FCAW Procedure

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L&T-MHI BOILERS PRIVATE LIMITED HAZIRA Welding Engineering

TITLE FCAW

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INDEX 1. Principles of Flux-cored arc welding (FCAW) This document is the property of L&T-MHI BOILERS PRIVATE LIMITED and must not be copied or lent without their permission in writing.

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2. Typical Flux-cored arc welding (FCAW) Setup 3. Conditions That Affects Weld Bead Shape 4. Gun Movement During Welding 5. Weld Bead Characteristics 6. Defects in Welding

Principles of Gas Metal Arc Welding (GMAW) This document is the property of L&T-MHI BOILERS PRIVATE LIMITED and must not be copied or lent without their permission in writing.

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Flux-cored arc welding (FCAW or FCA) is a semi-automatic or automatic arc welding process. FCAW requires a continuously-fed consumable tubular electrode containing a flux and a constantvoltage or, less commonly, a constant-current welding power supply. An externally supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the necessary protection from the atmosphere. The process is widely used in construction because of its high welding speed and portability. FCAW was first developed in the early 1950s as an alternative to shielded metal arc welding (SMAW). The advantage of FCAW over SMAW is that the use of the stick electrodes used in SMAW is unnecessary. This helped FCAW to overcome many of the restrictions associated with SMAW. FCAW can be done in three different ways: 1. Semiautomatic Welding - equipment controls only the electrode wire feeding. Movement of welding gun is controlled by hand. This may be called hand-held welding. 2. Machine Welding - uses a gun that is connected to a manipulator of some kind (not handheld). An operator has to constantly set and adjust controls that move the manipulator. 3.

Automatic Welding - uses equipment which welds without the constant adjusting of controls by a welder or operator.On some equipment, automatic sensing devices control the correct gun alignment in a weld joint.

Basic equipment for a typical FCAW semiautomatic setup: 1. Welding Power Source - provides welding power. 2. Wire Feeders (Constant Speed And Voltage-Sensing) - controls supply of wire to welding gun. Constant Speed Feeder - Used only with a constant voltage (CV) power source. This type of feeder has a control cable that will connect to the power source. The control cable supplies power to the feeder and allows the capability of remote voltage control with certain power source/feeder combinations. The wire feed speed (WFS) is set on the feeder and will always be constant for a given preset value. Voltage-Sensing Feeder - Can be used with either a constant voltage (CV) or constant current (CC) - direct current (DC) power source. This type of feeder is powered off of the arc voltage and does not have a control cord. When set to (CV), the feeder is similar to a constant speed feeder. When set to (CC), the wire feed speed depends on the voltage present. The feeder changes the wire feed speed as the voltage changes. A voltage sensing feeder does not have the capability of remote voltage control. 3. Supply of Electrode Wire. 4. Welding Gun - delivers electrode wire and shielding gas to the weld puddle. 5. Shielding Gas Cylinder - provides a supply of shielding gas to the arc.

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Typical Gas Metal Arc Welding (FCAW) Setup

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Conditions That Affects Weld Bead Shape:

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Gun Movement during Welding:

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Weld Bead Characteristics: Poor

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Weld Bead Characteristics: Good

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Activities to be done prior to welding        

Clean the surface to be welded Check seam no Check that machine is properly calibrated Get the preheat and interpass temperature sticks See that that the welder is qualified in the position in which joint is to be welded Refer WPS, shop weld plan for the respective joints. Check earthing lug is tightly fitted to prevent arc strike on the base metal Ensure proper set-up of the joint

Activities to be done while Welding   

Set welding parameters within the range as specified in WPS Ensure the temperature is between preheat and interpass temperature as specified in WPS Maintain preheat and interpass temperature as per WPS

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Defects in Welding: Porosity Porosity − small cavities or holes resulting from gas pockets in weld metal.

Possible Causes

Inadequate shielding gas coverage. Wrong gas. Dirty welding wire.

Workpiece dirty. Welding wire extends too far out of Inadequate shielding gas coverage.

Corrective Actions Check for proper gas flow rate. Remove spatter from gun nozzle. Check gas hoses for leaks. Eliminate drafts near welding arc. Place nozzle 1/4 to 1/2 in (6-13 mm) from workpiece. Hold gun near bead at end of weld until molten metal solidifies. Use welding grade shielding gas; change to different gas. Use clean, dry welding wire. Eliminate pick up of oil or lubricant on welding wire from feeder or liner. Remove all grease, oil, moisture, rust, paint, coatings, and dirt from work surface before welding. Use a more highly deoxidizing welding wire (contact supplier). Be sure welding wire extends not more than 1/2 in (13 mm) beyond nozzle. Check for proper gas flow rate. Remove spatter from gun nozzle.

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Excessive Spatter Excessive Spatter − scattering of molten metal particles that cool to solid form near weld bead

Possible Causes Wire feed speed too high Voltage too high.

Corrective Actions Select lower wire feed speed

Electrode extension (stickout) too long Workpiece dirty

Use shorter electrode extension (stickout).

Insufficient shielding gas at welding a Dirty welding wire.

Select lower voltage range

Remove all grease, oil, moisture, rust, paint, undercoating, and dirt from work surface before welding Increase flow of shielding gas at regulator/flowmeter and/or prevent drafts near welding arc Use clean, dry welding wire. Eliminate pickup of oil or lubricant on welding wire from feeder or liner.

Incomplete Fusion Incomplete Fusion − failure of weld metal to fuse completely with base metal or a preceeding weld bead. Possible Causes Workpiece dirty. Insufficient heat input. Improper welding technique.

Corrective Actions Remove all grease, oil, moisture, rust, paint, coatings, and dirt from work surface before welding. Select higher voltage range and/or adjust wire feed speed. Place stringer bead in proper location(s) at joint during welding. Adjust work angle or widen groove to access bottom during welding. Momentarily hold arc on groove side walls when using weaving technique.

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Keep arc on leading edge of weld puddle. Use correct gun angle of 0 to 15 degrees.

Lack Of Penetration Lack Of Penetration − shallow fusion between weld metal and base metal Possible Causes Improper joint penetration

Improper weld technique

Insufficient heat input.

Corrective Actions Material too thick. Joint preparation and design must provide access to bottom of groove while maintaining proper welding wire extension and arc characteristics. Maintain normal gun angle of 0 to 15 degrees to achieve maximum penetration. Keep arc on leading edge of weld puddle. Be sure welding wire extends not more than 1/2 in (13 mm) beyond nozzle. Select higher wire feed speed and/or select higher voltage range. Reduce travel speed.

Excessive Penetration Excessive Penetration − weld metal melting through base metal and hanging underneath weld. Possible Causes Excessive heat input.

Corrective Actions Select lower voltage range and reduce wire feed speed Increase travel speed.

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Burn-Through Burn-Through − weld metal melting completely through base metal resulting in holes where no metal remains

Possible Causes Excessive heat input.

Corrective Actions Select lower voltage range and reduce wire feed speed. Increase and/or maintain steady travel speed.

Waviness Of Bead Waviness Of Bead − weld metal that is not parallel and does not cover joint formed by base metal

Possible Causes Unsteady hand.

Corrective Actions Support hand on solid surface or use two hands.

Distortion Distortion − contraction of weld met al during welding that forces base metal to move.

Possible Causes Excessive heat input

Corrective Actions Use restraint (clamp) to hold base metal in position Make tack welds along joint before starting welding operation Select lower voltage range and/or reduce wire feed speed

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Increase travel speed.. Weld in small segments and allow cooling between welds.

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