Morris Asimow was among the first to give a detailed description of the complete design process in what he called the morphology of design. His seven phases of design are described below, with slight changes of terminology to conform to current practice. Figure 1 shows the various activities that make up the first three phases of design: conceptual design, embodiment design, and detail design. This eight-step set of design activities is our representation of the basic design process. The purpose of this graphic is to remind you of the logical sequence of activities that leads from problem definition to the detail design.
1 Phase I. Conceptual Design
Conceptual design is the process by which the design is initiated, carried to the point of creating a number of possible solutions, and narrowed down to a single best concept. It is sometimes called the feasibility study. Conceptual design is the phase that requires the greatest creativity, involves the most uncertainty, and requires coordination among many functions in the business organization. The following are the discrete activities that we consider under conceptual design.
Identification of customer needs: The goal of this activity is to completely understand the customers’ needs and to communicate them to the design team. Problem definition: The goal of this activity is to create a statement that describes what has to be accomplished to satisfy the needs of the customer. This involves analysis of competitive products, the establishment of target specifications, and the listing of constraints and trade-offs. Quality function deployment (QFD) is a valuable tool for linking customer needs with design requirements. A detailed listing of the product requirements is called a product design specification (PDS).
Gathering information: Engineering design presents special requirements over engineering research in the need to acquire a broad spectrum of information.
Conceptualization: Concept generation involves creating a broad set of concepts that potentially satisfy the problem statement. Team-based creativity methods, combined with efficient information gathering, are the key activities.
Concept selection: Evaluation of the design concepts, modifying and evolving into a single preferred concept, are the activities in this step. The process usually re- quires several iterations.
Refinement of the PDS: The product design specification is revisited after the concept has been selected. The design team must commit to achieving certain critical values of design parameters, usually called critical to quality (CTQ) parameters, and to living with trade-offs between cost and performance.
Design review: Before committing funds to move to the next design phase, a design review will be held. The design review will assure that the design is physically realizable and that it is economically worthwhile. It will also look at a detailed product- development schedule. This is needed to devise a strategy to minimize product cycle time and to identify the resources in people, equipment, and money needed to complete the project.
2 Phase II. Embodiment Design
Structured development of the design concept occurs in this engineering design phase. It is the place where flesh is placed on the skeleton of the design concept. An embodiment of all the main functions that must be performed by the product must be undertaken. It is in this design phase that decisions are made on strength, material selection, size, shape, and spatial compatibility. Beyond this design phase, major changes become very expensive. This design phase is sometimes called preliminary design. Embodiment design is concerned with three major tasks product architecture, configuration design, and parametric design.
Product architecture: Product architecture is concerned with dividing the overall design system into subsystems or modules. In this step we decide how the physical components of the design are to be arranged and combined to carry out the functional duties of the design.
Configuration design of parts and components: Parts are made up of features like holes, ribs, splines, and curves. Configuring a part means to determine what features will be present and how those features are to be arranged in space relative to each other. While modeling and simulation may be performed in this stage to check out function and spatial constraints, only approximate sizes are determined to assure that the part satisfies the PDS. Also, more specificity about materials and manufacturing is given here. The generation of a physical model of the part with rapid prototyping processes may be appropriate.
Parametric design of parts : Parametric design starts with information on the configuration of the part and aims to establish its exact dimensions and tolerances. Final decisions on the material and manufacturing processes are also established if this has not been done previously. An important aspect of parametric design is to examine the part, assembly, and system for design robustness. Robustness refers to how consistently a component performs under variable conditions in its service environment.
3 Phase III. Detail Design
In this phase the design is brought to the stage of a complete engineering description of a tested and producible product. Missing information is added on the arrangement, form, dimensions, tolerances, surface properties, materials, and manufacturing processes of each part. This results in a specification for each special-purpose part and for each standard part to be purchased from suppliers. In the detail design phase the following activities are completed and documents are prepared:
● Detailed engineering drawings suitable for manufacturing. Routinely these are computer-generated drawings, and they often include three-dimensional CAD models.
● Verification testing of prototypes is successfully completed and verification data is submitted. All critical-to quality parameters are confirmed to be under control. Usually the building and testing of several preproduction versions of the product will be accomplished.
● Assembly drawings and assembly instructions also will be completed. The bill of materials for all assemblies will be completed.
