TALAT Lecture 4102: Clinching

TALAT Lecture 4102

Clinching

13 pages, 14 figures

Basic Level

prepared by Lothar Budde, Universität-Gesamthochschule Paderborn

Objectives: − to describe the detailed processes of single-step and multiple-step clinching − to show the differences of the various clinching methods concerning the amount of

shearing − to illustrate the major differences in mechanical properties of clinch joints compared

with resistance spot welds Prerequisites: − General mechanical engineering background − TALAT Lecture 4101 Date of Issue: 1994 EAA - European Aluminium Association

TALAT 4102 2

4102 Clinching

Table of Contents

4102 Clinching .............................................................................................................2

4102.01 Definitions and Classifications................................................................. 3

• Definition of the Term Clinching With or Without Local Incision ....................3

• Trade Names for Clinching Methods...................................................................3

• Selected Standard Tool Combinations for Clinching ..........................................4

• Criteria for Classifying Clinching Processes .......................................................5

4102.02 The Clinching Process .............................................................................. 6

• Process Steps in Single-Step Clinching with Local Incision ...............................6

• Process Steps During Two-Step or Multi-step Clinching with Local Incision...7

• Geometry of a Clinched Joint Formed by Clinching With or Without Local

Incision.....................................................................................................................8

• A Comparison of the Properties of Clinched Joints and Spot Welded Joints.....9

• Process Steps of a Single-Step Clinching Process without Local Incision (Die

with Movable Parts).................................................................................................9

• Process Steps of a Single-step Clinched Joint without Local Incision (Die

without Movable Parts)..........................................................................................10

• Formation of a Flat Clinch Element without Local Incision..............................11

• Comparison of Clinch Elements with Varying Local Incisions and Formed Parts

12

• Holding and Stripping Systems for Clinching ...................................................12

4102.03 Literature/References ............................................................................. 13

4102.04 List of Figures............................................................................................ 14

TALAT 4102 3

4102.01 Definitions and Classifications

• Definition of the term clinching with or without local incision • Trade names for clinching methods • Selected standard tool combination for clinching • Criteria for classifying clinching processes

• Definition of the Term Clinching With or Without Local Incision Compared to the state of development of conventional fastening methods, the clinching technology for joining shaped sheet components and sections is still new, although the first patent for this process was granted as early as 1897. Clinching is a direct joining of materials using the forming technology. A flattening or material flow (impact extrusion) creates a quasi form locked joint (Figure 4102.01.01).

Training in Aluminium Application Technologies

alu Definition of the Term Clinchingwith or without Local Incision 4102.01.01

Source: Budde

With Local Incision

Without Local Incision

is a direct forming technology for joining materialsin the form of sheet, tube and profiles using asingle or multi-step fabricating process with a common displacement combined with local incision or plastic deformation and folowed by cold compression, so that a quasi form lockingjoint is produced by flattening or flow pressing.

Clinching

• Trade Names for Clinching Methods Within the scope of the general definition for clinching, each company is free to choose an own name, which generally reflects the tool design used for the fastening process. As a result, the individual process variations used in the metal processing industry are better known under their trade names (Figure 4102.01.02).

TALAT 4102 4

• Selected Standard Tool Combinations for Clinching A selection of standard tools for clinching based on local incision and/or forming processes illustrates the high state of the art for these mechanical fastening methods (Figure 4102.01.03). The joint strengths that can be attained depend, among others, on tool design so that the tools for the individual clinching processes are being constantly developed and improved.

alu


Source: DIN 8593, Part 5

(Single or Multi-Step) Clinching

With Local Incision Without Local Incision

- "CLINCH" - System- "S-" and "H-DRUCKFÜGE" - System- "LANCE-N-LOC" - System- "STITCH" - System- "T-SPOT-CLINCHING" - System- "PUNKTFÜGE" - System- ................................- ................................

