Stud welding machine and method for preventing welding defects in a stud welding machine

Abstract

To provide a stud welding technique that can prevent poor weld due to poor distance between a stud and a base metal.SOLUTION: A stud welder 1 comprises: a welding gun 2 for welding a stud S to a base material W; and a control part for controlling the welding gun 2. The welder is provided with a displacement meter 26 which measures an upward movement amount of the stud S with respect to the welding gun 2 when moving the welding gun 2 downward in a Z-axis direction and pressing the stud S arranged at a tip of the welding gun 2 against the base material W. On the basis of the movement amount measured by the displacement meter 26, the control part controls the operation of the welding gun 2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for preventing welding defects in a stud welder.

Background Art

[0002] Conventionally, there is stud welding as a method of welding a stud to a base material. In particular, the CD method stud welder (Capacitor Discharge Stud Welding) has been widely used. CD method stud welding is a method of charging a large-capacity capacitor based on an AC power source and using the discharge from this capacitor to weld the stud and the base material. An arc is formed between the lower end of the stud and the base material, and after melting the lower end of the stud and the base material, the molten parts are pressed together to weld the stud to the base material.

[0003] Known documents related to stud welding include, for example, Patent Document 1 and Patent Document 2. Patent Document 1 discloses a stud welding gun comprising a chuck for holding a welding tip which is a stud member, a tip holder for connecting the chuck and connected to the positive electrode side electric cord, a pressurizing spring for biasing the tip holder, an earth base pipe to which the ground side electric cord is connected, an insulating pipe for insulating the tip holder and the earth base pipe, a cylindrical metal ground pipe connected to the earth base pipe, and a switch for issuing a welding instruction signal.

[0004] Patent Document 2 discloses a stud welding machine comprising: a welding gun having a stud holding means for holding a stud and a driving means for moving the holding means to press the stud against a base material or away from the base material; a power supply connected to the welding gun to supply a predetermined power between the stud and the base material; and a controller that controls the power supply and the driving means to form an arc between the stud that has been separated from the base material and the base material, and controls the driving means to press the molten stud portion against the molten base material portion after the stud tip portion and the base material portion have been melted by the continuation of the arc, wherein the welding gun is provided with a buffering means between the driving means and the stud holding means to buffer the recoil when pressing the molten stud portion against the molten base material portion. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-346710 [Patent Document 2] Japanese Patent Publication No. 2000-301342 [Overview of the project] [Problems that the invention aims to solve]

[0006] The stud welding technology disclosed in Patent Document 1 uses a welding gun that can be held by hand by an operator. In addition to such devices, automated stud welding machines equipped with welding guns on carriages (movement mechanisms) that can move in the XYZ directions or on articulated robots are also widely available on the market. Such stud welding machines are equipped with a control unit (NC device) that controls the carriage and other components. The operator inputs data to operate the stud welding machine into the control unit. The stud welding machine also has a magazine containing various types of studs to be welded, and the studs in this magazine are loaded in such a way that they are all facing the same direction.

[0007] The welding gun mounted on the carriage has a predetermined stud attached from the magazine by the control unit, moves to a predetermined position on the base material, and welds the stud to that position. However, in actual field operations, human error is inevitable when loading studs into magazines. Studs may be loaded upside down, or the wrong studs may be loaded into the magazine.

[0008] In that case, as shown in Figures 2(b) to 2(e), the distance from the lower end of the stud (the part with the flange and projection) to the base material differed from the value in the control unit's program. Even if the carriage moved and the welding gun operated as commanded by the control unit, this caused welding defects. Patent Document 1 does not solve the above problem because it involves a worker holding the welding gun by hand while welding. The technology in Patent Document 2 is a technology for adjusting the pressure when pressing a stud against the base material, and is different from the technology that can prevent welding defects caused by poor distance between the stud and the base material, as shown in Figures 2(b) to 2(e).

[0009] Therefore, in view of the above problems, the present invention aims to provide a stud welding technology that can prevent welding defects caused by poor distance between the stud and the base material in a stud welding machine. [Means for solving the problem]

[0010] To achieve the above objectives, the present invention employs the following technical means. The stud welding machine according to the present invention is a stud welding machine comprising a welding gun for welding studs to a base material and a control unit for controlling the welding gun, wherein a displacement meter is provided to measure the amount of upward movement of the stud relative to the welding gun when the welding gun is moved in the Z-axis direction and the stud positioned at the tip of the welding gun is pressed against the base material, and the control unit is configured to control the operation of the welding gun based on the amount of movement measured by the displacement meter.

