When automakers decide to design a new powertrain component, it is the beginning of a lengthy and convoluted process. Decisions such as physical size, material and major component requirements are interrelated and contribute to a complexity unknown to the average consumer. During this multi-faceted product-design procedure, the method required to assemble the unit is often overlooked until the design is near completion.
Too often, the consideration of fastening together complex design components is made at a point in time when options become limited and opportunities for cost savings are lost. This article portrays a generic example; however, it is based on several actual occurrences, where cost savings were achieved by early integration of the fastener in the overall design process, in just one component of a new vehicle.
Automotive component engineers face challenges when new vehicle designs require reconfiguration of powertrain components. Power transfer units (PTU), transmissions and all-wheel drive units typically require many fasteners. These applications provide significant in-place cost savings opportunities when TAPTITE® thread-rolling screws are employed. Yet achieving this level of cost savings can only occur if the initial design team considers using TAPTITE® screws and bolts. During the design process automotive powertrain designers may invite input from vertically integrated divisions and/or external tier 1 suppliers. We have seen TAPTITE® screw success stories originate from both situations.
This example outlines how a powertrain component design team involved a fastener engineer (FE) during the initial design cycle of a power transfer unit (PTU). The FE’s goal was to prevent problems previously experienced, lower the in-place assembly cost and reduce or eliminate repair and warranty costs. During research, the FE found that serious problems had previously occurred in the assembling of the PTU cases, the most significant being cross threading when conventional bolts had been used to join the two halves of the case.
PTU cases are typically manufactured from die-cast aluminum. The designated fasteners are either automatically fed and driven into pre-tapped holes or hand driven. At times, regardless of whether the screws are driven automatically or by hand, they may not properly follow the path of the internal thread, causing them to lock up, freeze in the internal thread or destroy it. Cross threading can result in repair costs approaching USD $ 50.00 per fastening site, a significant percentage of the manufacturer’s total cost of the assembled unit.
In this example, to eliminate the possibility of cross threading, the FE and the PTU engineering team, with input from REMINC’s staff, decided to use thirteen M8 x 1.25 x 35 hex flange head TAPTITE 2000® screws, neutral hardened to grade 10 property class, instead of conventional machine screws, to assemble the cover to the case. Because TAPTITE 2000® screws form their own internal threads in plain holes, the need to tap and clean the nut members was eliminated. Therefore, the first cost savings in this case resulted from the elimination of tapping and cleaning on the assembly line, estimated by some companies to be approximately $0.04 per hole.