MoldMaking Technology

DEC 2018

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Surface Treatment 18 MoldMaking Technology —— DECEMBER 2018 The accuracy, speed and surface finish advantages of high-speed machining and EDM can complicate polishing, requiring polishers to rethink how they polish. By Christina M. Fuges Rethinking How to Polish E very shop wants to increase productivity, and polishing is often the bottleneck. Although companies understand the value of polishing, many are not willing to deal with polishing because they do not know how to do it properly. Polishing longer is not always the answer. Steve Smith, Gesswein & Co. polishing coach, says that the answer is more polishers. His experience has taught him that there should be one polisher for every ten people cutting steel. "So, if you have a 100-man shop cutting steel and programming, then you need ten polishers to keep up. Most shops would have three," Smith says. He also stands by a 10-hour work day. Smith believes that nine hours is optimal, as a polisher's fingers can only take so much of the vibration and abrasiveness associated with polishing. Machining Effect Despite the lack of skilled labor, today's shops seem to have enough polishers, but they have a weakness in their machin- ing. They are feeding polishers work that takes them too long, which yields parts that do not comply with the print because the polishers removed too much material. "Polishers must meet tolerances on molding areas, or they must scrap the part, but the amount of material a polisher removes depends on what the machinist puts in," Smith says. The quality of the part that the machinist gives to the polisher determines the amount of time that the polisher spends pol- ishing that part. The longer the polisher polishes, the more likely it is that the polisher changes the shape of the part. The secret to improving polishing efficiency and part qual- ity is improving the front end, or what is coming into the polishing department. For example, high-speed machining and EDM have advantages in accuracy, speed and surface finish, but these benefits can complicate polishing, requiring polishers to rethink how they polish. A common polishing challenge is removing the EDM recast layer and the hard layer that high-speed machining creates. Even though high-speed machining produces a surface that is shiny and very fine, there is a layer of really hard steel that reveals the pattern of the cutter when it is polished. If the polisher does not remove the pattern completely, the pattern will still be visible. According to Smith, the key to fixing this is "getting below that layer." The very fine surface that high-speed machining produces also entices polishers to start off with a 600- or 900-grit Internal process documentation helps polishers build upon experience and overcome surface finish challenges. Image courtesy of Vistatek.

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