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MIG Welding Machine Metal Transfer
For 1.2 mm diameter electrode wire the welding current above 200 A results in the formation of drops at the tip of a conical region. The cone attains a quasi-stationary state with the liquid metal flowing into the base of the cone and flowing out at its tip. It has been shown expediently that for 1.2 mm diameter electrode the pencil-point tip forms for current higher than at which the electrode tip is completely engulfed by the visible arc root.
The geometric form of the drop at the electrode tip depends on, amongst other factors, the electrode polarity. As a rule electrode positive is the polarity used for mig welding machine. With this polarity the anode spot forms almost symmetrically around the electrode tip and the form of the drop or molten region at the electrode tip is correspondingly axi-symmetric. However, certain commercial mig welding machine (GMAW Welding) steel wires are adequately treated and, therefore, may be used with electrode negative. At high currents the cathode spot wanders symmetrically over the lower part of the electrode melts and the metal transfer in drops.
Most of the above discussion is in connection with solid wire mig welding machine (GMAW Welding). However, high speed fils of metal transfer in flux-cored arc welding indicate that the character of the transfer varies according to the flux. For example, with rutile flux core a fine spray-like transfer occurs whereas with a basic flux core the transfer is in relatively large droplets that form asymmetrically. The flux appears partly to transfer as a solid material which presumably melts on transfer to the weld pool. Overall it appears that as with SMAW the dominant factor, both for metal transfer and droplet transfer frequency, is the composition of the flux.
The introduction of the pulsed mig welding machine in 1960’s offered the opportunity of obtaining spray transfer at lower mean currents by introducing current pulses to detach droplets at controlled intervals, against a lower background current which maintained the arc and allowed molten drops to form. This has made it possible to use spray transfer for thinner materials and also in various welding positions.
Like metal transfer in constant current MIG Welding Machine (GMAW Welding), in pulsed GMAW it can also be classified into projected or drop spray and streaming spray. All features of the two transfer processes are the same both for constant current and pulsed GMAW. The first droplet transferred in pulse current welding is in the drop spray mode but subsequent droplets transferred during the same current pulse will be in the streaming spray mode.
The time for the formation and detachment of a droplet is inversely proportional to the magnitude of the peak current but is independent of its duration. Once the necking process has initiated the droplet detaches after a specific time which is characteristic of the wire diameter and peak current, and is independent of the current level at the time of its detachment.
MIG Spot Welding
The process involves fusing two pieces of sheet metal together by penetrating entirely through one piece into the other. No joint preparation is required except proper cleaning of the overlap areas. The main operation in arc spot welding is to strike and hold an arc without travel at a point where the two parts to be joined are held tightly together.
A vented metal nozzle of a shape to suit the application is fitted to the MIG gun and is pressed against the workpiece at the desired area. The operation is carried out for a period of 1-5 seconds and a slug is melted between the parts to be joined. Timing is usually controlled automatically with the help of a timer. Thus, the process time can be varied to achieve welds of different sizes depending upon the thickness of the sheets. Arc initiation is a critical part of the process and therefore must be reliable and consistent. This is easy to achieve by a flat characteristics power source and clean surface of the work.
GMAW spot welding is a highly adaptable process which requires very little manipulative skill; does not require the use of a welding helmet. It is an extremely fast process and can be fully automated. Due to addition of extra metal the weld slug is free from piping defects. A wire composition different from the base metal may be used to control cracking, porosity, or strength. Argon and CO2 are shielding gases commonly used for GMAW spot welding.
GMAW arc spot process can be used more efficiently for downhand welding position. It can be successfully employed for horizontal position but fails for overhead welding position.
This process does not require a hole to be made in either member, thus in differs from plug welding in that respect. As the upper member is required to be melted through and through, its thickness is normally restricted to 3 mm. The thickness of the second member is not important. Through lap joints are the most often used type of joint for arc spot welding but fillet joints can also be successfully made by this process.
In this process the metal from the electrode wire scours deeply into the weld crater. This breaks up the oxide films at the faying surfaces so that the process can be used as successfully on aluminum as on mild, low alloys, and stainless steels.
