JP2014159044A - Seam welding method and system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seam welding method capable of preventing excessive heat generation in a contact area between an electrode roller and a work-piece.SOLUTION: A method includes the steps of estimating a total radius Rt of a pair of disk-like electrode rollers 15, 16 (STEP1), reducing a welding-current value I as the total radius Rt decreases (STEP2), and energizing between the electrode rollers 15, 16 with a plurality of work-pieces W interposed between the electrode rollers 15, 16 to supply welding-current to perform seam welding (STEP3).

Description

  The present invention relates to a seam welding method and system.

  Conventionally, seam welding is known in which a workpiece (workpiece) is sandwiched between a pair of electrode rollers, and the workpiece is continuously welded by rotating the electrode roller while applying pressure.

  Since the outer peripheral surface of the electrode roller is abutted against the workpiece and is worn, the outer diameter of the electrode roller becomes smaller as the number of seam welding is increased. Further, when the outer peripheral surface of the electrode roller is worn, irregularities (creeks) are generated and the welding current becomes unstable, which adversely affects the welding result of the workpiece. Therefore, it is necessary to periodically polish (dressing) the outer peripheral surface of the electrode roller, and this also reduces the outer diameter of the electrode roller.

  Patent Document 1 describes a technique for performing seam welding by changing the setting of the welding current according to the starting end welding condition section, the steady state welding condition section, and the terminal end welding condition section of the workpiece. Yes.

JP-A-11-333570

  However, for example, when seam welding is performed by applying the same pressure to the electrode roller, the radius of curvature of the outer peripheral surface of the electrode roller decreases as the outer diameter of the electrode roller decreases, so that the contact between the electrode roller and the workpiece is contacted. The area becomes smaller. As a result, the density of the energization current increases and the amount of heat generation increases. And when the state of excessive heat generation is reached, there arises a problem that scattering occurs.

  Patent Document 1 does not disclose changing the welding conditions in accordance with the wear of the electrode roller.

  In view of the above, an object of the present invention is to provide a seam welding method and system capable of preventing a contact portion between an electrode roller and a workpiece to be overheated.

  The seam welding method of the present invention performs seam welding by supplying a welding current for energizing the electrode rollers with a plurality of workpieces sandwiched between a pair of electrode rollers formed in a disk shape. A seam welding method for performing a step of obtaining an outer diameter of the pair of electrode rollers, and a step of reducing a current value of the welding current as the outer diameter of the electrode roller obtained in the step decreases. It is characterized by providing.

  According to the seam welding method of the present invention, as the outer diameter of the electrode roller decreases, the current value of the welding current energized between the electrode rollers is decreased. Thereby, even if the outer diameter of the electrode roller is reduced and the contact area between the electrode roller and the workpiece is reduced, an increase in the amount of generated heat is suppressed. Therefore, it is possible to solve the problem that scattering occurs due to excessive heat generation.

  The seam welding system according to the present invention is a seam welding system that performs seam welding by energizing the electrode rollers with a plurality of workpieces sandwiched between a pair of electrode rollers formed in a disk shape. A roller diameter obtaining means for obtaining an outer diameter of the pair of electrode rollers; a welding current supply means for supplying a welding current for energizing the electrode rollers; and the electrode roller obtained by the roller diameter obtaining means. And a control means for reducing the current value of the welding current supplied by the welding current supply means as the outer diameter decreases.

  According to the seam welding system of the present invention, the control means decreases the current value of the welding current energized between the electrode rollers as the outer diameter of the electrode rollers decreases. Thereby, even if the outer diameter of the electrode roller is reduced and the contact area between the electrode roller and the workpiece is reduced, an increase in the amount of generated heat is suppressed. Therefore, it is possible to solve the problem that scattering occurs due to excessive heat generation.

Schematic which shows the whole structure of the seam welding system which concerns on embodiment of this invention. The block diagram which shows the whole structure of a seam welding system. The graph explaining change of a welding current value. The conceptual diagram explaining the total radius of an electrode roller. The flowchart explaining the seam welding method which concerns on embodiment of this invention.

  A seam welding system 100 according to an embodiment of the present invention will be described with reference to the drawings. The seam welding system 100 is used when a plurality of workpieces (workpieces) W made of a thin metal plate are joined by the seam welding apparatus 10 to manufacture a window frame or a fuel tank of an automobile.

  As shown in FIG. 1, the workpiece W is seam welded by a seam welding apparatus 10 that is fixed at a predetermined position by a workpiece fixing base (not shown) and moved along a predetermined trajectory by a robot 20. . Referring to FIG. 2, the seam welding system 100 includes a control device 30 that controls the seam welding device 10 and the robot 20 and corresponds to the control means of the present invention.

