Report for MTE521 Metallurgy in Welding By ndrilon 2009
What is WELDING in engineering, any process in which two or more pieces of metal are joined together by the application of heat, pressure, or a combination of both.
Master chart of Arc Welding and Related Methods
Types of welds
Bead Groove Fillet Surfacing Tack Plug Slot Resistance
Bead weld
Produced by a single pass Stinger Beadwhich is made without weaving motion. Weave Beadmade by side-side oscillation
Groove weld
Groove welds are simply welds made in the groove between two members to be joined.
Surfacing welds
a surfacing weld is com posed of one or more stringer or weave beads. Surfacing, sometimes k nown as hardfacing or wearfacing. is often used to build up worn shafts, gears, or cutting edges.
Fillet weld
This weld is used to join two surfaces that are at approximately right angles to each other in a lap, tee, or comer joint
Plug and Slot weld
are welds made through holes or slots in one member of a lap joint.
Tack weld
is a weld made to hold parts of an assembly in proper alignment temporarily until the final welds are made. they are normally between 1/2 inch to 3/4 inch in length, but never more than 1 inch in length.
Basic Welding Positions
Common
Welding Types
Arc Welding (AW)
Oxyfuel Gas Welding(OFW)
Resistance Welding
Types of ARC Welding
Metal Arc Welding (SMAW) Submerged Arc Welding (S AW) Flux Cored Arc Welding (FCAW)
Gas Tungsten Arc Welding (GTAW or TIG)
Gas Metal Arc Welding (GMAW or MIG)
Shielded
SMAW is performed by striking an arc between a coated-metal electrode and the base metal. Flux- the coating of the metal electrode will form as shield to the molten metal.
Shielded Metal Arc Welding
SMAW OPERATION
Arc Welding MAchines
Electrode and Holder
Advantages of SMAW High quality welds are made rapidly at a low cost. Can be used easily even to thick and wide work piece to be joined. Can be used from thinner to thicker materials.
Disadvantages SMAW bigger electric current Dirty work finish Root pass is lower than TIG and MIG Prone to slag inclusions Weld deposits is prone to blue holes
Consumes
SUBMERGED ARC WELDING (SAW)
Is a process in which is done by an automatic electrode feeding machine wherein the tip of the electrode is submerged into a granular flux which shields the arc and the molten metal.
SAW operations
SAW Welding Machine
SAW block diagram
SAW APPLICATIONS
widely used in heavy steel plate fabrication work. welding of structural shapes. longitudinal seam of larger diameter pipe. manufacture of machine components for all types of heavy industry. manufacture of vessels. pressure and storage tanks.
Advantages of SAW
high quality of the weld metal. extremely high deposition rate and speed. smooth, uniform finished weld with no spatter. little or no smoke. no arc flash, thus minimal need for protective clothing. high utilization of electrode wire. easy automation for high-operator factor. normally, no involvement of manipulative skills.
Disadvantages of SAW
used only to weld mild and low-alloy high-strength steels. Unseen arc and puddle can cause poor penetration. high-heat input, slow-cooling cycle can be a problem when welding quenched and tempered steels. limited-position welding process only flat and horizontal
GTAW or TIG
Gas Tungsten Arc Welding or Tungsten Inert Gas or HELIARC Welding
is a process in which the joining of metals is produced by heating therewith an arc between a tungsten (non consumable) electrode and the work.
A shielding gas is used, normally Argon.
normally done with a pure tungsten or tungsten alloy rod, but multiple electrodes are sometimes used.
Filler metals are used such as stainless steel, Aluminum and Bronze.
Flux
Cored
Arc Welding (FCAW)
is an automatic or semi-automatic electric arc welding process that uses an arc between a continuously fed flux-filled electrode and the weld pool. The process is used with shielded gas from a flux contained within the tubular electrode with or without additional shielding from an externally supplied gas.
FCAW flux filled electrode and torch
No shielding gas (FCAW)
With Shielding Gas (FCAW)
Two Types of FCAW
no shielding gas - using flux core in the tubular consumable electrode
uses a shielding gas - gas that must be supplied by an external supply. This is known informally as "dual shield" welding.
Uses of FCAW Mild and low alloy steels Stainless steels Some high nickel alloys Some wear facing/surfacing alloys
Advantages of FCAW
FCAW may be an "all-position" process with the right filler metals (the consumable electrode) No shielding gas needed making it suitable for outdoor welding and/or windy conditions A high-deposition rate process (speed at which the filler metal is applied) in the 1G/1F/2F Some "high-speed" (e.g., automotive applications) Less pre cleaning of metal required Metallurgical benefits from the flux such as the weld metal being protected initially from external factors until the flux is chipped away
Disadvantages of FCAW
Melted Contact Tip ± happens when the electrode actually contacts the base metal, thereby fusing the two Irregular wire feed ± typically a mechanical problem Porosity ± the gases (specifically those from the flux-core) don¶t escape the welded area before the metal hardens, leaving holes in the welded metal More costly filler material/wire as compared to GMAW Less suitable for applications that require painting, such as automotive body works. Cannot be used in a rugged environment limited to shop use only.
