DE102007062375A1 - Spot-welding process used in automobile industry, first heats, softens and deforms weld location to eliminate dimensional and location errors, before applying full welding current and pressure - Google Patents

Abstract

At the spot weld location (5) a given control force (F R) is reached between the welding electrodes. A current causing heating and deformation (I U) is then supplied. Simultaneously, the electrodes (3, 4) apply a deformation force (FU) to the components being joined (1, 2), at least at specific locations. Forces applied at the electrodes (F1, F2) are measured with respect to time and/or displacement. They are controlled independently of each other. The forces or pressures applied, are varied in accordance with a program. Current (I) supplied via the electrodes to the weld location is measured and controlled as a function of time and/or displacement. The deformation force (F U) is increased following local deformation, until the given welding force (F S) is reached. The deformation force is applied to the weld location at the same instant (t5) that the deformation current is supplied, or there is a short interval between these actions. Increase in deformation force to reach the welding force, takes place earlier than the corresponding increase from deformation current to welding current. Reduction of welding pressure is initiated at the same instant (t8) as reduction in the welding current. The electrode forces are produced by an electrode drive and/or a spot-welding tong equalization drive.

Description

The The invention relates to a method for resistance welding arranged of components between two sides of the components Electrodes, in particular welding tongs, in which by the two electrodes in each case a compressive force on one with applied to a weld joint to be provided and the components by means of one over the electrodes supplied welding current welded together while the electrodes are the juncture respectively act on a predetermined welding pressure, wherein the pressure forces of the two electrodes are controlled in such a way that the two electrodes are the junction first apply a predetermined control force and that the compressive forces the two electrodes then each to the specified Welding pressure to be increased.

At the Resistance welding generates an electrical resistance in a welding zone at an electrical current passage a heat required for welding. By this heat will be the components to be connected by Melting heated. After the current flow arises after re-solidification the melt a welded joint. By squeezing during and after the current flow is in resistance welding supports the formation of an intimate connection of the components.

Welding machines, For example, welding tongs, weld the Components mostly under dimensional deviations, since the spatial coordinates of Components or the component flanges and / or the welding tongs were not set exactly or the components later have moved. Also the components to be welded may have a deviation from the nominal dimension after their production. When assembling such non-dimensional components is the deviation usually amplified. When welding Are the components or the component flange by the welding gun or by the pressure forces applied by means of the electrodes brought into the specified size or transferred to the desired position. The components are reshaped locally by these dimensional deviations and welded together under tension. The result is spatter, deep electrode impressions in the components, a bad Weld point strength and non-dimensional accuracy the joined components.

A method of the type mentioned is already from the WO 03/008146 A1 known. In this case, a welding gun is moved by means of a robot such that the two electrodes of the welding gun each act with the same control force on the components to be welded. In this position, the robot stops and the welding gun builds the final electrode force for welding. As a result, the components or the component flange are deformed strongly plastic and elastic cold. During welding of the components, mechanical stresses are thus frozen in and above the welding point, which then act as an additional load on the welding point during use of the welded components. This reduces the strength of the welds and the process reliability of the process. Dimensional deviations of the components or position deviations of the components or of the component flange can not be compensated. The result is non-dimensional assemblies and non-standard welds.

Other methods for resistance welding of components are described in EP 1 428 608 B1 , of the DE 103 28 593 A1 and the DE 199 55 691 A1 disclosed.

In front In this background, the invention is based on the object Specify method of the type mentioned, with the help Dimensional and position deviations of the components compensated and producing a welded joint with improved Goodness is enabled.

These The object is achieved by a method according to Features of claim 1. The dependent claims relate particularly expedient developments of the invention.

According to the invention, therefore, a method is provided, in which the connection point is supplied after reaching the predetermined control force, a bonding point warming Umformstrom and the electrodes act on the joint each with a component at least partially deforming forming force. By heating the joint, this is soft and can be locally deformed under the action of a low forming force and that until the components collide in the region of the joint. As a result, the components can be welded virtually stress-free and component tolerances compensated balanced. Furthermore, the component or flange position can be corrected if they deviate from the target specification. The components are only very slightly elastically deformed by the hot forming, which in particular the springback forces of the components are considerably reduced after the actual welding process. By reducing the mechanical stresses introduced in the components and the springback forces, the quality and reproducibility of the spot welds as well as the process reliability of the process are significantly improved. Gleichzei tig drop by the method according to the invention, the requirements for the dimensional stability of the components, whereby significant cost savings in the manufacture of components and other upstream processes can be achieved.

