自動墻壁清洗機畢業設計(doc畢業設計論文)-資料下載頁

　　

【正文】 ’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 unitDirect 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網 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 puterautomated process planning include the following:Automated process planning leads to more logical and consistent process plans than when process is done pletely manually. Standard plans tend to result in lower manufacturing costs and higher product quality.Increase productivity of process planner. The systematic approach and the availability of standard process plans in the data files permit more work to be acplished by the process planners. Reduced leaded time for process planned. Process planner working with a CAPP system can provide route sheets in a shorter lead time pared to manual preparation.Improve legibility. Computerprepared rout sheets are neater and easier to read than manually prepared route sheets. The CAPP program can be interfaced with other application programs, such as cost estimating and work standards.Computeraided process planning systems are designed around two approaches. These approaches are called: (1) retrieval CAPP systems and (2) generative CAPP systems .Some CAPP systems bine the two approaches in what is known as semigenerative CAPP.Concurrent Engineering and Design for ManufacturingConcurrent 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 to launching a new product, the two functions of design engineering and manufacturing engineering tend to be separated and sequential, as illustrated in Fig.(1).(a).The product design department develops the new design, sometimes without much consideration given to the manufacturing capabilities of the pany, There is little opportunity for manufacturing engineers to offer advice on how the design might be alerted to make it more manufacturability. It is as if a wall exits between design and manufacturing. When the design engineering department pletes the design, it tosses the drawings and specifications over the wall, and only then does process planning begin. Fig. Comparison: (a) traditional product development cycle and (b) product development using concurrent engineering By contrast, in a pany that practices concurrent engineering, the manufacturing engineering department bees involved in the product development cycle early on, providing advice on how the product and its ponents can be designed to facilitate manufacture and assembly. It also proceeds with early stages of manufacturing planning for the product. This concurrent engineering approach is pictured in Fig.(1).(b). In addition to manufacturing engineering, other function are also involved in the product development cycle, such as quality engineering, the manufacturing departments, field service, vendors supplying critical ponents, and in some cases the customer who will use the product. All if these functions can make contributions during product development to improve not only the new product’s function and performance, but also its, 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