Nissen Chemitec America, www.londonind.com

Unique Tool & Gauge Inc., Windsor, Ont., www.unique-tool.com

Aluminum tooling for high-volume plastic-molding applications? Making the switch from carbon-alloy steel while maintaining part quality has been on engineers’ minds for years, especially in the automotive industry.

Engineers from Unique Tool and Gauge Inc., Windsor, Ont., design aluminum molds for plastic molding that hold down tooling and production costs. For example, Unique built the tool for the rear tray on the Honda Accord which is currently assembled at Nissen Chemitec America (NCA), London, Ohio. Since August 2007, the tool has molded more than 350,000 production parts.

But aluminum tooling isn’t for every application, say Unique’s engineers. It depends on the material, part geometry, production volume, and the number and type of secondary operations. Designing and operating aluminum tooling also have to accommodate the ways in which the metal differs from steel, especially its lower hardness and greater thermal expansion.

Aluminum works best when molding polymers like thermoplastic polyolefins (TPOs), polyethylene (PEs), and polypropylene (PP). These plastics account for over 70% of the plastics in a typical car.

Lower production volumes that come with lean and just-in-time operations also tip the scales toward aluminum tooling because there are fewer parts over which to amortize tooling cost. Aluminum tools cost 5 to 10% less and have 10% shorter production lead times than steel versions.

The biggest savings come with complex tools that have more mechanisms and greater depth. They require more machining, spotting, drilling, and benching operations which are accomplished more quickly and easily on softer aluminum than on P-20 tool steel.

Tools for flat, low-profile parts requiring few man-hours will have lower cost savings. In fact, switching to aluminum may increase initial tool costs since aluminum costs more than tool steel.

Aluminum tools can cut costs further in production. The metal’s thermal conductivity is higher than that of steel, so tools heat up and cool down quicker. This translates to production cycle-time reductions of 20 to 40%. Cycle time on the Honda Accord rear tray, for example, was cut 20% after switching to aluminum. However, tool cycle time alone is not the only factor to consider, says Shawn Hendrix, senior vice president of NCA.

“If we have an aluminum tool that can run at a reduced cycle time, but also requires more labor to keep up with that faster pace, we have to look very closely at the trade-off between speed and additional cost,” says Hendrix.

Preventive maintenance and repair are other factors to consider for aluminum tools. NCA reports preventive-maintenance requirements are similar to those of steel, although textured mold surfaces require more frequent cleaning.