Flash welding joint evaluation method

Abstract

The invention relates to the field of metal material processing, in particular to a flash welding joint evaluation method, which comprises the following steps of: intercepting a welding joint sample: if cracks, incomplete fusion or large inclusion defects occur in a welding seam, directly judging that the welding seam is a defective product joint; for a welding joint section without obvious welding defects, measuring the outer surface width k1 of the welding seam section, the width k2 of the narrowest part of the middle part of the welding seam and the width k3 of the inner surface of the welding seam; the ratio of k1 to k3 is calculated, if the ratio is in the range of 0.9-1.1, it is judged that the connector is a qualified connector, and otherwise, it is judged that the connector is an unqualified connector; and selecting k1 or k3 according to the subsequent deformation direction of the joint, comparing the k1 or k3 with k2, and if k1 / k2 is greater than or equal to 1.4 or k3 / k2 is greater than or equal to 1.4, judging that the joint is a qualified joint. The method has the advantages that the quality of the flash welding joint can be quickly and accurately judged, and particularly for the joint without obvious welding defects, the symmetry and the deformation capability of the joint are quantitatively evaluated through the size proportion; potential risks are recognized in advance through the size proportion, and the joint is prevented from cracking in the chambering and bending processes.

Description

Technical Field

[0001] This invention relates to the field of metal material processing, and in particular to a method for evaluating flash welded joints. Background Technology

[0002] Flash welding is a quick and convenient welding method widely used in welding medium and heavy plates, such as automobile rims and train rails. Flash welding is a solid-state welding process. The welding process involves placing two welding surfaces opposite each other, applying electricity, and generating heat to melt the welding surfaces. Then, a clamping force is applied perpendicular to the end faces, causing the two molten ends to close together. During this closing process, the molten metal, overheated structures, and oxide inclusions in the welding surface area are squeezed out, while the unmelted metal adheres tightly together to form a weld joint. The performance of the flash weld joint is significantly affected by the heating energy and clamping force. In practical applications, some weld joints exhibit cracking along the weld seam during deformations such as hole expansion and bending. Metallographic analysis of the joint reveals no obvious defects such as inclusions, incomplete fusion, or cracks in the joint structure, making accurate assessment of the quality of flash weld joints a pain point in the industry.

[0003] In the prior art, patent CN116117292A discloses "a pulse flash welding method for straight seams of duplex steel wheel rims," ​​mainly addressing the technical problems of difficult processing and poor welding quality in existing high-strength duplex steel wheel rim straight seam welding. Patent CN112621107A discloses "a flash welding method for straight seams of high-strength steel wheel rims," ​​mainly addressing the technical problems of difficult processing, poor welding quality, and high welding cost in existing high-strength steel wheel rim straight seam welding. These patents propose specific solutions for the flash welding process of wheel steel, solving the problem of insufficient performance of flash welded joints of wheel steel through welding process and seam gap control. Summary of the Invention

[0004] The purpose of this invention is to provide a method for evaluating flash welded joints, which solves the difficulty in evaluating the performance of joints after flash welding of steel plates, especially the problem of weld cracking during the hole expansion deformation process when there are no obvious welding defects in the welded joint.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for evaluating flash welded joints, comprising:

[0007] Two identical steel plates are welded together using a flash welding process to form a welded joint. A sample of the welded joint is taken and then ground, polished, and etched to observe weld defects. If cracks, lack of fusion, or large inclusions appear in the weld, it is directly judged as a defective joint.

[0008] For welded joint sections without obvious welding defects, measure the dimensions of the outer surface width k1, the narrowest point width k2 in the middle of the weld, and the inner surface width k3 of the weld.

[0009] Calculate the ratio of the outer surface width k1 of the weld section to the inner surface width k3 of the weld. If the ratio of the outer surface width k1 of the weld section to the inner surface width k3 of the weld section is in the range of 0.9 to 1.1, it is judged as a qualified joint; otherwise, it is an unqualified joint.

