Page 42 - 2019 Mil/Aero eBook
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 SOS Engineering designs and manufactures a wide range of precision turned metal parts, including M39029 contacts (as seen above with green and red stripes).
4. Zone Annealing
M39029 contact materials are also selected based on their ease of crimping. Crimping is the process by which two pieces of metal — in this case the contact and a wire — are joined together by deforming one or both of them to hold the other. This deformity is called a crimp. A special ratchet tool is often used to crimp connector contacts. The softer the metal, the easier it is to crimp. Contacts made out of harder copper alloys, like leaded nickel copper or beryllium copper, need to go through a process called zone annealing before they can be crimped. Zone annealing is a heat treatment process that makes the copper alloy softer. Zone annealing treatment reduces hardness to increase ductility and helps eliminate internal stresses and the chance for cracking during the crimping process. Softer materials like crimpable brass (i.e., CDA353000) do not need to go through the zone annealing process to be crimped and, as such, offer significant time and manufacturing cost savings.
5. Plating
Plating materials are also vital to the performance characteristics of M39029 connector contacts. Plating materials are chosen for several performance characteristics including corrosion resistance, electrical conductivity, thermal conductivity, solderability, wear resistance, operational life. Depending on application performance requirements, different types of metal or alloys — including copper, tin, gold, cadmium, rhodium, zinc, silver, nickel, and chromium — can be used in the plating process. Plating the contacts with a thin layer of gold provides the most valuable benefits. The M39029 specification mandates that gold plating be used due to its many exceptional performance characteristics, which include corrosion prevention, enhanced durability and reliability, increased heat protection, diminished fretting degradation, and excellent electrical conductivity.

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