FUNDAMENTALS OF WELDING

ME 330
Manufacturing Processes
WELDING PROCESSES
Overview of processes
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Welding
1. Process in which two (or more) parts are coalesced at
their contacting surfaces by application of:
 Heat and pressure
2. Some welding processes use a filler material added to
facilitate coalescence
Principle of welding
Assembly two parts together by creating a fusion and/or
deformation in the interaction area, which is further based on
the physics laws such as fusion and solid state deformation.
Principle of welding
Fusion welding (FW)
Heat materials to melt the materials of
compositions and
melting points. Due to the high-temperature phase
transitions inherent to these processes, a heat-affected zone
is created in the material
Principle of welding
Solid State welding (SSW)
On the interface between two materials there is no melting
that happens but the interface of materials is reconfigured to
form many
structure.
Two Categories of Welding Processes
1. Fusion welding - coalescence is accomplished by melting
the two parts to be joined, in some cases adding filler
metal to the joint
 Examples: arc welding, oxyfuel gas welding, resistance
spot welding
2. Solid state welding - heat and/or pressure are used to
achieve coalescence, but no melting of base metals
occurs and no filler metal is added
 Examples: forge welding, diffusion welding, friction
welding
The general function of welding
1. Provides a permanent joint
2. One of the most economical ways to join parts in terms
of material usage and fabrication costs
Mechanical fastening usually requires additional hardware
(e.g., screws) and geometric alterations of the assembled
parts (e.g., holes)
3. Not restricted to a factory environment
Welding can be accomplished "in the field"
Limitations and Drawbacks of Welding
1. Most welding operations are performed manually and
are expensive in terms of labor cost.
2. Most welding processes utilize high energy and are
inherently dangerous.
3. Welded joints do not allow for convenient disassembly.
4. Welded joints can have quality defects that are difficult
to detect.
Welding
Fusion Welding (FW)
Solid State Welding (SSW)
Arc Welding (AW)
Principle of the process
Structure and configuration
Process modeling
Defects
Design For Manufacturing (DFM)
Process variation
Fusion Welding: Arc Welding (AW)
A fusion welding process in which coalescence of the metals
is achieved by the heat from an electric arc between an
electrode and the work
1. Electric energy from the arc produces temperatures ~
10,000 F (5500 C), hot enough to melt any metal.
2. Most AW processes add filler metal to increase volume
and strength of weld joint.
Fusion Welding: Arc Welding (AW)
A pool of molten metal is formed near electrode tip, and as
electrode is moved along joint, molten weld pool solidifies in
its wake
Welding
Fusion Welding (FW)
Solid State Welding (SSW)
Arc Welding (AW)
Consumable electrodes
Non-consumable electrodes
Two Basic Types of Arc Welding (Based on
Electrodes)
1. Consumable electrodes
 consumed during welding process
 added to weld joint as filler metal
 in the form of rods or spools of wire
2. Non-consumable electrodes
 not consumed during welding process but does get
gradually eroded
 filler metal must be added separately if it is added
Arc welding (AW): Arc Shielding
1. At high temperatures in AW, metals are chemically
reactive to oxygen, nitrogen, and hydrogen in air
 Mechanical properties of joint can be degraded by
these reactions
 Arc must be shielded from surrounding air in AW
processes to prevent reaction
2. Arc shielding is accomplished by
 Shielding gases, e.g., argon, helium, CO2
 Flux
Arc welding (AW): Flux
 A substance that prevents formation of oxides and other
contaminants in welding, which comes from
1. granules that are created from the welded material.
2. a coating on the stick electrode that melts during
welding to cover operation.
3. a core that is within tubular electrodes and is released
as electrode is consumed.
 Melts during welding to be liquid slag that hardens when
cooled. The slag should be removed for a clean look by
brushing or grinding off.
Consumable Electrode AW Processes
 Shielded Metal Arc Welding (or Stick Welding)
 Gas Metal Arc Welding (or Metal Inert Gas Welding)
 Flux-Cored Arc Welding
 Electro-gas Welding
 Submerged Arc Welding
AW: Consumable: Shielded Metal Arc Welding
(SMAW)



Uses a consumable electrode consisting of a filler metal rod and
coating around rod.