  The robot 20 is an articulated robot such as a six-axis robot in which a plurality of arms are connected by joints, and is fixed to the base 21. Although not shown, the robot 20 includes a driving unit such as a servo motor at each joint and a detecting unit such as an encoder that detects the shaft angle of the servo motor, and is configured to be feedback-controlled by the control device 30. .

  An equalizing mechanism 22 is provided at the tip of the arm located at the tip of the robot 20. The seam welding apparatus 10 is elastically supported at the tip of the arm of the robot 20 by an equalizing mechanism 22. Thereby, even if there is a minute change in the portion to be welded, the seam welding apparatus 10 can follow the change.

  The seam welding apparatus 10 includes a base 11 that is attached to the robot 20 via an equalizing mechanism 22. The base 11 is provided with a guide rail 12 extending in the vertical direction, and the guide rail 12 is provided with a movable base 14 that can be moved in the vertical direction by the driving means 13 along the guide rail 12. ing. Here, the drive means 13 is the air cylinder 13, and the movable table 14 is connected to the tip of the piston rod 13 a of the air cylinder 13. The driving means may be a hydraulic cylinder, a rotary motor equipped with a ball screw mechanism, a linear motor, or the like.

  An upper electrode 15 is pivotally supported on the movable base 14, and a lower electrode 16 is pivotally supported on the base 11. Accordingly, the lower electrode 16 is provided at a predetermined height position, and the upper electrode 15 is disposed so as to be vertically movable with respect to the lower electrode 16. The upper electrode 15 and the lower electrode 16 are disk-like electrodes, and are also referred to as electrode rollers 15 and 16 together.

  The electrode rollers 15 and 16 are connected to rotation drive means 17 and 18 for rotating the electrode rollers 15 and 16 at a rotation speed set in a preset rotation direction, respectively. Here, the rotation driving means 17 and 18 are servo motors, but they may be ordinary motors including a pulse motor and a rotary encoder.

  Furthermore, the upper electrode 15 is supplied with a current (welding current) necessary for welding and is connected to a welding power source 19 corresponding to the welding current supply means of the present invention. Here, the welding power source 19 supplies a DC pulse current, but it may supply an AC current.

  In this way, the piston rod 13 a of the air cylinder 13 is extended to lower the upper electrode 15, and the welding current is supplied from the welding power source 19 to the upper electrode 15 with the workpiece W sandwiched between the electrodes 15 and 16. To do. As a result, a welding current flows from the upper electrode 15 to the lower electrode 16 (earth electrode) through the workpiece W sandwiched between the electrode rollers 15 and 16, and seam welding can be performed.

  As described above, the air cylinder 13 functions as a pressurizing unit that pressurizes the workpiece W sandwiched between the electrode rollers 15 and 16 by pressing the upper electrode 15 toward the lower electrode 16.

  Further, the air cylinder 13 includes a stroke sensor (not shown) for detecting the position of the piston rod 13a. Thereby, referring to FIG. 3, the air cylinder 13 also functions as a measuring means for directly pressing the upper electrode 15 against the lower electrode 16 and measuring the total radius Rt = R1 + R2 of the two electrode rollers 15 and 16. To do.

  Since the vertical height of the lower electrode 16 is constant, when the piston rod 13a of the air cylinder 13 is extended and the upper electrode 15 is lowered and brought into contact with the lower electrode 16, the two electrode rollers 15, 16 The total radius Rt can be obtained from the stroke amount of the piston rod 13 a of the air cylinder 13 or the relative vertical distance between the base 11 and the movable base 14.

  Note that a distance measuring sensor that detects a relative vertical distance between the base 11 and the movable table 14 may be provided on the base 11 or the movable table 14, and the distance measuring sensor may be used as a measuring unit. As the distance measuring sensor, for example, a non-contact type laser distance meter, a contact type linear scale sensor, or a magnet scale sensor can be used. Further, the relative vertical distance between the base 11 and the movable base 14 may be obtained using an image sensor such as a line sensor.

  The control device 30 is an electronic circuit unit configured by a CPU or the like (not shown). As shown in FIG. 2, the control device 30 executes a control program held in the memory 31 by the CPU, thereby rotating the cylinder control unit 32 that controls the air cylinder 13 and the rotation drive units 17 and 18. It functions as a drive control unit 33, a power supply control unit 34 that controls the welding power source 19, and a robot control unit 35 that controls the robot 20, and controls the operations of the seam welding apparatus 10 and the robot 20.

