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MANUFACTURING LAB

A Report on Robotic Arm Welding

Prepared By : Submitted To :

Upendra Ajit Singh Dr. Abhay

Sharma ME15MTECH11040

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Contents

Aim 3

Theory 3

Experimental Setup 5

Procedure 6

Results 8

Precautions 8

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AIM

To form a weld bead over a given workpiece using robotic twin wire gas metalarc welding (GMAW).

THEORYWelding process 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.

Some of the welding methods include –

1. Shielded metal arc welding (SMAW)2. Gas tungsten arc welding (GTAW)3. Gas metal arc welding (GMAW)4. Flux-cored arc welding (FCAW)5. Submerged arc welding (SAW)6. Electroslag welding (ESW)

Gas metal arc welding (GMAW)

Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a welding process in which an electric arc forms between a consumable wire electrode and the workpiece metal(s), which heats the workpiece metal(s), causing them to melt, and join. Along with the wire electrode, a shielding gas feeds through the welding gun, which shields the process from contaminants in the air.

It is used extensively by the sheet metal industry, and hence, by the automobile industry. There, the method is often used for arc spot welding, thereby replacing riveting or resistance spot welding. It is also popular for automated welding, in which robots handle the workpieces and the welding gun to speed up the manufacturing process.

Any change in arc length results in a large change in heat input and current. A shorter arc length causes a much greater heat input, which makes the wire electrode melt more quickly and thereby restore the original arc length. Shielding gases are necessary for gas metal arc welding to protect the welding area from atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld

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metal embrittlement if they come in contact with the electrode, the arc, or the welding metal.

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There are four primary methods of metal transfer in GMAW, called globular, short-circuiting, spray, and pulsed-spray.

GlobularAs the weld is made, a ball of molten metal from the electrode tends to

build up on the end of the electrode, often in irregular shapes with a larger diameter than the electrode itself. When the droplet finally detaches either by gravity or short circuiting, it falls to the workpiece, leaving an uneven surface and often causing spatter. As a result of the large molten droplet, the process is generally limited to flat and horizontal welding positions, requires thicker workpieces, and results in a larger weld pool.

Short-circuiting (short arc GMAW)

The current is lower than for the globular method. As a result of the lower current, the heat input for the short-arc variation is considerably reduced, making it possible to weld thinner materials while decreasing the amount of distortion and residual stress in the weld area. As in globular welding, molten droplets form on the tip of the electrode, but instead of dropping to the weld pool, they bridge the gap between the electrode and the weld pool as a result of the lower wire feed rate. This causes a short circuit and extinguishes the arc, but it is quickly reignited after the surface tension of the weld pool pulls the molten metal bead off the electrode tip. This process is repeated about 100 times per second, making the arc appear constant to the human eye.

Spray

The weld electrode metal is rapidly passed along the stable electric arc from the electrode to the workpiece, essentially eliminating spatter and resulting in a high-quality weld finish. As the current and voltage increases beyond the range of short circuit transfer the weld electrode metal transfer transitions from larger globules through small droplets to a vaporized stream at the highest energies. Since this vaporized spray transfer variation of the GMAW weld process requires higher voltage and current than short circuit transfer, and as a result of the higher heat input and larger weld pool area (for a given weld electrode diameter), it is generally used only on workpieces of thicknesses above about 6.4 mm.

Pulsed-spray

A variation of the spray transfer mode, pulse-spray is based on the principles of spray transfer but uses a pulsing current to melt the filler wire and allow one small molten droplet to fall with each pulse. The pulses allow the average current to be lower, decreasing the overall heat input and thereby decreasing the size of the weld pool and heat-affected zone while making it possible to weld thin workpieces. The pulse provides a stable arc and no spatter, since no short-circuiting takes place. This also makes the process suitable for nearly all metals, and thicker electrode wire

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can be

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used as well. The smaller weld pool gives the variation greater versatility, making it possible to weld in all positions.

Robotic twin wire GMAW

Two wires are continuously fed through a special welding torch and are consumed to form a single molten pool. The wires are electrically isolated from each other within the contact tip. Systems normally comprise two separate wire feed units and two power sources, so the wires can be operated independently, i.e, with different wire diameters, current levels or operating modes (continuous or pulsed). The first wire is responsible for the penetration and is the limiting factor for welding speed. The second wire is responsible for the fill. The actual increase in welding speed is about 30% to 40% compared to a non-optimised single wire MIG welding process.

Figure 1: Twin wire robotic GMAW

Experimental Setup Welding gun

Wire feed unit

Welding power supply

Welding electrode wire

Shielding gas supply

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Procedure1. Switch on the MCB and turn on the controller of teach pendant. Then switch on

the MCB’s of robot and the controllers (master and slave). Turn on the knobs of both controllers.

2. Release the gases from both the cylinders.3. Fix the workpiece on the fixture.4. Release the emergency switch on the teach pendant.5. Turn the key on the teach pendant to manual mode, i.e, T1.6. Set the parameters in the power controller (Master & Slave) according to the

requirement of desired welding process.For this experiment these are –

Master SlaveCurrent 220 A Current 220 AContinuous Current Pulsed CurrentVoltage 24 V Voltage 24 VWire feed 7.7 m/min Wire feed 7.7 m/minArc length correction zero Arc length correction zeroPulse correction zero Pulse correction zero

7. In the teach pendant, select the local axis and bring the robot arm in Home position while pressing the driver.

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8. Select the Global Axis and bring the welding torch to reference point 1. Select the mode Point-to-Point (PTP) for this.

9. Select TOUCH UP, then YES. Select COM OK to finalize the command.10. Bring the welding torch at the start point of the weld. Select the mode Linear

(LIN) for this. Contact Tube Welding Distance (CTWD) should be kept 25 mm.

11. Select TOUCH UP, then YES. Select COM OK to finalize the command.12. Select ARC ON and also enter the program number in this line that is set in

Master & Slave controllers.13. Move the welding the torch in the direction of weld required until the end

position. Select the mode Linear (LIN) for this.14. Select TOUCH UP, then YES. Select COM OK to finalize the command.15. Select ARC OFF.16. Move the welding torch to the reference point 2. Select the mode Linear (LIN)

for this.17. Select TOUCH UP, then YES. Select COM OK to finalize the command.

Figure 2: Program for the welding operation

18. Dry run the program by holding the driver and the start button to ensure that the movement of welding torch is as desired.

19. Reset the program.20. Turn the key on the teach pendant to automatic mode, i.e, T1.21. Turn on the driver and start the operation.22. After completion, follow the switch on procedure in reversed order to shut

down the system.

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Results

Figure 3: Weld bead (smaller one) by robotic twin wire GMAW

Precautions1. Check the gas flow and wire feed before starting the process.2. Clean the work piece before welding to avoid welding defects.3. Wear shield glasses while the welding is in progress to prevent eyes from

harmful rays.4. Don’t go near the welding area as harmful fumes are released in the process.5. Do not remove the workpiece immediately after welding as it may bend due to

thermal stresses.