CPM Fastools Makes Really Cool Molds

For all the interest in using rapid prototyping systems to build injection mold inserts, there has been some justified skepticism on the part of experienced tooling engineers. They fear the quality and longevity of the tool insert will never approach that of precision machined or EDM’d tool steel. CPM Fastools may put those fears to rest with a new tooling process that combines rapid prototyping with a proprietary cryogenic treatment.

CPM creates the mold inserts on a EOS M250, a prototyping system that fabricates components from sucessive layers of laser-sintered metal powders. In CPM’s case, most of the core and cavity inserts are normally produced in a brass-nickel alloy. “That’s what most of the customers want,” says Steve Moore, co-owner of CPM Fastools. The same EOS system also supports tool and stainless steels as well.

The parts off the machine are essentially net shape, though they may need polishing or finishing like a traditional tool component. And the EOS parts are nearly fully dense. Moore notes that the tool steels have less than 0.5 percent porosity, while the brass-iron-nickel materials have about 5 percent porosity. “When you shot peen the parts, it fully densifies the surface to about 0.080-inches depth,” he explains. “So the porosity is only an issue if you’re using conformal cooling.”

CPM routinely uses the EOS laser sintering system to produce tight tolerance parts with feature sizes and shapes similar to what EDM can produce. One recent job, a personal digital assistant for the blind, had feature tolerance under 0.002 inches, Moore reports. The EOS machine has a build envelope of about one square foot, but CPM can tackle much larger parts by using CNC machine to produce a large substrate onto which it attaches precision laser-sintered features.

When Moore and co-owner Mark McGrath started CPM about a year ago, they evaluated several types of metal-capable rapid prototyping systems. And while they liked the EOS, they had some concerns about the thermal effects imparted by the system’s high-watt laser. “We’d heard about problems like internal stresses and distorted parts,” says Moore.

And that’s where the cryogenics comes in. “We both came from a drag racing background,” says Moore of himself and McGrath. “And we often sent out valve components for cryogenic processing as a way to relieve residual stresses after machining. We put one and one together and decided to try it with the EOS parts.” McGrath and Moore theorize that the cryogenic treatments, which take place at temperatures below -2440F, not only help relieve those internal stresses but also change the metal’s microstructure in ways that improve wear resistance.

But it’s not all theory. In the real world, some of the laser sintered parts have already withstood more than a hundred-thousand shots of filled engineering plastics. McGrath notes that company has also molded highly-abrasive filled plastics, including a museum piece made from a 50 percent mineral-filled PPS. “That part was a pretty good test of what the inserts can take,” McGrath says.

Cryogenic processing has worked out so well that the company also sticks other mold components in the deep freeze--including screw bushings, ejector pins, and even mold bases. “We now treat all the wear items,”McGrath says.

To make the rapid tools even more wear-resistant – and that much closer to production- quality tooling – CPM optionally sends the parts through an ion-beam deposition process that lays down a tough coating of chromium nitride. Between the cryogenics and the coating, the company has created tooling inserts as hard as 50 Rockwell C, Moore says.

CPM Fastools drops the finished and treated inserts into standard mold bases, like MUD and D-M-E, which helps reduce the turnaround times for finished molds. Typical lead times are 15 to 20 days from the time the company receives an order.

For more information on CPM Fastools, go to www.cpmfastools.com.