- "TOX" - System- "O-" and "R-DRUCKFÜGE" - System- "TOG-L-LOC" - System- "RIVET" - System- "R-SPOT-CLINCH" - System- ...............................- ...............................- ...............................

Trade Names for Clinching Methods 4102.01.02

TALAT 4102 5


alu Selected Standard Tool Combination for Clinching 4102.01.03

Source: Budde

Cutting Punch Punch Forming Punch Forming Punch

Cutting Die Spreading Die Form Die Form Die

Clinch-Process DRUCKFÜGE-Process RIVET-Process TOX-Process

CuttingLaminae

Anvil

CompressingPunch

O-Rings

WedgingPunch

• Criteria for Classifying Clinching Processes Based on the DIN standard 8593, part 5, it is possible to characterise clinching either according to the kinematics of the tool components (single or multi-step clinching) or the shape of the joint itself (clinching with or without local incision, see also Figure 4102.01.04).

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Classifying the Clinching Process

4102.01.04Criteria for Classifying Clinching Processes

According to the Kinematics of the Tool PartsIn Single and Multi-Step Clinching

According to the Joining Element FormIn Clinching with and without Local Incision

TALAT 4102 6

4102.02 The Clinching Process

• Process steps in single-step clinching with local incision • Process steps during two-step or multi-step clinching with local incision • Geometry of a clinched joint formed by clinching with or without local

incision • A comparison of the properties of clinched joints and spot welded joints • Process steps of a single-step clinching process without local incision (die

with movable parts) • Process steps of a single-step clinched joint without local incision (die

without movable parts) • Formation of a flat clinch element without local incision • Process steps of a multi-step clinched joint without local incision • Comparison of clinch elements with varying local incisions and formed

parts • Holding and stripping systems for clinching

• Process Steps in Single-Step Clinching with Local Incision Clinching with local incision creates an undetachable (permanent) joint under the combined action of shear and penetration processes, in which the penetration and incision limit the joint region, and a cold compression process, in which the sheet material pushed out of the sheet plane is compressed and flattened in such a manner that a quasi form locked joint is created. The single-step clinching process derives its name from the fact that the joint is created during an uninterrupted stroke of a single tool component (Figure 4102.02.01).

TALAT 4102 7


alu Process Steps in Single-Step Clinching with Local Incision 4102.02.01

Source: Budde

Die

Joined pa rts

Punch

• Process Steps During Two-Step or Multi-step Clinching with Local Incision The clinch joining element of a two-step or multi-step clinch process with local incision is created under the action of successive motions of the tool components . Although the multi-step clinching process works, unlike the single-step clinching process, with a single tool combination for the corresponding joint geometry, this process, because of its more complicated alignment technique, has not been very successful till now (Figure 4102.02.02).

TALAT 4102 8


alu Process Steps during Two-Step or Multi-Step clinchingwith Local Incision 4102.02.02

Cutting Die

CompressingPunch

Parts to be joined

Cutting Punch

Source: Budde

• Geometry of a Clinched Joint Formed by Clinching With or Without Local Incision

In recent years, a large number of fastening elements, based on the principles of the clinched joint element, have been developed. Characteristic for all these recent developments is an increase in the joint strength resulting from the enlarged shear area as well as from the reduction of the locally incised part which is replaced by a corresponding increase in the plastically formed part (see Figure 4102.02.03).

Geometry of a Clinched Joint Formed by Clinching with or without Local Incision 4102.02.03

increasing the sheared area

decreasing the sheared area

Source: Budde

alu


TALAT 4102 9

• A Comparison of the Properties of Clinched Joints and Spot Welded Joints Results of experiments with single-element clinch fastenings with various locally incised and formed parts as well as various shear areas demonstrate that under quasi static and dynamic impact loadings, these joints do not attain the strength of a single spot welded joint (see Figure 4102.02.04). This result is also valid for clinch joints with enlarged clinched elements. On the other hand, in the case of dynamic loading, the strength of clinched joints is superior to that of spot welded joints, especially if the local incision is reduced in favour of the formed part, thereby reducing the notch action.


