Laser welding process and welded product of nickel-plated copper and stainless steel

Abstract

The application discloses a kind of nickel copper plating and stainless steel laser welding process and welding product, it is related to laser welding technical field, wherein, nickel copper plating and stainless steel laser welding process includes steps: nickel copper plating workpiece is stacked on stainless steel workpiece above and forms to be welded area;Multiple independent welding points are struck on the surface of to-be-welded area using quasi-continuous laser and galvanometer welding head system;Wherein, the rated power of laser is 750W, and the fiber core diameter is 200 μm;Laser power is set to 55%-65% of rated power, pulse width is set to 30.0-35.0 ms, and pulse frequency is set to 0.5-2.0 Hz;The technical scheme provided by the application can prevent welding and false welding.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and in particular to a laser welding process and welded products for nickel-plated copper and stainless steel. Background Technology

[0002] Laser welding, as a highly efficient and precise joining technology, has been widely applied in the field of metal processing. Among these applications, laser welding of dissimilar metals is in high demand in industries such as electronics, battery manufacturing, and medical devices. For example, nickel-plated copper possesses excellent electrical conductivity and corrosion resistance, while stainless steel provides structural strength and stability; reliably joining the two allows for functional complementarity and integration. However, nickel-plated copper and stainless steel differ significantly in their thermophysical properties. Copper has extremely high thermal conductivity and low laser absorption, while stainless steel has relatively low thermal conductivity and high laser absorption. When welding with conventional continuous laser or high power density, short pulse width pulsed laser, the energy input is concentrated and intense, which can easily lead to the following typical process defects: (1) Welding through: The high energy density required to melt the lower stainless steel layer can easily cause the thinner upper copper layer to overmelt or even vaporize, resulting in welding through, material collapse and severe spatter; (2) Incomplete welding: If the energy input is reduced in order to suppress welding through, the heat transferred to the stainless steel interface is often insufficient due to the rapid heat conduction of copper, making it difficult to form a stable molten pool, thus causing the interface to not fuse or to be incompletely welded. Summary of the Invention

[0003] The main objective of this invention is to propose a laser welding process and welding products for nickel-plated copper and stainless steel, which aims to prevent burn-through and incomplete welds.

[0004] To achieve the above objectives, the present invention proposes a laser welding process for nickel-plated copper and stainless steel, comprising:

[0005] Nickel-plated copper workpieces are stacked on top of stainless steel workpieces to form the area to be welded; A quasi-continuous laser and galvanometer welding head system is used to create multiple independent weld points on the surface of the area to be welded. The laser has a rated power of 750W and an optical fiber core diameter of 200μm; the laser power is set to 55%-65% of the rated power, the pulse width is set to 30.0-35.0ms, and the pulse frequency is set to 0.5-2.0Hz.

[0006] In one embodiment, the laser power is 60% of the rated power.

[0007] In one embodiment, the pulse width is 33.0 ms.

[0008] In one embodiment, the pulse frequency is 1 Hz.

[0009] In one embodiment, the center-to-center distance between two adjacent solder joints is 0.3 mm.

[0010] In one embodiment, the diameter of the laser output spot is 0.8-1.2 mm.

[0011] In one embodiment, the nickel plating layer of the nickel-plated copper workpiece has a thickness of 0.03-0.05 mm, and the copper base layer has a thickness of 0.3 mm.

[0012] In one embodiment, the thickness of the stainless steel workpiece is 0.3 mm.

[0013] In one embodiment, the stainless steel workpiece is made of one of 304 stainless steel, 316 stainless steel, or 430 stainless steel.

[0014] The present invention also proposes a welded product obtained by laser welding of nickel-plated copper and stainless steel as described above.

