By: Dan Sebastian

1.
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

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

Pearlite
Ferrite
Lower Bainite

Martensite

Stress-Strain Diagram
Bending Stresses
Torsional Stresses
Compressive Stresses
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

Good Stresses vs.
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 S t1
& S t2

Good Stresses vs.
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)

Good Stresses vs.
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

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

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

IS There a Difference in
Coiling Methods
Residual 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

AIAG CQI-9 Requirements for
Stress 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

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

AIAG CQI-9 Requirements for
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 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

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