[0011] Preferably, the welding gun has a long, hollow cylindrical body and a through rod that penetrates the hollow portion of the cylindrical body, a chuck for gripping the stud is attached to the lower end of the through rod, the upper end of the through rod protrudes from above the cylindrical body, a cap member is fitted onto the upper protruding portion of the through rod, a biasing member is provided between the cap member and the upper end of the cylindrical body, and a displacement meter for detecting the amount of rise of the through rod from the cylindrical body is provided at the upper end of the through rod.

[0012] The present invention provides a method for preventing welding defects in a stud welding machine, characterized in that, in the stud welding machine described above, the control unit determines that normal stud welding is possible if the value of the displacement meter is within the reference range and performs welding with the welding gun, and refrains from performing welding with the welding gun if the value of the displacement meter is outside the reference range. [Effects of the Invention]

[0013] According to the technology of the present invention, welding defects caused by poor distance from the stud to the base material can be reliably prevented in a stud welding machine. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a welding gun (especially the gun head) and the Z-axis carriage that supports it. [Figure 2] This is a schematic diagram showing the relationship between the stud and the base material. [Figure 3] This is a flowchart for implementing welding defect prevention measures. [Modes for carrying out the invention]

[0015] Hereinafter, embodiments of the stud welding machine 1 according to the present invention and the method for preventing welding defects in this stud welding machine 1 will be described with reference to the figures. Note that the embodiments described below are examples of embodying the present invention, and do not limit the configuration of the present invention with specific examples. For example, in the following description, the explanation will proceed with a CD type automatic welding machine that automatically performs stud welding in mind, but the configuration of the stud welding machine 1 is not limited to this.

[0016] The stud welding machine 1 includes a table for installing the base material W, a magazine (stud feeder) loaded with studs S to be welded to the base material W, a welding gun 2, an X-axis carriage for moving the welding gun 2 in the X-axis direction (left and right direction), a Y-axis carriage for moving the welding gun 2 in the Y-axis direction (front and back direction), a Z-axis carriage 3 for moving the welding gun 2 in the Z-axis direction (up and down direction, or the direction approaching or moving away from the base material), a welding power supply unit, and a control unit for controlling these. The carriage may be composed of an articulated robot.

[0017] First, the base material W to which the stud S is to be welded is placed on the table. Although not shown, it is preferable that the table on which the base material W is installed has a positioning mechanism for positioning the base material W placed on this table, but it may also be a simple installation table. An earth cable is connected to the base material W arranged on the table, and the earth cable is connected to the welding power supply unit.

[0018] The welding gun 2 is movable in the X-axis direction and the Y-axis direction by the X-axis carriage and the Y-axis carriage. As shown in FIG. 1, it is also movable in the Z-axis direction by the Z-axis carriage 3. As shown in FIG. 1, the welding gun 2 has a long cylindrical body 21 that is hollow. The cylindrical body 21 is arranged so as to face the up and down direction and is connected to the Z-axis carriage 3. In the hollow portion formed in the cylindrical body 21 so as to face the up and down direction, a through rod body 22 is arranged so as to penetrate this hollow portion. At the lower end of the through rod body 22, a chuck 23 for gripping the stud S is attached. Inside the chuck 23, a stopper rod body 28 for preventing the stud S from entering the chuck 23 more than necessary is inserted from above.

[0019] The upper end of the through rod 22 protrudes upward from the cylinder 21, and a cap member 24 is fitted into the central portion of the protruding portion (the through rod 22 protruding from the cylinder 21). A string wound spring, which is a biasing member 25, is provided between the cap member 24 and the upper end of the cylinder 21. By this biasing member 25, the Z-axis carriage 3 can lower the cylinder 21 downward until the projection ST formed at the lower end of the stud S inserted into the chuck 23 contacts the base material W. After the projection ST contacts the base material W, by further lowering the cylinder 21 downward (re-lowering), the through rod 22 protrudes upward from the cylinder 21 and the string wound spring is extended. Due to the biasing force (the force pressing the stud S against the base material W) caused by this extension, the stud S is pressed against the base material W side in the molten state after welding starts to ensure welding.

[0020] Although details will be described later, as a characteristic configuration of the present invention, a displacement gauge 26 (linear gauge) is attached to the upper end of the through rod 22. This displacement gauge 26 can measure the upward movement amount (upward distance) of the through rod 22 during re-lowering. The measurement accuracy is preferably about 1 micron. The measured value of this displacement gauge 26 is taken into the control unit as a digital signal, and after being subjected to the processing described later, it is used for the determination of preventing welding defects. As the control unit, a PLC or a personal computer is adopted.