[0015] In the technical solution of this invention, a low-power, long-spot welding method is employed, creating a low-power-density, long-duration, slow-heating operation mode. This avoids the severe ablation of the upper thin copper layer by short-duration high energy, thus preventing solder burn-through; at the same time, the extended heat treatment time is sufficient to overcome the high thermal conductivity of copper, ensuring sufficient heat to penetrate the interface and melt the underlying stainless steel, thereby preventing incomplete soldering. Furthermore, the large spot size and slow-heating energy input method relatively slow down the cooling rate of the molten pool, which is beneficial for gas escape and reduces welding stress, thereby significantly reducing the tendency for porosity and cracking. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of an embodiment of the laser welding process for nickel-plated copper and stainless steel provided by the present invention.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] This invention proposes a laser welding process for nickel-plated copper and stainless steel.

[0023] Please see Figure 1 In one embodiment of the present invention, the laser welding process between nickel-plated copper and stainless steel includes: Step S1: Stack the nickel-plated copper workpiece on top of the stainless steel workpiece to form the area to be welded; Step S2: Using a quasi-continuous laser and galvanometer welding head system, multiple independent weld points are formed on the surface of the area to be welded.

[0024] The laser has a rated power of 750W and an optical fiber core diameter of 200μm. The laser power is set to 55%-65% of the rated power, the pulse width is set to 30.0-35.0ms, and the pulse frequency is set to 0.5-2.0Hz.

[0025] The quasi-continuous laser has a rated maximum output power of 750W, and its output laser is transmitted to the galvanometer welding head through a 200μm core optical fiber. The galvanometer welding head is equipped with a high-speed scanning galvanometer, which can precisely and quickly control the scanning and positioning path of the laser beam on the workpiece surface according to a preset program, thereby efficiently creating multiple independent weld points arranged in a certain spatial pattern. The specific model of the galvanometer welding head is N120. The 200μm fiber produces a relatively large focused spot.

[0026] The laser's power is set to 55%-65% of its rated power, i.e., a power range of 412.5W to 487.5W. This power range is significantly lower than the laser's peak power, designed to provide a moderate total heat input and avoid excessive instantaneous energy.

[0027] The pulse width is set to a long pulse width of 30.0ms to 35.0ms. The long pulse width means that the duration of a single laser emission is significantly extended, allowing sufficient time for heat to diffuse from the highly thermally conductive copper layer to the stainless steel layer.

[0028] The pulse frequency is set from 0.5Hz to 2.0Hz. This frequency controls the rhythm of spot welding, providing sufficient cooling time for each weld point and reducing the impact of heat accumulation on thin sheet metal workpieces.

[0029] During welding, the assembled workpiece is placed on the welding worktable, the scanning program of the galvanometer is set, and the positions of a series of independent welding points are planned. The welding system is started, and the laser emits pulsed laser light according to the above parameters. The galvanometer drives the laser beam to quickly and sequentially position and irradiate each target point. Under the action of the long-pulse laser, each welding point causes the interface between the nickel-plated copper plate and the stainless steel plate to melt together to form a weld nugget, achieving metallurgical bonding.

[0030] In the technical solution of this invention, a low-power, long-spot welding method is employed, creating a low-power-density, long-duration, slow-heating operation mode. This avoids the severe ablation of the upper thin copper layer by short-duration high energy, thus preventing solder burn-through; at the same time, the extended heat treatment time is sufficient to overcome the high thermal conductivity of copper, ensuring sufficient heat to penetrate the interface and melt the underlying stainless steel, thereby preventing incomplete soldering. Furthermore, the large spot size and slow-heating energy input method relatively slow down the cooling rate of the molten pool, which is beneficial for gas escape and reduces welding stress, thereby significantly reducing the tendency for porosity and cracking.

[0031] Specifically, in one embodiment of the present invention, the laser power is 60% of the rated power. The laser power is set to 60% of the rated power (750W) of the quasi-continuous laser, that is, the actual output power is 450W. This value is an optimal value determined after extensive process testing. The power level of 450W is significantly lower than the peak capability of 750W, which is sufficient to avoid thermal shock to the copper layer due to instantaneous overheating, thus reducing the risk of solder burn-through. At the same time, this power value can provide sufficient total energy input. When combined with a long pulse width (30.0-35.0ms), it can ensure that sufficient heat penetrates the copper layer and melts the interface with the stainless steel, eliminating the risk of poor soldering.

