SHINHOP laser

Due to the outstanding physical and mechanical properties of aluminum alloy materials, as well as their lightweight nature, they particularly align with current policies and regulations advocating for energy conservation and reduction of environmental pollution. Therefore, aluminum alloy materials are heavily applied in the automotive manufacturing industry, with filters becoming a significant application of aluminum alloy materials in automotive parts.
The chemical properties of aluminum alloy itself are relatively active, making it prone to surface oxidation and the formation of an oxide film, and it is difficult to dissolve. It has strong thermal conductivity, which can easily lead to issues of non-fusion during welding. Additionally, the oxide film can absorb moisture, making it particularly easy to produce pores during welding. Furthermore, aluminum alloys have a large linear expansion coefficient and strong thermal and electrical conductivity, which can easily result in defects such as edge biting and warping during welding, and the mechanical properties of the welded joint decrease after welding. When using conventional argon arc welding (TIG) and inert gas melting arc (MIG) methods to weld aluminum alloys, issues such as porosity, welding cracks, and significant welding deformation can occur, limiting their application in industry.
The emergence of laser welding application technology addresses the shortcomings of aluminum alloy material welding. It is a diversified, highly applicable, and reliable precision welding process that can be easily automated or made intelligent. Due to the high power density of lasers, the heat input during welding is low, ensuring a small heat-affected zone while maintaining sufficient penetration depth, resulting in minimal welding deformation. Laser welding does not require a vacuum device, thus it features high quality, high precision, and high speed. Additionally, with the continuous development of high-power, high-performance laser processing equipment, aluminum alloy laser welding technology has been widely applied in the automotive manufacturing industry.

Below, we will analyze the filter in automotive parts, understanding the key points of the welding process for automotive filters and related influencing factors. The filter weld is a ring weld, and the joint is a lock bottom butt joint, requiring the weld appearance to be uniform and aesthetically pleasing, with a weld width of over 2mm and a penetration depth of over 1.5mm, as shown in the sample.


1. Equipment, Materials, and Methods
Equipment: Trumpf disc laser; optical configuration: focusing lens with a focal length of 300mm, collimating lens of 200mm, and fiber core diameter of 300μm, as illustrated in Figure 2.

Materials: Using 6-series aluminum alloy.
Method: The laser welding head remains stationary while the workpiece rotates around a fixed axis to achieve ring weld welding, with high-purity Ar gas used for side protection during the welding process.
2. Common Problems in Welding Process
1. Issues caused by the direction of protective gas: When the direction of the protective gas is the same as the rotation direction of the workpiece, i.e., the protective gas is blown backward, the protective gas cannot timely expel the air at the weld during the welding process, which can easily lead to air mixing during welding, resulting in easy oxidation of the weld, causing the weld surface to turn black and have poor formation.

2. Using small diameter gas pipes leads to a narrow protection range and excessive gas blowing force per unit area: For example, when using a single copper pipe with an inner diameter of 4mm for gas protection, and the sample is placed vertically (as shown in Figure 4), due to the high fluidity of liquid aluminum alloy, under the influence of gas blowing force and its own gravity, the aluminum alloy in the molten pool tends to flow downward, leading to weld sagging after welding (as shown below). Additionally, the small diameter copper pipe has a small gas blowing area and high gas blowing force, which can also lead to unstable weld formation.

3. Impure protective gas leads to localized oxidation of the weld, causing a yellowish surface: Due to the active chemical properties of aluminum alloy, it is prone to oxidation at high temperatures. Therefore, when welding aluminum alloy filters, high-purity argon gas (purity 99.99%) should be used. When using pure argon (purity 99.9%) for protection, the intrusion of gas impurities during high-temperature welding can also lead to localized oxidation of the weld, or even poor welding, as shown below.

