CN116197509A - Electrode cap for resistance spot welding of aluminum workpiece and spot welding method - Google Patents

Abstract

The invention discloses an electrode cap for resistance spot welding of an aluminum workpiece and a spot welding method. The electrode cap comprises: a first surface which is located at the center of the electrode cap and faces the same side of the electrode cap and is recessed around the central axis; The second surface outside the first surface; and 2-5 annular ridges that are convex or concave around the central axis on the second surface; wherein, the cross-sectional central axis of each annular ridge perpendicular to the second surface; the highest point of the annular ridge is distributed on a spherical surface, and the center of the spherical surface is a center with the center of the second surface. The electrode cap of the present invention can effectively weld the aluminum alloy workpiece, make the current and pressure flow directionally during the welding process, and make the pressure on the annular ridge more uniform, thereby controlling the formation process of the weld nugget, avoiding the generation of defects such as cracks and shrinkage cavities, and improving The mechanical properties of the solder joints enable its welded structure to withstand high mechanical loads.

Description

Electrode cap for resistance spot welding of aluminum workpiece and spot welding method

technical field

The invention relates to the field of resistance spot welding, in particular to an electrode cap and a spot welding method for resistance spot welding of aluminum workpieces.

Background technique

Aluminum alloy resistance spot welding is an important manufacturing process in the current industry. Due to the high specific strength of aluminum alloy, it is a kind of material that is widely used in automobile, aerospace and other industries. During the spot welding process, low melting point eutectics are easily formed inside the nugget. During the spot welding cooling process, the solidification shrinkage is serious, and the tensile stress is relatively large. Defects such as cracks and shrinkage cavities are easily formed inside the nugget, and the existence of defects will be extremely large. The reduction of the mechanical properties of the solder joints leads to permanent failure of the welded structure under lower stress loads, thus hindering the application of resistance spot welding of aluminum alloys. At the same time, resistance spot welding of aluminum alloys is very prone to spatter and cannot form a large enough weld nugget, resulting in a decrease in the performance of the joint; The heat is unstable and the performance of the solder joint is unstable. The service life of the electrode is reduced and high-frequency grinding is required, resulting in an increase in manufacturing costs and a decrease in efficiency.

Therefore, there is still a lack of an electrode cap for effectively welding aluminum alloy workpieces and a spot welding method for it in the art, so as to avoid defects such as cracks and shrinkage cavities, improve the mechanical properties of the solder joints, and make its welding structure withstand higher Stress loading, while improving electrode life, improving manufacturing efficiency and reducing costs.

Contents of the invention

The object of the present invention is to provide an electrode cap and a spot welding method for resistance spot welding of aluminum workpieces. The electrode cap of the present invention can effectively weld aluminum alloy workpieces, avoid the generation of defects such as cracks and shrinkage cavities, and improve the mechanical properties of solder joints. performance, so that its welded structure can withstand higher mechanical loads, and at the same time improve the service life of electrodes, improve manufacturing efficiency and reduce costs.

In a first aspect of the present invention, there is provided an electrode cap for resistance spot welding of aluminum workpieces, the electrode cap comprising: a first surface located at the center of the electrode cap and facing a depression in the electrode cap around the central axis ; a second surface around the outer side of the first surface; and 2-5 annular ridges on the second surface that revolve and protrude around the central axis; wherein, the cross-sectional central axis of each annular ridge perpendicular to the second surface, so that the electrode pressure can make the pressure on the annular ridge more uniform along the direction of the central axis of the annular ridge when performing resistance spot welding; the highest point of the annular ridge is distributed on a spherical surface, and the The center of the sphere is a center with the center of the second surface.

In another preferred example, the number of said annular ridges is 3-4.

In another preferred example, the depth h of the first surface depression is 0.01-0.5 mm, and h does not exceed 0.2T, where T is the thickness of the aluminum workpiece.

In another preferred example, when the thicknesses of the aluminum workpieces are inconsistent, the T is the thickness of the thinner one of the aluminum workpieces.

In another preferred example, the depth h of the first surface is 0.02-0.3 mm.

In another preferred example, the first surface is a smooth curved surface, and the cross-sectional shape of the first surface on a vertical plane is an arc surface.

In another preferred example, the first surface and the second surface are connected through a circular arc transition, and the radius r of the circular arc is not less than 0.1 mm.

In another preferred example, the radius r of the arc is 0.6-3mm.

In another preferred example, the outermost diameter d0 of the first surface is 2-6 mm.

其中T为所述铝工件的厚度。In another preferred example, the diameter of the outermost circumference of the first surface is

Where T is the thickness of the aluminum workpiece.

In another preferred example, the electrode cap further includes a third surface, the third surface is located between the first surface and the second surface, and is an annular surface, and the third surface is not provided with the annular ridge.

