This lecture describes the combination of mechanical joining with adhesive bonding with respect to application criteria, productions considerations and resultant properties. General mechanical engineering background and familiarity with the subject matter covered in TALAT This lectures 4101- 4104 is assumed.

1. TALAT Lecture 4105
Combination of Joining Methods
16 pages, 19 figures
Basic Level
prepared by Lothar Budde, Universität-Gesamthochschule Paderborn
Objectives:
− to describe the combination of mechanical joining with adhesive bonding with
respect to application criteria, productions considerations and resultant properties
Prerequisites:
− General mechanical engineering background
− TALAT lectures 4101 - 4104
Date of Issue: 1994
 EAA - European Aluminium Association

2. 4105 Combination of Joining Methods
Table of Contents
4105 Combination of Joining Methods ..............................................................2
4105.01 Application Criteria.................................................................................. 3
Comparison of Functional Characteristics of Different Fastening Technologies ....3
Classification Index of Joints...................................................................................4
Advantages of Combined Joint Types .....................................................................4
Properties of Elementary Joints ...............................................................................5
Main Advantages and Disadvantages of Adhesive Joining .....................................5
Fold-Adhesive Joints ...............................................................................................6
Examples of Combined Joints Used in the Aircraft Industry ..................................6
Combination of Material Locking and Form Locking Joints...................................7
Fractured Surfaces of Combined Joints after Shear Testing....................................8
4105.02 Production Considerations...................................................................... 8
Production of Combined Joints................................................................................8
Production Variants for Combined Joints................................................................9
Technical Operations in the Production of an Adhesive-Clinch Joint Combination
...............................................................................................................................10
Methods of Producing Adhesively Joint and Clinched Fastenings........................10
Form of Clinched Joints With and Without Adhesives .........................................11
4105.03 Properties of Combination Joints.......................................................... 12
Criteria for the Use of Combined Joining Technologies .......................................12
Results of Fatigue Tests with Adhesive Joints ......................................................13
Impact Strength of Different Joints........................................................................13
Shear Strength of Different Joints With and Without Ageing...............................14
Comparison of Properties of Different Joining Technologies ...............................15
4105.04 Literature/References ............................................................................ 15
4105.05 List of Figures............................................................................................ 16
TALAT 4105 2

3. 4105.01 Application Criteria
• Comparison of functional characteristics of different fastening
technologies
• Classification index of joints
• Advantages of combined joint types
• Properties of elementary joints
• Main advantages and disadvantages of adhesive joining
• Fold-adhesive joints
• Examples of combined joints used in the aircraft industry
• Combination of material locking and form locking joints
• Fractured surfaces of combined joints after shear testing
Comparison of Functional Characteristics of Different Fastening Technologies
The functional characteristics of the different fastening technologies is important, since
this enables us to choose the most appropriate joining technology for light constructions
which are being developed and used increasingly.
A large number of the so-called "classical" fastening technologies currently in use fulfil
these requirements only partly, making it necessary to use solutions which are a
compromise (Figure 4105.01.01).
Joining
Technology Adhesive
Spot Welding Clinching Riveting
Joining
Characteristics
Functional Load-Carrying Load-Carrying Load-Carrying Load-Carrying
Characteristics
Fixing Fixing Fixing Fixing
Sealing Elec. Conduct. Elec. Conduct. Elec. Conduct.
Isolating Relatively Low Relatively Low Relatively Low
Fatigue Strenght Fatigue Strenght Fatigue Strenght
Damping
Equalising
Good Fatigue
Strength
Source: Budde
Comparison of Functional Characteristics
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of Different Fastening Technologies
4105.01.01
Training in A luminium Application Technologies
TALAT 4105 3

4. Classification Index of Joints
The joining technology used in light constructions should be such that the classification
index of the joint, a value for the functional characteristics relative to the corresponding
base material of the corresponding material combination, optimally approaches the
limiting value of 1 (Figure 4105.01.02).At increased stresses, the principles of force
actions, the reduction of disadvantageous notch effects, the constancy of the material
properties and the joint reliability become increasingly important.
A consequence of the above mentioned is that there is an increasing tendency to use
aluminium for highly stressed constructions.
Functional Properties
of the Joint
Functional Properties
of the Base Material
1
Increasing Stress Levels
Source: Wittke, Füssel
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Classification Index of Joints 4105.01.02
Training in Aluminium Application Technologies
Advantages of Combined Joint Types
A combination of joint types can be used, among others, to take advantage of the
specific material properties of aluminium, thus making it possible to optimise the joint
quality, allow certain materials and material combinations to be joint and/or to simplify
the fastening process. A combination of different joint types can be used either to
improve the statical and dynamical properties of the joint or to guarantee leakproof
joints (Figure 4105.01.03).
Combined Joints
Improving the Static and Dynamic Properties of Joints!
Guaranteeing the Joint Gas and Fluid Tightness!
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Advantages of Combined Joint Types 4105.01.03
Training in Aluminium Application Technologies
TALAT 4105 4

