JP2000271748A - Plasma arc welding apparatus and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a good welding while avoiding the development of explosive spattering at the welding time, in a plasma arc welding. SOLUTION: (A) The plasma arc 20 is ignited at the position for executing the welding. (B) Successively, a hole 31 is bored on an upper plate by using the plasma arc 20 having comparatively large power. (C) When the hole 31 is penetrated, a circular movement parallel to the welding surface is executed with the torch 1 with the hole 31 as the center point while spouting the arc 20. The arc 20 is worked as the upper plate 21 during the circular movement of the torch 1, and thus, this working portion is melted to form the hole 34 having the larger diameter than the diameter of the arc 20. Then, the torch 1 heats a lower plate 22 directly with the plasma arc 20. Vapor of the coating material having low b.p. on the surface of the lower plate 22 is escaped to the outside through the large hole 34 formed on the upper plate 21 with this heating. After vaporizing the coating material, the upper plate 21 and the lower plate 22 are suitably melted and welded with the plasma torch 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to plasma arc welding, and more particularly to a plasma arc welding technique suitable for welding a metal whose surface is coated with a substance having a boiling point lower than the melting point of a base material.

[0002]

2. Description of the Related Art Plasma arc welding, for example, plasma arc spot welding, has the advantage that it can be applied to a work having a complicated shape or a large work because it can be welded from one side of a superposed metal work. Have been.

However, in conventional plasma welding, when a metal whose surface is coated with a substance having a melting point lower than the melting point of the base metal (for example, galvanized steel sheet) is welded, the coating material on the surface evaporates, and the vapor is evaporated. There is a problem that high quality welding results cannot be obtained because a blast is generated by piercing the molten pool of the welded portion or a hole is left in the welded portion.

[0004] In order to solve this problem, the applicant of the present invention has proposed a welding method in Japanese Patent Application No. 6-061138, in which the power of a plasma arc is adjusted to continuously carry out two steps of steam removal and main welding. are doing. That is, first, at least one of the steel plates to be welded is formed with a through hole using a plasma arc having a relatively high power, and the vapor of the coating material is released through the through hole. Subsequently, the power of the plasma arc is reduced to an appropriate level, and the two steel plates are welded. However, in this method, if there is a gap between the two steel sheets to be welded, molten metal is consumed in the gap, so that the hole for steam release is not buried flat in the subsequent welding process, or high welding strength is obtained. I ca n’t get it,
If the gap is large, welding itself may not be performed.

[0005] Therefore, the present applicant has filed a Japanese Patent Application No.
No. 3038 proposes a welding method for detecting a gap amount between two steel plates to be welded and supplying a filler to a welded portion in accordance with the detected gap amount.

[0006]

[Problems to be Solved by the Invention] Japanese Patent Application No. Hei 6-06113
No. 8 and Japanese Patent Application No. 9-023038 each have a step of removing the coating material on the surface by evaporating the material before performing the main welding.
However, since the heat input range in which heat is input to the metal work to evaporate the coating material is limited, the removal of the coating material may be insufficient. Therefore, there is a problem that a blast may occur with a certain probability and the welding quality is not stable.

Accordingly, it is an object of the present invention to prevent explosion during welding in plasma arc welding and to achieve good welding.

[0008]

According to a first aspect of the present invention, there is provided a plasma arc welding apparatus for performing a drilling step of drilling a hole larger than the diameter of a plasma arc used for welding on a work, and thereafter welding the work. And a plasma control means for controlling a plasma arc so as to perform a main welding step for performing the welding.

In a preferred embodiment according to the first aspect of the present invention, a plasma torch for ejecting a plasma arc and a means for relatively moving a workpiece are further provided, thereby realizing a drilling step. You. The diameter of the hole drilled in the drilling step is in the range of 1.5 to 3 times the diameter of the plasma arc.

In the modification of the above embodiment, a robot is equipped with a plasma torch, and the robot has a small circle compass mechanism between the robot and the plasma torch, thereby realizing a hole making step.

In a plasma arc welding method according to a second aspect of the present invention, a plasma arc is used to form a hole having a diameter larger than the diameter of the plasma arc in a workpiece. And a main welding step of welding the workpiece by using the same. In the drilling step, a hole is formed in the workpiece by relatively moving the plasma torch for ejecting the plasma arc and the workpiece.

[0012]

FIG. 1 shows an overall configuration of an embodiment of a plasma arc welding apparatus of the present invention mounted on a robot.

