Welding Definition • Welding is a metal joining process by applying heat sometimes with pressure and some times with intermediate or filler metal having high melting point. • As per AWS:- A weld as a localized coalescence of metal or non metal produced either by heating the material to suitable temp. with or with out the application of pressure or by the application of pressure alone. As per IS:- The weld as a union between two pieces of a metal at faces rendered plastic or liquid by heat or pressure or both.
Transcript
Welding Definition
• Welding is a metal joining process by applying heat sometimes with pressure and some times with intermediate or filler metal having high melting point.
• As per AWS:- A weld as a localized coalescence of metal or non metal
produced either by heating the material to suitable temp. with or with out the application of pressure or by the application of pressure alone.
As per IS:- The weld as a union between two pieces of a metal at
faces rendered plastic or liquid by heat or pressure or both.
Welding Safety
Welding Training 2012-13 TRF
Before Getting Started
Because arc welding involves an electric arc, the source of power is the first point to check. Be certain the engine/generator or transformer is in good order.
Are all electrical connections tight and properly made? Is the generator or transformer safety-disconnect switch
operable and have an adequate amperage rating? Are detaching plugs on smaller equipment easily accessible?
Are all dials and gauges operable? Are your cables, clamps and electrode holder in good
condition?
Check Your Welding Equipment
Protective Clothing
Gloves: All leather or fire resistant welding gloves (gauntlet style) in good condition.
Goggles/Glasses: Tempered lenses, shade #5, good fit with little or no gap/opening for protection against sparks, flying slag and bright torch flames.
Welding Helmet/Face Shield: Good condition, tight fit with proper lens shade for the work at hand.
Hearing Protection: Ear plugs and/or muffs should be worn during noisy operations such as air arcing or grinding. Most welding operations are noisy.
Protective Clothing
Clothing: Made from flame retardant cloth (avoid high polyester and nylon content) , free of oil and grease. Avoid loose clothing, trousers with cuffs, open collared shirts with pockets.
“Leathers”: Sleeves, apron or chaps should be available.
Steel Toed Shoes: All leather, high-top shoes with rubber soles in good condition. Full metal toe covers should be available.
Proper Guarding In Place
To prevent accidental contact, welding machines must have mechanical and electrical protection.
Guard all moving parts and insulate all current carrying components.
Mechanical power transmission apparatus with clutches, gears and couplings should have these danger points screened or guarded.
Have curtains/shields/barricades to protect those working near you.
Check The Cables Frequently
It is important that the neutral wire (often referred to as the ground' wire) be fully insulated. When DC current is used this is a current-carrying wire, and becomes the 'hot' wire.
Always keep them in good repair and out of water, oil, or ditches.
Try to avoid abrasion caused by rubbing against sharp corners or being dragged over objects.
Do not leave cables in the paths of workers and vehicles/equipment. If it is necessary to cross the line of traffic, suspend cables overhead, or cover, if possible.
Watch Those Splices
When splicing cables, make sure the connectors are well insulated and have a capacity equal to or greater than the cable.
Make splices with insulated pressure connectors or welded joints. Connecting lugs should have more than one bolt for a reliable, tight connection,
and complete insulation. Cables with splices within 10 feet of the holder should not be used.
Holders should be kept fully insulated because they support the electrode and transmit the current from the cable to the electrode. Fully insulated holders are an added safety factor for operation in close quarters reducing the danger of striking an accidental arc. Inspect frequently and replace insulation parts as needed!
Maintain Safe Electrode Holders
Using The Correct Current Is Important
Too little current reduces the efficiency of the operation.
Too much current causes inferior welds, overloads and damages equipment.
For the correct current, refer to the operations manual supplied with the equipment.
Check the current load with an amp meter if there seems to be variation.
Welding Fire Hazards
Do not use welding equipment near flammable vapors, liquids, dust or any other combustible materials.
Move welding work to a safe location whenever possible, or try to remove all movable combustibles to a safe place. If neither is possible, use spark proof curtains (not tarpaulins) to confine the sparks. Weigh the fireproof curtain down tightly against the floor.
An extra person is recommended as a fire guard if ignition of material is possible.
A fire inspection should be performed prior to leaving a work area and for at least 30 minutes after the operation is completed.