In another preferred example, the third surface is a plane, and the width L of the third surface is not less than 0.2mm, so as to ensure that the initial contact surface is large enough when the spot welding pre-pressure is energized, so as not to make the electrodes/materials The contact area is too small and the current density is too high, resulting in high heat generation and electrode sticking.

In another preferred example, the width L of the third surface is 0.2≤L≤0.5 mm.

In another preferred example, the second surface is a curved surface with a radius of curvature R of 20-100 mm, and satisfies 15T≤R≤50T, where T is the thickness of the aluminum workpiece.

的圆柱侧曲面与所述第二表面的交汇处(为以所述电极帽的中心为中心的圆)上的一点p距离所述第三表面的高度为h2，满足h2≤0.15T，其中T为所述铝工件的厚度。In another preferred example, taking the center of the electrode cap as the center, the diameter is

The height of a point p on the intersection of the cylindrical side surface of the cylinder and the second surface (a circle centered on the center of the electrode cap) from the third surface is h2, satisfying h2≤0.15T, where T is the thickness of the aluminum workpiece.

In another preferred example, the outer diameter d1 of the circumference of the surface where the second surface is located is 8-15 mm; and the height difference h1 between the outer diameter of the circumference of the surface where the second surface is located and the third surface is no more than 0.2 T, where T is the thickness of the aluminum workpiece.

In another preferred example, the height difference h1 between the outer diameter of the surface where the second surface is located and the third surface is 10%T≤h1≤30%T, where T is the thickness of the aluminum workpiece.

In another preferred example, the fourth surface located outside the second surface and adjacent to the second surface is a tapered surface, which is parallel to the plane perpendicular to the central axis of the electrode cap (also called "basal surface"). The angle between the planes") is α, where 20°≤α≤70°.

In another preferred example, 30°≤α≤60°.

In another preferred example, the fourth surface located outside the second surface and adjacent to the second surface is an arc surface, and the radius of curvature of the arc surface is r2 ≥ 10 mm.

In another preferred example, the height H of the annular ridge is 20-300 μm, the bottom width B of the annular ridge is 0.1-0.5 mm; the aspect ratio B/H satisfies: 0.5≤B/H≤10.

In another preferred example, the cross-sectional shape of the annular ridge may be a triangle, trapezoid, semicircle, parabola, etc. formed by any straight lines and curves.

In another preferred example, the distance between the central axes of adjacent annular ridges is 200-1500 μm.

In another preferred example, the innermost annular ridge has a height of 50-200 μm, preferably 100-200 μm.

In another preferred example, when the electrode cap performs a welding operation, the annular ridge on the second surface first contacts the aluminum workpiece to be welded, and the electrode pressure and current pass through the annular ridge and initially A molten core is formed, and with the flow of electrode pressure and welding current, the third surface, the depressed first surface, and the outer annular ridge are gradually in contact with the aluminum workpiece, and the molten core is simultaneously inward and Expand outwards, but due to the electrode pressure on the outside, there is an electrode depression on the inside, and the workpiece is compressed and deformed inward, so that the central electrode in the depression contacts the aluminum workpiece earlier than the outer electrode, the current passes through, and the center base of the workpiece is melted. Material, the nugget expands inward, forming a nugget from the outside to the inside, and at the same time avoids too much concentration of energy at the contact position, which causes serious electrode adhesion due to heat concentration.

In a second aspect of the present invention, a resistance spot welding method is provided, the method comprising:

(a) providing a pair of the above-mentioned electrode caps;

(b) Pre-pressing stage: place a pair of electrode caps on both sides of the stacked aluminum workpiece respectively to perform pre-pressing. The applied electrode pressure is 2000-8000N and the duration is 200-1500ms, so that the electrodes said innermost annular ridge of the cap is in contact with said aluminum workpiece;

(c) Power-on welding stage: conduct one or more sections of welding current, the effective value of the welding current is 22KA-65KA, as time goes on, the center contact position of the aluminum workpiece corresponding to the inner annular ridge first Melting to form a melting center, the aluminum workpiece on the outside gradually deforms and expands inwards and outwards, and the third surface of the electrode cap, the first surface, the outer annular ridge and the outer The second surface is successively in contact with the electrode cap, and the melting center expands inwards and outwards simultaneously to form a complete aluminum nugget;

(d) Condensation stage: stop the welding current, maintain the state of the electrode cap and the aluminum workpiece for 30-300 ms, and the molten metal solidifies to form a complete solder joint.

In another preferred example, the welding current is in the form of multiple pulses, and the energized welding stage includes at least three welding current pulses, each of which has a cooling interval between the welding current pulses;

Wherein, the action time _tn of each welding current pulse does not exceed 20ms, and the time tn _-n+1 of the cooling interval does not exceed 5ms, and

In another preferred example, the action time t _n of the welding current pulse does not exceed 15 ms, and the cooling interval time t _n-n+1 is 2-5 ms.