alu 4102.02.04

Source: Budde

180

%

0

40

80

120

160

Frac

ture

Stre

ngth

Rea

pted

Cyc

le F

orce

Frac

ture

Wor

kAlMg5Mns = 1.25 mm

V=10 mm/ min V = 5.3 m/s

R=0.0 f=80Hz

1 32 4 1 32 4 1 32 4

1 32 4

180

%

0

40

80

120

160

180

%

0

40

80

120

160

SW CL with Local Incision

CL with ReducedLocal Incision

CL withoutLocal Incision

A Comparison of the Properties of Clinched Joints and Spot Welded Joints

• Process Steps of a Single-Step Clinching Process without Local Incision (Die with Movable Parts)

In the clinching process without local incision, a combined penetration and clinch operation (whereby the fastened region is limited by the penetration) is followed by a cold compression process (whereby the displaced volume of material is flattened by compression) leading to a quasi form locked joint formed by material flow (impact extrusion) (see Figure 4102.02.05). The displaced material of the clinch joint, relevant for the fastening strength, is formed by the varying flow characteristics of the material on the die and punch sides.

TALAT 4102 10


alu Process Steps of a Single-Step Clinching Processwithout Local Incision (Die with Movable Parts) 4102.02.05

RubberRing

Parts to be joined

Die with MovableParts

Source: Budde

• Process Steps of a Single-step Clinched Joint without Local Incision (Die without Movable Parts)

Tool systems with and without moving parts have been designed for the single-step clinching process without local incision . During the single-step clinching process with movable die parts, the different flow characteristics of the material of the parts to be joint is caused by a yielding of the sheets. On the other hand, in the single-step clinching process without movable parts, a grooved ring in the die forces the displaced material of the sheets to flow differently (Figure 4102.02.06). The advantage of the die without moving parts lies in the absence of wear of the components. The disadvantage is that oiled aluminium sheets can lead to the formation of a "hydrostatic cushion" in the closed die, leading eventually to the destruction of the die.


aluProcess Steps of a Single-Step Clinched Joint

Without Local Incision (Die Without Moveable Parts)

Punch

JoinedParts

Die withoutMoveable Parts

4102.02.06

Source: Budde

TALAT 4102 11

• Formation of a Flat Clinch Element without Local Incision New variations of the clinching process which overcome the process limitations of the single-step and multi-step clinching process with and without local incision, are being developed constantly. The basic principle, however, remains unchanged. Thus, it is possible to flatten the typical edged form of the clinch element without local incision in a second operation, so that this side can be used for the visible surface (Figure 4102.02.07).


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Starting Condition Intermediate Stage End Condition

FixingPunch

JoinedParts

CounterPunch

Round Form Flat Form

Formation of a Flat Clinch Elementwithout Local Incision 4102.02.07

Source: Budde

Similar to clinching with local incision, it is possible, in a two-step or multi-step process, to produce a clinch element without local incision (Figure 4102.02.08). The two-step or multi-step process for clinching uses about 20 % less energy than that required for single-step clinching, due to the fact that the penetration and compression (flattening) steps of the former occur in consecutive steps.


aluProcess Steps of A Multi-Step Clinched Joint

without Local Incision 4102.02.08

DisplacingPunch

Parts to bejoined

DisplacingDie

CompressingPunch

Source: Budde

TALAT 4102 12

• Comparison of Clinch Elements with Varying Local Incisions and Formed Parts

As illustrated in the comparison of clinch elements with varying local incisions and formed parts, reducing the local incision part in favour of the formed part is coupled with a reduction of notch effect - i.e. primarily an improved behaviour of the joint under dynamic loading - as well as reduced chip production. At the same time, however, this leads to the need for tools able to meet the added requirements.


alu

Source: Budde

4102.02.09Comparison of Clinch Elements with VaryingLocal Incisions and Formed Parts

ClinchingTool

ToolControl

ChipProduction

JoiningElement

Infuence ofJoining Part

Surface

LocalIncision

FormedPart

GeometricNotchEffect

This means that reducing the incision part amounts to an increased effort in aligning punch and die (Figure 4102.02.09). In order to align clinching tools accurately for joints without local incision, special clamps with double-C frames have been developed, making the use of clinching robots possible.