Keep shop clean in areas where welding is to be done.
Fire Hazards, cont. Never weld or cut on containers that have
held a flammable or combustible material unless the container is thoroughly cleaned or filled with an inert gas.
Fire extinguishers should be nearby, of proper size, type and number for the hazards involved.
Concrete floors are the safest welding locations.
Wood floors can be made fire-safe by covering them with a fireproof cloth.
Do not weld near electrical fittings or lines.
Electric Shock Hazards
Ground the frame of portable and stationary welding machines; as specified in the Grounding Section of the National Electrical Code.
Approved plugs and receptacles are recommended for cables of portable welding machines capable of carrying full-load machine circuits.
Keep welding supply cables away from power supply cables and other high tension wires.
Shock Hazards, cont.
When changing electrodes, never stand on wet or ungrounded surfaces; never use bare hands or wet gloves.
Always use dry gloves and wear rubber soled shoes.
Do not cool electrode holders by emersion in water.
Turn off power supply when welder is not in use and before performing maintenance.
Operating procedures are covered in the Electric Welding Section of the National Electrical Code.
The Keys To Eye Protection
Minimize reflective materials in the work area (paints, other wall coverings, etc.)
A tight fitting helmet in good condition.
All lens components in place and in good condition.
Utilizing the proper lens shade…….
Protect eyes and face from flying particles by use of safety glasses or face shield.
Wear adequate protective clothing.
Always wear leather gloves.
Wear high top shoes.
Keep collar, shirt pockets, etc. buttoned.
Handle hot metal with pliers or tongs.
Dispose of electrode stubs properly.
Preventing Burns
Commonly Welded Base Metal
Ferrous Metal Non Ferrous Metal Wrought Iron Aluminum & it's alloy Carbon Steel Copper & it's alloy Cast Steel Magnesium & it's alloy Stainless Steel Nickel & it's alloy Cast Iron Zinc & it's alloy Alloy Steel
Energy Sources For Welding
• Gas Flame • Electric Arc• Electron Beam• Laser Beam• Friction• Ultra Sound• Explosive• Electrical Resistance
Types of Welding
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Welding Applications• Ship Building• Air craft construction• Bridges• Earth moving machinery & cranes• Piping & Pipe lines• Rail road equipment• Chemical Process plant• Power Plant• Structural Building
Welding Process Model
Weld design
Process Selection
Developing Welding Procedure
Welding Operation
Testing
Information from Service condition (Field)
WELD TERMINOLOGY
WELD TERMINOLOGY
Max bead width (X) during welding will be 12 mm in GMAW processes and 2.5 to 3 times of rod dia. in SMAW. For Both Groove and fillet welds
X
WELD TERMINOLOGY
THROAT THICKNESS
HEAT AFFECTED ZONE (H AZ)
WELD TERMINOLOGY
TOETOE
DEPTH OF ROOT BEAD "PENETRATION"
TOE
EFFECTIVE THROAT THICKNESS PENETRATION
• A pool of molten metal is formed near electrode tip, and as electrode is moved along joint, molten weld pool solidifies in its wake
Arc Welding
SMAW
• Shielded Metal Arc Welding• Stick welding• Arc Welding
• A welding process where similar materials are joined with a heating process caused by an electric arc. In the most common use, this process includes the use of a filler metal.
Shielded Metal Arc Welding (SMAW)
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EquipmentA. Polarity switch
B. Power cord
C. Electrode holder
D. Electrode
E. Base metal
F. Ground clamp
G. Electrode lead
H. Ground lead
I. Amperage scale
J. Amperage adjustment
K. On/Off switch
L. Welder case
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Brushing Method
• Hold end of electrode about 1/4 - 1/2 inch above the surface.
• Lower helmet• Gently brush surface of the
metal with the end of the electrode.
• When arc starts, lift electrode 1/8 inch.
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Tapping Method
• Set up welder
• Hold the electrode at the travel angle and 1/4 - 1/2 inch above the metal.
• Quickly lower the electrode until it touches the metal and then lift it 1/8 inch.
SMAW ELECTRODE
• Smaw Electrode consist of a straight piece of solid metallic wire called core wire, having a concentric covering or coating of Flux.
