Die casting makes short work of small-lot parts

Switching from machined RF shields to precision die castings let Anritsu Co., Morgan Hill, Calif., cut costs in its Site Master series of analyzers, which are made in small lots. The company estimates payback on its die-casting investment will take only six months. “Most of these components are produced by traditional machining from plate or bar stock,” explains Anritsu Process Engineer Sam Krull. “Because we’re a lowvolume manufacturer, we sometimes don’t have the opportunity to use less-expensive production techniques. But we’ve seen payback in these parts in as little as three months.” Anritsu worked with Alloy Die Casting Corp. (ADC), Buena Park, Calif., to develop the A380 die-cast aluminum parts. “The shields are fairly complex, which makes some casting houses shy away from smaller production runs,” says ADC Design Engineer Gary Gray. “Some shields are just 0.03- in. thick. And any time an alumnum casting gets below 0.06 in., you can run into complications. So it’s important to get the right balance of injection speed and venting capacity, as well as precise temperature control.” The shields are cast from single- cavity tools, typically on a 250-ton press. The molten 1,200°F alloy goes through a small 2-in. plunger that fills the die in about 25 msec. The process, however, maintains a relatively low gate velocity, around 1,200 ips. Depending on the type of shield, shot sizes range from 4 oz to about a pound. “We typically run at a conservative speed of 70 and 80 cycles/hr,” says Gray. “We want the injection to be fast enough to fully atomize the material and give us a quick fill time. But we have to temper that with the understanding that higher gate velocities erode tool steel more quickly and can shorten die life.” Finishing operations for the shields include straightening and about 6 min