WO2014040847A1

WO2014040847A1 - Method for the resistance welding of components with a variable progression over time of the welding current, and component composite produced thereby

Info

Publication number: WO2014040847A1
Application number: PCT/EP2013/067631
Authority: WO
Inventors: André SCHULZE; Heiko. RUDOLF
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2012-09-13
Filing date: 2013-08-26
Publication date: 2014-03-20
Also published as: CN104619451B; DE102012018098A1; CN104619451A

Abstract

The invention relates to a method for the resistance welding of components (110, 120), wherein a compressive force is applied to the components (110, 120) at the welding point by means of electrodes arranged on both sides of the components (110, 120) and the components are welded to one another, while forming a weld nugget (140), by means of a welding current passed via the electrodes. According to the invention the welding current has a variable progression over time that is distinguished by alternating high-current energizing phases and low-current or current-free cooling and solidifying phases, whereby a weld nugget (140) is formed by a number of interlayered and/or adjacent melt zones (132, 133). The invention also relates to a component composite (110/120) produced by this method.

Description

description

Method for resistance welding of variable time components of the

Welding current, and hereby manufactured component composite

The invention relates to a method for resistance welding of components, wherein at the weld by means of electrodes arranged on both sides of a pressure force is applied to the components and the components are welded together by means of a guided over the electrodes welding current to form a weld nugget.

The invention further relates to a manufactured by such a method

Component assembly.

In resistance welding, the components to be welded to the

Joint or weld with electrodes more or less strong

compressed and heated by a guided over the electrodes electric current or welding current until melting. After completion of the current flow, a welded joint forms at the connection point, including a so-called weld nugget (lenticular solidification of the melt or of the melts). By compression during and after the current flow (what also as

Resistance pressure welding or resistance spot welding can be designated) the formation of a particularly load-bearing welded joint between the components is supported.

DE 10 2007 062 375 A1 describes a method for resistance welding of components in which the welding current supplied to and removed from the welding point via the electrodes is detected and regulated. As a result, the formation of the weld nugget can be influenced as a function of various parameters.

The invention has for its object to provide a method of the type mentioned that the disadvantages associated with the prior art not or at least only to a reduced extent.

This object is achieved by a method according to the invention with the features of claim 1. With the independent claim, the solution of the problem extends to a composite component, which produced by the method according to the invention has been. Preferred developments and refinements emerge analogously for both subject matters of the invention both from the dependent claims and from the following explanations.

The method according to the invention for resistance welding of at least two components is distinguished by the fact that the welding current (guided by the components at the welding point through the components) has a variable time characteristic, which is characterized by alternating high-current energization phases and low-current or current-free cooling and solidification phases. whereby a nugget of several layered and / or juxtaposed (solidified)

Melting areas is formed.

A high-current energizing phase is characterized in particular by a current flow (at the welding point) with a relatively high welding current. The

Welding current can be, for example, in the range of 2 kA [kiloampere] to 16 kA, but also higher welding currents are possible. A low-phase cooling and solidification phase is particularly characterized by a current flow (at the weld) with a relatively low welding current, ie. H. eg less than 2 kA, marked. A current-free cooling and solidification phase is understood in particular to mean that no current flow (at the weld) is present in this phase.

The proposed variable time profile of the welding current with alternating high-current energization phases and low-current or current-free cooling and solidification phases leads according to the invention to a weld nugget of a plurality of nested and / or juxtaposed melt regions being formed at the weld. The various forms of the nugget

Melt areas are delimited from each other and / or differ in their metallurgical microstructure. The delimitation of individual melt areas can lead to an advantageous reduction or refinement of dendrites (by interrupting the dendrite propagation) in the respective microstructures. In this way, a nugget with special properties can be formed.

In a high current energizing phase, a melt with a certain

Expansion generated. In the subsequent cooling and solidification phase, a specific microstructure is formed in the melt region. In the next or

subsequent high-current energization phase is now created in the previously incurred Melting again at least one melt with a different extent, the previously formed microstructure is at least partially remelted to form a new melt. In the subsequent cooling and

Solidification phase is formed in the melt area again a certain microstructure, which has a different extent and / or a different metallurgical structure than the previously formed microstructure. And so on. This way a can

Be formed nugget with special properties, which also can be relatively small.

