# Statistical Tolerance Analysis--A Survey on Awareness, Use and Need in German Industry
## 6 Current Use of Statistical Tolerance Analysis
The main reasons are well known and obvious: about 66.7% (=10 of 15) of the design engineers who did not perform tolerance analyses designated (i) the lack of time and (ii) a significant lack of knowledge of the method of tolerance analysis (\(\sim\)46.7% = 7 of 15) as reasons for not carrying out tolerance analyses. As previously stated, a variety of commercial software tools on computer-aided tolerancing (CAT) are available. These tools enable the design engineer to carry out statistical tolerance analyses of any given mechanical assembly in the virtual 3D-CAD environment. However, none of the respondents used such a commercial CAT software. Rather, of the 42 companies that performed tolerance analyses, only 20 relied on computer support. The majority (80% = 16 of 20) used the in-house developed Excel spreadsheets to carry out tolerance analyses. The remaining 22 respondents relied on the analytical calculation of tolerance stack-up problems by hand, using established and simple approaches, such as a worst-case tolerance analysis [61] or the \"root-sum-square\" approach [62]. Despite the intensive application of simple methods and tools in statistical tolerance analysis, the variety of different kinds of tolerances that are said to be taken into account in the industry are surprising and gratifying. The survey revealed that nearly all tolerance analysis carried out (\(\sim\)92.9% = 39 of 42) considers tolerances in size (so-called \"plus/minus tolerances\"). Further, form tolerances (\(\sim\)71.4% = 30 of 42), tolerances of orientation, location, run-out and profile (\(\sim\)59.0% = 29 of 42) as well as surface roughness (50% = 21 of 42) are taken into account when statistical tolerance analyses are performed in these companies. However, a critical consideration of the answers given leads to serious concerns about the quality and reliability of such statistical tolerance analyses. Further details concerning quality and reliability were not assessed in the survey. The knowledge gained confirms that in German industry, the design engineer usually carries out tolerance calculations using rather simple and easy-to-use methods and tools. No tolerance specialist, whose main task is to detect and analyze tolerance problems with the help of commercial software, was found among the surveyed companies, and the role is thus at least very rare in German industrial companies. Finally, the 28 companies that did not perform tolerance analyses but considered them useful and stated a need for them were asked about the reasons for not performing tolerance analyses (Figure 6). In particular, the lack of available time (\(\sim\)78.6% = 22 of 28) and no or insufficient knowledge of the necessary methods (\(\sim\)46.4% = 13 of 28) were mentioned. These results coincide with the results that were gained from the design engineers who did not perform tolerance analysis. Moreover, in \(\sim\)42.9% (=12 of 28) of these companies, the use of statistical tolerance analyses was \"not part of the company's corporate policy\". The 42 survey participants who performed tolerance analysis (=42 of 101; 1 abstention) felt rather confident in dealing with tolerances in their practice. Additionally, 55 of the remaining 59 survey participants (that did not perform tolerance analyses) assessed their handling of tolerances as comparatively good. However, ~61.4% (=35 of 55) of them could not state which tolerancing principle (independency principle vs. envelope principle) was applied in their company's technical drawings. This result showed a clear concordance with the results [PERSON] gained in 1995 [47]. The survey revealed that 65% of the participants were not aware of the difference between the tolerancing principles. This is particularly surprising, since in Germany, the ISO GPS is the established standard in the industry, but also ~17.9% (=17 out of 95) of the participants stated that they applied the AMSE Y14.5 standard.