JPH09108835A - Touch-start method of electric welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a touch-start method of the electric welding to prevent deposition of chip to a work, holing in the work, etc., by detecting the contact of the work with a torch from the increase of the input current of a driving mechanism to move the torch. SOLUTION: The current value in the normal movement in which a torch 1 is driven by a driving mechanism 5 and moved toward a work 6, and chip 2 is brought into contact with the work 6 is read by a micro computer 81 and averaged, and set to a comparator 99. When the chip 2 is brought into contact with the work 6, the motor current is increased by the servo function of the driving mechanism 5. A drive control part 71 monitors the deviation between the mean value of the driving current to be set in the comparator 99 and the present current value, and makes a judgment that the chip 2 is brought into contact with the work 6 when the deviation exceeds the prescribed value, and stops the driving mechanism 5. Because the contact can be detected without applying the voltage to the chip 2 and the work 6, the touch-start method of the electric welding in which the chip 2 is not deposited on the work 6 or the work is holed can be obtained.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a method for detecting a welding start position in electric welding.

2. Description of the Related Art FIG. 3 is a block diagram of a conventional electric welding apparatus. Welding by this welding device is called TIG welding, in which a voltage of several tens of volts is applied between the tip 2 which is a tungsten electrode attached to the torch 1 and the workpiece 6 by the welding voltage generator 11, and the gap An arc discharge is generated in the wire, the wire 3 is melted by the heat, and the wire 3 is transferred to the joint portion (molten pool) of the workpiece 6 to join the workpieces. Here, as a pre-stage before welding is started, it is necessary to set a gap having an appropriate distance in order to generate an appropriate arc discharge. Conventionally, the gap distance is automatically set as follows. That is, with the voltage applied between the tip 2 and the workpiece 6, the torch 1 is moved in the direction of the workpiece 6 by the drive mechanism 5 to bring the tip 2 into contact with the workpiece 6. At this time, a current flows between the chip 2 and the workpiece 6 and the voltage drops.
This voltage value is taken into the microcomputer 8 via the isolation amplifier 10 and the A / D converter. The microcomputer 8 determines that the chip 2 has come into contact with the workpiece 6 when recognizing a voltage drop of a predetermined amount or more preset in the memory, and the drive control unit 7
A stop command is issued to the drive mechanism 5 via. Thus, the torch 1 is positioned at the predetermined welding start position. A method in which the tip 2 is brought into contact with the workpiece 6 and the welding start position is determined as described above is called a touch start method.

In the conventional touch start method described above, as shown in FIG. 4, an insulating amplifier, an A / D converter, a microcomputer, a drive control unit, a drive mechanism and many other processes are performed. Therefore, it takes time from the detection of the voltage fluctuation to the stop of the driving mechanism. Therefore, depending on the material, the tip and the work piece may be welded or a hole may be formed in the work piece due to arc discharge generated when the tip contacts the work piece. Further, since the contact resistance varies depending on the material of the work piece, the amount of the chip biting into the work piece may become large at a certain judgment value of the voltage fluctuation set in the memory. Therefore, an object of the present invention is to provide a touch start method for electric welding that does not cause welding of a chip and a work piece or a hole in the work piece.

In order to achieve the above object, the touch start method of the present invention detects the contact between the workpiece and the torch by increasing the input current of the drive mechanism for moving the torch. . According to the method of the present invention,
Since the contact between the tip and the work piece can be detected without applying a voltage between the tip and the work piece, the tip and the work piece are not damaged.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of the essential parts of an electric welding apparatus for carrying out the touch start method of the present invention. That is, the drive control unit 71 has an A / D converter 91 and a comparator 99, and is connected to the microcomputer 81. A / D converter 9
The input end of 1 is connected to a power supply line from the drive control unit 71 to the drive mechanism 5. With such a configuration, the drive control unit 71 reads the digital value of the current of the motor for moving the torch 1 by the drive mechanism 5 via the A / D converter 91, makes a predetermined determination, and stops the drive mechanism 5. . The details are as follows. First, similarly to the conventional method, the torch 1 is driven by the drive mechanism 5 to drive the workpiece 6
Move toward. At this time, the microcomputer 81 reads the current value for a fixed period of time during which the chip 2 comes into contact with the workpiece 6 and averages the current value. This is because the current value of steady movement of the drive mechanism changes with age. This average value is set in the comparator 99. When the chip 2 then contacts the workpiece 6, the servo current of the drive mechanism 5 increases the motor current. The drive control unit 71 monitors the deviation between the average value of the drive current set in the comparator 99 and the current value, and determines that the chip 2 has come into contact with the workpiece 6 when a predetermined deviation amount is exceeded. Immediately, the drive mechanism 5 is stopped. The advantage of this method is that the contact between the tip and the workpiece can be detected without applying a voltage between the tip and the workpiece, and since arc discharge does not occur at the time of contact, the tip and the workpiece Does not cause damage. Further, as shown in FIG. 2, since there are few steps from the detection of the drive current to the stop of the drive mechanism, the response is quick. Furthermore, it is highly versatile because it is less affected by the material and surface condition of the workpiece.

As described above, according to the present invention, it is possible to provide a touch start method for electric welding in which the tip and the workpiece are not welded to each other or the workpiece has no holes.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the configuration of an electric welding apparatus for carrying out the method of the present invention.

FIG. 2 is a diagram showing a flow of operations of the apparatus of FIG.

FIG. 3 is a diagram showing a configuration of an electric welding apparatus for carrying out a conventional method.

4 is a diagram showing a flow of operation of the apparatus of FIG.

[Explanation of symbols]

1: Torch 2: Tip 3: Wire
4: Cup 5: Drive mechanism 6: Work piece 7, 71: Drive control unit 8, 81: Microcomputer 9, 91: A / D converter
99: Comparator 10: Insulation amplifier 11: Welding voltage generator

Claims (1)

[Claims] 1. In electric welding in which an electric discharge is generated between a work piece and a torch to weld the work piece, the work piece and the torch are brought into contact with each other by increasing an input current of a drive mechanism for moving the torch. A touch start method, which is characterized by detecting