Metal-matrix composite (MMC) castings are not new, of course: aluminum or other metal alloy parts are embedded with ceramic elements that give the finished part determinable qualities of material strength or heat resistance, overall or just in the location where those enhanced characteristics are needed. But it’s a complex process, difficult to execute, and expensive.
Lately, design and (especially) commercial factors are gaining some precedence over process and material considerations. Engineers often believe they can overcome established limitations, and financial and other resources shift quickly to address very specific problems.
Now, there are potentially lucrative applications in aerospace, lightweight automotive, and other industrial and commercial sectors. But at this moment, the MMC advantage may be slipping away from metalcasters.
Casting, it should be noted, is not the most common production route for MMC; that would be hot-isostatic pressing (HIP), because metal powders can be compressed into solid materials of specific shapes and sizes by simultaneous application of isostatic high pressure and high heat.
New research launched by Lightweight Innovations for Tomorrow (LIFT) aims to develop more cost-effective manufacturing methods for aluminum MMCs, for large-scale production in automotive and aerospace platforms. Casting is not on the list of alternatives being researched. The two-year program will consider extrusion, near-net-shape HIP, sintering, or thin sheet forming as alternatives to HIP.
LIFT, a “manufacturing innovation” partnership formed in 2014 and operated by the American Lightweight Materials Manufacturing Innovation Institute, coordinates academic and institutional research with likely and/or available industrial partners, with specific development targets for technologies needed to support automotive, aerospace, or other transportation sectors.
Materion Corp., a producer of beryllium and specialty alloys, and two types of metal-matrix composites (silicon-carbide reinforced aluminum and aluminum-beryllium) is LIFT’s primary industrial partner for the project. Together with other partners, they expect to identify processes that will reduce production time and costs, but preserve the “high specific modulus and strength-to-weight ratio” needed to supply aerospace and automotive components. Reduced production costs, it’s believed, would allow MMCs to be specified for current and future production.
“Right now, too much time and money is tied up in a production process which we believe can be improved upon,” stated Keith Smith, Materion’s v.p.- technology and government business development. “By pulling this team of experts together through LIFT, we will explore and refine those new methods to benefit not only our work, but that of the entire industry.”
Other partners are Boeing Corp., Lockheed Martin Corp., and GKN plc, a producer of powdered metals and drivetrain and aerospace parts. Academic research partners include Case Western Reserve University, Pennsylvania State University, the University of Tennessee, and the Massachusetts Institute of Technology. Oak Ridge National Labs is a partner from the federal research sector.
The research will run through 2018. In addition to validating new manufacturing processes through production trials of components defined by the industry partners, the initiative will develop the capacity for high-volume production to meet aerospace and automotive materials demands.
“Helping our members take a ‘lightweighting’ idea that has had some success on a small scale and helping ramp it up to be mass produced on a large scale is at the core of what we do at LIFT,” stated Alan Taub, chief technology officer at LIFT.
MMCs may seem novel in a commercial sense, but as an industrial technology it is comparatively mainstream. Two years ago researchers at Germany’s Institute of Plastics Processing (IKV) successfully combined injection-molded plastic and metal diecasting in a single process step.
Now, another process has emerged combining metal and plastic forming. Specialty chemical producer Evonik and IKV developed and commercialized a process for deep drawing and diecasting metal parts in a single, automated operation, using Evonik’s Vestamelt® Hylink copolyamide-based adhesion promoter. Subsequently, to improve the parts’ mechanical properties after conditioning, Evonik is offering bio-based Vestamid® Terra polyamide and polyphthalamide molding compounds, focusing on establishing finished-part characteristics that address demanding requirements for temperature or chemical and moisture resistance. As with current MMC cast parts, the applications determine the choice of forming process – but increasingly the materials are not determining the limits of production. The function determines the material and the method.