WELDING METHOD FOR THE CONNECTION OF A COMPONENT TO A WORKPIECE, AND A DEVICE FOR CARRYING OUT THE METHOD

Abstract: In a welding method for the connection of a component (6) to a workpiece (7) by means of an arc between the component end and a welding point on the workpiece (7), the arc voltage is set and is monitored continuously during the welding process. The component lift is in each case automatically adjusted accordingly.

Description: Welding method for the connection of a component to a workpiece, and a device for carrying out the method The invention relates to a welding method for the connection of a component to a workpiece according to the precharacter- lzing clause of Patent Claim 1, and to a device for carrying out the method. Such a method is known and is used for achieving a weld by means of an arc quickly and correctly. The components used are, for example, bolts or studs. In known methods, the arc voltage is set mechanically by means of the component lift. Specifically, the component lift is essentially proportional to the arc voltage. In this case, a value based on experience is set permanently. The arc voltage changes continuously during the welding process as a result of the surface characteristics of the parts to be welded and as a result cf tolerances m the material production and in the contact pressure of the welding head used, which leads tc quality fluctuations m the welds. Patent Specification EP-B-0 241 249 describes a control cir¬ cuit arrangement for the arc welding of components, a se- quence controller determining the trigger moments cf tne rearward movement and of the forward movement of tne welding arc, and a monitoring voltage being derived from a preweld current arc, which monitoring voltage is converted into a correction voltage and superimposed on a control voltage in order to control a changeover mode power supply unit which, using the control voltage corrected m this manner, adjusts its output current during the welding process to the resis¬ tance of the preweld current arc, said resistance being de¬ rived from the monitoring voltage. The trigger moments of tne rearward movement and of the welding arc can also be cor¬ rected in the sequence controller with the aid of the mom- toring voltage, which is derived from the preweld current arc. The magnitude of the output current and the welding time are thus adjusted for every welding process on the basis of the preweld current arc voltage. The component lift is ao- justed by means of a cylindrical coil and a spring. Here too, the arc voltage can vary continuously during tne welding process, as a result of the factors mentioneα above, whicn leads to undesirable reductions in quality. The known mechanical adjustment of the component lift ana tne insertion dimension for influencing the arc voltage allocs these parameters to be corrected only once per welα. In adα - tion, the mechanical adjustment of the component lift and tne insertion dimension results m tne rιs cf proαucing defec- tive quality results because of incorrect adjustment. Ir practice, with the time pressure to which tne operator is subject m each case, it is not always poεsiole to avoid cr to correct inaccuracies and deviations fror the optimum set¬ tings. This results in corresponding reductions m quality, and scrap. In addition, tne operation of tne known welding devices is subject to correspondingly stringent requirements. Furthermore, as a result of tne increasing qualit y re¬ quirements, it is desirable to ensure ana, _f necessary, t correct the quality directly m the production process it- self. The invention is based on the object of creating a metnod cf the generic type which avoids the disadvantages indicated above, complies with present-day quality assurance demands, and can be carried out easily. The stated object is achieved according tc tne invention m that a reference voltage profile is set for tne arc voltage and the arc voltage is measured and compared with tne current reference voltage repeatedly during the welding process in a control loop, as a controlled variable, a correction variable m each case being determined from the difference between tne measured arc voltage and the current reference voltage, bv means of which correction variable the component lift is m each case automatically corrected, as a manipulated variable. In consequence, the desired arc voltage is maintained pre¬ cisely during the entire welding process, which ensures a significant improvement m the welding quality for different workpiece surface characteristics. In addition, time-consum¬ ing adjustments and corrections of the distance between the workpiece and the stud are no longer necessary. A device for carrying out the method is characterized m that the device comprises a stuα welding apparatus, a welding heaα control unit having a stud holder, ana a microprocessor ccr- troller. Advantageous developments of the invention result trcr n tre further succlaims. A numoer of exemplary embodiments of tne invention are ex¬ plained m more detail in tne following text, with reference tc tne drawings, m which: Fig. 1 snows a sketch of one embodiment of tne device a. - - ccrding to the invention, and Fig. 2 snows a sketch of a further embodiment. Figure 1 shows schematically a first embodiment of the device according to the invention. A component which is to be weloeα to a workpiece is called a stud m the following text, for the sake of simplicity, although the invention is, of course, not limited to such components. The device comprises a stud welding apparatus 1 which is known per se and is suitable for the generation of an adjustable welding current during a welding time, which is likewise adjustable. The adjustment is carried out as a function of the material used and of tne weld diameter. A welding head control unit 2 comprises a hy¬ draulic control valve 3 with built-in electronics, which is known per se and is suitable for carrying out quick and pre¬ cise position control hydraulically, on the basis of an input signal. The control valve 3 is connected to a hydraulic cyl¬ inder 