Download Welding Processes

WELDING
• Welding is a materials joining process which produces
coalescence of materials by heating them to suitable
temperatures with or without the application of pressure
or by the application of pressure alone, and with or
without the use of filler material.
• Welding is used for making permanent joints.
• It is used in the manufacture of automobile bodies, aircraft frames,
railway wagons, machine frames, structural works, tanks, furniture,
boilers, general repair work and ship building.
TYPES
• Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a
state and forced together by external
pressure
(Ex) Resistance welding
plastic
• Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and allowed
to solidify
(Ex) Gas welding, Arc welding
Classification of welding processes:
(i). Arc welding
•
Carbon arc
•
Metal arc
•
Metal inert gas
•
Tungsten inert gas
•
Plasma arc
•
Submerged arc
•
Electro-slag
(ii). Gas Welding
•
•
•
Oxy-acetylene
Air-acetylene
Oxy-hydrogen
(iii). Resistance Welding
•
Butt
•
Spot
•
Seam
•
Projection
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Diffusion
Explosive
(vi)Newer Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cutting
Arc cutting
Hard facing
Brazing
Soldering
Arc welding
• Equipments:
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles
Arc Welding Equipments
Metal arc welding
Arc Welding
Uses an electric arc to coalesce
metals
Arc welding is the most common
method of welding metals
Electricity travels from electrode
to base metal to ground
Carbon Arc Welding
Arc welding
Advantages
• Most efficient way to join
metals
• Lowest-cost joining method
• Affords lighter weight through
better utilization of materials
• Joins all commercial metals
• Provides design flexibility
Limitations
• Manually applied, therefore high
labor cost.
• Need high energy causing danger
• Not convenient for disassembly.
• Defects are hard to detect at
joints.
Comparison of A.C. and D.C. arc welding
Alternating Current (from Transformer)
More efficiency
Power consumption less
Cost of equipment is less
Higher voltage – hence not safe
Not suitable for welding non ferrous metals
Not preferred for welding thin sections
Any terminal can be connected to the work or electrode
Comparison of A.C. and D.C. arc welding
Direct Current (from Generator)
Less efficiency
Power consumption more
Cost of equipment is more
Low voltage – safer operation
suitable for both ferrous non ferrous metals
preferred for welding thin sections
Positive terminal connected to the work
Negative terminal connected to the electrode
GAS WELDING
• Sound weld is obtained by selecting proper size of flame, filler material
and method of moving torch
• The temperature generated during the process is 33000c
• When the metal is fused, oxygen from the atmosphere and the torch
combines with molten metal and forms oxides, results defective weld
• Fluxes are added to the welded metal to remove oxides
• Common fluxes used are made of sodium, potassium. Lithium and borax.
• Flux can be applied as paste, powder,liquid.solid coating or gas.
GAS WELDING EQUIPMENT...
1. Gas Cylinders
Pressure
Oxygen – 125 kg/cm2
Acetylene – 16 kg/cm2
2. Regulators
Working pressure of oxygen 1 kg/cm2
Working pressure of acetylene 0.15 kg/cm2
Working pressure varies depends upon the thickness of the work
pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve
Oxy-Acetylene welding
TYPES OF FLAMES…
• Oxygen is turned on, flame immediately changes into a long white inner
area (Feather) surrounded by a transparent blue envelope is called
Carburizing flame (30000c)
• Addition of little more oxygen give a bright whitish cone surrounded by the
transparent blue envelope is called Neutral flame (It has a balance of fuel
gas and oxygen) (32000c)
• Used for welding steels, aluminium, copper and cast iron
• If more oxygen is added, the cone becomes darker and more pointed, while
the envelope becomes shorter and more fierce is called Oxidizing flame
• Has the highest temperature about 34000c
• Used for welding brass and brazing operation
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.
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.
