JP3472237B2 - Plasma arc spot welding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention comprises components such as an arc electrode, a nozzle, a shield cap, and a filler wire,
The present invention relates to a plasma arc spot welder for spot welding a work by using a plasma arc, and particularly to a plasma arc spot welder capable of monitoring the welding status based on a normal one-cycle welding sequence.

[0002]

2. Description of the Related Art Conventionally, TIG for welding galvanized steel sheets
There is a welding machine. A welding method using such a welding machine is disclosed in, for example, Japanese Patent Laid-Open No. 7-40050. According to the TIG welding method for galvanized steel sheet, the boiling point of zinc is generally as low as about 910 ° C, so the plate thickness is 1.5 and 3 mm.
When the galvanized portion of the overlapping plates is heated by the arc, it instantly melts and boils into zinc vapor. This zinc vapor penetrates into the molten pool containing the zinc plating having a low boiling point. If the arc heat input is continuously input to this molten pool,
The zinc vapor that has entered the molten pool expands and blows out from the surface of the molten pool.

At this time, the surface of the molten pool vibrates, and the height of the surface increases. As a result, the molten metal adheres to the tungsten electrode, short-circuits this electrode and the molten pool, and the electrode is contaminated and deformed. Further, when the short circuit between the electrode and the molten pool is broken and the arc is regenerated,
The arc easily occurs from above the electrode, and the voltage during arc regeneration becomes high. For this reason, the arc heat input becomes excessive,
It is said that burn-through will occur.

In order to solve such a problem, in the TIG welding of galvanized steel sheet disclosed in the above-mentioned publication, a boiling phenomenon occurs during welding, and the voltage drop of the arc is 2 to 2 before the vibration of the molten pool becomes large for the first time. It is detected that about 3V is generated. Furthermore, the welding current is 5 to 10 m according to this detection signal.
The TIG welding is performed while suppressing the boiling phenomenon by temporarily reducing the current value to a low current value capable of maintaining the arc or setting the welding current to zero for a period of seconds. The conventional TIG welding of the galvanized steel sheet prevents the electrode from being contaminated due to the short circuit between the tungsten electrode and the molten pool, and prevents the electrode from being burned down.

On the other hand, as shown in FIG. 8, there is known a plasma arc spot welding machine 10 for spot-welding a work 16 made of a galvanized steel plate in which an upper plate 16a and a lower plate 16b are superposed at intervals. . According to this welding, the upper plate 1 as shown in FIGS.
When a plasma arc blown out from the nozzle 12 is ignited on the welded portion of 6a and a hole is penetrated through the upper plate 16a, the welded portion of the lower plate 16b is heated by the plasma arc. After sufficiently heating the welded portions of the upper and lower plates 16a and 16b, the filler wire 14 made of an iron member is fed into the plasma arc and melted as shown in FIG. 1 plate of molten iron
6a, 16b are dropped onto the welded portions of each plate 16a, 16b
Spot weld.

At this time, when the molten upper plate 16a falls onto the lower plate 16b so as to cover a part of the molten upper plate 16a over a wide area as shown in FIGS. Since it is much smaller than the above, the zinc plating of the work 16 is rapidly vaporized and expanded due to the difference in melting temperature. Due to the explosive expansion, the zinc gas that is abruptly generated cannot escape, and the pressure of the zinc gas causes the explosion that blows off a part of the work 16 that forms the molten pool explosively.

[0007]

By the way, in the TIG welding method for galvanized steel sheet disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-40050, the arc voltage is reduced by several volts during welding. When the voltage drops by several volts, the current is reduced to a low current value that can maintain the arc, and the boiling phenomenon of the molten pool is suppressed. However, in the above plasma arc spot welding, the T
Unlike IG welding or the like, since the welding current, the flow rate of plasma gas, and the like are changed during the one-cycle welding process, the arc voltage also changes by itself. Therefore, in order to discriminate and control the welding phenomenon based on the change in the arc voltage, it is necessary to consider under what welding conditions the welding is currently performed.

In the plasma arc spot welding, the present inventors investigated the phenomenon during welding by measuring the arc voltage and photographing with a high speed camera, and clarified the relationship between the change in arc voltage and the phenomenon during welding. . As a result, in plasma arc spot welding, in addition to the above-mentioned bombings, welding defects due to leaks, keyhole formation defects, gas flow rate abnormalities, wire feed defects, etc. Knew that would occur.

(1) Concerning bombardment, the bombardment described above is caused by an extremely short circuit of about 5 msec at the longest during welding.
The bombing phenomenon can occur at any time during welding.
It may occur several times during the welding process of the cycle. The degree of influence of welding quality depends on the timing of occurrence and the number of occurrences. In plasma arc spot welding, the required amount of filler wire is supplied to the weld in a relatively short time, so if a portion of the molten metal is blown off by bombing, the probability of welding defects such as cutting of the work piece will occur. Is high.

When the bombing occurs at the beginning of welding, the filler wire is supplied after the bombing, so that the welding may not be abnormal. Even if it does not affect the welding itself, part of the blown molten metal adheres to the arc electrode, nozzle, shield cap, etc., and a new electrical path is formed instantaneously, so the arc voltage applied to the work (Power input) may be reduced, which may adversely affect subsequent welding.

