Joining Processes

ELHACHMI ESSADIQI , UIR

4th of Automotive Engineering

Introduction
• Joining process is where two or more pieces of parts are
joined together to produce a single product of required
shape and size.
• The joining process can be classified as

a. Permanent joining process

It is done by fusing the metal together. The metal is
heated to its melting state and then it is fused to become
one unit.
Ex. Welding, soldering and brazing

b. Semi – permanent or temporary joining process

In this the metal is not heated. Process is carried out
at room temperature. Temporary joining process can be
done using nuts, bolts, screws and adhesives.
 Welding Process

• Simple definition of welding -

"joining metals through heating them to a
molten state and fusing them together.“

• Technical definition of Welding -

“a localized coalescence of metals, wherein coalescence is
obtained by heating to suitable temperature, with or
without the application of pressure and with or without the
use of filler material. This filler material has the melting
point same as the base material.”

It is also know as a metallurgical

joining process of two metal pieces,
to produce a single piece of product.
 Welding Processes
Diffusion Welding
The process:

Two workpieces (1) at different concentrations

are placed between two presses (2). The
presses are unique for each combination of the
workpieces, with the result that a new design is
required if product design changes.
The heat equivalent to about 50-70% of the
materials melting point is then supplied to the
system, increasing the mobility of the atoms of
the two materials.

The presses are then pressed together, causing the atoms to start diffusing
between the materials at the contact area (3). The diffusion takes place due to
the workpieces being of different concentrations, while the heat and pressure
only make the process easier. The pressure is therefore used to get the
materials contacting surfaces as close as possible so that atoms can more
easily diffuse. When the desired proportion of atoms are diffused, the heat and
pressure are removed and the bonding processing is completed
 Welding Processes

Diffusion Welding

• Parts forced together at high temperature

(< 0.5Tm absolute) and pressure

• Heated in furnace or by resistance heating

• Atoms diffuse across interface

• After sufficient time the interface disappears

• Bond can be weakened by surface impurities

Kalpakjian, S., Manufacturing Engineering & Technology, p. 889, 1992

Welding Terminologies

• Base Metal – Work pieces that are needed to be joined

• Weld Bead - A weld bead is a weld deposit produced by a
single pass of the welding processes. It is also known as
bead
• Puddle – The molten base metal at the joint during the
welding operation
• Weld pass – Movement of weld torch from one end of the
joint to the other end.
• Tack Weld – it is the temporary joint done before welding
to keep the work pieces to be welded in place during
welding. The joints are done at the ends of the work
piece.
Classification of Welding Process

The welding process can be

classified based on the source of
energy to heat the metal and the
state of metal at the joint.
• Pressure Welding
• Fusion Welding
Pressure Welding
• The surfaces of the joint to be welded is heated to a
plastic state and forced together with external pressure to
finish the joint.

• Depends on the application of pressures and temperature

• ISO – 857 defines “Welding in which sufficient outer force

is applied to cause more or less plastic deformation of
both the facing surfaces, generally without the addition of
filler metal. Usually, but not necessarily, the facing
surfaces are heated in order to permit or to facilitate
bonding”
Fusion Welding

• Heating in to molten state and allowed to solidify

to form joint with or without the addition of
filler material.
• The process is carried out with out the
application of pressure.
• ISO – 857 defines “Welding without application
of outer force in which the facing surface must
be melted. Usually, but not necessarily, molten
filler metal is added”.
Shielded Metal Arc Welding (SMAW): “Stick welding”
• Older, simple technology
• The electrode is also the filler rod
• Only for steel
• Strong welds if done properly (but often not)
• Very high heat input: good for thick parts,
bad for grain growth and distortion
Gas Metal Arc Welding (GMAW): “MIG” (Metal-Inert-Gas)
• ~Complex mechanism but simple to perform and easy to automate
• The electrode is also the filler rod, fed continuously from a spool. It melts in the arc.
• For steel or aluminum
• Low skill level can achieve good weld
• Medium heat input: distortion and grain growth
are significant
Gas Metal Arc Welding (GMAW): “MIG” (Metal-Inert-Gas)

A fair/typical quality MIG weld (still hot!)

Gas Tungsten Arc Welding (GTAW): “TIG” (Tungsten-Inert-Gas)
• The electrode is tungsten (not consumed)
• The filler rod is separate and fed manually
• High skill level required to achieve good weld
• Difficult to automate
• Low heat input and small weld bead: distortion and grain growth are minimized
Gas Tungsten Arc Welding (GTAW): “TIG” (Tungsten-Inert-Gas)
• Typical good quality TIG welds
Resistance Spot Welding (RSW): “Spot Welding”
• No filler rod: electrical current is passed through metal under pressure
• Low skill level required
• Easy to automate
• Low heat input and no weld bead: distortion and grain growth are minimized
Distortion from Welding Processes
• Non-uniform shrinkage of weld bead
• Difficult to maintain alignments
• Solution: Rigid fixtures, pre-compensate for warping, loose tolerances
Weld bead profile: Convex or Concave?
• Solidification of molten bead leads to shrinkage
• Shrinkage of a concave bead leads to tension on surface → tends to crack
• Shrinkage of a convex bead leads to compression on surface → does not crack
• Generally, slightly convex beads are preferred.
Welding Flaws
Welding Flaws:
Incomplete Penetration
(not enough heat input)
 Advantages
• It is a high temperature process where the base
metals are heated above their melting temp.