4 on which a stud holder 5 is mounted, which is suit¬ able for holding a stud 6 which is to be welded to a work- piece 7. Furthermore, the control valve 3 is connected via a hydraulics and control line 9 to a hydraulic unit 8, which is known per se. The stud holder 5 is connected via a welding current line 10 to the stud welding apparatus 1. The hydrau¬ lic cylinder 4 is thus used, together with the stud holder z , as a welding head. The stud welding apparatus 1 is connected via an earth line 11 tc the workpiece 7. A microprocessor controller 12 is connected via a control line 13 tc the stuc welding apparatus 1. Furthermore, the microprocessor control¬ ler 12 is connected via a measurement line 14 tc the work¬ piece ~ , and via a measurement line 15 tc the stud holder Ξ. Finally, the microprocessor controller 12 is connected via a. control line 16 to the hydraulic unit S. The welding head control unit 2 can have a supporting foot for placing the stud 6 precisely onto the workpiece 7. However, the weidir.-r head control unit 2 is preferably combined with a position measurement system, which is not shown and is known per se . In order to weld a stud 6 to a workpiece 7, a reliable elec¬ trical contact is initially produced between the stud end and the welding point of the workpiece 7, by placing the stud c onto a welding point on the workpiece 7. This null position is measured by means of the position measurement system and is stored in the microprocessor controller 12 as a reference. The welding time and the welding current as well as the de¬ sired a c voltage (that is to say the reference voltage pro¬ file for the arc voltage control variable during the welding process) and the ratio between the arc voltage and the dis¬ tance between the stud and the workpiece are set in the mi- croprocessor controller 12 and are passed on via the control line 13 to the stud welding apparatus 1. In addition, further parameters relating to the insertion of the melted stud end into the melted welding point on the workpiece 7 can be ad- justed as described in the following text. The actual welding process is then carried out by lifting the stud 6 off the workpiece 7 and by producing an arc between the stud end and the welding point on the workpiece 7, m or- der to melt the latter. The current arc voltage is measured by the measurement lines 14 and 15, and is compared with the current reference voltage of the set reference voltage pro¬ file repeatedly as a controlled variable in a control loop by means of the microprocessor controller 12 throughout tne en- tire welding process, a correction variable in each case be¬ ing determined from the difference between the measured arc voltage and the current reference voltage. This correction variable is in each case fed via the control line l tc the hydraulic unit 8 which in each case produces a corresponding correction to the distance between the stud and the work- piece, by means of the control valve 3, via the hydraulics and control line 9. The distance between the stud and t e workpiece is thus m each case automatically corrected as a manipulated variable in the control loop, by converting t e determined ccrrection variable by means of the hydraulic unit 8 and the hydraulic control valve 3. The arc voltage is moni¬ tored continuously during welding, and the distance between the stud and workpiece is adjusted accordingly several hun¬ dred times per second. The resetting and insertion of the melted stud end into the melted welding point on the workpiece 7 is also detected and controlled via the microprocessor controller 12. On comple¬ tion of the formation of the arc, the automatic correction cf the distance between the stud and the workpiece by means cf the control loop is also completed. The last setting of the distance between the stud and the workpiece is measured by- means of the position measurement system and stored m the microprocessor controller 12, the stored null position being used as a reference value. The controlled resetting of tne distance between the stud and the workpiece and tne insertion are now carried out. The insertion depth (also called the in¬ sertion dimension) and the rate of insertion can be set m the microprocessor controller 12, the stored null position in each case being used as a reference value. Tne set values are converted into the insertion dimension and into the rate of insertion by means of the hydraulic control valve 3, wnicn is combined with the position measurement system. This is in turn done by means of a control loop, the insertion dimension in this case being measured and adapted, on tne basis cf the predetermined setting values, repeatedly as a controlled variable by means of the position measurement system. Ir. this way, high precision is achieved completely automatically even during the resetting and during insertion, whicn once again leads to an improvement in the weld quality. After achieving the set maximum insertion depth, a movement back tc the null position is carried out again after a resetting time, wnicn is likewise adjustable. The described hydraulic embodiment is primarily suitable for relatively large installations, it being pcssiole tc install the welding head control unit 2 permanently. Figure 2 shows a sketch of a further embodiment. In this case, the welding head control unit 2 comprises a control magnet 17 and a stud holder 18 which is connected thereto, is m turn suitable for holding a stud 6, which is to be welded to a workpiece 7, and is connected via the welding current line 10 to the stud welding apparatus 1 , so that the control magnet 17 is used, with the stud holder 18, as a welding head. The control magnet 17 is, for example, a modified hydraulic control valve. On the basis of a control valve with built-in electronics, which is known per se, is used in hydraulics and is suitable for carrying out quick and precise position control hydraulically on the basis of an input sig¬ nal, this control valve is modified such that the hydraulic valve part was omitted and the magnetically controlled shaft was connected directly to