In the high-current energization phases, heat can also be introduced into the material regions adjacent to the weld nugget, the heat introduction being due to the cooling and solidification phases between the high-current ones

Energizing phases can be dosed. The heat introduced into the material regions adjacent to the weld nugget can bring about advantageous changes in properties.

It is preferably provided that the high-current Bestromungsphasen differ in terms of the length of time and / or the welding current. These

However, energization phases can also be the same length and / or the same

Have welding currents.

Furthermore, it is preferably provided that the welding current within a

high-current energization phase is constant. The welding current within a high-current energization phase can also be variable and, for example, increase or decrease.

It is particularly preferably provided that the pressure force applied by the electrodes to the components is maintained during the entire welding process. The welding process involves the placement of the electrodes, the subsequent first high current energization phase up to the last cooling and solidification phase. The permanently applied compressive force can be constant or variable.

The temporal length of the high-current Bestromungsphasen may be 50 ms [milliseconds] to 1000 ms, preferably 75 ms to 800 ms and especially 100 ms to 750 ms. The length of time of the cooling and solidification phases may be 10 ms to 1000 ms, preferably 20 ms to 750 ms and in particular 25 ms to 500 ms. Preferably, up to eight high current Bestromungsphasen are provided, which differ in terms of the time length and / or the welding current.

In particular, three high current Bestromungsphasen are provided. These are a pre-phase with a relatively low welding current, a main phase with a relatively high welding current and a post-phase with a relatively low welding current. The pre-phase, main phase and post-phase may also differ with respect to their length in time, wherein it is particularly preferred that the main phase is not only the strongest current, but also the longest energization phase.

It is particularly preferably provided that at least one and preferably both components are formed from a high-strength or ultra-high-strength steel material (or steel sheet material) and in particular from a press-hardened steel material (or steel sheet material). Higher and highest strength steel materials have a strength greater than 700 MPa [Megapascal], and more particularly greater than 1000 MPa. A press-hardened

Steel material has a strength of up to 1600 MPa and more. At a

Press hardened steel material, these high-strength material properties are achieved by a curing process in which a previously heated sheet material in a cooled tool formed (or held in shape) and cooled simultaneously. For this purpose, z. A 22MnB5 sheet metal or the like. Especially that

Resistance welding of press-hardened sheet metal parts with the method according to the invention proves to be very advantageous since a welded joint with high strength and good ductility (elongation properties) can be produced. As a result of the alternating high-current energization phases and low-current or current-free cooling and solidification phases, a relatively large amount of welding energy can be introduced at the weld into the components. On the one hand, this leads to a very high strength of the welded connection, although the weld nugget may be relatively small due to the interruption of the dendrite propagation. On the other hand, in the adjacent to the weld nugget material areas, due to the cooling and

Solidification phases between the high current energization phases, relatively high heat are introduced, whereby a conversion of the brittle martensitic microstructure is brought about in a finer-grained and ductile structure. As a result, a brittle and uncontrolled fracture behavior of the welded components on the

Welding point averted. A component composite produced by the method according to the invention comprises at least two components which are welded to one another at at least one weld point, including a weld nugget, in such a way that the weld nugget merges into one another

layered and / or juxtaposed (solidified) melt areas. The components are in particular sheet metal parts. The component composite is in particular a component composite for a motor vehicle body. It is preferably provided that at least one and preferably both components are formed from a high-strength or high-strength steel material (or steel sheet material) and in particular from a press-hardened steel material (steel sheet material), to which reference is made to the preceding explanations.

The invention will be explained in more detail below in a non-restrictive manner with reference to the schematic figures. The features shown in the figures and / or explained below may, regardless of specific feature combinations, be general features of the invention.

Fig. 1 shows a resistance welding process in a sectional view.

Fig. 2 shows the temporal force and welding current during the

Resistance welding process of FIG. 1.

FIG. 3 shows, in three individual sectional views, the formation of a weld nugget with the welding current profile shown in FIG. 2.

4 shows in a sectional view a further embodiment of a weld nugget.

Fig. 5 shows in four individual sectional views an alternative embodiment of a

Nugget.

