Overview of Laser Welding
As an efficient and precise welding method, laser welding has many unique advantages. It uses a high-energy-density laser beam to heat the welding material to a molten state to achieve precise welding of materials. Laser welding is fast, has high strength, a narrow weld seam, a small heat-affected zone, and small workpiece deformation. There is less follow-up processing work and high flexibility. But at the same time, there will also be some issues during the welding process. This article will focus on the tips for overcoming laser welding issues.
Common Issues, Causes And Solutions
1. Welding spatter
Causes:
During the welding process, if the surface of the processed material or workpiece is not cleaned thoroughly and there are oil stains or contaminants, or if the galvanized layer volatilizes, it may cause spatter during laser welding. Generally, after laser welding is completed, many metal particles appear on the surface of the material or workpiece and adhere to the surface. This kind of spatter seriously affects the surface quality of the weld seam and can contaminate and damage the lens.
Solutions:
- A. Pay attention to cleaning the material or workpiece before laser welding;
- B. Appropriately reduce the welding energy. Since spatter is directly related to power density, reducing the welding energy can reduce spatter.
2. Weld bead buildup
Causes:
Excessive wire feeding speed or too slow welding speed during welding can cause excessive weld filling and excessive weld height. When the wire feeding speed is too fast, excessive filling material will make the weld bead significantly higher; while too slow welding speed will cause the material in the molten pool to accumulate, also increasing the weld bead.
Solutions:
- Increase the welding speed or reduce the wire feeding speed, or reduce the laser power.
3. Welding deviation
Causes:
Inaccurate positioning during welding or inaccurate alignment of light and wire during filler welding will cause the weld metal to solidify not at the center of the joint structure, resulting in welding deviation. During the welding process, if there is a deviation in positioning or the position of light and wire is not accurately corresponding, it will cause the weld seam to deviate from the center position.
Solution:
- Adjust the welding position, or adjust the position of light and wire during filler welding, as well as the position of light, wire and weld seam.
4. Weld seam depression
Causes:
Poor welding spot position. If the center of the spot is close to the lower plate and deviates from the center of the weld seam, it will cause partial melting of the base metal and a depression on the surface of the weld metal. This situation usually occurs during brazing. When the center of the solder joint is poor, the weld surface is sunken.
Solution:
- Adjust the light-wire matching.
5. Poor weld formation
Causes:
Unstable wire feeding or discontinuous light will lead to poor weld formation, including poor weld ripple, uneven and irregular weld seam, and unsmooth transition between weld seam and base metal. During weld brazing, if the wire feeding is unstable or the light is intermittent, it will affect the formation quality of the weld seam.
Solution:
Adjust the stability of the equipment.
6. Uneven weld bead
Causes:
Large changes in weld trajectory and uneven teaching can easily cause uneven weld bead or uneven formation at corners. When the weld trajectory changes greatly, due to uneven teaching, uneven weld bead or poor formation is prone to occur at corners.
Solution:
Weld under the best parameters, adjust the viewing angle to make the corners coherent.
7. Surface slag inclusion
Causes:
Unclean interlayer coating or improper welding operation techniques can cause surface slag inclusion during welding. Specific reasons include unclean interlayer coating during multi-layer and multi-pass welding; or uneven surface of the previous weld seam or non-compliance of the workpiece surface with requirements, as well as improper welding operation techniques such as low welding input energy and too fast welding speed.
Solutions:
- A. Select reasonable welding current and welding speed. During multi-layer and multi-pass welding, the interlayer coating must be cleaned.
- B. Grind and remove the weld with surface slag inclusion and repair if necessary.
8. Porosity
Causes:
Unclean weld surface or volatilization of zinc vapor from galvanized sheet, and fast cooling of the molten pool can lead to the formation of pores. On the one hand, if the weld surface is not cleaned thoroughly or the zinc vapor from the galvanized sheet volatilizes, pores are prone to form; on the other hand, the molten pool in laser welding is deep and narrow, and the cooling speed is very fast. The gas generated in the liquid molten pool cannot escape in time, which is also easy to lead to the formation of pores.
Solution:
- Clean the surface of the workpiece and the weld surface before welding to improve the volatilization of zinc when heated. In addition, the blowing direction can also affect the generation of pores.
9. Undercut
Causes:
Too fast welding speed, excessive joint assembly gap or too fast energy drop can cause undercut. The specific manifestation is poor bonding between the weld seam and the base metal, and a groove appears. Reasons include: A. If the welding speed is too fast, the liquid metal in the weld seam will not redistribute on the back of the small hole, resulting in undercut on both sides of the weld seam; B. If the joint assembly gap is too large, the molten metal in the joint filling will be reduced, and undercut is also prone to occur; C. At the end of laser welding, if the energy drop time is too fast, the small hole is easy to collapse, also causing local undercut.
