Laser Weld Joint Surface Remelting for Smoother Weld Beads

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Solution Overview

Problem

Laser welding of metal workpieces, particularly steel, aluminum, and magnesium, often results in a coarse top surface due to turbulence and gas trapping, leading to porosity defects, residual stress concentrations, and aesthetic issues.

Innovation Solution

A method involving a second laser beam is used to melt and resolidify the upper portion of the initially formed laser weld joint, smoothing the top surface by adjusting the beam travel speed, power level, and focal position to achieve a surface roughness reduction from 5 μm to 0.5 μm.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If laser welding is performed on metal workpieces, then the workpieces are joined together efficiently, but the top surface becomes coarse and rough

Engineering Contradiction:

Improvewelding efficiencyVSAvoidsurface roughness

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

A second laser beam is applied after the initial welding to melt and resolidify the top surface, smoothing it before final cooling. This preliminary surface treatment action eliminates the coarse texture without requiring re-welding of the joint.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The second laser beam uses different parameters (lower power, higher speed, specific focal position) compared to the welding laser to achieve surface melting rather than deep penetration, transforming the surface morphology from rough to smooth while preserving the weld integrity.

Inventive Principle:

Principle #35Parameter changes

2Length of stationary object

If high power density laser beam is used to create deep penetration weld, then welding depth is improved, but turbulence and gas trapping increase causing porosity

Engineering Contradiction:

Improveweld penetration depthVSAvoidporosity defects

Core Design Contradiction:

Length of stationary objectVSReliability

Solution Approach 1:

The second laser beam is applied after welding to smooth the surface and close surface pores. This preliminary surface treatment prevents porosity-related issues before they affect weld quality, without requiring reduction of the original welding parameters.

Inventive Principle:

Principle #10Preliminary action

3Speed

If laser welding is performed quickly to maintain productivity, then welding speed is improved, but surface smoothing is compromised

Engineering Contradiction:

Improvewelding speedVSAvoidsurface finish quality

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The laser beam application is segmented into two distinct phases: first for welding at high speed, then for surface smoothing at a different speed. This segmentation allows each process to be optimized independently, maintaining high welding productivity while achieving surface quality through the second slower pass.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The method effectively reduces surface roughness, mitigates residual stress concentrations, and enhances the aesthetic appearance of the weld joint while maintaining structural integrity.

Implementation Method 1

a laser beam is directed at an accessible top surface of the workpiece stack-up... The heat generated from the absorption of energy from the laser beam initiates melting of the metal workpieces

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

The heat generated from the absorption of energy from the laser beam initiates melting of the metal workpieces

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 3

the laser beam is removed from the laser weld joint to allow the upper portion of the joint to resolidify... The modified top surface of the laser weld joint is smoother than the initial top surface

Methodology Applied

Scientific EffectPhase change (melting and solidification): Phase Change

Data Source

PatentUS11235422B2Method for smoothing the surface of a laser weld joint

Publication Date: 2022.02.01 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A method for joining together metal workpiece (12,14 or 12,150, 14) includes forming a laser weld joint (66) in a workpiece stack-up (10) that fusion welds two or more overlapping metal workpiece (12,14 or 12,150 or 14) together. The laser weld joint (66) has an initial top surface (76). Once the laser weld joint (66) is formed, the method calls for impinging the laser weld joint (66) with a laser beam (24) and moving the laser beam (24) along the initial joint (66) including the initial top surface (76). The laser beam (24) is eventually removed from the laser weld joint (66) to allow the melted upper portion (78) of the joint (66) to resolidify and provide the laser weld joint (66) with a modified top surface (84) that is smoother than the initial top surface (76). By providing the laser weld joint with a smoother modified top surface, residual stress concentration points are removed and the laser weld joint is less liable to damage seal strips.