(2) Regarding leak, here, the leak means, for example, a short circuit generated between the nozzle and the shield cap, a short circuit generated between the nozzle and the filler wire,
A short circuit or the like that occurs between the nozzle and the work. As the causes of these short circuits, spatter is deposited in the gas passage between the nozzle and the shield cap to form a short circuit path, a part of the molten metal of the work rises and contacts the nozzle, and the molten filler wire For example, the tip may contact the nozzle. The leakage phenomenon occurs continuously or intermittently during one cycle of the welding process.

The difference from the above-mentioned bombardment is that the arc voltage decreases in a long duration time. Unless sputter deposits are removed as described above, they will occur at any time during welding. The sputter deposit may be naturally removed. If the leak occurrence time is long, it has a great influence on the welding quality, but the degree of the influence on the welding quality differs depending on the occurrence timing, the number of occurrences, etc., similarly to the above-mentioned explosion phenomenon.

In the plasma arc spot welding machine, the shield cap and the filler wire have the same potential as the work. For this reason, for example, when the electrically insulating nozzle and the shield cap are short-circuited, the nozzle has the same potential as the work. Therefore, a welding current flows through the arc electrode and the nozzle,
The resistance between the arc electrode and the work changes, and the arc voltage changes. Since the welding current flows through the arc electrode and the nozzle, the electric power applied to the work is reduced, which may result in poor welding. It often occurs after switching the plasma gas flow rate, which reduces the electrical insulation between the arc electrode and the nozzle. However, if a short circuit occurs before the start of welding, it may occur immediately after the start of welding.

(3) Regarding defective keyhole formation, when spot welding a work in which an upper plate and a lower plate are superposed with a gap therebetween, a plasma arc rides on the flow of plasma gas through a through hole of the upper plate. The arc length becomes the length between the arc electrode and the lower plate, and the arc voltage increases significantly. Therefore, if the arc voltage does not rise even at the keyhole formation timing, the keyhole formation is defective. Further, when the voltage rise due to the keyhole formation is too large, or when the keyhole formation time is long, the lower plate may be penetrated.

Under the welding conditions for forming the keyhole, if the formation of the keyhole in the work fails for some reason, welding defects such as through holes and breaks may occur in the work even if the filler wire is put into the plasma arc. Occurs. The upper and lower plates cannot be joined by filling the holes formed in the work, and the welding strength and the like are reduced.

(4) Regarding abnormal gas flow rate, in the plasma arc spot welding machine, the flow rate of the plasma gas is switched for the purpose of improving the ignitability of the plasma arc on the work to be welded. The arc voltage increases when the plasma gas flow rate is increased, and the arc voltage decreases when the gas flow rate is decreased. Therefore, when the plasma gas flow rate changes, the arc voltage changes, but if the plasma gas is insufficient or there is an abnormality in the gas supply device or related equipment such as piping, the plasma gas flow rate can be changed. Nevertheless, there is no change in arc voltage. Since the plasma gas flow rate has a great influence on the increase in the arc voltage at the nozzle restraint portion, the arc voltage is significantly increased when the plasma gas flow rate is higher than when the plasma gas flow rate is low.

(5) Regarding wire feeding abnormality, an example of this abnormality phenomenon is that the filler wire feeding is not performed as instructed even though the filler wire feeding instruction is output. . Causes include defective or insufficient shape of the filler wire, and failure of related devices such as a wire feeding device. Therefore, a mechanical abnormality in the filler wire feeding cannot be determined unless the instruction to feed the filler wire is issued.

The present invention has been made to solve such a conventional problem, and its specific object is to monitor the current welding condition from the behavior of the arc voltage according to a normal welding sequence of one cycle. It is intended to provide a plasma arc spot welder that discriminates various welding abnormalities by using various methods to stabilize the welding quality.

[0019]

[Means for Solving the Problems and Their Effects] The inventors of the present invention have made extensive studies to solve the above problems based on the phenomenon occurring in all steps of the one-cycle welding sequence as described above. Based on the normal behavior of the arc voltage generated during the one-cycle welding process, it was concluded that the above problem can be solved by monitoring the variation of the arc voltage continuously measured during welding.

That is, the voltage fluctuation is measured over the entire process of the optimum welding sequence from the start time to the end time of welding, and the voltage fluctuation is compared with the fluctuation voltage continuously measured during welding. When a large voltage drop occurs within 5 msec, it is judged to be an abnormal phenomenon due to the bombing. When this judgment is made, the welding is temporarily stopped and the torch is inspected, or the welding is continued as it is, and when the next abnormal phenomenon is detected, whether the abnormal phenomenon is caused by the previous bombing, etc. consider. Based on the examination result, the operation of the constituent members of the plasma arc spot welding machine of the present invention is controlled, or the program of the welding sequence is changed.