[0010] Select the outer surface width k1 or inner surface width k3 of the weld section according to the direction of subsequent deformation of the joint, and compare it with the width k2 at the narrowest point in the middle of the weld. If the ratio of outer surface width k1 / narrowest point width k2 in the middle of the weld is greater than or equal to 1.4, or the ratio of inner surface width k3 / narrowest point width k2 in the middle of the weld is greater than or equal to 1.4, then it is judged as a qualified joint; otherwise, it is an unqualified joint.

[0011] The ratio of the outer surface width k1 of the weld cross-section to the inner surface width k3 of the weld is used to determine the symmetry of the weld. If the ratio of the outer surface width k1 of the weld cross-section to the inner surface width k3 of the weld exceeds the range of 0.9 to 1.1, it is determined that there is misalignment in the joint or one-sided extrusion of the upsetting metal.

[0012] The ratio of the outer surface width k1 of the weld cross-section to the width k2 at the narrowest point in the middle of the weld, or the inner surface width k3 to the width k2 at the narrowest point in the middle of the weld, is used to determine the weld's deformation capacity. If the ratio of the outer surface width k1 to the width k2 at the narrowest point in the middle of the weld, or the inner surface width k3 to the width k2 at the narrowest point in the middle of the weld, is less than 1.4, it is determined that the upsetting force is too large or the heat input is too high, resulting in insufficient joint deformation capacity.

[0013] Weld defects were observed using a metallographic microscope or an electron microscope.

[0014] The measurement of the outer surface width k1, the width k2 at the narrowest point in the middle of the weld, and the inner surface width k3 of the weld cross-section are obtained using measuring tools.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] 1. By measuring the outer surface width k1, the narrowest point width k2 in the middle of the weld, and the inner surface width k3 of the weld cross-section, and analyzing the relationship between these dimensions, the quality of flash welded joints can be quickly and accurately judged. In particular, for joints without obvious welding defects, their symmetry and deformation capacity can be quantitatively evaluated through dimensional ratios, filling a technological gap in the industry.

[0017] 2. When k1 / k3 exceeds the range of 0.9 to 1.1, it can be determined that there is misalignment or one-sided extrusion of the upsetting metal in the joint. This directly indicates that the centering accuracy or upsetting force distribution needs to be adjusted. When k1 / k2 or k3 / k2 < 1.4, it indicates that the upsetting force is too large or the heat input is too high. Welding energy or upsetting parameters need to be optimized to avoid insufficient joint deformation capacity. The process optimization is highly instructive and can improve the overall performance and reliability of the welded joint.

[0018] 3. Traditional welded joint evaluation methods usually require complex testing methods and a long time. However, the method of this invention is simple and quick. It only requires measuring the outer surface width k1 of the weld cross section, the width k2 at the narrowest point of the weld middle section, and the inner surface width k3 of the weld and performing simple proportional calculations to complete the evaluation of the joint quality. This greatly shortens the testing time, improves production efficiency, and is particularly suitable for large-scale production environments.

[0019] 4. Identify potential risks (such as asymmetrical welds or columnar welds) in advance by using size ratios to prevent joints from cracking during deformation processes such as hole expansion and bending, thereby reducing scrap rates and preventing subsequent processing failures.

[0020] 5. The method of the present invention is applicable to the evaluation of various medium and heavy plate welded joints, including but not limited to automobile wheel rims, train rails, etc. No matter how the material and application scenario of the welded joint change, as long as the dimensions are measured and analyzed according to the method of the present invention, its quality can be effectively evaluated, and it has wide applicability.

[0021] 6. Only conventional metallographic sample preparation and dimensional measurement tools (such as microscopes) are required. No complicated equipment is needed. It is easy to implement on the production site, and the operation is simple and low-cost. Attached Figure Description

[0022] Figure 1 This is a diagram showing the location of various dimensions of the weld cross-section. Detailed Implementation

[0023] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0024] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0025] Example

[0026] See Figure 1 A method for evaluating flash welded joints, specifically including:

[0027] S1. Weld two identical steel plates using the flash welding process to form a welded joint. Take a cross-sectional sample of the welded joint, grind, polish it, and after corrosion, observe the weld defects. If welding defects such as cracks, lack of fusion, and large inclusions appear in the weld, it is directly evaluated as a defective joint. When cracks, lack of fusion defects, large inclusions, etc. appear in the joint, after the joint is stressed, the defect will become a crack source, causing the joint to break.