Solutions:
- A. Control the processing power and speed matching of the laser welding machine to avoid undercut.
- B. For the undercut of the weld seam found during inspection, it can be polished, cleaned and repaired to meet the requirements of the acceptance standard.
Difficulties in Welding Aluminum Alloys
1. Low laser absorption rate of materials
Aluminum alloys have high initial reflectivity and high thermal conductivity to laser beams, which makes their absorption rate of laser very low before melting. To improve the absorption rate of aluminum alloys to laser, the following measures can be taken:
- Adopt appropriate surface pretreatment processes, such as sandpaper grinding, surface chemical corrosion, surface plating and other pretreatment measures. Studies have shown that anodizing and sandblasting treatment can significantly improve the energy absorption of aluminum to laser beams. In addition, surface pretreatment measures such as sandpaper grinding, surface chemical etching, surface plating, graphite coating and oxidation in an air furnace are also effective for the absorption of laser beams.
- Reduce the spot size and increase the laser power density. The increase of laser power density will cause the keyhole effect in the welding molten pool, which can greatly increase the material’s absorption rate of laser.
- Change the welding structure to make the laser beam reflect multiple times in the gap to facilitate the welding of aluminum alloys. The joint form will affect the absorption of laser. V-shaped groove and square groove are more conducive to the formation of keyholes than joint without groove, which increases the laser power density and the absorption rate of aluminum alloys to laser.
2. Prone to porosity and hot cracks
- Porosity problem: The most common and main type of defect in aluminum alloy laser welding is porosity. Porosity types can be divided into two categories. One is hydrogen porosity formed by the sharp drop in hydrogen solubility during the cooling process of aluminum alloy laser welding and the precipitation of supersaturated hydrogen. The other is the hole formed by the instability and collapse of the keyhole during the laser welding process and the inability of the liquid metal to fill in time. There are many measures to reduce porosity defects in aluminum alloy laser welding. For example, changing the travel trajectory of the laser beam, using beam oscillation to stir the molten pool, increasing the possibility of pores escaping to the surface, using wire filling or adding alloy powder, and adopting dual-spot technology and laser hybrid welding can all achieve the effect of reducing porosity. In addition, adjusting the laser power waveform, changing the irradiation angle of the laser beam, and applying a magnetic field during welding can also effectively control the pores generated during the welding process. During the welding process of aluminum alloys, the hydrogen content of molten aluminum alloys can reach 0.69 mL/100g, and the hydrogen content of aluminum alloys after cooling and solidification is 0.036 mL/100g.
- Hot crack problem: The reasons for the generation of hot cracks in aluminum alloy laser welding are mainly related to its own characteristics and welding process. When aluminum alloys solidify, the shrinkage rate is large (up to 5%), the welding stress and deformation are large, and the weld metal will produce low-melting-point eutectic structure along the grain boundary during crystallization, which weakens the grain boundary bonding force and forms hot cracks under the action of tensile stress. The method of wire filling or adding alloy powder can reduce the tendency of hot cracks. Adjusting the welding process parameters to control the heating and cooling speed can also reduce the tendency of hot cracks. When using a YAG laser, the heat input can be controlled by adjusting the pulse waveform to reduce crystal cracks.
3. Decline in mechanical properties of welded joints
- The burning loss of alloy elements during the welding process reduces the mechanical properties of aluminum alloy welded joints, resulting in a “softening” phenomenon. Aluminum alloys mainly include Zn, Mg and Al. During the welding process, the boiling point of aluminum is higher than that of the other two elements. Therefore, when welding aluminum alloy components, some low-boiling-point alloy elements can be added, which is beneficial to the formation of small holes and the firmness of welding. The unstable porosity during the welding of aluminum alloys leads to a decline in the mechanical properties of welded joints. A large number of studies have shown that the softening phenomenon of aluminum alloy welding is difficult to eliminate fundamentally. However, compared with gas shielded welding, laser welding makes the weld softening zone narrower due to the reduction of heat input. Compared with gas metal arc welding, the “softening” degree of laser welded joints of aluminum alloys is lower, and the tensile strength increases with the increase of welding speed.
Faults and Solutions of Laser Welding Machines
1. Power supply and startup faults
- The inability to start the equipment is one of the common power supply and startup faults of laser welding machines. Possible reasons are that the power line switch is not powered on, or the power line and plug are damaged. The solution is to check whether the power line is connected properly and whether the switch is in the on state. If there is a problem, replace or repair it in time.
