CN102950373B - Welding method for the resistance spot welding of Al alloy parts - Google Patents

Abstract

The surface of acieral workpiece has and suppresses and the pellumina of the good contact of the binding face of sheet-material work piece for welding of lifetime of resistance spot welding electrode solder side and such as lamination.Sometimes, the surface of sheet material is also coated with binding agent or sealant, and this makes welding complicate further.But according to the present invention, the solder side of relative circular brazing electrode presses to the opposed outer surfaces of this sheet material, and applies welding current preferably to form each weld seam according to three stage welding schemes to electrode at stitch bond location.This welding scheme comprises regulation stage (stage 1), nugget shaping stage (stage 2) and nugget size regulation stage (stage 3).

Description

Welding method for the resistance spot welding of Al alloy parts

This application claims the rights and interests of provisional application 61/527155 based on entitled " for the welding scheme of resistance spot welding of Al alloy parts " submitted on August 25th, 2011, it is incorporated herein by this reference.

Technical field

The present invention relates to laminated aluminum base alloy workpiece (stack aluminum-base Alloy workpieces) in improvement in terms of resistance spot weld (resistance spot weld) formation.More specifically, the present invention provides a kind of method, use and apply current value and time so that the solder side of electrode preferably engages (engage) aluminum workpiece with changing with three single steps or stage in this type of resistance spot welding, preferably to cause the formation of melted nugget (weld nugget) at binding face (faying surface) center, contact area, in order to quickly realize target spot welding nugget size.

Background of invention

Resistance spot welding generally includes and the surface, circular weld face (weld face surface) of two relative high conductivity copper electrodes is pressed in two or three overlapping metal sheets is sometimes referred to as " lamination (stackup) ") opposition side on (, and in-between the electrodes the some milliseconds of galvanization to hundreds of millisecond through this sheet material to form nugget at sheet material-sheet interface (interface of referred to as fitting) place.

The aluminum workpiece (usually containing 85 weight % or the acieral of more aluminum) resistance spot welding under large volume is considered as extremely difficult because of Railway Project in the automotive industry.This workpiece may often be such that the aluminum alloy sheet of rolling, but can be extrusion or the foundry goods with the complementary shape being suitable to spot welding.When the acieral plate of complementary shape puts together and is connected by a series of spot welding in position, described aluminum workpiece can be coating on surface, equal or different thickness, identical or different aluminium alloy, it is possible to there is the binding agent or sealant applied along welded flange (weld flange).Can there is little gap between the plate of assembling, one or two relative welding electrode can be placed to be slightly different to the angle of its expection welding position.

Tough and tensile, that adhere to, nonconducting oxidation film is there is in one of subject matter on this aluminium base surface.It is the most overheated that this oxidation film can cause in electrode/sheet interface and sheet material-sheet material laminating interface.Electrode/common solution of sheet interface problems of excessive heat includes that using design to have reduces electric current density and thus reduce the electrode of the big and smooth solder side that these positions are heated.Big and smooth electrode is used to produce unacceptable consequence to manufacturing.The electrode 1 of these types) sensitive to the gap between workpiece, 2) sensitive to electrode directional (electrode orientation), i.e. tilt relative to surface of the work or off normal, and 3) need big flange to coordinate the solder side on big electrode body diameter and electrode on workpiece.

Several electrode design and the trim process that solve these problems can find in patent or patent application, including herein inventor's and have by assignee of the present invention one or two: United States Patent (USP) US 6,861,609(3/1/2005) with U.S. Patent application disclosed in 20100258536,20090302009,20090255908,20090127232,20080078749.Oxidation film problem and the electrode/sheet material caused are overheated by disposing geometric properties, as the micro-texture (micro texture) on solder side or a series of burr solve with groove, these geometric properties penetrate the oxide skin(coating) on aluminum to reduce contact resistance and the heating of this interface under weld load.Electrode/sheet material heating minimizing has two direct benefits.First, it allows use the less electrode with less thermal mass, it reduce flange requirement.Secondly, it is allowed to use the more sharp electrode welding face curvature (can preferably concentrate welding current).This makes this welding process the most sensitive to the existence in gap between electrode orientation on workpiece (i.e. electrode tilts relative to workpiece) and surface of the work.

Although achieving the improvement of processing performance aspect highly significant by solving the problem of high contact resistance at electrode/sheet interface, it is considered the most problematic needs before manufacture is the most pervasive on a large scale is solved in spot welding aluminum process.These problems many relate to there is surface oxide film at sheet material-sheet material or laminating interface, and this is not affected by electric welding junction improvement.These problematic portion relate to the character being generally used for the direct current welding procedure (it is so-called Medium Frequency Direct Current or MFDC) of car aluminum welding.The method uses contravariant welding controller (inverter type weld Control), its receive 480 volts of rms(in the U.S.) three-phase, 60Hz exchange electromotive force and under the frequency of about 1000Hz to MFDC transformator provide higher voltage about 650 volts single-phase square wave.The more significantly lower weldingvoltage (such as, being 13 volts under 50:1 transformer turn ratio) that the high voltage waveform that welding controller provides is reduced under more much higher electric current by this transformator.The low-voltage square wave output of transformator is transported to the DC electric current of welding electrode and workpiece lamination subsequently with high current capacity diode rectification with offer.During the configuration for manufacturing many same welding on a series of workpiece, predetermined suitable welding current and weld interval.Subsequently MFDC welding controller is programmed will to be delivered to press to the welding electrode of workpiece close to constant electric current (such as, 20 five to three ten kiloampere) in the welding interval of about 250 to 300 milliseconds.During any DC, wherein by current programmed be close to constant, as used during MFDC, when contact with aluminium base, one electrode (positive pole) is run obvious hotter than other electrode (negative pole).The temperature deviation of electrode can affect nugget formation and growth, particularly with thickness (that is, thick/thin ratio of height) and material (being such as welded on aluminium alloy 6111-T4 sheet by aluminium alloy 5754-O) asymmetric sheet-material work piece lamination.AA5754-O composition be limited to 2.6-3.6% Mg, < Si of 0.4%, < Mn of 0.5%, < Fe of 0.4% and < the Cu(surplus of 0.1% is essentially all aluminum), and AA-6111-T4 composition age-hardenable is limited to the Mn of Si, 0.1-0.45%, < Cu of Fe and 0.5-0.9% of 0.4% of Mg, 0.6-1.1% of 0.5-1.0.This can cause more preferable than other direction relative to polarity of electrode direction superimposed layer welding, including in one direction than producing the weld penetration (weld penetration) of bigger weld seam or bigger on other direction, this is unsatisfactory in production run.Additionally, the positive pole of hotter operation is more easy to wear, thus shorten electrode life because needing finishing frequently.

