【正文】 ing work elements to the individual stations of the line, a procedure called line balancing. The assembly line routes the work unit to individual stations in the proper order as determined by the line balance solution. As in process planning for individual ponents, any tools and fixtures required to acplish an assembly task must be determined, designed, built, and the workstation arrangement must be laid out. Make or Buy Decision An important question that arises in process planning is whether a given part should be produced in the pany’s own factory or purchased from an outside vendor, and the answer to this question is known as the make or buy decision. If the pany does not possess the technological equipment or expertise in the particular manufacturing processes required to make the part, then the answer is obvious: The part must be purchased because there is no internal alternative. However, in many cases, the part could either be made internally using existing equipment, or it could be purchased externally from a vendor that process similar manufacturing capability. In our discussion of the make or buy decision, it should be recognized at the outset that nearly all manufactures buy their raw materials from supplies. A machine shop purchases its starting bar stock from a metals distributor and its sand castings from a foundry. A plastic molding plant buys its molding pound from a chemical pany. A stamping press factory purchases sheet metal either fro a distributor or direct from a rolling mill. Very few panies are vertically integrated in their production operations all the way from raw materials, it seems reasonable to consider purchasing at least some of the parts that would otherwise be produced in its own plant. It is probably appropriate to ask the make or buy question for every ponent that is used by the pany. There are a number of factors that enter into the make or buy decision. One would think that cost is the most important factor in determining whether to produce the part or purchase it. If an outside vendor is more proficient than the pany’s own plant in the manufacturing processes used to make the part, then the internal production cost is likely to be greater than the purchase price even after the vendor has included a profit. However, if the decision to purchase results in idle equipment and labor in the pany’s own plant, then the apparent advantage of purchasing the part may be lost. Consider the following example make or Buy Decision. The quoted price for a certain part is $ per unit for 100 units. The part can be produced in the pany’s own plant for $. The ponents of making the part are as follows: Unit raw material cost = $ per unit Direct labor cost = per unit Labor overhead at 150%= per unit Equipment fixed cost = per unit ________________________________ Total = per unit Should the ponent by bought or made inhouse? Solution: Although the vendor’s quote seems to favor a buy decision, let us consider the possible impact on plant operations if the quote is accepted. Equipment fixed cost of $ is an allocated cost based on investment that was already made. If the equipment designed for this job bees unutilized because of a decision to purchase the part, then the fixed cost continues even if the equipment stands idle. In the same way, the labor overhead cost of $ consists of factory space, utility, and labor costs that remain even if the part is purchased. By this reasoning, a buy decision is not a good decision because it might be cost the pany as much as $+$+$=$ per unit if it results in idle time on the machine that would have been used to produce the part. On the other hand, if the equipment in question can be used for the production of other parts for which the inhouse costs are less than the corresponding outside quotes, then a buy decision is a good decision. Make or buy decision are not often as straightforward as in this example. A trend in recent years, especially in the automobile industry, is for panies to stress the importance of building close relationships with parts suppliers. We turn to this issue in our later discussion of concurrent engineering. Computeraided Process Planning There is much interest by manufacturing firms in automating the task of process planning using puteraided process planning (CAPP) systems. The shoptrained people who are familiar with the details of machining and other processes are gradually retiring, and these people will be available in the future to do process planning. An alternative way of acplishing this function is needed, and CAPP systems are providing this alternative. CAPP is usually considered to be part of puteraided manufacturing (CAM). However, this tends to imply that CAM is a standalong system. In fact, a synergy results when CAM is bined with puteraided design to create a CAD/CAM system. In such a system, CAPP bees the direct connection between design and manufacturing. The benefits derived from puterautom