MoldMaking Technology

SEP 2018

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Case Study / Mold Materials 40 MoldMaking Technology —— SEPTEMBER 2018 By Cynthia Kustush When Dramco Tool Co. Inc. (Grand Island, Nebraska) was tasked with building a compres- sion mold for an aerospace customer that would run carbon-fiber reinforced epoxy SMC, the com- pany knew that dimensional stability in the mold material would be critical. Dramco Tool Co. Inc. (Dramco) chose to build the tool with NAK-55, a pre-hardened mold steel that International Mold Steel Inc. (Florence, Kentucky) offers. "We knew from experience that there are inherent problems with using a softer steel like P20 for this type of compression molding application," Dramco President Larry Patten says. This tool was for an airframe part and measured about 40 inches long by eight inches wide and six inches deep, he says. The cus- tomer required Dramco to hold surface toler- ances to 0.003 inch in several places down the length of the mold. "We needed to use a hard-enough material to hold up to the amount of production that the customer required over the life of the tool (which the customer specified as a 10-year program of full production), but we did not want to spend a lot of time on the front end of the tool build by going all the way to the hardened tool steels like H13 if we did not have to. NAK-55 fit the bill." DRAMCO TOOL CO. INC. PROBLEM: Dramco had too many extra steps in the machining process using other material options, and it had to deal with multiple warpage issues. SOLUTION: Dramco used NAK55, a pre-hardened mold steel from International Mold Steel. RESULTS: Dramco experienced greatly improved machinability with no warpage, better weldability with no witness marks, the removal of extra steps and a more economical use of resources. Pre-hardened Mold Steel's Composition Makes Moldmaking Process More Efficient and Straightforward Dimensional Stability Saves Time and Money Patten explains that Dramco manufactured this mold for about $110,000 using NAK-55. If Dramco had built the mold using hardened tool steels, the price would have easily cost about 20 percent more. It also would have required at least three more weeks to complete. "If we built the tool out of H13, for example, many more steps would have been required using wire and sinker EDM because H13 is a harder material to machine," he says. "Keeping in mind that this part is 47 inches long, we would have been required to rough it out, leaving at least 0.10 inch of extra material because we know when it goes through the heat-treat cycle it will move, or warp, and we would have been required to machine that off in its hardened state. "Alternatively, if we built the tool using P20, rough machin- ing would release a lot of stress that was already in the workpiece, but it would also introduce some stress," he says. "When the machinist loosens the clamps after roughing, he or she might find that the part has a 0.03-inch bow to it, mak- ing it necessary to heat-treat it to remove any residual stress before re-machining it to make it straight again. With NAK- 55, the machinist machines it, and it is complete. It's a stable tool steel that does not move when large amounts of the Dimensional stability is a prime reason why Dramco Tool Co. Inc. chooses NAK-55, a pre- hardened mold steel from International Mold Steel Inc., when building compression and injection molds that require very tight tolerances. NAK-55's uniform hardness is another benefit because it protects the mold against wear from abrasive materials during the molding process. Images courtesy of Dramco Tool Co. Inc.

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