Laser Swing Welding: Principles, Characteristics, and Applications

Application background
Laser swing welding technology was born out of the urgent demand for welding quality and efficiency in modern manufacturing industry. Traditional welding technology has shortcomings in precision, strength, and complex structures, which has led to the rapid application of laser welding in various fields. However, it still has defects such as pores and cracks, and has limitations in welding dissimilar materials and complex shaped components. It is difficult to meet the strict requirements of high-end fields such as aerospace and automotive manufacturing, which affects product quality, safety, production efficiency, and increases manufacturing costs for enterprises.

In this context, laser swing welding technology has emerged. Laser swing welding technology has gone through two stages of development: in the first stage, the beam of the welding head swings along the vertical welding direction through a mechanical swing device, but the accuracy is low, the welding trajectory is single, and the scanning frequency is low; The second stage utilizes a galvanometer system to achieve scanning motion with higher frequencies (0-2K Hz) and more complex trajectories, improving accuracy and beam motion rate.
These studies indicate that regulating laser beam oscillation can improve welding performance, meet diverse and demanding manufacturing requirements, and promote the rapid development of high-end manufacturing industry.

What is laser swing welding
Laser swing welding, also known as laser scanning welding, uses a control system to regulate the swing mode, frequency, and amplitude, achieving the planning of laser swing and path.
*Schematic diagram of laser swing welding device

It mainly includes lasers, laser heads (collimation unit, focusing unit, oscillation unit, and control unit), and chillers.
Principle:
① After passing through the collimation unit, the laser beam is incident on two beam deflectors equipped with mirrors. These beam deflectors are controlled by mirror motors and can rotate along the X and Y axes to achieve beam deflection in any direction;
② After passing through the focusing unit, the laser can be emitted to various parts of the workpiece surface;
③ By using the control unit to control the galvanometer motor, regular deflection can be achieved, achieving the goal of laser welding along a periodic scanning trajectory on the surface of the workpiece.

Laser swing welding molten pool
Formation of molten pool
① Similar to ordinary laser welding, at the beginning of laser swing welding, the laser energy is absorbed by the surface of the base material, causing a rapid increase in the surface temperature of the material. Due to the high energy density of lasers, the surface temperature of materials can reach their melting point in a very short period of time.
② As the material melts, liquid metal begins to aggregate under the combined action of surface tension and gravity. During the laser oscillation process, the laser beam continuously scans an area on the surface of the base material, causing the metal in this area to continuously melt and the amount of liquid metal to increase, gradually forming a molten pool.
*Laser swing welding molten pool

*Schematic diagram of molten pool turbulence a) conventional laser b) oscillation frequency of 10Hz c) oscillation frequency of 50Hz

Gap, width, and melt depth
Welding gap
In traditional laser welding, the energy of the laser beam is highly concentrated, resulting in a relatively narrow molten pool. To avoid welding defects, strict gap requirements are imposed, requiring high-precision processing and assembly, which increases costs and production cycles. Usually, the gap is controlled below 10% of the plate thickness.
Advantages:
The maximum gap of laser swing welding far exceeds traditional methods, with a thickness of about 25% of the workpiece without filler metal and up to 315% with filler metal. This technology can effectively handle large assembly gaps, improve assembly flexibility and production efficiency, such as welding body parts of different thickness plates together in automobile manufacturing, or connecting multi-layer circuit boards in electronic equipment production.
*The maximum gap between traditional laser welding and swing laser welding

Weld width and penetration depth
Laser swing welding uses an oscillating laser beam to enlarge the surface of the molten pool, thereby increasing the width of the weld and reducing the depth of penetration. The oscillation in the molten pool generates turbulence, enhances convection, and improves heat transfer.
*Laser weld width and depth a) Laser swing welding b) Traditional laser welding

Welding defect control
crackle
Thermal stress relief: Laser beam oscillation redistributes heat from the melt pool, reducing temperature gradients and thermal stress concentration. Traditional welding thermal stress concentration can easily cause cold cracks in materials. By swinging the beam, the probability of crack initiation is reduced and the fatigue life of the welded structure is extended.
Grain structure optimization: During the solidification of the melt pool, oscillation promotes grain refinement and uniform growth in the heat affected zone, forming more equiaxed grains. Grain refinement enhances the crack resistance of welds, while more grain boundaries hinder crack propagation and reduce crack sensitivity.

*Solidification mode of laser welding a) conventional b) oscillation

stoma
Optimization of molten pool dynamics: In laser swing welding, laser beam oscillation causes strong turbulence and convection in the molten pool, changing the flow characteristics of the liquid in the molten pool. Traditional laser welding has a relatively static molten pool, which makes it difficult for gas to escape and easily forms pores; The dynamic molten pool of swing welding provides an effective channel for gas escape, accelerating the buoyancy and escape of bubbles, and reducing porosity. Experimental data shows that when welding specific materials, the porosity can be reduced from the traditional 10% to 1.5%.
Energy distribution control: The oscillation evenly disperses the laser energy in the molten pool, ensuring stable melting and solidification of the material with a uniform energy field, reducing the risk of local splashing and gas entrapment caused by uneven energy, and improving the density and quality stability of the weld seam. This is particularly effective in welding porous sensitive materials such as aluminum alloys and titanium alloys.

*Schematic diagram of pore formation


Welding parameters: power, speed, swing parameters
Laser power:
The heat input of the workpiece is positively correlated with the melting depth and weld width.
As shown in the welding experiment of 1050 aluminum alloy plate, when the power is increased from 200W to 800W, the penetration depth and weld width both increase.
*The influence of laser power on weld width and penetration depth

Welding speed:
Affects the solidification and metallurgical properties of the melt pool.
The increase in welding speed will lead to a decrease in grain size, mainly due to the enhanced turbulence in the molten pool during laser swing welding. The increased turbulence will cause the unmelted grains in the molten pool to break, resulting in a decrease in grain size.
Swing frequency:
Swing frequency is a key parameter in laser swing welding, which affects the behavior of the molten pool and the quality of the weld seam.
Increasing the oscillation frequency can reduce the sensitivity to thermal cracking, as it can promote the growth of equiaxed crystals and prevent crack initiation.
Increasing the oscillation frequency can reduce the degree of splashing. This is attributed to the strong stirring effect caused by high-frequency oscillation, which promotes the uniform flow of melted material and prevents splashing formation.
As the oscillation frequency increases, the keyhole becomes wider and shallower. It reduces the possibility of keyhole collapse and prevents the formation of pores in the weld seam.
Swing amplitude:
Affects the shape of the melt pool and the crystallization of the weld seam.
*Laser swing welding a) Swing amplitude of laser beam in X and Y directions b) Influence of swing amplitude on equiaxed crystal growth

Swing mode:
*Different swing modes

Application Cases
Battery and heat exchanger
*Application of laser swing welding
a) External heat exchanger b) Heat exchanger section c) Tube corner joint
d) Copper battery components (without pores or cracks) e) Stainless steel and copper welding (dissimilar welding)

Inspiration:
(1) Laser swing welding effectively improves and even solves the two key problems of cracks and porosity.
(2) Can swing welding be combined with circular spot welding to completely solve welding defects?
(3) Too many parameters need to be controlled for swing welding, which will increase the actual process development cycle.

Source: Yangtze River Delta Laser Alliance