180015_Leseprobe

Reisgen · Stein
ENGLISH EDITION
Fundamentals
of joining technology
Welding, brazing and adhesive bonding

Reisgen ∙ Stein
Fundamentals of
joining technology
Welding, brazing
and adhesive bonding

Bibliographic information published by the Deutsche Nationalbibliothek
The Deutsche Nationalbibliothek lists this publication in the Deutsche
Nationalbibliografie; detailed bibliographic data are available in the Internet
at htttp://dnb.dnb.de.
English Edition
Volume 13
ISBN 978-3-945023-76-1
All rights reserved.
© DVS Media GmbH, Düsseldorf · 2016
Printed by: Kraft Druck GmbH, Ettlingen

Preface
In almost every industrial or skilled manual production process, the joining of individual
parts constitutes the decisive step for the manufacturing of subassemblies,
assemblies and finished products. In addition to non-positive-locking and
positive-locking joining processes, material-locking joining processes such as
welding, adhesive bonding or brazing are frequently applied here because of
their specific advantages in both technological and economic respects. Not only
the possibilities, limits and necessary boundary conditions of the available processes,
the interactions between the utilised materials and the processes and
their effects on the component but also the fabrication aspects such as the
mechanisation and automation of the production sequences as well as occupational
health and safety must be taken into account at early stages in the concept
and design phases. The quality assurance of these comparatively complex processes
should also be borne in mind as early as possible.
The training to become a welding, brazing or also adhesive bonding specialist (to
be completed after the vocational qualification) is offered not only on the engineers’
level but also in the technologists' field. It generates and qualifies specialists
who are then mainly employed in fabrication. In most cases, all-rounders
or specialised designers, work planners or quality assurers are deployed in all
the other fields. As the experience of the authors teaches the fundamental
knowledge relating to all aspects of material-locking joining is often inadequate in
these vocational groups.
Consequently, this book is directed at engineers and technologists with tasks in
design, work planning, fabrication or quality assurance from industry and skilled
trades in companies of all sizes to help them to get into the subject of “joining
technology”. However, it should also serve the students of engineering sciences
as consolidation of the lecture material. In addition to welding, the allied processes
brazing and adhesive bonding are also taken into account as a digression.
The reader should thus be put in a position to select technologically and economically
suitable joining processes and to design his product in his fabrication environment
in a way which is as appropriate for joining as possible.
It is important to the authors to demonstrate the area of conflict resulting from
fabrication, material, design-related configuration, quality assurance and economic
boundary conditions. The book follows this idea in its structure and portrays not
only the joining processes and their technological and economic possibilities and
limits but also the incorporation into fabrication sequences, quality assurance and
occupational health and safety. A separate chapter is dedicated to material behaviour
during joining. Fundamental rules for the structural design are derived
from this. For reasons relating to clarity and simpler understanding, there is no
great depth of detail in many cases and reference is made to follow-up literature
and standardization instead.

The book was written with the aid of employees of the Welding and Joining
Institute at RWTH Aachen University. Here, the authors thank, in particular,
Dipl.-Ing. Jens Schoene for elaborating the “Adhesive bonding” chapter and the
other colleagues for looking through the text critically.
Aachen, in June 2016
Uwe Reisgen and Lars Stein