GAS CUTTING
• Ferrous metal is heated in to red hot condition and a jet of pure oxygen
is projected onto the surface, which rapidly oxidizes
• Oxides having lower melting point than the metal, melt and are blown
away by the force of the jet, to make a cut
• Fast and efficient method of cutting steel to a high degree of accuracy
• Torch is different from welding
• Cutting torch has preheat orifice and one central orifice for oxygen jet
• PIERCING and GOUGING are two important operations
• Piercing, used to cut a hole at the centre of the plate or away from the
edge of the plate
• Gouging, to cut a groove into the steel surface
GAS CUTTING…
Manual Gas Cutting
Weld joints
Brazing
and Soldering
• Brazing
It is a low temperature joining process. It is performed at temperatures
above 840º F and it generally affords strengths comparable to those of the
metal which it joins. It is low temperature in that it is done below the
melting point of the base metal. It is achieved by diffusion without fusion
(melting) of the base
Brazing can be classified as
Torch brazing
Dip brazing
Furnace brazing
Induction brazing
Brazing
Advantages
& Disadvantages
Advantages
•
•
•
•
Dissimilar metals which canot be welded can be joined by brazing
Very thin metals can be joined
Metals with different thickness can be joined easily
In brazing thermal stresses are not produced in the work piece. Hence there
is no distortion
• Using this process, carbides tips are brazed on the steel tool holders
Disadvantages
• Brazed joints have lesser strength compared to welding
• Joint preparation cost is more
• Can be used for thin sheet metal sections
Soldering
• It is a low temperature joining
process. It is performed at
temperatures below 840ºF for joining.
• Soldering is used for,
• Sealing, as in automotive
radiators or tin cans
• Electrical Connections
• Joining thermally sensitive
components
• Joining dissimilar metals
Fusion Welding Processes
Consumable Electrode
SMAW – Shielded Metal Arc Welding
GMAW – Gas Metal Arc Welding
SAW – Submerged Arc Welding
Non-Consumable Electrode
GTAW – Gas Tungsten Arc Welding
PAW – Plasma Arc Welding
High Energy Beam
Electron Beam Welding
Laser Beam Welding
Welding Processes
SMAW – Shielded Metal Arc Welding
Welding Processes
• Consumable electrode
• Flux coated rod
• Flux produces protective gas around weld pool
• Slag keeps oxygen off weld bead during cooling
• General purpose welding—widely used
• Thicknesses 1/8” – 3/4”
• Portable
Power... Current I (50 - 300 amps)
Voltage V (15 - 45 volts)
Power = VI  10 kW
Electric Arc Welding -- Polarity
Welding Processes
SMAW - DC Polarity
Straight Polarity
Reverse Polarity
(–)
(+)
Shallow penetration
(thin metal)
AC - Gives pulsing arc
- used for welding thick sections
(+)
(–)
Deeper weld penetration
GMAW – Gas Metal Arc Welding (MIG)
Welding Processes
• DC reverse polarity - hottest arc
• AC - unstable arc
Gas Metal Arc Welding (GMAW) Torch
• MIG - Metal Inert Gas
• Consumable wire electrode
• Shielding provided by gas
• Double productivity of SMAW
• Easily automated
Groover, M., Fundamentals of Modern Manufacturing,, p. 734, 1996
SAW – Submerged Arc Welding
Welding Processes
• 300 – 2000 amps (440 V)
• Consumable wire electrode
• Shielding provided by flux granules
Gas Metal Arc Welding (GMAW) Torch
• Low UV radiation & fumes
• Flux acts as thermal insulator
• Automated process (limited to flats)
• High speed & quality (4 – 10x SMAW)
• Suitable for thick plates
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GTAW – Gas Tungsten Arc Welding (TIG)
Welding Processes
Current I (200 A DC)
(500 A AC)
Power  8-20 kW
• a.k.a. TIG - Tungsten Inert Gas
• Non-consumable electrode
• With or without filler metal
• Shield gas usually argon
• Used for thin sections of Al, Mg, Ti.
• Most expensive, highest quality
Laser Welding
Welding Processes
• Laser beam produced by a CO2 or YAG Laser
• High penetration, high-speed process
• Concentrated heat = low distortion
• Laser can be shaped/focused & pulsed on/off
• Typically automated & high speed (up to 250 fpm)
• Workpieces up to 1” thick
Typical laser welding applications :
•Catheters & Other Medical Devices
•Small Parts and Components
•Fine Wires
•Jewelry
•Small Sensors
•Thin Sheet Materials Down To 0.001" Thick
Solid State Welding Processes
Friction Welding
Diffusion Welding
Ultrasonic Welding
Resistance Welding
Welding Processes
Friction Welding (Inertia Welding)
• One part rotated, one stationary
• Stationary part forced against rotating part
• Friction converts kinetic energy to thermal energy
• Metal at interface melts and is joined
• When sufficiently hot, rotation is stopped
& axial force increased
Welding Processes
Resistance Welding
Resistance Welding is the coordinated application of electric current and
mechanical pressure in the proper magnitudes and for a precise period of
time to create a coalescent bond between two base metals.
