Managing Function Constraints in Design Sheet™

Design Sheet™ is a constraint management system specially designed for doing conceptual design cost and performance tradeoff studies. It represents the design models as constraints between design variables, and uses graph-theoretic algorithms to decompose large systems of nonlinear equations into smaller pieces that can be solved robustly. This paper describes extensions to Design Sheet that enable it to manage functions as variables in a constraint network. The paper also discusses the new capabilities of function encapsulation and explicit differentiation that are built on top of these extensions. The ability to encapsulate a part of the constraint network into a function, and use it in other constraints, promotes model reuse and improves computational efficiency. The capability to automatically differentiate certain variables with respect to other design variables allows Design Sheet to be used for solving practical optimization problems. In combination with the tradeoff capability, this enables the designer to track changing optima in trade studies. The paper also provides a couple of optimization examples to demonstrate these new capabilities.

An Implementation of Expected Utility Theory in Decision Based Design

The development of a design science rests on the ideal that design is anchored in a set of fundamental axioms similar to the more ‘traditional’ sciences of mathematics and physics. However, the axioms upon which a design science is constructed must reflect that design is a science of the artificial. It is our contention that such axioms may exist in Decision-Based Design as those formulated by von-Neumann and Morgenstern for developing utilities under conditions of risk. In this paper we have a very narrow focus: evaluating a proposed framework for applying these axioms in the context of a simple design problem through the use of Monte Carlo simulation and expected utility theory.

Defining Product Architecture During Conceptual Design

Product architecture can have a significant impact on a product’s life-cycle and its development time. Modular product architecture allows for easy disassembly upon product retirement and allows for wide product variety. In a small company, the team structure of the company can correspond to the modules, and modules can be used across product lines. By using similar modules from one generation to the next, product development time can be reduced. The methodology described in this paper gives a small company the framework from which to develop modular products.

Modeling of Feature-Based Design Process

Capturing design process is becoming an important topic of feature-based modeling, as well as in product data exchange, concurrent design, and cooperative design. Three critical issues on the modeling of design process are considered in this paper, namely, feature concepts, feature evolution, and the semantic consistencies of the states of product models. A semantics-based product model is introduced to facilitate the description of both conceptual and detailed models, and to maintain the semantic consistencies of product states. The process is represented by feature states and their evolution records. Feature type variation and prototype-based design are proposed to support feature evolution. A conceptual description of the design process and an example are given.

Aggregation and Controlled Interaction: Automated Mechanisms for Managing Design Complexity

Complexity in modern product design is manifest through large numbers of diverse parts, functions, and design disciplines that require an intricate web of synergistic relationships to link them together. It is extremely difficult for designers to assimilate or represent such complex designs in their totality. In this research, we present a framework that utilizes the intricate relationships between design components to enhance the representational power of design models and to provide focal points for automating the management of design complexity. We introduce automated mechanisms, based on aggregation and interaction relationships between design components, that integrate model structure, a variety of conceptual and detailed design information, and product management controls into a single modeling framework. These mechanisms are easily incorporated into design models and they facilitate re-use and cooperative design by ensuring that related entities can be modified independently.

Classification of Iteration in Engineering Design Processes

As engineering design is subjected to increasingly formal study, an informal attitude continues to surround the topic of iteration. Today there is no standard definition or typology of iteration, no grounding theory, few metrics, and a poor understanding of its role in the design process. Existing literature provides little guidance in investigating issues of design that might be best approached in terms of iteration. We review contributions of existing literature toward the understanding of iteration in design, develop a classification of design iteration, compare iterative aspects of human and automated design, and draw some conclusions concerning management of iteration and approaches to design automation.

Quantitative Selection of Variation Reduction Plans

Quality has been a rallying call in the design and manufacturing world for the last two decades. One way to improve quality is to reduce the impact of manufacturing variation. Variation risk mitigation is challenging especially when a product has multiple quality characteristics and complex production and assembly. It is common wisdom that companies should identify and mitigate the risk associated with variation throughout the design process. As yield problems are identified, they should be mitigated using the most cost effective approach. One approach to variation risk mitigation is variation reduction (VR). VR targets reduction of variation introduced by existing manufacturing processes using tools such as Design of Experiments (DOE) and robust design. Many companies have specialized groups that specialize in these methods. VR teams have the role of improving manufacturing performance; however, these teams are limited in their resources. In addition, no tools exist to quantitatively determine where a VR team’s efforts are most effectively deployed. This paper provides a mathematical and optimization model to best allocate VR resources in a complex product.

On the Applicability of Product Variety Design Concepts to Automotive Platform Commonality

The issue of moving from a mass production operating mode to mass customization, or even limited customization, has many companies struggling to reorganize their product architectures. Enabling the production of several related products for different market segments, from a common base, is the focus of the product variety design research area. In this paper, the applicability of product variety design concepts to the design of automotive platforms is explored. Many automotive companies are reducing the number of platforms they utilize across their entire range of cars and trucks in an attempt to reduce development times and costs. To what extent can research on product variety design apply to the problem of platform commonization? This question is explored by comparing product variety design concepts (standardization, modularity, mutability, etc.) to platform structures and requirements. After assessing the applicability of these concepts, a platform representation and methods for measuring platform commonality are proposed that incorporate key characteristics of these concepts. An application to two platforms is included. Although preliminary, this work has led to insight as to why automotive platform commonization is difficult and how product design variety research can potentially aid commonization. The findings are potentially applicable to product platforms in general.

A Process Management Strategy for Re-Design: An Anchoring Adjustment Approach

Preceding research on the re-design process focused on the development and verification of an Anchoring and Adjustment design process model. Compared to the existing, predominantly top-down, models, this new model was tailored specifically to describe designers’ approaches to re-design tasks. Building upon that work, this paper presents an evaluation of a re-design process strategy that is based on the key elements identified in the Anchoring and Adjustment model (a general pattern for re-design activities and two evaluation metrics). The overall goal was to formulate an efficient and effective process management strategy unique to re-design activities. Data were collected from three industry re-design projects for the evaluation. First, an analysis of the data confirmed that the pattern of design activities and evaluation metrics used by the company’s designers could be mapped onto those that comprise the Anchoring and Adjustment model. Second, the analysis of the data suggested that with additional formalization — based on an anchoring and adjustment approach — the company’s current process management technique could provide more accurate feedback to the designers for the more efficient and effective management of their re-design processes. One of the industry case studies is detailed to illustrate the research results and conclusions.

A Design Methodology for Attachment Concept Development in Integral Snap-Fit Assemblies

The importance and foundation for conceptual-level design of integral snap-fit assemblies was first pointed out by Bonenberger at General Motors. Based on that work, a design methodology is presented to identify and address important issues at the conceptual-level in a systematic way and generate alternative attachment concepts. The methodology starts by exploring the design space to generate as many concepts as possible. Alternative concepts are generated by considering variation in interface geometry, assembly procedure, snap-fit features, and options for fully constraining all parts in the assembly. At the last step, alternatives are evaluated by using a quantitative tool, and the “best” attachment concept is selected based on design objectives for a particular application. Applying the design methodology to case studies confirms that it is a useful design aid for efficiently generating, evaluating, or simply checking attachment concepts.