Six Sigma Reliability of Pressure Vessel Achieved with PHX ModelCenter
Challenge: Determine Acceptable Manufacturing and Environmental Devitation
Six Sigma processes must be applied to a pressure vessel design to reduce the effect of manufacturing deviations on the performance of the equipment, thus creating a more robust and simultaneously cheaper design. Higher reliability comes at the expense of both a thicker vessel and higher manufacturing costs to hold tighter tolerances. Thus, the cost of improving a design’s reliability needs to be weighed against the cost of quality of the product being offered. Once the reliability calculation is set up, a multi-objective optimization study must be performed to evaluate this trade-off.
Solution: Use PHX ModelCenter to Maximize a Weighted Total Reliability Factoring Cost, Safety, and Volume
PHX ModelCenter was used to perform a DFSS analysis of a pressure vessel calculation. The vessel in question is presumed to be cylindrical with two hemispherical end caps. It lies horizontally, has some constant wall thickness, and is supported at both ends, creating a bending stress. The vessel can be analyzed using standard equations for hoop and longitudinal stress. Knowing the material the vessel is made of, the yield strength can be found and the safety factor computed. This calculation code was wrapped in PHX ModelCenter along with a Microsoft Excel cost model. These components were then gathered into an assembly (for convenience) and the Design for Six Sigma (DFSS) components were built around it. Using PHX ModelCenter, a probabilistic analysis was wrapped around the pressure vessel model and optimization techniques were used to determine how tightly deviations on design variables must be maintained while maintaining Six Sigma reliability. By performing a parametric study on geometry variables , the value needed for the design to achieve Six Sigma can be determined. Design Explorer’s optimizer maximizes a weighted total reliability, factoring reliability of cost, safety and desired volume . Thus, the reliability of the design can be known at the conceptual level and used to select the optimum dimensional offering for the customer.
Benefit: Accelerate Previously Time-Consuming Probabilistic Analyses with RSM Toolkit
Design for Six Sigma (DFSS) has been employed successfully by several organizations to reduce cycle time and increase quality. Six-Sigma has traditionally been viewed as statistical quality control on the manufacturing floor. But applied upstream, in the conceptual and detailed design phase of a product, it can yield substantial improvements in manufacturing cost. PHX ModelCenter®'s integration environment and built-in tools provide a rich platform for introducing Six-Sigma in a design or analysis-of-alternatives environment. Additionally, PHX ModelCenter’s RSM Toolkit can be used to speed up these analyses. Generally, probabilistic analyses are extremely time-consuming as they require many thousands of runs. The RSM Toolkit provides surrogate models which run quickly to accelerate this process.