  The memory 31 stores the teaching data of the robot 20, the amount of movement of the piston rod 13 a of the air cylinder 13, the rotational speed of the rotation driving means 17 and 18 according to the welding conditions, and the welding power supplied from the welding power source 19. Welding control data such as a current value is stored. Further, the memory 31 stores a welding current value calculation program for calculating a welding current value I supplied from the welding power source 19. When the CPU executes the welding current value calculation program, the control device 30 functions as a welding current value calculation unit.

  The control device 30 transmits control signals created by reading out the welding control data stored in the memory 31 according to the welding conditions to the air cylinder 13, the rotation driving means 17 and 18, the welding power source 19, and the robot 20.

  Here, the electrode rollers 15 and 16 are gradually consumed by performing seam welding, and further shaped by dressing. Therefore, the diameters of the electrode rollers 15 and 16 are reduced.

  Therefore, even when seam welding is performed on the same workpiece W, it is necessary to change the welding conditions in accordance with a decrease in the total radius Rt of the electrode rollers 15 and 16. For example, when the total radius Rt decreases, the applied pressure decreases even if the piston rod 13a of the air cylinder 13 is extended by the same stroke amount. Therefore, it is necessary to increase the stroke amount for extending the piston rod 13a in accordance with the decrease in the total radius Rt. Further, when the total radius Rt decreases, the rotation speed of the rotation driving means 17 and 18 and the movement speed of the electrode rollers 15 and 16 with respect to the workpiece W cannot be synchronized. Therefore, it is necessary to slow down the moving speed of the electrode rollers 15 and 16 with respect to the workpiece W in accordance with the decrease in the total radius Rt.

  Thus, even if the welding conditions such as the applied pressure are controlled to be constant, when the diameter of the electrode rollers 15 and 16 is reduced, the contact area between the electrode rollers 15 and 16 and the workpiece W is reduced. While the current density per unit contact area increases, the amount of heat generated increases because the electrode roller as a heat mass becomes smaller. If the heat generation amount is excessive, welding failure occurs, for example, the workpiece W melts and scatters to cause scattering.

  Therefore, when the total radius Rt of the electrode rollers 15 and 16 is reduced, the welding current supplied from the welding power source 19 is maintained in order to keep the current density at the contact portion between the electrode rollers 15 and 16 and the workpiece W substantially constant. A welding current value calculation program is set so as to reduce the value I. Thereby, the nugget generated by seam welding can be maintained in a nearly constant state, and the possibility of occurrence of welding defects such as scattering can be eliminated.

  For example, when the radius of the electrode rollers 15 and 16 at the time of a new article is 50 mm and the radius of the electrode rollers 15 and 16 at the limit of use is 40 mm, the difference in radius is 10 mm. Since the radius of the electrode rollers 15 and 16 is equal to the radius of curvature of the portion in contact with the workpiece W, if the pressing force is constant, the electrode rollers 15 and 16 and the workpiece W are proportional to the decrease in the diameter of the electrode rollers 15 and 16. The contact area with is small.

  Therefore, referring to FIG. 4, based on the total radius Rt of the electrode rollers 15 and 16, for example, a welding current value I for energizing the electrode rollers 15 and 16 is obtained by the following equation (1).

  I = I0−I0 × (Rt / Rt0) × α (1)

  Here, I0 is a welding current value in the electrode rollers 15 and 16 when new, and Rt0 is a total radius of the electrode rollers 15 and 16 when new. Α is a predetermined ratio, and is determined by an experiment or the like in consideration of a change in contact area between the electrode rollers 15 and 16 and the workpiece W, that is, a change in current density. For example, the ratio α can be obtained by the following equation (2).

  α = (I0−Iw) / (Rt0−Rtw) (2)

  Here, Iw is a welding current value for energizing the electrode rollers 15 and 16 at the use limit, and Rtw is a total radius of the electrode rollers 15 and 16 at the use limit. In advance, the total radius Rt0 of the electrode rollers 15 and 16 when new, the total radius Rtw of the electrode rollers 15 and 16 when used, the welding current value I0 for energizing the electrode rollers 15 and 16 when new, The welding current value Iw for energizing the electrode rollers 15 and 16 at the limit may be stored.

  The welding current value I may be a value obtained by rounding off to a set unit in the welding power source 19, for example, a mA unit, with respect to the values obtained by the equations (1) and (2). Further, the welding current value I is changed when the value obtained by the equations (1) and (2) is changed from the current set value beyond a preset range, for example, 2 mA. You may let them. Further, a map in which the total radius Rt of the electrode rollers 15 and 16 is associated with the welding current value I may be stored in the memory 31, and the welding current value I may be obtained from this map.

