Hot forming steel butt joint laser welding method based on annular light spots
The pulsed welding method using a ring-spot laser has solved the problems of porosity and spatter in the welding of hot-formed steel, achieving high-quality, low-cost welding results and improving the performance and stability of the welded joint.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI UNIV OF ENG SCI
- Filing Date
- 2026-01-22
- Publication Date
- 2026-05-12
AI Technical Summary
Existing hot-formed steel welding processes are prone to defects such as porosity, spatter, and poor fusion, which makes welding quality control difficult, production costs high, and traditional welding methods affect the strength and plasticity of the material.
Pulse welding using a ring-shaped laser spot is divided into two stages: preheating and welding. Energy is input using ring-shaped laser spots with different laser power ratios, and combined with precise superposition parameters, a continuous butt weld is formed.
It effectively reduces porosity and spatter, improves weld quality and joint reliability, maintains the toughness and plasticity of materials, and reduces production difficulty and cost.
Smart Images
Figure CN122007629A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of laser welding technology, and specifically to a laser welding method for hot-formed steel butt joints based on an annular spot. Background Technology
[0002] With the rapid development of the new energy vehicle industry, lightweighting and safety have become key goals in vehicle body design. Hot-formed steel, due to its high strength and excellent collision resistance, is widely used in the body structure, especially in key safety parts such as the A-pillar and B-pillar. In some high-end models, the proportion of hot-formed steel used has reached more than 85%. The use of hot-formed structures helps to reduce the weight of the vehicle body. For example, a certain new energy vehicle has reduced its body weight by about 20% by using hot-formed steel, effectively improving the overall vehicle energy efficiency and dynamic performance.
[0003] However, existing hot-formed steels face numerous technological challenges during welding. Their high hardness and high-temperature resistance make weld nugget embrittlement common. In actual welding, when the material hardness reaches 500 HV, the probability of weld nugget cracking increases by 40% compared to ordinary steel. Furthermore, defects such as porosity, spatter, and poor fusion are easily generated during welding, significantly increasing the difficulty of welding quality control and production costs. In addition, traditional resistance spot welding of hot-formed steel requires only a low current to melt the sheet due to its high resistivity. However, in the "hot forming + hot forming" combination, the contact resistance is high. While the weld nugget diameter can quickly reach the required size, problems such as insufficient nugget volume and shallow penetration exist, easily leading to interface fracture. Simultaneously, the heat-affected zone exhibits significant softening, with a large area width, affecting the overall structural strength, potentially causing safety hazards, especially in critical load-bearing areas.
[0004] To address the shortcomings of traditional welding processes, laser welding technology is increasingly being applied to the welding of hot-formed steel. Compared to traditional spot welding, laser welding offers significant advantages: First, the high energy density of the laser beam allows welding to be completed in a short time, greatly improving production efficiency; second, welding precision can be controlled within 0.1mm, and the weld surface is smooth and flat, ensuring high-quality weld appearance; third, it can integrate multiple parts into a single piece, reducing the number of parts and eliminating spot weld overlaps between parts, further contributing to vehicle lightweighting; in addition, the heat-affected zone formed by laser welding is small, having minimal impact on the forming performance of hot-formed steel, and can improve the overall vehicle quality stability and crash safety performance. However, in practical applications, it has been found that when welding hot-formed steel with a single continuous laser, the high concentration of energy leads to excessively rapid heating and cooling, making it difficult to avoid welding defects such as porosity, spatter, and poor fusion, and thus failing to fully meet the high-quality welding requirements of hot-formed steel butt joints.
[0005] Therefore, it is necessary to invent a laser welding method for thermoformed steel butt joints based on annular light spots to solve the above problems. Summary of the Invention
[0006] The purpose of this invention is to provide a laser welding method for hot-formed steel butt joints based on annular light spots, in order to solve the problems of welding defects such as porosity, spatter, and poor fusion that are easily generated in the traditional resistance spot welding and continuous laser welding of hot-formed plates, and the easy occurrence of weld nugget embrittlement, which in severe cases reduces the toughness and plasticity of the weld joint, greatly increasing the difficulty of controlling welding quality and the production cost.
