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Distributor's Link Magazine Summer 2018 / Vol 41 No3


144 THE DISTRIBUTOR’S LINK SPIROL COLD HEADED VS MACHINED SOLID PINS from page 60 Dies provide cavities used to form the desired It’s also important to recognize that free fit hinges geometry, while a blow describes the physical process do not require press fit holes and should not require pin of upsetting material with a machine stroke. Additional diameter tolerances tighter than ± 0.025mm (± .001”). dies and blows are needed as geometry becomes more complex. There are limitations to the amount of material Tolerance that can be displaced per blow. Typically, the outside diameter (OD) is the most Cold heading sometimes includes a wire drawing critical Solid Pin dimension. Both cold heading and process that work hardens the material, increasing both machining can achieve the tolerance specifications the yield and tensile strength. Machined pins produced needed for the majority of Solid Pin applications. In fact, with the same base material will have lower yield and cold heading produces Solid Pins with OD total tolerances tensile values because the material grain structure has of 0.05mm (.002”) (less than the thickness of a human been interrupted. hair). Machining can achieve tighter OD tolerances than cold heading, but this generally requires special ground Solid Pin Design Specifications & OD rod. This should be avoided (if possible) as ground OD Manufacturing Capabilities rod can be more than three times the cost of standard The first step in designing a joint is to establish the rod. functional requirements of both host components and For Solid Pin length tolerances, machining and fasteners. Performance requirements should be achieved cold heading can achieve the same tolerance levels of without over specifying the design. An ideal joint satisfies approximately ± 0.25mm (± .010”). This varies by pin performance and quality requirements at the lowest length. possible cost. The information below will help designers TOLERANCE CAPABILITIES understand the differences in Solid Pin OD capabilities between cold heading Manufacturing Raw Material Raw Material Metric Imperial Method Cost and machining as it pertains to Cold Heading Wire $ ± 0.025mm ± .001" design specifications for Solid Standard rod $ ± 0.0125mm ± .0005" Pins and host component holes. Machining Ground OD rod $$$ ± 0.0025mm ± .0001" Press Fit Pin Overview Press fit dowels and straight pins are typically retained in the assembly by being pressed into holes that are smaller than the pin diameter. In most applications, interference must be limited to keep insertion forces within practical limits. The acceptable press fit for most metals (steel, brass, and aluminum) is 0.0125mm to 0.025mm (.0005” – .001”) of material displacement. Since this tolerance threshold includes the sum of the tolerances of both the pin and hole diameter, pins must be precision machined and holes must be reamed and/or honed. This increases cycle time and manufacturing costs associated with hole preparation. TABLE 2 SIDE VIEW: COLD HEADED PIN VS MACHINED PIN COLD HEADED PIN MACHINED PIN CONTINUED ON PAGE 174


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