By: Dan Sebastian

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

Basic Metallurgy Iron-Carbon Phase DiagramTTT Curves

FCC Structure

BCC Structure

BCT Tetragonal Structure

Size Effect of Cubic Structure

Time Temperature Transformation (TTT)

Face Center Cubic (FCC) Structure Austenite

Body Center Cubic (BCC) Structure

Pearlite

Ferrite

Lower Bainite

Body Center Tetragonal Cubic (BCT) Structure

Martensite

Martensite is 4.3 % larger by volume

How Residual Stresses are Created

Stress-Strain DiagramBending Stresses

Torsional Stresses

Compressive Stresses

Multi-Stresses

Bending Stress

Torsional Stress

Compressive Stresses

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

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

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)

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

Shot Peening

How Does it Work

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

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

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

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

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

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

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