I. What is Undercut? Why is it important?

Undercut in handheld laser welding refers to the depression or groove formed on the base material along the weld toe (the junction between the weld and the base material). It is not only a surface defect but also a stress concentration point, significantly reducing the load-bearing capacity and fatigue strength of the weld joint. It is a defect that must be eliminated in important structures.

II. Three Main Causes and Countermeasures for Undercut in Handheld Laser Welding Machines

The main cause of undercut in laser welding machines is improper heat input control. Here are three core causes and their corresponding solutions:

Cause 1: Excessive Power or Speed

Insufficient energy input from the handheld laser welding machine over-melts the base material, causing the liquid metal to be blown away or unable to recover due to surface tension, resulting in edge collapse.

Solution: Optimize parameter combinations. Appropriately reduce laser power or increase welding speed. Follow the principle of "set speed first, then fine-tune power" to find a balance point that allows for penetration without overheating.

Cause 2: Improper Welding Angle and Oscillation

An excessively vertical welding torch angle or insufficient dwell time at the edge during oscillation fails to provide enough filler metal to the edge.

Solution: Adjust operating technique. Maintain a 75-85 degree angle between the welding torch and the workpiece. If the equipment has an oscillation function, widen the oscillation range and pause slightly at both edges to ensure the edge is fully melted and bonded with the filler metal.

Cause 3: Shielding Gas and Focus Issues

Excessive gas flow can cause interference, while a too-deep focus position can exacerbate erosion of the base material.

Solution: Check auxiliary processes. Adjust the flow rate of the shielding gas (usually high-purity nitrogen or argon) to a suitable range (e.g., 15-20 L/min). Simultaneously, check and calibrate the focal position of the cutting head to ensure it falls on the workpiece surface.

Summary and Prevention: Solving the undercut problem in handheld laser welding machines is a collaborative process involving parameters, technique, and settings. By systematically adjusting the power and speed, optimizing the operating angle, and calibrating the gas and focal point, you can easily eliminate undercut defects and obtain perfect, strong welds.