[0021] The stud welder 1 described in this embodiment can weld a plurality of types of studs S. Therefore, a magazine capable of storing a plurality of studs S is arranged at a predetermined position of the stud welder 1, and the studs S are arranged to be stacked vertically in this magazine. The studs S have various diameters and lengths. Also, as shown in FIG. 2, the tip of the stud S is a flange-shaped flange portion SF. A projection ST is formed at the center thereof. The cylinder 21 is lowered by the Z-axis carriage 3 so that the projection ST contacts the base material W and is further pressed with a predetermined pressure.

[0022] The operating mode of the stud welding machine 1 described above will now be explained. First, the control unit of the stud welding machine 1 stores the welding conditions and welding position for each stud S. Each carriage moves the welding gun 2 according to this stored data. First, it goes to attach the chuck 23 capable of gripping the stud S to be welded, and then attaches the stud S loaded in the magazine to the chuck 23. After that, each carriage moves the welding gun 2 to a predetermined position (especially the XY position) on the base material W, and the Z-axis carriage 3 lowers the welding gun 2 to weld the stud S to the base material W (see Figure 2(a)).

[0023] In detail, the Z-axis carriage 3 moves the stud S to a position where the projection ST at the tip of the stud S contacts the base material W. Furthermore, it is lowered again by a few millimeters from that position. This applies a pressing force to the stud S. Once the stud S contacts the base material W, and then the Z-axis carriage 3 lowers again, the through rod 22 pushes up the measuring probe 27 of the displacement meter 26, causing the displacement meter 26 to start measuring, and the measured value is transmitted to the control unit.

[0024] Subsequently, if the "welding defect detection logic" described later determines that the welding is normal, the control unit sends the specified current to the stud S through the welding power supply unit and starts welding. After welding is complete, the Z-axis carriage 3 rises and the welding gun 2 moves upward and moves to the magazine to grip the next stud S. Traditionally, the welding process described above occasionally resulted in the following problem: Since the stud S was loaded into the magazine by the worker, human error was unavoidable.

[0025] For example, one might consider loading the stud S upside down into the magazine. In that case, as shown in Figure 2(b), even if the welding gun 2 is lowered by the Z-axis carriage 3 and moved to a position where the projection ST of the stud S is in contact with the base material W (a position according to the program), a gap will remain between the stud S and the base material W. One possibility is that an incorrect stud S (for example, a stud S that is longer than specified) may be loaded into the magazine. In that case, as shown in Figure 2(c), when the welding gun 2 is lowered by the Z-axis carriage 3 to the position where the projection ST of the stud S contacts the base material W (the position according to the program), the tip of the stud S will reach a position lowered more than necessary. Another possibility is that an incorrect stud S (for example, a stud S that is shorter than specified) may be loaded into the magazine. In that case, as shown in Figure 2(d), even if the welding gun 2 is lowered by the Z-axis carriage 3 to the position where the projection ST of the stud S contacts the base material W (the position according to the program), a large gap will remain between the stud S and the base material W. In stud welding, the projection ST of the stud S is pressed against the base metal W during welding. If the side without the projection ST is pressed against the base metal W, or if there is a large gap between the stud S and the base metal W, applying welding current (turning on the welding signal) will not result in a high-strength weld, and the welding will be defective.

[0026] Furthermore, as shown in Figure 2(d), if a stud S with a crushed projection ST at its tip is loaded, even if the welding gun 2 is lowered by the Z-axis carriage 3 to a position (programmed position) where the projection ST of the stud S is in contact with the base material W, a gap will remain between the stud S and the base material W. The cause of the crushed projection ST of the stud S is likely a defect in the manufacturing process.

[0027] In either situation, the distance between the stud S and the base material W is not as planned, resulting in welding defects such as insufficient strength because the welding is not performed under the correct conditions. Next, we will explain the concept (welding defect prevention logic) of detecting situations that could lead to welding defects based on the values ​​read by the displacement gauge 26 and preventing welding defects. This logic is shown in the flowchart in Figure 3 and is implemented in the control unit, which issues control commands to each component (for example, the Z-axis carriage 3).

[0028] First, when welding begins, the welding gun 2 moves with each carriage and attaches the chuck 23 to its tip at the chuck station (S1, S2). Subsequently, the welding gun 2 is moved to the magazine by each carriage, and the stud S is inserted into the chuck 23 in the magazine and attached (S3, S4). Subsequently, welding gun 2 moves on its carriage to the welding position (S5).

