A laser welding method for back parts of mirror-finish stainless steel sheet

Abstract

This invention relates to a laser welding method for parts on the back of mirror-finish stainless steel sheet. The method includes: aligning the parts to be welded with a stainless steel foil sheet, the stainless steel foil sheet including a protrusion extending outward along the contour of the surface to be welded of the parts; and using laser spiral spot welding to weld multiple weld points formed by welding the protrusion around the circumference of the parts in a symmetrical sequence to the back of the mirror-finish stainless steel sheet. This method utilizes the stainless steel foil to reduce the rigidity of the parts to be welded, and the full deformation of the stainless steel foil during welding, combined with the spiral spot welding method to increase the diameter of the weld points, and welding in a symmetrical sequence, utilizes extremely low heat input to reduce the tensile stress on the mirror-finish stainless steel sheet during laser welding. This solves the problem of mirror deformation caused by tensile stress generated by the weld or weld points when welding parts to the back of mirror-finish stainless steel sheet, while also preventing the parts to be welded from shaking. The welding strength far exceeds the design requirements, which is beneficial for improving product quality, saving processes, and reducing costs.

Description

Technical Field

[0001] This invention belongs to the field of welding mirror stainless steel thin sheets, and specifically relates to a laser welding method for parts on the back of mirror stainless steel thin sheets. Background Technology

[0002] With the continuous improvement of living standards, mirror-finish stainless steel sheets are increasingly widely used in elevators, bathroom fixtures, kitchen appliances, and other fields. The raw material for mirror-finish stainless steel sheets used in general decorative structural components is 300 series stainless steel sheet, with a thickness of 2-3mm. Even slight deformation is enough to cause visible image distortion, so the requirements for the flatness of the mirror surface are extremely high.

[0003] To prevent deformation of the mirror surface, there are currently two main methods for assembling small parts such as studs, nuts, plates, and tubes on the back of mirror-finish stainless steel sheets: One method involves bending and bolting, or gluing, which increases product weight and material processing costs, shortens service life, or releases harmful gases. The other method uses arc welding or laser spot welding to directly weld the parts to the back of the mirror-finish stainless steel sheet. However, this inevitably generates strain and stress around the weld points, requiring mirror polishing after welding. This method also requires specialized equipment or tooling, increasing the difficulty and cost of polishing. Therefore, improving the welding method for parts on the back of mirror-finish stainless steel sheets is of great significance for improving product quality, saving processes, and reducing costs.

[0004] Existing methods for improving welding techniques to reduce deformation of stainless steel parts focus on replacing arc welding with laser welding, which involves higher heat input. Further adjustments to welding parameters reduce the heat input and thus the deformation. However, when used for welding parts on the back of mirror-finish stainless steel sheets, the high rigidity of the parts makes them difficult to deform. The tensile stress generated by the weld or weld point only affects the mirror-finish stainless steel sheet, still causing concave deformation and image distortion, impacting the product's aesthetics. Furthermore, reducing the heat input or the number of weld points can lead to insufficient welding strength, thus failing to meet the design requirements for welding parts on the back of mirror-finish stainless steel sheets. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the above-mentioned technical problems. The present invention provides a laser welding method that can solve the problem of mirror deformation caused by welding tensile stress when welding parts on the back of mirror stainless steel thin sheets, while taking into account the welding strength.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A laser welding method for parts on the back of a mirror-finish stainless steel sheet, the method comprising:

[0008] The parts to be welded are combined with stainless steel foil with their centers aligned, the stainless steel foil including a protrusion that protrudes outward along the contour of the surface to be welded of the parts to be welded;

[0009] Multiple weld points, formed by welding the protrusion around the circumference of the part to be welded in a symmetrical sequence, are welded onto the back of a mirror-finish stainless steel sheet using laser spiral spot welding. The thickness of the stainless steel foil is 6%-14% of the thickness of the mirror-finish stainless steel sheet. If the stainless steel foil is too thin, its rigidity is too low, and the part to be welded will shake as a whole. If the stainless steel foil is too thick, its rigidity is too high, and it will not be easy to deform, thus causing the mirror surface to deform.

