A mold for metal projection welding, a metal projection welding apparatus, and a projection structure for metal projection welding

Abstract

This invention discloses a mold, a metal projection welding device, and a projection structure for metal projection welding. The mold includes a punch and a die that cooperate with each other. The punch includes a first working surface and a protrusion protruding from the first working surface toward the die. The width of the protrusion gradually decreases from the first working surface toward the die. The die includes a second working surface and a recessed groove from the second working surface toward the side away from the protrusion. The groove includes a bottom groove at the bottom and a closing structure on both sides of the bottom groove. The closing structure includes a first curved surface, a second curved surface, and a first inclined surface. The first curved surface, the second curved surface, and the first inclined surface are arranged sequentially from the bottom groove to the second working surface. The bottom groove, the first curved surface, and the second curved surface are all arc-shaped surfaces. The openings of the bottom groove and the second curved surface face the protrusion, and the opening of the first curved surface faces the side away from the protrusion.

Description

Technical Field

[0001] This invention belongs to the field of metal projection welding technology, specifically relating to a mold suitable for metal projection welding, a metal projection welding device including the mold, and a projection structure formed after projection welding a metal plate using the mold or the metal projection welding device. Background Technology

[0002] The existing metal projection welding process has the following main technical problems: the head size of the projection welding mold is small, resulting in high stress and limited mold life; for materials with low ductility such as magnesium alloys, traditional processes are prone to material cracking when forming the projection; the existing projection structure results in a large melting contact area at the head during welding, which places very stringent requirements on the precise control of the melting effect and the stability of the welding current.

[0003] Existing patent CN105829009A discloses a protruding portion of a metal plate for projection welding, comprising a first convex segment with a first radius and a second convex segment with a second radius. However, the opening directions of the first and second convex segments are the same, and the radii and curvatures of the first and second convex segments are excessively large. In this patent, the effective height of the projection weld is entirely determined by the mold and cannot be controlled by the mold's stroke. Furthermore, this patent does not reduce the tensile stress exerted on the material by the mold during projection welding, which can easily lead to material cracking, especially with materials of low elongation.

[0004] The above background information is disclosed only to assist in understanding the inventive concept and technical solution of this invention, and does not necessarily belong to the prior art of this invention. In the absence of clear evidence that the above information was disclosed before the filing date of this invention, the above background information should not be used to evaluate the novelty and inventiveness of this invention. Summary of the Invention

[0005] In view of this, in order to overcome the shortcomings of the prior art, the object of the present invention is to provide an improved mold suitable for metal projection welding, which can effectively avoid cracking during projection welding of low elongation materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A mold suitable for metal projection welding, the mold comprising a mating punch and a die, the punch including a first working surface and a protrusion protruding from the first working surface toward the die, the width of the protrusion gradually decreasing from the first working surface toward the die; the die including a second working surface and a recessed groove from the second working surface toward the side away from the protrusion, the groove including a bottom groove at the bottom and converging structures on both sides of the bottom groove, the converging structures including a first curved surface, a second curved surface and a first inclined surface, the first curved surface, the second curved surface and the first inclined surface being arranged sequentially from the bottom groove to the second working surface, the bottom groove, the first curved surface and the second curved surface being arc-shaped surfaces, the openings of the bottom groove and the second curved surface facing the protrusion, and the opening of the first curved surface facing the side away from the protrusion.

[0007] In this invention, the first curved surface, the second curved surface, and the first inclined surface form a convergent structure. This convergent structure guides and constrains the material flow during the convex hull forming process, prevents stress concentration, effectively avoids cracking of low-ductility materials (such as magnesium alloys) during forming, and ensures the geometric integrity of the forming point before welding.

[0008] The preferred protrusion is trapezoidal. This trapezoidal protrusion can maximize the structural strength of the punch head and extend the mold life. Furthermore, its arc-shaped trapezoidal edge design matches the concave mold's closing structure (first curved surface, second curved surface, and first inclined surface), making it easier to squeeze into the corresponding concave mold structure in subsequent molding and achieve precise molding.

[0009] According to some preferred embodiments of the present invention, the radius of the second surface is smaller than the radius of the first surface, the radius of the first surface is 0.1~0.5mm, the radius of the second surface is 0.05-0.5mm, and preferably the radius of the second surface is 0.05-0.3mm.

[0010] According to some preferred embodiments of the invention, the radius of the bottom groove is greater than the radius of the first curved surface, and the radius of the bottom groove is 0.2-0.5 mm; the width of the bottom groove is 0.2-0.7 times the width of the groove, preferably 0.1-0.35 times the width of the groove; the width of the groove is 1-3 mm, preferably 1.5-2 mm. The main melting width area of ​​the metal plate is determined by the bottom groove.

[0011] According to some preferred embodiments of the present invention, the first inclined surface is a plane, and the angle between the first inclined surface and the second working surface is 40°-80°. Preferably, the angle between the first inclined surface and the second working surface is 55°-65°, more preferably 60°.

[0012] According to some preferred embodiments of the present invention, the closing structure includes a second inclined surface and a third curved surface sequentially disposed between the second curved surface and the first inclined surface, wherein the third curved surface is an arc-shaped surface and the opening of the third curved surface faces away from the protrusion. That is, in some embodiments of the present invention, in order to better form the closing structure and improve the closing effect, a second inclined surface and a third curved surface are added between the second curved surface and the first inclined surface, so that the second curved surface is further closed (recessed towards the interior of the die).