In another preferred example, the number of welding current pulses is no less than four.

In another preferred example, the amplitudes of each of the welding pulse currents may be different, for example, they tend to increase gradually.

The electrode cap of the present invention can be applied to high-quality resistance spot welding of different aluminum workpieces by setting the structure and size of the specific shape; the main mechanism is to use the raised annular ridge and the central concave surface of the electrode cap to make the electrode pressure and welding current Conveying according to a predetermined path to control the melting and forming process of the weld nugget and the cooling and solidification process; to enable directional nucleation and expansion during melting to reduce the generation of spatter and surface adhesion, and to distribute the electrode pressure according to the surface morphology of the electrode during solidification, which is beneficial to reduce Formation of internal shrinkage cavities and cracks. And the use of multiple short-time main welding pulses during welding can reduce the temperature between the electrode and the surface of the aluminum plate without reducing the internal temperature to reduce the occurrence of surface adhesion; use the preheating pulse to establish stable electrical contact, and use the tempering current to reduce Solidification shrinkage stress of solder joints reduces the formation of solidification cracks and improves welding quality.

It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (such as embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, we will not repeat them here.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the sectional view that is used for the electrode cap of aluminum workpiece resistance spot welding in an example of the present invention;

Fig. 2 is a partial schematic diagram at the first surface of the electrode cap in Fig. 1;

Fig. 3 is a schematic diagram of the circumference diameter dimensions of a plurality of annular ridges in an example of the present invention;

Figure 4 is a cross-sectional view of the annular ridge involved in the present invention;

Fig. 5 is the schematic diagram that electric current changes with time in the resistance spot welding process in an example of the present invention;

Fig. 6A is the schematic diagram of current variation with time in the resistance spot welding process in another example of the present invention;

Fig. 6B is the schematic diagram of current variation with time in the resistance spot welding process in another example of the present invention;

Fig. 7 is the schematic diagram that electric current changes with time in the resistance spot welding process in another example of the present invention;

Fig. 8 is the schematic diagram of the actual current output of the resistance spot welding process in an example of the present invention;

Fig. 9 is a schematic diagram of the process of welding an aluminum alloy workpiece with an electrode cap in an example of the present invention;

Fig. 10 is a cross-sectional view of a solder joint obtained by welding a 0.8 mm 6-series aluminum alloy to a 1.0 mm 6-series aluminum alloy through the electrode cap shown in Fig. 1 ;

FIG. 11 is a cross-sectional view of a weld spot welded to a 3.0 mm cast aluminum alloy through the electrode cap shown in FIG. 1 .

In each attached drawing, each mark is as follows:

1-electrode cap;

12 - first surface;

11 - second surface;

111 - annular ridge;

10 - third surface;

13 - a circular arc transition surface between the first surface and the second surface;

14 - outer surface;

21 - the first welding electrode cap;

22 - the second welding electrode cap;

3- The first aluminum alloy workpiece;

4- the second aluminum alloy workpiece;

5- Welding current;

6 - initial weld nugget;

7- Final weld nugget;

为圆周直径的圆柱侧表面与第二表面交线距离第三表面的高度；L-第三表面的宽度；α-第四表面与基面之间的夹角。d1-the diameter of the surface where the outermost circumference of the second surface is located; d0-the diameter of the surface where the outermost circumference of the first surface is located; R-the radius of curvature of the arc where the second surface is located; h1-the height of the outer circumference of the second surface from the third surface Poor; h2- centered on the central axis of the electrode cap

is the height of the intersection line between the side surface of the cylinder and the second surface and the third surface; L-the width of the third surface; α-the angle between the fourth surface and the base surface.

Detailed ways

After extensive and in-depth research, and through a large number of screenings, the inventor first developed an electrode cap and a spot welding method for resistance spot welding of aluminum workpieces, which can effectively avoid defects such as cracks and shrinkage cavities, and improve the mechanical properties of solder joints. performance, so that its welded structure can withstand higher stress loads, and the present invention is completed on this basis.

the term

As used herein, the terms "second surface" and "second base surface" and the like are used interchangeably.

As used herein, the terms "aluminum workpiece", "workpiece" and "aluminum alloy workpiece" and the like are used interchangeably.

As used herein, the terms "electrode cap" and "welding electrode" and the like are used interchangeably.

The invention provides an electrode cap for resistance spot welding of aluminum workpieces, which is an electrode cap with a specific structure.

