Analysis & On-site Rectification Solutions for Common Defects in Laser Welding

As a professional solution provider for laser processing heads, we have long been deeply engaged in optical path adaptation and on-site process debugging for laser welding. We fully understand that on-site welding is frequently plagued by various defects such as porosity, cracks, spatter and incomplete penetration. These issues not only compromise the appearance and airtightness of products but also directly reduce weld strength, leading to batch rework and cost losses.

Today we have compiled practical industry technical knowledge, summarizing the 7 most common types of welding defects on site, complete with real defect reference images, accurate cause analysis, and ready-to-use on-site solutions. It serves perfectly for process debugging, quality inspection and patrol checks, new employee training, and technical explanation for customers, enabling quick comparison and troubleshooting. Worth collecting and sharing with peers in the welding industry!

 

1. Weld Porosity (Most Common Defect)

Appearance Features

Round or irregular small holes appear inside or on the surface of the weld, with surface pits and internal cavities on the fracture section, reducing structural strength and airtightness.

 

Causes

· Oil contamination, oxide scale, moisture or coating on the material surface vaporize at high temperature to form bubbles.

· Insufficient purity of shielding gas (below 99.99%), unstable flow rate or poor gas coverage.

· Excessively fast welding speed leads to rapid solidification of the molten pool, leaving bubbles no time to escape.

· Unstable laser keyhole causes entrapment of metal vapor, forming internal porosity.

Solutions

· Thorough pre-welding cleaning: remove oil stains with alcohol or special cleaning agents, and eliminate oxide layers with sandpaper.

· Adopt high-purity argon gas with purity above 99.99%, set flow rate at 10–20 L/min, and align the nozzle directly facing the molten pool.

· Reduce welding speed and appropriately lower power density to extend the solidification time of the molten pool.

· Optimize the defocusing amount of the welding head to stabilize the keyhole and minimize internal bubble formation.

 

2. Welding Cracks (Fatal Defect)

Appearance Features

Fine cracks (longitudinal, transverse, crater cracks) occur on the weld surface or heat-affected zone, with intergranular cracking visible on the fracture, easily causing structural fracture.

Causes

· Excessive thermal stress: rapid cooling of high-carbon steel, aluminum alloy and other materials forms hardened structures.

· Large difference in thermal expansion coefficient of dissimilar metals leads to excessive shrinkage stress.

· Improper welding parameters: excessive laser power, fast welding speed and concentrated heat input.

· Excessive workpiece restraint restricts deformation and causes stress concentration.

Solutions

· Preheat the workpiece (100–200°C for steel), and conduct slow cooling or stress relief annealing after welding.

· Select matching welding wires; adopt transition filler materials for dissimilar metal welding.

· Use pulsed laser to reduce power density and narrow the heat-affected zone.

· Optimize fixtures to reduce restraint and arrange welding sequence reasonably.

 

3. Welding Spatter (Affecting Appearance & Equipment)

Appearance Features

Molten metal particles splash during welding, adhering to the workpiece surface, contaminating the lens of the welding head and resulting in rough weld seams.

 

Causes

· Excessively high laser power density causes violent keyhole fluctuation and excessive metal vapor pressure.

· Contaminated material surface triggers molten pool boiling due to vaporization.

· Excessively deep focal position concentrates energy at the bottom of the molten pool.

· Improper flow rate and angle of shielding gas fail to suppress vapor eruption.

Solutions

· Appropriately reduce laser power, increase welding speed and lower power density.

· Strictly clean the workpiece surface to remove oil stains, rust and coatings.

· Adjust the focal position to stabilize the keyhole and reduce vapor eruption.

· Optimize the nozzle angle and flow rate of shielding gas to stabilize the molten pool surface.

 

4. Undercut (Weld Edge Depression)

Appearance Features

Grooves form at the junction of weld and base metal with unfilled edges (depth over 0.5mm), weakening joint strength.

 

Causes

· Excessively fast welding speed leaves insufficient time for liquid metal to backfill the weld edge.

· Excessive assembly gap leads to insufficient filling metal.

· Excessively high laser power causes over-melting of base metal at the edge.

· Rapid energy drop at weld end results in keyhole collapse and local undercut.

Solutions

· Reduce welding speed to allow sufficient backfill of molten metal at the weld edge.

· Control assembly gap (≤0.1mm for thin plates, ≤0.2mm for medium plates).

· Appropriately lower laser power to match welding speed and heat input.

· Extend the energy attenuation time at weld end to avoid keyhole collapse.

 

5. Incomplete Penetration / Incomplete Fusion (Insufficient Strength)

Appearance Features

Incomplete Penetration: No fusion trace on the back of the weld; only superficial adhesion of the joint.

Incomplete Fusion: Incomplete bonding with gaps between weld and base metal or weld layers.

Causes

· Insufficient laser power and energy density.

· Focal point deviation results in oversized light spot and scattered energy.

· Excessively fast welding speed leads to inadequate heat input.

· Over-thick plates and high-reflective materials (aluminum/copper) cause strong laser energy reflection.

Solutions

· Increase laser power or adopt a welding head with higher power density.

· Precisely calibrate the focal length to ensure the focal point falls on or slightly above the workpiece surface.

· Reduce welding speed to increase heat input per unit length.

· Adopt preheating, slight defocusing and high-power mode for welding aluminum and copper.

 

6. Weld Burn-through (Common for Thin Plates)

Appearance Features

Complete penetration of the weld with hole formation.

Causes

· Excessive heat input: over-high laser power or overly slow welding speed.

· Over-low focal position concentrates energy on the back of the plate.

· No back support for thin plates leads to molten pool collapse under self-weight.

· Excessive assembly gap causes loss of molten metal.

Solutions

· Reduce laser power and increase welding speed to lower heat input.

· Adjust the focal point to the upper surface or positive defocus state of the workpiece.

· Add copper backing plates for support and forced cooling for thin plates.

· Strictly control the assembly gap to avoid excessive clearance.

 

7. Weld Offset / Poor Weld Forming

Appearance Features

Weld deviates from the joint center with uneven width, fluctuating height and rough surface.

 

Causes

· Inaccurate workpiece positioning and loose fixtures.

· Optical path deviation and incorrect focal point of the welding head.

· Misalignment between wire feeding and light spot leads to uneven filling.

· Fluctuating welding speed and unstable laser power output.

Solutions

· Calibrate tooling fixtures to ensure accurate workpiece positioning.

· Regularly calibrate the optical path of the welding head to guarantee spot alignment.

· Adjust the wire feeding mechanism to keep the welding wire coaxial with the light spot.

· Stabilize laser output and maintain uniform welding speed.

 

8. Quick Troubleshooting Checklist

 

The above covers the core common defects and complete rectification solutions in laser welding. In fact, most welding defects are related to process parameters, material properties and operation details. Meanwhile, the optical path accuracy, focal point stability and sealing protection performance of the laser welding head also play a decisive role.