Metal Inert Gas Welding 6b6g2t

Metal Inert Gas Welding Mohak Patel

30th August, 2011 9003045

Background Metal inert gas (MIG) welding or gas metal arc welding (GMAW) is a welding process in which a continuous and consumable wire electrode and shielding gas are fed through a welding gun. The basic advantage that MIG has over SMAW is the fact that it is a continuous process and doesn’t have breaks like in SMAW to put a new electrode rod after it is consumed. Moreover, the skill required in MIG is less as the welder only needs to maintain a constant distance between the welding gun and workpiece.

Figure 1 MIG Weld area

Today, MIG welding is the most common industrial welding process due to its versatility, speed and relative ease of adapting the process to robotic automation. The automobile industry particularly uses MIG welding almost exclusively. Initially, the cost of inert gas limited the use of it until the use of semi-inert gases like carbon dioxide started. Pure inert gases do not provide adequate penetration. Pure carbon dioxide on other had provides

deeper penetration but encourages oxide formation which adversely affects the weld ts mechanical properties.

Aim To study the influence of process parameters on weld geometry and melting efficiency in GMAW with DCEP polarity.

Procedure 1. 2. 3. 4. 5. 6. 7. 8. 9.

Wear the protective gear for welding The transformer is switched on with appropriate current rating. Practise making a straight weld on the sample metal sample. Measure the weight of the given metal sample. Set the current and voltage rating on the transformer. Perform the welding operation on the transverse cut made on the metal plate. Measure the weight of the slab after welding. Cut the slab equally in 3 parts and measure the bead width, height and penetration. Perform the welding operation for 2 different sets of current and voltage.

Experimental Data Sr. Voltage(V) Current(A) No. 1 17.6 195 2 24.2 140 3 28 190

Time(s) 14 8 6

Mass Deposited (g) 8.33 3.3 4.94

Width (mm) 8.02 4.76 6.57

Analysis

Where, Ein is the effective energy input ηprocess = 0.75 V is the measured voltage in Volts. I is the measured current in Ampere.

(

)

Height (mm) 3.89 3.32 2.18

Penetration (mm) 1.5 1.72 1.5

Where, Eutilised is the effective energy utilised in melting the electrode and base material m1 is rate of melting of mass of base material (kg/s). L1, is the latent heat of melting (~2.65x105 J/kg for steel). C is specific heat (~622 J/kg K for steel). T1Melt,is the melting temperature of base material and electrode (~1800K for steel). Tamb is ambient Temperature (~300K). And,

Cross-sectional area(mm2) 33.93 18.83 18.97

Ein 2574 2541 3990

Eutilised 712.81 494.17 986.35

ηmelt 0.2769 0.1944 0.2476

Efficiency vs Voltage 0.3 0.25 Efficiency

Sr. No. 1 2 3

0.2 0.15 0.1 0.05 0 0

5

10

15 Voltage (V)

Graph 1 Efficiency vs Voltage

20

25

30

Cross-sectional area vs Voltage Cross-sectional area (mm2)

40 35 30 25 20 15 10 5 0 0

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10

15

20

25

30

25

30

Voltage (V)

Graph 2 Cross-sectional area vs Voltage

Width (mm)

Width vs Voltage 9 8 7 6 5 4 3 2 1 0

0

5

10

15 Voltage (V)

Graph 3 Width vs Voltage

20

Height (mm)

Height vs Voltage 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0 0

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10

15

20

25

30

25

30

Voltage (V)

Graph 4 Height vs Voltage

Penetration vs Voltage 1.75 Penetration (mm)

1.7 1.65 1.6 1.55

1.5 1.45 0

5

10

15

20

Voltage (V)

Graph 5 Penetration vs Voltage

Conclusion The variation of process parameters with change in voltage was studied. Melting efficiency was found to increase with the voltage. The variation of weld geometry with current was tabulated.

Sources of Error 1. The accuracy of the weld made is low because of the fact that weld made is highly dependent on the skill of the welder. 2. The penetration depth was not clearly visible. 3. The cross-sectional area was assumed to be elliptical, whereas it is not uniform everywhere. 4. The current reading changes rapidly and continuously.

Suggestions to improve the experiment 1. More time should be given for practising the welding operation. 2. The weld bead was not clearly visible. Some chemical method should be used for the same.