[0013] Preferably, the radius of the second curved surface is smaller than the radii of the first and third curved surfaces. The radius of the first curved surface is 0.1~0.5mm, the radius of the third curved surface is 0.1~0.5mm, the radius of the fourth curved surface is 0.1~0.5mm, and the radius of the second curved surface is 0.05-0.5mm, preferably 0.05-0.3mm. For the second curved surface, a smaller radius results in a better closing effect, but an excessively small radius leads to greater mold stress and reduced lifespan. Therefore, the present invention preferably uses a radius of 0.05-0.3mm for the second curved surface. Furthermore, the addition of a third curved surface and a second inclined surface can reduce the chamfer or curvature of the second curved surface, thereby improving the closing effect.

[0014] According to some preferred embodiments of the present invention, the second inclined plane is a plane, and the angle between the second inclined plane and the second working surface is greater than the angle between the first inclined plane and the second working surface, further increasing the convergence feature and further changing the original material stretching tendency to the material extrusion tendency, thereby reducing the principal tensile stress.

[0015] According to some preferred embodiments of the invention, the angle between the second inclined plane and the second working surface is 55°-85°. Preferably, the angle between the second inclined plane and the second working surface is 75°~85°, more preferably 78°~80°.

[0016] According to some preferred embodiments of the present invention, a fourth curved surface is provided between the first inclined surface and the second working surface, the fourth curved surface being an arc-shaped surface with its opening facing away from the protrusion.

[0017] According to some preferred embodiments of the present invention, the protrusion includes a bottom surface, a fifth curved surface and a third inclined surface located on both sides of the bottom surface, the bottom surface, the fifth curved surface and the third inclined surface being arranged sequentially, the bottom surface being a plane, the fifth curved surface being an arc-shaped surface, and the opening facing the protrusion.

[0018] According to some preferred embodiments of the invention, the width of the bottom surface is 0.5-1.5 times the width of the bottom groove. Preferably, the width of the bottom surface is 0.6-1.2 times the width of the bottom groove, and more preferably, the width of the bottom surface is equal to the width of the bottom groove.

[0019] According to some preferred embodiments of the present invention, the third inclined plane is a plane, and the angle between it and the first working surface is 40°-85°, preferably 45°-80°, more preferably 70°-80°; the angle between two corresponding third inclined planes is 25°-90°, preferably 25°-35°, more preferably 30°.

[0020] According to some preferred embodiments of the present invention, a sixth curved surface is provided between the third inclined surface and the first working surface, the sixth curved surface being an arc surface with its opening facing the second working surface.

[0021] According to some preferred embodiments of the invention, the mold is used to form a bump on the metal plate, the bump having a length of 3-10 mm; the metal plate is iron, or an alloy material containing one or more of iron, magnesium, and aluminum; the mold is particularly suitable for projection welding of low elongation materials with an elongation of 5% to 12%.

[0022] The present invention also provides a metal projection welding apparatus including a mold suitable for metal projection welding as described above.

[0023] Preferably, the metal projection welding equipment includes a frame, a drive mechanism mounted on the frame, a punch assembly, and a die assembly. The punch assembly is located above the die assembly, and the drive mechanism drives the punch assembly to move closer to or away from the die assembly. The drive mechanism is a servo pressure driver. The die assembly includes the aforementioned die, and the punch assembly includes the aforementioned punch, a pressure block, a connecting sleeve, a clamping sleeve, and an elastic element. The pressure block and the connecting sleeve are fitted over the punch, the connecting sleeve is connected to the pressure block, and the clamping sleeve is disposed between the punch and the connecting sleeve. Vertically, the elastic element is disposed between the top of the clamping sleeve and the bottom of the pressure block; horizontally, the elastic element is disposed between the punch and the connecting sleeve. The bottom of the clamping sleeve has an opening for the punch to pass through. Initially, the bottom of the clamping sleeve is lower than the bottom of the punch. During projection welding, as the punch moves toward the die, the clamping sleeve first contacts the metal plate and compresses the elastic element. The punch then extends through the opening to contact the metal plate, and with the cooperation of the die, performs projection welding on the metal plate, forming a protrusion on the metal plate. The clamping sleeve, under the elastic restoring force of the elastic element, keeps the metal plate pressed tightly to prevent it from warping upwards, ensuring that the metal plate remains flat except for the projection welding area after projection welding.

[0024] This invention also provides a projection structure formed after projection welding a metal plate using the aforementioned mold or equipment suitable for metal projection welding. Specifically, corresponding to the structure of the die in the mold, the projection structure includes: Miniaturized melting head: The top of the convex humb has a protruding melting area with a radius of 0.2-0.5mm corresponding to the bottom groove. This area has a predetermined miniaturized contact radius. Compared with traditional convex humbs, this miniaturized contact radius significantly reduces the melting contact area during welding, thereby precisely controlling the formation of the weld nugget and reducing the welding current requirement. The miniaturized melting head is formed by the bottom groove of the die.

[0025] Double-sided closing sections: Symmetrical closing sections formed by corresponding die closing structures are provided on both sides of the forming body of the convex bulge. The die closing structures, together with the bottom groove, guide and constrain material flow during the convex bulge forming process of the metal sheet, preventing stress concentration and effectively avoiding cracking of low-ductility materials (such as magnesium alloys) during forming, ensuring the geometric integrity of the forming points before welding. The double-sided closing sections are formed by the die closing structures (including at least the first curved surface, the second curved surface, and the first inclined surface on both sides of the bottom groove).

[0026] In this invention, the mold with the above structure significantly alters the stress distribution within the metal plate during forming by optimizing the geometry of the mold cavity. The core mechanism is as follows: Stress state control: The cavity surface of the mold of the present invention adopts a streamlined design that is adapted to the plastic deformation of the metal plate. During the molding process, the force exerted by the mold on the metal plate is more evenly transmitted to all areas of the metal plate, so that most areas of the metal plate are under the stress state dominated by compressive stress, and only a small amount of tensile stress exists in local small deformation areas.