Typically, the electrode cap 1 of the present invention includes a first surface 12 located at the center of the electrode cap and facing the same side of the electrode cap around the central axis, and a second base surface 11 surrounding the outside of the first surface, and on the base There are 2-5 annular ridges 111 that are convex or concave around the central axis on the surface; the cross-sectional central axis of the single annular ridge is perpendicular to the base surface, so that the electrode pressure can be along the surface when resistance spot welding is performed. The direction of the central axis of the annular ridge makes the pressure on the annular ridge more uniform, the highest point of the annular ridge is distributed on a spherical surface, and the center of the spherical surface and the center of the base surface are a center.

Referring now to FIG. 2, the first surface 12 has a depression with a depth h of 0.01-0.5 mm (preferably 0.02-0.3 mm) and a cross-sectional shape of an arc surface, and h does not exceed 0.2T, and there is a circle between it and the base surface. Arc r transition, the transition fillet r is not less than 0.1mm, preferably 0.5-5mm.

The first surface 12 has an outer diameter d0 of 2-6mm; preferably

The third surface 10 is a plane, and its width L is not less than 0.2 mm; to ensure that the initial contact surface is large enough during spot welding preloading, so as not to make the electrode/material contact area too small and the current density too large, resulting in relatively high heat generation High enough to cause electrode adhesion; preferably 0.2≤L≤0.5mm, preferably 0.25≤L≤0.4mm.

The second base surface 11 is a curved surface with a radius of curvature R between 20-100, and satisfies 20T≤R≤50T.

的圆周面与第二基表面的交点所在位置为p，其距离第三表面(又可称为“顶表面”)10的高度为h2，满足h2≤0.15T。Rotating around the center of the electrode, the diameter is

The position of the intersection of the circumferential surface of and the second base surface is p, and its height from the third surface (also called "top surface") 10 is h2, satisfying h2≤0.15T.

The outer diameter d1 of the surface circumference where the second base surface is located is 8-15mm; and the height difference h1 is not more than 0.3T; preferably 10%T≤h≤30%T.

The outer surface 14 of the second base surface is a conical surface, and the angle between it and the electrode end plane is α, generally 20°≤α≤70°, preferably 30°≤α≤60°.

The height H of each annular ridge is 20-300 μm, the width B of the bottom of the annular ridge is 0.1-0.5 mm; the aspect ratio B/H satisfies: 0.5≤B/H≤20; the number of annular ridges is 2-5 ; Preferably 3-4.

The cross-sectional shapes of the annular ridges may be triangles, trapezoids, semicircles, parabolas, etc., which are composed of arbitrary straight lines and curves; they may be the same or different from each other.

The height of the innermost annular ridge is 50-200 μm.

The spacing between adjacent annular ridges is 100-500 μm.

When performing welding, the second base surface 10 and the annular ridge are first in contact with the workpiece, and a molten core is initially formed, and as the electrode pressure and welding current flow, the depressed first surface 12, the outer annular ridge and the second base surface 11 simultaneously Both are in contact with the workpiece, and the melting core expands inward and outward at the same time, but due to the electrode pressure on the outer side, the inner side has an electrode depression, and the workpiece is compressed and deformed inward. It expands inward to form a nugget from the outside to the inside, and at the same time avoids the excessive concentration of energy at the contact position, which will cause serious electrode adhesion due to heat concentration.

The invention also provides a resistance spot welding method. Typically, the resistance spot welding method utilizes a pair of electrode caps as described above, which perform a resistance spot welding process comprising the following steps:

Place the welding electrodes on both sides of the stacked aluminum alloy workpieces respectively, and perform preloading. The electrode pressure is 3000-6000N, and the time is 200-1000ms, so that the innermost annular ridge of the electrode cap and the second base surface 11 contact with aluminum workpieces;

Through one or more sections of welding current, as time goes on, the annular ridge corresponds to the melting of the inner aluminum workpiece and the outer aluminum workpiece gradually deforms inward and expands to contact the third surface 10 of the welding electrode and the outer annular ridge and the second base surface 11, The weld nugget expands in this direction to form a complete aluminum nugget;

Stop the welding current for a period of time, and the molten metal solidifies to form a complete solder joint.

The welding current pulse includes multiple welding current pulses: the process includes at least 3 welding current pulses; there is a cooling time interval between each welding current pulse; generally the effective value of the welding current is 25KA-50KA.

且满足/>

Among them, the current action time t _n of each welding pulse does not exceed 20ms, and the cooling interval t _n-n+1 does not exceed 5ms, and

and satisfy />

When the welding current pulse time t _n does not exceed 15ms, the number of welding pulses is not less than 4; the cooling time interval t _n-n+1 is 2-5ms;

The amplitude of each welding pulse current can be different, showing a tendency of increasing gradually.

