A Design Process Model That Unifies General Design Theory and Empirical Findings

This paper proposes a new design process model that unifies theoretical results of General Design Theory (GDT) and empirical findings obtained from design experiments. It first reviews the design process models that were developed within theoretical work on GDT. Then, we describe experimental work on design based on protocol analysis, which resulted in a cognitive design process model from which further a computable design process model was derived. While these experimental results are supposed to support the theoretical conclusions obtained from GDT, we could also find out incompatibilities. We then propose a new design process model, called the refinement design process model, that can unify both theoretical results of GDT and experimental finding obtained from design experiments. The refinement model has better agreements with experimental findings and suggests various issues as a guiding principle to develop a future, advanced CAD system that helps a designer to focus on functional information. We propose and illustrate the concepts of such an advanced CAD system equipped with intensive design knowledge, called a computational framework for knowledge intensive engineering.

Elementary Education and Engineering Design: Concrete Experiences in Mathematics and Science

The education community has focused attention recently on a number of initiatives to evolve, and perhaps revolutionize, approaches for teaching science, mathematics, and engineering. In this paper, we present a new engineering and design technology program, initiated in 1992 and referred to as DTEACh, that focuses on the elementary grades. Two components comprise this new program: (1) open-ended design and exploration lessons that use hands-on models to teach integrated mathematics and science principles, and (2) a two-part teacher preparation program to provide teachers with the necessary engineering, mathematics, and science fundamentals for DTEACh. In this paper, we focus on a description of the teacher preparation program, including discussions of a novel teaching model, the subject matter for engineering and design fundamentals, and evaluation of the program. Results of the evaluation that teachers are more confident and equipped to facilitate the instruction of mathematics, science, and engineering principles.

Near Optimal Approach to General Manufacturing Feature Extraction

Computers are being used increasingly in the process planning function. The starting point of this function involves interpreting design data from a CAD model of the designed component Feature-based technology is becoming an important tool for this. Automatic recognition of features and extraction of feature information from CAD data can be used to drive a process planning system. In this paper a new approach to automatic feature extraction called the Blank-Surface Concave-edge (BS-CE) approach is illustrated. This approach attempts to remove as much of the blank material with a given machine setup as possible. Hence intuitively one can say that the manufacturing cost of material removal may be minimized if this technique is employed. This feature extraction method is explained along with examples of its implementation. An analysis of alternate feature extraction results is performed and the cost of manufacture is compared to demonstrate the near optimal performance of this technique.

Introducing the Industrial Product Realization Process Into Mechanical Engineering Design Education

The process by which new products are brought to market — the product realization process, or PRP — can be introduced in engineering design education. In industry, the PRP has been evolving to concurrent engineering and product teams. The PRP includes components such as concept generation, analysis, manufacturing process development and customer interaction. Also, it involves the sequencing of the components and their connections which includes teamwork, project planning, meetings, reports and presentations. A capstone senior engineering project, along with classroom lectures and presentations can be structured to provide knowledge and experience to the students in many of the PRP components and the connections. This paper will give an overview of the PRP and a project/lecture structure at the author’s university. The instructor recently joined the academic ranks after years in industry with responsibility for directing product development and R&D and for leading product development teams.

Estimating Errors in Concept Selection

Numerical concept selection methods are used throughout industry to determine which among several design alternatives should be further developed. The results, however, are rarely believed at face value. Uncertainties (or errors) in subjective choices, modeling assumptions, and measurement are fundamental causes of this disbelief. This paper describes a methodology developed to predict overall error ranges, in addition to estimating a confidence measure in the numerical evaluation results. Each numerical assignment is given an associated error tolerance, and then treated as a probability error to create a simple means to propagate the uncertainties. A degree of confidence is also derived, similar to a statistical t-test, to indicate an induced confidence level in the final decision. Two preliminary concept selections are shown, to illustrate the methodology. Results from these concept selections indicate that (1) uncertainties can be suitably captured and quantified; (2) critical design questions are addressed during the process of numerical concept selection with error propagation; and (3) designers can make more informed and confident decisions through error estimation.