A plasma torch 1 is attached to the end of an arm of a robot 10. The movement and posture of the robot 10 are controlled by the robot controller 4 and the work 2 is controlled.
Can be welded in any direction, and a circular motion or the like parallel to the welding surface can be performed (the circular motion of the robot 10 will be described later in detail). The welding power source 3 is used for power required for performing plasma arc welding,
The plasma gas and the shield gas are supplied to the plasma torch 1, and welding conditions including a plasma gas flow rate, a shield gas flow rate, a welding current value, a welding time, and the like are also controlled. The high-frequency unit 5 generates high-frequency power for causing dielectric breakdown when a pilot plasma arc is generated. A gas flow switch 6 is attached to the gas inlet of the plasma torch 1 (FIG. 2). The gas flow rate switch 6 switches the flow rate of the plasma and the shield gas between large and small in response to a command from the welding power supply 3. A filler nozzle 7 is attached near the tip of the plasma torch 1. A wire-like filler (filler) is sent out from the filler feeding device 8, and is supplied to the front of the plasma torch 1 through the filler nozzle 7. The filler feeding device 8 sends out or stops the filler in response to a command from the welding power source 3.

FIG. 2 shows the configuration of the welding power source 3 together with related elements.

The welding power source 3 includes a gas controller 12 for supplying a plasma gas and a shielding gas at controlled pressures to the plasma torch 1. The flow rates of the plasma gas and the shield gas can be respectively switched between large and small by switching the on-off valve in the gas flow rate switching device 6. The gas flow switch 6 is located as close as possible to the plasma torch 1 so that there is no substantial time delay between the switching operation of the gas flow switch 6 and the actual flow change of the gas ejected from the plasma torch 1. (For example, a gas inlet of the plasma torch 1).

The welding power source 3 is connected to a plasma arc 20.
Plasma power supply 11 for supplying controlled electric power (voltage and current) required for generation and maintenance of plasma to plasma torch 1 and gap 23 between two steel plates 21 and 22 of work 2
And a gap determination device 13 that measures the size (interval) of the gap. During welding, the plasma power supply 11 performs constant current control so that the supply current (the current of the plasma arc 20) matches the target value (the target current value is changed according to the process as described later). The gap determining device 13 determines the voltage generated by the plasma power source 11 during welding (that is, the plasma torch 1 and the workpiece 2).
Voltage, ie, voltage drop at plasma arc 20)
Is monitored, and the size of the gap 23 between the steel plates 21 and 22 is determined by a method described later.

A filler heater 15 for heating the filler 9 in advance is provided near the filler nozzle 7, and a power supply 16 for the filler heater 15 is also included in the welding power supply 3. Preheating the filler 9 has the advantage of increasing the welding speed by shortening the time from when the filler 9 enters the plasma arc 20 until it melts.

The welding power source 3 is further provided with a welding controller 14 for controlling the various elements described above. The welding controller 14 controls the above-described various elements in a procedure as described later. The control operation includes driving and stopping the gas controller 12, the gas flow switch 6.
To switch the flow rate, filler feeder 8
And the power supply 16 for the filler heater.
Drive and stop, drive and stop the plasma power supply 11, give a current target value to the plasma power supply 11, monitor the supply voltage of the plasma power supply 11, and monitor the supply voltage of the plasma power supply 11 according to the size of the gap 23. Acquiring welding conditions, such as the filler supply amount and welding time, monitoring the supply voltage of the plasma power supply 11 and determining the change timing of the welding process are included.

FIGS. 3 and 4 show the flow of one embodiment of the plasma arc welding method according to the present invention.

First, as shown in FIG. 3 (A), a plasma arc 20 is ignited at a position where welding is to be performed, and then, as shown in FIG. A hole 31 is drilled in a steel plate (hereinafter, referred to as an upper plate) 21 on the side close to the plasma torch 1. At this time,
In order to increase the power of the plasma arc 20, one or both of the plasma current and the plasma gas flow rate are controlled to a high value. When the plasma arc 20 acts on the upper plate 21, the spot portion is melted and blows off as shown in the drawing or rises around the hole 31, and
1 penetrates. Since the high power plasma arc 20 is used, the hole 31 can be formed in a short time.

When the hole 31 penetrates, next, as shown in FIG. 3C, the plasma torch 1
A circular motion parallel to the welding surface is performed while ejecting the plasma arc 20 with the (center point of 1) as the center point (the diameter of this circular motion is assumed to be larger than the diameter of the plasma arc 20). During the circular motion of the plasma torch 1, the upper plate 21
When the plasma arc 20 acts on the plasma arc 20, the acting portion is melted, and a hole 34 having a diameter larger than the diameter of the plasma arc 20 is formed.

As soon as the large hole 34 is formed, the power of the plasma arc 20 is reduced to a value suitable for welding (ie, the plasma current and the plasma gas flow rate are controlled to values suitable for welding), and FIG. As shown in (D), the plasma torch 1 moves to the center point of the large hole 34, and the steel plate (hereinafter, referred to as the lower plate) 22 farther from the plasma torch 1 is moved.
Is directly heated by the plasma arc 20. By this heating, the vapor of the coating material having a low boiling point on the surface of the lower plate 22 escapes through the large holes 34 formed in the upper plate 21.

