Metallic Arc Welding
Definition :- The metallic arc welding process in which the welding speed and feed of the electrode is controlled manually by the welder himself ; is called Manual Metallic Are welding ( MMAW ) .
Features :-
1. It is an are welding process in which the heat required for the welding is obtained from an electric arc .
2. The electric arc develops when electriesly jumps across an air gap which is ionised between the end of the metallic electcode and the welding job surface .
3. The metallic electrode is generally coated with a flux which is consumable .
4. The are created due to the ionisation of air between the electrode tip and the base metal generates an intense arc heat having a temperature between 3600 ° c - 4000° c .
5. The welding current is provided by an A.C or D.C Machine .
6. The interse heat of the are melts a small portion ( melton pool ) on the job directly under the arc and the end of the electrode instantaneously .
7. The melted electrode fuses into the molten pool of the welding job and produces a homogeneous weld on cooling .
8. The flux coating on the electrode also melts and provides a gaseous shield around the are which protects the malten metal from atmospheric contamination . Hence this arc is called shielded arc and the process is called shielded Metallic Arc Welding ( SMAW ) .
9. The welding speed and feed of the clectrode is controlled manually by the welder himself . This is why it is called Manual Metallic Arc Welding ( MMAW ) .
10. When the weld metal solidifies , the slag ( burnt flux ) gets deposited on its surface as it is lighter than the metal and the weld metal is allowed to cool gradually and slowly .
Tools And Equipments For MMAW
Some very important items, used by a welder during MMAW are given below.
1. Welding Machine :- [ Either a DC or Ac welding Machine ] - for contralling the voltage and current for works .
2. Two Cables or Leada :- [400Amps] To carry the welding current from the welding machine to the work and back.
[ The cable on lead from the welding machine to the electrode holder is called electrode cable on welding cable and the cable on lead from the work on job through the earth clamp is called earth or ground cable . Cables are made of super filexible rubber insulation , having fine copper wings and amen fabric reinforcing layers .
3. Electrode Holder :- [400 Amps]
To grip and manipulate the electrode during welding .
[ It is a clamping device , made of copper or copper alloy for better electrical conductivity . Both partially and fully insulated electrodes holder are made in various sizes i.e. 250 , 400 , 600 amps ] .
4. Earth Clamp :- [400 Amps]
To connect the earth cable firmly to the job or welding table .
[It is also made of copper on capper alloy .]
5. Cable Lugs :- To connect the earth cable and welding cable or lead to the welding machine .
6. Welding Trade :-
To set the welding job properly.
7. Welding Handscreen & Helmet :- To protect the eyes and face of a welder from arc radiation and sparks during arc welding.
[ Hand screen are designed to hold in hand and made of non - reflective , non - flammable , insulated , dull coloured , light material with coloured filter glasses filted with plain glasses on both sides to see the arc and molten pool when welding . The welding helmet provides better protection and allows the welder to use both hands freely ].
8. Chipping Hammer :- To remove the slag from the weld bead .
[ it is made out of medium carbon steel with a suitable handle . ]
9. Wire Brush :- For cleaning the working ruface prior to welding and for general cleaning of the weldment .
[ It is made of steel wires fitted on wooden piece in three to five rows . The wires are hardened and tempered for long life to ensure good clean action . ]
10. Tongs :- For holding that job and for holding the pieces in position . Except these , there are also needed some marking and measuring tools , such as file , centre punch , Divider , Steel Rule , Trysquare etc. and also some safety items like hand gloves , apren , shoes etc.
Applications :-
1. MMAW is used for welding thin gauge as well as thick gauge metals in small and medium scale industries .
2. This process is used in welding roof structures for work shop , broken and cracked castings , water and all tanks .
3. MMAW is used in welding bridges , bus bodies , domestic items like grills for gate , windows , doors , chairs and tables .
4. Whenever welding is done in outdoor work , where electric supply is not available , this process is very useful as a diesel generator welding set can be used .
5. This process is used for redonditioning , hard facing , rectifying broken parts and repair Welding .
Advantages :-
MMAW is the process which is widely used because of the following advantages .
1. All kind of light and heavy gauge weldable metals can be welded .
2. This process can be used for fabrication , construction as well as maintenance works .
3. All types of metals ( ferrous , non - ferrous & alloys ) can be welded .
4. This process permits a skilled operator to perform the welding operation quickly and easily .
5. It is more suitable for short length welds .
6. It is less expensive that the other are welding process .
7. It is portable .
