Report for MTE521Metallurgy in WeldingBy 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 Bead-

which is made without weaving motion.

Weave Bead- made 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

 composed  of  one  or  more stringer  or  weave  beads.  Surfacing,  sometimes  known 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 sur- faces 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

Shielded Metal Arc Welding (SMAW) Submerged Arc Welding (SAW) Flux Cored Arc Welding (FCAW)

Gas Tungsten Arc Welding (GTAW or TIG)

Gas Metal Arc Welding (GMAW or MIG)

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

Consumes 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

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 steelsStainless steelsSome high nickel alloysSome 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 method 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 the weld joint because of

the concentrated heat source. is very good for joining thin 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 the 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 without the 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 than that

for other processes, such as SMAW, which require less precise controls.

MANY LIMITATIONS and cannot be used in full welding operations

Limitations of GTAW

SLOWER WELDING PROCESS

slower than consumable electrode arc welding. FAST CONTAMINATION

1. During transfer of molten tungsten from the

electrode to the weld.

2. tungsten inclusion(unbalance gas shielding the inclusion is hard & brittle)

3. During exposure of the hot filler rod to air.

4. When there is improper welding techniques along the line

GMAW or MIG is an electric arc welding process which

joins metals by heating them with an arc established between a continuous filler metal (consumable) electrode and the work.

Shielding of the arc and molten weld pool is obtained entirely from an externally supplied gas or gas mixture both 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 SMAW 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 the vertical or overhead welding positions due to the high heat input and the fluidity of the weld puddle.

Has complex equipment compared to equipment used for the shielded metal-arc welding process.

Oxygen Fuel Gas Welding (OFW)

is a group of welding processes which join metals by heating with a fuel gas flame or flares with or without the application of pressure and with or without the use of filler metal.

Types of Oxy-fuel Gas Welding Oxy-Acetylene or Oxygen- Acetylene

Gas Welding Oxy-Hydrogen or Oxygen- Hydrogen

Gas Welding Methylacetone-Propadiene Gas

Welding Pressure Gas Welding.

Advantages of Oxy-fuel Gas Welding

Easy to use both welding and cutting

Controlled heat input

Controlled bead size

Convenient to use in welding thin sheets, tubes and small diameter pipes

Disadvantages of Oxy-Fuel

Gas Welding

Cannot be use to weld on thick 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 through the material to the other electrode.

SEAM Welding

is like spot welding

except that the spots overlap each other, making a continuous weld seam.