The first aspect of the present invention is a plasma arc spot welding machine, which comprises constituent members such as an arc electrode, a nozzle, a shield cap, and a filler wire, and which spot-welds a workpiece using a plasma arc. A voltage measuring means for measuring an arc voltage, a storage means for storing a voltage fluctuation reference curve generated in accordance with a normal welding sequence of one cycle, and a plurality of pieces which are continuously measured by the voltage measuring means and are caused by various abnormal weldings. Of the
It's definitive a plurality of regions corresponding on the voltage variation reference curve and the actual measurement voltage variation of order set measured variable voltage regions
At least two or more differences comparing each reference fluctuation voltage
It is characterized by comprising a comparing means in the normal occurrence area and a judging means for judging an abnormality when each comparison value compared by the comparing means exceeds a preset allowable range.

Here, the voltage fluctuation reference curve means the arc voltage drop at the time of switching the gas flow rate, the arc voltage drop at the start of the feeding of the filler wire, and the filler wire of the same during one cycle of the normal welding process. It is a reference curve showing a change in a normal arc voltage due to an increase in the arc voltage at the end of the feeding, and the fluctuation of the arc voltage with respect to the welding time obtained in a normal welding process, which is previously calculated by the control unit. .

In the first aspect of the present invention, the actually measured fluctuating voltage region which is continuously measured during one cycle of welding is the whole region of the welding process or the region of a specific time zone. Although it can be determined, for example, in the case of bombing, there is a possibility that it will occur in the entire welding process, so it is necessary to measure the voltage in all areas, or abrupt fluctuations in voltage due to fluctuations in gas flow rate cause gas supply flow rate. Since it is likely to occur at the time of switching of the filler wire, the above-mentioned region is set as a time zone when switching the gas flow rate, and for example, to monitor a decrease in voltage drop due to defective feeding during feeding of the filler wire, etc. It is necessary to set the time zone of as the area.

The present invention is characterized in that a plurality of regions set as described above are constantly monitored, and a plurality of regions on the voltage fluctuation reference curve prestored in accordance with a normal welding sequence of one cycle are used. The reference fluctuating voltage in the above region and the actually measured fluctuating voltages in the corresponding plurality of regions are continuously or intermittently compared. When the comparison value exceeds a preset allowable range, it is determined that there is an abnormality that hinders normal welding.

With the above configuration, the current welding state can be continuously or intermittently monitored from the behavior of the arc voltage according to the normal welding sequence of one cycle, and various welding abnormalities can be immediately discriminated. At the same time, since it can be used as a material for investigating the causal relationship between the abnormal phenomena, the maintenance thereof is easy and stable welding quality can always be effectively obtained.

Further, for example, a plurality of superposed works may be targets for welding. In this case, the arc voltage when the first work is ignited and the through hole is opened is different from the arc voltage when the next work is ignited through the through hole. That is, when the size of the gap between the works is wide, the arc voltage increases greatly, and when the size of the space between the works is narrow, the increase of the arc voltage is small. The size of the gap between the works is measured by monitoring the change in the arc voltage at this time.

By monitoring the change of the arc voltage in this manner, the supply time and the supply amount of the plasma gas flow rate can be effectively controlled, and the arc heat input to the work can be appropriately controlled. Further, based on this control, if the supply time and the supply amount of the filler wire after forming the holes of the works are increased or decreased, various works can be welded accurately and efficiently.

A second invention according to claim 2 is characterized in that a part of the actually measured fluctuating voltage region is at least a leak generating region. In the second invention, when the actually measured fluctuating voltage region is compared with the reference fluctuating voltage of the corresponding region on the voltage fluctuating reference curve during one cycle of the welding process, the comparison value is a preset allowable range. When the arc voltage drops to the outside, and the decreasing time continues for more than about 5 ms, it can be determined that a leak has occurred.

According to the second aspect of the present invention, when the arc voltage outside the permissible range is continuously or intermittently decreased during the welding process of one cycle for a preset leak occurrence time or number of times or more. Can be determined as a leak, and a momentary drop in the arc voltage within about 5 msec can be determined as a bomb. It is possible to individually and accurately grasp each abnormal phenomenon such as leak or explosion generated during the one-cycle welding process.

A third invention according to claim 3 is characterized in that a part of the actually measured fluctuating voltage region is at least a plasma gas supply amount switching region. The arc voltage drops when the plasma gas is switched from a large flow rate to a small flow rate during welding. According to the third aspect of the present invention, it can be determined that the gas flow rate abnormality has occurred when the value does not decrease by a value within a predetermined allowable range (voltage decrease range) within a certain time from the start of plasma gas switching. . If the required arc voltage does not change within a certain period of time despite the switching of the plasma gas supply amount, it can be determined that the plasma gas flow rate was not smoothly switched, and the gas supply device or It can be seen that there is an abnormality in related equipment such as piping.

A fourth invention according to claim 4 is characterized in that a part of the actually measured fluctuating voltage region is at least a keyhole forming region. According to the fourth aspect of the invention, when the keyhole is formed, the arc voltage rise is monitored within a preset time from the start of the keyhole formation. When the arc voltage increase due to the monitoring deviates from the allowable range, it can be determined that some abnormality has occurred in the device related to the keyhole formation. At this time, it is also possible to detect the abnormality by monitoring the rise time of the arc voltage.