In addition to polarity effect, the standard constant current welding scheme of the production application having been used for spot welding aluminum can manufacture other unacceptable problem.These schemes apply constant current, such as 27 kiloamperes based on being set the time (such as 200 milliseconds (ms)) under the electrode constant force to surface of the work.The problem having been found that includes that wear to electrodes is excessive, the weld spacing sensitivity of big thickness lamination, the inconsistent size welded first and quality, cause the weld seam microstructure (weld microstructure) of unacceptable welding breaking pattern and cause too early splash and deteriorate the weld appearance of welding quality.Unacceptable fracture mode (it exists stripping or tensile load) includes the welding breaking along laminating interface or the fracture of nugget periphery, thus cannot form the ball (button) passing completely through sheet thickness.Finally, standard constant current welding scheme is the most pervasive in the presence of sealant or binding agent.When there is binding agent or sealant, these schemes often lead to the nugget with more defect, and this nugget tends to unacceptable mode fracture, especially when imposing peeling load.

The improvement of the resistance spot welding that need nonetheless remain for aluminum alloy sheet metal works and other workpiece section bar is implemented.

Summary of the invention

The lamination (assembly) using two or three acieral sheet-material work piece is described the enforcement of the present invention.Sheet-material work piece is generally of the thickness of about 0.5 to about 4 millimeter, and the lamination for welding can be formed by identical or different aluminium alloy and have different thickness.In many welding operations, the weld seam more than can be concurrently formed on the lamination of sheet material, and use welding equipment to arrange device during work shift to form hundreds of weld seams on many laminations.Welding equipment and technique must be managed reliably and repeatedly to manufacture homogeneous good weld seam on Al alloy parts.

Embodiment of the present invention are based on the finding that by changing welding current in each resistance spot weld forming process in different welding stages or step, can be formed more reliably good weld seam on aluminum workpiece.According to embodiment of the present invention, welding current applies with varying level during three particular step in each spot welding cycle, has cool time or " stopping " time between each step.The equipment that unidirectional current waveform is transported to welding electrode generally includes the high conductivity arm or the welding gun of high conductivity cable having for electric current is delivered to electrode, MFDC transformator, and contravariant programmable electronic controller.In order to provide the suitable waveform of the aluminum workpiece for welding of automotive specification, this welding system, the most programmable contravariant welding controller, MFDC transformator and welding gun allow for the programming scheme to determine in welding job setting up procedure and provide the output of high electric current and the fast rise time (rise times) being transported to welding electrode.This base part of this welding system is commercially available.The current rise time recorded at electrode should the most about 10 milliseconds to reaching 40 kiloamperes, or about 4 kiloamperes/millisecond.The significantly slower rise time will produce required waveform unsatisfactorily, and welding performance is by impaired.Each part of welding gun system, i.e. control, transformator and rifle, affect maximum current output and current rise time.

The first stage of our dot welding method is considered as regulation stage or step.When two relative welding electrodes have disposed to be engaged the two opposite sides of the such as lamination of two sheet-material work piece with predetermined stabilization clamp clamp force, this step starts.Run the voltage that Electronic Control is carried by welding transformer with restriction.This can control to realize for suitable automatic voltage compensation model (AVC) or icotype by making welding able to programme.As the replacement of voltage compensation mode, can with constant current mode with flat grade through 10 milliseconds or more for a long time from low current value (about 3 kiloampere) until final required regulation electric current is exchanged current and is programmed.Equally, it is therefore intended that obtain consistent, stable resistance in welding site, without making this sheet material melt in laminating interface.Electric current is through several milliseconds of levels being gradually increased to resistance is reduced at electrode/sheet interface with following binding face consistent low value.In many welding are arranged, electric current is improved to about 10 kiloamperes by about 3 kiloamperes.Generally, it is preferred to by electric current regulation to being just below the level of electric current when substrate starts melted.The electric current in regulation stage keeps about 20 milliseconds to about 60 milliseconds.Electric current suitably keeps a period of time to stablize and consistent levels of current to obtain.

During regulating step, electrode/workpiece interface is heated；The formed features making electrode welding face can preferably through oxide coating and contact with surface of workpiece.The resistance recorded between electrode reduces, and the nugget being better equipped to now be provided for melting causes and growth.About 10 milliseconds of electric current was cut off to cool down electrode by welding controller before the next stage of this pinpoint welding procedure.The length of stop time makes levels of current decay to zero.Longer cool time can be used, but only can reduce the volume of production of welding machine.

The second stage of our pinpoint welding procedure is a weld through nugget shaping stage.Design this shaping stage with cause good, circular, concentrate (on the axle of contrary electrode), the formation of melted nugget, and do not consider angle orientation (alignment) that workpiece is slightly slanted by the polarity of welding electrode or electrode or the undesirable assembling of workpiece or presence or absence non-metallic cement or sealant at binding face.This can realize through relatively short time (such as, about six to ten milliseconds and the minimum time of the most about six to five ten milliseconds) flowing with relatively high value (such as 20 kiloamperes are to 50 kiloamperes) by making electric current.High target current and short time need to use suitable welding system parts.As it was previously stated, in order to realize target forming current through these of short duration times, it is necessary to it is suitably designed contravariant welding controller, MFDC transformator and welding gun to be capable of target current and current rise time.Rise time prevents from reaching target current in the little time window of forming step slowly, and this is necessary for the function of this step.Rise time can be because welding slowly and control hardware or software, not enough MFDC transformer voltage or high welding gun inductance slowly.The purpose of high current step is to cause in laminating interracial contact district center as quickly as possible to form liquid (melted) nugget.When managing to initially form the nugget suitably with at least about three mm dias, this stage is the shortest.Levels of current remains sufficiently low to avoid the adhesion between electrode and workpiece and avoids the metal expulsion at electrode/sheet interface.The electric current of welding aluminum workpiece setting and the determination of time can be determined by experience and/or test.The splash of laminating interface can occur, but owing to melted nugget is also not fully developed, final nugget structure or form are not resulted in destruction.If it is considered to be necessary to use the curring time more than about 30 milliseconds, two shorter current impulses with intercooling or stop time are preferably used to reduce electric current.

Once nugget shapes and is complete, and by controller, electric current is closed about 5 milliseconds to make it decay.The purpose of this type of electric current stop time is dual.First, it allows the certain cooling at electrode-sheet interface.Secondly, prevent the melted nugget caused overheated.Remove the overheated and serious interface splash during this cooling step often results in size regulating step.The nugget cooling that order causes contributes to controlling this process.But, cooling step can not be long, because there is nugget solidification.If nugget solidifies, it will cause short circuit (short) between sheet material, and the further electric current during size regulates will not obtain required weld size.