[0010] Furthermore, the part to be welded and the stainless steel foil are an integral structure, including the stainless steel foil structure being processed during the part processing stage of the part to be welded.

[0011] Furthermore, the parts to be welded and the stainless steel foil are combined by welding, including laser welding and resistance welding. The welding strength between the parts to be welded and the stainless steel foil is greater than the design requirement for the welding strength between the parts to be welded and the mirror stainless steel sheet. After welding, the stainless steel foil is flat and has little deformation, thus avoiding affecting the further welding and assembly of the stainless steel foil and the mirror stainless steel sheet.

[0012] Furthermore, laser spiral spot welding is used to weld multiple weld points formed by welding around the circumference of the parts to be welded in a symmetrical group sequence onto a stainless steel foil. Spiral spot welding ensures the welding strength between the parts to be welded and the stainless steel foil while reducing the welding heat input. Combined with the symmetrical group welding sequence, it reduces the influence of tensile stress on the deformation of the stainless steel foil, thereby keeping the stainless steel foil flat.

[0013] Furthermore, the stainless steel foil is shaped to be 1.5-2 times larger than the shape of the surface to be welded of the part to be welded. After the part to be welded and the stainless steel foil are aligned and combined, the size and shape of the protrusion are optimized to avoid the protrusion being too large, which would increase the overall weight and cost excessively, and to avoid the protrusion being too small, which would reduce the number of weld points excessively and reduce the connection strength of the part to be welded.

[0014] Furthermore, the spacing between weld points needs to be strictly controlled for different stainless steel thicknesses. During laser spiral spot welding, the spacing between adjacent weld points should be greater than 1 times the thickness of the mirror stainless steel sheet and less than 2 times the thickness of the mirror stainless steel sheet. This is to avoid the weld point spacing being too small, which would cause excessive tensile stress superposition between adjacent weld points and increase mirror deformation. Conversely, the weld point spacing should not be too large, which would reduce the number of weld points and decrease the connection strength of the parts to be welded.

[0015] Furthermore, it is preferable to have multiple weld points evenly spaced around the circumference of the part to be welded, which further improves the reliability of the welding strength.

[0016] Furthermore, during the laser spiral spot welding, the diameter of the weld spot is 1.5-2.5 times the thickness of the stainless steel foil. This avoids the weld spot diameter being too small, which would lead to a decrease in welding strength, and avoids the weld spot diameter being too large, which would lead to excessive total heat input, resulting in increased tensile stress on the mirror-finished stainless steel sheet and further increase mirror deformation.

[0017] Furthermore, during the laser spiral spot welding, after the stainless steel foil sheet is brought into close contact with the back of the mirror stainless steel sheet using a tooling, laser spot welding is performed using a single-mode pulsed laser and a galvanometer welding head in a spiral scanning manner. On the one hand, the close contact improves the assembly gap, thereby further improving the welding accuracy. On the other hand, the spiral scanning of the single-mode pulsed laser and the galvanometer welding head increases the weld point diameter and maintains the weld point strength, while the extremely low heat input along the scanning path reduces the tensile stress of laser welding on the mirror stainless steel sheet, thereby further reducing deformation.

[0018] Furthermore, the power of the single-mode pulsed laser is 100-300W, and the power percentage during laser spiral spot welding is 17-26%, which further optimizes the welding heat input, avoids excessive heat input causing increased tensile stress and further deformation, and avoids insufficient heat input leading to insufficient penetration and further reduction of weld strength.

[0019] Furthermore, during the laser spiral spot welding, the duty cycle is 47-62%, the frequency is 120-160KHz, the pulse width is 350-500ns, and the welding speed is 170-210mm / s. The duty cycle, frequency, and pulse width are all negatively correlated with the pulse energy and laser processing capability, and the welding speed is negatively correlated with the local temperature. Further optimization of welding parameters can minimize heat input while maintaining welding strength.

