Expanding Tolerance Analysis for a Robust Product Design Expanding Tolerance Analysis for a Robust Product | Page 2

2 Expanding Tolerance Analysis for a Robust Product Design 1. Introductiona 2.2 Applied Forces Available software tools can help standardize the process of creating a robust product design. Taguchi defines Product Robustness as “The ability of the product to perform consistently as design with minimal effect from changes in uncontrollable operating influences” (1). In this paper, the primary sources of variation and the steps necessary to secure a robust product design will be discussed. Specific case studies are addressed that implement these steps in creating a robust product design. Almost all products are subjected to some external force. At a minimum they will be subjected to the force of gravity. Most will also have some form of dynamic forces applied, whether from the user of the product, interaction with other systems, environmental forces, etc. Typically designs are analyzed using expected worst-case applied forces along with engineering factors of safety to insure they will always perform as expected, but dynamic loading over time creates fatigue that is more difficult to predict. 2.3. Temperature 2.0. Sources of Variation What Taguchi identified as ‘uncontrollable operating influences’ can also be called sources of variation. Figure (1) below lists some of the primary sources of variation. Temperature fluctuations influence almost all other material properties. In addition to causing dimension changes, properties such as brittleness, thermal conductance, electrical conductivity, pressure of a gas, chemical reaction time, etc. all change as the operating temperature fluctuates. Design nominal at ambient temperature must take into account such changes if the standard operational temperatures are higher or lower. . 2.4. Environmental Electrical, water, wind and other environmental elements alter the physical properties of materials. In addition to the impact changes in the environment have on the applied forces and temperatures, they can also lead to varying rates of corrosion that impact the material properties and often lead to premature failure. Managing for this variation is required due to the impact such variation can have on the robustness of the product. For example, material selection to avoid galvanic corrosion is a top priority when designing for salt-water environments. Fig. 1. Sources of Variation 2.1. Material Properties Choosing materials is a fundamental part of design. Input from marketing, production, quality and other departments have a major impact on the material of choice. But each material reacts differently to external forces. Mold cooling time can impact the integrity of plastics, density can impact flexibility. All of these sources of variation needs to be understood and managed in order to have a robust design. * Corresponding author. Tel.: [phone]; . E-mail address: [email protected] fax [phone]. Assembly Method Changes in the method or sequence of assembly can alter how the part variation impacts the position and orientation between the parts. When problems occur due to different people using different techniques to assembly the parts troubleshooting the root cause can be very difficult. Also important is trying to prevent parts from being assembled incorre ctly, such as inserting a battery the wrong way, or at a | www.sigmetrix.com