SMAW ELECTRODE• The Electrode size refers to the Dia of it’s core wire.• Coating Factor:- The coating factor of a electrode is the
ratio of coating dia to the core wire dia. C.F. = D/d As Per IS 814-1991 On the basis of coating factor electrodes are often
referred to as Light-Coated Up to 1.3 CF Medium-Coated 1.3 to 1.5 CF Heavy-Coated Above 1.5 CF
Function Of Flux Coating
• Providing Gas Shield around the arc.• Facilitate the arc striking and maintain it.• Produces slag over the weld bead.• Helps to deoxidized & refine the weld metal.• Support to Increase the deposition efficiency. • Provide to achieve good penetration.
• China Clay,Mica,Sodium Silicates.• Cellulose,Starch,Calcium Carbonate• Ferromanganese, Ferrosilicon• Calcium Carbonate,Pottasium Silicate• Sodium Silicate,Sugar,Asbestus • Glycerin, China Clay,Talc,Mica• Iron Power
• Provides Deep Penetration• Increased electrode burn off rate• Can be use for any welding position• Mainly used for D.C. Supply
Example:-As Per Aws E6010,E6011 etc.
Rutile Electrode
• Gives smooth weld bead a)- Viscous Type:- Suitable for Butt & Fillet weld, for flat &
horizontal position with A.C. b)- Fluid Type:- Suitable for Vertical & over head position with
D.C. Example:- As per Aws E6012,E6013,E7013 etc.
Iron Oxide Coating
a)- Inflated Type:- Applicable for deep groove welding for flat
position with both A.C. & D.C.
b)- Solid Type:- Gives the thick covering, used for single run of
fillet weld & suitable for A.C. & D.C. Example:- As per Aws E6030,E7030
Lime Fluorspar(Basic)
• Low hydrogen Electrodes• Suitable for all position• Before use it required backing.
Example:- As per Aws E7016,E7018
Flux Coating Method
• Dipping Method
• Extrusion Method
Selection of Electrode
• Compare with the Chemical composition of base metal.• Thickness of work piece.• Nature of Electrode coating.• Welding position.• Type of joint & run/no. passes.• Type of Polarity.• Weld bead geometry.• Surface finish.• Mechanical Properties.• Cost of electrode.
ELECTRODE CATEGORY
Non Consumable Electrode
• Carbon or Graphite Electrodes
• Tungsten Electrodes
Consumable Electrode
• Bare Electrodes
• Flux Coated Electrodes
Electrode Performance Groups
• Fast Freeze Electrodes
• Fast Fill Electrodes
• Fill Freeze Electrodes
• Low Hydrogen Electrodes
Fast Freeze Electrodes
• Quick solidification of weld pool.
• Deep penetrating.
• Recommended for vertical & over head position.
• Called reverse polarity electrode.
Fast Fill Electrodes
• Highest deposition rate.
• Stable arc.
• Thick flux.
• Shallow penetration.
• Flat position and horizontal laps only
Fill Freeze Electrodes
• General purpose electrodes.
• Medium deposition rate.
• Called straight polarity electrode.
Low Hydrogen Electrodes
• Welding characteristics of fill-freeze.
• Producing x-ray quality deposits.
• Less possibility of weld crack.
• Designed for medium carbon and alloy steels.
Electrode Classification
• Constituents of flux coating.• Nature of slag.• Current & polarity.• Arc behavior.• Welding position.• Weld appearance.• Quality of Weld.
1 - Welding position: 1 = ALL, except vertical down
3 – Indicates coating type (RUTILE), welding current and polarity
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Electrode Classification
•The AWS system designates:
1 tensile strength,
2 weld position3 coating (flux) 4 current.
Electrode Classification (Example)
E7018
• E indicates electrode
• 70 indicates 70,000 psi tensile strength
• 1 indicates use for welding in all positions
• 8 indicates low hydrogen
E 7018
Care & Storage of Electrodes• Electrodes are damaged by rough treatment,
temperature extremes and moisture.• The should be kept in their original container
until used.• Electrode should be stored in dry & well ventilated store
room.• Storage temp. should be about 12°C above that of external
air temp. with 0-60% humidity.• Low hydrogen electrodes should be dried in an oven at
about 120°C to 150°C for 1 to 2 hours before use.
