Junction Relay Boxes

Industry: Automotive

Use: Main electrical junction box used to hold fuses, relays, and diodes


The main junction and relay boxes used in automotive applications have special requirements for injection molding. These parts pose many challenges, both from the molding perspective, as well as the mold construction and maintenance intervals.

This style of electrical connector can include over 100 terminal pockets. In some applications, these terminal pockets can include integral locking features that are used to retain the micro fuses in the assembly. Some of the challenges producing these molded components revolve around getting the material to flow into these small locking features while not overpacking other areas.

In addition to the molding requirements, these molds can have hundreds of small mold inserts, most with very tight dimensional requirements. These mold inserts tend to be extremely fragile. Many of these terminal inserts are unique in design and shape. Maintaining and assembling these tools require a special level of skill.

In some cases, the shut-off between two of these inserts, coming together from both halves of the mold, can be a ​​quarter-turn shut-off angle. This means these inserts must be machined and held in positions to within one ten-thousandth of an inch (0.0001).

Completing a preventive maintenance routine can be extremely laborious and challenging. When there is a stack of multiple inserts, the entire stack cannot be out of tolerance by more than one-thousandth of an inch (0.001). This means that every insert in the stack must be held much closer than the entire stack.