[0020] Furthermore, during laser spiral spot welding, the outer diameter of the spiral is 0.25-0.38 mm, and the spiral spacing is 0.08-0.13 mm.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] (1) This invention utilizes stainless steel foil sheets arranged in a convex pattern to reduce the rigidity of the parts to be welded. After the convex part is laser-welded to the mirror stainless steel sheet, on the one hand, by optimizing the thickness ratio of the stainless steel foil sheet to the mirror stainless steel sheet, the rigidity of the stainless steel foil sheet is maintained to prevent the parts to be welded from shaking. At the same time, the welding process causes sufficient deformation of the stainless steel foil sheet, reducing the deformation effect on the mirror stainless steel sheet. On the other hand, by using a spiral spot welding method, the diameter of the weld spot can be increased. While ensuring the welding strength, the total heat input is kept at a low level. Combined with welding in a symmetrical group sequence, the tensile stress effect on the mirror stainless steel sheet is reduced. This solves the problem of mirror deformation caused by tensile stress generated by the weld or weld spot when welding parts to the back of the mirror stainless steel sheet, while also taking into account the welding strength.

[0023] Compared to the existing assembly method of bending and bolting, this method greatly reduces the weight of the overall structure.

[0024] Compared to adhesive bonding, this method significantly improves service life and reduces indoor environmental pollution.

[0025] Compared to traditional welding methods, this method avoids deformation of the mirror-finish stainless steel, greatly improving its aesthetics.

[0026] Compared to the traditional method of welding followed by polishing, this method reduces the number of steps, improves production efficiency, and lowers production costs.

[0027] (2) In this invention, after the stainless steel foil is brought into close contact with the back of the mirror stainless steel sheet using a tooling, laser spot welding is performed by a single-mode pulse laser and a galvanometer welding head in a spiral scanning manner. By further optimizing the weld point spacing, weld point diameter, and welding heat input, while maintaining the weld point strength, the extremely low heat input on the scanning path reduces the tensile stress of laser welding on the mirror stainless steel sheet, further optimizing the mirror flatness, and the welding strength far exceeds the design requirements. Attached Figure Description

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 This is a structural diagram of the part to be welded according to Embodiment 1 of the present invention;

[0030] Figure 2 This is a structural diagram of the assembly of the part to be welded and the stainless steel foil in Embodiment 1 of the present invention;

[0031] Figure 3 This is a top view of the welded structure of Embodiment 1 of the present invention;

[0032] The diagram shows: 1. Stainless steel stud, 101. Stainless steel foil, 2. Protrusion, 201. 3. First weld point, 4. Second weld point, 5. Mirror-finish stainless steel sheet.

[0033] Figure 4 This is a cross-sectional view of the second weld point in Embodiment 1 of the present invention, with the red area indicating the penetration depth.

[0034] Figure 5 These are comparison images of mirror deformation tests between Embodiment 1 and Comparative Example 1 of the present invention. Figure 5 a represents the reflection of a straight object on the mirror surface in Example 1. Figure 5 b represents the reflection of a straight object on the mirror surface in Comparative Example 1. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] Example 1:

[0037] This is a preferred embodiment of the laser welding method for back-side components of a mirror-finish stainless steel sheet according to the present invention. The mirror-finish stainless steel sheet is 10K grade, made of SUS304, with a length of 100mm, a width of 50mm, and a thickness of 2mm. One stainless steel stud component needs to be welded to the back side. The dimensions of the stainless steel stud component are as follows... Figure 1 As shown, the maximum tensile force of the stainless steel stud is required to be >100N. The laser welding method specifically includes the following steps:

[0038] Step S1: Cut stainless steel foil sheet 2. The stainless steel foil sheet 2 is made of SUS304, is square, and has a length of 8mm, a width of 8mm, and a thickness of 0.2mm.

[0039] Step S2: Assemble the parts to be welded, namely the stainless steel stud 1 and the stainless steel foil 2, together using tooling to ensure that the centers coincide.