[0007] To achieve the above objectives, the present invention provides the following technical solution: a laser welding method for hot-formed steel butt joints based on annular spot laser, comprising welding the hot-formed steel butt joints using annular spot laser, wherein the welding method employs pulse welding, and the formation of each pulse weld point includes two stages: The first step is the heating stage, in which an annular pulsed laser spot with a central laser power to annular laser power ratio of (0.5~3.0):(9.5~7.0) is used to preheat the weld area, forming an unmelted circular heating zone; the second step is the welding stage, in which an annular pulsed laser spot with a central laser power to annular laser power ratio of (9.5~7.0):(0.5~3.0) is used to weld the preheated weld area, causing it to melt and form a molten pool; A continuous butt weld is formed by sequentially stacking multiple single-pulse weld points along the weld seam direction.
[0008] Preferably, during the heating phase, the ratio of the central laser power to the ring laser power is in the range of 1:9.
[0009] Preferably, during the welding stage, the preferred ratio of the central laser power to the ring laser power is 9:1.
[0010] Preferably, the pulse welding points are superimposed in such a way that the overlapping length b of adjacent welding points in the weld length direction satisfies: b = (0.25 ~ 0.5)C, where C is the diameter of the annular spot.
[0011] Preferably, the pulse weld points are stacked in such a way that the overlapping height 'a' of adjacent weld points in the weld height direction satisfies: a ≥ D + 0.2 mm, where D is the required butt weld width.
[0012] Preferably, the thickness of the hot-formed steel is 0.5-2.0 mm.
[0013] Preferably, the diameter of the weld point formed by the single pulse welding is 0.5 mm to 2.5 mm.
[0014] Preferably, the fiber core diameter of the central laser is 0.1 mm, and the fiber core diameter of the ring laser is 0.35 mm; the focal spot diameter of the central laser is 0.2-0.3 mm, and the focal spot diameter of the ring laser is 0.8-1.0 mm.
[0015] Preferably, when the thickness of the hot-formed steel is 1 mm and the required weld width D is 1.0 mm, the total laser power in the heating stage is 2 kW, of which the central laser power is 0.2 kW and the ring laser power is 1.8 kW; the total laser power in the welding stage is 2 kW, of which the central laser power is 1.8 kW and the ring laser power is 0.2 kW; the defocusing amount is 1 mm, the overlapping height a is not less than 1.2 mm, and the overlapping length b is not less than 0.6 mm.
[0016] The technical effects and advantages provided by the present invention in the above technical solution are as follows: 1. This invention fundamentally overcomes the inherent defects of traditional resistance spot welding by adopting non-contact annular light spot pulse welding. This method does not require electrode pressure, avoids workpiece deformation and electrode wear caused by mechanical contact, and achieves high-efficiency, low-deformation precision welding. It is particularly suitable for the high-quality connection requirements of high-strength steel lightweight structural components. 2. This invention achieves precise and flexible control of heat input through a two-step energy input and pulsed action mode of "preheating + welding". The first step, annular spot preheating, can slow down the subsequent cooling and shrinkage of the molten pool. The second step, central spot welding, achieves rapid penetration. This combination strategy, combined with pulse adjustment, can effectively suppress defects such as porosity, spatter and poor fusion, and significantly improve the weld formation quality and joint reliability. 3. This invention greatly enhances the adaptability of the process to ultra-thin and ultra-high strength hot-formed steel by adjusting the energy distribution of the annular laser spot and coordinating the pulse parameters. By precisely controlling the power ratio, spot size and superposition parameters of the center and the annular laser, the heat input can be precisely controlled within the optimal window, effectively preventing weld burn-through and reducing the heat-affected zone, thereby enabling high-quality welding of thin-walled high-strength hot-formed steel components less than 2mm thick. 4. This invention integrates annular light spot, two-step pulse, and optimized superposition path to form a welding solution with flexible parameter layout, wide process window, and high stability. It achieves fewer pores, less spatter, high quality, and long-term reliability in hot-formed steel welding. This method not only ensures stable welding process and low defect rate, but also improves the microstructure of the weld and maintains the toughness and plasticity of the joint, thereby comprehensively improving the overall performance and service life of the welded joint, while reducing the difficulty and cost of production quality control. Attached Figure Description
[0017] Figure 1This is a schematic diagram of the hot-formed steel butt joint structure of the present invention; Figure 2 This is a schematic diagram of a single pulse weld point on hot-formed steel according to the present invention; Figure 3 This is a schematic diagram of the first heating step and the second heating step of the present invention; Figure 4 This is a schematic diagram of the superimposed size of the annular light spot in this invention. Detailed Implementation
[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.
