MANNUAL METAL ARC WELDING (M.M.A) OR SHIELDED METAL ARC WELDING (S.M.A.W)
Manual Metal Arc Welding is also called as Shielded Metal Arc Welding. This process uses Constant Current Power Source (or) Droping Characteristic. Polarity used in this welding Process is D.C.E.P. In this Welding Process the heat source is an Electric Arc, which is formed between a Consumable Electrode and Parent Metal. The Arc is formed by touching the tip of electrode to plate and then lifting the electrode to give a gap of 3mm-6mm between the tip and plate. The small Arc in the gap causes the air in gap to become ionized (or) made Conductive.
MANUAL METAL ARC WELDING
The average temperature of arc is 6000 degree centigrade which is sufficient to simultaneously melt the parent metal, the consumable core wire and flux coating. The flux forms gas and slag layer which protects the weld pool from surrounding atmosphere. The molten slag solidifies and cools and must be chipped off from the weld bead once the weld run is complete. This M.M.A Welding Process is not a continuous process as it allows short lengths of weld to be made. This process is versatile & can be used in all positions.
EQUIPMENTS:
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- A transformer/rectifier, generator, Inventor
- Power Cable and Power Return Cable.
- Electrode Holder
- Electrodes
- Correct Visor/Glasses, All safety clothing and good extraction.
PARAMETERS & INSPECTION POINTS:
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- Amperage
- Open Circuit Voltage (O.C.V)
- AC / DC Polarity
- Travel Speed
- Electrode type & diameter
- Electrode condition
- Insulation
TYPICAL WELDING IMPERFECTION:
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- Slag inclusion
- Porosity
- Lack of root fusion
- Lack of penetration
- Under cut
- Arc strike
- Hydrogen cracking
ADVANTAGES:
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- Field or shop use
- Range of consumables
- All positional
- Very portable
- Simple equipment
DISADVANTAGES:
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- Arc strike
- Slag inclusion
- High skill factor required
- Hydrogen control
- Discontinuous process
M.C.Q IMPORTANT POINTS:
- Arc temperature is approx 6000 degree centigrade
- It can be used in al positions
- It is a discontinuous process
- To strike and produce arc O.C.V is used
- O.C.V is 50-90 volts
- Welding voltage is 20-30 volts
- Welding current is 30-350 amps
- Current is related to penetration
- Silicon is added to steel & covering flux of M.M.A in order to give DE-OXIDATION
- Low-hydrogen electrode is often used for BASIC ELECTRODE.
- A hydrogen controlled MMA electrode can always be recognized by EN CODE LETTER.
- A typical range for baking Basic coated electrode is 300-350 degree centigrade.
- Weld spatter during MMA is due to EXCESSIVE CURRENT.
- Included angel for MMA welding of a full penetration pipe butt joint is 70 Degree.