By measuring the arc voltage during the formation time of the keyhole, for example, when forming a keyhole in a plurality of superposed works, there is no fear of penetrating the work arranged at the lowest position and the desired key is formed. It is possible to instantly form holes and prevent welding defects such as through holes and breaks. By properly setting the gap size between multiple works, the plasma gas flow rate, the welding current, the start timing of the filler wire feeding, etc. according to a normal one-cycle welding sequence, a work keyhole is effectively formed. It

A fifth aspect of the present invention is characterized in that a part of the actually measured fluctuating voltage region is at least a filler wire feeding region. In the state where the filler wire is fed, the distance between the arc electrode and the filler wire becomes a substantial arc length, and in the state where the filler wire is not fed, the distance between the arc electrode and the work is Become the arc length. Since the filler wire and the work are configured to have the same potential, the arc voltage when the filler wire is fed is smaller than the arc voltage when the filler wire is not fed, and the arc voltage drops.

According to the fifth aspect of the invention, it is possible to monitor the state of decrease in the arc voltage within a preset time from the start of the feeding of the filler wire fed according to the normal welding sequence of one cycle. When the decrease in the arc voltage within the preset time deviates from the allowable range, it can be determined that some abnormality has occurred in the device related to the filler wire feeding. Even when the filler wire is retracted, it is possible to monitor the arc voltage increase within a preset time. When the arc voltage deviates from the permissible range within a preset time from the end of the feeding of the filler wire, for example, when the arc voltage greatly rises above the reference line or when the rise is extremely small, an abnormality occurs. It can be determined that it has occurred.

By measuring the arc voltage, it is possible to immediately determine the feeding or retracting state of the filler wire. Further, it is possible to detect the moment when the filler wire enters the arc, that is, the welding current flows through the filler wire. Also, the detection timing is somewhat delayed from the timing of the feed command due to the play amount of the filler wire at the filler wire feeder and the tip of the torch, the hardness of the feeding wire, etc. It is possible to monitor the mechanical errors of the wire feeding related equipment.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing a main part of a plasma torch applied to a plasma arc spot welding machine, which is a typical embodiment of the present invention, with a part cut away, and FIG. 2 is a normal welding process of one cycle. FIG. 6 is a waveform diagram showing the relationship between the arc voltage waveform generated according to the above and time. In the figure, substantially the same members as those of the conventional plasma torch shown in FIG. 8 are designated by the same reference numerals and member names.

In FIG. 1, a plasma torch 15 of a plasma arc spot welding machine 10 according to this embodiment includes an arc electrode 11 and a nozzle 1 incorporating the arc electrode 11.
2. A component such as a shield cap 13 arranged on the outer peripheral portion of the nozzle via a cooling cap 13 ′ for cooling the nozzle 12 is provided. There is a predetermined gap between the shield cap 13 and the cooling cap 13 ', and an insulating ring 17 is interposed. At the open end of the shield cap 13, three leg portions 18, 18, 18 are projected at equal intervals.

A filler feeding device 20 for feeding the filler wire 14 made of the same material as the work, for example, iron, to the welding point is attached to the main body of the shield cap 13 through the attachment member 19. A filler nozzle 22 is attached to the tip of a pipe-shaped guide member 21 provided in the filler feeding device 20. The tip of the filler nozzle 22 is screwed through a through hole formed in the lower end of the shield cap 13. The filler wire 14 is driven by a motor (not shown) to guide the guide member 2 based on a wire feeding signal sent from the controller 27.
1 is continuously extruded from the tip end opening portion of the filler nozzle 22, and the exposed end portion of the wire 14 is exposed below the plasma outlet of the nozzle 12 at a predetermined interval.

A high temperature plasma gas is supplied between the arc electrode 11 and the nozzle 12, and blows out from the tip outlet of the nozzle 12. The plasma gas is an argon gas or a mixed gas of argon and hydrogen. In this embodiment, a mixed gas of argon and hydrogen is used. The shield cap 13 and the cooling cap 13 '
Shield gas flows between and. The shield gas is argon gas, carbon gas, or a mixed gas of argon and oxygen. In this embodiment, a mixed gas of argon and oxygen is used.

The plasma torch 15 has a main arc power source (DC power source) 23, and the fixed contact of the arc electrode 11 is connected to the negative side of the DC power source 23. The work 16 made of a galvanized steel sheet in which the upper plate 16a and the lower plate 16b are superposed at a required gap is connected to the positive side of the DC power source 23 via a lead wire, and the filler is also connected via the lead wire. It is connected to the nozzle 22. The nozzle 12 is connected to the positive side of the power source 23 via a pilot arc power source having a switch 24 and a resistor 25. The shield cap 1
3 and the filler wire 14 are configured to have the same potential as the work 16. The DC power supply 23 is connected to a voltage measuring means 26 for measuring an arc voltage, and the voltage measuring means 26
Is connected to the control unit 27 which constitutes a part of the characteristic part of the present invention.

