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- 1. Tolerance Design
- 2. Design Specifications and Tolerance <ul><li>Develop from quest for production quality and efficiency </li></ul><ul><li>Early tolerances support design’s basic function </li></ul><ul><li>Mass production brought interchangeability </li></ul><ul><li>Integrate design and mfg tolerances </li></ul>
- 3. Definition <ul><ul><li>“ The total amount by which a given dimension may vary, or the difference between the limits” </li></ul></ul><ul><li>- ANSI Y14.5M-1982(R1988) Standard [R1.4] </li></ul>Source: Tolerance Design , p 10
- 4. Affected Areas Product Design Quality Control Manufacturing Engineering Tolerance
- 5. Questions <ul><li>“Can customer tolerances be accommodated by product?” </li></ul><ul><li>“Can product tolerances be accommodated by the process?” </li></ul>
- 6. Tolerance vs. Manufacturing Process <ul><li>Nominal tolerances for steel </li></ul><ul><li>Tighter tolerances => increase cost $ </li></ul>
- 7. Geometric Dimensions <ul><li>Accurately communicates the function of part </li></ul><ul><li>Provides uniform clarity in drawing delineation and interpretation </li></ul><ul><li>Provides maximum production tolerance </li></ul>
- 8. Tolerance Types <ul><li>Size </li></ul><ul><li>Form </li></ul><ul><li>Location </li></ul><ul><li>Orientation </li></ul>
- 9. Size Tolerances
- 10. Form Tolerances
- 11. Location Tolerances
- 12. Orientation Tolerances
- 13. Tolerance Buildup
- 14. Statistical Principles <ul><li>Measurement of central tendency </li></ul><ul><ul><li>Mean </li></ul></ul><ul><ul><li>Median </li></ul></ul><ul><ul><li>mode </li></ul></ul><ul><li>Measurement of variations </li></ul><ul><ul><li>Range </li></ul></ul><ul><ul><li>Variance </li></ul></ul><ul><ul><li>Standard deviation </li></ul></ul>USL LSL tolerance 3 X
- 15. Probability <ul><li>Probability </li></ul><ul><ul><li>Likelihood of occurrence </li></ul></ul><ul><li>Capability </li></ul><ul><ul><li>Relate the mean and variability of the process or machine to the permissible range of dimensions allowed by the specification or tolerance. </li></ul></ul>
- 16. Tolerance SPC Charting Figure Source: Tolerance Design , p 125
- 17. Tolerance Analysis Methods <ul><li>Worst-Case analysis </li></ul><ul><li>Root Sum of Squares </li></ul><ul><li>Taguchi tolerance design </li></ul>
- 18. Initial Tolerance Design Figure Source: Tolerance Design , p 93 Initial Tolerance Design
- 19. References <ul><li>Handbook of Product Design for Manufacturing: A Practical Guide to Low-Cost Production , James C. Bralla, Ed. in Chief; McGraw-Hill, 1986 </li></ul><ul><li>Manufacturing Processes Reference Guide, R.H. Todd, D.K. Allen & L. Alting; Industrial Press Inc., 1994 </li></ul><ul><li>Standard tolerances for mfg processes </li></ul><ul><ul><li>Machinery’s Handbook ; Industrial Press </li></ul></ul><ul><ul><li>Standard Handbook of Machine Design ; McGraw-Hill </li></ul></ul><ul><ul><li>Standard Handbook of Mechanical Engineers ; McGraw-Hill </li></ul></ul><ul><ul><li>Design of Machine Elements ; Spotts, Prentic Hall </li></ul></ul>Figure Source: Tolerance Design , p 92-93
- 20. Worst-Case Methodology <ul><li>Extreme or most liberal condition of tolerance buildup </li></ul><ul><li>“… tolerances must be assigned to the component parts of the mechanism in such a manner that the probability that a mechanism will not function is zero…” </li></ul><ul><li> - Evans (1974) </li></ul>
- 21. Worst-Case Analysis <ul><li>N e + T e => Maximum assembly envelope </li></ul><ul><li>N e - T e => Minimum assembly envelope </li></ul>Source: “Six sigma mechanical design tolerancing”, p 13-14.
