Theory of Residual Stresses, Stress Relieving and CQ19
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Transcript of Theory of Residual Stresses, Stress Relieving and CQ19
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By: Dan Sebastian
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What are we going to talk about1. 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 controlb. Physical control
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Basic Metallurgy Iron-Carbon Phase DiagramTTT Curves
FCC Structure
BCC Structure
BCT Tetragonal Structure
Size Effect of Cubic Structure
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Time Temperature Transformation (TTT)
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Face Center Cubic (FCC) Structure Austenite
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Body Center Cubic (BCC) Structure
Pearlite
Ferrite
Lower Bainite
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Body Center Tetragonal Cubic (BCT) Structure
Martensite
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Martensite is 4.3 % larger by volume
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How Residual Stresses are Created
Stress-Strain DiagramBending Stresses
Torsional Stresses
Compressive Stresses
Multi-Stresses
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Bending Stress
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Torsional Stress
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Compressive Stresses
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Multi-Stresses1. Forces vectors are in different direction to the residual stresses
2. Coil springs
a. Torsionb. Bending
c. Compressive
d. Shear
3. Torsion Springs-Bending
4. Metal Stampings
a. Bending
b. Shear
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Good Stressesvs.
Bad Stresses
Good Stresses:
1. Directly opposite to the creating force (uni-directional) a. Bending
i. Torsion Springs
ii. Leaf Springs
b. Compression Springs
i. Set Out
c. Belleville Washers
i. Die Roll St1 & St2
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Good Stressesvs.
Bad Stresses
2. Adding Compressive Stresses
a. Shot Peening Compression Springs
i. Non-Stress relieved
b. Shot Peening Compression Springs
i. Stress relieved
c. Leaf Springs (one side)
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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
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Shot Peening
How Does it Work
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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
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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
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IS There a Difference inCoiling Methods
Residual Stresses?
• Single Point Coiling
• Dual Point Coiling• Forming Through the Quill
Proper Stress Relieving is Energy DependentNot Related to Forming
The forming method could effect other characteristics but is not stress related
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AIAG CQI-9 Requirementsfor
Stress Relieving of SpringsE1.2 Continuous strip chart and/or data loggers
Systematic requirement to provide proof of temperature exposurePhysical 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 heatingchamberPhysical Control continuous SPC control charts are definitive documentation in real time with no time lap
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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 doesnot go over or under set limits and documentation that it isMeasured to be accurate every 2 hoursPhysical 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 timePhysical Control continuous SPC control charts are definitivedocumentation that all the parts are exposed to the temperature for the appropriate amount of time
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AIAG CQI-9 Requirementsfor
Stress 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 thiswas not necessary as there was no way to optically see a difference
Note: With the establishment of an industrystandard any deviation from the standard could
affect your exposure in any product liability claim
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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