[0027] High tensile stress suppression: Compared with traditional molds, the mold of this invention effectively reduces the range of tensile stress inside the metal sheet and lowers the peak value of tensile stress. During the forming process, the plastic deformation of the metal sheet is mainly driven by compressive stress, avoiding the risk of material damage, cracking, and fracture caused by local tensile stress concentration, thus ensuring the stability and reliability of metal sheet forming from the source of stress.

[0028] Stress distribution uniformity: The mold cavity transition area of ​​the present invention has no sharp edges, which reduces stress concentration points and makes the stress distribution inside the metal plate more uniform, further improving the molding quality.

[0029] Due to the adoption of the above technical solutions, the advantages of this invention compared to the prior art are as follows: In the die of this invention, which is applicable to metal projection welding, the concave die has a guiding and constraining effect on the plastic flow of the material during the metal plate projection forming process by setting a gathering structure on both sides of the bottom groove, thus dispersing the stress peak in the deformation zone; for low ductility materials such as magnesium alloys and high-strength steel, it effectively suppresses the cracking problem caused by the material flow transition of low ductility materials, significantly broadening the material applicability range of projection welding process; in the punch, the punch with a trapezoidal reinforced structure significantly increases the cross-sectional area and rigidity of the die head, effectively dispersing the impact load and thermal stress during the stamping process, and significantly improving the wear resistance and deformation resistance of the punch. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic cross-sectional view of the mold suitable for metal projection welding in Embodiment 1 of the present invention; Figure 2 This is a schematic cross-sectional view of the mold suitable for metal projection welding in Embodiment 2 of the present invention; Figure 3 This is a three-dimensional structural diagram of the metal projection welding equipment in an embodiment of the present invention; Figure 4 This is a partial cross-sectional structural diagram of the metal projection welding equipment in an embodiment of the present invention; Figure 5 This is a three-dimensional structural diagram of the bulge formed after projection welding of a metal plate in an embodiment of the present invention; Figure 6 This is a simulation diagram of the projection welding process using the mold in Example 2; Figure 7 This is a simulation diagram of the projection welding of the mold in Comparative Example 1; Figure 8 This is a simulation diagram of the projection welding process using the mold in Comparative Example 2; Figure 9 This is a simulation diagram of the projection welding process using the mold in Comparative Example 3; In the attached diagram, the metal projection welding equipment is 1, the frame is 11, the drive mechanism is 12, the punch assembly is 13, the die assembly is 14, the punch is 21, the first working surface is 211, the protrusion is 212, the die is 22, the second working surface is 221, the groove is 222, the pressure block is 31, the connecting sleeve is 32, the clamping sleeve is 33, the elastic element is 34, the bottom groove is 41, the first curved surface is 42, the second curved surface is 43, the first inclined surface is 44, the second inclined surface is 45, the third curved surface is 46, the fourth curved surface is 47, the bottom surface is 51, the fifth curved surface is 52, the third inclined surface is 53, the sixth curved surface is 54, the metal plate is 6, and the protrusion is 61. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] In the existing technology, the metal projection welding process mainly has the following technical problems: the head size of the projection welding mold is small (the bottom is completely arc-shaped), resulting in high stress and limited mold life; in the early stage of metal plate 6 forming, due to the lack of an effective clamping mechanism, metal plate 6 is prone to local arching and deformation under welding pressure, affecting the forming positioning accuracy and consistency; for low ductility materials such as magnesium alloys, traditional processes are very prone to material cracking when forming the projection 61; the existing projection 61 structure results in a large melting contact area at the head during welding, which places very stringent requirements on the precise control of the melting effect and the stability of the welding current, increasing the technical difficulty and cost.

[0034] Based on the above problems, the purpose of this invention is to provide an improved mold suitable for metal projection welding, a metal projection welding device 1 including the mold, and a projection bulge 61 structure formed after projection welding of a metal plate 6 using the mold or the metal projection welding device 1, which aims to improve the technical problems of mold life, metal plate 6 deformation, cracking of difficult-to-process materials, and head size optimization.

[0035] Specifically, the metal projection welding equipment 1 of the present invention includes a frame 11, a drive mechanism 12 disposed on the frame 11, a punch assembly 13, and a die assembly 14. The punch assembly 13 is located above the die assembly 14, and the drive mechanism 12 is used to drive the punch assembly 13 to move closer to or away from the die assembly 14. Preferably, the drive mechanism 12 is a servo pressure driver, which can realize online adjustment of the pressing stroke. With the mold structure of the present invention, it is possible to realize projection 61 structures of different heights without changing the mold, and adapt to different material combinations.

[0036] The mold is used to form a protrusion 61 on the metal plate 6 and connect two layers of metal plates 6. The overall length of the protrusion 61 is 3-10 mm, preferably 8-9 mm. The metal plate 6 is iron, or an alloy material containing one or more of iron, magnesium, and aluminum. The mold of the present invention is particularly suitable for projection welding of low elongation materials with an elongation of 5% to 12%, and can avoid breakage or cracking during the projection welding process.

