Mass Reduction In Trucks Using Hybrid Material Solution

This project required some out of the box thinking to come up with a unique answer to the long standing need for mass reduction. The specific component addressed was a light duty truck tailgate assembly.

Truck manufacturers need to reduce mass of components to improve fuel economy without compromising performance attributes. A typical tailgate must conform to design studio's intended form and have both structural strength and stiffness. Also fit and finish requirements must be consistently met in volume production. Furthermore, any proposed design solution must be compatible with existing manufacturing and assembly flow-path designed for high volume production, while minimizing economic impact. Traditional tailgates are an assembly of several sheet steel stamped components joined together using resistance spot welding process and subsequently painted in variety of colors with the truck body. The finished assembly of about 7 components weighs about 40 lbs.

Our investigation showed that tailgates are part of the working vehicle and hence are expected to be strong and tough and "take" rough field use while looking good for the life of the truck. Demographic shifts that have resulted are showing a growing female group of owner/users who prefer a lighter gate for ease-of-handling. Each manufacturer has similar requirements that vary slightly in details. Also, they all seem to use the same material sheet steel. Past attempts have involved substituting other materials but always using a single material and product form. Our innovation involved considering and finally applying use of two different materials and product forms - namely sheet aluminum and molded plastic. We were able to preserve the stamping process for the sheet component while consolidating the functions of all other parts into a single molded plastic part. In doing so we adjusted the joining and assembly process slightly and were able to reduce the mass by almost 50% and part count by 2/3 while reducing / simplifying the assembly process by several steps. This unique patented design solution had minimal cost impact to the manufacturer even though it used more expensive per unit materials.

The lightweight hybrid material tail gate design, shown in the figures above retained the shape, form and size of the steel surrogate. The surrogate's outer skin was stamped steel sheet while the new design used an aluminum skin with only minor increase in gage. Inside this shell of lightweight aluminum, a molded plastic reinforcing module was inserted that replaced all other components. The module was adhesively bonded to the skin with a few rivets to fixture the system until the system cured. The edges of the skin were hemmed as usual and the assembly painted in the normal manner. All other hardware assembly and mounting to the vehicle process remained unchanged. Prototypes were built and tested, as shown below, to prove out the solution. The details of this work has been published in a SAE paper and a link to additional information is available by contacting this consultant directly.

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