Welding is a joining method that involves melting and fusing the edges of two or more metal parts together. There are different types of welding, depending on the equipment, the power source, the shielding gas, and the filler material used. Some of the most common types of welding are:

• MIG (metal inert gas) welding: This type of welding uses a continuous wire electrode that is fed through a welding gun and forms an arc with the workpiece. The electrode also acts as a filler metal, and a shielding gas (usually argon or carbon dioxide) protects the weld pool from atmospheric contamination.
• TIG (tungsten inert gas) welding: This type of welding uses a non-consumable tungsten electrode that creates an arc with the workpiece. A separate filler metal is added manually or automatically, and a shielding gas (usually argon or helium) protects the weld pool from atmospheric contamination. TIG welding produces high-quality welds but requires more skill and precision than MIG welding.
• Stick (shielded metal arc) welding: This type of welding uses a consumable electrode that is coated with a flux that produces a protective gas and slag when burned. The electrode forms an arc with the workpiece and melts both the base metal and the filler metal. Stick welding is simple and versatile, but it produces more spatter and slag than other types of welding.
• Fluxcore (flux-cored arc) welding: This type of welding is similar to MIG welding, but it uses a tubular wire electrode that contains a flux core instead of a solid core. The flux core produces a shielding gas and slag when burned, eliminating the need for an external gas supply. Fluxcore welding is suitable for outdoor applications and can weld thicker materials than MIG welding.
• Ultrasonic welding: This type of welding uses high-frequency vibrations to create heat and pressure at the interface of two metal parts. The vibrations cause plastic deformation and interlocking of the metal grains, forming a solid-state bond. Ultrasonic welding does not require filler metal or shielding gas, and it can weld dissimilar metals and thin materials.
• Friction welding: This type of welding uses rotational or linear motion to generate friction and heat at the interface of two metal parts. The friction causes plastic deformation and interlocking of the metal grains, forming a solid-state bond. Friction welding does not require filler metal or shielding gas, and it can weld dissimilar metals and complex shapes.

Avoiding Welding Defects

There are many potential errors that can occur during metal welding, which can compromise the quality, strength, and appearance of the weld. Some of the common errors are:

• Porosity: This is the formation of gas bubbles or holes in the weld, which reduce its density and durability. Porosity can be caused by contamination, improper shielding gas, excessive welding speed, or incorrect electrode angle. To avoid porosity, it is important to clean the base metal and the filler material before welding, use the appropriate gas flow rate and type, adjust the welding parameters, and maintain a steady arc length and travel speed.
• Inclusions: These are foreign materials that get trapped in the weld, such as slag, flux, or oxides. Inclusions can weaken the weld and cause cracks or corrosion. Inclusions can be prevented by removing slag or flux between each pass, using a proper welding technique, and choosing a compatible filler material.
• Undercutting: This is a groove or notch that forms along the edge of the weld, which reduces its cross-sectional area and makes it prone to cracking. Undercutting can result from excessive heat input, high welding current, incorrect electrode angle, or poor fit-up. To prevent undercutting, it is advisable to use a lower heat input and current, hold the electrode perpendicular to the joint, and ensure a good gap and alignment between the base metal pieces.
• Poor joint penetration: This is when the weld does not fully fuse with the base metal, leaving gaps or voids in the joint. Poor joint penetration can affect the strength and performance of the weld. It can be caused by insufficient heat input, low welding current, improper joint design, or incorrect electrode size. To improve joint penetration, it is recommended to use a higher heat input and current, select a suitable joint type and preparation, and use an appropriate electrode diameter.
• Burn-through: This is when the weld melts through the base metal, creating holes or excessive reinforcement on the backside of the joint. Burn-through can weaken the weld and cause distortion or leakage. It can be caused by excessive heat input, high welding current, thin base metal, or improper electrode angle. To avoid burn-through, it is necessary to use a lower heat input and current, select a thicker base metal or use a backing plate, and hold the electrode at a low angle to the joint.
• Overlap: This is when the weld metal extends beyond the toe of the weld, creating an irregular shape and reducing the contact area between the weld and the base metal. Overlap can reduce the strength and appearance of the weld. It can be caused by low welding speed, high welding current, large electrode size, or incorrect electrode angle. To prevent overlap, it is important to increase the welding speed, reduce the welding current, choose a smaller electrode size, and hold the electrode at a right angle to the joint.
• Craters: These are depressions that form at the end of the weld when the arc is terminated abruptly. Craters can create stress concentrations and cracks in the weld. Craters can be avoided by gradually reducing the welding current at the end of the weld, filling the crater with filler metal, or using a crater-fill function on the welding machine.