• Heat provided by resistance to electrical current (Q=I2Rt)
• Typical 0.5 – 10 V but up to 100,000 amps!
• Force applied by pneumatic cylinder
• Often fully or partially automated
- Spot welding
- Seam welding
Welding Processes
Resistance Welding
Resistance Welding is the coordinated application of electric current and
mechanical pressure in the proper magnitudes and for a precise period of
time to create a coalescent bond between two base metals.
• Heat provided by resistance to electrical current (Q=I2Rt)
• Typical 0.5 – 10 V but up to 100,000 amps!
• Force applied by pneumatic cylinder
• Often fully or partially automated
- Spot welding
- Seam welding
Welding Processes
Diffusion Welding
Welding Processes
• 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
• Good for dissimilar metals
• Bond can be weakened by surface impurities
Kalpakjian, S., Manufacturing Engineering & Technology, p. 889, 1992
Soldering & Brazing
Metal Joining Processes
Soldering & Brazing
• Only filler metal is melted, not base metal
• Lower temperatures than welding
• Filler metal distributed by capillary action
• Metallurgical bond formed between filler & base metals
• Strength of joint typically
– stronger than filler metal itself
– weaker than base metal
– gap at joint important (0.001 – 0.010”)
• Pros & Cons
– Can join dissimilar metals
– Less heat - can join thinner sections (relative to welding)
– Excessive heat during service can weaken joint
Soldering
Metal Joining Processes
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)
PCB Soldering
Manual PCB Soldering
Metal Joining Processes
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
PCB Reflow Soldering
Automated Reflow Soldering
Metal Joining Processes
SMT = Surface Mount Technology
• Solder/Flux paste mixture applied to PCB using screen print or similar
transfer method
• Solder Paste serves the following functions:
– supply solder material to the soldering spot,
– hold the components in place prior to soldering,
– clean the solder lands and component leads
– prevent further oxidation of the solder lands.
Printed solder paste on a printed circuit board (PCB)
• PCB assembly then heated in “Reflow” oven to melt solder and secure connection
Brazing
Metal Joining Processes
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)
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
Applications:
• Automotive - joining tubes
• Pipe/Tubing joining (HVAC)
• Electrical equipment - joining wires
• Jewelry Making
• Joint can possess significant strength
Brazing
Metal Joining Processes
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)
• Flux also used
• Types of brazing classified by heating method:
– Torch, Furnace, Resistance
Applications:
• Automotive - joining tubes
• Pipe/Tubing joining (HVAC)
• Electrical equipment - joining wires
• Jewelry Making
• Joint can possess significant strength
Brazing
Metal Joining Processes
Brazing
Figuring length of lap for flat joints.
X = Length of lap
T = Tensile strength of weakest member
W = Thickness of weakest member
C = Joint integrity factor of .8
L = Shear strength of brazed filler metal
Let’s see how this formula works, using an example.
Problem: What length of lap do you need to join .050" annealed Monel sheet to a metal of equal or greater strength?
Solution:
C = .8 T = 70,000 psi (annealed Monel sheet)
W = .050"
L = 25,000 psi (Typical shear strength for silver brazing filler metals)
X = (70,000 x .050) /(.8 x 25,000) = .18" lap length
Soldering & Brazing
Metal Joining Processes
Brazing
Figuring length of lap for tubular joints.
X = Length of lap area
W = Wall thickness of weakest member
D = Diameter of lap area
T = Tensile strength of weakest member
C = Joint integrity factor of .8
L = Shear strength of brazed filler metal
Again, an example will serve to illustrate the use of this formula. Problem: What length of lap do you need to join 3/4" O.D. copper
tubing (wall thickness .064") to 3/4" I.D. steel tubing?
Solution:
W = .064"
D = .750"
C= .8
T = 33,000 psi (annealed copper)
L = 25,000 psi (a typical value)
X = (.064 x (.75 – .064) x 33,000)/(.8 x .75 x 25,000)
X = .097" (length of lap)