The process of the evaporation will be described with reference to FIGS.

As shown in FIG. 5A, after the large hole 34 is formed, the portion of the lower plate 22 corresponding to the center of the hole 34 is heated by the plasma arc 20, and the heated portion of the coating material (for example, galvanized) ) Evaporates. Then, as the heating time becomes longer, the evaporation range D of the zinc plating
Increases to a size equal to or greater than the diameter of the hole 34 (for good welding, the evaporation range D
Is preferably larger than the diameter of the hole 34).

The same applies to the case where three steel plates are overlapped and welded as shown in FIG. That is, after the large holes 34 are formed in the steel plates other than the lower plate 22 (the steel plate farthest from the plasma torch 1), the heated portion of the lower plate 22 evaporates the galvanized portion. Then, as the heating time becomes longer, the evaporation range D of the zinc plating increases.

Since the diameter of the vapor vent hole 34 is larger than the diameter of the plasma arc 20, the plasma arc 2
Even when 0 is heating the lower plate 22 to evaporate the coating material, the edge portion of the upper plate 21 of the hole 34 is less likely to be heated by the arc. Therefore, the plasma arc 2
0 means that only the lower plate 22 can be efficiently heated without enlarging the hole 34. However, if the hole 34 is too large, it will be difficult to fill the hole 34 with a filler later. Therefore, the diameter of the hole 34 is optimally within the range of 1.5 to 3 times the diameter of the plasma arc. It is.

After evaporating the coating material, the plasma torch 1 appropriately melts and welds the upper plate 21 and the lower plate 22 (this operation is hereinafter referred to as "main welding"). At this time, the filler 9 is fed into the plasma arc 20 as shown in FIG. Then, the filler 32 melted by the plasma arc heat is supplied to the welding spot,
The gap 23 and the hole 34 between the steel plates are filled. Finally,
As shown in FIG. 4 (F), the hole 34 is buried back and the gap 23 is buried, so that welding between the steel plates 21 and 22 is established. At this stage, the filler 9 is drawn out of the plasma arc 20 to stop its supply, and then the plasma arc 20 is extinguished. This completes one welding operation.

The supply amount of the filler 9 required to completely fill the hole 34 is determined by factors such as the thickness of the upper plate 21, the size of the hole 34, the size of the gap 23, and the like. The factor that fluctuates every time is usually the size of the gap 23. Since it is desirable not to leave the hole 34 as a recess after the welding is completed, in order to achieve this,
As one method, the filler supply amount in one welding cycle can be set in advance in accordance with the maximum value of the gap 23 expected in advance (in a welding apparatus using this method, FIG.
Is unnecessary.) This method is simple and can surely fill the hole 34, but when the gap 23 is smaller than the expected maximum value, the bulge is necessarily left in the welded portion, so that the appearance is not good. Therefore, as another method, the size of the gap 23 is measured (for example, using the gap determination device 13 shown in FIG. 2) at each welding cycle, and the filler supply amount is adjusted to an appropriate amount according to the measured value. It can also be controlled (the details of this method will be described later). In addition, as a method of adjusting the filler supply amount, for example,
In the main welding step shown in FIG. 4 (E), there is a method of maintaining the feed rate of the filler constant and adjusting the feed time length. When this adjusting method is used, it may be necessary to adjust the time length of the main welding step according to the filler feeding time length.

FIGS. 7, 8, 9 and 10 show the state shown in FIG.
3 shows an example of a structural diagram of a robot 3 capable of performing a circular motion of the plasma torch 1 performed in the step of FIG.

In FIG. 7, since the robot 3 can take any posture and movement within its operating range, the plasma torch 1 at the tip of the robot 3 performs the above-described circular motion by the robot plasma torch. That is,
The intended purpose is achieved by incorporating into the robot controller 4 possible motion programs for this welding.

In FIG. 8, the robot hand 2 of the robot 3
A small circle compass 27 is provided between the plasma torch 5 and the plasma torch 1. The robot controller 4 also incorporates a motion program for controlling the small circle compass 27. After the first small hole 31 has penetrated, the robot hand 25 is fixed and the plasma torch is moved only by the movement of the small circle compass 27. 1 performs the above-described circular motion to form a large hole 34 for steam release.