The phase III of this welding process regulates for growth and the size of the just nugget of initiation.This size regulation stage is started when nugget is still in molten condition.The welding current lower than in nugget shaping stage is used in the size regulation stage.Such as, the welding current of about 15 to about 40 kiloamperes is suitable to this phase III.Thickness according to sheet material the thinnest in two sheet stacks and determine size regulating time according to the thickness of the second thin sheet material in three sheet stacks.Sheet material to two millimeters thick manufactures the nugget of appropriate size, such as diameter about six millimeters.Regulation electric current nugget size needed for obtaining.The persistent period in this stage is the longest in whole welding scheme, it usually needs about 20 milliseconds to about 200 milliseconds.If welding electrode excessive wear, preferably electric current is split into and have approximately ten to about 30 milliseconds of heating and continuous phases (working time) and the pulse of the of short duration cool time (stop time) of one millisecond to ten milliseconds.

In addition to the of short duration cool time between the spot welding stage, this welding process is continuous print, it usually needs the total weld interval (the merging time of step 2 and step 3) more shorter than conventional MFDC or the AC spot welding of aluminum.Have been found that the three stage welding schemes of the present invention manufacture good welding more reliably, and realize this result in the formation of many weld seams.Additionally, consumption less electrical energy.

The present invention includes following aspect:

1. the method forming resistance spot weld on acieral workpiece, described method includes:

Forming the lamination of the sheet material of two or more acieral workpiece, the workpiece of this lamination has binding face and has contrary outer surface in this welding position in resistance welding position；

The solder side of relative resistance welding electrode is pressed at this welding position the described outer surface of this workpiece；This solder side is pressed to this workpiece simultaneously,

First stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the very first time of Millisecond, this electric current is improved to the first stage current value making resistance between described solder side be reduced to certain steady resistance value, and heat this workpiece to engage with described solder side, without melting this workpiece at their binding face, subsequently, at once by current reduction to zero, and described electrode still presses to the described surface of this workpiece；

Second stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the second time of Millisecond, this peak point current is risen above the second stage current value of first stage current value, for causing melted nugget to be formed at the binding face of this welding position, and reduce electric current, and described electrode still presses to the described surface of this workpiece；

Phase III welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the 3rd time of Millisecond, this electric current is the phase III rms current value less than second stage peak current value, nugget for completing to melt at the binding face of this welding position is formed, phase III is more longer than second stage, and stops electric current equally to cool down this welding position and to make this nugget solidify；Subsequently

Remove the solder side of described relative welding electrode so that it is do not contact with the described outer surface of this workpiece.

2. in terms of the method forming resistance spot weld on acieral workpiece as described in 1, wherein the solder side of this welding electrode is that spherical and with the circular shape concentric ring with prismatic protrusion workpiece engages.

3. in terms of the method forming resistance spot weld on acieral workpiece as described in 1, wherein the solder side of this welding electrode is spherical and engages with the workpiece with rough surface.

4. in terms of the method forming resistance spot weld on acieral workpiece as described in 1, wherein this first stage instantaneous welding current is slowly raised to the value of about 10 kiloamperes, and this first stage the most about 20 is to about 60 milliseconds.

5. in terms of the method forming resistance spot weld on acieral workpiece as described in 1, wherein this second stage peak value welding current is quickly increased to about 20 to about 50 kiloamperes, and second stage the most about 6 is to about 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface.

6. in terms of the method forming resistance spot weld on acieral workpiece as described in 1, wherein this phase III rms welding current value is of about 15 to about 40 kiloamperes, and the phase III the most about 20 is to about 200 milliseconds.

7. in terms of the method forming resistance spot weld on acieral workpiece as described in 1, wherein this phase III welding current passes between said electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

8. in terms of the method forming resistance spot weld on acieral workpiece as described in 2, wherein this first stage instantaneous welding current is slowly raised to the value of about 10 kiloamperes, and the first stage the most about 20 is to about 60 milliseconds.

9. in terms of the method forming resistance spot weld on acieral workpiece as described in 2, wherein this second stage instantaneous welding current value is quickly increased to about 20 to about 50 kiloamperes, and second stage the most about 6 is to about 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface.

10. in terms of the method forming resistance spot weld on acieral workpiece as described in 2, wherein this phase III rms welding current value is of about 15 to about 40 kiloamperes, and the phase III the most about 20 is to about 200 milliseconds.

11. in terms of the method forming resistance spot weld on acieral workpiece as described in 2, wherein this phase III welding current passes in-between the electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

12. in terms of the method forming resistance spot weld on acieral workpiece as described in 3, wherein this first stage instantaneous welding current is slowly raised to the value of about 10 kiloamperes, and the first stage the most about 20 is to about 60 milliseconds.

13. in terms of the method forming resistance spot weld on acieral workpiece as described in 3, wherein the instantaneous welding current of second stage is quickly increased to about 20 to about 50 kiloamperes, and second stage the most about 6 is to about 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface.

14. in terms of the method forming resistance spot weld on acieral workpiece as described in 3, wherein phase III rms welding current value is of about 15 to about 40 kiloamperes, and the phase III the most about 20 is to about 200 milliseconds.

15. in terms of the method forming resistance spot weld on acieral workpiece as described in 3, wherein phase III welding current passes in-between the electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

16. methods forming resistance spot weld on acieral workpiece, described method includes:

Forming the lamination of two or more acieral workpiece, the workpiece of this lamination has binding face and has contrary outer surface at this welding position in resistance welding position；

The solder side of relative resistance welding electrode is pressed at welding position the described outer surface of this workpiece；This solder side is pressed to this workpiece simultaneously,

First stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue time first stage of Millisecond, this transient current is slowly improved to the first stage current value making resistance between described solder side be reduced to certain steady resistance value, and heat this workpiece to engage with this solder side, without melting this workpiece at their binding face, subsequently, at once by current reduction to zero, and described electrode still presses to the described surface of this workpiece；

Second stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the second stage time of Millisecond, this transient current is quickly risen above the second stage peak value of first stage peak point current, for causing melted nugget to be formed at the binding face of this welding position, and reduce electric current, and described electrode still presses to the described surface of this workpiece；

Phase III welding current is made to pass between said electrodes and by this workpiece at this welding position, continue time phase III of Millisecond, this rms electric current is the phase III value less than second stage peak current value, nugget for completing to melt at the binding face of this welding position is formed, time phase III is more longer than the second stage time, and stops electric current equally to cool down this welding position and to make this nugget solidify；Subsequently

Remove the solder side of described relative welding electrode so that it is do not contact with the described outer surface of this workpiece.

