JPH04339570A - Plasma machining device - Google Patents

Abstract

PURPOSE:To reduce the capacity, size and weight of a transistor inverter for plasma machining and to increase electric power consumption efficiency thereof. CONSTITUTION:The plasma machining device is provided with a first setting device 1 to set a low current value for a starting arc, a second setting device 2 to set a high current value for a machining arc and a changeover means 7 to select a set value of the second setting device 2 for a target value of PWM control of the inverter when a set value of the first setting device 1 is changed to the machining arc by further supplying second gas H2 with high potential gradient when the starting arc is generated by supplying first gas Ar with low potential gradient to a torch. Since a selective current value is low on the starting arc where a high peak current with the low arc voltage is carried, the required capacity of the inverter is low and voltage loss is reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus for welding, cutting, or heating an object using a plasma arc, and more particularly to a power supply for the apparatus.

0002

[Prior Art] In this type of plasma processing, a power supply device with constant current characteristics (dripping characteristics) is used so that the plasma current value does not fluctuate due to fluctuations in plasma arc length. uniformity is ensured. In order to accurately determine the output current value to a value suitable for plasma processing, it is recommended to use a transistor inverter in the power supply (for example, Japanese Patent Laid-Open Nos. 63-299880 and 64-44).
No. 280, Japanese Unexamined Patent Publication No. 2-112881). According to the transistor inverter, the output current value can be accurately controlled by PWM (pulse width modulation) control. When the output current value fluctuates, the PWM control functions to suppress the fluctuation by feedback control, but since the response speed is fast, the fluctuation width of the output current value is small and the stability of the constant current output is high. In addition, the power supply device becomes smaller and lighter, and operability and workability are improved. Transistor inverters have traditionally been used for relatively low-heat plasma processing because transistors are vulnerable to overloads, but as the demand for high processing quality has increased even in plasma processing that requires high heat, transistor inverters are being used with high current capacity. Transistor inverters using transistors have become available. Along with this, because of the above-mentioned advantages, transistor inverters are used in various processing modes such as plasma welding and cutting.

0003

On the other hand, in plasma processing, the current value of the plasma torch and the type of gas used are variously selected depending on the processing content. Along with this, the required drooping characteristics of the power supply device also vary. For example, (a) plasma gas is Ar60%, H240%, flow rate 40 liters/min.
In the case of plasma cutting, the drooping characteristics shown in FIG.
, 300A of power is required. (b) Argon plasma gas
In the case of plasma welding with a flow rate of 100% and a flow rate of 1 liter/min, the drooping characteristics shown in FIG.

Furthermore, in the case of (a) above, when starting the arc, only Ar having a low potential gradient is supplied to the torch, and the
An arc of V and 300 A is generated, and then H2 having a high potential gradient is added to generate an arc of 120 to 200 V and 300 A for cutting. For example, in case (a), before cutting, only Ar is supplied to the torch, and the arc is maintained in the C point region of the drooping characteristic shown by the solid line in Fig. 3, and when cutting, the torch is supplied with only Ar. H2 is supplied in addition to Ar to the arc, and an arc is maintained in the A and B point regions.

In PWM control of a transistor inverter, the output current pulse of the inverter is as shown in FIG. That is, the output current pulse has T period (e.g. 8KHz
), point A in FIG. 3 corresponds to pulse Pa in FIG. 4, point B to pulse Pb, and point C to pulse Pc in FIG. PWM control determines the pulse widths Ta, Tb, and Tc so that the output current value (time-series average value of pulse current) is kept at a constant value (target value), so Ia x Ta = Ib x Tb = Ic x Tc. The pulse width is determined as follows. Therefore, point A (Pa)
Point B (Pb) is higher than the current pulse peak value of B
The current pulse peak value at point C (Pc) is higher than the current pulse peak value at point (Pb). The transistor allowable current value of the transistor inverter must be less than the maximum peak value. Therefore, the capacitance of the transistor inverter is the pulse Pc
It must be determined corresponding to the range (area C in FIG. 3). That is, for example, as shown in FIG.
When the range of V and arc voltage is wide, it is necessary to select a transistor according to the lowest point of the arc voltage, that is, the highest peak point of the current pulse (point C = Pc), Since the transistors used are more expensive, the more current pulses are used, the more expensive and larger the power supply becomes. Moreover, although pulses Pa, Pb, and Pc have the same current value (time series average value), their effective value is
The pulse Pb is better than the pulse Pb, and the pulse Pc is better than the pulse Pb.
becomes larger nonlinearly. Since the heat loss of the inverter's transistors and transformers is proportional to this effective value,
In a pulse (Pc) with a narrow width and a large peak value, power loss due to heat loss is large. Therefore, there is a problem in that the higher the current pulse is used, the greater the power loss of the power supply device becomes.

