New insights for the specification of copper alloy strip metals forconnectors

摘要

The American Society for Testing and Materials publishesspecifications that prescribe the temper of several metals, includingcopper alloy strip metals. Most of the strip metals used for connectorsare included. Manufacturers of these strip metals are obliged to producethem so that they meet ASTM specifications. The mechanical properties inspecifications ordained by the Society are published by themanufacturers in promotional materials. Thus, it's not surprising thatthe specifications most often found in purchasing documents and onengineering drawings coincide with the values published by this Societyand the manufacturers. While the effect of this practice onstandardization is some what laudable, it often leads to the wrongspecification for connector spring metals. At best, mis-specification isdiscovered in the prototype stage of development, and“merely” causes delay in getting parts on test and intoproduction. At worst, the metal does provide prototype parts that meetinitial performance requirements; it is only later, perhaps even afterseveral production shipments, that manufacturing problems develop. Orworse, field failures are reported. It is only then discovered that thestrip metal was inadequately specified. ASTM specifications primarilyensure that a particular temper is being obtained, that the metal has aparticular breaking strength. Obviously, connector springs are notdesigned with the breaking strength in mind. Meeting the typical Societyspecification does not offer assurance that there is enough strength forthe required contact force, that the contact force will endure, thatthere is enough conductivity, that there is a given spring constant, noreven that the part can be stamped without fracture. These problems willbe eliminated (or greatly minimized) by using the new insights in thispaper for specification