JPS6015083A - Electron beam working machine - Google Patents

Abstract

PURPOSE:To prevent the generation of electric discharge in an electron gun in beam welding by interrupting a high voltage electric circuit constituted of a high voltage power source and the electron gun which is the load thereof for optional time by changing the degree of vacuum in the electron gun thereby stopping the operation of the electron gun. CONSTITUTION:A high voltage power source 1, electron gun 2 and a vacuum tube 17 constitute a main high voltage circuit. The gun 2 is attached to a vacuum chamber 10 for welding and the inside of the chamber 10 and a vacuum chamber 7 for the electron gun is continuously evacuated with vacuum pumps 9, 8. The gun 2 controls the thermoelectron released by the cathodic heating by a cathode power source 3 with a bias power source 4 and welds the material 6 in the chamber 10. The pipe 17 is made electrically conductive in a steady state but when the degree of vacuum of the chamber 7 decreases just prior to the generation of the electric discharge owing to entry of gas and molecules of metallic vapor into the chamber 7, the output from a detector 11 for said decrease changes and is compared with a voltage setter 12 in a circuit 13 which emits the output signal of DC. Then a multivibrator 14 and a transistor 16 operate and the output of a control grid power source 15 is applied to the tube 17, by which the high pressure circuit is interrupted. The output of the vibrator 14 is made zero after the interruption and the operation of the gun is resumed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electron beam processing machine, and more particularly to a beam control device suitable for preventing electric discharge occurring within an electron gun.

[Background of the invention]

Conventional technology detects the high-voltage circuit current when a discharge occurs in the electron gun, and if this value exceeds a current limit of, for example, 0.6 A, the electron gun is shut off in less than 25 microseconds ( A high-voltage circuit control device that can return (turn-off) after 35 milliseconds has elapsed (turn-off) is provided,
It was developed for the purpose of protecting equipment due to overload.

However, when performing, for example, welding work using an actual electron beam processing machine, the most important thing is to prevent lightning from occurring within the electron gun.

Furthermore, as a result of conducting actual welding tests, the following drawbacks were found in this technology.

(1) In an electron beam processing machine with an accelerating voltage of 30 KV or more, if the turn-off time is 25 microseconds or less, the machine will be damaged by a surge (L is mainly the inductance of the high-voltage cable and high-voltage transformer).

(2) When the interruption elapsed time is 35 milliseconds, for example, welding continuity cannot be maintained in horizontal penetration welding with a thickness of 100 mm, and void defects occur.

As a result of the above, it is currently impossible to prevent welding defects such as voids occurring in the welded portion due to metal vapor entering the electron gun and generating electric discharge.

[Purpose of the invention]

The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art, and
An object of the present invention is to provide an electron beam processing machine that prevents discharge from occurring within an electron gun and provides good welding results in electron beam welding.

[Summary of the invention]

In order to achieve such an object, the present invention provides an electron beam processing machine that uses metal vapor or the like to enter the electron gun in a high voltage electric circuit consisting of a high voltage power source of an electron beam processing machine and an electron gun that is a load of the power source. A change in the vacuum chamber is detected, and according to the detection signal, the electron gun vacuum chamber changes to a set value (10"' to l
The high-voltage circuit is equipped with a shut-off and control mechanism that shuts off the high-voltage electric circuit for a selected period of time and stops the operation of the electron gun when the voltage drops below lXl0-' with respect to O-"l'orr). It is characterized by:

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail based on illustrated embodiments. FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, in the electron beam processing machine, a high voltage power supply 1, an electron gun 2, and a vacuum tube 17 constitute a high voltage main circuit. In this electron beam processing machine, an electron gun 1 is attached to a welding vacuum chamber 10, and a vacuum chamber exhaust pump 9 is attached to the welding vacuum chamber 10.
Also, the electron gun vacuum chamber 7 is equipped with an electron gun vacuum pump 8.
The workpiece 6 is placed in the welding vacuum chamber 1o and processed in vacuum.

The electron gun welds a workpiece 6 by controlling thermoelectrons emitted by cathode heating by a cathode power supply 3 with a bias power supply 4 . In a steady state, the vacuum tube 17 is in a conductive state and welding proceeds as described above.

However, when electron beam welding is performed, by melting the workpiece 6, gas components contained in the material and molecules turned into metal vapor are released from the surface of the workpiece 6. These gas and metal vapor molecules enter the electron gun vacuum chamber 7.

If a large amount of these molecules enters the electron gun vacuum chamber 7, the high voltage insulation (between the cathode and the anode, or between the bias and the anode) is broken, and a discharge occurs within the electron gun. When we investigated this by welding killed steel plates with a thickness of 100m+, we found that minute discharges occurred once or twice every 10 minutes, and complete discharges occurred once every 20 minutes.
The vacuum level at that time is I
I X 1O-tTorr near the workpiece 6 indicated by
Tonashi, the electron gun vacuum chamber 7 is 10-'~lO-"l'o
The differential pressure at RR was extremely large at 102 to 103 Torr, making it easy for molecules such as metal vapor to be sucked in. Furthermore, just before the discharge occurs, the degree of vacuum in the electron gun vacuum chamber 7 momentarily changes from 101 to 10-10-4T, and it is clear that the discharge is caused by the intrusion of released molecules due to welding. It became.

