During development of its 2004 Sportster motocycle, Harley Davidson (Milwaukee) wanted to eliminate a six-piece forging and stamping process from the assembly line. The company turned to Signicast Corp. (Hartford, WI) to solve the problem.
Signicast suggested its investment casting process. Investment casting is one of the oldest manufacturing processes in use. Intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process. The process can also be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures.
Signicast's investment casting process produced a 8.75- by 8- by 4-inch component to replace the six-piece forging and stamping process. This new component is now used as the starting point for the entire motorcycle. The part sets up the overall alignment of the vehicle and is heart of the main feature of the Sportster-reduced vibration.
Dimensional stability is critical. Solidification modeling was used to predict where sectional changes would be required for sound casting. These design enhancements were also used in the sections as a stiffness transition to aid in the handling of the high-stress areas. Sculpted shapes of sockets were used to lower the stress levels at the weld joint, providing a better joint with less stress, and increased strength of the overall frame.
The new component interacts with the mounting system and drive line to provide a mounting for an isolation system. It also allows for mounting holes for brake components, passenger pegs and wire harnesses.
Replacing the former process with this one-piece casting has increased the reliability of the motorcycle due to reduced part variation and welding distortion on the frame. Overall part cost was also reduced by 15 percent and allowed Harley Davidson to remove a welded subassembly from the manufacturing process. These changes reduced fixture costs and improved throughput time by 25 percent.
For more information on investment casting, call 262-673-2700 or visit www.signicast.com.