[0028] S2. Further analyze the cross-section of the welded joint without obvious welding defects, measure the outer surface width k1 of the weld cross-section, the width k2 at the middle of the weld (the narrowest part of the weld), and the inner surface width k3 of the weld. The distance k2 at the narrowest part of the weld is shown in Figure 1 .

[0029] S3. Compare the sizes of k1 and k3. If k1 / k3 = 0.9 - 1.1, it is judged as a qualified joint; otherwise, it is an unqualified joint. For the flash welding of the same steel plates, misalignment during the flash welding process or the extrusion of molten metal to one side during upsetting will cause the weld to be asymmetric and the joint performance to be unstable. Through data comparison and analysis, controlling k1 / k3 within the range of 0.9 - 1.1 can eliminate the deviation in the manufacturing process of flash welded joints.

[0030] S4. Compare the weld size on the side with larger subsequent deformation of the flash welded joint (select k1 for outward bending and k3 for inward bending) with the size k2 at the narrowest part of the weld. When k1 / k2 ≥ 1.4 or k3 / k2 ≥ 1.4, it is judged as a qualified joint; otherwise, it is an unqualified joint. During the flash welding process of the steel plate, the joint metal is heated to the molten state and then upset. The molten metal is extruded from the upper and lower surfaces of the steel plate, causing the heat of the upper and lower surfaces to increase and the cooling rate to be less than that of the core. On the weld cross-section, it shows that the widths of the upper and lower surfaces are greater than that of the core. When k1 / k2 < 1.4 or k3 / k2 < 1.4 in the weld, there are two situations:

[0031] First, when the upsetting force is too large and too much of the heated weld metal is extruded, the weld presents a columnar or linear shape. At this time, k1 / k2 < 1.4 or k3 / k2 < 1.4 in the weld.

[0032] Second, when the flash time of the welded joint is long and the welding heat input is too large, the joint will overheat. In the case of insufficient upsetting ability, the size of the joint also shows the situation of k1 / k2 < 1.4 or k3 / k2 < 1.4. In this case, the weld has poor deformation ability and is extremely likely to have the risk of weld cracking during subsequent processing.

[0033] The present invention evaluates the flash welded joint conveniently and quickly by analyzing the relationship between the various dimensions of the wheel joint, as shown in Table 1.

[0034] Table 1 shows the dimensions of the weld joints in the examples and comparative examples.

[0035]

[0036] Table 1 lists examples and comparative effects of flash welding of materials with different thicknesses. In the case of defect-free welded joints, when both k1 / k2 and k3 / k2 are greater than 1.4, no cracking occurs in the hole-expanding process. However, in the comparative examples, when both k1 / k2 and k3 / k2 are less than 1.4, weld cracking occurs in the hole-expanding process. This indicates that in the absence of welding defects, the welding process has a significant impact on the hole-expanding performance of the welded joint. This invention can accurately determine the risk of hole-expanding cracking in defect-free welded joints, providing a basis for adjusting welding processes and judging hole-expanding cracking in industrial production.

[0037] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Particularly for defect-free welded joints, the key points described in this invention can help determine the risk of weld cracking during subsequent processing and provide reference indicators for process adjustments. The embodiments of this invention are highly effective and have significant practical value.