The control unit 27 includes a CPU, ROM, RA
It is composed of a microcomputer having M and the like. The control unit 27 stores in advance an arithmetic expression indicating a voltage fluctuation reference curve calculated based on a voltage fluctuation curve generated according to all steps of a one-cycle welding sequence when welding is performed in a normal state. There is. In this embodiment, the variation of the arc voltage in the actually measured fluctuating voltage region is continuously measured over the entire welding process according to the one-cycle welding sequence. The measured actually measured fluctuating voltage is read by the control unit 27.

Here, the voltage fluctuation reference curve refers to the arc voltage drop at the time of switching the gas flow rate, the arc voltage drop at the start of feeding the filler wire, the This is a modeled arithmetic expression obtained by previously calculating, in the control unit 27, a temporal change in the normal arc voltage caused by an increase in the arc voltage at the end of the feeding of the filler wire, and the welding in the normal welding process. The variation of the arc voltage for one cycle with respect to time is represented as a reference curve.

The actually measured fluctuating voltage region means the entire region of the welding process or the region of a specific time zone. For example, if a bomb is blown, it is necessary to measure the voltage in all areas because it may occur in the whole welding process. Since abrupt fluctuations in voltage due to fluctuations are likely to occur when switching the gas supply flow rate, use it as a time zone when switching the gas flow rate, or monitor the decrease in voltage drop due to feeding failure during filler wire feeding, etc. In this case, the time zone during the feeding of the filler wire is set as the actually measured variable voltage area.

The most characteristic feature of the present invention resides in that the plurality of actually measured fluctuating voltage regions set as described above are constantly monitored. In the present embodiment, reference fluctuation voltages in a plurality of areas on the voltage fluctuation reference curve prestored in accordance with a normal welding sequence of one cycle, and measured fluctuation voltages in a plurality of areas corresponding to the respective areas. Are continuously or intermittently compared by the calculation unit of the control unit 27. The determination unit of the control unit 27 determines whether or not the obtained comparison value deviates from the preset range. When it is determined that even one voltage fluctuation is abnormal in each area, the command is converted into a required signal and output to an alarm display device such as a monitor, a buzzer or a lamp (not shown).

According to the present embodiment, the workpiece 16 made of galvanized steel sheets, in which the two upper plates 16a and the lower plates 16b are overlapped with a gap therebetween, is the welding target. The lower plate 16b is ignited through the arc voltage when the upper plate 16a is ignited to form a hole and the through hole formed in the upper plate 16a.
It is different from the arc voltage at the time of ignition. When the size of the gap between the upper and lower plates 16a and 16b is wide, the voltage change is large, and when the size of the gap between the plates 16a and 16b is narrow, the voltage change is small. By monitoring such changes in the arc voltage, the gap size between the works 16 is measured, and the plasma gas flow rate is controlled based on the measured gap size.

With this configuration, it is possible to grasp the gap size between the plates of the plurality of workpieces 16 that are overlapped with each other, and effectively supply the amount of plasma gas and the amount of plasma gas required when forming the workpiece holes. In addition to the above, it is possible to appropriately control the heat input of the arc, the supply amount and the supply time of the filler wire 14 when the filler wire 14 is supplied to the work 16 having different gap sizes.

FIG. 2 shows two upper plates 16a and a lower plate 16b.
3 shows a relationship between a normal arc voltage waveform generated in accordance with a one-cycle welding sequence of the work 16 in which the two are closely adhered to each other and time. As shown in the figure, the plasma arc spot welding of the present invention is performed on the basis of the voltage fluctuation generated according to all steps of a normal welding sequence of one cycle.

In a time zone (0.05 to 0.2 seconds) T1 when forming a hole in the work 16, the arc voltage is linearly several V (1.
5V) rise. At this time, the upper plate 16 of the work 16
A plasma gas of about 4 liters per minute is flown at the time of plasma ignition to a, and a gas flow rate is switched at the time of plasma ignition to the lower plate 16b of the work 16 to flow about 1 liter of plasma gas per minute. When the plasma gas is switched from the large flow rate to the small flow rate within the time zone (0.2 to 0.5 seconds) T2 when the gas flow rate is switched, the arc voltage is preset according to the switching amount of the gas flow rate. It falls within the voltage drop range B. The decrease of the arc voltage at this time has a width of about 13 V and draws a gentle quadratic curve. Then, the reduced arc voltage is changed to the time zone (0.5 to 0.8).
5 seconds) At T3, the voltage value of about 39 to 42 V is maintained in the predetermined lower limit region B1 of the voltage drop range B.

Thus, the upper plate 16a of the work 16 is
The ignitability of the plasma arc can be improved and the drilling ability of the upper plate 16a can be improved by increasing the flow rate of the plasma gas only when the hole is drilled. The upper plate 16
After forming the through hole of a, by reducing the plasma gas flow rate at the time of plasma ignition to the lower plate 16b,
The arc heat input to the work 16 is lowered to prevent a part (molten pool) of the work 16 from blowing away.