5. Properties of Elementary Joints
Depending on the load carrying capacity and the design of the light construction, the
types of joints used may be of the material locking kind or of the force or shape locking
type (Figure 4105.01.04). The choice of the elementary joints to be used in combination
is based on the principle of elimination. According to this principle, those particular
combinations of joints which do not fulfil any one out of a required list of criteria, are
eliminated.
Elementary Joints
Form Locking Force Locking Material Locking
Strength
Temperature
Stability
Sealing Props.
Safety against
Loosening
Detachability
Corrosion
Resistance
Electrical /Tthermal
Conductivity
Function Fulfilled
Function not Fulfilled
Source: Wittke, Füssel
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Properties of Elementary Joints 4105.01.04
Training in Aluminium Application Technologies
Main Advantages and Disadvantages of Adhesive Joining
Adhesive joining plays an important role in the design of ultralight constructions. The
main advantages of adhesive joints are the transmission of forces over large areas and
the possibility of joining different and non-metallic materials as well as material
combinations. The disadvantage of adhesive joining is the fact that, as a rule, the
components have to be held rigidly in a fixture during the hardening process. In addition
to this, adhesive joints have a limited high-temperature strength (Figure 4105.01.05).
One-Sided Overlapped Adhesive Joints
Advantages: Disadvantages:
- Force Transmission over - Sensitive to Peeling Forces
Large Areas
- No Thermal Influence of - Aging Problems
Material Microstructure
- Suitable for Different Types - Limited Warm Strength
of Materials and for Non-Metals
Source: Budde
Main Advantages and Disadvantages
alu
4105.01.05
Training in Aluminium Application Technologies of Adhesive Joining
The specific disadvantages of adhesive joining can be compensated for by using a
TALAT 4105 5

6. combination of this material locking joint type with force and shape locking types of
joints. Examples of such combined joints can be found in the automotive (mass
production) and aircraft (small series production) industries.
Fold-Adhesive Joints
In the automotive industry, the combination of adhesive joining and folding can be used
for fastening car-body parts. If applied properly, the folded and adhesively joint parts
possess the combined advantages of both fastening technologies (Figure 4105.01.06).
The main advantage of folded joints is that these can be loaded immediately, i.e., a
rational production is possible. The surfaces of the folded joints produced remain
smooth and clean. The additional use of adhesives in the fold leads to leakproof joints.
At the same time, the adhesive used improves the damping characteristics of the whole
aluminium construction.
Folding and Adhesive Joining in Body Building
Adhesive Joint
Function: Sealing
Interior Part
Exterior Part
Folding Joint
Aluminium Sheet
Function: Strength
Soucre: Hoesch Company Document
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Fold-Adhesive Joints 4105.01.06
Training in Aluminium Application Technologies
Examples of Combined Joints Used in the Aircraft Industry
Some adhesive and sealed joints are prone to a deleterious ageing, especially if exposed
to industrial atmosphere, water, solvents or aggressive chemicals.
Examples of combined adhesive and sealed joints used in aircraft construction illustrate
how this deleterious effect can be reduced by the judicious choice of adhesive and
sealant, the long-time testing of the joints, a specific design as well as the application of
protective layers on the surface of the adhesive and sealed joints (Figure 4105.01.07).
TALAT 4105 6