[0040] Step S3: According to Figure 3 As shown, the positions of the first weld points 3 are evenly marked around the circumference of the stainless steel stud 1 at the overlapping position of the stainless steel stud 1 and the stainless steel foil 2. There are 8 first weld points 3. The 8 first weld points 3 are arranged in pairs along the radial direction of the stainless steel stud 1 to form four symmetrical groups: A, B, C and D. The distance between two symmetrical first weld points 3 is 4.4 mm.

[0041] Step S4: Select a 200W single-mode nanosecond pulse laser, equip it with the corresponding galvanometer welding head, and set the welding parameters as follows: power percentage of 40%, duty cycle of 50%, frequency of 150KHz, pulse width of 500ns, welding speed of 180mm / s, and use laser spiral spot welding method with spiral outer diameter of 0.4mm and spiral spacing of 0.1mm.

[0042] Step S5: Perform laser spot welding in a spiral scanning manner. During spot welding, a symmetrical welding sequence is adopted. That is, after completing the welding of a first weld point 3, the symmetrical weld point position of the previous first weld point 3 is found along the radial direction of the stainless steel stud 1, and the next first weld point 3 is welded. This completes the welding of a group of symmetrical first weld points 3. The diameter of each first weld point 3 is 0.4mm.

[0043] like Figure 2 As shown, the stainless steel stud 1 is welded onto the stainless steel foil 2. The welding strength between the stainless steel stud 1 and the stainless steel foil 2 is greater than 100N. After welding, the stainless steel foil 2 is flat. The assembled stainless steel foil 2 includes a protrusion 201 that protrudes outward along the contour of the surface to be welded of the part to be welded.

[0044] Step S6: With the back side of the mirror stainless steel sheet 5 facing up, place the stainless steel foil 2 and stainless steel stud 1 obtained in step S4 at the corresponding positions of the mirror stainless steel sheet 5 according to the design requirements, so that the stainless steel stud 1, stainless steel foil 2, and mirror stainless steel sheet 5 are arranged from top to bottom. Use a tooling to clamp the stainless steel foil 2 and the mirror stainless steel sheet 5 so that the stainless steel foil 2 and the back side of the mirror stainless steel sheet 5 are in close contact.

[0045] Step S7: According to Figure 3 As shown, the positions of the second weld points 4 are evenly marked on the protrusion 201 around the circumference of the stainless steel stud 1. There are 8 second weld points 4 in total. The 8 second weld points 4 are arranged in symmetrical pairs along the radial direction of the stainless steel stud 1. The distance between two symmetrical second weld points 4 is 7.4 mm, that is, the distance between adjacent second weld points 4 is 2.8 mm. See Appendix. Figure 4 The melting depth is 68μm.

[0046] Step S8: Select a 200W single-mode nanosecond pulse laser, equip it with the corresponding galvanometer welding head, and set the welding parameters as follows: power percentage of 20%, duty cycle of 50%, frequency of 150KHz, pulse width of 500ns, welding speed of 200mm / s, and use laser spiral spot welding method with spiral outer diameter of 0.3mm and spiral spacing of 0.1mm.

[0047] Step S9: Perform laser spot welding in a spiral scanning manner. During spot welding, a symmetrical welding sequence is adopted. That is, after completing the welding of a second weld point 4, the symmetrical weld point position of the previous second weld point 4 is found along the radial direction of the stainless steel stud 1, and the next second weld point 4 is welded. This completes the welding of a group of symmetrical second weld points 4. In this way, all symmetrical groups of second weld points 4 are welded. The diameter of each second weld point 4 is 0.3mm. That is, the protrusion 201 is welded to the back of the mirror stainless steel sheet 5, realizing the welding of the stainless steel stud 1 on the back of the stainless steel sheet.

[0048] Example 2: The difference from Example 1 is that the thickness of the stainless steel foil is 0.25mm, and the power in step S8 is increased by 22% accordingly.