  Further, when it is possible to detect the radii of the upper electrode 15 and the lower electrode 16, a map in which the radii of the upper electrode 15 and the lower electrode 16 are associated with the welding current value I is stored in the memory 31. The welding current value I may be obtained from this map in advance.

  Next, a seam welding method according to an embodiment of the present invention using the above-described seam welding system 100 will be described with reference to the drawings.

  As shown in the flowchart of FIG. 5, first, a step of obtaining the total radius Rt of the electrode rollers 15 and 16 is performed (STEP 1). More specifically, in this step, the electrode rollers 15 and 16 are determined from the stroke amount of the piston rod 13a when the piston rod 13a of the air cylinder 13 is extended and the upper electrode 15 is lowered and brought into contact with the lower electrode 16. Can be obtained from the relative vertical distance between the base 11 and the movable base 14.

  Next, a step of obtaining an optimum welding current value I is performed (STEP 2). In this step, specifically, the CPU of the control device 30 executes the welding current value calculation program, and the equation (1) and the equation (2) are used to respond to the total radius Rt of the electrode rollers 15 and 16. The optimum welding current value I is obtained.

  Next, a process of seam welding to the workpiece W is performed (STEP 3). In this step, the optimum welding current value I obtained in STEP 2 is supplied from the welding power source 19 to the upper electrode 15.

  Then, if there is a large change in the total radius Rt of the electrode rollers 15 and 16 due to dressing or the like (STEP 4: YES), the process proceeds to STEP 1 to determine the total radius Rt of the electrode rollers 15 and 16, which is obtained here. Based on the total radius Rt, a step of obtaining an optimum welding current value I in STEP 2 is performed.

  If there is no significant change in the total radius Rt of the electrode rollers 15 and 16 (STEP 4: NO), the process of seam welding to the workpiece W is continued until the seam welding is completed (STEP 5: YES) (STEP 3).

  As described above, in the present embodiment, the optimum welding current value I corresponding to the total radius Rt of the electrode rollers 15 and 16 is obtained (STEP 2). Therefore, as the diameter of the electrode rollers 15 and 16 is reduced, the welding current value I to be passed between the electrode rollers 15 and 16 is reduced, so that the amount of heat generated at the contact portion between the electrode rollers 15 and 16 and the workpiece W is excessive. In addition, it is possible to eliminate the possibility of welding failure such as scattering.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this. For example, the case where the upper electrode 15 can be moved up and down and the lower electrode 16 is fixed has been described. However, the present invention is not limited to this, and even if the upper electrode 15 is fixed and the lower electrode 16 can move up and down, both the upper electrode 15 and the lower electrode 16 may move up and down.

  Further, the case where the upper electrode 15 and the lower electrode 16 are arranged vertically has been described. However, the present invention is not limited to this, and the upper electrode 15 and the lower electrode 16 may be arranged horizontally or inclined.

  DESCRIPTION OF SYMBOLS 10 ... Seam welding apparatus, 11 ... Base, 12 ... Guide rail, 13 ... Drive means, air cylinder, 13a ... Piston rod, 14 ... Movable stand, 15 ... Upper electrode (electrode roller), 16 ... Lower electrode (electrode roller) , 17, 18 ... Rotation drive means, 19 ... Welding power supply (welding current supply means), 20 ... Robot, 21 ... Base, 22 ... Equalize mechanism, 30 ... Control device (control means), 31 ... Memory, 32 ... Cylinder Control part 33 ... Rotation drive control part 34 ... Power supply control part 35 ... Robot control part 100 ... Seam welding system W ... Workpiece (workpiece to be welded).

Claims (2)

A seam welding method for performing seam welding by supplying a welding current for energizing between the electrode rollers in a state where a plurality of workpieces are sandwiched between a pair of electrode rollers formed in a disk shape,
Obtaining an outer diameter of the pair of electrode rollers;
And a step of reducing the current value of the welding current as the outer diameter of the electrode roller determined in the step decreases. A seam welding system for performing seam welding by energizing between the electrode rollers in a state where a plurality of workpieces are sandwiched between a pair of electrode rollers formed in a disk shape,
Roller diameter obtaining means for obtaining an outer diameter of the pair of electrode rollers;
Welding current supply means for supplying a welding current for energizing the electrode rollers;
A seam welding system comprising: control means for reducing the current value of the welding current supplied by the welding current supply means as the outer diameter of the electrode roller obtained by the roller diameter finding means decreases.

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