Needle Fatigue Analysis for High-Speed Knitting Machines

In modern, high capacity circular knitting machines, the small and fragile latch needles are often a performance-limiting machine element (Schuler, 1980). For these machines, the operating circumferential speed may exceed 1.5 m/sec. Due to the kinematics of the process, the cam driven needles are exposed to periodic excitation with frequency proportional to the speed. Increase in rotational speed gives rise to needle head fatigue breakages unless special design measures are undertaken. Frequencies up to 15 kHz have been observed and up to 60 kHz may be expected in the vibration spectrum. To understand what particular features of needle design may be responsible for their longevity, several techniques were developed to apply Finite Element Analysis software to estimating the fatigue life under a non-harmonic periodic loading. The known FEA packages handle dynamics of a system with such loading as a general non-stationary problem, whereas much more efficient solution can be constructed by combining the analytical solution for a one DOF system under recurring impulses (5-functions of amplitude A) at the moments 0, T, 2T, …, and the natural modes of the system (with the driving point fixed) provided by FEA. As applied to the system in question, from the broad frequency range of the excitation forces and displacements, only frequencies close to those providing maxima to the transfer functions from the driving point to the head of the needle were selected. These frequencies are referred to further on as the response frequencies. Then the time history simulating polyharmonic stresses in the dangerous area was generated and processed according to the chosen fatigue criteria (a corrected linear hypothesis of damage summation, see below). Thus for any given node of the needle a point on the S-N diagram was obtained. A wide spread desktop package, ALGOR, was selected as a Linear Stress Analysis solver. The described procedure is built on top of this package and allows design engineers to make judgements as to what design is more advantageous for needle longevity.

Design and Analysis of Fluidless Cooling Devices for High Speed Machining

In high speed machining, the generated heat produces very high temperatures at the tool-work interface. Heat generated at the cutting area may shorten tool life, damage work piece surface, affect surface characteristics, and hence increase production cost. To deal with these problems, cutting fluids are used. Unfortunately, these fluids cause harmful effects to the operators and serious problems of pollution to the environment. Therefore, a new approach is developed to reduce the cutting tool temperature without using external coolants, and thus considerably reduce the amount of the hazardous waste being disposed to the environment. It removes a portion of the generated heat from the tool-work interface by flowing water in a closed cooling cycle system. The approach was analyzed and verified using Finite Element Analysis. Results were compared to the dry and wet cutting cases obtained from literature, and it was found that temperatures on the flank and rake faces of the tool can be lowered, and the overheated area of the tool tip, and consequently its wear, can be reduced significantly.

Flame: A Manufacturability Evaluator for Use at Different Levels of Abstraction

How can design for manufacture be implemented very early on a design time-line, for example, when only the function is known? Our response is embodied in an approach to design for manufacture at the function level of abstraction based on the notion of design using available assets. In this paper we focus on the solution scheme and computer implementation of our approach to design for manufacture. Our solution scheme takes the form of a Heuristic Selection Decision Support Problem, and our computer tool is called FLAME: the Function Level of Abstraction Manufacturability Evaluator. We use this tool to identify, evaluate and select potential manufacturing alternatives for products modeled at the function level of abstraction. We illustrate some of its uses by exploring the selection of manufacturing processes and materials for a component from a design of an aircraft evacuation system, although our focus is on the method rather than on the results per se.

Protocol Analysis As a Research Technique for Analysing Design Activity

This paper offers a review of protocol analysis as a research technique for the investigation of design activity. It draws particularly on the results of a special international research workshop on protocol analysis of design activity, held in Delft, The Netherlands, in September 1994. The paper identifies major themes and issues in the use of protocol analysis arising from the workshop.

Design for Product Variety: Key to Product Line Structuring

This study develops a method to capture the broadest customer preference in a product line while minimizing the life-cycle cost of providing variety. The paper begins with an overview of product variety and its importance in overhead costs: supply chain, equipment and tooling, service, and recycling. After defining the product structure graph as a representation of variety, the paper introduces an approximate measure for the customer importance and life-cycle cost of product variety The cost measure utilizes the concept of late point identification which urges standardization early in the manufacturing process and differentiation at the end of the process. The variety importance-cost map allows engineers to identify cost drivers in the design of the product or the manufacturing system and seek improvements. The refrigerator door example illustrates the concept. On-going work seeks to validate and enhance the method with several companies from different industries.