17. in terms of the method forming resistance spot weld on acieral workpiece as described in 16, wherein the solder side of this welding electrode is that spherical and with the circular shape concentric ring with prismatic protrusion workpiece engages.

18. in terms of the method forming resistance spot weld on acieral workpiece as described in 16, wherein the solder side of this welding electrode is spherical and engages with the workpiece with rough surface.

19. in terms of the method forming resistance spot weld on acieral workpiece as described in 16, wherein this first stage instantaneous welding current is slowly raised to the value of about 10 kiloamperes, and the first stage the most about 20 is to about 60 milliseconds；Wherein the instantaneous welding current of second stage is quickly increased to about 20 to about 50 kiloamperes, and the second stage time is of about 6 to about 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface；And wherein phase III rms welding current is of about 15 to about 40 kiloamperes, and the phase III the most about 20 is to about 200 milliseconds.

20. in terms of the method forming resistance spot weld on acieral workpiece as described in 19, wherein this phase III welding current passes in-between the electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

The detailed description of the following preferred embodiment from description, other purpose of the present invention will be apparent to advantage.By the accompanying drawing with reference to description description below.

Summary of drawings

Fig. 1 is to include welding electrode and the welding system of two aluminum alloy sheet workpiece, as can be used for implementing the schematic side elevational diagram of the system of the welding method of the present invention.

Fig. 2 is the figure for changing over welding current (chain-dotted line), voltage (short dash line), power (dot-dash dotted line) and the resistance (solid line) of the lamination of 2.0 millimeters thick AA 5754 sheet materials with AA 5754 sheet material of 2.0 millimeters thick of conventional continuous constant current resistance spot welding scheme welding.

Fig. 3 is shown under three kinds of different conditions the figure of the weld size of 2.0 millimeter of 5754 lamination using continuous Galvanostatic Regime to weld.For Galvanostatic Regime continuous to routine, weld size shows with changing weld interval.Show the weld size of sample under the conditions of three kinds, i.e. horizon sample or be perpendicular to electrode orientation sample (in Fig. 2 be referred to as " flange ", there is diamond data points), to the sample (triangular data points) of electrode incline 6 ° and the sample (square data points) with 0.8 millimeter of gap.Hollow symbology has the sample of unacceptable fracture mode, i.e. face of weld tear or hemisphere (half button).

Fig. 4 is for 2.0 millimeters of AA with regulation (CSS) scheme welding of the regulation of the present invention, shaping and size The figure that the welding current (chain-dotted line) of 5754 pairs 2.0 millimeters AA 5754 laminations, voltage (short dash line), power (dot-dash dotted line) and resistance (solid line) change over.

Fig. 5 is the figure changed with weld interval for regulation, shaping, size regulation welding scheme weld size.Show the weld size of sample under the conditions of three kinds, i.e. horizon sample (flange, diamond data points), to the sample (triangular data points) of electrode incline 6 ° and the sample (square data points) with 0.8 millimeter of gap.Equally, hollow symbology has the sample of unacceptable fracture mode, i.e. face of weld tear or hemisphere.

Preferred embodiment describes

The welding scheme of the present invention can use as in Fig. 1, the welding equipment of schematic description is implemented.Fig. 1 in this specification also serves as Fig. 1 in our open US 2011/0266260 of co-pending U.S.Patent application and presents, and also serves as the US 6 such as us, and the Fig. 1 in 861,609 presents, and the most as described below.

In FIG, describe there is the representational spot-welding gun equipment 10 of relevant device (project 30,32,34,36,38,40 and 42 the most hereinafter described) used in the spot-welding equipment for acieral workpiece.In this type of welding operation, prepare the assembly of two or more aluminum alloy sheet plates 12 and 14 to be welded, and be transported to welding gun equipment 10 by conveyer or other device.This welding gun equipment is typically mounted in robot, and the edge (such as the flange of welding) of this Robot aluminum alloy sheet plate 12,14 is mobile to be quickly completed a series of single resistance spot weld.

In FIG, outstanding (poised) axially aligning for a pair and between relative electrode 16 and 18 at welding gun arm 20 of metallic plate 12 and 14 display.Rifle arm 20 has C configuration so that the solder side (being 52 to electrode 16) of relative electrode 16 and 18 can load and be squeezed on the contrary side of aluminium alloy plate 12 and 14.In the layout of display, electrode 16 is arranged in axle portion (shank) 17, and this axle portion inserts in the fixture 22 being connected on the fixed arm 24 of welding gun arm 20.Relative electrode 18 is arranged in axle portion 19 and is inserted on cylinder or servomotor 28 in another fixture 26 carried.Cylinder or servomotor 28 are suitable to move axially electrode 18 and engage to the outer surface clamping with plate 14.Source of high pressure air (not shown) from distant source carries air through air conditioner 30 to cylinder 28 able to programme to provide clamping force through air line 32.Or, controller for servomotor provides electric current and voltage to provide clamping force to servomotor.During point welding process, air pressure that cylinder 28 applies in time or the mobile propelling fixture 26 of servomotor so that electrode 18 towards fixed electrode 16 with the power extruded sheet 12 and 14 of about 500 to 1500 pounds.

Welding gun 20(is typically mounted on the end of robots arm) it is connected on robot controller 34.Robot controller 34 manages and handles air conditioner 30 able to programme, also handles the welding controller 36 of programming.Welding controller 36 regulates welding current (primary welding current) passage to welding transformer, and this welding transformer supplies electric current to electrode.When welding controller 36 sends order, primary current is delivered to welding transformer 40 through primary current circuit 38.AC electric current is converted into more low-voltage, the secondary welding electric current of higher AC electric current by welding transformer 40, and it becomes DC electric current by suitable diode rectification subsequently and provides through the second current circuit 42 and electrode holder 26 and the rifle arm 20 of conduction and electrode holder 22.

When for the assembly of new Al alloy parts or the lamination (aluminum sheet 12 in such as Fig. 1, 14) when considering welding operation, would generally consider that measured test (actual testing) or previous welding experience are to prepare welding gun assembly and by relevant robotic gun controller (controller 34 in such as Fig. 1) programming, with by the welding gun welding position on workpiece lamination or a series of welding position under predetermined clamping pressure, and the regulation of each weld seam according to practice formation under this invention, shape and size regulation welding step determines for operating welding transformer 40 and for carrying the programming of the welding controller 36 of suitable DC welding current sequence.

