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SEP 2018

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Case Study / Topic 42 MoldMaking Technology —— SEPTEMBER 2018 Case Study / Mold Materials FOR MORE INFORMATION Dramco Tool Co. Inc. / 308-382-5251 / dramcotool.com International Mold Steel Inc. / 800-625-6653 / imsteel.com the mold. NAK-55's better thermal conductivity allows more heat to be drawn out of the mold than is the case with other types of tool steels. Material Provides Better Weldability and Surface Treatment Patten says that NAK-55 is very weldable, and that weldability is especially beneficial when it comes to repairing a compres- sion mold that will run for many years. "Any tool that runs for 10 years is going to need repair at some point," he says. "Somebody's going to drop a bolt in there or crash it. Or in this case, with running a very abrasive SMC, there may be wear in critical areas that will need restoration. The benefit is that NAK-55 is one of the easiest mold materials to weld. In fact, the machinist can weld a cavity in NAK-55 and make it absolutely impossible to tell where that weld was, even under an optical polish." According to Britton, when a machinist welds NAK-55, the material softens. To restore its original base material proper- ties, the machinist only has to re-age it at 950°F. "The weld and the base material are identical. The machinist will see no evidence of the weld on the part," he says. By comparison, if the cavity is made from P20 and is welded, the heat-affected zone hardens. "Depending on the surface finish that the machinist is trying to achieve, a difference of even a couple of Rockwell points between the base material and the weld will show evidence of the weld on the molded part, so the machin- ist has to color match it or bring it down." Speaking of surface finishes, Patten notes that NAK-55 pol- ishes better than P20. "We're taking these SMC tools up to a B2 finish using a 400 stone, which polishes very well up to that finish," he says. Britton concurs, saying, "It can go up to an A2 or A3, but NAK-55 does have sulfur in it, so the machinist has to be care- ful about that when polishing because sulfur-bearing steel will only have polishability to a certain level. That goes for all sulfur-bearing steels. Sulfur is basically dirt, but it aids in machinability, and what it gives in machinability it takes away in polishability." Extending Cutting-Tool Life Another side benefit that Patten says that he has noticed when machining NAK-55 is the cost savings that he has gained in cutting-tool usage. "It is difficult to produce hard numbers on that, but I would say that our tooling costs are on par with machining P20 and significantly less than machining H13," he says. "P20 is about 30 HRC, and we do experience hard spots that can cause premature cutter wear, whereas we do not get any variance in hardness with NAK-55 because it is a very uni- form steel, so tool life is extended. This is especially helpful in gundrilling operations." Britton says, "Anytime dimensional stability is critical to a project, NAK-55 is a nice option, whether for the type of appli- cation Dramco had for this aerospace customer or in others like injection molds, blow molds, injection blow molds and so on." "We have been building this type of mold since 2000, and NAK-55 has always been in our back pocket," Patten says. "Stability matters, even in a 12-inch part. We can't pigeonhole NAK-55 for use only with long pieces. I can get stresses that make a 12-inch part move when I do not want it to, and I need to protect for it. We use NAK-55 for small inserts. It is just another tool in our arsenal to use specifically when we need a good, pre-hardened material that is well above 40 Rockwell and is stable." [NAK-55] is a stable tool steel that doesn't move when large amounts of the cavity are removed because it comes from the mill with no stress in it. All of the extra steps are not needed. maintenance tracking MADE EASY. Drop-down Menus | Standardized Terms | Tech Tips Status Alerts | Powerful Reports | FREE TRIAL Simple-to-use maintenance software that gives you total mold control. NOW OFFERING: Mold maintenance training courses. moldtrax.com

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