1 Introduction
Production, i.e. the processing of raw materials and semi-finished products in
order to create usable products, is almost as old as mankind itself. Hand axes as
very early known tools have already been proven amongst the early humans and
constitute not only a processed product but also a tool, e.g. for the production
and manufacturing of food.
These monolithic first “products” still did without any joining technology. However,
the refinement of these still very primitive tools into more effective weapons or
processing tools (e.g. by mounting a stone blade on a wooden shaft in order to
manufacture an axe as a tool for wood processing) already made it necessary to
develop joining processes. In the case of the mummy of a human originating from
the beginning of the Copper Age which was discovered in the Ötztal Alps in September
1991 and subsequently became known as “Ötzi”, a large number of
equipment items and weapons were found in addition to the preserved clothing
which was definitely the result of really complex processing, Fig. 1. Emphasis
should be placed on the axe in which a cast blade which was made of pure copper
and was manufactured by cold peening was glued into a carefully processed
shaft made of wood using birchwood tar and the joint was reinforced by wrapping
narrow leather strips around it. The same technique was also found in the case of
the arrows found in a quiver sewn from chamois hide [1].
Fig. 1. Axe and arrows from the beginning of the Copper Age
(© South Tyrol Museum of Archaeology – www.iceman.it).
The fire welding of gold [2] which was discovered in Sumer around 2500 BC as
well as brazing are other examples for joining techniques from antiquity. These
enabled metal craftsmen to fabricate permanently joined products from several
individual parts. A lot of finds from early cultures prove the use of fire welding and
brazing/soldering processes, mostly for the fabrication of jewelry and cult objects.
Dated around the middle to the end of the 18th century, there is first evidence of
oxy-fuel gas technology and also of the first electric welding processes. Mile-
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stones on the path to modern welding technology certainly were the invention of
the air separation process by Carl von Linde in 1902 as well as the oxyacetylene
blowpipe by Messer in 1905. AEG already delivered the first spot welding machines
to the sheet metal goods industry in 1906. In 1907/1908, Kjellberg received
patents for coated stick electrodes which were to help welding with the
stick electrode to make a breakthrough later on. Early variants of arc welding with
a consumable electrode can be found as from 1922 and were then subsequently
refined into gas-shielded metal arc welding (1926) and submerged arc welding
(approx. 1934). A lot of developments which have ultimately led to the large
number of welding processes available today for skilled manual and industrial
fabrication were initiated parallel to this.
During the production of a modern motor vehicle, joining processes are utilised in
all areas (drive, bodywork, chassis, electrics and electronics, interior equipment
etc.) today. Taking account of the function in question, the utilised materials as
well as the demanded mechanical-technological properties of the joint, a large
number of individual parts are assembled into subassemblies which give rise to
assemblies which then result in the ready-for-sale vehicle after further joining
processes, Fig. 2.
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Fig. 2. Multimaterial mix in a lightweight car body [3].
Both in the past as well as today, the skilled manual and industrial production of
goods was and is inconceivable without joining processes. DIN 8580 [4] therefore