- 22. Assembly gaps
- 23. Worst Case Scenario Example Source: Tolerance Design , pp 109-111
- 24. Worst Case Scenario Example Source: Tolerance Design , pp 109-111
- 25. Worst Case Scenario Example Source: Tolerance Design , pp 109-111 <ul><li>Largest => 0.05 + 0.093 = 0.143 </li></ul><ul><li>Smallest => 0.05 - 0.093 = -0.043 </li></ul>
- 26. Non-Linear Tolerances Wource: “Six sigma mechanical design tolerancing”, p 104
- 27. Root Sum-of-Square <ul><li>RSS </li></ul><ul><li>Assumes normal distribution behavior </li></ul>Wource: “Six sigma mechanical design tolerancing”, p 16
- 28. RSS method <ul><li>Assembly tolerance stack equation </li></ul>Wource: “Six sigma mechanical design tolerancing”, p 128
- 29. Pool Variance in RSS Wource: “Six sigma mechanical design tolerancing”, p 128
- 30. Probability Wource: “Six sigma mechanical design tolerancing”, p 128
- 31. Probability for Limits Wource: “Six sigma mechanical design tolerancing”, p 128
- 32. Dynamic RSS Wource: “Six sigma mechanical design tolerancing”, p 128
- 33. Nonlinear RSS Wource: “Six sigma mechanical design tolerancing”, p 128
- 34. RSS Example Wource: “Six sigma mechanical design tolerancing”, p 128 <ul><li>Largest => 0.05 + 0.051 = 0.101 </li></ul><ul><li>Smallest => 0.05 - 0.051 = -0.001 </li></ul>
- 35. Taguchi Method Input from the voice of the customer and QFD processes Select proper quality-loss function for the design Determine customer tolerance values for terms in Quality Loss Function Determine cost to business to adjust Calculate Manufacturing Tolerance Proceed to tolerance design Wource: “Six sigma mechanical design tolerancing”, p 21
- 36. Taguchi <ul><li>Voice of customer </li></ul><ul><li>Quality function deployment </li></ul><ul><li>Inputs from parameter design </li></ul><ul><ul><li>Optimum control-factor set points </li></ul></ul><ul><ul><li>Tolerance estimates </li></ul></ul><ul><ul><li>Initial material grades </li></ul></ul>Wource: “Six sigma mechanical design tolerancing”, p 22
- 37. Quality Loss Function <ul><li>Identify customer costs for intolerable performance </li></ul><ul><li>Quadratic quality loss function </li></ul>Wource: “Six sigma mechanical design tolerancing”, p 208
- 38. Cost of Off Target and Sensitivity <ul><li>Cost to business to adjust off target performance </li></ul><ul><li>Sensitivity, </li></ul>Wource: “Six sigma mechanical design tolerancing”, p 226-227
- 39. Manufacturing Tolerance
- 40. Summary <ul><li>Importance of effective tolerances </li></ul><ul><li>Tolerance Design Approaches </li></ul><ul><ul><li>Worst-Case analysis </li></ul></ul><ul><ul><li>Root Sum of Squares </li></ul></ul><ul><ul><li>Taguchi tolerance method </li></ul></ul><ul><li>Continual process </li></ul><ul><li>Involvement of multi-disciplines </li></ul>
- 41. <ul><li>This module is intended as a supplement to design classes in mechanical engineering. It was developed at The Ohio State University under the NSF sponsored Gateway Coalition (grant EEC-9109794). Contributing members include: </li></ul><ul><li>Gary Kinzel…………………………………. Project supervisor </li></ul><ul><li>Phuong Pham.……………. ………………... Primary author </li></ul>Credits <ul><li>Reference: </li></ul><ul><ul><li>“ Six Sigma Mechanical Design Tolerancing”, Harry, Mikel J. and Reigle Stewart, Motorola Inc. , 1988. </li></ul></ul><ul><ul><li>Creveling, C.M., Tolerance Design , Addison-Wesley, Reading, 1997. </li></ul></ul><ul><ul><li>Wade, Oliver R., Tolerance Control in Design and Manufacturing , Industrial Press Inc., New York, 1967. </li></ul></ul>
- 42. Disclaimer <ul><li>This information is provided “as is” for general educational purposes; it can change over time and should be interpreted with regards to this particular circumstance. While much effort is made to provide complete information, Ohio State University and Gateway do not guarantee the accuracy and reliability of any information contained or displayed in the presentation. We disclaim any warranty, expressed or implied, including the warranties of fitness for a particular purpose. We do not assume any legal liability or responsibility for the accuracy, completeness, reliability, timeliness or usefulness of any information, or processes disclosed. Nor will Ohio State University or Gateway be held liable for any improper or incorrect use of the information described and/or contain herein and assumes no responsibility for anyone’s use of the information. Reference to any specific commercial product, process, or service by trade name, trademark, manufacture, or otherwise does not necessarily constitute or imply its endorsement. </li></ul>

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