The design of products and services is partially dependent on the productive system design, and vice versa. The concept is so well recognized in the mechanical industries that a term has been coined for the process of designing products from the point of view of producibility â€“ production design.
The producibility and minimum possible production cost of a product are established originally by the product designer. The most clever production engineers cannot change this situation; he or she can only work within the limitations of the product design. Therefore, the obvious time to start thinking about basic modes of production for products is while they are still in the design stage. This conscious effort to design for producibility and low manufacturing costs is referred to as â€œproduction designâ€ as distinct from functional design. To be sure, the product designerâ€™s first responsibility is to create something that meets functional requirements. But once functional requirements are met, there are ordinarily alternative designs, all of which meet functional requirements. Which of these alternatives will minimize production costs and foster product quality?
Given the design, process planning for manufacture must be carried out to specify in careful detail the processes required and their sequence production design first sets the minimum possible costs that can be achieved through such factors as the specification of materials, tolerances, basic configurations, and the methods of joining parts. Final process planning then attempts to achieve that minimum through the specification of processes and their sequence that meet the exacting requirement of the design. Here, process planners may work under the limitations of available equipment. If the volume is great and the design is stable, however process planners may be able to consider special-purpose process technology, including semiautomatic ands automatic processes, and special purposes layout. In performing their functions, process planners set the basic of the productive system.
The thesis of a production design philosophy is that design alternatives that still meet functional requirements nearly always exist. Then, for the projected volume of the product what differences in cost would result? Here we must broaden our thinking because the possible areas of cost that can be affected by design are likely to be more pervasive than we imagine. There are the obvious cost components of direct labor and materials. But perhaps not so obvious are the effects of equipment costs, tooling costs, indirect labor costs, and the non-manufacturing costs of engineering.
Indirect costs tend to be hidden, but suppose one design requires 30 different parts, whereas another requires only 15 (e.g. the reciprocating automobile engine versus the rotary engine). There are differences in indirect costs as a result of greater paper work and the cost of ordering, storing and controlling 30 parts instead of 15 for each completed item.
Design and Redesign:
The design process is an iterative one. In a sense, it is never done. New information feeds in from users, and we find ways to improve designs that reduce production costs and improve quality.
As an example of production design and redesign, Bright (1958) describes the development of electric light bulb manufacturing during the period from 1908 to 1955. Initially, a batch process was used that involved manual operation and simple equipment. The conversion from batch to continuous operation was achieved by adopting a systematic layout, standardizing operations, and effecting operation sequence change. Then, however, the light bulb itself was redesigned a number of times to facilitate process changes and to permit mechanical handling. Finally an evolution took place in which individual standardized manual operations were replaced by mechanical operations, and these operations were in turn integrated to produce a fully automated process.
Designs for components parts need to be specified carefully so that any part from a lot will fit. This is accomplished by establishing tolerances for part dimensions that take into account the manufacturing tolerances of mating parts. The result of design for interchangeable parts is interchangeable assembly. Assembly costs are then much lower than they would be if workers had to select combinations of mating parts that fit.
Custom products are likely to be more costly than standardization products, but managers must attempt a balance that clients and customers will accept. Given the appropriate balance, there are many economic benefits to standardization. The cost items affected are raw materials inventory, in-process inventory, lower set-up costs, longer production runs, improved quality controls with fewer items, opportunities for mechanization and automation, more advantageous purchasing, better labor utilization, lower training costs, and so on.
When two or more parts are finally assembled rigidly together, perhaps the unit can be designed as one piece, thus eliminating an assembly operation. This is often feasible when a single material will meet the services requirements for all the surfaces and cross sections of the part. Another example is the substitution of a plastic snap on cap in place of a screw-on cap for some applications. The costs of the materials and labor for the snap-on cap are much less. Simplifying the design of services offered has similar implications.
If the same component or subassembly can be used in variety of products, or in a product family, production costs can be reduced. Thus, modular design is one way to offer product variety while holding the number of components and sub assemblies to some reasonable level. For the modular components, we can have the advantages that result from volume and the experience curve while offering product variety in the market place.