It is given below and determines for regulating, shape and the method for welding current of size regulating step.This generally realizes with representing metal laminated sample to be welded.Use electric current, voltage, power and the resistance at the instrument monitoring electrode separated with welding controller.For regulating step regulating step, electric current regulation starts levels of current when occurring melted to being just below substrate.Once it is determined that this levels of current, regulating time is to guarantee to obtain stable, consistent resistance between two electrodes.It is typically inserted into of short duration cooling or stop time to reset welding to control software in regulation thickness.For forming step, by improving levels of current until forming circular nugget placed in the middle and substrate/electrode reaction not occurring, i.e. electrode adheres on electrode or substrate surface melts, and thus lowers current in the shortest time (about 6-10 millisecond).If there is substrate/electrode reaction in forming process, increasing curring time with little increment, and carrying out electric current regulation to cause gratifying nugget in the case of there is no substrate/electrode reaction simultaneously.Nugget causes the melting zone that should be included in the contact surface immediate vicinity formation diameter formed close to sheet material laminating interface more than 3 millimeters.For exceeding the curring time of about 30 milliseconds, forming current pulse should split into two shorter pulses and have of short duration cooling between which.Due to the high levels of current reached in forming step, once nugget shapes, and inserts the of short duration cooling of about 5 milliseconds or stop time in order to make electrode/sheet material and laminating interface cool down.The function setup size regulating time determining thickness as lamination.For two sheet stacks, the thinnest sheet material is to determine thickness.For three sheet stacks, the second thin sheet material is to determine thickness.Size regulating time is determining that to 1.0 millimeters thickness is of about 30 milliseconds and determines that thickness is of about between 100 milliseconds change to 3.0 millimeters.Once determining size regulating time, regulation electric current is to reach required weld size.If electrode excessive wear, change size regulation continuous current pulse to include heating and cooling pulse, usually the heating of 10 milliseconds to 30 milliseconds and the cooling of 1 millisecond to 10 milliseconds.

Commercialization robot controller is available, it is possible to select this controller to manage the welding electrode open and close relative to workpiece.Also there is the commercialization welding controller able to programme that can be used for implementing the three step weldings of the present invention.It is presented herein below and transformator, the required feature that electrically connects and have the relevant welding controller able to programme of the welding gun of welding electrode.

Contravariant welding controller is programmable, in order to load for carrying out the regulation of this welding scheme, shaping and the predetermined instruction of size regulating step.Additionally, Programmable inversion type welding controller needs have sufficient primary current capacity to realize secondary current based on transformer turn ratio.Typical transformer turn ratio for 50:1, this contravariant welding controller needs at least 1000 amperes, and the primary current capacity of preferably 1200 amperes is to realize the 50kA target secondary current (turn ratio is multiplied by maximum primary current) needed for last aluminum sheet is reproduced these welding schemes.It is readily available the welding controller with these primary current capacity.This welding controller can also be by the hardware used by controller or software impact secondary current rise time.Some controller is by design or simply due to internal processor or software lack speed and limits current rise rate.Assuming that other turn ratio that the typical turn ratio of transformator is 50:1(40:1 to 60:1 also can obtain), experience have shown that, the welding controller primary current rise time should be at least 80 amperes/milliseconds or 10 milliseconds to realize 800 amperes of outputs, it is converted to the rise time of 4 kiloamperes/millisecond for the transformator that turn ratio is 50:1.

As it has been described above, by electric current, voltage, power and resistance at outside monitoring electrode, develop this regulation, shaping and size regulation welding scheme, welding controller the most only monitor current, it is common that primary current, is secondary current once in a while.Welding controller not monitoring voltage, resistance and power.The purpose that welding controls is the most to be set up required regulation by the above-mentioned program that arranges, shaped and size regulation (CSS) waveform, then replicate this waveform.

MFDC transformator also should meet minimum requirements.This includes required waveform is reached target maximum secondary current.For the welding of vehicle structure, target maximum electric current is typically about 50 kiloamperes, and the welding of the cover plate for lighter specification, this target is usually 35 kiloamperes.Output from transformer core and diode is required to realize these levels of current.Such as, the transformator of the turn ratio in its iron core with 40:1 cannot realize 50 required kiloampere outputs for using the structure welding of 1000 amperes or 1200 amperes contravariant controllers.Equally, some transformator diode is the most restricted in terms of levels of current so that this transformator is not suitable for this CSS tri-step welding.

Assuming that this welding controller produces enough primary currents supplies this transformator and transformer core with the primary current rise time, and this diode has enough current capacities, then can be exported by two final controlling factors transformators: welding gun arm and/or the resistance of cable and inductance.When each aspect of welding system is suitable to manufacture required waveform, if rifle resistance and inductance are unsatisfactory, then maximum current and current rise time can be impaired.Rifle resistance can be measured suitably along rifle arm between electrode and transformator.Such as, typical resistivity measurements is each arm 50 microhm, and two arms amount to 100 microhms.This resistance level will make 1200 amperes of contravariant welding controllers realize 60 kiloamperes together with 50:1 turn ratio MFDC transformator.Higher resistance reduces attainable maximum current by starting.Second current rise time of rifle inductive impact, described rifle inductance is directly related with the loop area that rifle arm and/or cable are formed.Big loop area can slow down electric current and rise.For the transformator of 50:1 turn ratio, loop area preferably should be less than about 300 square inches, takes advantage of 30 inches for such as 10 inches.This transformator has the maximum voltage of 13 volts.The biggest loop area would be required to transformator and has the highest voltage or the lowest turn ratio, such as 40:1 turn ratio and 16.25 volts.In a word, whole welding system must design the welding current needed for realizing and rise time, and this needs appropriate welding controller, MFDC transformator and welding gun capacity.

In order to realize required waveform in this welding position, by relatively high electric current (in units of kiloampere, kA) under relatively low voltage through the Millisecond time, typically less than 200 milliseconds are transported to this electrode.This welding system can be to electrode conveying required voltage and electric current.Electric current, voltage, resistance and the power consumed at electrode is generally measured independently in welding position.This welding controller can be used for measuring once or secondary current.Use cincture once or the single-turn circular coil of secondary current circuit carries out current measurement (measure independently or measured by welding controller).Directly voltage is measured independently to the voltage of electrode by report.Resistance (R=V/I) and power (P=VI) is calculated by this electric current and voltage measuring value.The measurement of electric current, voltage, power and resistance is carried out in the specimen that welding designs to represent actual metal lamination.According to the preferred embodiments of the invention, the solder side (in such as Fig. 1 52) of welding electrode each presents and has the sphere of concentric convex hole to engage with the pellumina on sheet-material work piece surface, although the electrode with microtexture solder side also benefits from the present invention.