[0037] The die assembly 14 includes a die 22, and the punch assembly 13 includes a punch 21, a pressure block 31, a connecting sleeve 32, a clamping sleeve 33, and an elastic element 34. The pressure block 31 and the connecting sleeve 32 are sleeved on the punch 21, the connecting sleeve 32 is connected to the pressure block 31, and the clamping sleeve 33 is disposed between the punch 21 and the connecting sleeve 32. Viewed vertically, the elastic element 34 is disposed between the top of the clamping sleeve 33 and the bottom of the pressure block 31; viewed horizontally, the elastic element 34 is disposed between the punch 21 and the connecting sleeve 32. In this embodiment, by integrating a clamping sleeve 33 driven by an elastic element 34 (spring or gas spring) on ​​the metal projection welding equipment 1, a pre-clamping force is applied before the punch 21 presses into the metal plate 6, which is equivalent to building a rigid support boundary around the projection welding area; this solves the problem of local arching deformation of the metal plate 6 caused by the lack of clamping in the traditional process, ensures the precise alignment of the punch 61 and the metal plate 6, and creates stable contact conditions for subsequent welding; and avoids abnormal warping of the metal plate 6 during the projection welding process due to lack of clamping.

[0038] The bottom of the clamping sleeve 33 has an opening for the punch 21 to pass through. Initially, the bottom of the clamping sleeve 33 is lower than the bottom of the punch 21. During projection welding, as the punch 21 moves towards the die 22, the clamping sleeve 33 first contacts the metal plate 6 and compresses the elastic element 34. Then, the punch 21 passes through the opening and contacts the metal plate 6, and with the cooperation of the die 22, performs projection welding on the metal plate 6, forming a protrusion 61 on the metal plate 6. Under the elastic restoring force of the elastic element 34, the clamping sleeve 33 always presses the metal plate 6 firmly, preventing the metal plate 6 from warping upwards and ensuring that the metal plate 6 remains flat except for the projection welding area after projection welding.

[0039] The cooperating punch 21 and die 22 constitute a mold suitable for metal projection welding. The structure of the punch 21 and die 22 is described in detail below.

[0040] The die 22 includes a second working surface 221 and a groove 222 recessed from the second working surface 221 toward the side away from the protrusion 212. The groove 222 includes a bottom groove 41 at the bottom, a gathering structure on both sides of the bottom groove 41, and a fourth curved surface 47 located between the gathering structure and the second working surface 221. The gathering structure includes a first curved surface 42, a second curved surface 43, and a first inclined surface 44. The first curved surface 42, the second curved surface 43, and the first inclined surface 44 are arranged sequentially from the bottom groove 41 to the second working surface 221. The bottom groove 41, the first curved surface 42, and the second curved surface 43 are all arc-shaped surfaces. The openings of the bottom groove 41 and the second curved surface 43 face the protrusion 212, and the opening of the first curved surface 42 faces the side away from the protrusion 212. That is, the first curved surface 42 is located between the bottom groove 41 and the second curved surface 43, and the opening direction is opposite to the opening direction of the bottom groove 41 and the second curved surface 43. The fourth curved surface 47 is located between the first inclined surface 44 and the second working surface 221. The fourth curved surface 47 is an arc-shaped surface with its opening facing away from the protrusion 212. The entire cross-section of the groove 222 forms an inverted "mountain"-shaped protrusion 61 structure. From the cross-section, the first curved surface 42 protrudes from the inner wall of the groove 222 into the groove 222, causing the second curved surface 43 to gather the material during projection welding, expanding the distribution area of ​​compressive stress, reducing the deformation area dominated by tensile stress, and effectively avoiding cracking and fracture of the material. The main melting width area of ​​the metal plate 6 is determined by the width of the bottom groove 41.

[0041] Preferably, the radius of the first curved surface is 0.1~0.5mm, and the radius of the second curved surface 43 is 0.05~0.5mm, more preferably, the radius of the second curved surface 43 is 0.05~0.3mm. The width of the bottom groove 41 is 0.2-0.7 times the width of the groove 222, preferably 0.1~0.35 times the width of the groove 222, and the radius of the bottom groove 41 is 0.2-0.5mm; the width of the groove 222 is 1-3mm, preferably 1.5-2mm. The first inclined surface 44 is a plane, and the included angle between the first inclined surface 44 and the second working surface 221 is 40°-80°, preferably 55°-65°, more preferably 60°.

[0042] The convergence structure formed by the first curved surface 42, the second curved surface 43, and the first inclined surface 44 guides and constrains the material flow during the forming process of the convex hull 61, prevents stress concentration, effectively avoids cracking of low ductility materials (such as magnesium alloys) during forming, and ensures the geometric integrity of the forming point before welding.

[0043] The bottom groove 41 is a special melting area with a miniaturized contact radius (0.2-0.5mm), significantly reducing the initial contact area between the welding head and the metal plate 6 during welding. According to Joule's law, precise control of the contact resistance concentrates heat in the micro-area, thereby reducing the critical current required to achieve a reliable weld nugget and resulting in significant energy savings. Simultaneously, because the melting area is controlled, it avoids the problems of weld nugget spatter or an excessively wide heat-affected zone caused by the excessively large contact surface of the traditional convex 61, improving the consistency of the weld joint.

[0044] In some preferred embodiments, the closing structure further includes a second inclined surface 45 and a third curved surface 46 sequentially disposed between the second curved surface 43 and the first inclined surface 44. The third curved surface 46 is an arc-shaped surface, and its opening faces away from the protrusion 212. That is, in order to better form the closing structure and improve the closing effect, a second inclined surface 45 and a third curved surface 46 are added between the second curved surface 43 and the first inclined surface 44, so that the second curved surface 43 is further closed (recessed towards the interior of the die 22). The radius of the third curved surface 46 is 0.1~0.5mm. The added third curved surface 46 and second inclined surface 45 can further reduce the chamfer or curvature of the second curved surface 43, thereby further improving the closing effect.