7. Adhesively Fastened Longitudinal Stiffener
Adhesive
Sealant Coating
Reinforced Rivet-Adhesive Joint
Surface Sealant
Adhesive
Sealant Coating
Sealed Riveted Joints
Sealant
Adhesive
Sour ce: Endlich
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Training in Aluminium Application Technologies
Combination Joints Used in the Aircraft Industry 4105.01.07
Combination of Material Locking and Form Locking Joints
Joints, consisting of a combination of both adhesive joining and locally active fastening
methods, mostly use spot welding or mechanical joining methods like riveting and
clinching. In the automotive industry, spot welding is used mainly to shorten production
times in spite of the long hardening times of the adhesives. The combination of adhesive
and riveted joints is used primarily in the aircraft industry for parts subject to dynamic
loading (Figure 4105.01.08).
Clinching with or without local incisions is an interesting technology which could be
used for combined joints and shall, therefore, be illustrated for combinations with
adhesive joining. The following remarks generally apply also to other mechanical
fastenings.
Adhesive Joining
(Material Locking)
+ Spot Welding + Conventional Riveting + Clinching
(Material Locking) (Quasi Form Locking) (Quasi Form Locking)
Source: Budde
Combination of Material Locking and
alu
4105.01.08
Training in Aluminium Application Technologies Form Locking Joints
TALAT 4105 7

8. Fractured Surfaces of Combined Joints after Shear Testing
During the clinching process, aluminium shaped sheet components and profiles are joint
together according to the quasi form locking principle simply through the action of local
plastic material deformation without using auxiliary parts or thermally influencing the
microstructure.
Material spray, which occurs as a joint defect due to the high material pressure in the
spot welded region, thereby reducing the joint strength, is absent in joint combinations
of clinching and adhesive joining (Figure 4105.01.09).
35 mm
Spot Welding and
Adhesive Joining
Clinching and
Adhesive Joining
Source: Budde
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Fractured Surface of Combined Joints after Shear Testing 4105.01.09
Training in Aluminium Application Technologies
4105.02 Production Considerations
• Production of combined joints
• Production variants for combined joints
• Technical operations in the production of an adhesive-clinch joint
combination
• Methods of producing adhesively joint and clinched fastenings
• Form of clinched joints with and without adhesives
Production of Combined Joints
Joint combinations consisting of more than one elementary joint can be fabricated by
producing the individual joints either simultaneously or one after the other (see Figure
4105.02.01). This chronological order can influence the properties of the joint.
TALAT 4105 8

9. Fabricating
Combined Joints
No. of
Processes One Process Multiple Processes
Chronological
Order of Process Simultaneously Consecutively
Moment of
Reaching the Prior Prior Prior
During During During
Required to to to
Use Use Use
Properties Use Use Use
Source: Füssel
alu
Production of Combined Joints 4105.02.01
Training in Aluminium Application Technologies
Production Variants for Combined Joints
In principle, three variants are possible for the consecutive production of adhesive
joining and mechanical joining (see Figure 4105.02.02).
(4.) (4.) (3.)
(3.)
=RT..200°C =RT..200° =RT..200° (4.)
(2.)
(2.) (1.) (2.)
(1.) (1.)
(3.)
"Capillary Method"
Variant 1 Variant 2 Variant 3
1. apply adhesive 1. place parts together 1. apply adhesive
2. place parts together 2. mechanical joining 2. place parts together
3. mechanical joining 3. apply adhesive 3. curing adhesive
4. curing adhesive 4. curing adhesive 4. mechanical joining
Source: Stepanski
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Production Variants for Combined Joints 4105.02.02
Training in Aluminium Application Technologies
In the so-called "capillary" method, a mechanical joint is first prepared and then an
adhesive of low viscosity is brought into the joint crevice. In this variation - which is
characterised by a clear separation of the parts to be joint - the adhesive serves generally
as a sealant and/or as an inhibitor for corrosion.
The adhesive joining of sheet and profile parts followed by a mechanical fastening
process, the latter being used to improve the peeling strength of the joint, has till now
played only a secondary role.
Another fastening process has been found to be industrially most suitable for making
combined joints, especially for mass production. In this process, the adhesive is first
TALAT 4105 9

10. applied to the parts and then, before the adhesive hardens, followed by a mechanical
joining process which goes through the unhardened adhesive. The hardening then
follows as usual, depending on the type of adhesive used.
Technical Operations in the Production of an Adhesive-Clinch Joint Combination
A closer look at the individual process steps involved in the production of the combined
adhesive-clinch joint shows that the combined adhesive-mechanical joining process can
be easily integrated in the mass production of thin sheet constructions (Figure
4105.02.03).
Surface Adhesive Finished Part
Raw Parts Handle
Element Application
Fix
Join
Setting
Source: Budde
Operations in the Production
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of an Adhesive-Clinch Joint Combination 4105.02.03
Training in Aluminium Application Technologies
Methods of Producing Adhesively Joint and Clinched Fastenings
The advantage of using clinching instead of spot welding in combination with adhesive
joining is that the former allows the use of not only fluid and pasty adhesives but also of
adhesive foils and bands (Figure 4105.02.04).
Solid adhesives have special advantages, both as far as process technology as well as
health aspects are concerned.
TALAT 4105 10

