Electric heating – Metal heating – By arc
Reexamination Certificate
1998-02-24
2001-01-23
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S125100
Reexamination Certificate
active
06177650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arc welding method using an industrial robot.
2. Description of the Related Art
In arc welding using an industrial robot, arc welding is performed while relatively moving a welding torch and a workpiece along a taught welding line. In some cases, the arc welding is performed by fixing the welding torch and by moving the workpiece. In general, however, the welding torch is mounted to a wrist at a distal end of a robot arm, and arc welding is performed by operating the robot with respect to the fixed workpiece so that the welding torch is moved along the taught welding line. However, there has been a problem such that, at the start of welding, a hole is apt to be made in the workpiece due to excessive heating of the workpiece before the robot is accelerated (before a speed of the welding torch relative to the workpiece is accelerated). Since the welding heat is concentrated on an end portion of the welding line in the case where the end portion is identical with an end portion of the workpiece, it is necessary to reduce a welding condition so as to weld at a lower welding speed.
In TIG (Tungsten Inert Gas) arc welding for aluminum which is a heat-sensitive material, the temperature of the workpiece progressively rises during welding so that a welding speed must gradually be raised in accordance with the rise of temperature of the workpiece. In welding the entire periphery of a workpiece with a small diameter, it is necessary to increase a final welding speed two to three times the initial welding speed. Besides, other welding conditions (current, and voltage) must also be varied gradually in accordance with the variation of the welding speed.
Thus, in the prior art, there has been employed a method, in which, for the purpose of varying welding conditions, auxiliary points are taught to specify the welding speed, voltage and current between the teaching points, thereby gradually increasing or decreasing the welding conditions such as welding speed, voltage, and electric current. In this case, a trial and error method is employed to determine a section between the auxiliary teaching points, and the welding conditions within the section, such as welding speed, voltage and current.
For example, in practice, even in the case of a linear weld line, when starting welding, a plurality of auxiliary teaching points are given between a welding start position and a position on the weld line, spaced out by a predetermined amount, and progressively increasing welding speed, voltage and current are taught between the respective points. Further, in practice, if an end portion of a weld line is identical with an end portion of a workpiece, the auxiliary teaching points are given to divide a range from a position set by a predetermined amount ahead of the end portion of the weld line to the end portion into a plurality of sections, and progressively decreasing welding speed, voltage and current are taught between the respective points.
As stated above, in the conventional method, a large number of auxiliary teaching points must be taught for the purpose of varying welding conditions such as welding speed, voltage and current. Furthermore, it is necessary to individually teach each of the welding conditions between the teaching points. Besides, since the trial and error method is employed to determine the section between the auxiliary points, welding speed, voltage and current value, the teaching processes are very complicated and difficult, resulting in a heavy burden on a teaching operator.
SUMMARY OF THE INVENTION
It is an object of the present invention is to provide an arc welding method in which welding conditions such as welding speed, voltage and electric current can easily be varied.
According to the arc welding method of the present invention, positions of a start point and an end point of a section in which a welding condition is to be varied are taught, and welding conditions at the start point and at the end point are taught, so that the welding is performed with the welding condition gradually varied from the welding condition at the start point to the welding condition at the end point while a welding torch is moved from the start point to the end point. The welding condition between the start point and the end point can be determined based on a predetermined function with a distance of movement from the start point as a variable. The welding condition includes a voltage and an electric current for welding. A first value is obtained by dividing a difference between the set value of the welding condition at the end point and the set value of the welding condition at the start point by the total number of interpolations of a motion command for the section between the start point and the end point. A second value is obtained by multiplying the first value by an integer N. The second value is added to the set value of the welding condition at the start point, and the resultant value is outputted for each N-th interpolation period while the welding torch is moved from the start point to the end point, so that the welding condition is gradually varied from the set value of the welding condition at the start point to the set value of the welding condition at the end point.
Further, in order to vary a welding speed, (1) an amount of a motion command to be output to each axis of the robot is obtained for each interpolation period based on a distance from the present position to the position of said end point and the present speed, and the total number of interpolations is obtained. (2) the amount of the motion command is outputted to each axis for each interpolation period so as to drive the robot. (3) the present speed is added to a value obtained by multiplying a quotient of a speed difference by the total number of interpolations by a set number of times of interpolation, to update the current speed for each set number of times of interpolation, said speed difference being obtained by subtracting the present speed from the welding speed at the end point, so that the welding speed is gradually varied from the set value of the welding speed at the start point to the set value of the welding speed at the end point.
Further, in order to vary the welding condition in accordance with the variation of the welding speed, the welding condition at the start point as well as the welding condition at the end point are set and, the welding condition can be gradually varied in the section from the start point to the end point in the same manner as the welding speed.
When arc welding is TIG (Tungsten Inert Gas) welding, an electric current of the welding conditions is varied. Further, when the welding speed has to be varied, it can be done according to the above-mentioned method of varying the welding speed.
It is thereby possible to avoid a poor weld due to excessive heating of a workpiece at a start of welding, or due to concentration of welding heat when an end point of welding is identical with an end of a workpiece, and a poor weld due to progressive heating of a workpiece during welding in aluminum TIG welding.
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European Search Report for European Patent Application No. 95103654.0
Ito Takayuki
Kosaka Tetsuya
Nishi Hiroji
Takahashi Hiromitsu
Watanabe Atsushi
Fanuc Ltd.
Shaw Clifford C.
Staas & Halsey , LLP
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