[0045] The second inclined plane 45 is a plane, and the angle between the second inclined plane 45 and the second working surface 221 is greater than the angle between the first inclined plane 44 and the second working surface 221. The angle between the second inclined plane 45 and the second working surface 221 is 55°-85°, preferably 75°~85°, and more preferably 78°~80°.

[0046] Based on the design of the groove 222 in the die 22, the final required head protrusion 61 can still obtain and accurately meet the width requirement of the bottom groove 41. When it is necessary to adjust the height of the boss within a certain range, it can be achieved directly by controlling the pressing depth of the drive mechanism 12.

[0047] The punch 21 includes a first working surface 211 and a protrusion 212 protruding from the first working surface 211 toward the die 22. The width of the protrusion 212 gradually decreases from the first working surface 211 toward the die 22, and the bottom of the protrusion 212 is flat. Preferably, the protrusion 212 is trapezoidal. This trapezoidal structure of the protrusion 212 can maximize the structural strength of the head of the punch 21, extend the mold life, and its arc-shaped trapezoidal edge design matches the closing structure of the die 22 (first curved surface 42, second curved surface 43, first inclined surface 44), which facilitates smoother extrusion into the corresponding die 22 structure in subsequent molding, achieving precise molding.

[0048] The protrusion 212 includes a bottom surface 51, a fifth curved surface 52 located on both sides of the bottom surface 51, a third inclined surface 53, and a sixth curved surface 54 disposed between the third inclined surface 53 and the first working surface 211. The bottom surface 51, the fifth curved surface 52, and the third inclined surface 53 are arranged sequentially. The bottom surface 51 is a plane, and the fifth curved surface 52 is an arc-shaped surface with its opening facing the protrusion 212. The radius of the fifth curved surface 52 is 0.1~0.5mm. A suitable chamfer can effectively improve the pressing effect. An excessively large chamfer is not conducive to material extrusion, while an excessively small chamfer will cause the mold to wear too quickly. The sixth curved surface 54 is an arc-shaped surface with its opening facing the second working surface 221. The width of the bottom surface 51 is 0.5-1.5 times the width of the bottom groove 41. Preferably, the width of the bottom surface 51 is 0.6~1.2 times the width of the bottom groove 41, and more preferably, the width of the bottom surface 51 is equal to the width of the bottom groove 41.

[0049] The third inclined plane 53 is a plane, and the angle between it and the first working surface 211 is 40°-85°, preferably 45°-80°, more preferably 70°-80°; correspondingly, the angle between the two third inclined planes 53 is preferably 25°-90°, preferably 25°-35°, more preferably 30°.

[0050] The projection bulge 61 structure formed on the metal plate 6 after projection welding using the aforementioned mold or metal projection welding equipment 1 suitable for metal projection welding connects the two metal plates 6. Specifically, corresponding to the structure of the die 22 in the mold, the projection bulge 61 structure includes: Miniaturized melting head: The top of the convex hull 61 is a protruding melting area with a radius of 0.2-0.5 mm, which has a predetermined miniaturized contact radius. Compared with the traditional convex hull 61, this miniaturized contact radius significantly reduces the melting contact area during welding, thereby precisely controlling the formation of the weld nugget and reducing the welding current requirement. The miniaturized melting head is formed by the corresponding bottom groove 41 of the concave mold 22.

[0051] Double-sided closing portions: Symmetrical closing portions formed by corresponding closing structures of the die 22 are provided on both sides of the forming body of the convex 61. The closing structures of the die 22, together with the bottom groove 41, guide and constrain the material flow during the forming process of the convex 61 of the metal plate 6, preventing stress concentration and effectively avoiding cracking of low-ductility materials (such as magnesium alloys) during forming, ensuring the geometric integrity of the forming points before welding. The double-sided closing portions are formed by the closing structures of the die 22 (including at least the first curved surface 42, the second curved surface 43, and the first inclined surface 44 on both sides of the bottom groove 41).

[0052] Example 1: As Figure 1As shown, based on the metal projection welding equipment 1 and mold structure described above, the groove 222 in this embodiment includes a bottom groove 41 located at the bottom, a convergence structure located on both sides of the bottom groove 41, and a fourth curved surface 47 located between the convergence structure and the second working surface 221. The convergence structure sequentially includes a first curved surface 42, a second curved surface 43, and a first inclined surface 44. The radius of the first curved surface 42 is 0.25 mm, the radius of the second curved surface 43 is 0.2 mm, and the radius of the fourth curved surface 47 is 0.2 mm. The radius of the bottom groove 41 is 0.3 mm, the width of the bottom groove 41 is 0.47 mm, the width of the groove 222 is 1.7309 mm, and the width of the bottom groove 41 is 0.272 times the width of the groove 222. The angle between the first inclined surface 44 and the second working surface 221 is 60°. The overall depth of the groove 222 (the distance between the second working surface 221 and the bottom of the bottom groove 41) is 0.7 mm.

[0053] The bump 212 includes a bottom surface 51, a fifth curved surface 52 located on both sides of the bottom surface 51, a third inclined surface 53, and a sixth curved surface 54 disposed between the third inclined surface 53 and the first working surface 211. The radius of the fifth curved surface 52 is 0.15 mm, and the radius of the sixth curved surface 54 is 0.3 mm. The width of the bottom surface 51 is 0.3698 mm, which is less than the width of the bottom groove 41. The angle between the third inclined surface 53 and the first working surface 211 is 75°, and the angle between the two third inclined surfaces 53 is 30°. The overall height of the bump 212 (the distance between the first working surface 211 and the bottom surface 51) is 1.2 mm, and the overall width (the distance between the outer sides of the two sixth curved surfaces 54) is 1.7035 mm.