[0049] Example 3: The difference from Example 1 is that the distance between the two symmetrical second solder points 4 is 8mm, that is, the distance between adjacent second solder points 4 is 3.0mm.

[0050] Comparative Example 1: The difference from Example 1 is that stainless steel foil is not added, and step S7 is performed according to... Figure 3 The location of the first weld point is shown. The stainless steel bolt is directly welded to the back of the mirror stainless steel sheet, and the spacing between adjacent weld points is reduced to 0.84 times the thickness of the mirror stainless steel sheet.

[0051] Comparative Example 2: The difference from Example 1 is that the thickness of the stainless steel foil in step S1 is 0.1 mm.

[0052] Comparative Example 3: The difference from Example 1 is that the thickness of the stainless steel foil in step S1 is 0.3 mm.

[0053] Comparative Example 4: The difference from Example 1 is that the spacing between adjacent second solder joints in step S7 is 2 mm.

[0054] Comparative Example 5: The difference from Example 1 is that the spacing between adjacent second solder joints in step S7 is 4 mm.

[0055] Comparative Example 6: The difference from Example 1 is that the power percentage in step S8 is 30%.

[0056] Comparative Example 7: The difference from Example 1 is that the power percentage in step S8 is 10%.

[0057] Comparative Example 8: The difference from Example 1 is that the diameter of the second solder joint in step S9 is 0.2 mm.

[0058] Comparative Example 8: The difference from Example 1 is that the diameter of the second solder joint in step S9 is 0.6 mm.

[0059] The products obtained from the above-described examples and comparative examples were tested:

[0060] A. Tensile test: A tensile testing machine was used, with the tensile speed set to 10 mm / min, to perform a tensile test on a single stud.

[0061] B. Deformation detection: Hold the mirrored stainless steel plate under the long fluorescent tube with the mirror facing upwards, and swing the mirrored stainless steel plate. Observe with the naked eye whether there is any deformation in the reflection of the tube in the mirror, and pay special attention to the location of the weld points.

[0062] C. Bolt wobbling test: Manually shake the stud to determine if it wobbles.

[0063] The test results and evaluation are shown in Table 1 below:

[0064] Table 1. Comparison of welding results under different methods

[0065]

[0066] As can be seen from Table 1, see Figure 5 As can be seen from the comparison results of Examples 1-3 and Comparative Example 1, although the tensile strength requirement can be met without the addition of foil, the mirror surface is severely deformed. The present invention utilizes stainless steel foils that are centered and combined to protrude and reduce the rigidity of the parts. After the protrusions are laser-welded to the mirror stainless steel sheet, the welding causes sufficient deformation of the stainless steel foil. Using a spiral spot welding method, the total heat input is kept at a low level while ensuring the welding strength. Combined with welding in a symmetrical group sequence, the problem of mirror surface deformation caused by tensile stress generated by the weld or weld point when welding parts to the back of the mirror stainless steel sheet can be solved, while also taking into account the welding strength.

[0067] The comparison results of Examples 1-3 with Comparative Examples 2 and 3 show that if the stainless steel foil is too thin, its stiffness is too low, and the parts to be welded will shake as a whole. If the stainless steel foil is too thick, its stiffness is too high, and it is not easy to deform, thus causing mirror deformation. Therefore, the thickness of the stainless steel foil should be 6%-14% of the thickness of the mirror stainless steel sheet.

[0068] As can be seen from the comparison results of Examples 1-3 with Comparative Examples 4 and 5, if the spacing between weld points is too small, the adjacent weld points will be too close, which will easily cause a large superposition of tensile stress on the mirror stainless steel sheet between the weld points, increasing the mirror deformation. If the spacing between weld points is too large, the adjacent weld points will be too far apart, resulting in a relatively reduced number of weld points and a decrease in the connection strength of the parts to be welded. Therefore, the spacing between adjacent weld points is preferably greater than 1 times the thickness of the mirror stainless steel sheet and less than 2 times the thickness of the mirror stainless steel sheet.

