A Set-Based System for Eliminating Infeasible Designs in Engineering Problems Dominated by Uncertainty

This paper gives an overview of a system which eliminates infeasible designs from engineering design problems dominated by multiple sources of uncertainty. It outlines methods for representing constraints on sets of values for design parameters using quantified relations, a special class of predicate logic expressions which express some of the causal information inherent in engineering systems. The paper extends constraint satisfaction techniques and describes elimination algorithms that operate on quantified relations and catalogs of toleranced or adjustable parts. It demonstrates the utility of these tools on a simple electronic circuit, and describes their implementation and test in a prototype software tool.

Production Yield Estimation by the Metamodel Method With a Boundary-Focused Experiment Design

The need for yield estimation strategies in the design stage is a priority recognized by industry. Yield estimates can be employed to assess the manufacturability of a design, and allow for modification to produce a robust design. Therefore, low yield of products can be avoided and costs for manufacturing can be reduced. This paper presents an accurate and time-efficient yield estimation approach for use with simulation models. We use a metamodel-based method, which is time-efficient compared to crude Monte Carlo yield estimation using the original simulation code. The approach employs a boundary-focused experiment design, which overcomes the inaccuracy of yield estimates that can occur when using a metamodel method. The results of two examples demonstrate the effectiveness of this new approach.

Shape Grammars and Their Languages: A Methodology for Product Design and Product Representation

This paper argues that shape grammars and the languages they define are an ideal means to generate and represent products where basic functionality can be decomposed into discrete processes, forms can be created to fulfill those functional processes, and variation in those forms differentiates between competitive products. A shape grammar for the design of coffee makers is highlighted and used to illustrate how an infinite set of a class of products can be articulated through a concise shape grammar. Novel coffee makers and coffee makers in the market today are generated from the grammar.

Creative Design Methodology and the SIT Method

The paper presents SIT (Structured Inventive Thinking) — a structured method for enhancing creative problem solving in engineering design. The method is a three step procedure: problem reformulation, general search strategy selection, and an application of idea provoking techniques. The most innovative part of the method is the problem reformulation stage. The given problem is modified through the application of objectively defined and empirically tested set of sufficient conditions for creative solutions. The paper describes the sufficient conditions and the empirical study that demonstrates their appropriateness. Then the whole SIT mechanism is presented with illustrative examples.

Using Key Characteristics to Balance Cost and Quality During Product Development

Corporations are spending significant resources to reduce the effect of manufacturing variation on product quality as well as adopt lower cost manufacturing and assembly technologies to reduce the end costs in product development. However, to ensure that these investments have a positive return, efforts must be made to put resources into those areas where there will be the largest return. This paper describes a formalized method to make these decisions. The analysis focuses the tradeoff studies on the Key Characteristics (KCs) of the product. KCs, in use in a variety of industries, are the product features that are most sensitive to existing manufacturing and process variation and will affect the end quality of the product. Two examples from the aircraft manufacturing environment are used describe the application of the proposed methods.

Concurrent Engineering Design of Sheet Stamping by Using an Inverse FE Approach

An inverse finite element (FE) algorithm is proposed for sheet forming process simulation. With the inverse finite element analysis (FEA) program developed, a new method for concurrent engineering (CE) design for sheet metal forming product and process is proposed. After the product geometry is defined by using parametric patches, the input models for process simulation can be created without the necessity to define the initial blank and the geometry of tools, thus simplifying the design process and facilitating the designer to look into the formability and quality of the product being designed at preliminary design stage. With resort to a commercially available software, P3/PATRAN, arbitrarily three-dimensional product can be designed for manufacturability for sheet forming process by following the procedures given.

Collaborative, Sequential, and Isolated Decisions in Design

The Massachusetts Institute of Technology (MIT) Commission on Industrial Productivity, in their report Made in America, found that six recurring weaknesses were hampering American manufacturing industries. The two weaknesses most relevant to product development were 1) technological weakness in development and production, and 2) failures in cooperation. The remedies to these weaknesses are considered the essential twin pillars of CE: 1) improved development process, and 2) closer cooperation. In the MIT report, it is recognized that total cooperation among teams in a CE environment is rare in American industry, while the majority of the design research in mathematically modeling CE has assumed total cooperation. In this paper, we present mathematical constructs, based on game theoretic principles, to model degrees of collaboration characterized by approximate cooperation, sequential decision making and isolation. The design of a pressure vessel and a passenger aircraft are included as illustrative examples.

Simultaneous Engineering of Quality Through Integrated Modeling

Simultaneous engineering has become the means to ensure quality through incorporation of manufacturing. This proves difficult without quantitative support tools. We present here a modeling based approach to simultaneously design a product and its production process. We demonstrate an approach of examining sensitivities of output to all inputs of a system, from product design specifications, process variables, and material specifications. We further develop mathematics of estimating the effects of in-line process control changes to increase quality. We demonstrate a method to choose noise sources to measure and process variables to control in-line based upon these measurements, and estimate the error reduction that such process control changes will provide. The tool allows simultaneous engineering of the product and process to increase quality.

Design for Purchasing: A Methodology for Reducing the Materials Cost of Engineered Products

This paper gives an overview of a methodology for reducing the cost of purchased materials for engineered products. The methodology has been successfully employed for a wide range of applications, ranging from low value-added products, such as simple processed materials (e.g., steel sheet or profiles), to high value-added equipment, such as machine tools and major components of industrial plants. We have applied the methodology in some 80 projects, achieving cost savings averaging 17% on top of the 10% savings achieved using traditional purchasing optimization approaches. The key distinguishing features of the methodology are a product-oriented as opposed to materials group-driven approach, the establishment of interdisciplinary teams that include engineers and purchasing professionals, and a well-defined, systematic method for addressing the most important drivers of materials cost together with key suppliers. The methodology is introduced by performing pilot projects, then anchored in the enterprise through organizational and procedural changes.

To Injection Mold, to Stamp, or to Assemble? Part I — A DFM Cost Perspective

This paper presents a DFM cost comparison of injection molding and stamping, the processes most commonly used in the production of consumer oriented special purpose components. The general guidelines obtained and conclusions drawn in order to determine if a component should be injection molded or stamped, and/or if several components should be combined into a single component or not, are discussed. The cost evaluation and comparison are primarily in terms of the functional equivalence of feature, component, and assembly.