In FIG. 9, the plasma torch 1 has a multi-stage structure, in which a mechanism capable of eccentric movement is built in some of the step structures, and the above-described circular movement is performed by the eccentric movement (FIG. 9). Inside, the plasma torch 1 has a two-stage structure, and has a mechanism for circularly moving the lower portion of the plasma torch 1 (plasma arc ejection side) in a step structure on the upper portion of the plasma torch 1). Therefore, after the first small hole 31 penetrates, the lower portion of the plasma torch 1 performs a circular motion by the above-described eccentric motion while the robot 3 is fixed, thereby forming a large hole 34 for vapor release.

Alternatively, as shown in FIG. 10, after penetrating the first small hole 31, only the lower portion of the plasma torch 1 moves so as to form an angle with the plasma torch center axis and the welding surface normal, and is fixed as it is. The rotation of the plasma torch 1 may cause the tip of the plasma arc 20 to make a circular motion on the upper plate 21 (therefore, regarding the formation of the large hole 34 for vapor release, the center axis of the plasma torch). And the weld surface normal need not be parallel).

FIG. 11 shows an embodiment of a method for controlling the plasma current, the plasma gas flow rate, the shield gas flow rate, and the filler feed when performing the welding method shown in FIG.

In one welding, a pre-flow step for adjusting a proper atmosphere by flowing a gas before the plasma arc is ignited, a hole making step for penetrating a vapor vent hole with a high-power plasma arc, and a gap being formed with a filler. It consists of four steps: a main welding step in which welding is performed with a plasma arc of appropriate power while filling the holes, and an after-flow step in which gas is flown even after extinguishing the plasma arc to prevent oxidation of the welded portion.

In the control method shown in FIG. 11, the plasma gas flow rate and the shield gas flow rate are each maintained at a predetermined constant value through the above four steps. The plasma current (referred to here as the current of the main plasma arc substantially acting on the steel plate, excluding the pilot plasma arc) is controlled to a relatively high value in the drilling process, and in the subsequent main welding process. It is controlled to a lower welding appropriate value.
Filler feeding is performed only during the main welding process for a time length corresponding to the set filler feeding amount. As described above, by increasing the main plasma arc current in the hole making step, the power of the plasma arc is increased, and a hole for steam release can be made at high speed.

FIG. 12 shows another embodiment of the control method of the plasma current, the plasma gas flow rate, the shield gas flow rate, and the filler feed.

In this control method, the main plasma arc current is maintained at a constant value, and instead, the plasma gas flow rate is increased so that a large plasma arc power is obtained in the drilling step. If the plasma gas flow rate is increased from the preflow step before the hole making step, the start of the hole making step is smooth. In order to increase the plasma arc power in the drilling step, it is also possible to use a combination of increasing the plasma current as in the method of FIG. 11 and increasing the plasma gas flow rate as in the method of FIG. is there.

The control method shown in FIG. 11 or FIG.
, The plasma current can be controlled by adjusting the target current value for the plasma power supply 11, and the flow rates of the plasma gas and the shield gas can be controlled by adjusting the pressure of the gas controller 12 and the gas flow rate switching device. 6 and the filler feed control can be performed by driving / stopping the filler feeder 8. These operations are performed by a computer (not shown) in the welding controller 19 giving commands to the plasma power source 11, the gas controller 12, the gas flow rate switching device 6, and the filler feeding device 8 according to a program. .

FIGS. 13, 14 and 15 show "comparison of galvanized removal range" and "depth of explosion occurrence frequency" obtained by testing a conventional welding method and two kinds of welding methods according to the present invention. 2 shows a comparison and a comparison of welding strength.

Here, the conventional welding method is described in Japanese Patent Application No. Hei 9-1997.
No. 023038, that is, a method in which a plasma torch is fixed and a hole is formed, and then a main welding process is performed. The test result is shown in FIG.
, And the test result of the welding method according to the present invention is shown by a graph of “Plasma torch rotation method”. Further, the zinc plating removal range on the vertical axis in FIG. 13 is the diameter of the circular portion where the zinc plated on the surface of the lower plate 22 is evaporated (removed) by being heated by the plasma arc 20. The “gap” on the horizontal axis in FIGS. 14 and 15 means the upper plate 21 and the lower plate 2
The “explosion frequency” on the vertical axis in FIG. 14 is the rate of occurrence of explosions in the main welding process, and the “welding strength” on the vertical axis in FIG. Is the tensile strength obtained by conducting a tensile test between the upper plate 21 and the lower plate 22 having one weld formed by spot welding. The specific conditions used in the test are as follows.

In "Comparison of galvanized removal range" in FIG. 13, the upper plate is a 0.8 mm-thick galvanized steel plate and the lower plate is a 0.8 mm-thick galvanized steel plate.

In the "comparison of bomb blast frequency" in FIG. 14, the upper plate is a 0.8 mm thick galvanized steel plate and the lower plate is a 0.8 mm thick plate.
mm galvanized steel sheet.

