tailieunhanh - Dimensioning and Tolerancing Handbook Episode 2 Part 4

Tham khảo tài liệu 'dimensioning and tolerancing handbook episode 2 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 9-8 Chapter Nine a column titled Fixed Variable. This identifies which dimensions and tolerances are fixed in the analysis and which ones are allowed to vary variable . Typically we have no control over vendor items so we treat these dimensions as fixed. As we make adjustments to dimensions and tolerances we will only change the variable dimensions and tolerances. The mean for Gap 6 is Gap 6 a1d1 a2d2 a3d3 a4d4 a5d5 a6d6 a7d7 a8d8 a9d9 a10d10 a11d11 Gap 6 -1 A 1 B 1 C 1 D 1 E 1 F 1 G 1 H 1 I -1 J 1 K Gap 6 -1 .3595 1 .0320 1 .0600 1 .4305 1 .1200 1 1 .1200 1 4305 1 .4500 -1 1 .0300 Gap 6 .0615 Determine the Method of Analysis Eq. only calculates the nominal value for the gap. The next step is to analyze the variation at the gap. Historically mechanical engineers have used two types of tolerancing models to analyze these variations 1 a worst case WC model and 2 a statistical model. Each approach offers tradeoffs between piecepart tolerances and assembly quality. In Chapters 11 and 14 we will see that there are other methods based on the optimization of piecepart and assembly quality and the optimization of total cost. Fig. 9-6 shows how the assumptions about the pieceparts affect the requirements gaps using the worst case and statistical methods. In this figure the horizontal axis represents the manufactured dimension. The vertical axis represents the number of parts that are manufactured at a particular dimension on the horizontal axis. Worst Case Worst Case Assembly Figure 9-6 Combining piecepart variations using worst case and statistical methods Traditional Approaches to Analyzing Mechanical Tolerance Stacks 9-9 In the Worst Case Model we verify that the parts will perform their intended function 100 percent of the time. This is oftentimes a conservative approach. In the statistical modeling approach we assume that most of the manufactured parts are centered on the mean dimension. This is usually less conservative than a worst case .