Resistance Welding Defects And Preventive Measures

Resistance welding is widely used in automobile manufacturing, aerospace, electronic manufacturing and other industries due to its efficiency and energy-saving properties. However, it can experience various defects during the welding process, which can negatively impact the welding quality and potentially compromise the performance and safety of the product. This article provides an overview of common resistance welding defects, along with their causes and preventive measures.

I. Common defects and causes of resistance welding

1. Crack

Cracks are a significant defect in resistance welding and often occur in welds or heat-affected zones. Multiple factors contribute to crack formation. Firstly, high levels of carbon, sulfur, phosphorus, and other elements in the welding parts material increase brittleness, making it more prone to cracking during welding. Secondly, welding stress, including thermal stress and residual stress from thermal expansion and contraction, can cause cracks if not adequately released. Lastly, improper settings of welding parameters such as current, time, and electrode pressure can result in overheating or overcooling of the weld, leading to crack formation.

2. Pore

Pores are voids inside or on the surface of the weld that significantly affect welding quality. There are three main reasons for pore formation. Firstly, insufficient gas protection occurs when oxygen, nitrogen and other gases cannot be effectively eliminated, allowing them to enter the weld and the form pores. Secondly, welding material contamination arises from pollutants like oil and rust on the surface of the welding parts or welding rod, hindering the proper discharge of gas during welding. Lastly, improper welding parameter settings, such as unreasonable current, time and other parameters, can negatively affect gas spillage.  

3. Unfused

Slag inclusion refers to non-metallic inclusions in the weld, such as welding slag and oxides, which can negatively affect the weld's strength and toughness. Slag inclusions are primarily caused by poor quality welding materials containing many inclusions. Failure to promptly remove welding slag from the molten pool and improper welding parameter settings, such as welding current and welding speed, can hinder the removal of inclusions.

4. Slag

Slag inclusion refers to non-metallic inclusions in the weld, such as welding slag and oxides, which can negatively affect the weld's strength and toughness. Slag inclusions are primarily caused by poor quality welding materials containing many inclusions. Failure to promptly remove welding slag from the molten pool and improper welding parameter settings, such as welding current and welding speed, can hinder the removal of inclusions.

5. Undercut

Undercut is a groove formed when the arc melts the parent material at the weld edge without adding weld metal. It can weaken the weld's strength and load-bearing capacity. Undercut is mainly caused by excessive welding current, improper electrode angle, and excessively fast welding speed.

II. Resistance welding defect prevention measures

1. Crack prevention measures

(1) Material selection: Use low alloy steel and avoid materials with high carbon, high sulfur, high phosphorus and other elements. Preheat before welding to reduce material brittleness.

(2) Process optimization: Set parameters such as welding current, welding time and electrode pressure appropriately to prevent overheating or overcooling of the weld. Implement post-weld heat treatment to release welding stress.

2. Pore prevention measures

(1) Gas protection: Enhance gas protection during welding by using inert gases like argon to shield the weld from oxygen, nitrogen and other air gases.

(2) Welding material cleaning: Clean the surface of the welding parts and welding rod thoroughly to remove oil, rust, and other contaminants and maintain a clean welding material surface.

(3) Parameter adjustment: Properly adjust parameters such as welding current and welding time to ensure complete gas spillage.

3. Unfused prevention measures

(1) Joint design: Design joint gap and groove shape for complete fusion of weld.

(2) Parameter optimization: Increase welding current and extend welding time for full melting of weld.

(3) Electrode pressure: Increase electrode pressure for close contact of weld.

4. Slag prevention measures

(1) Welding material quality: Use qualified welding rods or welding wires to avoid inclusions in the welding material.

(2) Welding operation: Clean the welding slag promptly during welding to maintain a clean molten pool.

(3) Parameter adjustment: Properly adjust welding current and welding speed to facilitate the discharge of inclusions in the molten pool.

5. Undercut Prevention Measures

(1) Current control: Reduce welding current to avoid excessive melting of the base material.

(2) Electrode angle: Adjust electrode angle for even melting of the weld edge.

(3) Speed control: Reduce welding speed to ensure full melting and supplementation of the weld edge.

Resistance welding defects are caused by various factors, such as materials, welding process, and welding operation. To ensure welding quality, it is important to select suitable materials, optimize the process, clean before welding, and control the welding operation. In practice, specific preventive measures should be chosen based on the circumstances, and quality monitoring and testing should be enhanced to ensure product reliability and safety.