A particularly advantageous embodiment of the method is also characterized created that the pressure forces of the two electrodes Time and / or path-dependent recorded and independent be regulated by each other. This allows the connection point from either side with the same or different in a desired relative relationship Pressure forces are applied. The contact pressure to the Contact points between the respective electrode and the component and the contact pressure between the components can be adjusted and thereby the contact resistance can be influenced. By means of the Contact pressure or the contact resistance, the heat development controlled in the component and the formation of the as welding nugget trained weld point to be influenced. For example the nugget can be moved or the number and the formation of the welding lenses can be variable be set. The regulation of the pressure forces takes place depending on the component material and the component thicknesses as well as depending on whether two or more components to be welded together.

Farther it proves to be useful when the compressive forces be changed in a power program. Here you can depending on the number of welds to be welded Components, component materials and component thicknesses different force characteristics be provided for the pressure forces or adjusted become. Ramps and pulses can also be driven which in particular influences the heat development in the connection plane becomes.

In a further variant of the invention Method is provided that of the connection point over the electrodes supplied current time and / or path-dependent is recorded and regulated. This may cause the formation of the weld nugget depending on the temperature behavior of the components, the Alloying and the Aufmischungsgrades be influenced. At the same time, an adaptation of the current profile to the pressure force curve is made possible.

there it has proven to be particularly practical that the supplied Current in a power program is changed. The power program is advantageously on the selected or set Power program matched, with ramps also in the power program and pulses can be driven.

Thereby, that the forming force after the sectional deformation of the components is increased until reaching the predetermined welding pressure, can immediately after the hot forming of the components in the Area of the junction of the actual welding process be initiated. This can in particular the process time the process of the invention can be reduced.

A further reduction of the process time is also achieved by that a start of the application of the junction with the Forming force and a start of the supply of Umformstromes at the same time or at a short time interval respectively. As a result, the connection point is supplied Energy used particularly effectively.

A Another advantageous embodiment of the present invention Procedure is also created by starting to increase the forming force on the welding pressure force earlier occurs as a beginning of the increase of the forming current the welding current. This will achieve that the joint of the for the welding provided contact pressure has already formed when the welding current is supplied. Due to the contact pressure or the contact pressure Dependent contact resistance can be the heat development controlled in the components and the formation of the weld nugget to be influenced.

to further improvement of the welding result is provided that is the beginning of a reduction in welding pressure and a beginning of a reduction in the welding current take place at the same time. This results in a defined Formation of the weld nugget in the area of the joint instead of.

A again another advantageous development of the present method is also created by the pressure forces of the two electrodes by a working drive associated with the electrodes and / or a pliers balancing drive are generated. The pliers balancing drive is faster and more accurate than a robot, for example has lower mass and reacts much better.

The Invention allows for numerous embodiments. To further clarify its basic principle, one of them is in the drawing and will be described below. These shows in

1 a current-force-time diagram for a method according to the invention for resistance welding of two components;

2 a time sequence of a method for resistance welding of components according to the prior art;

3 a temporal sequence of the method according to the invention for resistance welding of components.

1 shows a current-force-time diagram for a method according to the invention for resistance welding of two components 1 . 2 , between two sides of the components 1 . 2 arranged and relative to the components 1 . 2 movable electrodes 3 . 4 , In the diagram is for the two electrodes 3 . 4 in each case a pressure force F ₁ or F ₂ and a welding current I applied over a process time t in the form of two pressure force curves F ₁ (t) and F ₂ (t) and a current profile I (t).

