JPH0211353B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a butt resistance welding method in which, during the welding process,
This invention relates to an upset welding method that does not cause flashing.

In general, a welding method called upset welding among butt resistance welding methods differs from flash welding in that the welding current is increased even when the objects to be welded are not in contact with each other by repeating short circuits, melting spatter, and arcing during the welding process. This process does not involve a flashing process, and involves clamping the objects to be welded together on a fixed table and a moving table, moving the moving table forward toward the fixed table, and pushing the butt end surfaces of the objects to be welded together. At the same time, while applying a constant pressure, welding current is applied to heat the welded part to an appropriate temperature (reaching the melting point The welding process involves a heating process in which the weld is heated to the same temperature as before), and then the pressurizing force is rapidly increased to switch to the upset process, which creates a large plastic flow in the welded part and welds.

Thereafter, the welding current is cut off, the welding object is allowed to cool while the pressure is maintained, and after a certain period of time, the clamp is released and the welding process is completed.

By the way, in this type of upset welding method, the timing of switching from the heating process to the upset process is extremely important. If the timing of switching to the upset process is earlier than the appropriate value, heating will be insufficient, resulting in welding defects, and the process will not be properly performed. If it is slower than this value, the temperature of the weld will rise too much and the partially melted part will become spatter and scatter, or the specified pressure will not be obtained when the weld solidifies, resulting in weak welding, etc., resulting in poor welding quality. This poses a problem.

Conventionally, a timer or a limit switch is installed to detect the timing to shift to upset, and the stage is turned off from the heating process after a preset period of time or a certain distance, based on the point at which the moving table starts moving. I was trying to switch to the process. However, when the worker clamps the workpiece to a fixed table and a moving table, there may be variations in the distance between the opposing butt surfaces of the workpiece, or the state of the butt end faces of the workpiece, that is, the shape of the butt end faces, may vary. Since the degree of unevenness, surface roughness, etc. are not necessarily constant, the condition of the abutting surfaces of the workpiece during clamping before welding starts varies. Therefore, in the conventional method of welding by setting an origin in time or distance during clamping, the degree of temperature rise of the welded part during the heating process is difficult to be constant, and it is not always possible to start the upset process at the appropriate timing. I had a problem with not being able to switch.

Figure 1 is a graph showing the changes over time in the welding process in the standard upset welding method, where the curve represents the displacement of the moving table, the curve represents the change in welding current, and the curve represents the change in pressurizing force. ing. In the figure, P ₀ is the position before the moving table that clamps the workpiece starts moving, and P ₁ is the position where the moving table starts moving toward the fixed table, and the butt end surfaces of both the workpieces are in contact with each other. P 2 is the position of the moving table when the moving table stops, P ₂ is the position of the moving table when the welding current starts flowing, and P ₃ is the position of the moving table when the welding current starts flowing. Ps 1 is the position where the moving table moves until the welding current flows intensively to the part, softening that part and making uniform contact, Ps ₁ is the position of the moving table at the time of switching from the heating process to the upset process, Ps ₂ Ps 3 is the position of the moving table when the welding current is cut off, and Ps ₃ is the position where the moving table stops when it comes into contact with the stopper of the device, or the position where the moving table stops when the reaction force due to the compression of the welded object and the pressure are balanced. Each represents the position where the movement of has stopped.

Now, if we assume that the moving table starts moving from the point P ₀ as a reference and starts the upsetting process after moving a distance of la from this position, there will be variations in the clamping position where the workpiece is clamped. As a result, the distance lo ₁ from P ₀ to P ₁ is uncertain, so the distance from the point P ₂ where welding current starts to Ps ₁ where the upset process begins changes, resulting in variations in heating time. becomes.

