Casting Study: Panel Nut – Ignition Switch

Ignition switch corrosion was the source of customer frustration and concern. Standard panel nuts, like the ones used to secure the ignition switch to the riding mower control panel, are made of stamped steel. The die cast company’s technical staff proposed changing the shape of the nut to include a shoulder. This allows a plastic boot to fit over the nut providing protection as well as an enhanced and finished appearance for the operator panel. A nut with this type of shoulder cannot be effectively stamped because of the significant difference in the cross-sectional area. Moulding/casting is the most cost-effective method to produce the designed shoulder. The shape can be plastic moulded but plastic’s inherent creep does not stand up to the vibrations from internal combustion engines. Zamak 3 is used as the nut material because it provides the durability and creep resistance needed. While steel is stronger than zinc, the increased thickness (0.125 in. vs. 0.285 in.) of the new nut provides more than enough torque. In addition, zinc can be cast net shape with high production cycle speeds. The redesigned nut prolonged ignition switch life and customer satisfaction.