The diagram is subdivided into a total of five time segments I to V, wherein the individual process steps of the method according to the invention are assigned to the time segments I to V, respectively. In a first period I, the two electrodes 3 . 4 in the direction of the components 1 . 2 proceed until the electrode 3 during the second period of time, the upper component 1 at a time t1 in the region of a connection point 5 contacted and acted upon at a time t2 with a control force F _R. The second electrode 4 meanwhile is not in contact with the lower component 2 , During the third period III now also contacts the second electrode 4 at a time t3, the lower component 2 until the electrode 4 the connection point 5 At a time t4, a reaction force F _{R is} applied, so that both electrodes 3 . 4 the connection point 5 apply an equal control force F _R. After both electrodes 3 . 4 the connection point 5 acted upon by the same control force F _R, the connection point 5 at a time t5 across the electrodes 3 . 4 one the components 1 . 2 heating forming current I _U supplied and the control force F _R is increased until both electrodes 3 . 4 the connection point 5 pressurize each having a same deformation force F _U. This will make the components 1 . 2 locally reshaped until they are in the area of the junction 5 collide. After the hot forming of the components 1 . 2 During a fourth time interval IV, the forming force F _{U is} increased (t6) until both electrodes are pressed 3 . 4 the connection point 5 each act on a predetermined welding force F _S. In addition, the forming current I _{U is} increased (t7) until the predetermined welding current for the welding process I _{S is} reached. This forms in the region of the connection point 5 one the components 1 . 2 connecting weld nugget 6 out. After welding the components 1 . 2 the supply of welding current is terminated (t8) and the junction 5 is by retracting the electrodes 3 . 4 relieved to its initial position (period V).

The 2 shows a temporal sequence of a method for resistance welding of two components 1 . 2 according to the prior art in a schematic representation. First, the electrodes 3 . 4 in a first method step a on the components 1 . 2 to move and apply the components 1 . 2 in the process steps b and c each with a directional arrows 7 symbolized pressure force F ₁ and F ₂ . As a result of the pressurization, the components 1 . 2 plastically and elastically deformed and it will be by directional arrows 8th illustrated mechanical stresses in the components 1 . 2 initiated. In the further course (step d) is the components 1 . 2 over the electrodes 3 . 4 a welding current I _U fed while the components 1 . 2 are respectively applied with a pressing force (weld force F _S). This forms between the components 1 . 2 one as a nugget 6 formed weld joint. When returning the electrodes 3 . 4 (Step e) load strong, dashed arrows 9 illustrated, springback forces the welded joint. By these spring-back forces and when welding in the components 1 . 2 initiated mechanical stresses, the strength and process reliability of the weld or process are significantly reduced.

3 shows the temporal sequence of the inventive method for resistance welding of two components 1 . 2 in a schematic representation. First, the electrodes 3 . 4 on the components 1 . 2 moved to (step a) and act on the components 1 . 2 in a second process step b each with a directional arrows 7 symbolized pressure force. If both electrodes 3 . 4 the components 1 . 2 with an equal control force F _{R act} on the electrodes 3 . 4 a Umformstrom I _U supplied and the control force F _R increases, until a predetermined forming force F _U is reached. This will make the components 1 . 2 locally heated and reshaped so that they collide under the desired electrode forces (steps b and c). This hot forming process reduces the required electrode pressure and components 1 . 2 or brought the component flange in the predetermined desired position. In addition, thereby the welding process (step d) in the components 1 . 2 introduced mechanical stresses (direction whistle 8th ) significantly reduced. Also when returning the electrodes 3 . 4 (Step e) occurring springback forces (direction arrows 9 ) are minimized by the hot forming process preceding the welding process. Furthermore, the strength of the welded joint is improved and the welding process or the weld nugget 6 is reprodu ible. Also the requirements for the dimensional accuracy of the components to be welded 1 . 2 become smaller. The components 1 . 2 or the component flange are first adjusted by the method according to the invention or by the welding tongs to the desired position or the desired dimension and then the components 1 . 2 welded in comparison to the prior art significantly lower component voltages.

