Gas Metal Arc Welding" (or GMAW).

What is MIG welding?
Working process
Process Parameters
Advantages
Limitations
Applications
MIG welding is an arc welding process in which a continuous solid wire electrode is fed through a welding gun and into the weld pool, joining the two base materials together.
A shielding gas is also sent through the welding gun and protects the weld pool from contamination.
In fact, MIG stands for “Metal Inert Gas”. The technical name for it is "Gas Metal Arc Welding" (or GMAW).

1. GAS METAL ARC WELDING (MIG ) Presented by N.SANKAR/AP /MECH

2. Basics What is MIG welding? Working process Process Parameters Advantages Limitations Applications Contents

3. Welding is a process of joining two metal pieces by the application of heat. Welding is the least expensive process and widely used now a days in fabrication. Welding joints different metals with the help of a number of processes in which heat is supplied either electrically or by mean of a gas torch. Different welding processes are used in the manufacturing of Auto mobiles bodies, structural work, tanks, and general machine repair work. Basics

4. Different Welding Processes Welding Processes Beam Processes LBW, EBW Arc Welding : SMAW, GMAW, GTAW, PAW Solid state Welding USW, FRW, EXW Resistance Welding Spot, Seam, Projection

5. MIG welding is an arc welding process in which a continuous solid wire electrode is fed through a welding gun and into the weld pool , joining the two base materials together. A shielding gas is also sent through the welding gun and protects the weld pool from contamination. In fact, MIG stands for “Metal Inert Gas”. The technical name for it is "Gas Metal Arc Welding" (or GMAW). What is MIG welding?

6. Along with the wire electrode, a  shielding gas  feeds through the welding gun, which shields the process from contaminants in the air. The process can be semi-automatic or automatic. A constant  voltage ,  direct current (dc)  power source is most commonly used with GMAW, but constant  current  systems, as well as  alternating current , can be used.

7. What equipment, types of shielding gases, and electrodes are used in the MIG welding process?

8. Power Supply Gas Supply Wire feeder Gun and Whip Process

9. A. Most welders used for MIG welding are direct current machines of the constant voltage type. B. MIG welding machines must be designed to produce a constant voltage. With a constant voltage MIG machine, the output voltage will change very little with large changes in current . C. Welding voltage has an effect on bead width, spatter, undercutting, and penetration. D. The constant voltage welding machines are designed so that when the arc voltage changes, the arc current is automatically adjusted or self-corrected. MIG Welders

10. MIG Welders

11. E. Most MIG welding units have three adjustments which must be in balance to achieve a quality weld. These are voltage control, wire feed speed, and shielding gas flow rate. MIG Welders

12. To move the electrode wire from the spool to the MIG welding gun, run the wire through a channel and system of drive wheels. Wire Feeder

13. The constant rate of wire feed is necessary to assure a smooth even arc . Wire speed varies with the metal thickness being welded, type of joint, and position of the weld. These drive wheels, depending upon their location in the wire feed unit, are either the push type or the pull type. The pull-type drive wheels are located relatively close to the MIG gun and exert a pulling action on the wire. Pull-type drive wheels are used on most spool guns. Wire Feeder

14. The electrode holder is commonly referred to as the MIG gun. The MIG gun has a trigger switch for activating the welding operation , a gas nozzle for directing the flow of the shielding gas, and a contact tip. MIG Gun

15. The nozzle is made of copper alloy to help remove the heat from the welding zone. MIG Gun

16. The contact tip helps to guide the wire electrode into the puddle as well as transmit the weld current to the electrode wire. The electrode wire actually touches the contact tip as it is fed through the MIG gun. During this contact, the weld current is transmitted to the electrode. Contact Tip

17. A 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 spatter. In the metal fabrication industry, argon is used to create an inert gas shield during welding. Argon is frequently blended with carbon dioxide (CO 2 ), hydrogen (H 2 ), helium (He) or oxygen (O 2 ) to enhance the arc characteristics or facilitate metal transfer in Gas Metal Arc Welding (GMAW or MIG). Shielding Gas