The present invention aims to improve this type of problem.

[0007]

[Means for Solving the Problems] The present invention provides plasma
First supply means for supplying the first gas (Ar) with a low potential gradient to the plasma torch (23, 29); The potential gradient is high after the start of supply of the first gas (Ar) Second supply means for supplying the second gas (H2) to the plasma torch (23, 29) in addition to the first gas (Ar); transistor inverter (16, 17);
Current setting means (1 to 17) for setting the output current of
13); and a power supply device including a controller (14, 15) that controls the output current of the inverter (16, 17) to a current value set by the current setting means (1 to 13). In a plasma processing device, a first current value for setting a relatively low first output current value (100 A) to maintain an arc in a first gas (Ar) atmosphere in a plasma torch (23, 29). Setting means (1): Set a relatively high second output current value (300A) on the plasma torch to maintain the plasma processing arc in a mixed atmosphere of the first gas (Ar) and the second gas (H2). and a second current value setting means (2) for controlling the first gas (A) by the second supply means.
r) until the supply of the second gas (H2) added to the first output current value (100A
) and the second gas (H2) is supplied to the controllers (14, 15) until the plasma processing is completed after the supply of the second gas (H2) is started.
It is characterized by comprising a switching means (7) that provides an output current value (300A). Note that symbols in parentheses indicate corresponding elements or corresponding matters in the embodiments shown in the drawings and described later.

[0008]

[Operation] The switching means (7) causes the second supply means to
Until the supply of the second gas (H2) added to the gas (Ar) is started, the controllers (14, 15) are supplied with a relatively low first output current to maintain the arc in the first gas (Ar) atmosphere. value(
100 A), the arc is started and maintained at the first output current value (100 A) in the first gas (Ar) atmosphere. This state is, for example, point C' in Figure 3, and the pulse current is Pc' in Figure 4, and although the arc voltage is low, the set current value is low, so the pulse current peak value is significantly lower than before. Become.

After the switching means (7) starts supplying the second gas (H2) in addition to the first gas (Ar), the controllers (14, 15) control the plasma processing operation until the plasma processing is finished. - Since the second output current value (300A) that maintains the
Plasma processing is performed in a mixed atmosphere. During this plasma processing, for example, at points A and B in Figure 3, the pulse current is as shown in Figure 4.
Pa, Pb, and although the pulse current value is high, the
Since the peak voltage is high, the peak value of the pulse current is low as in the conventional case, so there is no problem even if the transistor allowable current value of the transistor inverter is lowered, and the power loss of the power supply device is small.

That is, the current pulse (Pc'
; Since the current peak value at point C' is lowered, the allowable transistor current value of the transistor inverter can be lowered accordingly. In other words, small capacity, low cost transistors can be used. Furthermore, the power loss of the power device is reduced, power consumption efficiency is increased, and the power device is made smaller and lighter.

Other objects and features of the invention will become apparent from the following description of embodiments with reference to the drawings.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, and FIG. 2 shows the timing at which electrical signals are generated in each part of the circuit shown in FIG. In this example, the above-mentioned (a) plasma gas is Ar60%.
, H240%, flow rate 40 liters/min, output current 300 A (arc start current 100 A) plasma cutting (points A, B, C' in Fig. 3), and the highest peak current pulse in this process. In order to be able to perform two types of machining under other conditions, one is to perform machining at the highest peak value lower than the peak value.
It includes three sets of current setting circuits (1 to 6), a changeover switch 10 for selecting one of them, and a tap selection switch 40 for selecting an output voltage corresponding to each of the three types of processing. FIG. 1 shows the state in which the plasma processing described in (a) above is set.