In addition, by means of the method according to the invention, in particular by means of a force difference control of the welding tongs, the formation of the weld nugget 6 to be influenced. In this way, the contact pressure at the contact points, in particular at the electrode component and the component-component contact can be adjusted and thereby the contact resistance can be influenced. This is the heat in the components 1 . 2 controlled and the nugget 6 can be moved as desired, for example in the direction of the lower component 2 , which is particularly advantageous when welding different thickness sheets, multi-sheet metal and sheets with different alloys.

For the implementation of the invention Procedure only needs a new software in a control unit an existing plant for resistance welding installed become.

1

component

2

component

3

electrode

4

electrode

5

junction

6

nugget

7

arrow

8th

arrow

9

arrow

F ₁

thrust

F ₂

thrust

F ₁ (t)

Pressure force curve

F ₂ (t)

Pressure force curve

F _R

regulating force

F _U

forming force

F _S

Welding pressure force

I

electricity

I (t)

current profile

I _U

Umformstrom

I _S

welding current

I

period

II

period

III

period

IV

period

V

period

t

process time

t1

time

t2

time

t3

time

t4

time

t5

time

16

time

t7

time

t8

time

a

step

b

step

c

step

d

step

e

step

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 03/008146 A1 [0004]
• - EP 1428608 B1 [0005]
• - DE 10328593 A1 [0005]
• - DE 19955691 A1 [0005]

Claims (10)

Method for resistance welding of components ( 1 . 2 ) between two sides of the components ( 1 . 2 ) arranged electrodes ( 3 . 4 ), in particular a welding tongs, in which by the two electrodes ( 3 . 4 ) each have a compressive force (F ₁ , F ₂ ) on a provided with a weld joint ( 5 ) is applied and the components ( 1 . 2 ) by means of a via the electrodes ( 3 . 4 ) Supplied to the welding current (I _S) are welded together, while the electrodes ( 3 . 4 ) the connection point ( 5 ) each act on a predetermined welding pressure force (F _S ), wherein the pressure forces (F ₁ , F ₂ ) of the two electrodes ( 3 . 4 ) are controlled in such a way that the two electrodes ( 3 . 4 ) the connection point ( 5 ) first apply a predetermined control force (F _R ) and that the pressure forces (F ₁ , F ₂ ) of the two electrodes ( 3 . 4 ) are then each increased to the predetermined welding pressure force (F _S ), characterized in that the connection point ( 5 ) after reaching the predetermined control force (F _R ) a the connection point ( 5 ) warming Umformstrom (I _U ) is supplied and the electrodes ( 3 . 4 ) the connection point ( 5 ) each with a component ( 1 . 2 ) act on at least partially deforming forming force (F _U ). A method according to claim 1, characterized in that the pressure forces (F ₁ , F ₂ ) of the two electrodes ( 3 . 4 ) are time-dependent and / or path-dependent detected and regulated independently of each other. Method according to claims 1 or 2, characterized in that the pressure forces (F ₁ , F ₂ ) are changed in a force program. Method according to at least one of the preceding claims, characterized in that that of the connection point ( 5 ) over the electrodes ( 3 . 4 ) supplied current (I) time and / or path-dependent is detected and regulated. Method according to at least one of the preceding Claims, characterized in that the supplied Current (I) is changed in a current program. Method according to at least one of the preceding claims, characterized in that the forming force (F _U) after the portion-wise deformation of the components ( 1 . 2 ) is increased until reaching the predetermined welding pressure force (F _S ). Method according to at least one of the preceding claims, characterized in that a start of the application of the connection point ( 5 ) With the forming force (F _U ) and a start of the supply of Umformstromes (I _U ) at a same time (t5) or in a short time interval. Method according to at least one of the preceding claims, characterized in that a beginning of the increase of the forming force (F _U ) on the welding pressure force (F _S ) takes place earlier than a beginning of the increase of the forming current (I _U ) to the welding current (I _S ). Method according to at least one of the preceding claims, characterized in that a beginning of a reduction of the welding pressure force (F _S ) and a beginning of a reduction of the welding current (I _S ) take place at the same time (t8). Method according to at least one of the preceding claims, characterized in that the pressure forces (F ₁ , F ₂ ) of the two electrodes ( 3 . 4 ) by a the electrodes ( 3 . 4 ) associated working drive and / or pliers balancing drive can be generated.