● A detailed product specification, updated with all the changes made since the conceptual design phase, will be prepared.
● Decisions on whether to make each part internally or to buy from an external supplier will be made.
● With the preceding information, a detailed cost estimate for the product will be carried out.
● Finally, detail design concludes with a design review before the decision is made to pass the design information on to manufacturing.
Phases I, II, and III take the design from the realm of possibility to the real world of practicality. However, the design process is not finished with the delivery of a set of detailed engineering drawings and specifications to the manufacturing organization. Many other technical and business decisions must be made that are really part of the design process. A great deal of thought and planning must go into how the design will be manufactured, how it will be marketed, how it will be maintained during use, and finally, how it will be retired from service and replaced by a new, improved design. Generally these phases of design are carried out elsewhere in the organization than in the engineering department or product development department. As the project proceeds into the new phases, the expenditure of money and personnel time increases greatly.
One of the basic decisions that must be made at this point is which parts will be made by the product developing company and which will be made by an outside vendor or supplier. This often is called the “make or buy” decision. Today, one additional question must be asked: “Will the parts be made and/or assembled in the United States or in another country where labor rates are much lower?”
4 Phase IV. Planning for Manufacture
A great deal of detailed planning must be done to provide for the production of the design. A method of manufacture must be established for each component in the system. As a usual first step, a process sheet is created; it contains a sequential list of all manufacturing operations that must be performed on the component. Also, it specifies the form and condition of the material and the tooling and production machines that will be used. The information on the process sheet makes possible the estimation of the production cost of the component. High costs may indicate the need for a change in material or a basic change in the design. Close interaction with manufacturing, industrial, materials, and mechanical engineers is important at this step.
The other important tasks performed in phase IV are the following:
● Designing specialized tools and fixtures
● Specifying the production plant that will be used (or designing a new plant) and laying out the production lines
● Planning the work schedules and inventory controls (production control)
● Planning the quality assurance system
● Establishing the standard time and labor costs for each operation
● Establishing the system of information flow necessary to control the manufacturing operation
All of these tasks are generally considered to fall within industrial or manufacturing engineering.
5 Phase V. Planning for Distribution
Important technical and business decisions must be made to provide for the effective distribution to the consumer of the products that have been produced. In the strict realm of design, the shipping package may be critical. Concepts such as the shelf life of the product may also be critical and may need to be addressed in the earlier stages of the design process. A system of warehouses for distributing the product may have to be designed if none exists. The economic success of the design often depends on the skill exercised in marketing the product. If it is a consumer product, the sales effort is concentrated on advertising in print and video media, but highly technical products may require that the marketing step be a technical activity supported by specialized sales brochures, performance test data, and technically trained sales engineers. 6
6 Phase VI. Planning for Use
The use of the product by the consumer is all-important, and considerations of how the consumer will react to the product pervade all steps of the design process. The following specific topics can be identified as being important user-oriented concerns in the design process: ease of maintenance, durability, reliability, product safety, convenience in use (human factors engineering), aesthetic appeal, and economy of operation. Obviously, these consumer-oriented issues must be considered in the design process at its very beginning. They are not issues to be treated as afterthoughts.
Phase VI of design is less well defined than the others, but it is becoming increasingly important with the growing concerns for consumer protection and product safety. More strict interpretation of product liability laws is having a major impact on design. An important phase VI activity is the acquisition of reliable data on failures, service lives, and consumer complaints and attitudes to provide a basis for product improvement in the next design cycle.
7 Phase VII. Planning for Retirement of the Product
The final step in the design process is the disposal of the product when it has reached the end of its useful life. Useful life may be determined by actual deterioration and wear to the point at which the design can no longer function, or it may be determined by technological obsolescence, in which a competing design performs the product’s functions either better or cheaper. In consumer products, it may come about through changes in fashion or taste.
In the past, little attention has been given in the design process to product retirement. This is rapidly changing, as people the world over are becoming concerned about environmental issues. There is concern with depletion of mineral and energy resources, and with pollution of the air, water, and land as a result of manufacturing and technology advancement. This has led to a formal area of study called industrial ecology. Design for the environment, also called green design, has become an important consideration in design. As a result, the design of a product should include a plan for either its disposal in an environmentally safe way or, better, the recycling of its materials or the re-manufacture or reuse of its components.
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