The design review is a vital aspect of the design process. It provides an opportunity for specialists from different disciplines to interact with generalists to ask critical questions and exchange vital information. A design review is a retrospective study of the design up to that point in time. It provides a systematic method for identifying problems with the design, determining future courses of action, and initiating action to correct any problem areas.
To accomplish these objectives, the review team should consist of representatives from design, manufacturing, marketing, purchasing, quality control, reliability engineering, and field service. The chairman of the review team is normally a chief engineer or project manager with a broad technical background and broad knowledge of the company’s products. In order to ensure freedom from bias, the chairman of the design review team should not have direct responsibility for the design under review.
Depending on the size and complexity of the product, design reviews should be held from three to six times in the life of the project. The minimum review schedule consists of conceptual, interim, and final reviews. The conceptual review occurs once the conceptual design has been established. This review has the greatest impact on the design, since many of the design details are still fluid and changes can be made at this stage with least cost. The interim review occurs when the embodiment design is finalized and the product architecture, subsystems, and performance characteristics, and critical design parameters are established. It looks critically at the interfaces between the subsystems. The final review takes place at completion of the detail design and establishes whether the design is ready for transfer to manufacturing.
Each review looks at two main aspects. The first is concerned with the technical elements of the design, while the second is concerned with the business aspects of the product. The essence of the technical review of the design is to compare the findings against the detailed product design specification (PDS) that is formulated
at the problem definition phase of the project. The PDS is a detailed document that describes what the design must be in terms of performance requirements, the environment in which it must operate, the product life, quality, reliability, cost, and a host of other design requirements. The PDS is the basic reference document for both the product design and the design review. The business aspect of the review is concerned with tracking the costs incurred in the project, projecting how the design will affect the expected marketing and sales of the product, and maintaining the time schedule. An important outcome of the review is to determine what changes in resources, people, and money are required to produce the appropriate business outcome. It must be realized that a possible outcome of any review is to withdraw the resources and terminate the project.
A formal design review process requires a commitment to good documentation of what has been done, and a willingness to communicate this to all parties involved in the project. The minutes of the review meeting should clearly state what decisions were made and should include a list of “action items” for future work. Since the PDS is the basic control document, care must be taken to keep it always updated.
1. Redesign
A common situation is redesign. There are two categories of redesigns: fixes and updates. A fix is a design modification that is required due to less than acceptable performance once the product has been introduced into the marketplace. On the other hand, updates are usually planned as part of the product’s life cycle before the product is introduced to the market. An update may add capacity and improve performance to the product or improve its appearance to keep it competitive.
The most common situation in redesign is the modification of an existing product to meet new requirements. For example, the banning of the use of fluorinated hydrocarbon refrigerants because of the “ozone-hole problem” required the extensive redesign of refrigeration systems. Often redesign results from failure of the product in service. A much simpler situation is the case where one or two dimensions of a component must be changed to match some change made by the customer for that part. Yet another situation is the continuous evolution of a design to improve performance. An extreme example of this is shown in Fig. The steel railroad wheel has been in its present design for nearly 150 years. In spite of improvements in metallurgy and the understanding of stresses, the wheels still failed at the rate of about 200 per year, often causing disastrous derailments. The chief cause of failure is thermal buildup caused by failure of a railcar’s braking system. Long-term research by the Association of American Railroads has resulted in the improved design. The chief design change is that the flat plate, the web between the bore and the rim, has been replaced by an S-shaped plate. The curved shape allows the plate to act like a spring, flexing when overheated, avoiding the buildup of stresses that are transmitted through the rigid flat plates. The wheel’s tread has also been redesigned to extend the rolling life of the wheel. Car wheels last for about 200,000 miles. Traditionally, when a new wheel was placed in service it lost from 30 to 40 percent of its tread and flange while it wore away to a new shape during the first 25,000 miles of service. After that the accelerated wear stopped and normal wear ensued. In the new design the curve between the flange and the tread has been made less concave, more like the profile of a “worn” wheel. The new wheels last for many thousands of miles longer, and the rolling resistance is lower, saving on fuel cost.
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Fig An example of a design update. Old design of railcar wheel versus improved design.
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