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Theory of Residual Stresses, Stress Relieving and CQ19

Theory of Residual Stresses, Stress Relieving and CQ19. By: Dan Sebastian. What are we going to talk about. Basic metallurgy and how/why do we get residual stresses. 2. How residual stresses are created. 3. Good stresses vs. bad stresses. 4. Shot peening.

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Theory of Residual Stresses, Stress Relieving and CQ19

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  1. Theory of Residual Stresses, Stress Relieving and CQ19 By: Dan Sebastian

  2. What are we going to talk about • Basic metallurgy and how/why do we get residual stresses 2. How residual stresses are created 3. Good stresses vs. bad stresses 4. Shot peening 5. How does stress relieving effect residual stresses 6. Is there a difference in coiling methods 7. CQI-9 and why it is related to residual stresses a. Systematic control b. Physical control

  3. Basic Metallurgy Iron-Carbon Phase Diagram TTT Curves FCC Structure BCC Structure BCT Tetragonal Structure Size Effect of Cubic Structure

  4. Time Temperature Transformation (TTT)

  5. Face Center Cubic (FCC) Structure Austenite

  6. Body Center Cubic (BCC) Structure Pearlite Ferrite Lower Bainite

  7. Body Center Tetragonal Cubic (BCT) Structure Martensite

  8. Martensite is 4.3 % larger by volume

  9. How Residual Stresses are Created Stress-Strain Diagram Bending Stresses Torsional Stresses Compressive Stresses Multi-Stresses

  10. Bending Stress

  11. Torsional Stress

  12. Compressive Stresses

  13. Multi-Stresses 1. Forces vectors are in different direction to the residual stresses 2. Coil springs a. Torsion b. Bending c. Compressive d. Shear 3. Torsion Springs-Bending 4. Metal Stampings a. Bending b. Shear

  14. Good Stressesvs.Bad Stresses Good Stresses: 1. Directly opposite to the creating force (uni-directional) • Bending i. Torsion Springs ii. Leaf Springs b. Compression Springs i. Set Out c. Belleville Washers i. Die Roll St1 & St2

  15. Good Stressesvs.Bad Stresses 2. Adding Compressive Stresses a. Shot Peening Compression Springs i. Non-Stress relieved • Shot Peening Compression Springs i. Stress relieved c. Leaf Springs (one side)

  16. Good Stressesvs.Bad Stresses Bad Stresses: 1. In direction of the creating force 2. Multi-Directional creating force a. Compression Springs b. Torsion Springs that open c. Compression Springs that are used in Extension

  17. Shot PeeningHow Does it Work

  18. Shot Peening How Does it Work What is important: 1. Intensity-Almen Strip 2. Coverage-Optical Examination Negative Consequences: 1. Poor Coverage (Competing Fields) 2. Bending Stresses Post Peening

  19. Stress RelievingHow Does it Work 1. Equalizing Energy Fields a. Under Stress Relieving-Some Stress Remain b. Optimum occurs @ Material Change (tempered material) c. Equilibrium between strain strengthening and forming 2. Restoration of Physical Properties

  20. IS There a Difference inCoiling MethodsResidual Stresses? • Single Point Coiling • Dual Point Coiling • Forming Through the Quill Proper Stress Relieving is Energy Dependent Not Related to Forming The forming method could effect other characteristics but is not stress related

  21. AIAG CQI-9 RequirementsforStress Relieving of Springs E1.2 Continuous strip chart and/or data loggers Systematic requirement to provide proof of temperature exposure Physical Control continuous SPC E2.4 Temperature Uniformity Surveys (TSU) shall be performed annually and after major re-build Systematic requirement to provide proof of temperature is controlled with in tolerance limits in every part of the heating chamber Physical Control continuous SPC control charts are definitive documentation in real time with no time lap

  22. E3.1 Monitor primary temperature control instruments requiring over and under temperature control alarms and a sign off every 2 hours or between lots Systematic requirement to provide proof that temperature does not go over or under set limits and documentation that it is Measured to be accurate every 2 hours Physical Control continuous SPC control charts are definitive documentation in real time with no time lap E3.6 Monitor time in furnace cycle or belt speed twice/shift and after any change in belt speed Systematic requirement to provide proof that temperature was reached and was at the proper temperature for the prescribed time Physical Control continuous SPC control charts are definitive documentation that all the parts are exposed to the temperature for the appropriate amount of time

  23. AIAG CQI-9 RequirementsforStress Relieving of Springs E4.1 Microstructure shall be checked with each production run or each shift at a minimum Systematic requirement to provide metallurgical proof that exposure Physical Control after SMI review with AIAG the realized that this was not necessary as there was no way to optically see a difference Note: With the establishment of an industry standard any deviation from the standard could affect your exposure in any product liability claim

  24. What Did We Talk About? 1. Basic metallurgy and how/why we get residual stresses 2. How residual stresses are created 3. Good stresses vs. bad stresses 4. Shot Peening 5. How does stress relieving effect residual stresses 6. Is there a difference in coiling methods 7. CQI-9 and why is it related to residual stresses a. Systematic control b. Physical control

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