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w w w . a u t o s t e e l . o r g
Mechanical Attachment of Fasteners
to UHSS Materials
Rob Edwards
PROFIL System Incorporated
w w w . a u t o s t e e l . o r g
Agenda
1. Mechanical Fastener Basics
2. Evolution: Market Demands
3. Response to Evolution
4. UHSS Challenges
5. Initial Response to UHSS
6. Second Generation UHSS
7. Conclusion
Mechanical Attachment of Fasteners to UHSS Materials
w w w . a u t o s t e e l . o r g
Joining Configuration
Clinch Rivet
Panel is packed into the fastener Fastener is formed around the panel
Panel Preparation
Self-Pierce Pre-Pierce and Form
Mechanical Fastener Basics
w w w . a u t o s t e e l . o r g
Evolution: Market Demands
IF
Mild IS
IF
BH
TRIP
HSLA
CMn
DP MART
High Strength Steels Mild Steels AHSS UHSS
And Beyond 70 Years of Evolution
Innovation Drivers
Material advancements Structural demands
CAFE standards Assembly efficiencies
1500+
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Response to Evolution
IF
Mild IS
IF
BH
TRIP
HSLA
CMn
DP MART
High Strength Steels AHSS UHSS
Rectangular
Pierce Nuts
Mild Steels
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Response to Evolution
IF
Mild IS
IF
BH
TRIP
HSLA
CMn
DP MART
AHSS UHSS Mild Steels High Strength Steels
Round Clinch
Fasteners
Rectangular
Pierce Nuts
w w w . a u t o s t e e l . o r g
Response to Evolution
IF
Mild IS
IF
BH
TRIP
HSLA
CMn
DP MART
UHSS Mild Steels High Strength Steels AHSS
Round Clinch
Fasteners
Rectangular
Pierce Nuts
Round Rivet
Fasteners
w w w . a u t o s t e e l . o r g
Response to Evolution
IF
Mild IS
IF
BH
TRIP
HSLA
CMn
DP MART
AHSS Mild Steels High Strength Steels UHSS
Round Clinch
Fasteners
Rectangular
Pierce Nuts
Round Rivet
Fasteners
1500+
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UHSS Challenges
Fastener Challenges in UHSS
1000+ MPa
Hot form / post quench
– Dimensional variability due to thermal deformation
Post quench holes require special processing
– Laser cutting
– Non-traditional piercing
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Initial Response to UHSS
Panel Preparations
No Emboss
Laser Hole
Emboss
Laser Hole
No Emboss
No Hole
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Initial Response to UHSS
Thermal Deformation – Panel Preparation
Pre-press hardening
Installed fastener position
Press hardening
Laser cutting
Case 1 Case 2
Intended Actual Actual
Emboss
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Initial Response to UHSS
No Emboss – Laser Hole
Laser cut hole after press hardening
punch
nut
die button
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Initial Response to UHSS
Emboss – Laser Hole
Emboss formed during press hardening
Laser cut hole after hardening
punch
nut
die button
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Initial Response to UHSS
Emboss – Laser Hole
Emboss formed during press hardening
Laser cut hole after hardening
punch
stud
die button
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Initial Response to UHSS
Series Production Application
Emboss formed during press hardening
Laser cut hole after hardening
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Initial Response to UHSS
Rivet Performance
1.5 mm sheet thickness
RND Nut - M6
Mild Steel
(210 MPa)
HSS
(600 MPa)
UHSS
(1500 MPa) OEM – A OEM – B
Destruct Test Test
Torque (Nm) 31.8 31.9 27.2 15.5 14.0
Push-Out (kN) 5.9 8.1 12.8 na 4.9
Property Class 8 10 10 10 8
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Second Generation UHSS
Goal: Improve Manufacturing Efficiency
Eliminate laser hole cutting
– Time savings
– Solves positional accuracy issues – hole and emboss
Eliminate emboss positional deviation from thermal deformation
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Second Generation UHSS
Development Criteria
1. Self-piercing
2. Post-quenching installation – 1500 MPa minimum
3. Minimal stress concentration resulting from piercing
4. > 30 Nm torque performance
5. >2.0 kN push-out performance
w w w . a u t o s t e e l . o r g
Second Generation UHSS
Development Criteria
1. Self-piercing
2. Post-quenching installation – 1500 MPa
minimum
3. Minimal stress concentration resulting from
piercing
4. > 30 Nm torque performance
5. >2.0 kN push-out performance
w w w . a u t o s t e e l . o r g
Second Generation UHSS
Development Criteria
1. Self-piercing
2. Post-quenching installation – 1500 MPa
minimum
3. Minimal stress concentration resulting from
piercing
4. > 30 Nm torque performance
5. >2.0 kN push-out performance
w w w . a u t o s t e e l . o r g
Second Generation UHSS
Development Criteria
1. Self-piercing
2. Post-quenching installation – 1500 MPa
minimum
3. Minimal stress concentration resulting from
piercing
4. > 30 Nm torque performance
5. >2.0 kN push-out performance
w w w . a u t o s t e e l . o r g
Second Generation UHSS
Development Criteria
1. Self-piercing
2. Post-quenching installation – 1500 MPa
minimum
3. Minimal stress concentration resulting from
piercing
4. > 30 Nm torque performance
5. >2.0 kN push-out performance
Cutting edge at 20 draft, creating an under cut to set the panel material into,
achieving push-out performance
00 20
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Second Generation UHSS
Benchmarking
Development nut vs weld nut - dynamic load durability
Laser cut hole preparation vs self-pierced hole
Microstructure grain orientation bias
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Second Generation UHSS
Benchmarking
Development nut vs weld nut - dynamic load durability
Development Nut Weld Nut
w w w . a u t o s t e e l . o r g
Second Generation UHSS
Benchmarking
Laser cut hole preparation vs self-pierced hole
Self-Pierced
1.000
10.000
100.000
1.000 10.000 100.000 1.000.000 10.000.000
Number of Cycles n
Pe
ek
Fo
rce
F [
N]
Nut: Pierce Nut RSE08, Self-Piercing / Pre-Pierced by Laser Sheet metal: USIBOR, 1.7 mm Counterpart: DC04, 5 mm Screw: M8 PC 8.8 with flange Fastening Torque: 24 Nm Load Transmission: Chuck
Forth Ratio Fu/Fo: R = 0.1
Laser Cut
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Second Generation UHSS
Benchmarking
No microstructure grain orientation bias
00 Orientation 450 Orientation
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Second Generation UHSS
Installation tooling and feeding equipment to support production
Photo 1 Photo 2
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Conclusion
Self-piercing is an ideal process for press-hardened steel
Push out and torque values are production worthy
Dynamic properties are superior to weld fasteners
No cracking has been observed during micro inspection
Feeding equipment and installation tooling are production ready
Die button has demonstrated acceptable performance at over 10,000 hits
This is the Next Generation of UHSS fasteners