Fig. 1 shows two components 1 10 and 120 which are pressed together at the weld shown with two electrodes 210 and 220 attached. The applied pressure force is designated by P. At the same time a welding current I is passed through the components 1 10 and 120 via the electrodes 210 and 220 at the weld. As a result, the components 1 10 and 120 are heated at the weld until melting. To

Switching off the welding current I solidifies the melt, whereby at the weld a welded joint is formed to form a weld nugget. The welding current I is typically an alternating current. The embodiment shown the Electrodes 210 and 220 are only examples. From the prior art, other electrode forms are known. Furthermore, from the prior art

Resistance welding method with only one electrode known, to which the invention can be applied as well. The components 1 10 and 120 are examples of press-hardened sheet-metal shaped parts.

According to the invention it is provided that the welding current I has a variable time course, which is characterized by alternating high current energizing phases and

characterized low-current or current-free cooling and solidification phases, whereby a weld nugget of a plurality of nested and / or juxtaposed melt areas is formed. This will be explained in more detail with reference to FIGS. 2 to 5.

Fig. 2 shows the timing of the pressing force P and the welding current I during a welding operation. In the horizontal direction (from left to right) the time course is shown. In the vertical direction is qualitatively the strength or welding current. The welding process begins at time 0 with the placement of the electrodes 210 and 220 and ends at time 1 with the lifting of the electrodes 210 and 220.

The time course of the compressive force P is shown in dashed line. By way of example, the compressive force P has a constant course of force during the welding process. The compressive force P can be, for example, between 1 kN [kilonewton] and 16 kN. The time course of the welding current I is shown in solid line. The welding current I has a variable time course, which is characterized by alternating high-current

Energizing phases B, D and F and current-free cooling and solidification phases C, E and G are distinguished. The energization phases B, D and F can be referred to as pre-phase, main phase and post-phase. The phase designated G can also be referred to as the Nachhaltephase. The phase labeled A can be called the retention phase. Preferred times for the individual phases are given above.

The welding process starts with a holding phase A. In this phase no flows

Welding current I. During the first energizing phase B (pre-phase), a melt is generated with a certain extent, resulting in the subsequent cooling and solidification phases C forms a relatively small weld nugget 131, as shown in Fig. 3a. As a result, the components 1 10 and 120 are held together by a material fit, which due to the very high-strength properties of the component materials for themselves subsequent second Bestromungsphase D (main phase) is advantageous because the components 1 10 and 120 by means of the electrodes 210 and 220 otherwise not sufficient

can be pressed together to ensure an optimal flow of current (by reducing the contact resistance) and to avoid spatter.

In the second energizing phase D (main phase), wherein this energizing phase is longer than the first energizing phase B and the welding current during this energizing phase is higher than in the first energizing phase B, a melt is generated with a certain extent, wherein the previously formed nugget 131rd is completely melted. In the subsequent cooling and solidification phases E, a relatively large weld nugget 132 is formed, as shown in FIG. 3b. The welding lens 132 is carrier of the edge stresses to the components 1 10 and 120th

In a third energizing phase F (post-phase), wherein this energizing phase is shorter than the second energizing phase D and the welding current during this Bestromungsphase is lower than in the second Bestromungsphase D, within the weld nugget 132, a melt is generated with a certain extent. In the subsequent cooling and solidification phases G (retention phase), an internal weld nugget 133 forms within the weld nugget 132, as shown in FIG. 3c. Advantageously, thereby any dendrites (tree or shrubby

Microstructures) in the outer weld nugget 132, resulting in a finer texture and concomitant improved ductility

Brittle fracture tendency and higher strength leads.

The welding lens, generally designated 140, is thus composed of several solidified melt regions 132 and 133, wherein the different melt regions 132 and 133 forming the weld nugget 140 are delimited from one another and / or differ in their metallurgical microstructure. The structure or the

The composition of the weld nugget 140 can be compared to the construction of an onion (onion-like structure or onion-like structure). The weld nugget 140 may also be referred to as a "lens in lens" with the fusion line of the inner ones

Welding lens 133 extends completely within the outer weld nugget 132. An exemplary study showed that the weld joint comprising such weld nugget 140 has both high strength and good ductility. This is partly due to the fact that the adjacent to the weld nugget 140 Material areas by the introduced welding energy have undergone a heat treatment, as explained above.

