A fundamental shift to aluminum tooling for higher volume automotive applications is on the horizon. Major automakers started work to create standards for aluminum tooling to achieve their goals of lower tooling and production costs while maintaining part quality previously achieved only with carbon alloy steel. Aluminum tooling is being used on selected high-volume applications at OEMs with production runs already reaching hundreds of thousands of parts. Aluminum works best when molding polymers like thermoplastic polyolefins (TPOs), polyethylene (PEs) and polypropylene (PP). These plastics account for over 70% of the plastics used in a typical car. As automakers move to lower volumes, the cost efficiencies of aluminum tooling will make it an attractive candidate for even more applications. However, aluminum tooling is not for every application. Application of aluminum tooling 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. It involves developing new ways of designing tools specifically for aluminum, allowing for the softer material and different thermal expansion rates vs steel, and also to develop new operating guidelines, different from those for cutting steel. A properly planned and executed aluminum tooling program will result in faster tool construction and overall reduced tooling costs with the potential for truly dramatic molding cycle-time savings and corresponding impact on part cost. Automakers can realize savings of 5-10% on construction of new tools for the majority of their applications, as well as the added benefit of shortening tooling lead times by 10% or more vs. steel. 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 20-40%. In addition to faster cycles, aluminum tooling’s thermal-conductivity advantage also helps to produce parts with less warpage and tighter tolerances. 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 can cut costs further in production. However, aluminum tooling also requires more labor to keep up with that faster pace. 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. Guidelines and best practices that will be of value to tool builders and producers as they consider aluminum tools for higher volume plastics applications - Planned secondary operations after the molding process should be thoroughly investigated for potential cycle improvements, so that tool design can be optimized when possible to match the thermal conductivity advantages inherent in aluminum. There will be no advantage in faster molding if the secondary operations can’t keep pace. If the part in question is to be molded and then moved somewhere else in the plant, or will be immediately shipped out, then the molder can take full advantage of all the benefits of cycle-time reduction. From a design point of view, applications using less abrasive materials like PP, TPO, or PE, and low-visibility or hidden parts, are probably the best way to go with aluminum tools, at least initially. Start with fairly shallow parts, which have less side molding pressure, and tools should be designed with fairly flat parting-line run offs and with seal-offs that are not extreme, no less than 5°. These types of parts typically lend themselves to high volumes with low tool maintenance. In a similar vein, non-grained parts and parts that don’t require a high surface finish are good places to start with aluminum. Finally, parts that are less likely to have engineering changes should be considered. As regards maintenance, issues like flash and parting lines are considerations for any tool, steel included. Maintenance personnel will need to develop additional skills for welding aluminum. Aluminum is not more difficult to weld than steel, but there are differences in process and technique that must be learned. Techniques have to be developed to reduce the “halo effect” common with heat-affected areas when welding aluminum. Preventive-maintenance requirements are similar to those of steel, although textured mold surfaces require more frequent cleaning. Very few technologies available to automotive manufacturers today that can match aluminum tooling’s powerful potential for significant reductions in piece part cost over a broad array of applications. (Source : Darcy King, Jessica Shapiro)