[0032] Specifically, in one embodiment of the present invention, the pulse width is 33.0 ms. Setting the pulse width to 33.0 ms ensures that the heat has sufficient time to overcome the rapid thermal conductivity of copper, reaching and melting the underlying stainless steel, while avoiding excessive heat input due to excessive time, which could cause excessive expansion of the molten pool or unnecessary thermal damage to the upper copper layer. This facilitates the formation of an alloy bonding layer with a smoother compositional transition and moderate thickness, maximizing the positive effect of the nickel plating layer on improving wettability, while simultaneously inhibiting the continuous growth of brittle intermetallic compounds (such as Fe-Ni-Cu phases), thus improving the mechanical strength and electrical conductivity reliability of the welded product.

[0033] Specifically, in one embodiment of the present invention, the pulse frequency is 1 Hz. A pulse frequency of 1 Hz means that the laser emits one pulse per second, with each pulse having a period of 1 second. The 1 Hz frequency provides a 1-second interval between two adjacent weld points. This is crucial for welding thin sheet materials, allowing sufficient time for the heat generated by the previous weld point to diffuse and dissipate into the surrounding substrate, effectively preventing heat accumulation and avoiding the risk of overall workpiece heating and deformation due to heat accumulation, or over-melting of subsequent weld points due to increased substrate temperature.

[0034] Furthermore, in one embodiment of the invention, the center-to-center distance between two adjacent weld points is 0.3 mm. In specific implementation, this parameter needs to be set in the programming software controlling the galvanometer welding head. The operator plans the weld point sequence according to the shape and length of the workpiece to be welded area and fixes the center-to-center distance between adjacent weld points at 0.3 mm. The welding system drives the laser beam to perform a skip-scanning motion along this planned path, triggering a laser pulse at each target position in sequence, ultimately forming a series of uniformly spaced and closely arranged independent weld point arrays. The 0.3 mm spacing allows the heat-affected zones of adjacent weld points to effectively overlap or closely connect, thereby forming a nearly continuous metallurgical bonding band on the interface, composed of closely connected discrete weld nuggets. This design retains the advantage of controllable heat input in pulse spot welding and achieves overall connection strength and sealing similar to a continuous weld through multi-point relay. At the same time, the discrete weld points can distribute welding stress to multiple points, effectively suppressing the linear warping deformation that is prone to occur in long welds. The 0.3mm spacing, combined with a 1Hz pulse frequency, ensures sufficient physical space and cooling time between the two solder joints. This balances heat accumulation and heat dissipation, preventing the rapid heat buildup in areas caused by overly dense solder joints, thus preventing the thin sheet workpiece from undergoing wavy deformation or severe surface oxidation due to overall overheating; it also avoids the problem of insufficient connection strength that may result from overly sparse solder joints.

[0035] Specifically, in one embodiment of the present invention, the diameter of the laser output spot is 0.8-1.2 mm. During the welding process, after the laser beam passes through the welding head optical system, the diameter of the laser output spot formed on the surface of the workpiece to be welded is 0.8 mm to 1.2 mm. This spot size is larger than the small spot size (usually 0.2-0.5 mm) conventionally used for precision spot welding. In practice, this is usually achieved by adjusting the defocusing amount of the welding head, that is, defocusing the laser focus by a specific distance (e.g., +1 mm to +3 mm), thereby expanding the diameter of the spot irradiated on the workpiece surface to 0.8 mm to 1.2 mm. When the laser power is fixed within a certain range, setting the spot diameter to 0.8-1.2 mm can reduce the power density and completely avoid the risk of ablation and perforation of the thin copper layer due to high energy density. The large spot size of 0.8-1.2 mm provides a heat source with a wider distribution area and a gentler energy gradient. When this wide-beam laser acts for 33 ms, heat can be uniformly and slowly introduced over a relatively large area. This helps overcome the high thermal conductivity of the upper copper layer, allowing sufficient time and space for heat to diffuse laterally, ensuring that heat can be more effectively conducted downwards to the stainless steel interface, and promoting the two metals at the interface to melt together and fully to form a good weld nugget, effectively preventing cold solder joints.