In the "comparison of welding strengths" in FIG. 15, the upper plate is a 0.7 mm thick galvanized steel plate, and the lower plate is a 0.7 mm thick plate.
Is a galvanized steel sheet.

Further, as common conditions of all the above tests, the nozzle diameter of the plasma torch is φ2.2 mm, the rotation diameter of the “torch rotation method” is φ6 mm, the plasma gas and the shielding gas are argon + 7% hydrogen, the plasma gas The flow rate was 4.2 l / min during the drilling step and 1.6 l / min during the main welding step. Filler diameter is φ
0.9 mm.

As can be seen from FIG. 13, the "plasma torch rotating method" of the present invention spreads zinc plated on the lower plate 22 over a wider range ("the plasma torch fixing method") than the conventional "plasma torch fixing method". (About twice as large as the “fixed method”).

From the results shown in FIG. 13, it is assumed that the frequency of the explosion caused by zinc is suppressed by the "plasma torch rotation method" of the present invention. This is apparent from FIG. This is particularly remarkable when the gap is in the range of 0.2 to 0.5 mm. In the conventional “plasma torch fixing method”, the frequency of bomb blasting is high when the gap is 0.2 to 0.5 mm (in the figure, it peaks when the gap is 0.2 mm). In the “plasma torch rotation method” of the invention, the gap is stable at a relatively low value over a wide range of 0 to 1.2 mm.

Regarding the welding strength, as can be seen from FIG. 15, the "plasma torch rotating method" of the present invention has a comparatively high tensile strength regardless of the size of the gap as compared with the conventional "plasma torch fixing method". It is stable at a high value.

In the "plasma torch rotation method" of the present invention, it is possible to change the welding conditions in accordance with the gap amount. Two methods for measuring the gap will be described below. The first method is to determine the gap amount from the plasma arc voltage value at the end of the hole making step, and the second method is to determine the gap amount from the time-dependent gradient of the plasma arc voltage during the hole making step. It is a method of determining. First, the first method will be described.

FIG. 16 shows the changes in the plasma arc current and the voltage when the control method shown in FIG. 11 is performed (measured under the condition that the flow rate of the shield gas is 6 L / min). In the control method shown in FIG. 11, as described above, the plasma arc current is controlled to a relatively high value during the drilling step, and is decreased to a relatively low value after the drilling step. In the process, the low value is controlled to be constant. The current waveform in FIG. 16 shows such a change in the plasma arc current, and the voltage waveform shows the change in the plasma arc voltage at that time. As shown in the drawing, when the drilling step is completed, the plasma arc voltage decreases and stabilizes to a substantially constant value at time t1 (in the example of FIG. 16, 0.8 to 0.85 seconds from the start of the drilling step). However, the settled plasma arc voltage shows different values V1 and V2 depending on the gap amount. That is, the larger the gap amount, the higher the value. The reason is that the larger the gap amount, the lower the lower plate 2
It is presumed that the plasma arc column becomes longer and the voltage drop increases by the distance of the plasma torch 1 from the plasma torch 1. FIG. 17 shows a schematic relationship between the settled plasma arc voltage and the gap amount. The plasma arc voltage is almost proportional to the gap amount with a certain offset value V0. Accordingly, the relationship between the gap amount and the plasma arc voltage as shown in FIG. 17 (actually, the relationship between the filler feed amount (feed time) and the plasma arc voltage corresponding to the gap amount) is shown in FIG. In the welding controller 14, for example, a look-up table is stored, and in each welding cycle, the plasma arc voltage is measured at time t1 after the end of the drilling process (for example, 0.8 mm from the start of the drilling process).
The plasma arc voltage is sampled every 0.001 second in a time interval of ~ 0.85 seconds to obtain an average value), and the lookup table is addressed using the measured value, so that the gap amount (actually, The filler feed amount (feed time) corresponding to the gap amount can be determined.

FIG. 18 shows the configuration of the gap determining device 13 for implementing the gap measuring method.

The gap determining device 13 has a measuring unit 132, a filter unit 133, an arithmetic unit 134, a temporary storage unit 135, a reference value storage unit 136, and a comparison unit 137. These elements are mutually connected via an interface unit 138. It can communicate with the welding controller 14. The measurement unit 132 samples the plasma arc voltage generated by the plasma power supply 11 for 0.8 to 0.85 seconds from the start of the drilling step. The filter unit 133 performs a filtering process on the sampled plasma arc voltage sample value to remove a noise component. The arithmetic unit 134
An average value is calculated from a series of sample values obtained in the measurement section. The temporary storage unit 135 temporarily stores a series of sample values and average values. The reference value storage unit 136 stores the above-described lookup table. Comparison section 137
Determines the filler feed time corresponding to the gap amount by addressing the lookup table using the average value, and also determines the time of the main welding process according to the filler feed time. The conditions are notified to the welding controller 14. The welding controller 14 controls the filler feeding device 8 and the plasma power supply 11 in the main welding process according to the determined filler feeding time and the main welding process time.

