One of the costliest areas of product development is physical testing. Even when considering the time and resources already invested in design and prototyping, they can easily be eclipsed by the testing budget. Coupon-level testing, subassembly testing, full-sized test articles…different usage conditions requiring their own testing regimens. And what happens when something fails in testing where it shouldn’t have, or fails too early?..the testing cycle repeats itself, with budgets quickly ballooning out of control after each iteration. This looming reality will often frustrate design teams and turn them towards more conservative designs. In a similar vein, designers wishing to evaluate material and process changes for established products in critical applications (for example, looking for less-expensive material grades that will still provide desired performance) are faced with the testing involved in requalification.

This is the problem that faced Eaton Vehicle Group (EVG), a division of Eaton Corporation and a global automotive Tier 1 supplier of transmission components (gears, bearings, housings, etc.). EVG was investigating multiple proposed changes to its manufacturing processes, and wanted to quickly determine the effects of these changes on the fatigue durability of their gears. Some of the manufacturing processes in their investigation impact gear tooth surface and in-depth residual stresses (shot peening); other processes impact the material itself (the degree of carburizing heat treatment, and how much intergranular oxidation occurs in the microstructure). Since the processes are not specifically related (that is, changing the duration/intensity of the peening has no effect on how many oxidation sites there are near the surface, and vice-versa), it would be a large task to study the effects of these changes via physical testing.

• First, the parameters must be identified for each of the manufacturing processes (residual stress profiles, intergranular oxidation as a function of atmospheric carburization).
• Next, the extent of the parameter changes must be quantified, and a design of experiments (DOE) would need to be set-up.
• Then, coupon-level testing on the individual material/process interactions would be performed to collect baseline mechanical property data.
• Finally, full-scale component testing would need to be performed for each portion of the DOE.

What initially seemed to be a straightforward and simple evaluation of two manufacturing processes becomes very intensive, when one considers all of the resources and lead time that testing protocols demand. At the end of this DOE there might be one or two feasible choices for EVG, or there might be none. What’s more, decisions would have to be made based only on results from a handful of expensive tests…often with only one or two tests having been repeated at the same exact processing and testing conditions. Can the risk to part performance be truly quantified with such a small test population?

VEXTEC partnered with EVG to take advantage of virtual simulation technology, by utilizing our VPS-MICRO® software. Over a short period of 2 months, VEXTEC’s engineering team worked with Eaton to understand the material and design information already in-hand (material property data, FEA structural design files), and helped to develop material and stress models that appropriately captured the current-state of production, as well as the proposed variations. VPS-MICRO was used to simulate the testing of thousands of gears in a virtual DOE, providing a level of confidence and parameter sensitivity that could never be gained with physical testing. EVG now had the ability to independently, or simultaneously, pull different “levers” of their manufacturing process, and understand the risk to performance in making the process changes.

An example of the detailed virtual DOE output is shown below. The depth of intergranular oxidation from the surface was evaluated in terms of its impact on fatigue life of a vehicle transmission gear. Similar computational evaluations were performed for the shot peening options being explored. These virtual studies were completed before comparing to physical prototype testing results, to validate VPS-MICRO.

Now, certain prototype designs can be evaluated by Eaton as high-value and implemented in production more quickly. Bleak prototype designs could be effectively dismissed without tying up valuable resources. The technology has helped EVG evaluate different material suppliers for its multitude of transmission products efficiently and quickly, at a fraction of the time and cost it would take to complete the study using physical tests only.

Please contact us about your specific needs, and to see if VEXTEC’s VPS-MICRO software and engineering services could assist in providing valuable insights into the performance of your metallic products.