[0029] Next, the Z-axis carriage 3 lowers and then lowers again until the projection ST at the lower end of the stud S contacts the base material W (a value set in the program) (S5, S6). At this time, the biasing member 25 applies a pressing force to the stud S. Once the stud S contacts the base material W and the Z-axis carriage 3 lowers further, the through rod 22 pushes up the measuring probe 27 of the displacement meter 26. The displacement meter 26 itself measures the amount the measuring probe 27 is pushed up and transmits the measured value to the control unit (S7).

[0030] The control unit determines whether the measurement value of the displacement gauge 26 is within the range of 3 mm ± 0.3 mm (sometimes called the reference range). If it is within the reference range (Yes in S8), the condition of the tip of the welding gun 2, in other words, the distance between the stud S and the base material W is appropriate as shown in Figure 2(a), and optimal welding is performed when welding current is applied in this state (S9). Note that the width (tolerance) of the reference range is set to 0.3 mm, but it is not limited to this value.

[0031] Meanwhile, the control unit determines whether the value of the displacement gauge 26 is within the range of 3 mm ± 0.3 mm, and if it is outside the reference range, it is determined to be No in S8. If it is outside the reference range, it is determined that the condition of the tip of the welding gun 2, in other words, the distance from the lower end of the stud S to the base material W, is as shown in Figures 2(b) to 2(e). That is, it is determined that the stud S is installed upside down in the chuck 23, or that a long or short stud S is installed, or that a stud S with a crushed projection ST is installed.

[0032] In situations like these (Figures 2(b) to 2(e)), proper welding will not be achieved, so the welding current should not be applied in this state. Without welding, the welding gun 2 is raised by the Z-axis carriage 3 and the work is stopped (S10). After warning the worker, the defective stud S is removed from the chuck 23 and replaced with the correct stud S or the orientation of the stud S is changed (S11). By performing these operations, it is possible to prevent welding defects.

[0033] In other words, following the flowchart in Figure 3, it is possible to prevent welding defects caused by improper distance from the stud S to the base material W in the stud welding machine 1. In conclusion, the embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. For example, the amount of indentation of the stud S measured by the displacement gauge 26 is not limited to 3 mm. It may be changed as appropriate depending on the shape of the welding gun 2 and the size of the stud S. Similarly, the tolerance is not limited to 0.3 mm, and an appropriate value should be selected.

[0034] Furthermore, although the welding gun 2 was moved using a carriage in this embodiment, the welding gun 2 may be attached to the tip of an articulated robot. Alternatively, the welding gun 2 may be held by an operator. In particular, matters not explicitly stated in the embodiments disclosed herein, such as operating conditions, handling conditions, dimensions of components, and weight, do not deviate from what is normally practiced by those skilled in the art, and are matters that can be easily anticipated by those skilled in the art. [Explanation of symbols]

[0035] 1 Stud welder 2. Welding gun 3 Z-axis carriage 21 Cylinder 22 Penetrating rod 23 Chuck 24 Cap member 25. Biasing member 26 Displacement Gauge 27 Measuring element 28 Stopper rod S Stud SF flange section ST protrusion W Base material

Claims

1. A stud welding machine comprising a welding gun for welding studs to a base material and a control unit for controlling the welding gun, A displacement sensor is provided to measure the amount of upward movement of the stud relative to the welding gun when the welding gun is moved in the Z-axis direction and the stud positioned at the tip of the welding gun is pressed against the base material. Based on the amount of movement measured by the displacement sensor, the control unit is configured to control the operation of the welding gun. A stud welding machine characterized by the following features.

2. The welding gun has a long, hollow cylindrical body and a through-rod that penetrates the hollow portion of the cylindrical body. A chuck for gripping the stud is attached to the lower end of the through rod, the upper end of the through rod protrudes from above the cylindrical body, a cap member is fitted onto the upper protruding portion of the through rod, and a biasing member is provided between the cap member and the upper end of the cylindrical body. A displacement sensor is provided at the upper end of the through-rod for detecting the amount of upward movement of the through-rod from the cylindrical body. The stud welding machine according to feature 1.

3. In the stud welding machine according to claim 1 or 2, the control unit determines that normal stud welding is possible if the value of the displacement meter is within the reference range and performs welding with the welding gun, and refrains from performing welding with the welding gun if the value of the displacement meter is outside the reference range. A method for preventing welding defects in a stud welding machine, characterized by the features described herein.

Images