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1、PART TWO,16.1 Text 16.2 Words and Phrases 16.3 Complex Sentence Analysis 16.4 Exercise,Lesson 16 Product Test and Quality Control, 16.1 Text Product Test Product test can be thought of as the culmination of all process control work. It can also be thought of as a quality check of the inspection proc
2、ess itself. If the quality plan is adequate and carried out properly, then the products performance should have been verified and a total test is redundant. For this reason, a test of the completed product is often nothing more than a contractual requirement that must be performed before the custome
3、r accepts the product. But product test is also more than proving. And testing to whole is equal to the sum of the parts. 1It allows for gathering data that support the design theory of the product, for interpretations to be made for further improvements in design so that future products will be bet
4、ter than present ones, and for evaluation of design evolution toward better performance costs. In addition, it is a means of verifying design, since not all design parameters can be fully calculated or predicted. Product test engineers work closely with design engineers to provide useful data for te
5、sting. They must also work in close harmony with engineers all other phases of manufacturing. Not infrequently, product testing will turn up deficiencies in design that requires major revisions in manufacturing processes. This is particularly true if the company produces many prototypes and has shor
6、t production runs. Therefore, manufacturing engineers are as interested in product tests results as are design engineers. For complex products, product test becomes a very important part of the total process control function. It gives the company a high degree of confidence that the product will per
7、form as the customer expects it to, and this is a valuable marketing tool as it helps to establish the proper reputation with the customers., 16.1 Text Geometric Errors Geometric errors are defined here as errors in form of individual machine components (e.g., straightness of motion of a linear bear
8、ing). Geometric errors are concerned with the quasi-static accuracy of surface, which bear upon the moving relative of the surfaces. Geometric errors can be smooth and continuous (systematic) or they can exhibit hysteresis (e.g., backlash) or random behavior. 2Many factors affect geometric errors in
9、cluding: surface straightness (see Fig.16.1), surface roughness, bearing preload, kinematics versus elastic design principles and structural design philosophies.,Fig.16.1 Straightness Errors Caused by Surface Form and Finish Errors, 16.1 Text Fit and Tolerance Fit is defined as the relation resultin
10、g from the difference between the sizes of two mating parts. And tolerance is defined as the difference between the maximum limit and the minimum limit. The tolerance is also equal to the algebraic difference between the upper and lower deviations (see Fig.16.2).,Fig.16.2 Diagram Illustrating Basic
11、Size, Deviations and Tolerances, 16.1 Text Fit and Tolerance Depending upon the actual limits of the hole or shaft, a fit may be classified as follows: (1) Clearance fit is a fit that always provides a clearance between the mating parts. In this case, the tolerance zone of the hole is entirely above
12、 that of the shaft. (2) Interference fit is a fit that always provides interference between the mating parts. Here, the tolerance zone of the hole is entirely below that of the shaft. (3) Transition fit is a fit that may provides either a clearance or interference between the mating parts depending
13、on the actual dimensions of the finished products. A tolerance is designated by a letter (in some cases, two letters), a symbol, and a numerical symbol. Capital letters are used for holes and small letters for shafts. The letter symbol indicates the position of the zone of tolerance in relation to t
14、he zero line representing the basic size. The numerical symbol represents the value of this zone of tolerance and is called the grade or quality of tolerance. Both the position and the grade of tolerance are functions of the basic size. A size with tolerance is thus defined by its basic value follow
15、ed by a letter and a number, e.g., 20H7 or 20g6 In engineering drawing practice, the tolerance for hole and shaft is written a little above and little below the basic size, respectively. 3Similarly, a fit is indicated by the basic size common to both the mating components, followed by the appropriat
16、e symbols corresponding to each component, e.g., 16.1 Text Quality Planning This is the planning and strategy activity of process control, and is sometimes referred to as process planning or inspection planning. The engineers involved develop the plans for checking the adequacy of performance of sho
17、p operations to ensure that the final product performs as designed. Using plans and methods produced by measurement of productivity and work measurement (MP in this way quality planning can report to management whether quality levels are improving or declining. Quality status can be reported by stat
18、istically evaluating the numbers of deviations and their seriousness. This leads naturally to an evaluation of the cost of doing the repair work caused by the deviation. Repair work, which constitutes manufacturing losses, is an important measurement of organizational quality levels. Manufacturing losses are a significant measure of the adequacy of attention to detail of the operators and their foremen. High losses indicate a poorly managed operation. Quality planning engineers are responsible for setting the manufacturing losses, budgets, and measurements policy.,