classifies joining in its own main group, Table 1, whose purpose it is to alter the
shape of the workpieces by increasing the cohesion (the joining).
Table 1. Systematics of the production processes according to DIN 8580, Table 1
[4].
Creation of
shape
Create
cohesion
Main Group 1
Primary forming
Preserve
cohesion
Main Group 2
Forming
Change in shape
Decrease
cohesion
Main Group 3
Cutting
Increase cohesion
Main
Group 4
Joining
Main
Group 5
Coating
Change of
material properties
Main Group 6
Change material
property
1.1 Systematics of joining
According to DIN 8593, the term “joining” designates the permanently designed
connection or miscellaneous bringing-together of two or more workpieces with
geometrically defined shapes or of just such workpieces with shapeless material.
In this respect, the cohesion is created locally in each case and is increased in
the whole [5]. Here, the joint may be mobile or immobile and the forces necessary
for the cohesion are transmitted via the effective faces.
A systematic distinction is made between detachable joints (which can be detached
without damaging the joined parts [5]) and undetachable joints (which can
only be detached once by accepting the damage or destruction of the joined
parts [5]).
Fig. 3. Fundamental possibilities of cohesion.
Furthermore, a distinction can be made between three fundamental mechanisms
for the transmission of the forces necessary for the cohesion, Fig. 3.
– Positive locking transmits the joining forces by preventing any movement directed
perpendicular to the effective plane. Positive-locking joints may be detachable
or undetachable and, depending on the design, also still permit linear
or rotatory movements in one or more spatial axes. Examples are groove-andfeather-key
joints, Fig. 4, or dovetail joints.
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Fig. 4. Positive locking – Feather key in
a shaft/hub joint.
Fig. 5. Non-positive locking – Shrink-fit
shaft/hub joint, assembly by cooling the
shaft (source: IES GmbH, Krefeld).
– Non-positive locking uses friction for the transmission of the joining forces. The
prerequisite for this is a force which is directed perpendicular to the effective
plane which, linked via the coefficient of static friction, gives rise to the cohesive
force. The joints may be implemented in both detachable and
undetachable designs and are not mobile. Examples are shrink-fit and pressed
joints, Fig. 5. Clamped joints are also rely based on non-positive locking.
Fig. 6. Material locking – Multipass weld with the submerged arc process.
– Material locking transmits the joining forces on an atomic or molecular level.
The joints are always immobile and, as a rule, undetachable. Examples are
welded joints, Fig. 6, adhesive-bonded joints or brazed as well as soldered
joints.
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There are also joining processes which combine several of these mechanisms:
Fig. 7 shows a clamped fastening on a machine tool. The movement of the
workpiece on the machine table is prevented by non-positive locking and that
force perpendicular to the effective plane which is necessary for this purpose is
applied by the screw by means of pretension and positive locking by the screw
head and the sliding block. The axial displacement of the nut is prevented by
positive locking. The unintended unscrewing of the nut on the thread is prevented
by non-positive locking. The sliding block is fixed in the T groove by positive locking
as well.
Fig. 7. Combination of joining mechanisms resulting from positive locking and nonpositive
locking.
The main group (“Joining”) according to DIN 8580 [4] is divided further into subgroups
according to their effective principles. Of these, the following groups are
to be addressed within the framework of this book: 4.6 “Joining by welding” and
4.7 “Joining by brazing / soldering” and, as a digression, 4.8 “Joining by adhesive
bonding”, Fig. 8.
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Fig. 8. Subdivision of Main Group 4 “Joining” according to DIN 8580 [4].
For simplified international communication, EN ISO 4063 [6] defines a system of
reference numbers which can be used in order to specify the welding processes
planned by the designer without any language barriers. For example, 141 stands
for tungsten inert gas welding with solid wire or rod filler.
1.2 Joining in the area of conflict between design, material and
economic viability
The selection of a joining process suitable for a specific task must be approached
from various perspectives, Fig. 9.
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Fig 9. Factors influencing the selection of a joining process.
● The design of the component firstly implements the function of the subsequent
product and defines the requirements on the material and on the joint itself. At
the same time, it defines not only the boundary conditions (the accessibilities to
the joint, the heat dissipation conditions as well as the space available for any
necessary clamping or fixing) in which the joint must be manufactured but also
the operating conditions (stress conditions and levels, temperatures and loads)
in which it must function. The structural design thus determines the joining reliability
not only in relation to reliable manufacturing but also in relation to the reliable
operation of the joint when the finished product is used.
● The selected process must permit the manufacturing of the joint in the stipulated
boundary conditions and, at the same time, be suitable for the material(s) to
be joined.
● In contrast, the material(s) must not only satisfy the mechanical-technological
requirements of the design but also be suitable for the processing with the corresponding
joining process.
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According to the definition, the careful coordination of joining reliability, joining
suitability and joining possibility determines the joinability. The representation on
the base area of the tetrahedron is intended to illustrate the interacting dependencies,
Fig. 9. These are (for example):
● The function of the component roughly determines its geometrical shape. Together
with the operating forces, this determines the forces and stress conditions
to be transmitted by the joint and, together with the miscellaneous operating
conditions, stipulates the requirements on the material. The geometry of the
workpiece also stipulates the requirements on the joining process.