In the present invention, when one molecule of metal vapor or the like enters the electron gun and the degree of vacuum in the electron gun vacuum chamber decreases immediately before discharge occurs, the output voltage of the vacuum degree detector 11 changes, and the voltage setting device 1
2 and a comparator circuit 13, and outputs a DC output signal.

As a result, the multivibrator 14 and the control transistor 16 operate, and the output of the control grid power supply 15 is applied to the vacuum tube 17, which can cut off the high voltage circuit. Immediately after the cutoff, the output of the multivibrator 14 becomes 0, the vacuum tube 17 becomes conductive again, and the operation of the electron gun 2 is restarted. Symbol 18 is vacuum tube 1
7 screen grid power supply.

FIG. 2 shows a more detailed representation of the operation of the circuit described above.

In steady state, a beam acceleration voltage V is applied to the electron gun,
Electron beam welding is performed at a vacuum level of P within the electron gun. However, when molecules such as metal vapor emitted from the weld metal enter the electron gun, the degree of vacuum within the electron gun deteriorates. A large amount of molecules invaded, and the degree of vacuum reached Pl! (immediately before the occurrence of discharge), that is, when the deterioration occurs from point 19 to point 20, a DC voltage is output from the comparison circuit described above,
The multivibrator will turn on immediately. During this time, the degree of vacuum moves from point 20 to point 21, but during this time 1. is a negligible time of several microseconds or less.

By turning on the multivibrator, the plate voltage of the vacuum tube is maintained so that the acceleration voltage changes from point 22 to point 23 (zero potential) in i2 seconds. The output of this multipipe rake is set so that the plate voltage starts to turn off after 13 seconds, and the plate voltage becomes zero after 14 seconds. Accordingly, the acceleration voltage of the electron gun returns from point 23 to point 24 to point 25, which is the initially set value V, and continuous electron beam welding becomes possible again.

At this time, the true value has been restored to point 26, which is the initial set value P1. The most important of the operations of each element above is P2 +
These are the values of t2 + '3 and t4. These specific setting values and their results are shown below.

t2 and t4 should be set from 500 microseconds to 1 millisecond for protective aspects of the device. This is because electronic parts, sometimes operating amplifiers, etc., are damaged. Experimentally, when the acceleration voltage was 30 KV and the beam current was 100 mA, the damage occurred when t2 was 100 microseconds or less. For this reason, it has been found that it is effective to set the time period between 500 microseconds and 1 millisecond depending on the beam current used.

The vacuum inside the electron gun is usually 101 to 10'' Torr, and experimentally the vacuum level is 10-3 to 1O-4T just before the discharge occurs.
Since it deteriorates to Orr, P2 is 1 to 5 x 10-'T
It was set to orr.

t3 is the most important value for maintaining welding continuity.

Welding speed 100mm/ through 'iL through plate thickness 100mw class
As a result of electron beam welding with mTA, t2 +ta-1-
Good results were obtained when t4 was 12 milliseconds or less, and when t4 exceeded this, void defects occurred despite rapid recovery. This situation is shown in Figure 3, Figure 9M4. Figure 3 shows plate thickness 1
The cross section of the welded part is shown in (a) and its A.
-A longitudinal section f shown in (b). Weld metal 29 showed good quality gold with no defects in any cross section. Further, the back bead 30 also shows a uniform and good shape. On the other hand, when the time was longer than 12 milliseconds, as shown in the longitudinal section of FIG. 4, depressions 31 on the bead surface and protrusions 32 on the back surface were formed, and void defects 33 were observed in some parts.

From the above, it is desirable that ts be 10 milliseconds or less.

This time t3 is related to recovery of the vacuum level within the electron gun, and it is an essential condition that the vacuum level is reliably recovered during this time.

[Effects of the Invention] According to the present invention, in electron beam welding, it is possible to prevent discharge occurring within an electron gun and to eliminate bath contact defects caused by discharge.

Furthermore, it is possible to eliminate damage to electronic components of the device due to surges caused by discharge.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a diagram showing the operation of the control device, and Fig. 3 (a) is a cross-sectional view showing a part of the welded part of the workpiece by this device. Figure 3(b) is the third
The AA cross section in FIG. 4A is an explanatory diagram of the occurrence of defects in the welded portion of the workpiece by a method other than the present invention. 1... Flat pressure power supply, 2... Electron gun, 3... Cathode power supply, 4... Bias power supply, 5... Electron beam, 6...
- Applied Nikko materials, 7... Electron gun vacuum chamber, 8... Electron gun vacuum exhaust pump, 9... Vacuum chamber exhaust pump, 10...
・Welding vacuum chamber, 11...Vacuum level detector, 12...Voltage setting device, 13...Comparison circuit, 14...Multiple breaker-115...Control grid power supply,
16... Control transistor, 17... Vacuum tube, 1
8...Screen speed 1 knot °Electric figure 1 figure 2 time

Claims (1)

[Claims] 1. In a high-voltage electric circuit consisting of a high-voltage power supply of an electron beam processing machine and an electron gun that is a load of the power supply, a change in the degree of vacuum inside the electron gun is detected, and according to the detection signal, a change in the degree of vacuum inside the electron gun is detected. When the degree of vacuum decreases to 1X10-'Torr or less, the high-voltage electric circuit is cut off for a selectable period of time;
An electron beam processing machine characterized in that a high-voltage electric circuit is equipped with a shutoff and control mechanism for stopping the operation of an electron gun.