4 shows a welded joint between the components 110 and 120 in which the "onion-like" weld nugget 140 comprises a further internal weld nugget 134, which was brought about by a fourth energization phase according to the above explanations cut off in the center weld nugget 133.

FIG. 5 shows in analogy to FIG. 3 in four individual views the alternative embodiment of a weld nugget 140 which has a plurality of juxtaposed and stacked ones

Has melting areas. With regard to FIGS. 5a and 5b, reference is made to the above explanations in connection with FIGS. 3a and 3b.

Starting from the state shown in Fig. 5b is shown by a third energizing phase of the state shown in Fig. 5c, in which two further welding lenses or

Melting areas 135 a between the large weld nugget 132 and the outer surfaces of the components 1 10 and 120 are formed, brought about. After a cooling and

Solidification phase or optionally without such Abkühl- and

Solidification phase is brought about by a further energization phase of the final state shown in FIG. 5d, in which the two melt regions 135b penetrate the weld nugget or the melt region 132 and touch or adjoin one another approximately in the parting plane between the two components 110 and 120. In this case, the weld nugget 140, which is designated as a whole by 140, is composed of a plurality of solidified melt regions 132 and 135b, which are both adjacent to one another and also stacked or nested or interleaved one inside the other.

LIST OF REFERENCE NUMBERS

1 10 first, lower component

120 second, upper component

131 welding lens or melting area

132 weld nugget or melt area

133 Welding lens or melting area

134 Welding lens or melting region 135a / b Welding lens or melting region 140 Welding lens

210 electrode

220 electrode

A ... G phases of the welding process

I welding current

P pressure force, electrode force

0 Starting point of the welding process

1 end point of the welding process

Claims

claims

Method for resistance welding of components (1 10, 120), wherein at the weld by means of both sides of the components (1 10, 120) arranged electrodes (210, 220) a compressive force (P) is applied to the components (1 10, 120) and the components (210, 220) by means of a guided over the electrodes (210, 220)

Welding current (I) are welded together to form a weld nugget,

characterized in that

the welding current (I) has a variable time characteristic which is characterized by alternating high-current energizing phases (B, D, F) and low-current or current-free cooling and solidifying phases (C, E, G), whereby a welding lens (140) consists of a plurality of nested layers and or

adjacent melt areas (132-135) is formed.

Method according to claim 1,

characterized in that

the energizing phases (B, D, F) differ with regard to the length of time and / or the welding current intensity.

Method according to claim 1 or 2,

characterized in that

the welding current is constant within an energizing phase (B, D, F).

Method according to one of the preceding claims,

characterized in that

the pressure force (P) applied by the electrodes (210, 220) to the components (110, 120) is maintained during the entire welding process.

5. Method according to one of the preceding claims,

characterized in that

the time length of the energization phases (B, D, F) is 50 ms to 1000 ms, preferably 75 ms to 800 ms and in particular 100 ms to 750 ms, and / or that the time length of the cooling and solidification phases (C, E, G ) Is 10 ms to 1000 ms, preferably 20 ms to 750 ms and in particular 25 ms to 500 ms.

6. Method according to one of the preceding claims,

characterized in that

up to eight high current Bestromungsphasen are provided, which differ in terms of their time length and / or the welding current.

7. Method according to one of the preceding claims,

characterized in that

three high-current Bestromungsphasen (B, D, F) are provided: a pre-phase (B) with a relatively low welding current, a main phase (D) with a relatively high welding current and a post-phase (F) with

relatively low welding current.

8. Method according to one of the preceding claims,

characterized in that

at least one and preferably both components (1 10, 120) made of a high-strength or high-strength steel material and in particular of a press-hardened

Steelmatetrial are formed.

9. composite component produced by a method according to one of the preceding

Claims has been made, with at least two components (1 10, 120) which are welded together at least one weld with the inclusion of a weld nugget, characterized in that

the weld nugget (140) has a plurality of nested and / or nested ones

having juxtaposed melt areas (132-135).

10. component composite according to claim 9,

characterized in that

Steelmatetrial are formed.