• Holding and Stripping Systems for Clinching A faultless holding system, a prerequisite for producing high quality clinching, must clamp the aligned parts, so that the material flow during the clinching process does not cause a movement of the position of joining groups relative to each other. Appropriate holding systems can be used to clamp the joining parts as well as strip the finished part from the dies.

TALAT 4102 13

Just as in the case of clinching, holding systems must also be adapted for use in punch riveting (Figure 4102.02.10).


alu

Single-Step Clinchingwith Local Incision

Single-Step Clinchingwithout Local Incision

Holding and Stripping Systems for Clinching 4102.02.10

4102.03 Literature/References 1. Budde, L. Untersuchungen zur Kombination quasi-formschlüssiger und

stoffschlüssiger Verbindungsverfahren. Dissertation Uni-GH-Paderborn, 1989

2. Liebig, H.P. Nieten und Durchsetzfügen. Blech Rohre Profile 39 (1992) 3, 220-221

3. Boldt, M. Mechanisches Verhalten von Durchsetzfüge- und Punktschweißverbindungen bei quasistatischer und dynamischer Beanspruchung. Dissertation Uni-GH-Paderborn, 1992

4. Steimmel, F. Einfluß der Blechoberflächen auf das Festigkeitsverhalten. Bänder Bleche Rohre 31 (1990) 11, 33-36

5. Schmid, G. Methoden der Qualitätssicherung beim Durchsetzfügen. Bänder Bleche Rohre 32 (1991) 61-64

6. Schröder, D. Neue Verbindungstechniken für Aluminiumwerkstoffe. Bänder Bleche Rohre 32 (1991) 5, 83-87

7. Beyer, R. Kostengünstig und technisch interessant - Druckfügen. Industrie-Anzeiger 110 (1988) Nr. 16, 26-29

8. Reuter, H. Erfahrungen mit dem Durchsetzfügen in der Automobilindustrie. Tagungsband “Umformtechnisches Fügen von Blech“, Chemnitz 1990

9. Bober, J. und Liebig, H.P. Prozeßanalyse beim Druckfügen. Bänder Bleche Rohre 31 (1990) 10, 143-146

TALAT 4102 14

4102.04 List of Figures

Figure No. Figure Title (Overhead) 4102.01.01

Definition of the Term Clinching with or without Local Incision

4102.01.02 Trade Names for Clinching Methods 4102.01.03 Selected Standard Tool Combination for Clinching 4102.01.04 Criteria for Classifying Clinching Processes 4102.02.01

Process Steps in Single-Step Clinching with Local Incision

4102.02.02 Process Steps during Two-Step or Multi-Step Clinching with Local Incision 4102.02.03 Geometry of a Clinched Joint Formed by Clinching with or without Local

Incision 4102.02.04 A Comparison of the Properties of Clinched Joints and Spot Welded Joints 4102.02.05 Process Steps of a Single-Step Clinching Process without Local Incision (Die

with Movable Parts) 4102.02.06 Process Steps of a Single-Step Clinched Joint without Local Incision (Die

without Movable Parts) 4102.02.07 Formation of a Flat Clinch Element without Local Incision 4102.02.08 Process Steps of a Multi-Step Clinched Joint without Local Incision 4102.02.09 Comparison of Clinch Elements with Varying Local Incisions and Formed

Parts 4102.02.10 Holding and Stripping Systems for Clinching

Education

TALAT Lecture 4102: Clinching