Subsequently, the time zone (0.85 to 0.9) during the feeding of the filler wire 14 according to the normal welding sequence.
(Sec) At T4, the arc voltage linearly and instantaneously drops within a preset machining voltage range C by several V (5 to 6 V), and is about 36 in a predetermined lower limit region C1 of the machining voltage range C.
A voltage value of about 37 V is reached. This arc voltage continues while gradually decreasing gradually over a preset time period (0.9 to 2.3 seconds) T5 until the end of the feeding of the filler wire 14. The arc voltage at this time maintains a voltage value within a preset welding voltage range D. In addition, the time zone (2.3 when retracting the filler wire 14 due to the end of welding) (2.3
(˜2.6 seconds) At T6, the arc voltage rises by several V (5 to 6 V) within the preset voltage rise range E and reaches a predetermined upper limit region E1 of this voltage rise range E.

While the filler wire 14 is being fed, the filler wire 14 and the arc electrode 1 are
The distance to 1 is the arc length. When the filler wire 14 is not fed, the distance between the arc electrode 11 and the work 16 is the arc length. As described above, since the filler wire 14 and the work 16 have the same potential, the arc voltage between the arc electrode 11 and the work 16 is about several V higher than the arc voltage between the arc electrode 11 and the filler wire 14. Become. For example, the arc voltage increases by about 1 V each time the arc length extends by about 1 mm.

When welding the work 16 using the plasma arc spot welding machine 10 of the present invention constructed as described above, first, the switch 24 is closed to electrically connect the nozzle 12 and the arc electrode 11. At the same time, an arc discharge is caused to occur, and the plasma arc is blown onto the flow of the plasma gas to blow out from the plasma outlet of the nozzle 12.

After the plasma arc is generated, the switch 24
Is opened and the circuit between the nozzle 12 and the arc electrode 11 is cut off, the welding current flows through the arc electrode 11, the filler nozzle 14, and the work 16. Simultaneously with the start of welding, the measurement of the arc voltage is started over the entire process of the one-cycle welding sequence.

Now, the plasma arc ignites the surface of the upper plate 16a of the work 16. A through hole is made in the upper plate 16a by the plasma arc, and then the plasma arc is ignited on the surface of the lower plate 16b through the through hole. After the upper and lower plates 16a, 16b are perforated by the plasma arc to sufficiently heat the plates 16a, 16b, the filler wire 14 is fed into the plasma arc. By melting the filler wire 14 while feeding it at a predetermined feeding speed, the holes of the plates 16a, 16b are filled and the plates 16a, 16b are joined. After the welding of the plates 16a and 16b is completed, the filler wire 14 is retracted, the surface of the upper plate 16a is smoothed by the plasma arc, and then the generation of the plasma arc is stopped.

When the plasma arc spot welding is carried out in a stable state as described above, the arc voltage and the arc current are in the range of the reference fluctuation value on the potential fluctuation curve according to the normal welding sequence of one cycle. (AE) is maintained. However, during welding, welding defects may occur due to the above-described explosion, leakage, defective formation of keyholes, abnormal gas flow rate, abnormal wire feeding, and the like.

In the present embodiment, the arc voltage is continuously measured and the welding abnormality and the welding failure are monitored in accordance with the above-described welding sequence from the start time to the end time of welding. It should be noted that it is possible to detect the above-mentioned abnormal phenomenon by about 2
The arc voltage is continuously measured in a cycle of msec. Hereinafter, a monitoring mode at the time of welding in the present invention when the feeding abnormality or the welding defect occurs will be described. In the case of (1) bombardment, FIG. 3 shows an example of the bombing phenomenon that occurred during the welding process of one cycle. According to this embodiment, this monitoring mode constantly monitors at a cycle of about 2 msec.
The actually measured fluctuating voltage region shown in FIG. 3 continuously measured by the voltage measuring means 26 corresponds to corresponding time zones T1 to T6 on the voltage fluctuation reference curve during the normal welding process of one cycle shown in FIG. Is compared with the reference fluctuation voltage of.

As shown in FIG. 3, with respect to the reference fluctuation voltage of about 35 V in the corresponding time zone (0.9 to 2.6 seconds) T5 on the voltage fluctuation reference curve, the arc in the actually measured fluctuation voltage region is set. The voltage instantaneously drops to about 22V over the preset welding voltage range D. At this time, it can be determined that a bombing has occurred.

After the filler wire 14 is fed according to a normal welding sequence of one cycle, for example, the arc voltage drops to about 5V or more from the Nth voltage at the (N + 1) th sampling, and (N + 4). ) If the voltage has returned to the N-th voltage at the time of the sampling, it can be determined that the bombing has occurred. The number of bombs is stored in the control unit 27. When the number of bombs exceeds a preset number, a signal for prompting replacement of consumables and cleaning of the plasma torch 15 is output to the alarm device. Further, the arc voltage measured continuously is lower than the preset voltage threshold value, and it can be determined that the bombing has occurred when the preset time has elapsed.

FIG. 4 shows a current waveform for explaining the extension of the welding time when the explosion occurs. As shown in the figure, in the welding sequence in which the bombing has occurred, the welding time is extended by adding a predetermined correction time to the preset normal welding time, and the welding conditions for bombing correction are set.
Welding conditions before and after the bombing can be automatically corrected so that the bombing does not occur.