In other words, if the objects to be welded are clamped when the relative distance between the objects is shorter than the normal value, lo ₁ will become shorter and the distance of the heating process will become longer, so the heating period will become longer and the The temperature rises too much and spatter occurs. Conversely, if the objects to be welded are clamped when the relative distance between them is longer than the normal value, lo ₁ becomes longer and the distance of the heating process becomes shorter, so the heating time becomes shorter. Poor welding occurs due to insufficient heating.

On the other hand, if there are irregularities on the butt end surfaces of the workpiece, the welding current will first concentrate on the locally abutting part and soften that part, so that the movable table may It will move by the distance indicated by lo ₂ , but the amount of movement lo ₂ will not be constant depending on the condition of the butt end faces, and if the butt end faces are smooth and a uniform contact can be obtained from the beginning, the above movement amount
lo ₂ is close to zero. This also applies to the shape of the abutting part of the welding object, that is, whether it is sharp or not.In this way, depending on the condition of the abutting end surface of the welding object, it is possible to Since the amount of movement of the moving table differs, similar to the above-mentioned variation in the clamping position of the workpiece, an error occurs in the heating time, causing welding defects or spatter.

The present invention has been made in view of the above circumstances, and its purpose is to clamp the workpieces to be welded together on a fixed table and a moving table, respectively, and move the moving table in the direction of the fixed table. However, in an upset welding method that includes a heating process in which welding current is passed while both workpieces are in contact with each other and pressurized, there is an influence on the clamping position of the workpieces and the condition of the butt end surfaces. To provide an upset welding method that can always switch to an upset process at an appropriate timing without being affected by welding.

In order to achieve the above object, the present invention is characterized by being configured as follows. In other words, it detects the moving speed of the moving table that clamps and moves the workpiece,
The heating process is switched to the upsetting process when the moving speed of the moving table reaches a preset speed, except for a certain period from when the moving table starts moving until immediately after starting the welding current. With this method, it is possible to always switch to the upset process at the appropriate timing without being affected by variations in the initial movement of the moving table, and it is not affected by the clamping position of the workpiece or the condition of the butt end surfaces. First, it is possible to perform welding of uniform quality without welding defects.

The present invention will be explained below based on the embodiment shown in FIG.

In the figure, 1 is a fixed base that clamps one workpiece 2A, and 3 is a movable base that clamps the other workpiece 2B. This movable base 3 is driven forward and backward in the direction of the fixed base 1 by a drive cylinder 4. I'm trying to make it possible.

Further, hydraulic pressure from a hydraulic source 5 is supplied to the drive cylinder 4 via a hydraulic control valve 6 and an upset valve 7, which is normally necessary for moving the movable platform 3 forward and backward through the hydraulic control valve 6. The hydraulic pressure required for the upset is supplied, and the upset valve 7 is opened only after the upset process, and the hydraulic pressure necessary for the upset is supplied.

Further, the hydraulic control valve 6 has a function of switching the amount of hydraulic pressure supplied to the drive cylinder 4 and the direction of supply of the hydraulic pressure, and is operated in accordance with the excitation current output from the movable table drive circuit 8.

Further, the movable table drive circuit 8 outputs an excitation current according to a certain control procedure output from the control circuit 10, and in this embodiment, in the welding process excluding the upsetting process and after, the workpiece 2A, 2B
The hydraulic pressure control valve 6 is controlled so that the pressurizing force acting on the welding table changes over time as shown by the curve in FIG. Control valve 6.

By the way, the moving speed of the moving table 3 is determined by the rack gear 11 attached to the moving table 3 and the pinion gear 12 attached to the rotating shaft of the pulse generator 13.
is meshed with the rack gear 11, and the number of pulse signals output from the pulse generator 13 per unit time is counted by the first counter 14 and the second counter 15.
By counting every moment with
The output value corresponds to the moving speed of the robot.

The first counter 14 is used to monitor the moving speed of the movable base 3 from the time when the movable base 3 starts moving until the initial movement of the movable base 3 stops when the welding current is applied, that is, in the first half of the welding process. The output thereof is supplied to the control circuit 10 and used for executing a program stored in the control circuit 10.