Before further describing the three step weldings of the present invention, it is useful for describing permanent DC electric current practice currently used in the resistance welding of acieral sheet-material work piece.Fig. 2 shows for 1200 Under lb electrode force, 2.0 millimeters of aluminium alloy 5754 sheet materials are spoted weld constant continuous current (CCC) welding scheme of the typical case on 2.0 millimeter of 5754 sheet material.This is equivalent in the case of not having branch path in advance the first welding between sheet material.The parts of the aluminum EV1 automobile of the GM that this type of scheme produces several years ago for welding.Aluminum current association is at their reference materialWelding Alunimium Theory and PracticeThe scheme of middle recommendation similar 167 milliseconds.Current curve (chain-dotted line) is shown from 0 millisecond through some ms(milliseconds) rise to welding current (27 kiloampere).The slope that electric current rises is generally inessential for these schemes, because once reaching target current, it can keep relatively long time welding interval.Electric current keeps about 200 milliseconds of this electric current after rising.Cut off now electric current and be reduced to zero through some milliseconds.Corresponding resistance (solid line) and voltage (short dash line) curve all show high initial peak.High voltage peak (about 1.0 volts) when electric current starts causes forming electric arc at electrode/sheet interface and destroying electrode welding face.

When the electric current of CCC welding scheme starts, voltage input is at a relatively high, but levels of current is low.This combination is not the most provided that enough power (dot-dash dotted line) is reliably to cause nugget.Nugget can cause the most in time, or can cause in the random areas in the laminating interface contact region set up by the welding electrode closed.

The nugget of time delay causes may affect weld size, and causes the significantly change of the weld size observed under conditions of including high thickness ratio, different alloys and variable weld spacing.It also results in needs longer weld interval to guarantee will suitably to regulate the size of this weld seam under various conditions (i.e. welding under there is gap or tilting).

Fig. 3 shows the weld size of 2.0 millimeter of 5754 lamination using constant continuous current scheme to weld under conditions of three kinds of differences.Noting, for the sample being orientated relative to electrode incline 6 °, welding initiation is delayed by.This need longer weld interval to realize gratifying performance, the weld size of the most about 6 millimeters.Unacceptable fracture mode (open symbols) occurred outside the weld interval of 65 milliseconds, and the weld size more than 5 millimeters proves that the program lacks universality further.

There is no to concentrate (focused) and be positioned at laminating interracial contact district center but the nugget initiation that is randomly dispersed in whole laminating interface contact region can cause the best weld penetration, subsequently resulting in unacceptable welding seam breaking and the best weld shape, the best weld shape can cause splash and the best welding quality.Random nugget causes the best welding quality also resulting in the position that there is binding agent or sealant, because the initiation most probable in spreading all over the several little position of binding agent or sealant carries more substantial sealant or binding agent secretly, thus produces unacceptable hole in weld seam microstructure.

The present invention is to use the welding scheme of three independent steps, for manufacturing the high quality welds with consistent size and shape under conditions of varied.Three different steps include regulation, shape and size regulation (CSS).Fig. 4 is that this three stage welding schemes are applied to 2.0 millimeters thick AA 5754 sheet-material work piece to welding current (chain-dotted line), voltage (short dash line), power (dot-dash dotted line) and the figure of resistance (solid line) the in-between the electrodes during lamination of 2.0 millimeters thick AA5754 sheet materials.

Step 1-regulates: once electrode realizes clamping the stable weld force of this lamination at welding position, and this step starts.Welding controller being inserted regulation or limits the pattern of the voltage applied by welding transformer, described pattern is referred to as automatic voltage and compensates (AVC pattern).Fig. 4 describes during this regulating step, and the voltage at electrode, from the beginning of about 0.5 volt, is reduced to 0.4 volt.Making welding current progressively reach makes electrode/sheet material be reduced to the level of consistent lower value with the resistance of laminating interface.This electric current is generally brought up to 5,000 to 10,000 amperes by the lower value of about 3,000.It is typically chosen accurate levels of current so that it is just below, in laminating interface, melted levels of current occurs.Equally, electric current keeps 20 milliseconds to 60 milliseconds.Require minimum 20 milliseconds to guarantee that resistance has punctured and substantially stabilized.The electric current exceeding about 60 milliseconds generally will not reduce resistance further, but only slows down welding process.For the embodiment in Fig. 4, implement regulation to 50 milliseconds, and reach the electric current of about 10 kiloamperes.As the voltage compensation mode used by welding controller an alternative it is possible to exchange current programming with constant current mode, described constant current mode has from low current value (about 3 kiloampere) until the gentle slope of final required regulating step electric current.Equally, it is therefore intended that obtain consistent steady resistance in welding position, without making this sheet material melt in laminating interface.

During this regulating step, producing heat at welding position, this makes the ring of electrode set up at electrode/sheet interface to contact more closely.The contact improved prevents from, in the forming process applying high levels of current, excessive electrode damage occurs.Additionally, the resistance as recorded in-between the electrodes is reduced to consistent value.In this embodiment, Fig. 4, it is of about 0.04 microhm.For given lamination, such as above-cited lamination, consistent resistance value should be identical, no matter how or whether welding gun polarity exists any additive or sealant.This step guarantees that the electric current occurred in forming step produces consistent weld size result.At the end of regulating step, by failure of current about 10 milliseconds to cool down this electrode before forming step.This is shown as electric current and the reduction of voltage at 50 milliseconds in the diagram.Longer cooling (or stopping) time can be used, but this only can slow down welding process.Depending on that welding controller operates, this cooling step can also make this welding controller reset, in order to provide maximum power when forming step starts.

Step 2 shapes: designs this step and causes to produce consistent melted nugget, preferably concentrate between the relative solder side of electrode, and do not consider welding condition, i.e. rifle polarity, the electrode that whether there is adhesive/sealant, sheet metal workpiece face-to-face engagement the best at they binding faces, inclination etc..Generally, electric current is forced to flow under extremely high value to cause melted nugget as quickly as possible in laminating interracial contact district center.Obtain very high currents in short time and welding system is proposed high request.As it was previously stated, in order to reach target forming current in the shortest time, contravariant welding controller, MFDC transformator and welding gun must be appropriately designed so as to realize this target current and current rise time.Rise time prevents from reaching target current in the little time window of forming step slowly, this for the function of this step it is critical that.Rise time can be to control hardware or software, not enough MFDC transformer voltage or high welding gun inductance and cause by welding slowly slowly.Fig. 4 shows that the rise time of 35 kiloamperes is only 6 millimeters, or 5.8 kiloamperes/millisecond, and this is the fastest.Shaped pulse provides the most high-power pulse to this lamination.For the embodiment in Fig. 4, find that power reaches the peak value of 35 kilowatts when about 70 milliseconds.Compare the peak value reached in Fig. 2 and be only 22 kilowatts.

