Gas metal arc welding (GMAW) is a high-speed, economical process that is sometimes referred to as metal inert gas (MIG) welding (Figure 1). In this process, an arc is struck between the base metal and a continuously supplied consumable electrode, which provides filler metal for the weld (2).

What are the 2 methods of striking an arc?

• Scratching.
• Tapping.

Why my welder won't strike an arc?

One of the most common reasons your welder won’t spark is because the connection points between the welder and the metal pieces are not clean or clear. This means that both the workpiece where you want to form an arc as well as the connection point for the work lead clamp need to be bare metal.

How does arc welding work?

Arc welding is a welding process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals, when cool, result in a binding of the metals. … Arc welders can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes.

Why is it important to strike the arc only in the weld joint?

It can cause damage to the inside of the machine resulting in damage to the machine. Why is it important to strike the arc only in the weld joint? Arc strikes that are not covered up by the weld are considered weld defects on most codes. … Turn down the amperage on the machine.

What causes arc burn?

A flash burn occurs when you are exposed to bright ultraviolet (UV) light. It can be caused by all types of UV light, but welding torches are the most common source. That’s why it is sometimes called ‘welder’s flash’ or ‘arc eye.

What causes arc strikes?

Arc strike This is a defect caused by instantaneously striking an arc on the base material. In other words, an arc strike is a spot of failed arc ignition which was not fused by subsequent welding and remained on the base material. Arc strike may be the cause of cracking in the base material.

How does welding happen?

Welding is a fabrication process whereby two or more parts are fused together by means of heat, pressure or both forming a join as the parts cool. Welding is usually used on metals and thermoplastics but can also be used on wood. The completed welded joint may be referred to as a weldment.

What causes slag inclusions?

Slag inclusions are nonmetallic particles trapped in the weld-metal or at the weld interface. Slag inclusions result from faulty welding technique, improper access to the joint, or both. … Dipping the tungsten electrode in the molten weld-metal or using too high current that melts the tungsten can cause inclusions.

What are the procedures in carrying out welding?

• Step 1: Safety. …
• Step 2: Gather necessary equipment. …
• Step 3: Clean your metal. …
• Step 4: Cut your metal. …
• Step 5: Set up your work-piece. …
• Step 6: Turn on the welder and adjust the settings. …
• Step 7: Tack-weld the work-piece. …
• Step 8: Fill in the remaining areas with ‘bead’ welds.

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What are the causes of welding defects?

Most defects encountered in welding are due to an improper welding procedure. Once the causes are determined, the operator can easily correct the problem. Defects usually encountered include incomplete penetration, incomplete fusion, undercutting, porosity, and longitudinal cracking.

Why is striking an arc difficult?

The principal difficulty encountered in striking the arc is “freezing,” or when the electrode sticks or fuses to the work. This is caused by the current melting the electrode tip and sticking it to the cold base metal before it is withdrawn from contact.

How do you start an arc welder?

The arc is started by touching the electrode momentarily against the work to complete the electrical circuit before raising the electrode to establish the arc. This needs to happen quickly to avoid welding the rod to the work. “Tap Starting” and “Scratch Starting” are the two common methods of starting the arc.

How does arc length affect a weld?

As arc length decreases, the arc cone becomes narrower and the arc is more focused (see Figure 7). The result is a weld bead that is more narrow and ropy and the level of weld penetration may decrease very slightly. Conversely, as arc length increases, the arc cone becomes wider and the arc is broader.

What four factors must an arc welder control in order to produce an acceptable bead?

The movement or weaving of the welding electrode can control the following characteristics of the weld bead: penetration, buildup, width, porosity, undercut, overlap, and slag inclusions.

What gases prevent the atmosphere from contaminating the weld metal as it transfers across the arc gap?

Gas Tungsten Arc Welding The weld pool area is protected from the atmosphere and possible contamination by a shielding inert gas, such as argon. A filler metal normally is used, although some welds, known as autogenous welds, do not require it.

What causes undercutting in welding?

Undercutting. Undercutting is a groove or crater that occurs near the toe of the weld. … Causes: Excessive heat, as well as poor welding techniques, can both lead to undercutting on a weld joint. Cures: Reducing the welding current and voltage is the first step to rectifying undercutting.

What causes pits in welds?

Porosity is caused by the absorption of nitrogen, oxygen and hydrogen in the molten weld pool which is then released on solidification to become trapped in the weld metal. … Leaks in the gas line, too high a gas flow rate, draughts and excessive turbulence in the weld pool are frequent causes of porosity.

What is the cause of undercut defect in welding?

One reason for this defect is excessive current, causing the edges of the joint to melt and drain into the weld; this leaves a drain-like impression along the length of the weld. Another reason is if a poor technique is used that does not deposit enough filler metal along the edges of the weld.

Where do Arc flashes occur?

An arc flash occurs when the electrical current flows outside its intended path, through an air gap, to another conductor. With this in mind, you can see that an arc flash can occur anywhere that the electrical current has a chance to escape.

What causes arc flash and arc blast?

An Arc Flash is an energy discharge of light and heat that forms when a fault occurs in an electrical circuit. … An Arc Blast, separate from an Arc Flash, is a supersonic shockwave produced when the uncontrolled arc vaporizes the metal conductors.

How can arc flash be prevented?

1. De-energize electrical equipment.
2. Wear suitable Personal Protective Equipment (PPE)
3. Keep at a safe distance.
4. Reduce the energy output from an incident.
5. Carry out a risk assessment.
6. Train on-site workers to control risks and interrupt faults.

How can inclusions be prevented in welding?

1. Use welding techniques to produce smooth weld beads and adequate inter-run fusion to avoid forming pockets to trap the slag.
2. Use the correct current and travel speed to avoid undercutting the sidewall which will make the slag difficult to remove.

Does GMAW produce slag?

In GMAW, inert or active shielding gas is supplied at the welding zone. … The flux (electrode coating) produces slag on weld bead. This slag can lead to defects or can hamper appearance.

How slag is formed?

The slag occurs as a molten liquid melt and is a complex solution of silicates and oxides that solidifies upon cooling. … These impurities consist of carbon as gaseous carbon monoxide, and silicon, manganese, phosphorus and some iron as liquid oxides, which combine with lime and dolime to form the steel slag.

What would happen if an operator welder decrease the arc length?

Arc welding is a constant current process, but the arc length has an effect on voltage. Reducing the arc length will decrease the voltage, and this reduces the heat in the weld.

What is striking in welding?

Striking an arc means to establish a welding current across a gap between the welding electrode and the base metal. 1. Welding training programs may offer instruction in how to strike the arc in different types of welding methods, including TIG welding.

Why electrode is coated with flux?

The electrode is coated in a metal mixture called flux, which gives off gases as it decomposes to prevent weld contamination, introduces deoxidizers to purify the weld, causes weld-protecting slag to form, improves the arc stability, and provides alloying elements to improve the weld quality.

When striking an arc in SMAW The general rule is that the arc length should be?

When striking an arc in SMAW welding, the general rule is that the arc length should be the same as the diameter of the electrode. When practicing welding, reuse weld coupons (metal you are welding on) until all surfaces have been welded on.

Who invented arc welding?

The production of an arc between two carbon electrodes using a battery is credited to Sir Humphry Davy in 1800.

How does an electrode work in welding?

In electrode welding, contact between the rod electrode and workpiece ignites the arc. This creates a short circuit for a fraction of a second between the two poles, meaning that current can then flow. The arc burns between the workpiece and the electrode. This creates the required fusion heat.