JPH0422584A - Method and device for controlling welding current of spot welding machine - Google Patents

Abstract

PURPOSE:To improve welding quality by monitoring expansion of materials to be welded by generating an actual nugget to control the welding current in welding current control of spot welding. CONSTITUTION:In spot welding which is performed by controlling the welding current carried to the materials 10 and 11 to be welded held between electrodes 12 and 13 so that the specified nugget diameter is formed, the interval displacement quantity between both electrodes is measured after the welding current flow is started and control is executed so that the current flow is finished when it attains the predetermined reference quantity corresponding to the nugget diameter generated properly. Consequently, since the welding current is controlled based on the nugget diameter generated actually, the welding quality is improved and the excessive current is not carried and the energy is also saved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method of spot welding by controlling the magnitude of the welding current or the current application time so as to sandwich the material to be welded between the electrodes and form an appropriate nugget diameter. The present invention relates to a welding current control method and device for a spot welder for welding.

(Prior art) The welding current is set in advance by setting the magnitude or energization time according to the material, plate thickness, etc., or by setting the welding current in advance according to the
There is also a well-known method in which a resistance change curve between electrodes is measured in advance according to No. 5, and the curve is adaptively controlled to match the curve during actual energization.

(Part 1 to be solved by the invention) All of these methods attempt to control the plow welding current based on the welding current or the resistance between the electrodes, and therefore, in order to ensure quality, a large welding current must be applied. This shortened the life of the electrodes and increased the amount of dust.

In view of this point, it is an object of the present invention to provide a welding current control method and apparatus for a spot welding machine, which detects the actually generated nugget diameter and controls the welding current.

[Means to solve the problem]

In order to achieve this object, the present invention measures the amount of displacement in the direction of increasing the distance between both electrodes after the welding current starts flowing,
When this amount of displacement reaches a predetermined reference displacement amount corresponding to a properly generated nugget diameter, the flow of welding current is terminated.

The equipment for carrying out this method is to perform spot welding by controlling the welding current that is passed through the material to be welded between the fixed electrode and the movable electrode so that a predetermined nugget diameter is formed. In the welding current control device of a spot welding machine, there is a displacement sensor that detects the amount of displacement of the movable electrode after the welding current starts flowing, and a standard for increasing the distance between the two electrodes corresponding to the appropriately generated nugget diameter. A displacement amount setting means for setting a displacement amount in advance, and a displacement amount evaluation means for detecting when the displacement amount detected by the displacement sensor reaches a reference displacement amount and terminating the flow of welding current. do.

[Effect]

When the welding current is started to flow (B in the same figure) while the stacked workpieces 1 are held and pressurized by the electrodes 2 and 2a (Fig. 1A), a nugget 3 is formed in the welded part of the workpiece 1. As a result, the workpiece 1 expands and the distance between the electrodes 2 and 2a increases. At this time, the displacement sensor measures the amount of displacement in the gap between the electrodes 2.2a, and when the welding current reaches a predetermined value, the welding current is stopped, and the required nugget diameter is reduced by cooling due to the stoppage of the current. The welding process ends with the formed state (D in the same figure).

(Embodiment) FIG. 2 illustrates a welding current control device that implements the welding current control method of the present invention.

In the same figure, two workpieces 1O111 are connected to the fixed electrode 12.
and a movable electrode 13, and is pressurized by a cylinder rod 16 of a cylinder 15.

The welding current supply means 20 supplies the welding current supplying means 20 to the electrode 12.13 while gradually increasing the level of the welding current that can be controlled in units of 1 ms, for example, in accordance with externally set welding material conditions to the welding machine main body. , a displacement sensor 21 which is attached above the upper end of the cylinder lot 6 and measures the amount of displacement of the upper end surface 17 based on the deviation of the incident position of the reflected light from the reference position by emitting, for example, a laser beam.

A displacement evaluation means 22 in which a reference displacement corresponding to an appropriate nugget diameter is registered in advance according to the thickness, material, etc. of the workpiece 10.11 set externally, and the registered reference displacement and displacement sensor 21 A displacement amount setting means 23 is attached for generating a welding current stop signal to the welding current supplying means 20 when the detected actual displacements ΔL are compared and they match.

It has been confirmed that there is a correlation between the nugget diameter and the amount of displacement, as shown in Figure 3 when, for example, continuous dotting is performed on a rust-proof steel plate. work 1 according to the requirements and quality standards.
Since the required nugget diameter can be defined depending on the type of workpiece 10.11, the reference displacement amount for the type of workpiece 10.11 is set in advance in the displacement evaluation means 22.

The operation is as follows.

With the workpiece 10.11 held between the electrodes 12.13 and pressurized to an appropriate pressure value by the cylinder rod 16, the welding current supply means 20 starts passing welding current and gradually increases the current. . With the nugget generation, the cylinder rod 16 retreats upward, and the displacement amount setting means 23 sets the displacement amount △ of the rod upper end surface 17 detected by the displacement sensor 21.
When it is detected that L has reached a reference displacement amount corresponding to externally set welding material conditions, the supply of welding current to the welding current supply means 20 is interrupted. This allows the welding current to be controlled based on the actual nugget diameter produced.

In addition, the present invention provides an energization time control type in which a constant value of welding current is passed until the displacement amount △L reaches a reference displacement amount, or an energization time control type or phase control of the welding current at the commercial power frequency when high-speed control is not intended. It can also be applied to welding current supply means that performs.・It is also possible to use another type of displacement sensor instead of the laser beam type.

(Effects of the Invention) As described above, according to the present invention, the welding quality can be improved because the welding current is controlled by monitoring the expansion of the welded material due to actual nugget formation. Additionally, there is no need to pass an excessive amount of current to ensure quality, leading to energy savings.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the present invention in detail, FIG. 2 is a diagram showing the configuration of a welding current control device for implementing the method of the present invention, and FIG. 3 is a diagram explaining the operation of the same embodiment. 1.10.11--Work, 2.2 a-electrode,
12-...Fixed electrode, 13...Movable electrode, 1
6... Cylinder rod, 21-... Displacement sensor.

Claims (1)

[Scope of Claims] 1) Welding current control of a spot welding machine that performs spot welding by controlling the welding current passed with the material to be welded held between electrodes so that a predetermined nugget diameter is formed. In this method, the amount of displacement in the direction of increasing the distance between both electrodes is measured after the welding current starts flowing, and when this amount of displacement reaches a predetermined standard displacement amount corresponding to the appropriately generated nugget diameter, the welding current is increased. A welding current control method characterized by: terminating the flow of the welding current. 2) In a welding current control device for a spot welding machine that performs spot welding by controlling the welding current that is passed between the fixed electrode and the movable electrode with the material to be welded held between them so that a predetermined nugget diameter is formed, A displacement sensor that detects the amount of displacement of the movable electrode after the welding current starts flowing, and a displacement amount setting that presets a reference displacement amount in the direction of increasing the distance between the two electrodes corresponding to the appropriately generated nugget diameter. Welding current control characterized by comprising: a displacement amount evaluation means for detecting when the displacement amount detected by the displacement sensor reaches the reference displacement amount and terminating the flow of welding current. Device.