The main advantages of the present invention include:

(a) Effective welding of aluminum alloy workpieces;

(b) Avoid defects such as cracks and shrinkage cavities;

(c) Improve the mechanical properties of solder joints so that their welded structures can withstand higher stress loads;

(d) There is no adhesion, cracks and other defects on the surface of solder joints, and the surface quality is good;

(e) Use shorter welding heat input to reach the final nugget, saving welding energy.

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, the drawings are schematic diagrams, so the device and equipment of the present invention are not limited by the size or scale of the schematic diagrams.

It should be noted that in the claims and description of this patent, relative terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or Any such actual relationship or order between such entities or operations is implied. Furthermore, the term "comprises", "comprises" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes elements not expressly listed. other elements of or also include elements inherent in such a process, method, article, or apparatus. Without further limitations, an element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

Example

The electrode cap used for resistance spot welding of aluminum workpieces in this embodiment is shown in FIG. 1 . The electrode cap 1 includes: a first surface 12 located in the center of the electrode cap and facing the same side of the electrode cap around the central axis, and a second surface 11 surrounding the outer side of the first surface, and having a surrounding surface on the second surface. 2-5 annular ridges 111 protruding or recessed on the central axis, the cross-sectional central axis of each annular ridge is perpendicular to the base surface, so that the electrode pressure can be used along the direction of the central axis of the annular ridge when performing resistance spot welding The pressure on the annular ridge is more uniform, the highest point of the annular ridge is distributed on a spherical surface, and the center of the spherical surface is the same as the center of the base surface; when performing resistance spot welding, the innermost annular ridge First contact with the aluminum workpiece, then turn on the welding current so that 1-2 annular ridges outside the first annular ridge are in contact with the surface of the workpiece, and the aluminum workpiece is heated and deformed outward so that the first surface 12 is gradually in contact with the aluminum workpiece, When the current passes through the first surface 12, a complete weld nugget is formed inside the aluminum workpiece; when the current passes through the first surface 12, at least the third and fourth annular ridges outside the first annular ridge also gradually contact the aluminum workpiece, and the current passes through ; so that the order of current passing is outside-in-out, so that the current density is more evenly distributed and controllable during the welding process, reducing the adhesion between the electrode and the aluminum workpiece and forming a large enough weld nugget.

2 is a schematic cross-sectional view of the first surface at the center of the welding electrode. The first surface 12 has a maximum depth h of 0.01-0.3mm, and the cross-sectional shape of the depression is an arc surface, and the base surface transitions with a circular arc. The arc is called the arc transition surface 13 between the first surface and the second surface, and its radius r is not less than 0.1mm, preferably 0.6-3mm.

其中T为所述铝工件的厚度。所述电极帽还包括第三表面10，所述第三表面位于所述第一表面和所述第二表面之间，为环形表面，且所述第三表面上不设置所述环形脊。在另一优选例中，所述第三表面为平面，所述第三表面的宽度B不小于0.2mm，以保证在点焊预压时初始接触面足够大，进而不至于使电极/材料接触面积太小而电流密度太大，导致产热量较高而发生电极粘连。在另一优选例中，所述第三表面的宽度L为0.2≤L≤0.5mm。The outermost diameter d0 of the first surface is 2-6mm, and satisfies

Where T is the thickness of the aluminum workpiece. The electrode cap also includes a third surface 10, the third surface is located between the first surface and the second surface, and is an annular surface, and the annular ridge is not provided on the third surface. In another preferred example, the third surface is a plane, and the width B of the third surface is not less than 0.2 mm, so as to ensure that the initial contact surface is large enough during spot welding preloading, so as not to make the electrode/material contact The area is too small and the current density is too high, resulting in high heat generation and electrode adhesion. In another preferred example, the width L of the third surface is 0.2≤L≤0.5 mm.

的圆柱侧曲面与所述第二表面的交汇处(为以所述电极帽的中心为中心的圆)上的一点p距离所述第三表面的高度为h2，满足h2≤0.15T，其中T为所述铝工件的厚度。所述第二表面所在表面圆周的外径d1为8-15mm；且所述第二表面所在表面圆周的外径距离所述第三表面的高度差h1为不超过0.3T，其中T为所述铝工件的厚度。在另一优选例中，所述第二表面所在表面圆周的外径距离所述第三表面的高度差h1为10％T≤h1≤30％T，其中T为所述铝工件的厚度。The second surface is a curved surface with a radius of curvature R of 20-100mm, and satisfies 15T≤R≤50T, where T is the thickness of the aluminum workpiece. In another preferred example, taking the center of the electrode cap as the center, the diameter is

The height of a point p on the intersection of the cylindrical side surface of the cylinder and the second surface (a circle centered on the center of the electrode cap) from the third surface is h2, satisfying h2≤0.15T, where T is the thickness of the aluminum workpiece. The outer diameter d1 of the circumference of the surface where the second surface is located is 8-15mm; and the height difference h1 between the outer diameter of the circumference of the surface where the second surface is located and the third surface is no more than 0.3T, where T is the The thickness of the aluminum workpiece. In another preferred example, the height difference h1 between the outer diameter of the surface where the second surface is located and the third surface is 10%T≤h1≤30%T, where T is the thickness of the aluminum workpiece.