11. Clinching and Adhesive Joining
Adhesive Fluid Pasty Solid
Combined With
Without Local With Local
Clinching
Incision Incision
Source: Budde
Methods of Producing Adhesively Joint and
alu
4105.02.04
Training in Aluminium Application Technologies Clinched Fastenings
Form of Clinched Joints With and Without Adhesives
Clinching without local incision can be used as the mechanical fastening partner for
adhesive joining using pasty adhesives. On the other hand, clinching with local incision
is used together with adhesive foils and bands.
The geometry of the joint element of combined clinched fastenings illustrates that in
spite of the presence of adhesives, an optimal form of the clinch joint is created,
assuming of course that an appropriate process technology is applied (Figure
4105.02.05).
Clinching with Without Adhesive With Adhesive Film
Local Incision
Clinching without
Local Incision Without Adhesive With Pasty Adhesive
Source: Budde
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Form of Clinched Joints with and without Adhesives 4105.02.05
Training in Aluminium Application Technologies
TALAT 4105 11

12. 4105.03 Properties of Combination Joints
• Criteria for the use of combined joining technologies
• Results of fatigue tests with adhesive joints
• Impact strength of different joints
• Shear strength of different joints with and without ageing
• Comparison of properties of different joining technologies
Criteria for the Use of Combined Joining Technologies
In principle, the choice of the combined technology, mechanical fastening and adhesive
joining, which may be used for joining in light constructions depends mainly on two
application criteria.
In mechanical fastenings combined with adhesive joining, the former is the main joining
process. The adhesive used serves primarily as a sealant, corrosion inhibitor and/or as a
damping material.
In adhesive joints combined with mechanical joining, the former is the main joining
process. The mechanical joining serves as a positioning (fixing) help and helps the
adhesive joint to withstand peeling forces and long-time static forces (Figure
4105.03.01).
Mechanical Joining Combined with Adhesive Joining
Clinching is the main joining process. The applied adhesive serves
primarily as sealant, corrosion protection and/ or damping material
and relieves the joint in regions where the force lines lie outside the
joining point.
Adhesive joining Combined with Mechanical Fastening
Adhesive joining is the main joining process. The mechanical joint
serves as a help in fixing and relieves the adhesive layer during
fabrication or peeling loads or long-time static loads.
Source: Budde
alu Criteria for the Use of Combined
Training in Aluminium Application Technologies Joining Technologies 4105.03.01
TALAT 4105 12

13. Results of Fatigue Tests with Adhesive Joints
The properties of the adhesive used are the main deciding criteria for the application.
Under quasi static, dynamic and impact loading, the load carrying capacity of, for
example, clinched adhesive joints compares well with that of spot welded joints (see
Figure 4105.03.02). Under the action of dynamic loads, the geometric notch effect of
the "point formed" joint element has a deleterious effect on the load carrying capacity of
the combined joint.
A Adhesive Joint B Spot Welded C Clinched-
Adhesive Joint Adhesive Joint
Pasty Epoxy
Resin Adhesive
N / mm2
f = 80 Hz / R =0,0
6,0
5,0
Force Amplitude
F 35
45
F
4,0
A
1,0
B 1,0
105
3,0
C
Al Mg 5 Mn
2,0
3 4 5 6 7 8
10 10 10 10 10 10
Source: Budde No. of Cycles
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Training in Aluminium Application Technologies
Results of Fatigue Tests with Adhesive Joints 4105.03.02
Impact Strength of Different Joints
Joints made with ductile adhesives having a high deformability and low strength behave
differently. Here again, depending on the loading, the joint strength is determined
mainly by the clinch joint (Figure 4105.03.03). By giving proper consideration to
factors like property profile and processing properties of the adhesive, it is basically
possible to design combined joints with properties which are a combination of the
individual properties of the joints.
TALAT 4105 13