FCAW Equipment set up
TIG WELDING
GTAW or TIG process
GTAW Welding Equipment
TIG Welding Machine
TIG Torch
ADVANTAGES of GTAW
most popular met hod for welding aluminum stainless steels, and nickel-base alloys. Produces top quality welds. No smoke or fumes clean no slag and spatter to be clean during welding reduced distortion in t he weld joint because of t he concentrated heat source. is very good for joining t hin base metals because of excellent control of heat input.
ADVANTAGES of GTAW especially
useful for joining aluminum and magnesium which form refractory oxides, excellent to use for t he reactive metals like titanium and zirconium, which dissolve oxygen and nitrogen and become brittle if exposed to air while melting.
welding
process by fusion alone wit hout t he addition of filler metal.( non-consumable electrode) Used in very critical service application and on very expensive metal or parts.
Disadvantages of GTAW
EXPENSIVE a. Arc travel speed and weld metal deposition rates are lower. b. high price of Inert gases for shielding such as Argon and Helium. c. price of Tungsten electrode is high. d. Equipment costs are greater t han t hat for ot her processes, such as SMAW, which require less precise controls.
M ANY
LIMITATIONS and cannot be used in
full welding operations
Limitations of GTAW
SLOWER WELDING PROCESS slower t han consumable electrode arc welding.
FAST CONTAMINATION 1.
During transfer of molten tungsten from t he electrode to t he weld.
2. tungsten inclusion(unbalance gas s hielding t he inclusion is hard & brittle) 3.
During exposure of t he hot filler rod to air.
4. When t here is improper welding techniques along t he line
GMAW
or
MIG
is an electric arc welding process which joins metals by heating t hem wit h an arc established between a continuous filler metal (consumable) electrode and t he work.
Shielding
of t he arc and molten weld pool is obtained entirely from an externally supplied gas or gas mixture bot h inert and reactive gases.
GMAW Welding Operations
MIG Machine with Spool feeder
GUN used in GMAW
MIG Torch
GMAW Weld Diagram
Advantages of GMAW
Produced High quality welds & much faster than with SM AW and TIG welding.
No flux is used no slag entrapment in the weld metal.
Very little loss of alloying elements as the metal transfers across the arc. Minor
weld spatter is produced, and it is easily removed.
Advantages of GMAW
Versatile and can be used with a wide variety of metals and alloys, such as Aluminum, Copper, Magnesium, Nickel, Iron and many of their alloys. The process can be operated in several ways, including semi- and fully automatic. MIG
welding is widely used by many industries for welding a broad variety of materials, parts, and structures.
Disadvantages of GMAW
IT cannot be used in t he vertical or overhead welding positions due to t he high heat input and t he fluidity of t he weld puddle.
Has complex equipment compared to equipment used for t he shielded metal-arc welding process.
Oxygen Fuel Gas Welding (OFW) is a group of welding processes which join metals by heating wit h a fuel gas flame or flares wit h or wit hout t he application of pressure and wit h or wit hout t he use of filler metal.
Types of Oxy-fuel Gas Welding Oxy-Acetylene or Oxygen- Acetylene Gas Welding Oxy-Hydrogen or Oxygen- Hydrogen Gas Welding hylacetone-Propadiene Gas Welding Met Pressure Gas Welding.
Advantages of Oxy-fuel Gas Welding
Easy to use bot h welding and cutting
Controlled heat input
Controlled bead size
Convenient to use in welding t hin sheets, tubes and small diameter pipes
Disadvantages of Oxy-Fuel Gas Welding
Cannot be use to weld on t hick work piece.
Expensive gas
Oxy-Acetylene Diagram Welding Equipment
Complete
Oxy-Acetylene Welding Equipment
Resistance Welding
is a process in which the fusing temperature is generated at the joint by the resistance to the flow of an electrical current.
is accomplished by clamping two or more sheets of metal between copper electrodes and then passing an electrical current through them. When the metals are heated to a melting temperature, forging pressure is applied through either a manual or automatic means to weld the pieces together. Two common types are Spot and Seam welding
2 Types of Resistance Welding SPOT WELDING SEAM WELDING
SPOT WELDING The metal to be joined is placed between two electrodes and pressure is applied. A charge of electricity is sent from one electrode t hrough t he material to t he ot her electrode.