Coating composed of chemicals that provide flux and shielding.
Low cost welding system: Power supply, connecting cables, and
electrode holder available for $300 to $400.
SMAW Applications
 Used for steels, stainless steels, cast irons, and certain
nonferrous alloys.
 Not used or rarely used for
and its alloys,
copper alloys, and titanium.
 Can be used in windy weather.
 Can be used on dirty metals (i.e. painted or rusted
surfaces).
 Good for repair work.
 Makes thick welds.
AR: Consumable: Gas Metal Arc Welding
(GMAW) or Metal Inert Gas (MIG) Welding
Uses a consumable bare metal wire as electrode with
shielding by flooding arc with a gas
1. Wire is fed continuously and automatically from a spool
through the welding gun.
2. Shielding gases include argon and helium for aluminum
welding, and CO2 for steel welding.
3. Bare electrode wire (no flux) plus shielding gases
eliminate slag on weld bead. No need for manual
grinding and cleaning of slag
4. Medium cost welding system: $1000 to $1200
Gas Metal Arc Welding
GMAW Advantages over SMAW
1. Continuous welding because of continuous wire
electrode. Sticks must be periodically changed in SMAW.
2. Higher deposition rates.
3. Eliminates problem of slag removal.
4. Can be readily automated.
5. Has better control to make cleaner & narrower welds
than SMAW.
GMAW Applications
1. Used to weld ferrous and various non-ferrous and
metals.
2. Good for fabrications such as frames and farm
equipment.
3. Can weld thicker metal (not as thick as SMAW).
4. Metal must be clean to start weld.
Non-consumable Electrode Processes
 Gas Tungsten Arc Welding
 Plasma Arc Welding
 Carbon Arc Welding
 Stud Welding
AW: non-consumable: Gas Tungsten Arc
Welding (GTAW) or Tungsten Inert Gas (TIG)
Welding
Uses a non-consumable tungsten electrode and an inert gas
for arc shielding
1. Melting point of tungsten = 3410C (6170F).
2. Used with or without a filler metal. When filler metal
used, it is added to weld pool from separate rod or
wire.
3. Applications: aluminum and stainless steel mostly.
4. High cost for welding system: $4000.
Gas Tungsten Arc Welding
Filler rod
Advantages and Disadvantages of GTAW
Advantages:
1. High quality welds for suitable applications
- Welds are cleaner and narrower than MIG
2. No spatter because no filler metal through arc
3. Little or no post-weld cleaning because no flux
Disadvantages:
1. More difficult to use than MIG welding
2. More costly than MIG welding
GTAW Applications
1. Used to weld ferrous and various non-ferrous and metals.
2. Can weld various dissimilar metals together.
3. Good for fabrications such as aircraft or race car frames.
4. Used for welding thinner metal parts (not as thick as
MIG).
5. Metal must be very clean to start weld.
Welding
Fusion Welding (FW)
Solid State Welding (SSW)
Arc Welding (AW)
Oxyfuel gas welding
Oxyfuel Gas Welding (OFW)
Group of fusion welding operations by a high temperature
flame that burns various fuels mixed with oxygen
 Oxyfuel gas is also used in flame cutting torches to cut
and separate metal plates and other parts
 Most important OFW process is oxyacetylene welding
(has high temperatures – up to 3480C)
 Filler metal is sometimes added
 Composition must be similar to base metal
 Filler rod often coated with flux to clean surfaces and
prevent oxidation
 Low cost for welding system: $400
Oxyacetylene Welding
Oxyacetylene Torch
1. Maximum temperature reached at tip of inner cone, while
outer envelope spreads out and shields work surface from
atmosphere
2. Shown below is neutral flame of oxyacetylene torch indicating
temperatures achieved
Oxyacetylene Gas Welding Applications
 Suitable for low quantity production and repair jobs
 Used for welding thinner parts
Summary
Welding
Fusion Welding (FW)
Solid State Welding (SSW)
Oxyfuel welding
Shielding
Flux
Non-consumable electrodes
Arc welding
Consumable electrodes
Various welding processes (AW) are developed to address
the two issues: shielding and flux