[0054] In this embodiment, the metal projection welding equipment 1 is provided with a clamping sleeve 33 on the pressing side of the punch 21. The clamping sleeve 33 is driven and clamped by the elastic element 34 (spring or gas spring). Before the punch 21 contacts the metal plate 6 for forming, the clamping sleeve 33 presses the surface of the metal plate 6 first and applies a pre-tightening force around the projection welding area to effectively suppress the local arching deformation of the metal plate 6 in the early stage of projection welding.

[0055] Example 2: Figure 2 As shown, the difference between the mold structure in this embodiment and that in Embodiment 1 is that the gathering structure in this embodiment further includes a second inclined surface 45 and a third curved surface 46 sequentially disposed between the second curved surface 43 and the first inclined surface 44. The third curved surface 46 is an arc-shaped surface, and the opening of the third curved surface 46 faces the side away from the protrusion 212. The added third curved surface 46 and second inclined surface 45 can further reduce the chamfer or curvature of the second curved surface 43, thereby further improving the gathering effect.

[0056] In this embodiment, the groove 222 sequentially includes a bottom groove 41 (width 0.5589mm, radius 0.3mm), a first curved surface 42 (radius 0.25mm), a second curved surface 43 (radius 0.08mm), a second inclined surface 45, a third curved surface 46 (radius 0.2mm), a first inclined surface 44, and a fourth curved surface 47, with an overall depth of 0.75mm. After adding the third curved surface 46 and the second inclined surface 45, the radius of the second curved surface 43 needs to be reduced to increase the convergence feature and prevent the flatness of the second curved surface 43 from reducing the convergence effect.

[0057] The angle between the second inclined plane 45 and the second working surface 221 is greater than the angle between the first inclined plane 44 and the second working surface 221. In this embodiment, the angle between the second inclined plane 45 and the second working surface 221 is preferably 78°.

[0058] Comparative Example 1: Figure 7 As shown, the groove 222 in the die 22 of this comparative example only includes a bottom groove 41, a first inclined surface 44 disposed on both sides of the bottom groove 41, and a fourth curved surface 47 located between the first inclined surface 44 and the second working surface 221. The radius of the bottom groove 41 is 0.3 mm, and the angle between the first inclined surface 44 and the second working surface 221 is 45°. The remaining shapes and parameters are basically the same as those in Embodiment 2.

[0059] Comparative Example 2: Figure 8 As shown, the punch 21 in this comparative example is the same as that in Example 2, and the die adopts the corresponding shape in patent CN105829009A. Specifically, H1=0.75mm, R1=2mm, R2=0.45mm, R3=0.45mm, W1=1mm, W2=1.5mm, W3=2mm. The remaining shapes and parameters are basically the same as those in Example 2.

[0060] Comparative Example 3: Figure 9 As shown, in this comparative example, the bottom of the protrusion 212 in the punch 21 is set with an arc-shaped chamfer with a radius of 0.3944mm. The remaining shapes and parameters are basically the same as those in Example 2.

[0061] Results Verification: The projection welding process was simulated using the metal projection welding molds from the examples and comparative cases. Except for the mold shape, the projection welding process parameters remained consistent. The simulation results are as follows: Figures 6 to 9 As shown in the figure, dark blue represents compressive stress, and the other colors represent tensile stress.

[0062] 1) Figure 6The stress cloud diagram corresponding to Example 2 shows that high tensile stress (red / orange area) is significantly confined to a small local area on the upper part of metal plate 6, and the peak value is low (maximum principal stress peak value 266.11 MPa). The two sides of the bulge 61 of metal plate 6 are mainly blue / cyan (compressive stress or low tensile stress), indicating that the area is more strongly subjected to compression and tensile stress is effectively suppressed. Overall, the mold structure of Example 2 allows more areas to be dominated by compressive stress, reducing the deformation area dominated by tensile stress that can contribute to damage from the source. Specifically, the tensile stress peak values ​​of Example 2, Comparative Example 1, and Comparative Example 2 are compared as follows: In Example 2, the maximum principal stress peak was 266.11 MPa. The high tensile stress zone was concentrated locally, while the conventional sections on both sides were dominated by compressive stress / low tensile stress. The smaller and more dispersed tensile stress means less "dangerous tensile stress work" during plastic deformation, resulting in a lower probability of crack initiation. Figure 6 As shown, except for the intermittent, localized areas with low tensile stress at the second curved surface 43 and the bottom groove 41 (the tensile stress at the converging part and the bottom of the head of the convex hull 61 is about 70 MPa, cyan), the rest of the transition sections (the side of the head area, the first curved surface 42, the second inclined surface 45, the third curved surface 46, and the first inclined surface 44, dark blue) are all under compressive stress.

[0063] In Comparative Example 1, the peak value of the maximum principal stress was 395.01 MPa, and the range of high tensile stress was wider, especially in the transition areas on both sides of the mold, where the tensile stress was more concentrated, higher in value, and larger in range. Under the same pressure and material, it was easier to trigger Latham-Cockcroft damage accumulation, and the risk of fracture was significantly higher. Figure 7 As shown, the tensile stress area is concentrated in the transition area on both sides of the mold, and is continuously distributed and runs through the thickness direction of the material. The tensile stress is about 200MPa in the contact area and can reach 280-300MPa in the extended area, which poses an extremely high risk of fracture.

[0064] In Comparative Example 2, the peak value of the maximum principal stress reached 401.4 MPa, with high tensile stress concentrated at the head and the transition section of the curve. Compared to the mold in Example 2, the tensile stress in Comparative Example 2 was significantly increased and more dispersed, indicating a higher probability of "dangerous tensile stress work" and a greater risk of cracking. Figure 8 As shown, the convex hull 61 has a continuous distribution of high tensile stress extending from top to bottom. The tensile stress in the contact area is about 300 MPa, and the stress in the extended area can reach 300-340 MPa, which poses an extremely high risk of fracture.

