Technical Article

Pain Points and Solutions in Laser Welding: Melt Flow and Asymmetric Parts

September 09, 2021 by Jeff Kerns

We finish exploring some challenges and trends in laser welding with melt flow and asymmetric parts.

In parts one and two, we briefly explain coherent beam combining (CBC) and optical phased arrays that deliver new control parameters and flexible beam shaping options to solve the first two pain points, porosity and cracking. In our final part of the series, we explore laser technology and the final two pain points in addition to some industry trends in welding and materials.

Pain points in laser processing explored include:

  • Porosity
  • Cracks
  • Melt flow
  • Asymmetric parts.


Pain Point: Melt Flow

The Problem With Melt Flow

Poor melt flow can cause multiple problems, such as spatter and inconsistent welds. Spatter is when material is ejected from the melt pool, often caused by vapor escaping the keyhole. This material can land on other joint areas or parts, solidify, and cause various issues.


Figure 1. A schematic showing melt flow. Image used courtesy of ResearchGate


Inconsistent welds, such as undercuts and humping on the weld seam, can occur when the velocity of the melt is too high. When welding, liquid materials flow from the leading edge, around the laser beam, and surpass the vapor capillary toward the trailing edges of the melt pool. Welding at high speeds increases the velocity of this liquid material flow and the possibility of inconsistent welds.


Solution for Melt Flow

Higher power or speeds can be managed to create a more stable keyhole. A wider weld or larger weld pool can slow down the melt flow and mitigate cooling. It is possible to oscillate the beam or use multiple core techniques to create a wider weld, larger melt pool, and more stable keyhole. However, there are still limitations in power, speed, and melt flow.

Spatter and inconsistent welds can be mitigated with greater control in beam shape, frequency, processing speeds, and intensity control. Dynamic beam lasers deliver ways to manipulate the weld flow. Changing shapes and frequencies with different intensities gives researchers and manufacturers more control options to reduce spatter, improve weld consistency, and increase overall quality without speed limitations.

The solutions to each pain point form a pattern centered around flexibility and the need for precise control of many variables to hone the beam for each problem, process, and material.


Pain Point: Asymmetric Parts

The Problems With Thickness and Gaps

Different materials and thicknesses require different processing parameters. For example, a machined part requires different power, shape, or cooling periods than welding sheet metal. However, what weld parameters are used when welding a thicker machined part to a piece of sheet metal?


Figure 2. A chart showing metal thickness and gauges. Image used courtesy of Meta Fab


The seam where two parts join presents a gap, often varied in size. They are often caused by geometric dimensioning, tolerancing, and processing variation. While common, larger gaps can challenge autonomous and laser welding. For example, if welding a 0.1 mm gap with a 0.3 mm laser, one-third of the energy will pass through the gap, and the process is only using the edges of the laser to generate the weld.


The Solutions for Thickness and Gaps

Currently, most manufacturers try to find the lowest setting that will weld the thicker part without deforming, damaging, or fully penetrating the thinner part. This solution is not ideal. 

Adjusting energy input on either side of the weld to create an asymmetric heat field for each material and geometry would present the best weld.

A larger or oscillating beam might help bridge larger gaps. However, this idea still wastes energy and time with some of the laser passing through the gap between the two parts. As time increases, quality decreases. Additionally, multiple-core beams or DOEs are not flexible enough to conform to changing gaps and weld geometries. An ideal solution would look more like two beams on either side of the weld that can move and change intensity dynamically with the gap and weld geometries.


Figure 3.  A schematic showing dynamic beam lasers. Image used courtesy of ResearchGate


This dual-beam solution for both asymmetric problems is possible with dynamic beam lasers without flexibility or geometry limitations. The dynamic beam laser is programmed to form a shape with two points at the same or different frequencies or intensities. This is possible through the precise control of each beam through the entire process of splitting, amplifying, and recombining the beams.


Future Industry Trends in Lasers and Materials

Each pain point and solution presents challenges. With recent trends in electrification and electro-mobility, the demand for electric systems, electric motors, battery modules, and cooling plates are driving the industry to improve speed, quality, and processing capabilities in materials such as aluminum and copper. Working with more thermally conductive materials can increase the pain points. Additionally, some applications are using dissimilar materials.

The flexibility and control provided by dynamic beam lasers deliver the flexibility for custom beams to solve the problems presented. For example, welding multiple materials, traditional techniques do not create homogeneous welds in thicker materials.

Currently, it is possible to join thin mixed materials. For example, 0.5 mm could use oscillation or multi-core solutions; but, as material thickness approaches 1 mm, the weld’s quality is noticeably less homogeneous. The lack of mixing also reduces strength, conductivity, and creates brittle intermetallic faces. Through greater control of the melt flow, dynamic beam lasers deliver thicker multi-material homogeneous welds.

As industry trends continue to demand more materials, low cost, and greater control, technology must become more flexible to provide not just a solution, but the best solution. Dynamic beam lasers are proven to deliver flexibility and control to provide researchers and manufacturers a custom beam for each process, material, geometry, and more. Unlike any previous solution, dynamic beam lasers can change beam shape, shape frequency, shape sequence, and focus. These control features can adjust in microseconds to improve laser processing and the future of manufacturing.