14. A Spot Welding B Clinching C Adhesive Joining
with Adhesive Band
J
20 D
Vs= 5 m/s
15
F 35
45
F
Rupture Energy
1,0
10 1,0
105
Al Mg 5 Mn
5
A B C D
0
Source: Budde
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Impact Strength of Different Joints 4105.03.03
Training in Aluminium Application Technologies
Shear Strength of Different Joints With and Without Ageing
In connection with combined fastenings of mechanical and adhesive joints, the aspect of
ageing of the combined joint plays a central role.
It has been found that corrosion increases the strength of riveted and clinched joints of
aluminium sheets (see Figure 4105.03.04). This is due to the fact that the corrosion
products of aluminium occupy a larger volume than the uncorroded aluminium material.
This increases the strain on the joint causing the force locking component to increase.
Although the mechanical fastening process can cause aluminium sheets to be pulled
apart in the joint vicinity, the supporting action of the mechanical joint in the combined
mechanical-adhesive joint greatly reduces the decrease in joint strength caused by
ageing.
Single-Element Samples
kN without Corrosion
AlMg4.5Mn
with Corrosion v=10mm/min
s=1.0mm
10
Elementary Combined
Joint Joint
8
Rupture force
6
4
2
0
Adhesive Clinching Punch Clinching and Riveting and
Joining Riveting Adhesive Adhesive
Joining Joining
Source: Singh
Shear Strength of Different Joints
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4105.03.04
Training in Aluminium Application Technologies with and without Ageing
TALAT 4105 14

15. Comparison of Properties of Different Joining Technologies
Mechanical fastening methods, used alone or in combination with adhesive joining,
improve the standard of quality as far as rigidity, damping of noise and vibrations,
pressure tightness and corrosion protection are concerned, making this an interesting
proposal for highly stressed aluminium constructions (Figure 4105.03.05).
Joining
Technology Adhesive
Spot Welding Clinching Riveting
Joining
Characteristics
Joint Large Surface Local Local Local
Plane Surface Uneven Surface Deformed Damaged
Surface Surface
Properties Very Sensitive Conditionally Conditionally Sensitive to
to Environment Sensitive to Sensitive to Environment
Environment Environment
Depend on Depend on Depend on Depend on
Direction Direction Direction Direction
Source: Budde
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Comparison of Properties of Different
Joining Technologies 4105.03.05
Training in Aluminium App licatio n Tech nologies
4105.04 Literature/References
1. Budde, L. Untersuchungen zur Kombination quasi-formschlüssiger und
stoffschlüssiger Verbindungsverfahren. Dissertation Uni-GH-Paderborn, 1989
2. Wittke, K. und Füssel, U. Kombinierte Fügeverbindungen. Wissenschaftliche
Schriftenreihe der TU Chemnitz 13/1986
3. Patrick, E. and Sharp, M.L. Joining methods for aluminium car body structures.
Automotive Technology International (1993), 61-70
4. Füssel, U. Kombinierte Fügeverbindungen. Habilitation TU Chemnitz, 1989
5. Endlich, W. Klebdichten. Angewandte Technik 1 (1988) 4, 4-31
6. Stepanski, H. Punktschweißkleben von Karosserieblechen aus Stahl und
Aluminium. Dissertation TH Aachen, 1980
7. Budde, L. Alternative Lösungen für Fügeprobleme durch
Verbindungskombinationen. Der Konstrukteur 23 (1992) 1/2, 22-25
TALAT 4105 15

16. 4105.05 List of Figures
Figure No. Figure Title (Overhead)
4105.01.01 Comparison of Functional Characteristics of Different Fastening Technologies
4105.01.02 Classification Index of Joints
4105.01.03 Advantages of Combined Joint Types
4105.01.04 Properties of Elementary Joints
4105.01.05 Main Advantages and Disadvantages of Adhesive Joining
4105.01.06 Fold-Adhesive Joints
4105.01.07 Examples of Combined Joints Used in the Aircraft Industry
4105.01.08 Combination of Material Locking and Form Locking Joints
4105.01.09 Fractured Surface of Combined Joints After Shear Testing
4105.02.01 Production of Combined Joints
4105.02.02 Production Variants for Combined Joints
4105.02.03 Operations in the Production of an Adhesive-Clinch Joint Combination
4105.02.04 Methods of Producing Adhesively Joint and Clinched Fastenings
4105.02.05 Form of Clinched Joints with and without Adhesives
4105.03.01 Criteria for the Use of Combined Joining Technologies
4105.03.02 Results of Fatigue Tests with Adhesive Joints
4105.03.03 Impact Strength of Different Joints
4105.03.04 Shear Strength of Different Joints with and without Ageing
4105.03.05 Comparison of Properties of Different Joining Technologies
TALAT 4105 16