Causes and countermeasures for stud welding defects

Stud welding is used in a variety of industries, including construction, office equipment, and electrical equipment. Are you a welder or quality control manager struggling with defects in stud welding?

This article aims to solve your problems by explaining the causes of inconsistent stud welding quality and how to address them.

What is stud welding? Click here if you want to learn the basics of stud welding.
[Related Article] What is stud welding? Explanation of basic principles, types, and characteristics

Inconsistent stud welding quality is usually not due to a single cause, but rather a complex interplay of multiple factors. This article focuses on nine major causes of stud welding defects, explaining each cause and providing concrete solutions that can be implemented immediately.

If the voltage is too high, the arc will become excessively strong, causing the base material to melt and burn through, or generating excessive spatter (metal particles like sparks), which can cause burning to spread around the weld.

On the other hand, if the voltage is too low, the arc will not be sufficiently stable, and the stud bolt will not melt sufficiently with the base material. As a result, insufficient penetration will occur, and the stud bolt will not be firmly bonded to the base material, resulting in insufficient strength that will cause it to easily detach during impact bending tests.

The solution is to perform "test welding." It is essential to find the optimal voltage range according to the material and diameter of the stud bolt. Several stud bolts are welded while slightly changing the welding conditions, and impact bending tests are performed each time to identify the optimal conditions.

If welding force is too strong, the molten pool (pool of molten metal) created by the arc will be pushed outwards from the base material, resulting in insufficient bonding area between the stud bolt and the base material, and thus insufficient strength.

If welding force is too weak, the stud bolt will not sink into the molten pool, resulting in insufficient contact area with the base material and insufficient strength.

Adjusting welding force of the welding gun and working with the appropriate welding force is fundamental.

We have customer examples where adjusting welding conditions has become easier, improving work efficiency and quality!

Oils and paints can burn due to the arc, causing bubbles (blowholes) to form.
Furthermore, the paint acts as an insulator, and in some cases, no arc may be generated at all.

Rust, thick oxide films, and zinc plating have high electrical resistance, which can hinder the arc's rise or cause it to become unstable and jumpy. This can lead to insufficient penetration, increased spatter, and blowhole formation. If air bubbles are present inside, the material will easily break off during impact bending tests.

Checking the surface of the base material can help prevent defects.

In stud welding, the role of "earthing" is extremely important for supplying a stable welding current. Poor earthing contact or placing the earth extremely far from the welding point increases electrical resistance and causes a voltage drop.

It is important to handle grounding properly.

(1) Check that the contact surface of the earth clamp is neat and tidy.
(2) Grounding should be done diagonally whenever possible.
(3) The ground cable should be inspected regularly to check for damage to the insulation or breaks in the internal wires.

Chuck wear: The chuck can no longer hold the stud bolt securely, causing the threads of the stud bolt to short-circuit.
Leg wear: This can cause the gun's verticality to be compromised, leading to malfunctions.
Shaft movement: Poor movement can lead to insufficient penetration and insufficient strength.

No unevenness in the legs is required, and horizontal alignment is essential.

Parts of a welding gun

Welding guns always require maintenance. Chucks and legs are consumable parts. Replace them with new ones if necessary.

If the polarity is set incorrectly, the material will not penetrate sufficiently, resulting in unstable strength.

Positive connection (connect the gun to the negative terminal)

Reverse polarity connection (connect the gun to the positive terminal)

Check the material and set the polarity.

Positive electrode connection: Iron, stainless steel, aluminum
Reverse polarity connection: Iron (bonderized steel sheet) may be connected with reverse polarity.

The material and shape of the stud bolts significantly affect stud welding, as they can lead to welding defects and reduced weld strength. Please use appropriate studs.

To avoid quality issues, it is crucial to use genuine or recommended parts from reliable manufacturers. When introducing a new batch of stud bolts, always perform test welding and verify quality through impact bending tests to maintain more consistent weld quality.

If the positioning punch holes are too deep, the space between the stud and the base material will disappear, resulting in a weak weld.

It is necessary to maintain a space between the base material and the weld that is equal to the height of the protrusion.
To ensure consistent punch depth, it is necessary to use spring punches and to educate all workers on the importance of punching itself and how to do it accurately.

Partial breaks within the cable prevent sufficient power from the welding machine from being transmitted to the stud bolts, resulting in an inability to obtain the required voltage. This makes it easier for defects to occur that would cause the impact bending test to fail, even if the welding machine settings are optimized.

Before welding, visually inspect the power cable to check for any significant deterioration.

This article explains the causes of defects in stud welding and how to address them.

If you have any suggestions for improvement or efficiency improvements in your daily work, please feel free to contact Daido Kogyo.

For those looking for a high-quality stud welder!