A Guide to Stick and MIG Welding Processes

Different Welding Processes  

Welding is a fabrication process used to permanently join two or more pieces of metal by applying heat. In welding, the metals are typically melted at the joint to fuse together, often with the help of a filler material, which forms a molten pool that solidifies into a strong bond as it cools. Different metals require different forms of welding. Below is a simple explanation of Stick and MIG welding processes to assist in understanding and deciding what is needed before buying any welding equipment. 

Stick Welding 

Stands for Shielded Metal Arc Welding; the other abbreviations for this type of welding are SMAW, FCAW, and MMA. 

This process involves manual welding, where an electric current generates an arc between a flux-coated stick electrode and the metals intended for joining. The heat produced by the arc simultaneously melts the electrode's tip and the base metal. The molten metal from the electrode forms droplets deposited into the weld pool, effectively filling the gap between the workpieces. Additionally, the flux coating on the electrode melts and vaporizes, producing a protective gas shield around the weld pool to safeguard against atmospheric contamination, such as oxygen and nitrogen gas. As the flux melts, it also creates slag, a solid layer that envelops the weld, providing protection from oxidation during the cooling process. This process is facilitated by a constant current (CC) power source that utilizes input power in either single-phase or three-phase AC at 50/60Hz, with an output of either AC or DC.

This welding technique is frequently employed in industrial fabrication for joining materials such as carbon steel, stainless steel, cast iron, various alloy steels, etc. It is commonly utilized in Construction, Fabrication, Shipbuilding, Mining and Repair & Maintenance.

Advantages: 

a.    Portability
•    MMA welding equipment is designed to be compact and user-friendly and requires minimal preparation. It operates simply by needing a power supply, an electrode holder, a ground clamp, and an electrode.
•    Since MMA welding does not require gas cylinders or complex equipment, it's highly portable and well-suited for on-site and fieldwork, even in remote locations.

b.    Versatility
•    MMA welding applies to metals such as carbon steel, stainless steel, cast iron, and various alloy steels. Additionally, the use of specialized electrodes facilitates the welding of dissimilar metals.
•    This procedure can be executed in various positions (horizontal, vertical, or overhead), making it ideal for complex welding tasks in hard-to-reach areas.

c.    Cost-Effective
•    MMA welding is typically more cost-effective than other welding configurations, such as those employed in TIG or MIG welding.  No external shielding gas or specialized equipment is required, reducing overall costs. The process only requires electrodes and electricity.

Disadvantages: 

a.    Slag Removal 
•    The flux coating on the electrode generates slag that solidifies on the weld. This slag must be eliminated after each welding pass, typically with a chipping hammer or wire brush, which increases the time required for the welding process and may impact overall productivity.

b.    Slower Process
•    MMA welding is generally slower than other welding methods, such as MIG or flux-cored arc welding, primarily because it has a lower deposition rate of the filler metal. Electrodes are consumed quickly, meaning frequent interruptions to replace them during the welding process, which can reduce efficiency on large projects.

c.    Limited on Thin Materials
•    MMA welding is not the most suitable option for joining very thin materials, as it tends to burn through them. Techniques such as TIG or MIG welding are more appropriate for working with thin gauge metals.

MIG Welding 

It stands for Gas Metal Arc Welding and is called MIG, MAG or GMAW. The welding process used a shielding gas and filler wire that heats the two metals that must be joined. The process involves shielding gas usually an inert or semi-inert gas such as argon or carbon dioxide, which protects the weld pool from contaminants in the surrounding air. The electric arc heats the wire to form the weld pool that joins the material. The process uses a constant voltage DC power source, but AC can be used in a few, depending on applicability. Four primary methods are used for metal transfer, each with pros, cons, and properties. 

1.  Globular

It is amongst the least preferable methods, as it leads to poor weld quality, high heat transfer, and huge spatter around. The benefits cover using CO2 as the shielding gas, which is economical. Argoshield gas can also be used. The process produces higher deposition rates, thus considered widely when speed is needed over weld appearance. It is primarily used for carbon steel.  

2.  Short Circuiting

The process requires a lower current and less heat input than globular welding. It enables the efficient welding of thinner material. It decreases the residual stress and distortion of the weld zone, resulting in less spatter, better quality welds, and welding in all possible positions. However, the speed with which it is done is slow, as putting the proper parameters before starting the welding is essential to ensure a stable arc. This process is not recommended for welding thicker materials as lower arc energy can lead to a lack of penetration and fusion. It is also recommended for use with ferrous metals.

3.  Spray Arc

It was the first metal transfer procedure using the GMAW process and is suited to aluminium, carbon steel and stainless steel. The welding helps achieve a high-quality weld, deep penetration, higher deposition rate and moderate spatter as the molten metal is quickly transferred from wire to the weld pool in the form of continuous fine droplets. Due to the higher voltage and current needed to complete the welding, it is usually applicable with thicker materials, limiting it to be done in only flat and horizontal welding positions. In addition to this, Spray Arc is not suitable for root pass welds.  

4.  Pulsed Spray 

In this process, a specialized metal transfer mode combines spray Arc and short-circuiting transfer benefits. This process involves a controlled sequence of pulsing the welding current, allowing precise control over the weld pool and droplet transfer. This mode alternates between high and low current levels, producing a pulsing effect. The high current creates a spray of fine droplets, while the low current allows the weld pool to cool slightly, preventing excessive heat buildup. Pulsed spray transfer provides excellent penetration into the base material while minimizing distortion and burn-through, making it suitable for both thin and thick materials.

Equipment to be used in the MIG process:

The equipment required to weld in the MIG process includes an appropriate power source supply, wire feed unit, welding gun, wire spool, regulator, heater, a correct earth cable set, and shielding gas supply. MIG welding is among the most common types preferred by most welding companies worldwide. 

Advantages: 

a.    Faster Process
•    MIG welding is fast, allowing for quicker welding and increased productivity.
•    The automatic wire feed of the wire minimizes downtime.

b.    Versatility
•    Can weld various metals, including steel, stainless steel, aluminium, etc. 
•    Capable of welding in different positions.

c.    Clean Welds
•    Produces cleaner welds with minimal post-weld cleanup required.
•    Creates aesthetically pleasing weld beads.

d.    Minimized Distortion
•    The process generally produces less heat distortion, especially with pulsed spray and short-circuiting transfer modes.

Disadvantages: 

a.    Equipment Cost:
•    MIG welding equipment, gas supply, and wire feed systems can be expensive.
•    Requires regular maintenance and replacement of consumables, which can add to long-term costs.

b.    Skill Requirement for Quality:
•    While basic MIG welding is easy to learn, achieving high-quality welds requires practice and understanding of various settings.

c.    Limited Portability
•    Since MIG welding requires gas cylinders or complex equipment, it's a little challenging to use in remote locations.