[0036] Specifically, in one embodiment of the present invention, the nickel plating layer of the nickel-plated copper workpiece has a thickness of 0.03-0.05 mm, the copper base layer has a thickness of 0.3 mm, the copper base layer as the base layer has a thickness of 0.3 mm, and the nickel plating layer covering the surface of the copper base layer has a thickness of 0.03 mm to 0.05 mm.

[0037] If the nickel plating layer thickness is less than 0.03 mm, the nickel plating amount is insufficient and may be completely diluted or burned off under laser irradiation. This prevents the formation of an effective barrier layer and wetting-promoting layer between copper and stainless steel, making it difficult to inhibit the formation of brittle copper-iron compounds. If the thickness is greater than 0.05 mm, the melting point of nickel is significantly higher than that of copper, requiring more heat to completely melt the thicker nickel layer. This may interfere with the thermal balance under the "long pulse width, low power density" mode, and even lead to incomplete fusion of the nickel layer. A thickness of 0.03-0.05 mm allows for complete melting under slow heating conditions of 450 W and 33 ms, spreading evenly at the interface. This effectively blocks the direct interdiffusion of copper and iron, while significantly improving the wettability of liquid copper on stainless steel, thereby obtaining a joint with a gentle compositional gradient and excellent mechanical properties.

[0038] Specifically, in one embodiment of the present invention, the thickness of the stainless steel workpiece is 0.3 mm. The equal thickness design of the stainless steel workpiece and the copper base layer makes it easier to achieve a balance in the conduction and distribution of heat between the upper and lower layers under welding heat input.

[0039] Furthermore, in one embodiment of the present invention, the stainless steel workpiece is made of one of 304 stainless steel, 316 stainless steel, or 430 stainless steel. When implementing this process, one of the three grades needs to be selected based on the final usage environment requirements of the product (such as corrosion resistance, strength, and cost). For example, 316 stainless steel can be used for marine environment electronic components requiring high corrosion resistance; 430 stainless steel can be used for general electronic casings seeking high cost-effectiveness; and 304 stainless steel is the most versatile choice.

[0040] The present invention also proposes a welded product obtained by the above-mentioned laser welding process of nickel-plated copper and stainless steel.

[0041] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A laser welding process for nickel-plated copper and stainless steel, characterized in that, include: Nickel-plated copper workpieces are stacked on top of stainless steel workpieces to form the area to be welded; A quasi-continuous laser and galvanometer welding head system is used to create multiple independent weld points on the surface of the area to be welded. The laser has a rated power of 750W and an optical fiber core diameter of 200μm; the laser power is set to 55%-65% of the rated power, the pulse width is set to 30.0-35.0ms, and the pulse frequency is set to 0.5-2.0Hz.

2. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The laser power is 60% of the rated power.

3. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The pulse width is 33.0 ms.

4. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The pulse frequency is 1 Hz.

5. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The center-to-center distance between two adjacent solder joints is 0.3 mm.

6. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The diameter of the laser output spot is 0.8-1.2mm.

7. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The nickel plating layer of the nickel-plated copper workpiece has a thickness of 0.03-0.05 mm, and the copper base layer has a thickness of 0.3 mm.

8. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The thickness of the stainless steel workpiece is 0.3 mm.

9. The laser welding process for nickel-plated copper and stainless steel as described in claim 1, characterized in that, The stainless steel workpiece is made of one of 304 stainless steel, 316 stainless steel or 430 stainless steel.

10. A welding product, characterized in that, Obtained by laser welding process of nickel-plated copper and stainless steel as described in any one of claims 1 to 9.

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