Issue 053, February 21, 2024
Pat K. Bowen, Ph.D., Vice President of Research & Development, Quality, and Regulatory
Grant Justice, Research & Development Manager
Mike Bielecki, Product Design Engineer
Finite element analysis (FEA) has become an invaluable tool for the design of electrical contacts, especially when combined with materials property and applications expertise. Such tools allow for the analysis of force-deflection behavior far beyond the relatively simple geometries considered by Pitney1.
Accurate analysis of force deflection behavior is crucial to the design of electrical contacts to ensure the correct load is applied at each contact and to verify the load remains within acceptable limits for all possible tolerance stack-ups. Finite element analysis also assists in optimizing the design to avoid any high stress areas that are at risk for failures due to yielding or fatigue.
In one case, the Design Engineering team at Deringer-Ney was approached with a proposed design change for a potentiometric wiper. The subassembly comprised a stamped metal wiper affixed to a solid molded plastic body. The designer was asked to review mechanical behavior of the sliding contact and requested to comment on materials for the application. Of immediate interest were bi-metallic wipers with the area of potential contact made from precious metal alloys in the Paliney® family joined to a spring made of non-precious age-hardenable copper alloys. DNI commonly uses this arrangement to reduce the intrinsic metal content in each part.
The wiper was deflected from the first, unassembled position (“free height”) to a second, assembled position (“working height”), and local stresses in the bending members calculated. In the results shown in Figure 1, an elastic modulus of 110 GPa (16 Msi) was used, and a force of 24 gf per arm was imposed on the contact. The modulus was taken as nominal for the Cu-Sn-Ni alloy C72900. This nonprecious material is often utilized in bimetallic contact configurations, typically with Pd-based alloy Paliney® 6. Results of the FEA were used to optimize the design until the final design was achieved with FEA results detailed in Figure 1.
Figure 1: FEA output for a deflected contact with an elastic modulus of 110 GPa.
Deringer-Ney has extensive expertise assisting with the development and optimization of electrical contacts for a wide range of applications. This includes complex stampings of bi-metallic materials that offer the performance of precious metal at the point of contact combined with the low cost of a non-precious metal body. DNI also has experience in the assembly of the contacts with molded plastic bodies.
References:
- K. E. Pitney, Ney Contact Manual: Electrical Contacts for Low Energy Uses, Revised 1st Edition. Bloomfield, Connecticut: Deringer-Ney Inc., 2022.