ALBUQUERQUE, N.M. — Researchers at Sandia National Laboratories and General Motors are working together to develop an economical way to make durable aluminum engines by spraying a wear-resistant coating onto the cylinder walls.
Manufacturers are using more aluminum in automobiles as a way to reduce weight, which in turn provides better fuel economy and reduces total emissions. Although an aluminum engine block is approximately half as heavy as a comparable cast iron engine, aluminum is typically not as wear resistant and, without some process to improve its durability, would wear out prematurely. Successful approaches have included iron liners that are cast or pressed into the aluminum block, special high-silicon aluminum alloys, cast-in ceramic fiber sleeves, and electroplating the cylinder walls with a wear-resistant coating.
Cast iron sleeves are currently used in high-volume production. Other methods have been successful to varying degrees, and several have been used for limited production in specialty cars. However, high production cost, complexity, design limitations, and other problems have provided incentives to look at alternative methods.
Under a cooperative research and development agreement (CRADA), General Motors and Sandia have been testing and improving a method of depositing wear-resistant materials onto aluminum using a small, supersonic oxygen-fuel jet with a temperature of more than 3,000 degrees Fahrenheit. In this process, a steel wire is continuously melted, and molten steel is atomized to form small droplets that are entrained in the supersonic jet. The spray of molten steel is directed onto the cylinder walls of an aluminum engine block, where it rapidly builds up a highly wear-resistant metal/metal-oxide composite coating.
“The GM/Sandia spray-bore process was initially based on a standard, commercially available spray device, and it is similar to other thermal spray coating processes that have been successfully used for many years in various industrial, aerospace, and biomedical applications,”explains Mark Smith, an engineer in Sandia’s Thermal Spray Research Laboratory and one of the project managers for the research.
Smith and an interdisciplinary research team of other Sandia and General Motors scientists and engineers are working to increase fundamental understanding of this technology by using laser and optical emission diagnostics, computer modeling, combustion science, and materials analysis.
William Oberkampf in Sandia’s Engineering Sciences Center is overseeing the modeling work. Richard Neiser, also in the Thermal Spray Research Laboratory, is the lead researcher on the diagnostic work. The goal of the research is to optimize the process for high-volume, low-cost production.
“The spray-bore process clearly has the potential of providing the desired durability and reliability at significantly lower cost than sleeving or the other alternative technologies. However, the demands of high-volume automotive production are unique, and some specific process improvements had to be achieved before this technology could be adopted for widespread use in the automotive industry,”Smith explains.
But, Smith adds, at the same time this collaborative research benefits Sandia because the improved technology is also being implemented into defense-related production applications that enhance production efficiency and economy. He cites improved process monitoring and control technology that has been jointly developed with GM in the course of this CRADA research that will soon be implemented at Sandia in one of its own production spray facilities. One such application is spraying aluminum coatings onto neutron generators.
“The improvements in efficiency, reliability, and product quality resulting from this new technology will save money for Sandia and American taxpayers for many years to come,”Smith says.
The spray bore process is being evaluated for use at General Motors. “There are still significant hurdles that have to be overcome, but the potential added customer value makes this an attractive project,”says Mark Gillman, manager of advanced manufacturing engineering, GM Powertrain Group, located in Pontiac, Michigan. “There has been an excellent spirit of cooperation and collaboration in the GM/Sandia CRADA team, and it has given us a better understanding of how the thermal spray process works.”
Although the CRADA for the thermal spray characterization was negotiated between Sandia and General Motors, the research has become a part of the Partnership for a New Generation of Vehicles, a cooperative effort of federal government agencies and the three U.S. automobile manufacturers with a goal of improving national competitiveness as well as vehicle performance and efficiency. In another CRADA, Sandia is working with General Motors, Ford, and Chrysler on methods to measure the thickness, strength, and durability of thermal spray coatings.