In another preferred example, the fourth surface located outside the second surface and adjacent to the second surface is a conical surface, as shown in FIG. The angle between them is α, where 20°≤α≤70°. In another preferred example, 30°≤α≤60°. In another preferred example, the fourth surface located outside the second surface and adjacent to the second surface is an arc surface. As shown in FIG. 3 , the radius of curvature of the arc surface is r2 ≥ 10 mm.

Referring to FIG. 3 and FIG. 4 , the second surface 11 is a plane or a curved surface with a curvature radius R not less than 20 mm, generally R≤100 mm. There are multiple annular ridges 111 on the second surface 11, the width of the bottom of the annular ridge is 0.1-0.5mm, preferably 0.2-0.4mm, and the aspect ratio B/H satisfies: 0.5≤B/H≤10. The height of each annular ridge is 20-300 μm, preferably 50-250 μm, and the shape and size of each annular ridge can be the same or different; wherein the height of the first innermost annular ridge is 50-200 μm, preferably 100-200μm, which helps to ensure that it first makes contact with the workpiece and transitions to subsequent annular ridge contact in the form of a fixed concept when performing resistance spot welding, so that the electrode pressure and welding current distribution are more directional and controllable, and heat generation efficiency is improved And reduce electrode adhesion. As shown in Figure 4 is the cross-sectional shape structure of the annular ridge in the present invention; the cross-sectional shape of the annular ridge can be any shape including triangle, trapezoid, semicircle, and other straight lines and curves.

The distance between the central axes of each annular ridge is 200-1500 μm, preferably 400-1000 μm. The diameter of the surface where the center of the bottom of the first annular ridge is d2, the diameter of the surface where the center of the bottom of the second annular ridge is d3, the diameter of the surface where the center of the bottom of the third annular ridge is d4, and the diameter of the surface where the center of the bottom of the fourth annular ridge is d5, wherein satisfying :

3≤d2≤5mm, 4≤d3≤6mm, 6≤d4≤8mm, 7≤d5≤9mm.

In another preferred example, the annular ridge further includes a fifth annular ridge, wherein the diameter of the surface where the center of the bottom of the fifth annular ridge is located is d6, and d6 satisfies 8≤d6≤10mm.

The electrification sequence of the electrode cap during the welding process is the first annular ridge, the second annular ridge, the first surface (i.e. the central concave surface) 12, the third annular ridge, the fourth annular ridge, and the optional nth annular ridge Order. This welding sequence ensures that the nucleation mode is outside-in-out, making the size of the weld nugget controllable; and it is easy to form weld nuggets of different target sizes according to different plate thicknesses and reduce the formation of spatter.

The present invention also provides a resistance spot welding method, which comprises the following steps:

(a) providing any one of the electrode caps;

(b) Pre-pressing stage: place a pair of electrode caps on both sides of the stacked aluminum workpiece respectively to perform pre-pressing, the applied electrode pressure is 2000-8000N, preferably 3000-7500N, and the duration is 200 - 1500 ms, preferably 300-1000 ms, bringing said innermost annular ridge of said electrode cap into contact with said aluminum workpiece;

(c) Power-on welding stage: conduct one or more sections of welding current, the effective value of the welding current is 22KA-65KA, as time goes on, the center contact position of the aluminum workpiece corresponding to the inner annular ridge first Melted to form a melting center, the aluminum workpiece on the outside gradually deforms and expands inwardly, and the third surface of the electrode cap, the first surface, the annular ridge on the outside and the second surface on the outside Contacting the electrode cap successively, the melting center expands inward and outward simultaneously to form a complete aluminum nugget;

(d) Condensation stage: stop the welding current, maintain the state of the electrode cap and the aluminum workpiece for 300-300ms, and the molten metal solidifies to form a complete solder joint;

优选地为/>

T单位为mm，tn单位为ms；每一个主焊接电流脉冲In＞25KA；Wherein, the welding current is in the form of multiple pulses, and the energized welding stage includes at least three main welding current pulses, each of which has a cooling interval between the main welding current pulses; the effect of each welding current pulse Time t _n , n is the total number of welding pulses, satisfying

preferably />

The unit of T is mm, the unit of tn is ms; each main welding current pulse In>25KA;

Wherein, the action time t _n of each main welding current pulse does not exceed 20 ms, and the cooling interval time 3 ms≤t _n-n+1 ≤5 ms. When the action time t _n of the welding current pulse does not exceed 15 ms, the time t _n-n+1 of the cooling interval is 2-3 ms. When the action time t _n of the welding current pulse does not exceed 10 ms, the time t _n-n+1 of the cooling interval is 1-2 ms. The number n of welding current pulses is not less than 4. The amplitude of each of said welding pulse currents may be the same or different. For example, it is the same as shown in Figure 5; for example, as shown in Figures 6A and 6B, it is gradually increasing, and I _n+1 -I _n ≥ 2KA, and I _n+1 is the current amplitude of the n+1th segment value.