Electrode Angle• Travel Angle• Work Angle
The travel angle is the angle of the electrode parallel to the joint.
The correct travel angle must be used for each joint. Beads = 15o from vertical or 75o from the
work. Butt joint = 15o from vertical or 75o from the
work. Lap joint = 45o. T joint = 45o. Corner = 15o from vertical or 75o from the
work.
• The work angle is the angle of the electrode perpendicular to the joint.
Electrode Angle
• The appropriate angle must be used for each joint. Beads = 90o
Butt joint = 90o
Lap joint = 45o
T joint = 45o
Corner = 90o
Arc Length
The arc length is the distance from the metal part of the electrode to the weld puddle.
The best arc length is not a fixed distance, but should be approximately equal to the diameter of the electrode.
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Arc Travel SpeedThe speed of travel is measured in inches per minute The ideal speed can be calculated using the volume of the joint and the deposition rate of the electrode.The correct welding speed is indicated by the shape of the ripples.
Too fast = narrower width, elongated ripple pattern, shallow penetration.
Recommended = width 2-3 times diameter of electrode, uniform ripple pattern, full penetration.
Too slow = excessive width, excessive penetration
SMAW Joints
• Butt Joint
• Lap Joint
• T Joint
• Corner Joint
• Edge Joint57
Basic Types of Joints & Terms
Types of joints
Basic Welded Joints • Butt Joint
A Joint between two members aligned Approximately in the same Plane.
Different Edge Shapes and Symbols for some Butt-Joints
Basic Welded Joints
Corner Joint
Corner joint - a joint between two members located at right angles to each other
Some Different Edge Shapes and Symbols for Corner Joints
Basic Welded Joints
T- joint - a joint between two members located approximately at right angles to each other in the form of a T
T-Joint
Some Different Edge Shapes and Symbols for T-Joint
Basic Welded Joints
Lap JointLap Joint- a joint between two overlapping members
Some Different Edge Shapes and Symbols for Lap Joints
Basic Welded Joints
Edge Joint
Edge joint- a joint between the edges of two or more parallel or nearly parallel members
Some Different Edge Shapes and Symbols for Edge Joints
• Welding Symbol is a method of representing the weld symbol on the drawing.
Reference Line (Required element)
•Reference Line
Always Horizontal
Reference Line (Required element)
Arrow
Arrow Line
Reference Line (Required element)
Arrow
Tail
Tail
Reference Line (Required element)
Arrow
Tail
Reference Line must always be horizontal,
Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area.
The tail of the welding symbol is used to indicate the welding or cutting processes, as well as the welding specification, procedures, or the supplementary information to be used in making the weld.
Reference Line (Required element)
Arrow
Tail
Reference Line must always be horizontal,
Arrow points to the line or lines on drawing which clearly identify the proposed joint or weld area.
The tail of the welding symbol is used to indicate the welding or cutting processes, as well as the welding specification, procedures, or the supplementary information to be used in making the weld.
Basic components of a WELDING SYMBOL
Tail omitted when reference not used
Arrow connects reference line to arrow side member of joint or arrow side of joint
A circle at the tangent of the arrow and the reference line means welding to be all around.
All the way Around
A flag at the tangent of the reference line and arrow means Field Weld.
Field Weld Symbol
ARROW SIDE/NEAR SIDE
OTHER SIDE/FAR SIDE
Weld Symbol Terminology
Break in arrow means arrow side mustbe side that beveling or other preparation required.
Fillet Weld (Arrow Side Only)
Fillet Weld (Other Side)
10
10
Size of Fillet Weld Noted
10
10
Depth of preparation or groove
Example of Double Bevel Groove weld
Plug or Slot Weld Symbol
Arrow Side
Single-Bevel-Groove and Double Fillet weld Symbols
SMAW Welding Techniques
Weld Bead• A weld resulting from a pass
Stringer BeadWeave Bead
Passes
• Weld Pass - A single progression of welding along a joint. The result of a pass is a weld bead or layer
Root Pass Hot Pass
Fill Pass Cover Pass
Techniques• Stringer (drag) (whip)• Weave
– Circles– crescent– zig zag– box weave– double J
Welding Defects
UNDERCUT
POROSITY
INCOMPLETE FUSION
OVERLAP
UNDERFILL
SPATTER
EXCESSIVE CONVEXITY
EXCESSIVE CONCAVITY
EXCESSIVE WELD REINFORCEMENT
INCOMPLETE PENETRATION&
EXCESSIVE PENETRATION
UNACCEPTABLEWELD PROFILES
Preheat Treatment
• Preheat reduces the temperature differential between the weld region and the base metal– Reduces the cooling rate, which reduces the chance of
forming martensite in steels– Reduces distortion and shrinkage stress– Reduces the danger of weld cracking– Allows hydrogen to escape
PRE HEATING OF WELD JOINTS.