Depending on sheet stack, use the forming step current time of 6 milliseconds to 50 milliseconds, peak current value is usually 20 kiloamperes to 50 kiloamperes.Assuming that this welding system, i.e. contravariant controller, MFDC transformator and welding gun can realize required > current rise time of 4 kiloamperes/millisecond, in several limit, determine shaping peak point current and curring time.Curring time keeps the shortest to obtain required initial melted nugget, its diameter generally at least about 3 millimeters.Due to inverter design, transformer voltage and bonding machine inductive impact current rise time, it generally takes about 5 to 12.5 milliseconds with the target peak levels of current reaching 20 kiloamperes to 50 kiloamperes.Curring time is at least 6 milliseconds, but typically larger than 10 milliseconds.Shaping should be less than 50 milliseconds.For the fine sheet such as the AA5754-0 of 1.0 millimeters, use and such as the low forming current reached in 6 milliseconds, such as 24 kiloamperes, following table can be seen in the short time.Medium-scale sheet material, as the AA5754-0 of 2.0 millimeters need the curring time of 20 milliseconds.For heavier sheet material, such as the AA5754-0 of 3.0 millimeters, need longer curring time.In this case, the curring time of 50 milliseconds is used.In order to prevent excessive electrode/sheet material reaction, curring time is split into the pulse (a 20 ms pulse) of 20 milliseconds, is followed by of short duration cool time, be followed by the pulse (a 30 ms pulse) of 30 milliseconds.Generally, when shaping need to require more than 30 milliseconds with manufacture gratifying welding cause some time, in shaped pulse being split two and insert of short duration about 3 millisecond between the two pulses.Keep below peak current level and weld interval and between sheet material and electrode welding face, produce overreaction with bound form or cause sheet material outer surface those dissolved actual.

Table 1 below shows and forms particular sheet material 1 and sheet material 2 aluminium alloy with thickness regulation, shaping and the Exemplary temporal of size regulation.4th hurdle describes the shaping peak value RMS current value forming each sheet material.Last hurdle shows the recommendation weld interval in units of millisecond of aluminum association.

Table 1: regulate, shape and size regulation welding parameter

*Welding Aluminium Theory and Practice, company of aluminum association, in June, 1991, page 13.3.

Once being complete fully formed, welding controller stops driving about 5 milliseconds of electric current.In this time course, electric current quickly reduces, until being less than the level for size regulation but being above zero.This electric current is preferably decreased to less than size regulation level, but remains above at least 10 kiloamperes.The step for purpose be dual.First, it allows the certain cooling at electrode/sheet interface.Secondly, prevent the nugget caused overheated because of the high power pulse that applies in forming process.Removing this of short duration cooling step causes the nugget during size regulating step overheated and the serious interface splash of motlten metal.The nugget cooling that order causes contributes to controlling this process, and contributes to stable dimensions regulating step.But, cooling step can not be long so that there is nugget solidification.If nugget solidifies, it will cause short circuit between sheet material, and thus the extra current during size regulating step will can not realize required weld size.

Step 3 size regulates: once nugget pass through forming step and causes in laminating interracial contact district center and make it cool down, regulate RMS current level extremely less than the level of peak point current used by forming step to realize target spot welding nugget size.Generally low than the peak point current reached in forming step shown in table more than 1 kiloamperes of this RMS value.It can also shape the high several kiloamperes of minimum current reached in thick cooling step by ratio.Size regulation current value (RMS) generally changes between to 15 kiloamperes of light scale aluminum alloy sheet to 40 kiloamperes to very weight-normality module material.Can with constant current implement size regulation so that peak value is identical with RMS current value, if or wear to electrodes become problem, can with a series of current impulses enforcement size regulate, described current impulse has the RMS value of low several kiloamperes than peak value forming current.Size regulation is generally carried out with the electric current phase of 20 milliseconds to 200 milliseconds, is part the longest in welding scheme.When using current impulse, each pulse is generally made up of the working time (heating) of ten to three ten milliseconds and the stop time (cooling) of one to five milliseconds.

Size regulating step generally ratio is generally used for producing the time much shorter of welding with constant current scheme.Upper table 1 compares the size regulating step for various 5754 aluminum sheet combinations and those recommended constant continuous current (CCC) scheme of prior art by aluminum association.For our CSS scheme, for the material especially for heavier specification, weld interval wants much shorter.Shorter weld interval causes thermograde steeper around nugget, and it works to cool down more quickly nugget, produces finer microstructure.Fine microstructure has been found that the microstructure than using common welding scheme to obtain is more tolerant of the fracture under peeling load.

Additionally, the time that nugget shaping adds nugget size regulation is the shortest, the fewest for manufacturing the energy of nugget.In this embodiment, the energy of few about 40% is for manufacturing nugget or the ball of acceptable size.It reduce MFDC transformator and weld gun component, such as rifle arm, cable, the thermic load of branch.

Such as, Fig. 5 shows the weld size of 5754 laminations using weld under three kinds of different conditions 2.0 millimeters of CSS scheme.Take weld interval when forming step starts, thus include shaping and size regulation pulse.Note, even after 15 milliseconds, all three condition has been formed nugget the most.The quick formation of nugget eliminates the transmutability in the method significantly.

Under the weld interval of only 115 milliseconds, weld size is of about 6 millimeters or bigger.Pervasive size is had been realized under the time more shorter than constant continuous current (CCC) scheme.This extends electrode life, and this weld seam microstructure that becomes more meticulous.Under the extremely short weld interval of 35 milliseconds, only there occurs unacceptable fracture mode.Not observing unacceptable fracture mode under 65 milliseconds and longer time, this is the performance improved compared to CCC scheme (Fig. 2).

In the case of the many of resistance spot welding aluminum sheet metal works, it is preferably used such as United States Patent (USP) US 6,861,609(3/1/2005) and those welding electrodes disclosed in U.S. Patent application US 20100258536,20090302009,20090255908,20090127232,20080078749.These electrodes have solder side that is coarse or that shape, it has been found that can be used for the resistance spot welding of aluminum, and when implementing spot welding according to the welding scheme of this specification, the performance of this type of electrode is good.

