Common Weld Defects Found in the Automotive Industry

Common Weld Defects: Types, Causes, and Preventions in the Automotive Industry

Welding is an essential process in the automobile industry. It is done to join together different metal parts of a car. Automakers use different welding techniques depending on the type of metal used and the desired result. In car manufacturing, the welding techniques, which are majorly applied are resistance welding, GMAW, MIG, and TIG welding. Welding has extensive applications in the automotive industry and is pivotal in repairing and making after-market car parts, like custom bumpers, exhaust systems, etc. The welding process has its challenges, and weld defects can compromise the safety and structural integrity of the welded components.

Weld Defects:

Welding services in automotive or any industry often lead to a few imperfections, called “Weld Defects, " which could occur internally or externally in the welded metal. The weld defects can take many forms, from cracks to porosity to lack of penetration to distortion. Each has its unique characteristics and causes, and understanding these could be great in producing high-quality welds.

1. External Weld Defects – As the name refers, they are visual welding defects and can be detected through visual inspection strategies like magnetic particle inspection or dye liquid penetrants. Common examples of these are porosity, spatter, cracks, overlaps, etc.
2. Internal Weld Defects – They are not visible at the weld’s surface and can be seen through ultrasonic or radiographic testing. Some examples of these are incomplete penetration, fusion, and slag inclusions.

What could cause Weld Defects:

Before delving into specific weld defects that could occur commonly in the automotive industry, let’s look at the causes that can trigger them.

• Inadequate beveling or fit-up of the workpieces could result in defects.
• Inappropriate setting of welding current, voltage, or travel speed could lead to defects.
• Surface contaminants like oil, rust, and paint, in many situations, can hinder fusion.
• Low-quality consumables or filler metals can compromise the weld’s integrity.
• Untrained or less skilled operators are more likely to produce defective welds.

Weld Defects in MIG/TIG Welding

Now, let’s discuss the most common weld defects seen during MIG/TIG welding in the automotive sector.

1. Porosity

These defects are wormhole welds, which occur when air or gas bubbles get trapped in the weld. Gases like carbon dioxide, hydrogen, and steam are frequently produced during welding, and these entrapped gases can be distributed uniformly or localised in a specific location throughout the weld. The bubbles can further weaken the weld joint, making it prone to damage or fatigue. In the automotive industry, porosity impacts the strength of the weld, and it could vary from part to part. For example, porosity can lead to leakage issues in fuel tanks.  

Possible Causes of Porosity:

• Contamination of filler wires, insufficient gas flow, consumables, etc.
• Moisture on the filler wire or work surface.
• Impurities like rust, oil, or primer on the joint faces.

Preventive Actions to Consider:

• The filler wire must be cleaned and free of rust.
• Use a low current.
• Proper connection of gas hoses or pipelines must be thoroughly checked before welding.
• Ensure the gas cylinder is full and not nearly empty.
• Ensure that the correct electrode is used to avoid porosity; for example, low hydrogen electrodes are the most suitable for welding bright, medium carbon steel alloys.
• Try doing re-work by grinding and re-welding as required.
• Ensure keeping the joint faces clean.

2. Distortion 

Distortion or warping is an accidental change in the shape of the surrounding metal of the weld. The excessive heating around the weld joint is usually the prime reason for distortion around its area. The weld defect mainly occurs in thin metals and can be classified into four kinds: angular, fillet, longitudinal, and neutral axis. In the automotive industry, it is a cause of concern when welding B – Pillars in 3-wheeler applications and seating systems for 4-wheeler applications along with exhaust systems or 2/3-wheeler under frames or chassis welding, the thickness of the base material is very thin, probably in the range of 0.8 mm to 4 mm.

Possible Causes of Distortion:

• Thin weld metal or sheet.
• Incompatible base metal and weld metal.
• High amount of weld passes.

Preventive Actions to Consider:

• Ensuring the use of suitable weld metals.
• Optimizing the number of weld passes.
• Selecting the right welding process depends on the joining metal. 

3. Spatter

The metal particles that eject from the welding arc are spatters. During Arc or Gas MIG welding, these particles scatter over the base metal. These welding flaws adhere to the length of the weld bead and could also occur in joint designs. In the automotive sector, spatters usually occur while welding on seating systems, brakes, and steering columns. If not cleaned, the spatter can adversely affect the movements of these critical parts of the automobile, endangering the lives of the passengers in the car.

Possible Causes of Spatter:

• The electrodes are wet.
• The arc is longer.
• The Voltage is low.

Preventive Actions to Consider:

4. Lack of Penetration

 It happens when the weld metal is not entirely pierced to the joint’s root. This is of grave concern because the strength of the weld lies in penetration. Lack of penetration in automotive applications like radiators can cause the radiators to malfunction. Even in seating systems, lack of penetration prevents the seats from being rooted to the base of the car and, in case of an impact, can uproot the seat and endanger the life of the occupants in the vehicle.

Possible Causes of Lack of Penetration:

• The welding travel speed is very high.
• Low ampere current.
• The preheat is done on low heat.
• Inappropriate edge preparation.

Preventive Actions to Consider:

5. Burn Through

Excessive heat during welding can cause the metal to burst through the centre. In such situations, burn throughs happen, and they typically occur in thin metal sheets which are less than ¼ inch thick. Though not very critical, burn through becomes one when it is overlooked in the automotive segment, especially while welding the chassis of 2/3-wheelers, which can reduce the strength of that specific joint, causing it to break due to continuous vibrations while riding on the road or carrying loads.

Possible Causes of Burn Through:

• The torch movement is very slow.
• There is a significant distance between metal pieces.
• The heat input is too high.
• The wrong welding technique or not distributing the heat evenly can cause burn through.
• Thin sheets or materials are more susceptible to burn through, especially while welding in a vertical or overhead position.

Preventive Actions to Consider:

• Avoid using a higher current setting.
• Avoid having many gaps between metal plates.
• Ensure the right welding technique distributes heat evenly and avoids overheating in a specific area.

How to Avoid Weld Defects:

The operators must have the necessary skills, quality equipment, and proper training to drive quality results. To avoid weld defects, here are a few tips.

• Invest only in high-quality, superior welding machines and equipment, consumables that provide precise control over welding parameters and could help reduce the risk of weld defects.
• Ensure your welding equipment and consumables are in top-notch condition through regular maintenance and calibration to ensure reliable results.
• It is equivalently significant to let your operators and welders receive training and education to improve their skills, be up to date with the trends in the industry, and reduce the likelihood of errors.

Undoubtedly, welding has been an essential component of automotive manufacturing for decades. In earlier times, techniques like gas metal arc welding and others were used to join metal components in cars. As technology advanced, the welding methods also saw changes in automotive production. Adopting robotic welding systems and digital solutions in automotive welding technology offers unparalleled efficiency and precision, letting operators produce superior welds at a rapid pace. Helping drive innovation and shaping the vehicles of tomorrow, welding is revolutionising the way cars are built, making them more environmentally friendly, safer, and efficient than ever before. As we look to the future, it is evident that welding will continue to play a crucial role in shaping the industry.