Pre heating :The Operation of heating the weld joint to some pre determined Temp before start of
welding called as Pre Heating .
Why Required : 1. To Controls the differential cooling rate i.e. slow down the cooling rate in weld which creates greater resistance to cracking . 2. To reduce the stress in weld and adjacent base metal 3. To improve some mechanical property like notch toughness in weld
Processes:* Heat the weld joint area by means of suitable heating torch before start of welding. * Use fuel or oxy fuel as per requirement. * The heating area shall be equals to base metal thk. of thickest member but not less than 75 mm in all directions . * Job shall be heated through the thickness and obtain the minimum pre heat temp at opposite surface as shown in table * For Different thick with different pre heat temperature the highest of the two shall be considered . and for alloy steel Min and max range shall be considered. * Checking of preheating shall be carried out just before arc striking and on the far side by thermal chalk or any other means . Material IS 2062(t>32
mm thk)C- 45 (t>16 mm thk)
HARDOX- 400 (t=20 to 45 mm)
SAILMA- 450 SAILMA- 350 SAIL HARD Had Field SS-304 any thk
SS -316L any thk
Pre Heat Temp ( .C)
65 to 110
150 -200
75 to 100
150 to 175
150 to 175
150 Normal Temp
Normal Temp
Normal Temp
Post weld Heat Treatment and Hydrogen Cracking
• Postweld heat treatment (~ 1200°F) tempers any martensite that may have formed– Increase in ductility and toughness– Reduction in strength and hardness
• Residual stress is decreased by postweld heat treatment• Rule of thumb: hold at temperature for 1 hour per inch of
plate thickness; minimum hold of 30 minutes
Steel
Penetration:• Incomplete penetration occurs when the depth of the welded joint is insufficient• Penetration can be improved by the following practices :• Increasing the heat Input• Reducing the travel speed during the welding• Changing the joint design• Ensuring the surfaces to be joined fit properly
Porosity• Caused by gases released during melting of the weld area but trapped
during solidification, chemical reactions, Contaminants• They are in form of spheres or elongated pockets• Porosity can be reduced by • Proper selection of electrodes• Improved welding techniques• Proper cleaning and prevention of contaminants• Reduced welding speeds
Slag Inclusions• Compounds such as oxides ,fluxes, and electrode-coating materials that are
trapped in the weld Zone• Prevention can be done by following practices :• Cleaning the weld bed surface before the next layer is deposited• Providing enough shielding gas• Redesigning the joint
Incomplete Fusion and Penetration• Produces lack of weld beads
• Practices for better weld :
• Raising the temperature of the base metal
• Cleaning the weld area, prior to the welding
• Changing the joint design and type of electrode
• Providing enough shielding gas
Weld Profile
• Under filling results when the joint is not filed with the proper amount of weld metal.
• Undercutting results from the melting away of the base metal and consequent generation of a groove in the shape of a sharp recess or notch.
• Overlap is a surface discontinuity usually caused by poor welding practice and by the selection of improper material.
Discontinuities in Fusion Welds
Fig : Schematic illustration of various discontinuities in fusion welds.
Cracks• Cracks occur in various directions and various locations
Factors causing cracks:
• Temperature gradients that cause thermal stresses in the weld zone
• Variations in the composition of the weld zone.
• Embrittlement of grain boundaries
• Inability if the weld metal to contract during cooling
Cracks
Fig : Types of cracks (in welded joints) caused by thermal stresses that develop during solidification and contraction of the weld bead and the surrounding structure. (a) Crater cracks (b) Various types of cracks in butt and T joints.