[0065] In Example 2, almost no large-scale high tensile stress was observed, while in the conventional mold of Comparative Example 1, there was a significant concentration of tensile stress in this area. This directly demonstrates that the mold of Example 2 can effectively suppress the tensile stress in this area, thereby reducing damage. Compared with Comparative Examples 1 and 2, the groove 222 in Example 2, through the formation of a converging structure consisting of a first curved surface 42, a second curved surface 43, a second inclined surface 45, a third curved surface 46, and a first inclined surface 44, combined with the small-diameter (0.2-0.5mm) tightening structure of the bottom groove 41, guides and constrains the plastic flow of the material during the forming process of the convex 61. The tensile stress that would lead to material cracking is transformed and concentrated into a more compacting force area through structural optimization. For low-ductility materials such as magnesium alloys, this effectively suppresses cracking caused by the transition of material flow in low-ductility materials. The mold structure of Example 2 expands the compressive stress area, reduces the deformation area that can contribute to damage, reduces the local tensile stress peak, and slows down the damage accumulation rate under the same plastic strain; ultimately achieving a lower fracture risk.

[0066] 2) In Example 2, the punch 21 adopts a trapezoidal structure, whose geometry can effectively match the shape of the die 22 of the present invention to guide the material forming, significantly improving the forming effect. At the same time, since the punch 21 increases the contact area for material forming, the mold life can be improved.

[0067] according to Figure 6 and Figure 9 In both Example 2 and Comparative Example 3, the same die 22 was used, but the punch 21 was different. With the same press-in stroke, Example 2 showed superior forming results, with the key convex dimensions of the die 22 being filled precisely. For the forming of the convex 61, thanks to the effective reduction of tensile stress and the shrinking effect of the die 22, the risk of cracking was also lower, and the tensile stress area within the formed convex convex was significantly reduced. In other words, with the cooperation of the trapezoidal punch 21 in Example 2, the forming effect was even better. Figure 6 During the projection welding of the mold in Example 2, the material can be further filled to the bottom of the die 22, while Figure 9 Comparative example 3 fails to achieve good fill and height control. Meanwhile... Figure 9 As can be seen from the example, during the pressing process of the mold in Comparative Example 3, although the tensile stress area at the protrusion 61 can be effectively reduced by the die 22, there is a large tensile stress position at the fourth curved surface 47 that cooperates with the protrusion 21, with the maximum principal stress peak reaching 336.46 MPa, which poses a certain risk of cracking.

[0068] The simulation results above show that: 1. Under traditional molds, the high tensile stress distribution inside the metal plate 6 is widespread, especially in the straight sections and arc transition sections on both sides of the mold, where the peak tensile stress significantly increases, forming multiple areas of concentrated tensile stress, which easily leads to early material damage. In contrast, under the mold of this invention, the high tensile stress inside the metal plate 6 is concentrated only in localized, extremely small deformation areas. The straight sections and arc transition sections on both sides of the mold, which are traditionally prone to problems, are covered by compressive stress or low tensile stress, significantly reducing the range of tensile stress and its peak value.

[0069] 2. Traditional molds have a wide range of tensile stress distribution and high peak value. During the plastic deformation process of metal plate 6, the deformation area dominated by tensile stress accounts for a large proportion, which is prone to damage accumulation. However, the mold of the present invention expands the distribution area of ​​compressive stress and reduces the deformation area dominated by tensile stress by optimizing the structure. This greatly reduces the driving force for damage accumulation during the molding process of metal plate 6, effectively avoids molding defects such as crack initiation and material cracking, and improves the molding qualification rate and reliability of the product.

[0070] This invention addresses cracking and energy consumption issues by miniaturizing the head and optimizing the mold structure and convex hull 61 shape through double-sided convergence; it solves deformation and lifespan issues through the clamping sleeve 33 and trapezoidal punch 21; and it addresses flexible production issues through servo drive, systematically improving the yield, material applicability, and equipment compatibility of the projection welding process. Compared with existing projection welding equipment and convex hull 61 structures, this invention has the following advantages: 1. Optimize the projection welding area to improve the quality of the weld nugget.

[0071] By reducing the width and radius of the bottom groove 41 in the groove 222 of the die 22, a special melting zone with a miniaturized contact radius is formed, significantly reducing the initial melting contact area between the head and the metal plate 6 during welding. According to Joule's law, precise control of the contact resistance allows heat to be more concentrated in the micro-area, thereby reducing the critical welding current required to achieve a reliable weld nugget, resulting in significant energy savings. At the same time, because the melting zone is controlled, the problems of weld nugget spatter or an excessively wide heat-affected zone caused by the excessively large contact surface of the traditional convex 61 are avoided, improving the quality of the weld nugget and the consistency of the weld joint.

[0072] 2. Overcome the molding bottleneck of low elongation materials and eliminate the risk of cracking.

[0073] By setting converging structures on both sides of the groove 222, the plastic flow of the material is guided and constrained during the forming process of the convex 61, thus dispersing the stress peak in the deformation zone. For low-ductility materials such as magnesium alloys and high-strength steel, this effectively suppresses cracking caused by the transition of material flow in low-ductility materials, significantly broadening the material applicability range of the projection welding process.

[0074] 3. Suppress the initial deformation of metal plate 6 to ensure welding positioning accuracy.

