Dimensional variation in assembled products directly affects product performance. To reduce dimensional variation, it is necessary that an assembly be robust. A robust assembly is less sensitive to input variation from the product and process components, such as incoming parts, subassemblies, fixtures, and welding guns. In order to effectively understand the sensitivity of an assembly to input variation, an appropriate set of metrics must be defined. In this paper, three product-oriented indices, including pattern sensitivity index, component sensitivity index, and station sensitivity index, are defined. These indices can be utilized to measure the variation influence of a pattern, an individual part, and/or component, and components at a particular station to the dimensional quality of a final assembly. Additionally, the relationships among these sensitivity indices are established. Based on these relationships, the ranges of the sensitivity indices are derived. Finally, a case study of a sheet metal assembly is presented and discussed to illustrate the applicability of these metrics. �DOI: 10.1115/1.2735341

Compliant sheet metal assembly is a hierarchical manufacturing process that plays a significant role in automotive product development. Parts are joined in different stations to form the final product (e.g., the vehicle body structure). Dimensional variation is a product attribute of major importance that characterizes quality, and is mainly affected by the variability of parts, fixtures, and joining methods at each of the multiple stations. The propagation of dimensional variation through the multistation assembly system is modeled as a linear process, where all three aforementioned sources of variability are taken into account at each station using finite element models. In this article we apply the analytical target cascading process to the tolerance allocation problem in multistation assembly systems. Specifically, we translate final product variation targets to tolerance specifications for subassemblies and incoming parts. We demonstrate the methodology by means of a vehicle side frame assembly example.

Dissolvable tools have been used more in unconventional oil and gas operations in recent years. Currently, more and more wells in Southwest of China quires high temperature (HT) dissolvable plug. The HT dissolvable plug needs to hold pressure in water at 150°C for 24 hours. On the other hand, the dissolvable plug needs to be dissolved in 1% KCl at 95°C in less than 15 days. These requirements put big challenges on dissolvable materials. Several HT dissolvable rubbers were developed to meet the requirements. The ambient and high temperature tensile testing were performed on the dissolvable rubbers. The dissolution testing of the dissolvable rubber was performed in brine at 140°C for 1 day and then at 95°C. Several dissolvable metals were developed and the slow strain rate testing (SSRT), Scanning electron Microscope (SEM)/Energy Dispersive Spectroscopy (EDS) testing were performed on these dissolvable metals. A special coating was developed to reduce the stress corrosion cracking of the dissolvable metals. Two HT dissolvable plugs were developed based on the dissolvable materials. The pressure holding testing and dissolution testing were performed on the two dissolvable plugs. It was found that the tensile strength of the HT dissolvable rubber at 150°C was higher than 1200 psi and elongation was higher than 700%, which was higher than that of most of the commercial HT dissolvable rubbers. The dissolvable rubber coupon disintegrated to tiny pieces at 95°C in 4 days. One dissolvable metal displayed better stress corrosion cracking resistance than the other dissolvable metals. The dissolvable metal promotes discontinuous grain boundaries and secondary phases within the grain boundary to prevent crack growth and propagation at the expense of strength. The dissolvable metal was used for lower slip of the dissolvable plug. The special coating on the dissolvable metal significantly reduced the dissolution rate of the dissolvable metal at high temperature. The two dissolvable plugs passed the pressure testing a of 10 ksi at 150°C in water for 24 hours. The dissolvable plug was dissolved in 1%KCl at 95°C in 14 days. The weight loss of the plug was more than 95%, All the remining residues of the dissolvable plug was less than 2 cm. The pressure holding and dissolution testing results of the dissolvable plug successfully meet the field testing requirements. This is the first time in the industry based on our knowledge a HT dissolvable plug passed 150°C, 10 ksi 24 hours pressure holding test in water and then dissolved in brine at 95°C in less than 15 days. The HT dissolvable rubber was specially designed to possess both high mechanical properties at 150°C and dissolution properties at 95°C. The dissolvable metal for lower slip was formulated to prevent crack growth.

Dimensional variation in assembled products directly affects product performance. To reduce dimensional variation, it is necessary that an assembly be robust. A robust assembly is less sensitive to input variation from the product and process components, such as incoming parts, subassemblies, fixtures, and welding guns. In order to effectively understand the sensitivity of an assembly to input variation, an appropriate set of metrics must be defined. In this paper, three product-oriented indices, including pattern sensitivity index, component sensitivity index, and station sensitivity index, are defined. These indices can be utilized to measure the variation influence of a pattern, an individual part, and/or component, and components at a particular station to the dimensional quality of a final assembly. Additionally, the relationships among these sensitivity indices are established. Based on these relationships, the ranges of the sensitivity indices are derived. Finally, a case study of a sheet metal assembly is presented and discussed to illustrate the applicability of these metrics.