18. Has a low ionization potential and therefore creates a very stable arc when used as a shielding gas . The arc is quiet and smooth sounding and has very little spatter . Argon is a good shielding gas for welding sheet metal and thin metal sections. Pure argon is also used for welding aluminum, copper, magnesium, and nickel. Pure argon is not recommended for use on carbon steels . 1. Argon

19. The most often used gas in MIG welding because it gives good bead penetration, wide beads, no undercutting and good bead contour and it costs much less than argon or helium . The main application of carbon dioxide shielding gas is welding low and medium carbon steels. When using pure carbon dioxide shielding gas, the arc is unstable, which causes a lot of spatter. 2. Carbon Dioxide

20. When used in a mixture with argon, oxygen helps to stabilize the arc, reduce spatter, eliminate undercutting, and improve weld contour. The mixture is primarily used for welding stainless steel, carbon steels, and low alloy steels . An argon-helium mixture is used for welding thick non-ferrous metals. This mixture gives the same arc stability as pure argon with very little spatter, and produces a deep penetrating bead. 3. Gas Mixtures

21. The tank supplying the shielding gas will have a gauge and a gas flow meter. The volume of gas directed over the weld zone is regulated by the flow meter. Gas Cylinder and Gauges

22. There are factors to consider when selecting the correct electrode. 1 . Consider the type of metal to be welded and choose a filler wire to match the base metal in analysis and mechanical properties . Electrode Wire

23. 2. Consider the joint design . Thicker metals and complicated joint designs usually require filler wires that provide high ductility. Ductility is the ability to be formed into a new form without breaking . 3. Examine the surface condition of the metal to be welded. If it is rusty or scaly, it will have an effect on the type of wire selected. 4. Consider the service requirements that the welded product will meet. Electrode Wire

24. MIG electrode wire is classified by the American Welding Society (AWS). An example is ER70S6 . For carbon-steel wire, the “E” identifies it as an electrode “R” notes that it is a rod Electrode Wire Classification

25. The basic technique for GMAW is very simple, since the electrode is fed automatically through the torch (head of tip). In shielded metal arc welding, the operator must frequently chip off slag and change welding electrodes. GMAW requires only that the operator guide the welding gun with proper position and orientation along the area being welded. MIG Welding technique

26. Keeping a consistent contact tip-to-work distance (the  stick out  distance) is important, because a long stick out distance can cause the electrode to overheat and also wastes shielding gas.  The orientation of the gun is also important it should be held so as to bisect the angle between the work pieces; that is, at 45 degrees for a fillet weld and 90 degrees for welding a flat surface. The travel angle, or lead angle, is the angle of the torch with respect to the direction of travel, and it should generally remain approximately vertical.

27. The welding process variables mainly affect the geometry of the weld bead such as the penetration, bead reinforcement, bead width and the deposition rate , which is the weight of the metal deposited per unit of time. These variables are as follows: Welding Current Welding Voltage Travel Speed Wire Electrode Size Type of Shielding Gas Electrode Extension Electrode Angle Weld Joint Position Process parameters

28. Welding Current &Voltage As the welding current and voltage are increased above the maximum recommended for short arc welding, metal transfer will begin to take on a different appearance. This welding technique is commonly known as globular transfer, with metal transferring through the arc. Usually, the drops of molten metal have a greater diameter than the wire itself. This mode of metal transfer can be erratic, with spatter and occasional short circuiting being common.

29. Minimum Current for Spray Arc Welding

30. The angle at which the MIG gun leans toward or away from the direction of movement. A travel angle of 10 degrees to 20 degrees is used for most welding. Travel angle is sometimes referred to as drag angle. Travel Angle

31. Is perpendicular to the line of travel and varies considerably, depending upon the type of weld being made and the welding position. The work angle for a flat position surfacing weld should be 15 degrees to 25 degrees . The Work Angle

32. Perpendicular to the base metal. The MIG gun may be held three different ways.

33. Leaning in the direction of travel, also known as the backhand or pull position. The MIG gun may be held three different ways.

