Welding-process

Purposes of this report: - to give an outline of welding processes
Welding is a process of metal joining by applying heat and sometime pressure
Introduction

Diversity of welding processes
welding
Solid state welding
Soldering and brazing
Fusion welding
Electrical energy
Chemical energy
Other processes
Non consumable electrode
Consumable electrode
Friction welding
Ultrasonic welding
Gas metal arc welding
Shielded metal arc welding
Submerged arc welding
Flux cored arc welding
Electrogas welding
Gas tungsten arc welding
Plasma arc welding
Oxyacetylene welding
Oxyfuel gas welding
Laser beam welding
Electron beam welding
Resistance welding
Electroslag welding
Soldering
Brazing

Solid state welding
It merges all the welding processes in which there is no fusion of the workpieces .
For example, in the solid welding process named resistance seam welding, the welding join is produced in the wheel electrodes region by applied a current and a pressure without fusion of the base metal.
The resistance seam welding
(source: Modern Welding (p73))

Soldering or brazing
In these processes, only the filler metals which join the two pieces to be welded are melted and not the base metal. The braze metals have higher melting temperatures than the solder metals.

Fusion welding
This process involves the partial melting of the two members welded in the join region. The thermal energy required for this fusion is usually supplied by chemical or electrical means.
Characteristics of the fusion weld joint
(Manufacturing Engineering and Technology: p820)
Base metal melt + filler melt

Fusion welding Process

Topics to Discuss
Introduction
Oxyfuel Gas welding
Arc-Welding Processes:Consumable electrode
Electrodes
Arc-Welding Processes:Non Consumable Process
Thermit Welding
Electron Beam Welding
Laser Beam Welding
Cutting
Welding Safety

Introduction
Definition : Fusion Welding is defined as melting together and coalescing materials by means of heat
Energy is supplied by thermal or electrical means
Fusion welds made without filler metals are known as autogenous welds

Oxyfuel Gas Welding
Fig : Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cutting operations: (a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame. The gas mixture in (a) is basically equal volumes of oxygen and acetylene.

Oxyfuel Gas Welding
Welding process that uses fuel gas combined with oxygen to produce flame
This flame heat melts the metals at the joint
Acetylene fuel is used in gas welding process
Primary combustion process
C2H2 + O2 2CO + H2 + heat
This reaction dissociates into carbon monoxide and hydrogen.
Secondary combustion process
2CO + H2 + 1.5 O2 2CO2 + H2O + heat

Types of flames
Neutral flame
Oxidising flame
Carburising flame
Filler Metals :
Additional material to weld the weld zone
Available as rod or wire
They can be used bare or coated with flux
The purpose of the flux is to retard

Welding practice & equipment
STEPS :
Prepare the edges to be joined and maintain the proper position
Open the acetylene valve and ignite the gas at tip of the torch
Hold the torch at about 45deg to the work piece plane
Inner flame near the work piece and filler rod at about 30 – 40 deg
Touch filler rod at the joint and control the movement according to the flow of the material

Torch used in Oxyacetylene Welding
Fig : (a) General view of and (b) cross-section of a torch used in oxyacetylene welding. The acetylene valve is opened first; the gas is lit with a park lighter or a pilot light; then the oxygen valve is opened and the flame adjusted. (c) Basic equipment used in oxyfuel-gas welding. To ensure correct connections, all threads on acetylene fittings are left-handed, whereas those for oxygen are right-handed. Oxygen regulators are usually painted green, acetylene regulators red.

Arc welding process : Consumable electrode
Process goes with the consumable electrode or non consumable electrode
Arc produced between the tip of the electrode & work piece
Arc temperature about 3000 deg
Oldest ,simple & versatile
50 % of industry uses this process
heat generated heats the electrode & immediate area of the base projected by arc
weld forms when molten metal ,mixture of base metal and electrode metal and substance from the coating on the electrode solidifies
electrodes are in the shape of thin,long stick, so the process is known as stick welding

Shielded metal arc welding process
Fig : Schematic illustration of the shielded metal-arc welding process. About 50% of all large-scale industrial welding operations use this process.
Fig : Schematic illustration of the shielded metal-arc welding process ( also known as stick welding, because the electrode is in the shape of a stick).

Submerged arc welding:
Fig : Schematic illustration of the submerged-arc welding process and equipment. The unfused flux is recovered and reused .

Submerged arc welding:
Weld arc is shielded by a granular flux ,consisting of silica, lime, manganese oxide, calcium fluoride and other compounds.
Flux is fed into the weld zone by gravity flow through nozzle
Thick layer of flux covers molten metal
Flux acts as a thermal insulator ,promoting deep penetration of heat into the work piece
Consumable electrode is a coil of bare round wire fed automatically through a tube
Power is supplied by 3-phase or 2-phase power lines

Gas metal arc welding:
GMAW is a metal inert gas welding (MIG)
Weld area shielded by an effectively inert atmosphere of argon,helium,carbon dioxide,various other gas mixtures
Metal can be transferred by 3 methods :
Spray transfer
Globular transfer
Short circuiting
Process capabilities
GMAV process is suitable for welding a variety of ferrous and non-ferrous metals
Process is versatile ,rapid,economical,welding productivity is double that of SMAW

Gas Metal-Arc Welding
Fig : Schematic illustration of the gas metal-arc welding process, formerly known as MIG (for metal inert gas) welding.