● The joining process sets geometrical boundary conditions for its applications
and thus restricts the freedoms of the design. Good accessibilities to the joint
leave more degrees of freedom both the human and the automatic machine
during the manufacturing of the joint and ultimately also have an influence on
the process reliability and the quality. Joining processes cannot be utilised universally
for all materials. In their application, they do not only depend on the
material properties but also alter these negatively in certain circumstances.
They therefore restrict the range of available materials.
● Boundary conditions (e.g. with regard to the heat control) which must be set via
the component geometry and the welding process are the prerequisites for the
material in order to set or preserve its specific properties.
Sufficient joinability which can often only can be achieved in an iterative process
consequently describes the intersection between the possibilities of joining reliability,
joining suitability and joining possibility and will frequently lead to more than
one technical solution for a certain joining task. In order to find the optimum solution,
these purely technological considerations must be subjected to an economic
consideration in addition. The following aspects (amongst others) are to be taken
into account:
● Quantities:
The planned quantities in which the product is to be fabricated essentially determine
the proportion in which the fixed costs contribute to the cost of one
product unit. High quantities justify high investments in installations, devices
and jigs if these are amortised by reducing the variable costs (consisting of the
material and processing costs in relation to one sales unit) to such an extent
that this results in an economic advantage all in all.
In contrast, low quantities (or even single-item production processes) offer
hardly any potential for the amortisation of high investments and can therefore
often be manufactured with better value for money by utilising universally usable
installations and high personnel expenses.
● Installation and device costs:
The selection of a process for a joining task determines which installations,
devices and jigs are needed for this. When selecting the process, it is necessary
to take account not only pure technological aspects but also aspects such
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as the availability in the company (Is it possible to use existing installations and
devices with which experience is already available? Do these have free capacities?),
the necessity of a new investment or, possibly outsourcing. In the case
of the variable costs, it is primarily the fabrication time which is incorporated into
the calculation.
● Costs of the joining parts:
The costs of the joining parts are composed of the material costs and the expenses
for their fabrication. In turn, the necessary fabrication expenses of the
individual parts depend on the utilised process and the chosen degree of
mechanisation. (As a rule of thumb, it may be stated: the more economically
viable the process and the higher the degree of mechanisation, the more precisely
the individual parts must be fabricated and positioned and/or the more
expensive the scope of jigs or sensors/monitoring must be in order to ensure
an adequate result.) In this respect, it may certainly make sense in the business
management analysis if processing steps are simplified or even omitted
by using more expensive input material (e.g. by using standard sections instead
of self-welded sections from sheets) or the utilisation of high-strength
structural steels instead of general structural steels which then cause higher
welding costs and need a subsequent heat treatment in order to achieve similar
strengths.
● Labour costs:
The labour costs essentially depend not only on the required qualification but
also on the required scope of time. Apart from the selection of the joining process,
they are influenced, above all, by the accessibility to the joint and the degree
of mechanisation.
● Testing costs:
The scope of testing depends not only on the stipulations imposed by the legislator
or the customer but also, to a great extent, on the defect probability and
thus on the process reliability of the process step in question. This can be influenced
by the process selection, the qualification of the personnel, the precision
of the part preparation and the jigs, the accessibility to the joint during the
manufacture and, not least, also the simple applicability of testing procedures.
Therefore, possible solutions should be assessed by the business management
analysis of the entire fabrication sequence. The optimum joining solution (or the
best compromise) is then that one with which the product to be fabricated can be
manufactured with the demanded properties at the most favourable price in the
end, Fig. 10.
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Fig. 10. Factors influencing the costs of a joint.
1.3 Selection of joining processes
Joining is a complex process in which a large number of intermeshing factors
make up both the technical quality and economic success of the product manufactured
in this way, Fig. 11. Only the careful coordination of all the influencing
factors with each other and with the function and design of the component results
in a product which can be fabricated at favourable costs in a reliable process and
a good quality.
Therefore, the systematic selection of a joining process ideally already begins at
a very early stage of the design process at a time when materials, sheet thicknesses
and also the mechanical-technological requirements on the joint in question
are known in a rough concept. On the basis of these criteria, those joining
processes with which the joining task can be performed in principle are preselected
from the large number of possible joining processes.
The next detail stipulation stage of the design which should already include deliberations
about the subsequent fabrication of the components too is tackled with
this subset. Here, additionally revealed information (e.g. about required processing
properties, planned quantities etc.) then permits the further delimitation of
the preselected processes. In this respect, it is already possible to take account
also of criteria such as the use of installations and experience already available in
the company for the new product.
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