It is worth noting that a section of preheating current pulse can also be included before the main welding current, the amplitude _I of the preheating current pulse is 10-20KA, and the duration is 20-60ms; The cooling interval between welding current pulses is t _0-1 0-5 ms, as shown in Figure 6A; preferably 0 ms, as shown in Figure 6B.

In addition, at least one segment of tempering current pulse is included after the main welding current pulse, as shown in Figure 7; the amplitude I _h of the tempering current pulse is 25-35KA, and the duration is 40-100ms; especially its The mean value I _w of all the aforementioned main welding pulse amplitudes is not exceeded, more narrowly it does not exceed 0.8 I _w . And the cooling interval between the tempering pulse current and the last stage of the main welding current is 5-50ms. The time point of applying the tempering current is when the inside of the weld nugget just starts to solidify and is not completely solidified. Generally, when the plate thickness When T does not exceed 1.0mm, the time interval is 5-10ms; when the plate thickness exceeds 1.0mm, it is 10-30ms; in order to reduce the shrinkage stress when the weld nugget solidifies, and reduce the generation of defects such as internal thermal cracks.

It is also worth noting that the amplitudes of all the above-mentioned current pulses are the current effective value of a single stage. Since the actual current rise process has a climbing and fluctuating stage, considering the time of the current rising and falling, the actual output cannot Guaranteed to be completely close to 0, as shown in Figure 8; and all the accompanying drawings are represented by a schematic diagram with a constant average value, and its meaning is understood by those skilled in the art.

This embodiment discloses the process of using the electrode cap of the present invention to weld aluminum alloy workpieces. As shown in FIG. Clamping for welding, wherein at least one of the first welding electrode cap 21 and the second welding electrode cap 22 is the above-mentioned electrode cap 1 . The first and second aluminum alloy workpieces 3 and the second aluminum alloy workpiece 4 are made of aluminum alloys such as aluminum-magnesium alloys, aluminum-silicon alloys, aluminum-magnesium-silicon alloys or aluminum-copper alloys. The thickness of the aluminum alloy workpieces is 0.5-4.0mm, preferably The ground is 0.8-3.5mm; it can be various aluminum workpieces formed by stamping, extrusion or casting. During welding, there can be two aluminum alloy workpieces (such as only 3 and 4) or a combination of more than two, and the thickness of each aluminum alloy workpiece can be the same or different. It should be noted that the term "workpiece" used herein refers to broadly including metal sheets, protrusions, castings and other aluminum alloy parts that can be resistance spot welded.

In the initial stage of performing resistance spot welding, the welding current 5 passes through the annular ridge that the edge contacts first, the second base surface 10 and the annular ridge 111 first contact the workpiece, and initially form the initial weld nugget 6, as the electrode pressure and the welding current 5 increase Flowing through, the concave first surface 12, the outer annular ridge and the second base surface 11 are all in contact with the workpiece at the same time, and the initial weld nugget 6 expands inward and outward at the same time, but due to the electrode pressure on the outer side, there is an electrode depression on the inner side, and the workpiece Inward compression deformation, the internal electrode first contacts the workpiece, the current passes through, the center substrate is melted, the nugget expands inward, and forms a nugget from the outside to the inside. The electrodes stick together, eventually forming a complete final nugget 7 .

The time taken for the first annular ridge to fully penetrate the workpiece from contacting to the workpiece does not exceed 30ms (calculated from the start of energization), and the time taken for the top of the first surface 12 to contact the workpiece does not exceed 300ms (calculated from the start of energization). In particular, when the thickness of the workpiece is less than 1.0 mm, the contact time between the first surface 12 and the workpiece does not exceed 150 ms (calculated from the start of energization).