Equipment used in Metal-Arc Welding Operations
Fig : Basic equipment used in gas metal-arc welding operations

Flux–cored Arc – Welding
Flux cored arc welding is similar to a gas metal arc welding
Electrode is tubular in shape and is filled with flux
Cored electrodes produce more stable arc improve weld contour and produce better mechanical properties
Flux is more flexible than others

Flux-Cored Arc Welding
Fig : Schematic illustration of the flux-cored arc-welding process. This operation is similar to gas metal-arc welding.

Electro gas Welding :
EGW is welding the edges of sections vertically in one pass with the pieces placed edge to edge
Weld metal is deposited into weld cavity between the two pieces to be joined
Mechanical drives moves shoes upwards
Single and multiple electrodes are fed through a conduit and a continuous arc is maintained using flux-cored electrodes at up to 750 A
Process capabilities :
Weld thickness ranges from 12mm to 75mm
Metals welded are steels, titanium, aluminum alloys
Applications are construction of bridges, pressure vessels, thick walled and large diameter pipes, storage tanks and ships.

Electrogas Welding
Fig : Schematic illustration of the electrogas welding process

Electroslag Welding:
Similar to Electro gas welding
Difference is Arc is started between electrode tip and bottom part of the part to be welded
Flux added first and then melted by the heat on the arc
Molten slag reaches the tip of the electrode and the arc is extinguished
Heat is then continuously produced by electrical resistance of the molten slag
Single or multiple solid as well as flux-cored electrodes may be used

Equipment used in Electroslag welding
Fig : Equipment used for electroslag welding operations.

Solid-State Welding Processes

Cold Welding
Pressure is applied to the workpieces through dies or rolls
Preferably both work pieces should be ductile
The work pieces should cleaned thoroughly
Can not join dissimilar metals
Fig: The roll bonding or cladding process

Ultrasonic Welding
Surfaces of the two components are subjected to a static forces and oscillating shearing force
Produces a strong, solid-state bond
Versatile and reliable for joining metals
Fig: a) Components of an ultrasonic welding machine for lap welds.The lateral vibration of the tool tip cause plastic deformation and bonding at the interface of the work piece b)Ultrasonic some welding using a roller c)An ultrasonically welded part

Friction Welding
Developed in the 1940’s
Parts are circular in shape
Can be used to join a wide variety of materials
Fig: Sequence of operation in the friction welding process 1)Left-hand component is rotated at high speed. 2) Right-hand component is brought into contact under an axial force 3)Axial force is increased;the flash begins to form 4) Left-hand component stops rotating;weld is completed.The flash can subsequently be removed by machining or grinding

Process can be fully automated
Can weld solid steel bars up to 250mm in outside diameter
Fig:Shape of friction zone in friction welding,as a function of the force applied and the rotational speed
Friction Welding

Inertia Friction Welding
Modification of Friction Welding
Energy is supplied by a fly wheel
The parts are pressed together by a normal force
As friction at the interface increases, the fly wheel slows down
The weld is completed when the flywheel stops
Fig : The principle of the friction stir welding process. Aluminum-alloy plates up to 75mm (3in) thick have been welded by this process

Linear Friction Welding
Parts are joined by a linear reciprocating motion
Parts do not have to be circular or tubular
In this application, one part is moved across the face of the other part using a balanced reciprocating mechanism

Friction Stir Welding (FSW)
New Process for welding aerospace metals
Research is being directed towards using this process for polymers
FSW uses a 3rd nonconsumable tool inserted between the two bodies to heat the material to be joined

Resistance Welding
Developed in the early 1900’s
A process in which the heat required for welding is produced by means of electrical resistance across the two components
RW does not requiring the following:
Consumable electrodes
Shield gases
Flux

Resistance Spot Welding
RSW uses the tips of two opposing solid cylindrical electrodes
Pressure is applied to the lap joint until the current is turned off in order to obtain a strong weld
Fig: (a) Sequence in the resistance spot welding

Surfaces should be clean
Accurate control of and timing of electric current and of pressure are essential in resistance welding
Fig: b)Cross-section of a spot weld,showing the weld nugget and the indentation of the electrode on the sheet surfaces.This is one of the most commonly used process in sheet-metal fabrication and in automotive-body assembly
Resistance Spot Welding

Resistance Seam Welding
RSEM is modification of spot welding wherein the electrodes are replaced by rotating wheels or rollers
The electrically conducting rollers produce a spot weld
RSEM can produce a continuous seam & joint that is liquid and gas tight
Fig : (a) Seam-Welding Process in which rotating rolls act as electrode (b)
Overlapping spots in a seam weld. (c) Roll spot weld (d) Resistance-welded gasoline tank

Resistance Projection Welding
RPW is developed by introducing high electrical resistance at a joint by embossing one or more projections on the surface to be welded
Weld nuggets are similar to spot welding
Fig: a) Resistance projection Welding b)A welded bracket c) & d) Projection welding of nuts r threaded hosses and stack

The electrodes exert pressure to compress the projections
Nuts and bolts can be welded to sheet and plate by this process
Metal baskets, oven grills, and shopping carts can be made by RPW
Resistance Projection Welding

Flash Welding
Heat is generated from the arc as the ends as the two members contacts
An axial force is applied at a controlled rate
Weld is formed in plastic deformation
Fig : (a)Flash-welding process for end-to –end welding of solid rods or tubular parts
(b) & (c) Typical parts made by flash welding (d)Design Guidelines for flash welding

Stud Welding
Small part or a threaded rod or hanger serves as a electrode
Also called as Stud arc welding
Prevent oxidation to concentrate the heat generation
Portable stud-welding is also available
Fig:The sequence of operation in stud welding,which is used for welding bars threaded rods and various fasteners onto metal plates