Concurrent Engineering and Design for Manufacturing

      CONCURRENT ENGINEERING  AND DESIGN FOR MANUFACTURING

Concurrent engineering refers to an approach used in product development in which the functions of design engineering, manufacturing engineering, and other functions are integrated to reduce the elapsed time required to bring a new product to market. Also called simultaneous engineering, it might be thought of as the organizational counterpart to CAD/CAM technology. In the traditional approach 10 launching a new product, the two functions of design engineering and manufacturing engineering tend to be separated and sequential. as illustrated in Figure 25.5(a). The product design department develops the new design, sometimes without much consideration given to the manufacturing capabilities of the company. There is little opportunity for manufacturing engineers to offer advice

Figure 15.5 Comparison of: (a) traditional product development cycle and (b) product development using concurrent engineering.

on how the design might be altered to make it more manufacturable. It is as if a wall exists between design and manufacturing. When the design engineering department completes the design, it tosses the drawings and specifications over the wall, and only then does process planning begin.

By contrast, in a company that practices concurrent engineering, the manufacturing engineering department becomes involved in the product development cycle early on, providing advice on how the product and its components can be designed to facilitate manufacture and assembly. It also proceeds with the early stages of manufacturing planning for the product. This concurrent engineering approach is pictured in Figure 2S.5(b). In addition 10 manufacturing engineering, other functions are also involved in the product development cycle, such as quality engineering, the manufacturing departments, field service, vendors supplying critical components, and in some cases the customers who will use the product. AU of these functions can make contributions during product development to improve not only the new product's function and performance, but also its produce ability. inspectability, testability, serviceability, and maintainability. Through early involvement, as opposed to reviewing the final product design after it is too late to conveniently make any changes in the design, the duration of the product development cycle is substantially reduced.

 Design for Manufacturing and Assembly

It has been estimated that about 70% of the life cycle cost of a product is determined by basic decisions made during product design. These design decisions include the material for each part. part geometry, tolerances, surface finish, how parts are organized into subassemblies. and the assembly  method, to he used. Once these decisions are made, the ability to reduce the manufacturing  cost of the product is limited. For example. if the product designer decides that a part is to be made of an aluminum sand casting but which possesses features that can he achieved only h) machining (such as threaded holes and close tolerances). the manufacturing engineer has no alternative except to plan a process sequence that starts WIth sand casting followed by the sequence of machining operations needed to achieve the specified features. In this example, a better decision might be to use a plastic molded part that can be made in a single step. It is important for the manufacturing engineer to be given the opportunity to advise the design engineer as the product design is evolving, to favorably influence the manuacturability of the product.

Terms used to describe such attempts to favorably influence the rnanufacturability of a new product are design .for manufacturing (DFM) and design for assembly (DFA). Of course, DFM and DFA arc inextricably linked, so let us use the term design for manufacturing and assembly (DFMIA). Design for manufacturing and assembly involves the systematic consideration of rnanufacturability and assemblability in the development of a new product design. This  includes: (l) organizational changes and (2) design principles and guideline,

Organizational  Changes in DFMIA. Effective implementation of DFMlA, involves making changes in a company's organizational structure. either formally or informally, so that closer interaction and better communication occurs between design and manufacturing personnel. This can he accomplished in several ways: (1) by creating project teams consisting of product designers, manufacturing engineers, and other specialties (e.g., quality engineers, material scientists) to develop the new product design; (2) by requiring design engineers to spend some career time in manufacturing to witness firsthand how manufacturabihty and assemblability are impacted by a product's design; and (3) by assigning manufacturing engineers to the product design department on either a temporary or fulltime basis to serve as producibility consultants.

Design     Principles    and  Guidelines. DFM/A   also relies on the use 01 design  principles and guidelines for how 10 design a given product to maximize manufacturability and asscrnblability. Some of these arc universal design guidelines that can be applied to nearly any product design situation, such as those presented in Table 25.4. In other cases, there are design principles that apply to specific processes, for example, the use of drafts or tapers in casted and molded parts to facilitate removal of the part from the mold, We leave these more process-specific guidelines to texts on manufacturing processes, such as .

The guideline. sometimes conflict with one another. for example. one of the guidelines in Table 25.4 is to "simplify part geometry; avoid unnecessary features." But another guideline  in  the same table states that "special geometric features must sometimes be added to components" to design the product for foolproof  assembly. And it may also be desirable to combine features of several assembled parts into one component to minimize the number of parts in the product. In these instances. design for part manufacture is in conflict with design for assembly, and a suitable compromise must be found between the opposing sides of the conflict.

Other  Product  Design  Objectives

To complete our coverage of concurrent engineering, let us hriefly discuss the other design objectives: design for quality, cost, and life cycle.

Design for Quality. It might be argued that DFM/A is the most important component of concurrent engineering because it has the potential for the greatest impact on product cost and development time. However. the importance of quality in international competition cannot be minimized. Quality does not just happen. It must be planned for during product design and during production. Design for quality (DFQ) is the term that refers to the principles and procedures employed to ensure that the highest possible quality is designed into the product. The general objectives of DFQ are [1]: (1) to design the product to meet or exceed customer requirements; (2) to design the product to be "robust," in the sense of Taguchi (Section 20.3.2), that is, to design the product so that its function and performance are relatively insensitive to variations in manufacturing and subsequent application; and (3) to continuously improve the performance, functionality. reliability, safety. and other quality aspects of the product to provide superior value to the customer.

Our discussion of quality in Part IV (Chapters 2023) is certainly consistent with the focus of design for quality, but our emphasis in those chapters was directed more at the operational aspects of quality during production. Among those chapters, the Taguchi quality engineering methods (Section 20.3) are applicable ill design for quality. Another approach that is gaining acceptance is quality function deployment, discussed in Section 24.5.

Design for Product Cost. The cost of a product is a major factor in determining its commercial success, Cost affects the price charged for the product and the profit made by the company producing it. Design for product cost (DFC) refers to the efforts of a company to specifically identify how design decisions affect product costs and to develop ways to reduce cost through design. Although the objectives of DFC and DFMIA overlap to some degree, since improved manufacturability usually results in lower cost, the scope of design for product cost extends beyond only manufacturing in its pursuit of cost savings, as indicated by the list of typical product cost components in Table 25.5.

Design for Life Cycle. To the customer, the price paid for the product may be a small portion of its total cost when life cycle costs are considered. Design for life cycle refers to the product after it has been manufactured and includes factors ranging from product delivery to product disposal. Most of the significant life cycle factors are listed in Table 25.6. Some customers (e.g., the federal government) include consideration of these costs in their purchasing decisions. The producer of the product is often obligated to offer service contracts that limit customer liability for out-of-control maintenance and service costs. In these cases, accurate estimates of these life cycle costs must be included in the total product cost .