FIG. 19 shows a flow of the operation performed by the gap determination device 13 of FIG.

First, a timer is started at the same time as the start of welding (S1) (S2), and while the timer indicates a measuring section (0.8 to 0.85 seconds from the start of the drilling step) (S3), the plasma arc is started. The voltage is sampled at 0.001 second intervals (S4), filtered (S5), and stored in the temporary storage unit 135. When the measurement section ends (S
6), the average value of all the sample values is calculated (S7), and the filler feed amount is read from the lookup table using this average value (S8). When reading the table, the filler feed amount is read from the address corresponding to the plasma arc voltage value in the table closest to the average value. And
The welding conditions of the main welding step are selected according to the read filler supply amount (S9), and the welding controller 14 is notified.

This first gap amount measuring method is not limited to the control method shown in FIG. 11, but can be adopted also in the control method shown in FIG. Also in the control method of FIG. 12, the plasma arc voltage is measured in a time interval in which the plasma arc voltage has just settled after the drilling step has been completed.

In the first gap measuring method, when the electrode 131 in the plasma torch 1 shown in FIG. 18 is consumed as the number of welding increases, the lookup table set first must be corrected. In addition, when the stand-off (distance from the work) of the plasma torch 1 is different for each work, there is a problem that the measurement cannot be performed. This is because the offset voltage V shown in FIG.
This is because 0 changes depending on the distance between the tip of the electrode 131 in the plasma torch 1 and the surface of the work 2.

The second gap measuring method solves this problem. FIGS. 20 and 21 show the relationship between the plasma arc current and the plasma arc voltage for explaining the principle of the second method.

In both cases shown in FIGS. 20 and 21,
The plasma arc current is switched between a large current value and a small current value a plurality of times, that is, a plurality of rectangular pulses of the plasma arc current having a large current value are repeatedly transmitted. Here, the large current value of the plasma arc current pulse is a current value that can surely make a hole in a steel sheet like the plasma arc current value in the drilling step shown in FIG. The small plasma arc current value at the time of the pulse pause between the pulse and the pulse is shown in FIG.
The plasma arc current value is lower than the current value used in the main welding process, and such that a hole cannot be formed in the steel sheet.

As can be seen from FIGS. 20 and 21, the plasma arc voltage at the time of the plasma arc current pulse is:
The plasma arc voltage at the rest of the pulse shows a lower value, but this lower plasma arc value rises linearly as the number of plasma arc current pulses increases. Therefore, when the gap amount is different (for example, when the gap amount is 0 mm and the gap amount is 1.2 mm), a rising line of the plasma arc voltage at the time of a series of plasma arc current pulses is obtained as shown by a dotted line in the figure. It can be seen that the slope of the rising straight line (that is, the rising rate of the plasma arc voltage) differs depending on the gap amount. Generally, a relationship as shown in FIG. 22 is recognized between the gap amount and the plasma arc voltage rise rate.
That is, when the plasma arc current pulse is applied, the plasma arc voltage rise rate is a certain offset rise rate R0.
Therefore, the distance changes almost proportionally to the gap amount. The characteristics shown in FIG. 22 are stable without being largely affected by the consumption of the electrodes or the change of the stand-off of the plasma torch.

FIG. 20 shows the case where the shielding gas flow rate is 4 liter / min, and FIG. 21 shows the case where the shielding gas flow rate is 10 liter / min. In the case of FIG. 20 where the shield gas flow rate is smaller, the difference of the plasma arc voltage increase rate according to the gap amount appears more remarkably.

In order to perform the second measurement method utilizing the above fact, a control method as shown in FIG. 23 is adopted.

In the control method shown in FIG. 23, the above-described plasma arc current pulse is supplied in the hole making step, and after the hole making step is completed, the gap amount (actually, the filler supply amount according to the gap amount) is reduced. A step of determining and selecting welding conditions is performed, during which the plasma arc current is slightly lower than the proper welding value, and thereafter, the plasma arc current is set to a proper welding value, and the main welding process is performed. The plasma gas flow rate is shown in FIG.
As in the case of the method of FIG.
As shown in FIG. 3 (that is, similar to the control method of FIG. 12), it is better to control the value to a large value until the drilling process is completed, and to return to the welding proper value after the drilling process, so that the drilling can be performed at high speed. This is desirable because the difference in the plasma arc voltage increase rate according to the gap amount becomes remarkable. In addition, the shield gas flow rate is set to a value slightly smaller than the appropriate value until the hole making step is completed, and is returned to the appropriate value after the hole making step. It is important to appropriately set the low shield gas flow rate in the drilling step so as not to be too small so as to cause a problem of oxidation of the welded portion. Filler feeding is performed in the main welding process for a time corresponding to the filler feeding amount determined in the welding condition selecting process.