the stud holder 18. A control mag¬ net 17 is thus implemented in a simple manner with high pre¬ cision, an integrated position measurement system addition¬ ally already being present. The control magnet 17 is ccn- nected via a control line 19 to the microprocessor controller 12. The sequence of the welding process is similar to that m the case of the hydraulic variant described above. Ail the re- quired position measurements can, however, be carried out di¬ rectly using the position measurement system integrated ir. the control magnet 17. The correction variable, which is in each case determined by the microprocessor controller 12, for the distance between the stud and workpiece is fed via tne control line 19 directly to the electronically controlled control magnet 17, which in each case produces a correspond¬ ing correction to the distance between the stud and the workpiece. The distance between the stud and workpiece is thus in each case corrected automatically as a manipulated variable in the control loop, by conversion of the determine:: correction variable by means of the control magnet 17. Even a simple analog controller is sufficient, for example, for this purpose, in the case of which the arc voltage is measured and compared in a comparator with the current refer¬ ence voltage continuously, the difference being processed via a filter and a PD or PID regulator and being fed to the con¬ trol magnet 17 as a correction signal. In this case, the in¬ ertia of the control magnet 17, although it is low, also con- tributes to the filtering of voltage spikes and thus to the avoidance of resonances. The resetting and insertion are also carried out in a similar manner to that described above with reference to Figure 1. In this case, the values which are set in the microprocessor controller 12 for the rate of insertion and the insertion di¬ mension are converted into the desired movement by means of the control magnet 17. The electromagnetic embodiment described can easily be oper- ated by hand if the control magnet 1 " is constructed, with the stud holder 18, as a welding gun. According to a further embodiment, which is net shown, the automatic correction cf the distance between the stud and workpiece and the setting of the insertion dimension are car¬ ried out by conversion of the determined correction variables by means of an electric motor and a spindle. The method according to the invention and the devices acccrα- ing to the invention for the automatic adjustment of tne dis¬ tance between the stud and the workpiece and the msertior dimension can be combined directly with any commercial_ available stud welding apparatuses using the lift-off igr.-- tion cr short-cycle methods. In the case cf stud weidmα a: - paratuses having a microprocessor controller, the microproc¬ essor controller 12 can be integrated.

Claims: Patent Claims 1. Welding method for the connection of a component (6) to a workpiece (7), having the following steps: - fitting the component (6) onto a welding point on the workpiece (7) , lifting the component (6) off the workpiece (7) and producing an arc between the component end and the welding point on the workpiece (7) , m order to melt the latter, resetting and inserting the melted component end into the melted welding point on the workpiece (7) , characterized in that a reference voltage profile is set for the arc voltage and the arc voltage is measured and compared with the current reference voltage repeatedly during the welding process in a control loop, as a con¬ trolled variable, a correction variable in each case be¬ ing determined from the difference between the measured arc voltage and the current reference voltage, by means of which correction variable the component lift is i each case automatically corrected, as a manipulated variable. 2. Method according to Claim 1, characterized in that the resetting and insertion are carried out automatically at an adjustable speed and as far as an adjustable in¬ sertion depth. 3. Method according to one of Claims 1 and 2, characterized in that the automatic correction of the component lift is carried out by conversion of the determined correction variables by means of a hydraulic unit (8ι and a hydraulic control valve (3) . 4. Method according to one of Claims 1 and 2, characterized in that the automatic correction of the component lift is carried out by conversion of the determined correction variables by means of a control magnet (17) . 5 5. Method according to one of Claims 1 and 2, characterized in that the automatic correction of the component lift is carried out by conversion of the determined correction variables by means of an electric motor and a 0 spindle. 6. Method according to one of Claims 1 to 5, characterized in that the arc voltage is measured and is compared by means of a comparator with the current reference voltage 5 continuously during the welding process, tne difference between the measured arc voltage and tne current refer¬ ence voltage being processed via a filter ano a PD cr PIE regulator, and being fed to the control magnet (l "1 as a correction signal for the component lift. C 7. Eevice for carrying out the method according to one cf Claims 1 to 6, characterized in that the device com¬ prises a stud welding apparatus (1) , a welding head cc^ - trcl unit (2) having a stud nolder (5; 18 , ana a icrc- 5 processor controller (12) . 8. Device according to Claim 7, characterized in that tne welding head control unit (2) comprises a hydraulic con¬ trol valve (3) with a hydraulic cylinder (4) , and tne 0 device is furthermore provided with a hydraulic unit 9. Device according to Claim 8, characterized in that the welding head control unit (2) is combined with a posi- 5 tion measurement system. 10. Device according to Claim 1 , characterized in that the welding head control unit (2) comprises a control magnet (17) with an integrated position measurement system.

Inventors: VON DAENIKEN KURT, VON DAENIKEN, KURT
Applicants: VON DAENIKEN KURT, VON DAENIKEN, KURT
Application year: 1995
Main classification: B23K9
IPC codes: B23K9, B23K11