MIG Welding Machine (Metal Inert Gas)
The arc which is struck by direct contact between the wire electrode and the workpiece, is maintained at a constant length by the interaction of electrical parameters. The power source used is invariably of the rectified dc type. Both, constant voltage and constant current type power sources are in use.
Depending upon the work material, the shielding gas may be argon, helium, nitrogen, carbon dioxide, hydrogen, and their mixtures. When inert shielding gas is used the process is more popularly known as MIG (metal inert gas) welding and when CO2 is used as the shielding gas it is referred to as CO2 welding or MAG (metal active gas) welding.
GMAW is an all-position semi-automatic welding process through its automatic versions is also available. GMAW is a very versatile process and can be used for welding all metals for which compatible filler wires have been developed. However, its typical applications include medium-gauge fabrication such as structurals, earth moving equipment, plate and box girders, and automobile bodies. This process has great potentials for use with robotic welding systems.
Plasma-MIG Welding Machine
This process, as the name implies, has been developed by combining the features of plasma arc welding and MIG welding processes. It has two variants; one with separate non-consumable tungsten electrode and the other uses the torch nozzle as non-consumable electrode.
Essentially plasma-MIG welding process differs from the existing GMAW process in that the electrode wire is enveloped in a plasma sheath which controls heat and droplet transfer in such a way that much higher speeds and deposition rates are attained that possible with GMAW process.
This process can be used both for welding and surfacing. Most of the materials that can be welded by GMAW can as well be welded by this process and at much faster rates.
MIG Welding Machine
Introduction:
MIG Welding machine is defined as metal inert gas welding. It is also one of the types of arc welding machine. In this process no pressure is applied for welding. In this process of welding wherein coalescence is produced by heat the work piece with an electric arc establish between a continues feed of metal electrode (copper coated) and the work piece. No flux is used as used in submerged arc welding (SAW Welding) but a shielding gas (Ar, He, Co2) is used. It is also known as gas metal arc welding (GMAW).
Principle of Operation
Before welding set the current, wire feed speed and electrical connections. Now arc is struck by one of the two methods.
1st method current and shielding gas flow is switched on and electrode is scratched against the job as usual practice.
For striking the arc by 2nd method-electrode is made to touch the job is restricted and moved forward to carry out welding but before striking the arc shielding gas, water and current is switched on during the welding. Torch should be 10 – 12 mm. Away from the work pieces and arc length is kept between 1.5 to 4.0 mm. Arc are basically two types.
I. Self adjusted arc
II. Self controlled arc
In self adjusted arc, with decreases in arc length (from L2 to L1) voltage decreases and current increases from l2 to l1 melting the electrode at faster rate resulting into making the arc length normal for self adjusting arc, welding source with flat characteristics is required for self-controlled arc, when arc length decreases, arc voltage also decreases with reduces speed of electric motor and hence the feed rate of electrode this brings arc length to a set value for self-controlled arc, a welding source with dropping characteristics is preferred.
Equipment Required for MIG Welding Machine
I. Welding power source with cables;
II. Welding gun filler wire on a coiled spool;
III. Shielding gas cylinder, pressure regulator and flow meter;
IV. Control switch.
Different Types of Material can be welded by MIG Welding Machine
I. Carbon and low alloy steel
II. Heat resistant alloys
III. Copper and its alloys
IV. High strength low alloy steel (HSLA)
V. Stainless Steel
VI. Magnesium alloys
VII. Aluminum and its alloys
Advantage of MIG Welding Machine
I. Less number of spatters as compared with MMA welding;
II. MIG is very faster process as compared with TIG Welding Machine;
III. Deep penetration can be achieved through this process;
IV. No use of flux during welding process;
V. Process can be easily mechanized;
VI. MIG produces a high quality, weld bead with minimum defeats;
VII. Large metal deposition rate are achieved by MIG welding process.
Limitations of MIG Welding Machine
I. Welding equipment is more costly and complex as compared to ARC Welding Machine;
II. Trained operator is required to perform the operation;
III. Process is not economically for job shop production;
IV. All types of material cannot be welded.
Application
I. For welding of Al, Cu, Mg, Ni and their alloys;
II. For welding of aircraft, pressure vessels and shipbuilding industry;
III. For manufacturing of refrigerator parts etc;
IV. Rail road industries;
V. Transport Industries.