(2) In the case of leakage, FIG. 5 shows an example of the leakage phenomenon which continuously occurs during the welding process of one cycle, and FIG. 6 shows the leakage phenomenon which occurs intermittently during the welding process. An example is shown. According to the present embodiment, this monitoring mode monitors at a cycle of about 2 msec as in the bombing. The actually measured fluctuating voltage region continuously measured by the voltage measuring means 26 is compared with the reference fluctuating voltage in the corresponding time zones T1 to T6 on the voltage fluctuation reference curve shown in FIG.

As shown in FIG. 5, the arc voltage in the actually measured fluctuating voltage region is set to a preset welding voltage range with respect to the reference fluctuating voltage of about 35 V in the corresponding time zone T5 on the voltage fluctuating reference curve. It sharply drops below 20 V beyond D and continuously maintains an arc voltage of about 16 to 20 V. At this time, it can be determined that a leak has occurred. Further, when the arc voltage is lower than a preset voltage threshold value and a preset time has elapsed, it can be determined that a leak has occurred. As shown in FIG. 6, when the leak occurs intermittently, the leak occurrence time and the number of occurrences of the leak can be stored, and the presence or absence of the leak can be determined by a program stored in advance in the memory of the control unit 27.

If it is determined that a leak has occurred, a leak occurrence signal is immediately output to the alarm device at the end of the welding sequence in which a leak has occurred, to clean the plasma torch 15, replace consumables, Check and correct. It is possible to prevent the start of the next welding and prevent continuous welding defects.

(3) In the case of defective keyhole formation, FIG. 7 shows an example of defective keyhole formation that occurred during one cycle of the welding process. This monitoring mode continuously monitors the welding process of one cycle for the above-mentioned bombardment and leak, whereas it monitors only a specific time. The voltage measuring means 26
Compared with the reference fluctuation voltage of the time zone (0.05 to 0.2 seconds) T1 at the time of forming the corresponding keyhole on the voltage fluctuation reference curve shown in FIG. To be done.

As shown in FIG. 7, when the keyhole is formed, the measured arc voltage is preset with respect to the reference fluctuation voltage in the preset machining voltage range A within the time zone T1. After gradually decreasing within the time zone T1 of time, the time zone T2 (0.2 seconds to
In 0.25 seconds), the voltage rise range A is rapidly deviated and the voltage rises by about 3V. In this case, a normal keyhole is not formed in the work 16.

In the time zone T1, the actually measured arc voltage is within a predetermined upper limit range A within the voltage increase range A.
When the reference fluctuation voltage of 1 has not risen, it can be determined that the keyhole is not formed in the work 16. When the arc voltage measured at the end of the keyhole formation has not dropped to the predetermined reference fluctuation voltage at the end of the keyhole formation, the lower plate 1 of the work 16 is
It can be determined that an abnormal keyhole penetrating 6a is formed.

If it is determined that the keyhole formation abnormality has occurred, the keyhole formation abnormality generation signal is immediately output to the above alarm device at the end of the welding sequence where the keyhole formation abnormality has occurred, and the welding current etc. is reviewed. Abnormality checks of consumables (not shown), related devices (not shown) such as gas flow rate, and confirmation and correction of welding points are performed.

(4) In the case of gas flow rate abnormality, this monitoring mode monitors only a specific time as in the above keyhole formation abnormality. The actually measured fluctuating voltage region continuously measured by the voltage measuring means 26 is a time zone (0.2 to 0.2) during the corresponding gas flow rate switching on the voltage fluctuation reference curve shown in FIG.
0.5 seconds) compared to the reference fluctuation voltage of T2.

As shown in FIG. 7, the arc voltage rising beyond the machining voltage range A due to a defective keyhole formation is suddenly and momentarily reduced past the time zone T2 at the start of plasma gas switching. It decreases by about 13 to 14V. The reduced arc voltage greatly linearly decreases after passing the time zone T2, and then decreases by about 5 V from the predetermined lower limit area B1 of the voltage drop range B in the time zone T3. When the plasma gas was switched from the large flow rate to the small flow rate, the actually measured arc voltage did not drop to the reference fluctuation voltage of the lower limit area B1 in the preset voltage drop range B within a certain time from the start time of the plasma gas switching. Then, it is possible to determine the abnormality of the gas flow rate.

If it is determined that the gas flow rate abnormality has occurred, a gas flow rate abnormality occurrence signal is immediately output to the alarm device at the end of the welding sequence in which the gas flow rate abnormality has occurred, and a gas cylinder (not shown), also shown in the figure. Check for abnormalities in the omitted gas piping and related equipment such as solenoid valves, and check and correct welding points.

(5) In the case of wire feeding abnormality, this monitoring mode monitors only for a specific time as in the case of gas flow rate abnormality and keyhole formation failure. The measured fluctuating voltage region continuously measured by the voltage measuring means 26 is the time zone (0.85 to 0.9 sec) T4 at the start of wire feeding corresponding to the voltage fluctuation reference curve shown in FIG. Is compared with the reference fluctuation voltage of. In the time zone T4, the actually measured arc voltage is within a preset machining voltage range C and is within a predetermined lower limit region C.
When the reference fluctuation voltage of 1 is not reduced, it can be determined that some abnormality has occurred in the device related to the filler wire feeding.