That is, the first point in time when the moving speed of the moving table 3 becomes zero after starting to move (the point in time when the abutting end surfaces of the objects to be welded come into contact with each other) is detected by the output of the first counter 14, and from that point on After a certain period of time _t1 has elapsed, a control signal is output to the welding current control circuit 16 to start applying the welding current.

Thereafter, the point in time when the moving speed of the moving table 3 becomes zero again (the point in time when the locally contacting part of the welding object softens and becomes uniform) is detected by the output of the first counter 14, and at that point After a certain period of time t ₂ has elapsed since then, control signals are output to the welding current control circuit 16 and moving table drive circuit 8, respectively, and the welding current is switched from I ₁ to I ₂ as shown in FIG. 1, and the pressurizing force is changed to F ₁
to _F2 .

On the other hand, the second counter 15 is used to monitor the moving speed of the movable base 3 after the initial movement of the movable base 3 stops after welding current is applied, that is, in the latter half of the welding process. A counting operation becomes possible based on a control signal output from the control circuit 10 after a time t ₂ has elapsed from the point in time when the moving speed of the moving table becomes zero immediately after the application of the welding current.

Further, the output of the second counter 15 is supplied to first and second comparators 17 and 18, respectively.
and a preset value preset in the second preset circuits 19 and 20.

That is, in the first comparator 17, the output of the second counter 15 is connected to the first preset circuit 19.
When _{the preset} value becomes equal to the preset value set in The welding current is controlled to be switched from _I2 to _I3 as shown in FIG.

Further, in the second comparator 18, when the output of the second counter 15 becomes equal to the preset value set in the second preset circuit 20, a control signal is output to the welding current control circuit 16 to adjust the welding current. cut off.

Then, the first preset circuit 19 stores the optimum moving speed Vs ₁ of the moving table 3 when switching to the upset process.
The second preset circuit 20 is set with a value corresponding to the optimum moving speed Vs of two movable bases ₃ when cutting off the welding current.

In addition, welding transformers 2 are installed on the fixed table 1 and the movable table 3.
The primary winding 22b of this welding transformer 22 is connected to a power source through an anti-parallel connection circuit of thyristors S ₁ and S ₂ .

Further, each gate of each of the thyristors S ₁ and S ₂ is supplied with a phase control signal output from the welding current control circuit 16, and the welding current supplied to the workpiece is controlled by the control circuit 10. and first,
Control is performed according to the control signals output from the second comparators 17 and 18 as shown by the curves in FIG.

According to such a configuration, the objects to be welded 2A and 2
When B is clamped to the fixed base 1 and the movable base 3, and a predetermined hydraulic pressure is supplied to the drive cylinder 4 via the hydraulic control valve 6, the movable base 3 starts moving forward in the direction of the fixed base 1, and first the workpiece is welded. The objects 2A and 2B move to a position _P1 where the abutting end surfaces abut each other and stop.

The curve in FIG. 1 represents the moving speed of the moving table 3. When the moving table 3 reaches P ₁ and its moving speed becomes zero, the output of the first counter 14 becomes zero, so from this point on, t After _one hour has passed, welding current starts flowing.

At the initial stage of applying welding current, the workpiece 2
As the welding current concentrates on the locally contacting parts of A and 2B and that part softens, the moving table 3 starts moving again and comes into uniform contact with each other P ₃
Move forward to the position.

When the moving table 3 reaches P ₃ and its moving speed becomes zero, the output of the first counter 14 becomes zero again. Therefore, after t ₂ hours have passed from this point, the welding current is switched from I ₁ to I ₂ and the welding current is The pressure is switched from F ₁ to F ₂ and at the same time the second counter 15 is enabled to perform a counting operation.

In this way, as the objects to be welded 2A, 2B are heated and the welded portions are softened, the moving speed of the movable table 3 increases.

