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mmsonline.com August 2017 MMS 81 FEATURE $60. It also included an intrinsic cylindrical disk feature. These elements proved expensive to manufacture in terms of the milling time for both the part itself and the slide bearing. In addition, the component required case hardening and a 6- to 8-Ra surface finish, which was difficult to achieve given its complex geometry. Parametric USA's first DFM redesign separated the disk feature from the component and replaced it with an inexpensive part that didn't require heat treating. The component's main geometry was changed from rectangular to cylindrical, with a 0.75-inch shaft and a bull-nose yoke (see images on page 77) to fit inside Mountz's design without af fe cting othe r compone nts. T his simplif ied machining, in moving from a milling operation to a turning operation, enabled the use of an off- the-shelf cylindrical slide bearing and offered the possibility for low-cost, precision grinding to achieve the required surface finish. This initial step cut overall manufacturing costs for t wo components by 50 percent, Mr. Teixeira says. However, using FEA, it was determined that the side load created deflection in the range of 0.0012 to 0.0015 inch, which was twice the target deflection range. Also, the bending stresses were above the fatigue strength sweet spot for this application. This called for a second DFM redesign. Mr. Teixeira explains that, by removing the bull nose so that the entire component had an outside diameter of 1 inch, the side-load bearing area was increased and the stress concentrations were reduced. This enabled the target deflection range of 0.0003 to 0.0007 inch to be achieved while further simplifying surface grinding to attain the required finish. In addition, it enabled an off- the-shelf $10 cylindrical slide bearing to be used instead of a machined part. Machining time was reduced, too, from 28 minutes per par t to 15 minutes. The potential savings in part quantities of 1,000 was estimated to be $33,000. (As noted before, two mechanical solutions were pursued by the customer, tested and vetted. This compo- nent ultimately morphed into a different version as a result of further development.) Mr. Teixeira has also used FEA to optimize and verif y designs for fixtures for tricky parts. The fixture shown on page 79 is good example of a simple design with minimal components that he devised and then proved out via FEA. The fixture is used to secure a printed circuit board (PCB) that is machined using a 0.012-inch-diameter end mill to house an optical mirror measuring only 3 by 3 mm. With this design, the clamping of the PCB is achieved solely via the natural deflection of the fixture's Delrin material instead of using springs, clamps or other conventional fixturing components. Two slots machined 0.125 inch apart create a beam that deflects to provide the clamp- ing force for the PCB. Mr. Teixeira initially performed first-order calculations and determined that an appropriate force of 1 pound would be generated from 0.01 inch of material deflection. This would provide sufficient clamping force for machining without causing the PCB to deflect. He then used FEA to tune the beam width, thickness and mate- rial type to achieve the target beam deflection and clamping force. Mr. Teixeira says the initial fixture he manufactured worked as expected with no modifications required. GROWING RELATIONSHIPS For Parametric USA, the key to selling its custom- ers on making some if not all its suggested DFM changes is to establish and grow relationships with the custome rs' de sign e ngine e rs. He re a re way s th e s h o p wo r k s to e s t a b l i s h s u c h close relationships: • Before suggesting DFM changes, first ask to understand the product application and the func- tion of the individual components to understand why the engineers designed features the way they did. For example, if a plastic part has undercuts, it is most likely to enable a snap fit. Recommend- ing removal of the undercut will only reduce respect and trust in future DFM suggestions. • Identif y potential par t features to modif y, a nd d ete r mine how the d e sign c ha ng e s w ill affect the part's functionality. DFM suggestions shouldn't be made until it is determined that the changes won't adversely af fect the product's desired performance. Parametric USA, call 408-654-9845 or visit parametric-usa.com. Solidworks, call 800-693-9000 or visit solidworks.com.