Further, the actually measured fluctuating voltage region is compared with the reference fluctuating voltage in the time zone (2.3 to 2.55 seconds) T6 at the end of wire feeding corresponding to the voltage fluctuation reference curve shown in FIG. To be done. When the measured arc voltage does not rise to the reference fluctuation voltage of the upper limit area E1 in the preset voltage rise range E within the predetermined time T6 from the end of wire feeding, it is determined that an abnormality has occurred. You can

When it is determined that the wire feeding abnormality has occurred, a feeding abnormality occurrence signal is immediately output to the alarm device at the end of the welding sequence in which the wire feeding abnormality has occurred, and the filler wire 14 Presence / absence check, abnormality check and correction of the filler feeding device 20 are checked.

As is clear from the above description, according to the plasma arc spot welding machine of the present invention, a plurality of actually measured fluctuating voltage regions continuously measured during one cycle of welding and one normal cycle of The pre-stored voltage fluctuation reference curve generated according to all steps of the welding sequence is continuously or intermittently compared with the reference fluctuation voltage of a plurality of corresponding regions. By comparing the comparison value with a preset allowable range, it is possible to determine whether there is a welding abnormality or the like.

For this reason, the current welding state can be intermittently or continuously monitored from the behavior of a plurality of arc voltages in accordance with a normal welding process of one cycle to immediately determine various welding defects and the like. In addition, the welding quality is stabilized.
It is possible to control the operation of the constituent members of the main body of the welder according to various welding phenomena that occur during welding, and to appropriately control the welding sequence.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a partial cutaway of a main part of a plasma torch applied to a plasma arc spot welding machine that is a typical embodiment of the present invention.

FIG. 2 is a waveform diagram showing a relationship between an arc voltage generated according to a normal welding process of one cycle which is a typical embodiment of the present invention and time.

FIG. 3 is a waveform diagram showing an example of an explosion phenomenon that occurs according to the welding process.

FIG. 4 is a current waveform diagram for explaining the extension of welding time when a bomb is blown.

FIG. 5 is a waveform diagram showing an example of a leak phenomenon that continuously occurs according to the welding process.

FIG. 6 is a waveform diagram showing an example of a leak phenomenon which is intermittently generated according to the welding process.

FIG. 7 is a waveform diagram showing an example of a keyhole formation defect that has occurred according to the welding process.

FIG. 8 is an explanatory diagram schematically showing an example of an abnormal phenomenon that occurs during welding.

[Explanation of symbols]

10 Plasma arc spot welder 11 arc electrode 12 nozzles 13 Shield cap 13 'cooling cap 14 Filler wire 15 Plasma torch 16 work 16a Upper plate 16b lower plate 17 Insulation ring 18 legs 19 Mounting member 20 Filler feeder 21 Guide member 22 Filler nozzle 23 DC power supply 24 switches 25 resistance 26 Voltage measuring means 27 Control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Aragaki 1200 Manda, Hiratsuka, Kanagawa Prefecture Komatsu Ltd. Research Headquarters (72) Inventor, Iwa Kurokawa 1200, Manda, Hiratsuka Kanagawa Prefecture Komatsu Ltd. Research Headquarters (72 ) Inventor Kengo Kamiya 100 Kanayama, Ichiriyama-cho, Kariya city, Aichi Toyota Auto Body Co., Ltd. (72) Inventor Tetsuya Taki 100 Kanayama, Ichiriyama-cho, Kariya city, Aichi Prefecture (72) Inventor Noma Ichihiro 100 Kanayama, Ichiriyama-cho, Kariya, Aichi Toyota Auto Body Co., Ltd. (72) Inventor, Hideto Uematsu 100, Kanayama, Ichiriyama-cho, Kariya City, Aichi Prefecture (56) 25046 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B23K 10/00 B23K 10/02

Claims (5)

(57) [Claims] 1. A plasma arc spot welding machine, comprising constituent members such as an arc electrode, a nozzle, a shield cap, and a filler wire, for spot welding a work by using a plasma arc, and a voltage measuring means for measuring an arc voltage. Storage means for storing a voltage fluctuation reference curve generated according to a normal welding sequence of one cycle , and various abnormalities continuously measured by the voltage measuring means.
At a plurality of preset at least two abnormal regions of comparing the respective reference variable voltage which definitive a plurality of regions corresponding on the voltage variation reference curve and the actual measurement voltage variation of measured variable voltage regions caused by welding A plasma arc spot welding machine, comprising: a comparing means; and a judging means for judging that there is an abnormality when each comparison value compared by the comparing means exceeds a preset allowable range. 2. The plasma arc spot welding machine according to claim 1, wherein a part of the actually measured fluctuating voltage region is at least a leak generation region. 3. The plasma arc spot welding machine according to claim 1, wherein a part of the actually measured fluctuating voltage region is at least a plasma gas supply amount switching region. 4. The plasma arc spot welding machine according to claim 1, wherein a part of the actually measured fluctuating voltage region is at least a keyhole forming region. 5. The plasma arc spot welding machine according to claim 1, wherein a part of the actually-measured fluctuating voltage region is at least a filler wire feeding region.