[0038] This application analyzes the relationships between the outer surface width k1, the narrowest point width k2, and the inner surface width k3 of the weld cross-section by measuring these dimensions. This allows for rapid and accurate assessment of the quality of flash welded joints, particularly for joints without obvious welding defects. The dimensional ratios are used to quantitatively evaluate the symmetry and deformability, filling a technological gap in the industry. When k1 / k3 exceeds the range of 0.9–1.1, it indicates misalignment or one-sided extrusion of the upsetting metal, directly suggesting adjustments to the alignment accuracy or upsetting force distribution. When k1 / k2 or k3 / k2 < 1.4, it indicates excessive upsetting force or heat input, requiring optimization of welding energy or upsetting parameters to avoid insufficient joint deformability. This process optimization provides strong guidance for adjustments and improves welding quality. The method of this invention improves the overall performance and reliability of welded joints. Traditional methods for evaluating welded joints typically require complex testing techniques and lengthy time. In contrast, the method of this invention is simple and quick. It only requires measuring the outer surface width k1, the narrowest point width k2, and the inner surface width k3 of the weld cross-section, and performing simple proportional calculations to evaluate the joint quality. This significantly shortens testing time, improves production efficiency, and is particularly suitable for large-scale production environments. Potential risks (such as asymmetric or columnar welds) can be identified in advance through dimensional proportions, preventing cracking during deformation processes such as hole expansion and bending, reducing scrap rates, and preventing subsequent processing failures. This method is applicable to the evaluation of various medium-thick plate welded joints, including but not limited to automobile wheel rims and railway rails. Regardless of the material and application of the welded joint, as long as the dimensional measurement and analysis are performed according to the method of this invention, its quality can be effectively evaluated, demonstrating broad applicability. Only conventional metallographic sample preparation and dimensional measurement tools (such as microscopes) are required; no complex equipment is needed, making it easy to implement on-site, simple to operate, and low in cost.

Claims

1. A method for evaluating flash welded joints, characterized in that, include: Two identical steel plates are welded together using a flash welding process to form a welded joint. A sample of the welded joint is taken and then ground, polished, and etched to observe weld defects. If cracks, lack of fusion, or large inclusions appear in the weld, it is directly judged as a defective joint. For welded joint sections without obvious welding defects, measure the dimensions of the outer surface width k1, the narrowest point width k2 in the middle of the weld, and the inner surface width k3 of the weld. Calculate the ratio of the outer surface width k1 of the weld section to the inner surface width k3 of the weld. If the ratio of the outer surface width k1 of the weld section to the inner surface width k3 of the weld section is in the range of 0.9 to 1.1, it is judged as a qualified joint; otherwise, it is an unqualified joint. Select the outer surface width k1 or inner surface width k3 of the weld section according to the direction of subsequent deformation of the joint, and compare it with the width k2 at the narrowest point in the middle of the weld. If the ratio of outer surface width k1 / narrowest point width k2 in the middle of the weld is greater than or equal to 1.4, or the ratio of inner surface width k3 / narrowest point width k2 in the middle of the weld is greater than or equal to 1.4, then it is judged as a qualified joint; otherwise, it is an unqualified joint.

2. The method for evaluating flash welded joints according to claim 1, characterized in that, The ratio range of the outer surface width k1 of the weld cross section to the inner surface width k3 of the weld is used to determine the symmetry of the weld. If the ratio of the outer surface width k1 of the weld cross section to the inner surface width k3 of the weld exceeds the range of 0.9 to 1.1, it is determined that the joint has misalignment or one-sided extrusion of upsetting metal.

3. The method for evaluating flash welded joints according to claim 1, characterized in that, The ratio of the outer surface width k1 of the weld cross-section to the width k2 at the narrowest point in the middle of the weld, or the inner surface width k3 to the width k2 at the narrowest point in the middle of the weld, is used to determine the weld's deformation capacity. If the ratio of the outer surface width k1 to the width k2 at the narrowest point in the middle of the weld, or the inner surface width k3 to the width k2 at the narrowest point in the middle of the weld, is less than 1.4, it is determined that the upsetting force is too large or the heat input is too high, resulting in insufficient joint deformation capacity.

4. The method for evaluating flash welded joints according to claim 1, characterized in that, The weld defects were observed using a metallographic microscope or an electron microscope.

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