The fasteners help isolate the assemblies in which they are installed from shock loads and vibration.

At its plant in Hamburg, Germany, Daimler AG (Stuttgart, Germany) recently decided to further streamline its manufacturing processes with respect to one of its steering column assemblies. Specifically, the company discovered that the phosphate-coated coiled pins it was using to attach the system’s aluminum housing and gear motor were failing during installation because of the high insertion forces required. The result was an unacceptable amount of scrap and decreased productivity due to the down time required to continually fix the problem.

Because the steering column was already a mature design, the hole sizes could no longer be changed without incurring unacceptably high engineering and revalidation costs. In addition, the customer had already invested in an expensive automated assembly system configured to insert the original pins within a specific force range.

To solve the issue, Daimler switched to a controlled-insertion, standard-duty pin from fastener and installation equipment manufacturer Spirol International Corp. (Danielson, CT).

Because of their superior quality, the Spirol coiled pins required far less insertion force than what Daimler had been using previously, thereby allowing the company to avoid damaging the columns’ housing assemblies. Spirol also recommended that the phosphate coating be removed to help cut materials costs.

Because the new pins provide the same shear strength as the original, they saved Daimler from having to perform a new set of validation tests. The end result was improved productivity and fewer scrapped assemblies.

Once assembled, the pin, which functions like a hinge, is subject to minimal loads. This meant Daimler had the option of going with a lighter-duty pin of similar design. However, doing so would have required running a full set of new validation tests, so the company chose to go with the sturdier configuration.

During installation, a coiled spring pin is compressed so that it will fit easily in a hole, or holes, and then allowed to relax once in place. It is this inherent flexibility that enables coiled pins to absorb wide manufacturing tolerances as well as provide self-retaining performance. In operation, the fasteners serve as a kind of “mini shock absorber,” in that they help isolate the assemblies in which they are installed from shock loads and vibration. The pins provide a uniform radial force against the surfaces of the holes in which they are installed across 270 degrees of contact. They do not require tight hole tolerances and easily lend themselves to automated installation.

For additional information on pins and mechanical fasteners, call 860-774-8571 or