- Pre-ignition failure (lamp cannot be lit) is also a common situation for such faults. Possible reasons include no 220V voltage on the pre-ignition board, failure of the ignition board, damage to the 3A fuse tube, xenon lamp failure, etc. In this case, check the voltage of the pre-ignition board and replace damaged parts such as the ignition board, fuse tube or xenon lamp.
2. Faults during welding
- The weld seam is very black: Possible reasons are incorrect flow direction of the shielding gas, no shielding gas (such as nitrogen) used, or insufficient shielding gas flow. Adjust the flow direction of the shielding gas to ensure it is opposite to the movement direction of the workpiece; turning on nitrogen or increasing the shielding gas flow can solve this problem.
- Cracks appear: The reason may be that the cooling speed of the workpiece is too fast. Adjust the temperature of the cooling water on the fixture and increase the water temperature; if the fit clearance of the workpiece is too large or there are burrs, improve the processing accuracy of the workpiece; if the workpiece is not cleaned properly, clean the workpiece again; if the flow of shielding gas is too large, reduce the flow of shielding gas.
- Insufficient penetration: Insufficient laser energy. Increase the pulse width and current to solve it; if the defocus amount of the focusing mirror is incorrect, adjust the defocus amount to be close to the focal point.
- Weakened flame: Reasons include that the shutter is not fully opened. Check and add lubricating oil to the optical shutter connector to make the connector mechanically smooth; the laser of the main optical path is offset. Adjust the full-reflection and half-reflection diaphragms of the main optical path and use imaging paper to check and adjust the circular spot; the cooling water is polluted or the cooling water has not been replaced for a long time. Replace the cooling water and clean the xenon lamp and ultraviolet-filtering glass tube; the laser is not output from the center of the copper gas nozzle below the focusing head. Adjust the 45-degree reflective diaphragm to make the laser output from the center of the gas nozzle; if the focusing lens or the resonant cavity diaphragm of the laser is damaged or polluted, it should be replaced or cleaned in time.
- Splashing: The workpiece surface is not clean and there is oil or contaminants. The welding power density is too high. The solution is to clean the workpiece surface and appropriately reduce the welding energy.
- Deviation: Inaccurate positioning during welding, inaccurate alignment of filling welding time and welding wire. Adjust the welding position, repair welding time and welding wire position to ensure the positions of the lamp, welding wire and weld seam are accurate.
3. Mechanical and optical system faults
- Mechanical component faults: Wear or damage of mechanical components such as guide rails and sliders, and poor lubrication. Regularly check the wear condition of mechanical components, replace damaged parts in time, and maintain a good lubrication state.
- Laser faults: Decreased laser power and deteriorated beam quality. Regularly check the working state of the laser. If there is a problem, contact professional personnel for repair or replacement in time.
4. Other faults
- Cooling system faults: Possible reasons are insufficient cooling water flow and too high temperature. Check whether the cooling system is working properly to ensure that the cooling water flow and temperature meet the requirements.
- Software faults: The software version is too old and there are bugs. Regularly check the software version and upgrade it in time according to the manufacturer’s instructions if there is an update.
In conclusion, laser welding machines may experience various faults during use, involving power supply, welding process, mechanical and optical systems, and other aspects. To ensure the normal operation of the equipment and prolong its service life, regular maintenance and inspection are needed to detect and deal with potential faults in time. At the same time, operators should master the correct usage methods and maintenance knowledge to reduce the occurrence of faults.
Processing Difficulties and Countermeasures of Laser Welding Technology
1. Low laser absorption rate of materials
When facing the problem of low laser absorption rate of materials in laser welding technology, multiple effective countermeasures can be taken. First of all, appropriate surface pretreatment processes are important means to improve absorption rate. For example, sandpaper grinding can remove the oxide layer and impurities on the material surface and increase the surface roughness, thereby improving the absorption of laser. Pretreatment measures such as surface chemical corrosion and surface plating can also change the physical and chemical properties of the material surface and make it easier to absorb laser energy. According to relevant research, the laser absorption rate of aluminum alloy materials after pretreatment such as sandpaper grinding can be increased by [X]% (this needs to be supplemented according to actual data).
Secondly, reducing the spot size can increase the laser power density. When the spot size is reduced, the laser energy per unit area increases, which enables the material to absorb energy faster and reach the melting temperature. At the same time, increasing the laser power density can also promote the heat conduction inside the material and improve the overall welding efficiency.
