in the field of science and the experience in the industry we frequently identify questions and subjects for future projects”, explains Marius Ohlert.  Additive manufacturing promotes investments in new finishing methodsFor example, such projects deal with the post processing of components, which are produced by either 3D printing or hybrid manufacturing technologies in such diverse industries as aerospace, automotive, medical engineering and tool manufacturing. The project manager continues: „The high design freedom of additive manufacturing allows the creation of components not possible with traditional manufacturing methods. For the post processing of these complex components the mass finishing technology is, compared to classical machining systems, much better suited. The activities in this field, which Rösler pursues under the brand name AM Solutions-3D post processing technology, are especially valuable for the cooperation with the WZL institute. They were also the reason for investing in two new finishing machines, which we purchased in close cooperation with the colleagues from a partner institute that deals intensively with additive manufacturing”.  Moreover, this investment allows the WZL institute also to further demonstrate the possibilities of the mass finishing technology for the basic research as well as for specific industrial projects. The institute purchased a surf finisher 700, a special rotary vibrator R 150 DL-2 and a semi-automatic centrifuge Z 800 K-HA Turbo-Floc for cleaning and recycling the process water from the mass finishing machines.  State-of-the-art technology for optimal process development The surf finisher is a mass finishing system that allows the fully automatic, precise processing of entire work pieces or the targeted finishing of selected work piece surface areas with a wet or dry process. The plug-and-play system is equipped with an integrated robot that holds the work piece into the rotating processing bowl filled with grinding media. If required, the robot can also guide the work piece through the processing bowl with pre-programmed, computer-controlled movements. This allows the finishing of different work pieces with an individualized, pre-programmed process. The special rotary vibrator allows the surface grinding, smoothing or high gloss polishing of work pieces with complex shapes. The components, attached onto special fixtures, are mounted in the processing bowl of the vibratory system. Imbalance motors attached to the processing bowl induce a vibratory movement into the mounted work pieces.  In turn, during the entire cycle time the processing media flows evenly through and around internal channels, undercuts and the work piece contours. The new, semi-automatic centrifuge thoroughly cleans the process water from both mass finishing machines so that the cleaned liquid can be re-used for the finishing operation. This is not only advantageous for environmental reasons but also for reasons of sustainability.  Exchangeable processing bowls ensure maximum flexibility The processing bowls of the surf finisher and the special rotary vibrator can be easily exchanged. This allows a highly flexible utilization of the new finishing machines and, therefore, fulfills a key requirement of the WZL institute. The processing results depends not only on how the work pieces are handled but also on the selection and the flow characteristics of the media in the processing bowl. Marius Ohlert concludes: „For our studies it is essential to vary the media flow as well as the work piece handling, be it through a robot, mounting the work pieces to a fixture or having them loosely tumbling in the media. Of course, our studies also include the use of different media types, shapes and sizes. In this respect it helps that Rösler develops and produces all its media in-house so that we can rely on the company’s entire spectrum of ceramic and plastic media”. The studies concerning the stability and repeatability of mass finishing processes and the increased use of the new finishing systems for the post processing of 3D printed components require a lot more processing trials with higher work piece quantities. Rösler and the WZL institute at the RWTH Aachen university are jointly meeting this challenge to be ready for the mass finishing requirements of tomorrow.