An investigation of robustness and concurrency issues in product and process design

Balaji Ramakrishnan, Purdue University

Abstract

The concepts of robust design using Taguchi's concept of quality loss, and concurrent product and process design are applied to the solution of a large engine connecting rod design problem. Design and analysis tools useful for the product and process design of a connecting rod are developed. A new general procedure for achieving robustness by minimizing the expected value of a loss function is developed. This procedure considers the issue of feasibility robustness and incorporates the variations in uncontrollable design parameters in the design formulation. An alternate methodology, that minimizes the weighted sum of the variance of design performance and the reciprocal of the sum of the design parameter variances, is also proposed. These are demonstrated by solving two structural design problems. The application of this general robust design methodology for solving large, computationally intensive, nonlinear optimization problems is also investigated. An efficient solution strategy that uses approximate expressions for the gradients and employs a fast reanalysis procedure for their evaluation is developed and validated and is used to solve the connecting rod product and process design problems. The robust design procedure along with design and analysis tools for connecting rod product and process design are integrated into a prototype concurrent product and process system called CFORGE. Concurrency is achieved by formulating the connecting rod design problem using a concurrent optimization formulation that uses the utility function method for reducing the multi-objective vector optimization problem to a scalar optimization problem. Design variables and constraints from both product and process domains are considered. An alternate procedure that simultaneously considers quality of the design along with product and process design issues using the robust design formulation is also proposed. These methods are illustrated by using CFORGE to synthesize a connecting rod to meet given specifications. A multi-objective optimization problem based on the utility function method with geometric, product (stress and buckling load) and process constraints (die stress, forging load and strain rates) is formulated and solved. A weighted sum of the forging weight of the connecting rod and the forging load is used as a measure of the design performance.

Degree

Ph.D.

Advisors

Rao, Purdue University.

Subject Area

Mechanical engineering|Automotive materials

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