34. Leaning opposite the direction of travel, also known as the forehand or push position. The MIG gun may be held three different ways.

35. Welding jobs can be performed faster with the MIG process. The continuous wire feed eliminates the need to change electrodes . Weld cleaning and preparation time is less for MIG welding than for stick electrode welds. Since the gaseous shield protects the molten metal from the atmospheric gases, there is no flux or slag, and spatter is minimal. MIG Welding Advantages

36. Little time is required to teach individuals how to MIG weld . Because of the fast travel speed at which MIG welding can be done, there is a smaller heat-affected zone than with the shielded metal arc welding process. The weld visibility is generally good. There is less smoke and fumes so operator environment is improved. MIG Welding Advantages

37. Both thick and thin metals can be welded successfully and economically with the MIG process. Less time is needed to prepare weld joints since the MIG welds are deep penetrating. Narrow weld joints can be used with MIG welding and still secure sound weldments . The MIG welding process can be used to join both ferrous and nonferrous metals. The development of electrode wire and the use of spool guns has made the MIG process widely used for aluminum, stainless steel, high-carbon-steel, and alloy-steel fabrication . MIG Welding Advantages

38. Sensitive to contaminants  – the process can only handle low to moderate levels of surface contaminants such as rust, mill scale, dirt, oil and paint. All these have potential to create problems such as porosity, incomplete fusion, bad bead appearance and even cracking. Portability  – moving the welding equipment may not be that tough, but you also have to handle the high pressure cylinders that contain the shielding gas. Proper care must be taken. limitations

39. Sensitive to wind  – the shielding gas used for MIG welding can easily be blown away when welding outdoors. Even inside, a fan or a wind draft of as low as 5mph can be enough to cause porosity Lack of fusion  – due to the ability to weld at low currents this process has the potential for lack of fusion when running in short circuit mode. Open arc process  – as with most welding process, GMAW exhibits an open arc. Proper care must be taking to shield the welder and bystanders from the harmful UV rays.

40. Applications of MIG Welding in M anufacturing Why MIG welding is used in Manufacturing? High productivity can lead to higher profits. In manufacturing, productivity is the central focus. The primary advantage of MIG welding is welding speed. It is much quicker than traditional welding. High productivity can be achieved in many manufacturing operations with the use of MIG welding for its clean welds. It welds metals quickly and highly economic.

41. 1. Automotive repair Repairs can be carried out on a number of different vehicles whether they be large, small, light, or heavy. Capable of proving a strong weld even down to 0.5mm.

42. 2. Rebuilding equipment: Rebuilding:- To repair , especially to dismantle and reassemble with new parts . Example to rebuild an old car. When it comes to fixing broken parts in the field, there are three steps to master: Cutting and removal of the failed component. Preparation of the new joint/part. Welding and cleanup. worn parts can be repaired by using MIG welding in a variety of coatings (stainless steel, bronze, nickel, aluminum or hard surfacing) and in a range of hardness, for a fraction of the cost of purchasing a new part.

43. 3 . w eld pipes It is more economical to use a track based roboticwelding system than it is to actually man the assembly line. Four Reasons to Choose Automated Pipe Welding with Robots: New Technologies Flexibility Weld Quality Productivity

44. 4 .To reinforce the surface of a worn out railroad track: It can even be used to reinforce the surface of a worn out railroad track. It can be difficult to join metals of different types, but by choosing the right filler wire you can actually achieve it over time.

45. Conclusion Other type of welding needs highly skilled workers to produce high quality weld. Maximum weld quality is assured by maintaining cleanliness—all equipment and materials used must be free from oil, moisture, dirt and other impurities, as these cause weld porosity and consequently a decrease in weld strength and quality. MIG welding is a huge improvement over some of the previous techniques. MIG welding will help contribute to the creation of automobiles, the building of bridges, and even more importantly, a more efficient way to weld.