4. Poor welding caused by mismatched process parameters: Laser welding is divided into heat conduction welding (power density between 10^5 W/cm² and 10^6 W/cm²) and deep penetration welding (power density between 10^6 W/cm² and 10^7 W/cm²). In heat conduction welding, the shallow layer of metal is primarily heated to melting by absorbing laser energy from the surface and conducting heat downward, resulting in a nearly semicircular weld with shallow penetration.
The appearance of small holes during the laser welding process can significantly increase the material's absorption rate of the laser. Small holes act as a black body, allowing the welded piece to gain more energy coupling, which is a prerequisite for achieving good welding quality.
Aluminum alloys have a very high initial reflectivity to lasers, with a reflectivity of up to 96% for CO2 laser beams and nearly 80% for Nd:YAG laser beams. The thermal conductivity of aluminum alloy is about three times that of ordinary medium carbon steel at room temperature. Therefore, in the actual welding process of aluminum alloys, it is necessary to ensure sufficient laser power to achieve the required penetration depth. In the laser welding of different aluminum alloys, a threshold of laser energy density has been found; if it is below this value, only surface melting occurs, and welding is conducted in a heat conduction manner, resulting in very shallow penetration, forming only a laser impact mark on the surface. However, once this value is reached or exceeded, plasma is generated, inducing small holes and significantly increasing penetration depth.
Therefore, to achieve deep penetration welding effects in aluminum alloy laser welding, a certain power value must be reached. However, the power cannot be too high, as excessive heat input can cause weld depression and severe edge biting, as shown in Figure 7a. When the energy is below the laser energy density threshold, a significant heat conduction welding morphology will appear, as shown below.

3. Solutions and Results
1. To address the instability of the molten pool and the narrow protection range of the weld caused by excessive blowing force and small blowing area of the protective gas, a gas pipe with a larger inner diameter (diameter 9mm) was used instead, as shown below. This gas pipe can form a larger protection range for the molten pool while reducing the interference of gas on the formation of the molten pool.

2. To meet the requirements for uniform and aesthetically pleasing weld surface formation and a weld width of over 2mm, slow, defocused welding was adopted. Additionally, during the welding process, an uphill adjustment time of 100ms and a downhill adjustment time of 300ms were implemented to reduce the arc pit formed at the end of the arc.
Select the parameters from Table 1 as the optimized welding process parameters. The post-weld sample is shown in Figure 9, and the arc shape is shown in Figure 10. The surface morphology and cross-sectional morphology of the weld seam are as follows.

It can be seen that the surface of the weld seam forms a dense and uniform fish scale pattern, with no surface cracks or defects such as pores. Additionally, the arc pit has been greatly reduced. From the figure, it can be detected that the weld width reaches 2.5mm, the weld depth reaches 1.7mm, and there are no defects such as pores or cracks inside.


IV. Summary of Experience:
From the above analysis, it can be seen that the main factors affecting the laser welding of automotive aluminum alloy filters are laser power, welding speed, and gas protection method.
1. If the welding heat input is too low, it will result in thermal conduction welding effects, with varying weld depth, making it difficult to meet the requirements.
2. If the welding heat input is too high, it will cause the weld seam to sag, resulting in severe undercutting.
During the laser welding of automotive aluminum alloy filters, only under suitable gas protection can a well-formed and aesthetically pleasing weld seam be obtained. The optimized laser welding process parameters for automotive aluminum alloy filters are: power 2400W, speed 2.4m/min, defocus amount -2mm, using high-purity argon for side protection.
The weld width reaches 2.5mm, the weld depth reaches 1.7mm, and the surface of the weld seam is uniformly formed and defect-free, meeting the requirements.
Laser welding of automotive filters needs to determine the relevant configuration of laser welding equipment based on the characteristics of the product. Choosing the appropriate production equipment is essential to weld high-quality products. Only manufacturers with relevant welding processing experience can provide good solutions. For a deeper understanding of the welding process and technical requirements of such products, you can contact SHINHOP automotive parts laser welding technology experts for discussions or visit the factory directly.