[0019] This invention provides, for example Figure 1-4 The method shown is a laser welding method for hot-formed steel butt joints based on annular spot laser. It includes welding the hot-formed steel butt joints using an annular spot laser. The welding method employs pulse welding, and the formation of each pulse weld point includes two stages: The first step is the heating stage, in which an annular pulsed laser spot with a central laser power to annular laser power ratio of (0.5~3.0):(9.5~7.0) is used to preheat the weld area, forming an unmelted circular heating zone. The second step is the welding stage, in which an annular pulsed laser spot with a central laser power to annular laser power ratio of (9.5~7.0):(0.5~3.0) is used to weld the preheated weld area, causing it to melt and form a molten pool. By stacking multiple single-pulse weld points sequentially along the weld direction, a continuous butt weld is formed. In the heating stage, the ratio of central laser power to annular laser power is 1:9, and in the welding stage, the preferred ratio of central laser power to annular laser power is 9:1.
[0020] In this embodiment, the core function of the two-step pulse method of "preheating before welding" is to precisely control heat input and improve weld quality. In the preheating stage (low center power ratio): the preheating energy dominated by the annular spot can slowly increase the workpiece temperature and reduce the temperature difference between the base material and the molten pool during subsequent welding. This can effectively slow down the solidification rate of the molten pool and provide time for gas to escape, thereby reducing porosity from the root. In the welding stage (high center power ratio): the welding dominated by the center spot can achieve rapid and concentrated energy input, forming a molten pool with a good depth-to-width ratio, ensuring penetration and fusion. At the same time, the extremely fast cooling rate can refine the grains, which helps to maintain the toughness and strength of the joint.
[0021] The superposition method of pulsed weld points is as follows: the superposition and overlap length b of adjacent weld points in the weld length direction satisfies: b = (0.25 ~ 0.5)C, where C is the diameter of the annular laser spot. The superposition method of pulsed weld points is as follows: the superposition and overlap height a of adjacent weld points in the weld height direction satisfies: a ≥ D + 0.2 mm, where D is the required butt weld width. The material thickness of hot-formed steel is 0.5-2.0 mm. The diameter of the weld point formed by a single pulse welding is 0.5 mm to 2.5 mm. The fiber core diameter of the central laser is 0.1 mm, and the fiber core diameter of the annular laser is 0.35 mm. The focal spot diameter of the central laser is 0.2-0.3 mm, and the focal spot diameter of the annular laser is 0.8-1.0 mm.
[0022] In this embodiment, by setting precise overlap length b and overlap height a, sufficient and uniform overlap between weld points is ensured, avoiding defects such as incomplete fusion and undercut caused by insufficient overlap, thus forming a smooth, dense, and uninterrupted continuous weld. The coordination between the small central focal spot and the large annular focal spot is the basis for achieving precise energy distribution. Matching the weld point diameter with the material thickness and weld width ensures sufficient connection strength and sealing, thereby jointly guaranteeing the continuity and formation stability of the weld.
[0023] When the thickness of the hot-formed steel is 1 mm and the required weld width D is 1.0 mm, the total laser power is 2 kW during the heating stage, with the central laser power being 0.2 kW and the ring laser power being 1.8 kW; the total laser power is 2 kW during the welding stage, with the central laser power being 1.8 kW and the ring laser power being 0.2 kW; the defocusing amount is 1 mm, the overlapping height a is not less than 1.2 mm, and the overlapping length b is not less than 0.6 mm.
