O.C. Tanner is an award and recognition me-dallion manufacturer. Most notably, they pro-duced the medals when the Olympic Games were held in Salt Lake City in 2002. In one of their processes called coining, O.C. Tanner uses hard, metal dies to form soft metals, such as gold, into medallions. Unfortunately, small features on the coining dies are break-ing off, making the dies unusable. Time and money are wasted remaking dies to continue production. Our task was to extend die life by preventing dies from breaking. One solution was to develop a method to quickly clean dies of metal that adheres to the die surface during the coining process.
We found that crushed walnut shell media, used in a blasting machine, gave the best cleaning results. This is an environmentally friendly solution (no chemicals) that we based on some existing sandblasting equipment we found during a tour of OC Tanner. Using a PLC-controlled piston to move the die back and forth under the stream of walnut sheet, the dies can be cleaned of residual metal in about 15 seconds. We also explored heat treatment methods to restore original hardness to dies that have seen significant use. This is necessary, because residual stresses can build up in the dies during repeated coining, and if they are not relieved the stresses contribute to failures that disrupt production.
These solutions will be beneficial to OC Tanner, as they clearly demon-strate potential to extend die life. For cleaning dies, our method and ma-chine will be familiar OC Tanner employees. In fact, when we tested the machine for the first time with production associates they were delighted with how easy the machine was to use and how well it cleaned their dies. OC Tanner now has a complete engineering package that will allow them to reproduce this machine as needed for their production requirements. They also have a heat treatment procedure to stress relieve dies using their existing equipment.
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