Page 44 - 2021 Connectivity Components: Everything but the Connectors eBook

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Roughness
The amount of roughness is of fundamental importance. When machining on lead-free brass with traditional tools that have cutting geometry for leaded brass, it is difficult to obtain the minimal roughness required by modern electrical connectors to ensure high specific amperages. If there are roughness problems, the tolerances are automatically affected as well. With an appropriate cutting-tool geometry, it is possible to obtain the previous level of roughness and reach the values required by the market, approximately Ra 0.40 μm.
» Examples of lead-free brass electrical connectors: on the left, machined with dedicated technology (cutting tools and cutting parameters), on the right, machined with traditional technology
Tolerances
Conventional cutting-tools are unreliable for achieving form tolerances because of the so-called “material rejection” phenomenon: sometimes the tool cuts well and sometimes it rejects what it is cutting. A small temperature or lubricant variation is enough to trigger this. Variations on the diameter (ovalities) or errors in length make it impossible to maintain the tolerances of ± 0.0004” on the diameters required by the latest high-tech connectors. A more aggressive cutting-tool geometry (like that of aluminum) makes the process more reliable.
» Roundness measurement of an electrical connector