Explaining this setting state, the activation signal (high level H) is held in the first latch 12 through the normally closed switch contact piece 11 and is applied to the first timer 26. The output of the first latch 12 rises at the same time as the start signal rises, and as a result, a high level H signal instructing to turn on is given to the current command circuit 13 and the pulse generation circuit 15. , a signal H (high level) is given to a valve driver (not shown) for supplying the first gas (Ar) without receiving a rise delay. As a result, the current command circuit 13 starts outputting the current value command signal, and the PWM pulse generation circuit 15 outputs a width corresponding to the current value obtained by feedback-correcting the current value specified by the current value command signal by the adder 14. A pulse (for example, Tc' in FIG. 4) is generated, and the switching driver 16 turns on the transistor of the transistor inverter 17 with the high level of this pulse. As a result, the direct current obtained by rectifying the output voltage of the three-phase AC power supply 18 by the rectifier 19 is transmitted during the ON period of the transistor.
It is applied to the primary circuit of transformer 20. A pilot energizing circuit 28 and a rectifier 21 are connected to the secondary circuit of the transformer 20 via a tap selection switch 40 . In this way, transistor inverter 17 is activated substantially simultaneously with the arrival of the activation signal. At this time, the changeover switch 7 passes the voltage (signal indicating 100A) set to the variable resistor 1 for setting the start arc current value through the changeover switch 10 and through the time constant circuit 36. ,
Since the current command circuit 13 supplies a signal instructing the start arc current value (100A) set to 1 to the PWM pulse generation circuit 15, the plasma torch Since electrode 23 is not discharging, it is
No problems occur. Time T after arrival of start signal (H)
After 1, the first timer 26 times out and its output is inverted from the low level L to the high level H, and this H is held in the second latch 27, and the second timer 38 starts timing. The output H of the second latch 27 is the pilot energizing circuit 2
8, a pilot energizing circuit 28 applies a pilot arc voltage between the electrode 23 and the nozzle 29 of the torch, thereby causing a pilot arc voltage between the electrode 2 and the nozzle 29.
A problem occurs. Since the secondary voltage (output voltage) of the transformer 20 is applied between the workpiece 24 and the electrode 23 via the rectifier 21, reactor 22, and current detector 30, when a pilot arc occurs, Electrode 23-
A start arc is generated between the workpieces 24. The current value of this start arc is detected by the current detector 30 and fed back to the adder 14, so that the current value becomes the current value (100 A) set by the variable resistor 1. P.W.
Since the M pulse generator 15 adjusts the pulse width, the current value is maintained at the set current value (100 A) on a steady basis, but the comparator 3
1 changes its output from L to H when the arc current value becomes the closest value to the set current value (100A). The third latch 32 holds this H, and the third timer 33 holds this H.
Starts timekeeping in response to . Due to the H held by the third latch 32, a valve driver (not shown) that supplies the second gas (H2) is energized, and the second gas is supplied to the torch (23, 29) in addition to the first gas (Ar). ). Second
When the time T3, which is longer than the delay time required for the gas (H2) to start ejecting from the tip of the torch, has elapsed, the third timer T3 times out and its output is reversed from L to H. The fourth latch 35 holds this H, and the fourth timer 41
starts measuring time in response to this H signal. Due to the H held by the fourth latch 35, the changeover switch 7 switches and contacts the variable resistor 2 that specifies the machining arc current value (300A), and the current command circuit 13 receives the machining arc current value (300A). 300
A voltage specifying A) is applied, and the current command circuit 13 outputs a signal corresponding to this voltage. As a result, the transistor inverter 17 outputs the machining arc current and starts the process.
Torarch turns into main arc.

In order to suppress discontinuous and large output current fluctuations during this switching, a time constant circuit 36 is provided, which controls the start arc current value (100 A).
) from the indicated voltage (output of 1) to the machining arc current value (300
A) Switching stage section (discontinuous section) of indicated voltage (output 2)
Smooth the curve into a smoothly continuous curve.

[0015] Due to the above process, machining arcs are generated. After a sufficient time for the machining arc to occur and stabilize, the fourth timer times out and its output is reversed from L to H. The fifth latch 37 holds this H. The H held by the fifth latch 37 energizes a torch drive device (not shown) to move the torch at a set speed.

Activation signal (H) disappears (reverses to L)
With this (L), all latches are cleared, the holding signal (H) disappears (L), and plasma processing ends. In addition,
Since a fall delay circuit 25 is inserted between the latch 12 and the valve driver for supplying the first gas (Ar), the supply of the first gas (Ar) is started after plasma processing is completed.
This continues for the delay time T5 of the circuit 25.