Then, the count value of the second counter 15 becomes the first
Optimal movement speed set in preset circuit 19
When the voltage becomes equal to Vs ₁ , the first comparator 17 outputs the upset starting circuit 21 and the welding current control circuit 1.
A control signal is output from 6 to change the pressurizing force from F ₂ to F ₃
At the same time, the welding current is switched from I ₂ to I ₃ to shift from the heating process to the upset process.

After that, the moving speed of the moving platform 3 increases rapidly,
When the count value of the second counter 15 becomes equal to the optimum moving speed Vs ₂ set in the second preset circuit 20, a control signal is output from the second comparator 18 to the welding current control circuit 16, and the welding current is cut off. be done.

After that, the objects to be welded 2A and 2B begin to cool, so after the movable table 3 moves a certain distance, the reaction and pressurizing force F ₃ generated by compressing the objects to be welded 2A and 2B.
When the movable table 3 stops moving when the
Release the clamps of A and 2B and complete the welding process.

As described above, in this invention, the timing to switch to the upset process is detected by the moving speed of the moving table that clamps the workpiece, and when the moving speed reaches a preset speed, the heating process is started. Since it is designed to switch to the upset process, unlike the conventional upset welding method that uses a timer or limit switch to detect the upset timing, it is difficult to determine the clamping position of the workpiece or the butt end face of the workpiece. It is not affected by the shape, unevenness, surface roughness, etc., and can always switch to the upset process at the appropriate timing, making it possible to perform welding of uniform quality without welding defects. It is possible.

Furthermore, according to this embodiment, not only the timing of switching to the upset process but also the timing of cutting off the welding current can be changed in the same manner as when switching to the upset process.
Since the moving table is cut off when the moving speed reaches a preset speed, the welding current is always optimized without being affected by the clamping position of the workpiece or the condition of the butt end surfaces. It can be shut off at the appropriate timing, and there is no risk of the welding part being under-heated or over-heated.

Incidentally, insufficient heating will cause welding defects, and excessive heating will cause the weld zone to become too soft and the required pressure cannot be obtained, resulting in insufficient pressure and coarse grains in the weld zone. This may cause metallurgical defects.

In addition, in this invention, in order to avoid malfunctions when switching to the upset process, the initial movement of the moving table that occurs during a certain period from the time when the moving table starts moving until immediately after the application of welding current is started is detected. Therefore, in this embodiment, the counting operation of the second counter 15 is enabled after a certain period of time _t2 has elapsed from the time when the initial movement of the moving table has stopped. Instead of using such a method, for example, the moving speed may be detected after a certain period of time has elapsed from the time when the moving table started moving.

Furthermore, in this embodiment, a combination of the pulse generator 13 and the second counter 15 is used as a means for detecting the moving speed of the moving table 3, but the invention is not limited to this, and a tachometer generator or the like may also be used. It may be hot.

In addition, the means for controlling the welding current and pressing force is also provided in a second manner.
The present invention is not limited to what is shown in the drawings, and can be modified in various ways without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a graph showing changes in displacement, moving speed, welding current, and pressurizing force of the moving table during the welding process, and FIG. 2 is a block diagram showing an example of an apparatus for carrying out the present invention. . 1...Fixing stand, 2A, 2B...Work to be welded, 3...
...Moveable platform.

Claims (1)

[Scope of Claims] 1. The objects to be welded to each other are clamped to a fixed table and a movable table, and the moving table is moved toward the fixed table, and welding is carried out with both objects to be welded in contact with each other and pressurized. In an upset welding method that includes a heating step in which a current is applied, the moving speed of the moving table is detected, and the welding process is performed except for a predetermined period from the time when the moving table starts moving to the time when welding current starts to be applied. . An upset welding method, characterized in that the pressure step is switched to the upset welding step when the moving speed of the moving table reaches a preset speed.