Welding Defects in Semi Trailer Manufacturing & How to Avoid Them

A technical guide to common welding defects seen in semi trailer and lowbed manufacturing — including cracks, porosity, undercut and lack of fusion — plus engineering methods to prevent them for stronger and safer chassis structures.

Manufacturing Quality Chassis Welding
📅 Published on 2025-11-24 | ✍️ Semi Trailer News Engineering Desk

Image: MIG/MAG welding line inspection on a lowbed trailer chassis

🔧 Why Welding Quality Defines Trailer Strength

A semi trailer’s structural life depends heavily on welding integrity. Even when using high-strength steel like S355 or S700, poor welding causes:

• Cracks around the neck
• Side-beam tearing
• Cross-member separation
• Axle hanger failures
• Permanent deformation under load

Below are the most common welding defects in trailer manufacturing and how to prevent them.

❌ Defect #1: Cracks

Cracks usually appear at:

• Neck-to-main beam joints
• Suspension brackets
• Cross-member connections
• Kingpin reinforcement plates

Causes:

• High residual stress
• Incorrect heat input
• Brittle HAZ zones
• Poor joint design

Prevention:

• Controlled heat during welding
• Smooth transitions between plates
• Double-pass welding in high-stress zones
• Use of S355/S700 compatible filler metals

❌ Defect #2: Porosity

Porosity creates weak points inside the weld bead. It may be invisible from outside.

Causes:

• Moisture in welding wire
• Dirty base metal
• Wrong shielding gas flow
• Rust, oil or paint not cleaned

Prevention:

• Clean surfaces before welding
• Correct gas flow (generally 12–18 L/min)
• Use dry storage for wires

❌ Defect #3: Lack of Fusion

This occurs when the weld fails to penetrate the base metal. One of the most dangerous defects for lowbed trailers.

Causes:

• Low heat setting
• Incorrect welding angle
• Welding too fast

Prevention:

• Higher current/voltage
• Proper joint preparation
• Slower and controlled welding speed

❌ Defect #4: Undercut

Undercut is a groove melted into the base metal along the weld toe. This creates a stress concentration that causes cracks over time.

Causes:

• Too high heat input
• Wrong electrode angle
• Moving the torch too quickly

Prevention:

• Optimised welding parameters
• Proper torch angle
• Weave technique for thick plates

❌ Defect #5: Spatter

Excess spatter does not weaken the joint itself, but indicates poor welding settings. It can also create corrosion points if not cleaned.

Prevention:

• Correct amperage
• Clean wire feed
• Anti-spatter spray

❌ Defect #6: Overlapping

Occurs when molten metal sits on top of the base metal without bonding.

Causes:

• Incorrect travel speed
• Wrong electrode angle

Prevention:

• Higher travel speed
• Correct torch direction

📋 Quality Control Processes to Avoid Defects

• Visual inspections for surface defects
• Ultrasonic testing (UT) for internal cracks
• Magnetic particle inspection (MPI)
• X-ray for critical welds
• Robotic MIG/MAG welding for consistency

🌍 African Market Challenges

African lowbeds and flatbeds face:

• Extreme vibrations
• High payloads
• Uneven roads & mining terrain

Any welding defect, even minor porosity, can quickly expand into:

• Main beam cracks
• Side beam bending
• Axle hanger failure

🏁 Final Thoughts

Welding defects are the hidden killers of trailer chassis life. Strong steel alone is not enough — weld integrity is essential for safety, durability and performance. With proper welding parameters, inspections and joint design, manufacturers can significantly extend trailer lifespan and reduce failure risks in demanding regions like Africa.

---

---

🔗 Related Articles