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moldmakingtechnology.com 53 The correct way to repair a crack is to first grind it out, making a U-shaped channel to allow enough weld to enter the area. CONTRIBUTOR Eric Hild is a laser and micro-TIG welding special- ist at Toolweld Inc. FOR MORE INFORMATION Toolweld Inc. 847-854-8013 / 847-809-3959 eric@toolweldmicro.com toolweldmicro.com process that involves cleaning and viewing the damaged area under a microscope to check for existing cracks. Heating for TIG welding. Pre-heating and post-heating molds for TIG welding is essential to avoid cracking. Properly heated molds have an easier time adjusting to the shock of drastic temperature changes. It is important for mold steels to be pre-heated, and it is an absolute necessity for die steels due to their hardness. Generally, mold and dies steels need to be pre-heated to 500-700°F before welding. Post-heating after welding helps control contraction in the weld's HAZ. In all cases, adhere to steel manu- facturer guidelines for pre- and post- heating. Peening for TIG welding. A welder can also peen the weld to reduce the effects of steel contraction during cooling. This involves periodically using a hammer and punch to beat into the welded area, reducing stresses (see image on facing page). This meth- od should be used immediately fol- lowing welding, while the weld is still hot and malleable. Peening is often used for TIG welding of large buildups. Micro-TIG welds are usually too small for this process. Crack repair. Cracks always need to be repaired, but the method of repair is critical. Simply burning down the crack with a micro-TIG torch or a laser weld- er is not the proper way to fix it, even though this may have been requested by the customer. The correct way to repair a crack is to first grind it out, making a U-shaped channel to allow enough weld to enter the area. Keep in mind that you may not be able to see the entire crack. Once you start to dig it out, you may find that it acutally is larger and more wide- spread. In this case, decide with your customer how much you want to grind the crack to repair it.