The example of the invention described above is used for illustrating and not limiting the scope of the invention.

Claims (20)

1. the method forming resistance spot weld on acieral workpiece, described method includes:

Forming the lamination of the sheet material of two or more acieral workpiece, the workpiece of this lamination has binding face and has contrary outer surface in this welding position in resistance welding position；

The solder side of relative resistance welding electrode is pressed at this welding position the described outer surface of this workpiece；This solder side is pressed to this workpiece simultaneously,

First stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the very first time of 20 to 60 milliseconds, this electric current is improved to the first stage current value making resistance between described solder side be reduced to certain steady resistance value, and heat this workpiece to engage with described solder side, without melting this workpiece at their binding face, subsequently, at once by current reduction to zero, and described electrode still presses to the described surface of this workpiece；

Second stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the second time of Millisecond, peak point current is risen above the second stage current value of first stage current value, for causing melted nugget to be formed at the binding face of this welding position, and reduce electric current, and described electrode still presses to the described surface of this workpiece；

Phase III welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the 3rd time of Millisecond, this electric current is the phase III rms current value less than second stage peak current value, nugget for completing to melt at the binding face of this welding position is formed, phase III is more longer than second stage, and stops electric current equally to cool down this welding position and to make this nugget solidify；Subsequently

Remove the solder side of described relative welding electrode so that it is do not contact with the described outer surface of this workpiece.

2. the method forming resistance spot weld on acieral workpiece as claimed in claim 1, wherein the solder side of this welding electrode is that spherical and with the circular shape concentric ring with prismatic protrusion workpiece engages.

3. the method forming resistance spot weld on acieral workpiece as claimed in claim 1, wherein the solder side of this welding electrode is spherical and engages with the workpiece with rough surface.

4. the method forming resistance spot weld on acieral workpiece as claimed in claim 1, wherein this first stage instantaneous welding current is slowly raised to the value of 10 kiloamperes.

5. the method forming resistance spot weld on acieral workpiece as claimed in claim 1, wherein this second stage peak value welding current is quickly increased to 20 to 50 kiloamperes, and second stage continues 6 to 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface.

6. the method forming resistance spot weld on acieral workpiece as claimed in claim 1, wherein this phase III rms welding current value is 15 to 40 kiloamperes, and the phase III continues 20 to 200 milliseconds.

7. the method forming resistance spot weld on acieral workpiece as claimed in claim 1, wherein this phase III welding current passes between said electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

8. the method forming resistance spot weld on acieral workpiece as claimed in claim 2, wherein this first stage instantaneous welding current is slowly raised to the value of 10 kiloamperes, and the first stage continues 20 to 60 milliseconds.

9. the method forming resistance spot weld on acieral workpiece as claimed in claim 2, wherein this second stage instantaneous welding current value is quickly increased to 20 to 50 kiloamperes, and second stage continues 6 to 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface.

10. the method forming resistance spot weld on acieral workpiece as claimed in claim 2, wherein this phase III rms welding current value is 15 to 40 kiloamperes, and the phase III continues 20 to 200 milliseconds.

11. methods forming resistance spot weld on acieral workpiece as claimed in claim 2, wherein this phase III welding current passes in-between the electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

12. methods forming resistance spot weld on acieral workpiece as claimed in claim 3, wherein this first stage instantaneous welding current is slowly raised to the value of 10 kiloamperes, and the first stage continues 20 to 60 milliseconds.

13. methods forming resistance spot weld on acieral workpiece as claimed in claim 3, wherein the instantaneous welding current of second stage is quickly increased to 20 to 50 kiloamperes, and second stage continues 6 to 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface.

14. methods forming resistance spot weld on acieral workpiece as claimed in claim 3, wherein phase III rms welding current value is 15 to 40 kiloamperes, and the phase III continues 20 to 200 milliseconds.

15. methods forming resistance spot weld on acieral workpiece as claimed in claim 3, wherein phase III welding current passes in-between the electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.

16. methods forming resistance spot weld on acieral workpiece, described method includes:

Forming the lamination of two or more acieral workpiece, the workpiece of this lamination has binding face and has contrary outer surface at this welding position in resistance welding position；

The solder side of relative resistance welding electrode is pressed at welding position the described outer surface of this workpiece；This solder side is pressed to this workpiece simultaneously,

First stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue time first stage of 20 to 60 milliseconds, transient current is slowly improved to the first stage current value making resistance between described solder side be reduced to certain steady resistance value, and heat this workpiece to engage with this solder side, without melting this workpiece at their binding face, subsequently, at once by current reduction to zero, and described electrode still presses to the described surface of this workpiece；

Second stage welding current is made to pass between said electrodes and by this workpiece at this welding position, continue the second stage time of Millisecond, transient current is quickly risen above the second stage peak value of first stage peak point current, for causing melted nugget to be formed at the binding face of this welding position, and reduce electric current, and described electrode still presses to the described surface of this workpiece；

Phase III welding current is made to pass between said electrodes and by this workpiece at this welding position, continue time phase III of Millisecond, this electric current is the phase III rms current value less than second stage peak current value, nugget for completing to melt at the binding face of this welding position is formed, time phase III is more longer than the second stage time, and stops electric current equally to cool down this welding position and to make this nugget solidify；Subsequently

Remove the solder side of described relative welding electrode so that it is do not contact with the described outer surface of this workpiece.

17. methods forming resistance spot weld on acieral workpiece as claimed in claim 16, wherein the solder side of this welding electrode is that spherical and with the circular shape concentric ring with prismatic protrusion workpiece engages.

18. methods forming resistance spot weld on acieral workpiece as claimed in claim 16, wherein the solder side of this welding electrode is spherical and engages with the workpiece with rough surface.

19. methods forming resistance spot weld on acieral workpiece as claimed in claim 16, wherein this first stage instantaneous welding current is slowly raised to the value of 10 kiloamperes；Wherein the instantaneous welding current of second stage is quickly increased to 20 to 50 kiloamperes, and the second stage time is 6 to 50 milliseconds, the value of second stage welding current and second stage time are for forming a diameter of at least 3 millimeters and the melted nugget that concentrates between electrode surface；And wherein phase III rms welding current is 15 to 40 kiloamperes, and the phase III continues 20 to 200 milliseconds.

20. methods forming resistance spot weld on acieral workpiece as claimed in claim 19, wherein this phase III welding current passes in-between the electrodes with two or more impulse forms, and described pulse has the heat time heating time of 10 to 30 milliseconds and the cool time of 1 to 10 millisecond.