Figure 10 shows a cross-sectional view of the solder joints obtained by welding 0.8mm 6-series aluminum alloys with 1.0mm unequal thickness 6-series aluminum alloys; the center of the electrode used has a depression (first surface 12) with a depth of 0.1mm, and the electrode cap The outer diameter of the circle where the second base surface is located is 6 mm, and the radius of curvature of the second base surface is 40 mm; there are two circles of annular ridges with trapezoidal cross-sectional shape on the second base surface, the height of the annular ridges is 0.15 mm, and the width is 0.2 mm. The welding process used is: electrode pressure 3500N, preheating 10KA, 50ms, the main welding current pulse is composed of 6 sections, each section is 32KA, the power-on time is 10ms, the cooling interval is 2ms, the tempering pulse current is 25KA, and the tempering time is 50ms It can be seen from the cross-sectional shape that the diameter of the weld nugget has reached 7.18mm and there is no splashing phenomenon. The electrode of the present invention helps to expand the diameter of the weld nugget and enhance the joint strength.

Fig. 11 shows the cross-sectional morphology of the welding spot obtained by resistance spot welding for a cast aluminum alloy of 3.0 mm; The outer diameter of the circle where it is located is 6mm, and the radius of curvature of the second base surface is 40mm; there are two circles of annular ridges with a triangular cross-sectional shape on the second base surface, the height of the annular ridge is 0.2mm, and the width is 0.3mm; the welding process is: electrode Pressure 4500N, preheating 15KA, 50ms, each main welding current pulse is 34KA, welding time is 20-30ms, the number of pulses is 8-10, cooling interval is 2-5ms, tempering current is 25KA, time 80ms; Press for 100ms. It can be seen from the cross-sectional shape that the weld nugget diameter has reached 9.81mm and there is no spatter phenomenon, which expands the weld nugget diameter, which is conducive to improving the strength of the joint.

All documents mentioned in this application are incorporated by reference in this application as if each were individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (10)

1. An electrode cap for resistance spot welding of aluminum workpieces, the electrode cap comprising:

a first surface located at the center of the electrode cap and facing the recess in the electrode cap about a central axis;

a second surface surrounding an outside of the first surface; and

2-5 annular ridges on the second surface that rotationally protrude about the central axis;

wherein a central axis of a cross section of each of the annular ridges is perpendicular to the second surface so that electrode pressure can be more uniform along the central axis of the annular ridge when resistance spot welding is performed;

the highest point of the annular ridge is distributed on a spherical surface, and the center of the spherical surface and the center of the second surface are the same.

2. The electrode cap of claim 1 wherein the first surface recess has a depth h of 0.01-0.5mm and h does not exceed 0.2T, where T is the thickness of the aluminum workpiece.

3. The electrode cap of claim 1 wherein the first surface and the second surface are connected by a circular arc transition, the radius r of the circular arc being no less than 0.1mm.

4. The electrode cap of claim 1 wherein the outermost diameter d0 of the first surface is 2-6mm.

5. The electrode cap of claim 1 further comprising a third surface, the third surface being between the first surface and the second surface, being an annular surface, and the third surface being devoid of the annular ridge.

6. The electrode cap of claim 5 wherein the third surface is planar and the width L of the third surface is not less than 0.2mm to ensure that the initial contact surface is large enough to prevent electrode/material contact area from being too small and current density too large when energized during spot welding pre-compaction to result in higher heat generation and electrode sticking.

7. The electrode cap of claim 1 wherein the second surface is a curved surface having a radius of curvature R between 20-100mm and satisfying 15T R50T, where T is the thickness of the aluminum workpiece.

8. The electrode cap of claim 1, wherein the outer diameter d1 of the surface circumference on which the second surface is located is 8-15mm; and the height difference h1 between the outer diameter of the surface circumference where the second surface is positioned and the third surface is not more than 0.2T, wherein T is the thickness of the aluminum workpiece.

9. The electrode cap of claim 1 wherein the innermost annular ridge has a height of 50-200 μm.

10. A method of resistance spot welding, the method comprising:

(a) Providing a pair of electrode caps as claimed in any one of claims 1 to 9;

(b) And (3) a pre-pressing stage: respectively placing a pair of electrode caps on two sides of the stacked aluminum workpieces, performing pre-pressing, and enabling the innermost annular ridge of the electrode caps to be in contact with the aluminum workpieces, wherein the applied electrode pressure is 2000-8000N and the duration time is 200-1500 ms;

(c) And (3) electrifying and welding: conducting one or more sections of welding current, wherein the effective value of the welding current is 22KA-65KA, the center contact position of the aluminum workpiece corresponding to the annular ridge on the inner side is melted firstly to form a melting center along with the time, the aluminum workpiece on the outer side is deformed and expanded inwards and outwards gradually, the aluminum workpiece contacts with the third surface of the electrode cap, the first surface, the annular ridge on the outer side and the second surface on the outer side in sequence, and the melting center is expanded inwards and outwards simultaneously to form a complete aluminum melting core;

(d) Condensation: stopping welding current, maintaining the state of the electrode cap and the aluminum workpiece for 30-300ms, and solidifying the molten metal to form a complete welding spot.

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