After the first timer 26 times out (
Start arc (100A) does not occur within time T2 (after starting pilot arc energization) (comparator 31
output remains at L), the second timer 38
and converts the output to H, which causes AND gate 4
The output of No. 2 changes to H, which opens the normally closed contact piece 11 and opens the first to fifth latches 12, 27, 32, 35, 37.
is cleared, the supply of the first and second gases is stopped, the pilot energization is stopped, and the energization of the inverter 17 is stopped. When the activation signal disappears (changes from H to L), the latch 39 is cleared, the output of the AND gate 42 returns to L, and the normally closed contact piece 11 returns to close.

When the tap selection switch 40 of the transformer 20 is switched to another tap (another processing mode), the changeover switch 10 is also switched to a variable resistor that sets the corresponding arc current. Switch to . In this embodiment, a total of three modes including the above-mentioned processing mode can be selected and set. In the above-mentioned processing mode, the variable resistor 1 is set to the first gas having a low potential gradient. This is used to set a low current value for energizing the start arc when supplying only the first gas, and the variable resistor 2 supplies the second gas with a high potential gradient in addition to the first gas. This is to set a high current value. Variable resistors 3 and 4 are used to set a low current value for energizing the start arc and a high current value for energizing the machining arc, respectively, in another machining mode. Variable resistors 5 and 6 are in the remaining processing mode,
A low current value for energizing the start arc and a high current value for energizing the machining arc are respectively set. The output voltages (current value indicating voltages) of these variable resistors 1 to 6 are limited within the range of upper and lower limit values corresponding to each mode. As a result, the maximum value of the planned current pulse peak is regulated among all three selectable modes, and the inverter 17 is given a permissible current value with the required margin above this maximum value. Transistors are used.

[0019]

Effects of the Invention: Since the current peak value of the current pulse (Pc'; point C') at a point when the arc voltage is high and is not substantially involved in plasma processing is reduced, the transistor of the transistor inverter can be reduced by that amount. Allowable current value can be lowered. In other words, small capacity, low cost transistors can be used. Furthermore, the power loss of the power device is reduced, power consumption efficiency is increased, and the power device is made smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of an embodiment of the present invention.

2 is a time chart showing the timing of generation of electrical signals in each part of the circuit shown in FIG. 1. FIG.

FIG. 3 is a graph showing drooping characteristics of a plasma arc power supply device during plasma cutting.

4 is a graph showing the output current pulses of the transistor inverter that generates the currents at points A, B, C, etc. shown in FIG. 3 of the plasma arc power supply device.

5 is a graph showing the drooping characteristics of a plasma arc power supply device in plasma processing; FIG. 5(a) shows the one for plasma cutting, and FIG. 5(b) shows the one for plasma welding.

[Explanation of symbols]

1-6: Variable resistor
7-9: Changeover switch 10: Selection switch
11: Normally closed contacts 12, 27, 32, 35, 37, 3
9: Latch 13: Current command circuit
14: Adder 15: PWM pulse generator 16: Switching driver 17: Transistor inverter 18:
Three-phase AC power supply 19: Rectifier
20: Transformer 21: Rectifier
22: Reactor 23: Torch electrode
24: Processing material 25: Falling delay circuit
26, 33, 38, 41: Timer 28: Pilot energization circuit 2
9: Torch nozzle 30: Current detector
31: Comparator 36: Time constant circuit
40: Tap selection switch 42: AND gate

Claims (1)

[Claims] [Claim 1] Plasma torch; first torch with low potential gradient
A first supply means for supplying gas to the plasma torch; a second supply means for supplying a second gas having a high potential gradient to the first gas after the start of supply of the first gas; and a transistor inverter; - a power supply device including a controller, a current setting means for setting the output current of the inverter, and a controller for controlling the output current of the inverter to a current value set by the current setting means; In a plasma processing apparatus having a plasma processing apparatus, a first current value setting means for setting a relatively low first output current value for maintaining an arc in a first gas atmosphere in the plasma torch; a second current value setting means for setting a relatively high second output current value for maintaining the plasma processing arc in a mixed atmosphere of the first gas and the second gas; a switching means that applies a first output current value to the controller until the supply of the added second gas is started, and applies a second output current value to the controller until the plasma processing is finished after the supply of the second gas has started; A plasma processing device comprising: