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Mechanical Attachment of Fasteners

to UHSS Materials

Rob Edwards

PROFIL System Incorporated

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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

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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

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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

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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

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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

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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

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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

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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

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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

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

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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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Second Generation UHSS

1.8 mm PHS 1500 MPa

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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

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Thank you for your attention

Questions and Discussion

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North American

Light Vehicle Metallic Material Trends

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