The second gap measuring method can be carried out by the gap judging device 13 having the structure shown in FIG. In this case, the measuring unit 132 samples the plasma arc voltage when the plasma arc current pulse during the hole making process is flowing. For example, if the plasma arc current pulse having the waveform shown in FIG. 20 is used, for example, 0.04 around the three time points of, for example, 0.1 second, 0.3 second, and 0.5 second from the start of the boring step The plasma arc voltage is sampled at, for example, 0.001 second intervals in three time intervals a, b, and c of a second width. The operation unit 134
Performs a linear regression calculation using the sampled 120 plasma arc voltage sampling values, and obtains the slope, that is, the plasma arc voltage rise rate, from the obtained regression line (that is, the dotted line in FIG. 20). The reference value storage unit 136 stores the plasma arc voltage increase rate and the gap amount (actually, the filler supply amount (supply time) corresponding to the gap amount).
Is stored. The comparison unit obtains a filler supply amount (supply time) corresponding to the gap amount by addressing the look-up table using the calculated plasma arc voltage increase rate, and sends the acquired filler supply amount to the control unit 138.

FIG. 24 shows the operation of the gap determining device 13 when the second gap measuring method is performed.

First, a timer is started at the same time as the start of welding (S11) (S12), and the timer measures the time of the measurement section (0.1, 0.3 and 0.5 seconds after the start of the drilling step, respectively). During the period of 0.04 seconds at the center (S13), the plasma arc voltage is sampled at 0.001 second intervals (S14), and the sampled value is filtered (S15). Temporary storage unit 135
To memorize. This is repeated for three measurement sections (S16), and when all measurement sections are completed (S17),
A linear regression calculation is performed using all the sample values to obtain a plasma arc voltage rise rate (S18). By addressing the look-up table using the plasma arc voltage increase rate, the filler supply amount corresponding to the gap amount is read (S19), and the welding conditions of the main welding process are determined according to the read filler supply amount. (E.g., filler supply time, main welding time) is selected (S20), and the welding controller 14 is notified.

The preferred embodiments of the present invention have been described above. However, it is needless to say that the present invention is not limited to these embodiments, but can be implemented in other various aspects. For example, in order to form the vapor vent hole 34, a mechanism other than the mechanisms shown in FIGS. 7, 8, 9 and 10 may be used. For example, a mechanism for grasping the position of the work table to which the work 2 is fixed on the XY plane and moving the work table on the XY plane while grasping the position may be used. That is, instead of moving the plasma torch 1 side while fixing the work 2 side as described above, the position of the plasma torch 1 and the work 2 can be relatively moved by moving the work 2 side while the plasma torch 1 side is fixed. That is to change it. The shape of the large hole 34 is desirably a perfect circle, but is not necessarily so. For example, various figures such as a polygon, an ellipse, or a combination thereof can be adopted. The merit of making holes other than a perfect circle in this way is that, for example, by forming an elliptical hole and also forming the welding nugget in an elliptical shape, it is possible to increase the welding nugget area even in an elongated portion,
This means that a higher welding strength can be obtained at one welding point.

The control patterns of plasma arc current, shield gas flow rate and filler supply are shown in FIGS.
In addition to the filler supply amount depending on the gap amount, other welding conditions (for example, plasma arc current, plasma arc voltage, plasma gas flow rate, plasma gas Type, shielding gas flow rate, shielding gas type, standoff, etc.) can also be optimally controlled.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an overall configuration of an embodiment of a plasma arc welding apparatus of the present invention mounted on a robot.

FIG. 2 is a block diagram showing a configuration of a welding power source 3 together with related elements.

FIG. 3 is a schematic diagram showing a flow of one embodiment of a plasma arc welding method according to the present invention.

FIG. 4 is a schematic view showing a flow of one embodiment of a plasma arc welding method according to the present invention.

FIG. 5: Coating material when welding two steel plates
FIG. 4 is a schematic view showing a process of evaporating (zinc plating).

FIG. 6: Coating material when welding three steel plates
FIG. 4 is a schematic view showing a process of evaporating (zinc plating).

FIG. 7 is a perspective view showing an example of the movement of the plasma torch.

FIG. 8 is a perspective view showing an example of the movement of the plasma torch.

FIG. 9 is a perspective view showing an example of the movement of the plasma torch.

FIG. 10 is a perspective view showing an example of the movement of the plasma torch.

