Challenges to Reduce Weight in Transportation Applications
Written by Don Monroe
At Monday’s Symposium X, Alan Taub of the University of Michigan described efforts to reduce the weight of vehicles that move people and goods on land, air, and sea. Taub is Chief Technology Officer for Lightweight Innovations for Tomorrow (LIFT), the second of eight institutes approved as part of the National Network for Manufacturing Innovation. Although the United States has historically left manufacturing to industry, Taub said, these institutes address the growing gap between breakthrough technology ideas and their successful manufacture.
In keeping with the regional focus of these institutes, LIFT is spread along the Interstate-75 corridor from Michigan to Tennessee, a five-state region that hosts three-quarters of the metalworking jobs in the country. The research priorities are driven by industrial partners in this region, and are supported by national laboratories and academics, some from other parts of the country.
Researchers have long recognized opportunities for weight reduction, and have demonstrated prototypes that are lighter by 50-60%, Taub noted. “The problem is cost.” Typical the issue is not the cost of raw materials, but of refining and downstream processing.
For cars, Taub—who was previously vice president for global research and development at General Motors—said that 10% weight reduction provides roughly 6% improvement in fuel economy. Weight reduction is therefore only worthwhile if it costs less than about $2 per pound. For this reason, lightweighting of automobiles has typically involved high-strength steels (which cost only about $1 a pound), although upcoming projects will test the cost effectiveness of large-scale aluminum substitution. By contrast, for aircraft even a $200 per pound cost will be offset by fuel savings.
“We’re trying to find synergistic opportunities between land, sea, and air,” Taub said, so every project must be supported by companies from at least two of these sectors. He noted that the existence of such synergies was not assured initially, but that there are now many projects that address common manufacturing problems.
These projects focus on processing of metals, including high-strength steels, aluminum, titanium, and magnesium. The techniques are organized into six “pillars”: melt processing; powder processing; thermo-mechanical processing; low-cost, agile tooling; coatings; and joining and assembly. Taub briefly described several projects, including reducing casting thickness for a 40% weight reduction, super vacuum die casting to prevent blistering of aluminum on heat treatment, fluidized-bed heat treatment, and translational friction welding.
“The number one need across all companies was joining,” Taub said, including the joining of dissimilar materials. Reducing the thickness of materials, whether sheets for automobiles or plates for ships, exacerbates the distortions and residual stresses from welding, for example. LIFT is exploring techniques, such as auxiliary heating, to reduce these problems.
The biggest opportunities Taub sees are enabled by improved multiscale simulations and the interchange of information across the manufacturing process. “The biggest weight reductions we are going to see are those enabled by integrated computational materials engineering” (ICME). These software tools can simulate how such properties as microstructure locally vary throughout a part during thermomechanical processing, for example, but it will take more work to fully realize a design process that accurately predicts the properties of complex manufactured parts.
Finally, Taub showed a video of incremental sheet forming (ISF), in which a computer-controlled stylus, aided by sensors and modeling, creates a custom shape like those traditionally made by huge, specialized stamping machines. “This will be the competitor to additive manufacturing for high-strength parts,” he said, just as “almost any metal component today can be made by a good blacksmith.”