In addition, changing the welding structure to make the laser beam reflect multiple times in the gap is also an effective method to improve the laser absorption rate of materials such as aluminum alloys. By designing a reasonable welding structure and allowing the laser beam to reflect continuously in the gap, the contact time and area between the laser and the material are increased, thereby improving the material’s absorption of laser. For example, in some specific welding structures, after the laser beam is reflected multiple times, the material’s absorption rate of laser can be increased to [X]% (this needs to be supplemented according to actual data).
2. Prone to porosity and hot cracks
During the laser welding process, porosity and hot cracks are common problems. To reduce the generation of porosity and hot cracks, the following measures can be taken.
Adjusting the laser power waveform is an effective method. By changing parameters such as the rise time, peak power and fall time of the laser power, the formation and solidification process of the molten pool can be controlled and the situation of unstable collapse of pores can be reduced. For example, using a trapezoidal wave with slowly decreasing energy instead of a rectangular wave can reduce the cooling speed and reduce the generation of pores. At the same time, changing the irradiation angle of the laser beam can also reduce the generation of pores. During the welding process, adjusting the irradiation angle of the laser beam can change the flow direction and temperature distribution of the molten pool, thereby reducing the formation of pores.
Applying a magnetic field is also an effective means to reduce porosity and hot cracks. Applying a magnetic field during the welding process can change the flow direction and speed of the liquid metal in the molten pool, promote the escape of pores and reduce the generation of pores. At the same time, the magnetic field can also refine the grains and improve the quality of the weld. According to experimental data, after applying a magnetic field during the welding process, the generation rate of pores can be reduced by [X]% (this needs to be supplemented according to actual data).
For the hot crack problem, methods such as wire filling or presetting alloy powder can be used for laser welding. During the welding process, adding an appropriate amount of welding wire or alloy powder can change the chemical composition and structure of the weld and reduce the generation of hot cracks. At the same time, when using a YAG laser, adjusting the pulse waveform and controlling the heat input can also reduce crystal cracks.
3. During the welding process, the mechanical properties of welded joints decline
To improve the mechanical properties of welded joints, the method of adding low-boiling-point alloy elements can be adopted. When welding materials such as aluminum alloys, adding some low-boiling-point alloy elements such as zinc and magnesium can reduce the welding temperature, promote the formation of small holes and improve the firmness of welding. At the same time, low-boiling-point alloy elements can also improve the structure of the weld and improve the strength and toughness of the weld.
For example, when welding aluminum alloys, adding an appropriate amount of zinc and magnesium elements can increase the tensile strength of the weld by [X]% (this needs to be supplemented according to actual data) and increase the hardness by [X] HV (this needs to be supplemented according to actual data). In addition, the mechanical properties of welded joints can also be improved by optimizing welding process parameters such as welding speed, laser power and defocus amount. At the same time, appropriate heat treatment of the welded workpiece, such as solution treatment and aging treatment, can also improve the structure and mechanical properties of the weld.
In Conclusion
As an efficient and precise welding method, laser welding technology plays an important role in modern industrial production. However, in practical applications, laser welding also faces a series of problems and difficulties.
From common problems such as welding spatter, weld bead accumulation, welding deviation, and weld depression, to the difficulties in aluminum alloy welding, and various faults that may occur in the use of laser welding machines, these all pose challenges to the application of laser welding. However, by taking corresponding solutions, such as cleaning the material surface before welding, adjusting welding parameters, and using appropriate shielding gas, the occurrence of these problems can be effectively reduced.
For the difficulties in aluminum alloy welding, by means of surface pretreatment, changing the welding structure, adjusting the laser power waveform, applying a magnetic field, and adding low-boiling-point alloy elements, the absorption rate of materials to laser can be improved, the generation of porosity and hot cracks can be reduced, and the mechanical properties of welded joints can be improved.
In the field of power battery welding, the HighLightFL – ARM adjustable annular spot mode laser of Coherent Company provides an effective solution to solve welding problems, reducing porosity, spatter and weld cracks, and improving welding quality and efficiency.
Although laser welding has many problems and difficulties, with the continuous progress and innovation of technology, the development prospect of laser welding technology is still broad. For example, intelligent development will combine laser welding technology with robot technology, sensor technology, etc., to achieve more intelligent and automated production; the characteristics of green environmental protection will make it more widely used in the future; diversified applications will also be realized with the continuous progress of technology and the expansion of application fields.
In short, although laser welding technology faces many problems and difficulties, through continuous research and technological innovation, these problems can be effectively solved. In the future, laser welding technology will play an important role in more fields and make greater contributions to the development of modern industry. If you need one for start, Pendstar’s laser welding machines would be your best choice.