FIG. 11 is a timing chart showing an embodiment of a control method of a plasma current, a plasma gas flow rate, a shield gas flow rate, and a filler feed when performing the welding method shown in FIGS. 3 and 4;

FIG. 12 is a timing chart showing another embodiment of a control method of a plasma current, a plasma gas flow rate, a shield gas flow rate, and a filler feed when the welding method shown in FIGS. 3 and 4 is performed.

FIG. 13 is a diagram showing a comparison of galvanized removal areas obtained by testing a conventional welding method and two kinds of welding methods according to the present invention.

FIG. 14 is a diagram showing a comparison of the frequency of blast occurrence obtained by testing a conventional welding method and two types of welding methods according to the present invention.

FIG. 15 is a diagram showing a comparison of welding strength obtained by testing a conventional welding method and two types of welding methods according to the present invention.

FIG. 16 is a waveform chart showing changes in plasma arc current and voltage when the control method shown in FIG. 11 is performed.

FIG. 17 is a diagram showing a relationship between a gap amount and a plasma arc voltage.

FIG. 18 is a block diagram showing a configuration of a gap determination device 13 for implementing the gap amount measuring method.

19 is a flowchart showing an operation performed by the gap determination device 13 in FIG.

FIG. 20 is a waveform chart showing a relationship between a plasma arc current and a plasma arc voltage for explaining the principle of the second gap amount measuring method.

FIG. 21 is a waveform chart showing a relationship between a plasma arc current and a plasma arc voltage for explaining the principle of the second gap measuring method.

FIG. 22 is a diagram showing a relationship between a gap amount and a plasma arc voltage rise rate.

FIG. 23 is a timing chart showing a control method for performing the second gap amount measuring method.

FIG. 24 is a flowchart showing the operation of the gap determination device 13 when performing the second gap amount measurement method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma torch 2 Work 3 Plasma power supply 6 Gas flow switching device 7 Filler nozzle 8 Filler supply device 9 Filler 11 Plasma power supply 12 Gas controller 13 Gap judgment device 14 Welding controller 15 Filler heater 16 Power supply for filler heater 20 Plasma arc 21 Upper plate 22 Lower plate 23 Gap 25 Robot hand 27 Small circle compass 29 Zinc plating removal range 31 Hole 32 Dissolved filler 34 Hole 131 Electrode 132 Measuring unit 133 Filter processing unit 134 Operation unit 135 Temporary storage unit 136 Reference value storage unit 137 Comparison unit 138 Interface section

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Iwao Kurokawa 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture, Komatsu Seisakusho Laboratories (72) Inventor Yosuke Imai 1200, Manda, Hiratsuka-shi, Kanagawa Prefecture Komatsu Seisakusho Laboratories 72) Inventor Yoshitaka Aragaki 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture, Komatsu Seisakusho Laboratory (72) Inventor Ken Ishii 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture Komatsu Seisakusho, Research Laboratories (72) Inventor Hiroshi Aoyama, Kanagawa 1200 Manda, Hiratsuka-shi, Japan Inside Komatsu Seisakusho Laboratory (72) Inventor Yoshinori Sunaga 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture Inside Komatsu Seisakusho Laboratory (72) Inventor Tohru Shiina 1200 Manda, Hiratsuka-shi, Kanagawa Komatsu Corporation Inside the Manufacturing Research Laboratory (72) Inventor: Hideto Uematsu 100 Kanayama, Ichiriyama-cho, Kariya City, Aichi Prefecture Inside Toyota Auto Body Co., Ltd. (72) Akiha Kengo Kamiya 100 Kanayama, Ichiriyama-cho, Kariya-shi, Aichi Pref.

Claims (5)

[Claims] 1. A method of forming a hole in a work, the step of forming a hole larger than the diameter of a plasma arc used for welding, and then performing a main welding step for welding the work.
A plasma arc welding apparatus comprising plasma control means for controlling the plasma arc. 2. The plasma arc welding apparatus according to claim 1, further comprising a means for relatively moving the work and the plasma torch for ejecting the plasma arc, whereby the drilling step is realized. . 3. The plasma arc welding apparatus according to claim 1, wherein a diameter of the hole drilled in the drilling step is in a range of 1.5 to 3 times a diameter of the plasma arc. 4. The plasma arc according to claim 1, wherein the plasma torch is mounted on a robot, and the robot has a small circle compass mechanism between the plasma torch and the plasma torch, whereby the drilling step is realized. Welding equipment. 5. A drilling step of drilling a hole having a diameter larger than the diameter of the plasma arc using a plasma arc, and a main welding step of welding the workpiece using a plasma arc after the drilling step. A plasma welding method comprising: a plasma torch that drills holes in a workpiece by relatively moving a plasma torch that ejects the plasma arc and the workpiece.