Strategies for Lightweighting Forgings in Heavy-Duty Vehicles
Provided by Gracious Ngaile, Department of Mechanical and Aerospace Engineering, North Carolina State University
During the past decade, there has been an increase in R&D efforts geared toward weight reduction in passenger cars. This column highlights an ongoing project to investigate the potential of forging technologies to reduce the weight of forged parts used in heavy-duty vehicles (HDVs) without diminishing their structural integrity.
This project encompasses four major objectives: conduct a survey of forged components used in powertrain, chassis and suspension systems and identify parts with high potential for weight reduction through innovative forging technologies or material substitution; evaluate the technical and economic feasibility of forging components that are currently produced by casting or other techniques; investigate cost-effective forging technologies that could be used in lightweight manufacturing; and conduct a preliminary investigation on the energy flow path/maps to which forged parts are subjected during their service life and systematically assess (from a mechanical and metallurgical viewpoint) the potential for weight reduction in specific components.
The research team conducted surveys of forgings used in HDVs to identify potential forgings for weight reduction. The study identified five potential approaches to reducing weight: geometrical part change, material substitution, the use of composite materials, heat-treatment schemes and manufacturing process substitution (Fig. 1.)
Current forging technologies used to produce engine parts, gearbox parts and axles were studied. Emphasis was given in documenting proven forging techniques not commonly used in industry, new techniques that are being tested and those under research. A number of forgings were identified as potential candidates for weight reduction using one or a combination of the methods given in Figure 1.
Figure 2, for example, shows that the geometric change of a 300-pound crankshaft may lead to a 20% weight reduction by removing material around the connecting rod (Fig. 2c). Figure 3 shows that weight savings of 14% can be achieved if an output shaft is hollow (1.75 inch OD; 1 inch ID).
The study is also taking a critical look at the economic viability of the process, since geometric change may not be economically viable for some parts. Therefore, the study assesses all five weight-reduction paths to identify which ones are cost-effective. For example, newly developed thermal treatments have increased the strength of forgings, facilitating weight reduction.
This is a FIERF- and AISI-funded research project being carried out by North Carolina State and Marquette. The NCSU team includes G. Ngaile, A. Akataruzzaman, J. Jongkind, S. Henkel and F. Morrow. The Marquette team is led by Joseph Domblesky. Researchers have visited Volvo Power Train North America and Sona BLW Precision Forge Inc.