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moldmakingtechnology.com 29 FOR MORE INFORMATION Toolweld, Inc. / 847-854-8013 / 847-809-3959 eric@toolweldmicro.com / toolweldmicro.com Considerations Size. Mold size may dictate the appropriate welding process. A laser welder is in a fixed position and cannot be moved, so any repair has to be positioned exactly beneath the laser head. This limits the size of the mold that can be repaired with this type of welder. Large laser welders with moveable arms are available that provide better access for larger molds, but this requires a long setup process. A TIG welding torch, on the other hand, can be moved around and positioned by an arm or wrist. This greatly increases mobility and eases the welding of large molds. However, this flexibility must be weighed against the pinpoint accuracy of laser welding, which cannot be achieved by other processes. Time. Laser welding does take longer than micro-TIG weld- ing for certain weld repairs because of the laser's fixed posi- tion, but this process does greatly reduce distortion and cre- ates smaller welds. Micro-TIG welding can produce larger weld deposits faster and more efficiently, but weld sink (material shrinkage) and cracking around the heat affected zone (HAZ) can be a problem. This sink can occur when the weld cools too rapidly, causing a contraction or ring of depression around the area where the weld meets the base material. To combat this effect, anything TIG-welded should receive a proper preheat and post-heat treatment to reduce the contraction effect. Following steel manufacturer specifications is advised. Damage. Weld sink and cracking are rarely problems for laser welding, as this process uses a wavelength of light concentrated in a tiny area. Most materials don't require a preheat to be laser welded, however, laser welding is more susceptible to porosity (imperfections in the weld), since a laser beam does not have sufficient power to break through rough surfaces such as an EDM finish. Most importantly, a laser welder can repair tiny details and small molds, which would bend or distort from the excess heat generated by a TIG or micro-TIG welder. No matter which process is selected, there are challenges to achieving the optimal mold repair. Following are the top two problems welders encounter. Problems Access. Access to the welding area is the most critical and most common challenge a welder faces, as mold damage and engineer- ing changes are often in areas that are difficult to reach. This is especially true when the revisions are in deep cavities, as any impurities (such as dirt, grease or oil) also require cleaning and grinding to achieve an optimal repair. Special coatings or platings on the mold surface are another problem, as they can cause poros- ity and/or surface cracking, which results in lesser weld quality. Re-cast layer. Another challenge to achieving optimal mold repair is an EDM finish's hardened re-cast layer, which can act as a bar- rier to the weld puddle. On a TIG machine, this requires increased welding amperage to break through the hardened surface layer. However, this increased amperage yields a difficult-to-control weld puddle that can cause unintended damage to surrounding details. On a laser welder, an EDM finish inhibits the laser beam from breaking through the re-cast layer, resulting in porosity and miniature surface cracking. The only solution here for either pro- cess is to grind down the re-cast layer as best as possible. In future articles, we will dig deeper into this particular welding problem. Remember that collaboration between welder and customer is key when discussing a mold repair project and prior to making a final decision on the appropriate welding process. This collabo- ration should help to identify a better and simpler way to per- form a weld repair. Next month, we will review understanding and diagnosing the repair task at hand. CONTRIBUTOR Eric Hild is a laser and micro-TIG welding specialist at Toolweld Inc. with 15 years of bench experience in mold repair welding. He has authored the hand- book, "Understanding Tool Welding: A Guide for Tool Makers." Technology Solutions and Business Strategies at your fngertips! MoldmakingTechnology.com