[0024] In this embodiment, the hot-formed steel structure has a thickness of 1.0 mm, a butt joint with no gap, and a weld width requirement of 1.0 mm. The first heating step uses a center-to-ring laser power ratio of 1:9, a total laser power of 2 kW, a center laser power of 0.2 kW, and a ring laser power of 1.8 kW. The second welding step uses a center-to-ring laser power ratio of 9:1, a total laser power of 2 kW, a center laser power of 1.8 kW, and a ring laser power of 0.2 kW. The defocusing amount is 1 mm, the beam overlap height a > 1.2 mm, and the beam overlap length b > 0.6 mm. The hot-formed steel is well welded and the connection is firm.
[0025] This set of parameters clearly demonstrates how the aforementioned core method (two-step power switching) and key parameters (superposition control) can be integrated and implemented in specific application scenarios. It proves that the method can stably weld high-quality joints that meet the requirements. Under these parameters, the welding process has minimal spatter, the weld formation is uniform and aesthetically pleasing, and the porosity is significantly lower than that of traditional methods. The heat-affected zone is narrow, which comprehensively reflects the core advantages of this invention: "few porosity, less spatter, high quality, and good reliability." It provides a reliable process benchmark for the production of similar products.
[0026] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A laser welding method for hot-formed steel butt joints based on annular spot laser, comprising welding the hot-formed steel butt joints using annular spot laser, characterized in that: The welding method employs pulse welding, and the formation of each pulse weld point includes two stages: The first step is the heating stage, in which an annular pulsed laser spot with a central laser power to annular laser power ratio of (0.5~3.0):(9.5~7.0) is used to preheat the weld area, forming an unmelted circular heating zone; the second step is the welding stage, in which an annular pulsed laser spot with a central laser power to annular laser power ratio of (9.5~7.0):(0.5~3.0) is used to weld the preheated weld area, causing it to melt and form a molten pool; A continuous butt weld is formed by sequentially stacking multiple single-pulse weld points along the weld seam direction.
2. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 1, characterized in that: During the heating phase, the ratio of the central laser power to the ring laser power is in the range of 1:
9.
3. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 1, characterized in that: During the welding stage, the preferred ratio of the central laser power to the ring laser power is 9:
1.
4. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 1, characterized in that: The pulse welding points are superimposed in such a way that the overlap length b of adjacent welding points in the weld length direction satisfies: b = (0.25 ~ 0.5)C, where C is the diameter of the annular spot.
5. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 4, characterized in that: The pulse welding points are superimposed in such a way that the overlapping height 'a' of adjacent welding points in the weld height direction satisfies: a ≥ D + 0.2 mm, where D is the required butt weld width.
6. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 1, characterized in that: The thickness of the hot-formed steel is 0.5-2.0 mm.
7. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 1, characterized in that: The diameter of the weld point formed by the single pulse welding is 0.5 mm to 2.5 mm.
8. The laser welding method for hot-formed steel butt joints based on annular spot according to claim 1, characterized in that: The fiber core diameter of the central laser is 0.1 mm, and the fiber core diameter of the ring laser is 0.35 mm; the focal spot diameter of the central laser is 0.2-0.3 mm, and the focal spot diameter of the ring laser is 0.8-1.0 mm.
9. The laser welding method for hot-formed steel butt joints based on annular light spots according to claim 1, characterized in that: When the thickness of the hot-formed steel is 1 mm and the required weld width D is 1.0 mm, the total laser power in the heating stage is 2 kW, of which the central laser power is 0.2 kW and the ring laser power is 1.8 kW; the total laser power in the welding stage is 2 kW, of which the central laser power is 1.8 kW and the ring laser power is 0.2 kW; the defocusing amount is 1 mm, the overlapping height a is not less than 1.2 mm, and the overlapping length b is not less than 0.6 mm.