[0069] The comparison results of Examples 1-3 with Comparative Examples 6 and 7 show that excessive heat input increases tensile stress and further causes deformation, while insufficient heat input leads to insufficient penetration and reduces weld strength. Therefore, the preferred power of the single-mode pulsed laser is 100-300W, and the power percentage during laser spiral spot welding is 17-26%.

[0070] As can be seen from the comparison results of Examples 1-3 with Comparative Examples 8 and 9, a small weld joint diameter leads to a decrease in welding strength. To avoid a large weld joint diameter, the total heat input is too large, which leads to an increase in tensile stress on the mirror stainless steel sheet and an increase in mirror deformation. Therefore, the weld joint diameter is preferably 1.5-2.5 times the thickness of the stainless steel foil.

[0071] By further optimizing the weld point spacing, weld point diameter, and welding heat input, while maintaining the weld point strength, the tensile stress on the mirror-finish stainless steel sheet caused by laser welding can be reduced by utilizing the extremely low heat input along the scanning path, thereby further optimizing the mirror flatness and making the welding strength far exceed the design requirements.

[0072] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "axial," "radial," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" or "several" means two or more, unless otherwise explicitly specified.

[0073] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser welding method for parts on the back of mirror-finish stainless steel sheet, characterized in that, The methods include: The parts to be welded are combined with stainless steel foil with their centers aligned, the stainless steel foil including a protrusion that protrudes outward along the contour of the surface to be welded of the parts to be welded; Multiple weld points, formed by welding the protrusion around the circumference of the part to be welded in a symmetrical group sequence, are welded onto the back of a mirror-finished stainless steel sheet using laser spiral spot welding. The thickness of the stainless steel foil is 6%-14% of the thickness of the mirror-finished stainless steel sheet. The parts to be welded and the stainless steel foil are combined by welding, and the welding strength between the parts to be welded and the stainless steel foil is greater than the design requirement for the welding strength between the parts to be welded and the mirror stainless steel sheet. During laser spiral spot welding, the spacing between adjacent weld points is greater than 1 times the thickness of the mirror-finished stainless steel sheet and less than 2 times the thickness of the mirror-finished stainless steel sheet. The diameter of the weld point is 1.5-2.5 times the thickness of the stainless steel foil. A single-mode pulsed laser is used for laser spiral spot welding. The power of the single-mode pulsed laser is 100-300W. The power percentage during laser spiral spot welding is 17-26%, the duty cycle is 47-62%, the frequency is 120-160KHz, the pulse width is 300-500ns, and the welding speed is 170-210mm / s.

2. The laser welding method for the back part of a mirror-finish stainless steel sheet according to claim 1, characterized in that, The stainless steel foil sheet is flat after welding the parts to be welded and the stainless steel foil sheet.

3. The laser welding method for the back part of a mirror-finish stainless steel sheet according to claim 2, characterized in that, Laser spiral spot welding is used to weld multiple weld points formed by welding around the circumference of the parts to be welded in a symmetrical grouping sequence onto a stainless steel foil.

4. The laser welding method for the back part of a mirror-finish stainless steel sheet according to claim 1, characterized in that, The stainless steel foil is shaped to be 1.5-2 times larger than the shape of the surface to be welded of the part to be welded.

5. The laser welding method for the back part of a mirror-finish stainless steel sheet according to claim 1, characterized in that, During laser spiral spot welding, multiple weld points are evenly spaced around the circumference of the part to be welded.

6. The laser welding method for the back part of a mirror-finish stainless steel sheet according to any one of claims 1 to 5, characterized in that, During the laser spiral spot welding, after the stainless steel foil sheet is brought into close contact with the back of the mirror stainless steel sheet using a tooling, laser spot welding is performed using a single-mode pulse laser and a galvanometer welding head in a spiral scanning manner.

7. The laser welding method for the back part of a mirror-finish stainless steel sheet according to claim 1, characterized in that, During laser spiral spot welding, the outer diameter of the spiral is 0.25-0.38 mm, and the spiral spacing is 0.08-0.13 mm.

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