• Strength of the joint obtained in welding is much

stronger than the parent metal

• Welding produces stronger joints.Hence this

process is used for fabrication and structural
applications
Disadvantages
• Requires certain finishing operations like
grinding , filing etc

• Since welding is carried out at high temp,

the metal adjacent to the weld portion
called the heat affected zone which is
affected to a large extent
 Applications
It can be employed in industry as a tool for,

✓Fabrication of automobile cars , Air- craft,

Refrigerators, Pressure vessels , Furnaces
etc

✓Repair and maintenance work

✓Joining broken parts
✓Rebuilding worn out components etc
 Brazing
• it is a method of joining two similar or dissimilar metals using a
special fusible alloy called as “Spelters”. Which is non ferrous
metal or alloy.

• The base metals do not melt; they are heated above 450 C°
but below their melting temperatures of base metal.

• Some diffusion of the filler metal with base metal takes place.

• There are two types of spelters used:

• Copper and Copper base alloys
• Silver and silver base alloys
 Brazing
Steel base metal + Brass filler rod is common
• Lower temp than welding: retains heat treatment (if
present), minimizes grain growth.
• Strong but slow (careful preparation, cleanup)
• Furnace brazing is easily automated
 Brazing
Use of low melt point filler metal to fill thin gap
between mating surfaces to be joined utilizing
capillary action

• Filler metals include Al, Mg & Cu alloys

(melt point typically above 840 F)

• Types of brazing classified by heating method:

– Torch, Furnace, Resistance

 Brazing

Applications:

• Automotive - joining tubes

• Pipe/Tubing joining (HVAC)

• Electrical equipment - joining wires

• Jewelry
Making

• Joint can possess significant

strength
Butt Joint
When two metals are positioned in a head-to-head
arrangement for brazing, it will result in a Butt joint.

Lap Joints
Lap joint is the type of joint that have a larger surface area
because it is formed by overlapping of two metals.

Butt-Lap Joint
It is a combination of both butt and lap type of joint and offers
the advantages of both. Butt-lap joint give the profitable
features of single thickness as well as of maximum strength
Advantages
• Dissimilar metals and parts having thin
sections can be joined easily.
• Brazing may avoid the metallurgical
damage to the base metals.
• Strong joint can be obtained by brazing.
• It is economical and quick process
• Less heating is required than for welding.
 Soldering
• Soldering is a method of uniting two thin metal pieces
using a dissimilar metal or an alloy by application of
heat.
• The alloy is called as solder.
• Two types of solder are:
• Soft solder
• Hard solder
• Usually the base metal is heated upto around 350 C°.
• Soldering is usually used for electrical & electronic
works and some low end sheet metal work.
Soft soldering is characterized by having a melting point of the
filler metal below approximately 400 °C (752 °F). Soft solder
filler metals are typically alloys (often containing lead) that have
liquidius temperatures below 350°C. Soft soldering can be done
with a heated iron whereas the other methods require a higher
temperature to melt the solder than can be achieved with a heated
iron.

These are some disadvantages of soft soldering:

•Soft soldering is not applicable at high temperatures as it loses
its strength and then melts.
•Soft soldering is unable to make strong joints.
•As this process is not sufficient to make strong joints, it is not
useful in case of high load bearing applications of mechanical
and other industries
Hard soldering use higher temperatures, typically requiring a
flame or carbon arc torch to achieve the melting of the filler. Hard
soldering, as used by jewelers, machinists and in some plumbing
applications, requires the use of a torch or other high temperature
source and is much stronger than soft soldering.

Altitudes"
"Our Attitude Decides Our
According to temperature at which solder melts, filler metals is
described as easy, medium or hard. The extra-hard solder
which is used in this process has silver content upto 80% and
melting point of 740 Co. For maintaining metal and solder
clean, flux made up of boric acid and alcohol is used. Hard
soldering or silver soldering is mostly used by jewellers and
plumbers as they need stronger joints.
 Soldering
Solder = Filler metal
• Alloys of Tin (silver, bismuth, lead)
• Melt point typically below 840 F

Flux used to clean joint & prevent oxidation

• separate or in core of wire (rosin-core)

Tinning = pre-coating with thin layer of solder

Applications:
• Printed Circuit Board (PCB) manufacture
• Pipe joining (copper pipe)
• Jewelry manufacture
• Typically non-load bearing

Easy to solder: copper, silver, gold

Difficult to solder: aluminum, stainless steels
(can pre-plate difficult to solder metals to aid process)
 PTH - Pin-Through-Hole connectors

• Soldering Iron & Solder Wire

• Heating lead & placing solder

• Heat for 2-3 sec. & place wire

opposite iron

• Trim excess lead

 ADVANTAGES
• It is simple and economical process
• Since it done at relatively low temperature, no
metallurgical damage to the base metal.
• The soft soldered joints can easily be dismantled by
simple heating
• Operator fatigue is less compared to welding process.

• DISADVANTAGES
• 1. The process is limited to minimum thickness (3mm)
• 2. Skilled operator is required.
• 3. Strength of joint when compared to welding is low.
Difference between Soldering and Brazing
Sl no Brazing Soldering
1 Melting point of the filler Melting point of the filler material
material is about 600 degree. is below 450 degree.

2 Dissimilar metals can be Only similar metals can be joined.

joined easily.

3 Good surface finish. Does not yield a good surface

finish

4 Stronger joints. Less stronger joint.

5 It is used for production of It is used for electrical and
heat exchangers and electronic applications.
radiators.
 Difference between Welding , Brazing and Soldering

Sl no Parameter welding brazing soldering

1 Temperature Very high, about Melting point of the Melting point of

more than 5000 filler metal is above the filler metal is
degree c 600 degree c below 450
degree

2 Type of metal Only similar metals Dissimilar metals Only similar

to be joined metals
3 Surface finish moderate good poor

4 strength Very high high weak