GMAW
• An arc welding process that uses an arc between a continuous filler metal electrode and the weld pool to produce a fusion (melting) together of the base metal
• The process is used with a shielding gas supplied from an external source without pressure.
Welding Circuit
Welder
Wire Spool
Welding Gun
Shielding Gas
Wire Feeder
Work CableWork Piece
GMAW welding Machine Setup
Welding Power SourceWork Clamp
Welding Gun
Wire Spool
Shielding Gas
Wire FeederRegulator
GMAW component diagram
How It Works
An arc is struck between a continuously fed filler wire and the work.
The arc is protected from oxidation by a shielding gas over the weld pool.
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Nomenclature of Area Between Nozzle and Work piece
GMAW EQUIPMENTS
Contact Tip & Nozzle Drive Rolls
GMAW EQUIPMENTS
Flow Meter Wire Feeder Unit
MODES OF METAL TRANSFER
• Metal transfer refers to how filler metal is deposited to the base metal to form the weld bead.
• The common modes of metal transfer are • Short-circuit • Globular• Axial-spray• Pulsed-spray transfers
MODES OF METAL TRANSFER
• The mode of metal transfer is determined by many mitigating factors:
• Base Metal Type• Filler Metal Composition• Electrode Diameter• Polarity• Arc Current• Arc Voltage/Arc Length• Shielding Gas Composition• Welding Position
GMAW Modes of Metal Transfer
Spray Globular
Short Circuiting Pulsed Spray
GMAW Equipment
• Power Supply– Direct Current Electrode Positive (DCEP)
• (Electrons flow from – to +)
• Wire Feeder– Electrical mechanical device that feed required amount
of filler material at a constant rate of speed
GMAW Equipment (Cont)
• Welding filler electrode– Small diameter consumable electrode that is supplied to
the welding gun by the roller drive system• Shielding Gas
– Gas used to protect the molten metal from atmospheric contamination
• 75%Argon (inert gas) & 25% Carbon Dioxide most common gas used for GMAW
Inert Gases
• Argon, helium, nitrogen, and carbon dioxide• Form a protective envelope around the weld area• Used in
– MIG– TIG– Shield Metal Arc
GMAW Filler Metal Designations
ER - 70S - 6Electrode
Rod (can be used with GMAW) Minimum ultimate tensile
strength of the weld metal
Solid Electrode
Composition6 = high silicon
Shielding Gas
• Shielding gas can affect– Weld bead shape– Arc heat, stability,
and starting– Surface tension– Drop size– Puddle flow– Spatter
• Correct metal identification– Metal properties vary
• Correct electrode selection – Depends on metal type, thickness and position of weld
• Correct amperage– Depends upon electrode type, size, position, and metal thickness– Influence “burn off rate” and affect arc length and speed of travel
Successful Arc Welding depends upon:
• Proper Arc length– Influences the amount of heat during the weld
• Correct speed of travel – Determines the width of bead and indirectly the strength
of the weld• Angle of electrode
– Determines the bead shape and controls slag and gas inclusions
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Safe Practices
• Safety most important consideration to both worker and employer
• Welding no more dangerous than other industrial operations
• Safety precautions and protective equipment required for MIG/MAG process essentially same as for any other electric welding process
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Clothing Regulations
• Standard arc welding helmets with lenses ranging in shade from no. 6 for work using up to 30 amperes to no. 14 for work using more than 400 amperes should be worn– Arc should never be viewed with the naked eye when
standing closer than 20 feet • Skin should be covered completely to prevent burns
and other damage from ultraviolet light– Back of the head and neck should be protected from
reflected radiation – Gloves should always be worn
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Clothing Regulations
• Shirts should be dark in color to reduce reflections– Have tight collar and long sleeves– Leather, wool and aluminum-coated cloth can
withstand action of radiant energy reasonably welld
22 - 156
Handling of Gas Cylinders
• Stored cylinders should be in protected area away from fire, cold, and grease and away from general shop activity
• Cylinders must be secured to equipment to prevent their being knocked over
• Proper regulators and flowmeters must be used with each special type of cylinder
22 - 158
Handling of Gas Cylinders
• Cylinders should not be dropped, used as rollers, lifted with magnets, connected into electric circuit, or handled in any other way that might damage cylinder or regulator
• When cylinders empty, should be stored in upright position with valve closed