[0075] By integrating a spring- or gas-spring-driven clamping sleeve 33 into the forming equipment, a pre-clamping force is applied before the punch 21 presses into the metal plate 6, which is equivalent to building a rigid support boundary around the projection welding area. This solves the problem of local arching deformation of the metal plate 6 caused by the lack of clamping in traditional processes, ensures the precise alignment of the protrusion 61 and the metal plate 6, and creates stable contact conditions for subsequent welding.

[0076] 4. Significantly extends the service life of molds and reduces maintenance costs.

[0077] The punch 21 adopts a trapezoidal reinforced structure, whose geometry significantly increases the cross-sectional area and rigidity of the die head, effectively dispersing the impact load and thermal stress during the stamping process, and significantly improving the wear resistance and deformation resistance of the punch 21. At the same time, the trapezoidal chamfer design, together with the closing structure and the precise fit of the die 22, makes the extrusion molding process smoother, reduces jamming and abnormal wear, greatly extends the overall service life of the die, and reduces the frequency of production line downtime for replacement.

[0078] 5. It comprehensively improves the reliability and yield of projection welding process.

[0079] The synergistic effect of these features enables optimization of the entire process from "pre-weld shaping" to "welding melting." On the one hand, it ensures the precise and non-destructive geometry of the pre-weld protrusion 61 (no cracking, no deformation), and on the other hand, it optimizes the heat input and electrode stress during the welding process. This ultimately results in a significant increase in the welding yield, making it particularly suitable for large-scale production in fields with stringent weld quality requirements, such as new energy vehicle battery connections and lightweight body structural components.

[0080] 6. Enable flexible production and significantly improve equipment compatibility and changeover efficiency.

[0081] By introducing a servo electronic press drive system, fully closed-loop precision control of the pressing depth of the punch 21 is achieved. This breaks the limitation of traditional mechanical drives that require "one mold, one height," enabling operators to quickly form punches 61 of different heights on the same mold without disassembling the mold when facing multi-variety, small-batch production tasks. This is achieved simply by modifying the displacement parameters in the control program, thus adapting to diverse welding process requirements. This significantly shortens product changeover time and reduces mold storage and management costs, making it particularly suitable for flexible production lines that require frequent specification changes, such as those for new energy vehicle battery connectors and body structural components.

[0082] The above embodiments prepared by the method of the present invention are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0083] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

Claims

1. A mold suitable for metal projection welding, characterized in that, The mold includes a punch and a die that cooperate with each other. The punch includes a first working surface and a protrusion protruding from the first working surface toward the die. The width of the protrusion gradually decreases from the first working surface toward the die. The die includes a second working surface and a recessed groove from the second working surface toward the side away from the protrusion. The groove includes a bottom groove at the bottom and a convergence structure on both sides of the bottom groove. The convergence structure includes a first curved surface, a second curved surface, and a first inclined surface. The first curved surface, the second curved surface, and the first inclined surface are arranged sequentially from the bottom groove to the second working surface. The bottom groove, the first curved surface, and the second curved surface are all arc-shaped surfaces. The openings of the bottom groove and the second curved surface face the protrusion, and the opening of the first curved surface faces the side away from the protrusion.

2. The mold according to claim 1, characterized in that, The radius of the second surface is smaller than the radius of the first surface, and the radius of the second surface is 0.05-0.5mm.

3. The mold according to claim 1, characterized in that, The radius of the bottom groove is greater than the radius of the first curved surface, and the radius of the bottom groove is 0.2-0.5mm; the width of the bottom groove is 0.2-0.7 times the width of the groove; the width of the groove is 1-3mm.

4. The mold according to claim 1, characterized in that, The first inclined plane is a plane, and the angle between the first inclined plane and the second working surface is 40°-80°.

5. The mold according to claim 1, characterized in that, The folding structure includes a second inclined surface and a third curved surface arranged sequentially between the second curved surface and the first inclined surface. The third curved surface is an arc-shaped surface, and the opening of the third curved surface faces away from the protrusion.

6. The mold according to claim 5, characterized in that, The second inclined plane is a plane, and the angle between the second inclined plane and the second working surface is greater than the angle between the first inclined plane and the second working surface.

7. The mold according to claim 5, characterized in that, The angle between the second inclined plane and the second working surface is 55°-85°.

8. The mold according to claim 1, characterized in that, A fourth curved surface is provided between the first inclined surface and the second working surface. The fourth curved surface is an arc-shaped surface with its opening facing away from the protrusion.

9. The mold according to any one of claims 1-8, characterized in that, The protrusion includes a bottom surface, a fifth curved surface located on both sides of the bottom surface, and a third inclined surface. The bottom surface, the fifth curved surface, and the third inclined surface are arranged sequentially. The bottom surface is a plane, and the fifth curved surface is an arc-shaped surface with its opening facing the protrusion.

10. The mold according to claim 9, characterized in that, The width of the bottom surface is 0.5-1.5 times the width of the bottom groove.

11. The mold according to claim 9, characterized in that, The third inclined plane is a plane, and the angle between it and the first working surface is 40°-85°.

12. The mold according to claim 9, characterized in that, A sixth curved surface is provided between the third inclined surface and the first working surface. The sixth curved surface is an arc surface with its opening facing the second working surface.

13. The mold according to claim 1, characterized in that, The mold is used to form a bulge on a metal plate, the overall length of which is 3-10 mm; the metal plate is iron, or an alloy material containing one or more of iron, magnesium, and aluminum.

14. A metal projection welding device, characterized in that, Including the molds suitable for metal projection welding as described in any one of claims 1-13.

15. A projection hull structure for metal projection welding, characterized in that, The metal plate is formed by projection welding using a mold suitable for projection welding as described in any one of claims 1-13.

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