JPS5856675B2 - Electron beam welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron beam welding method that prevents various defects occurring at the penetration tip based on the essential penetration mechanism of the electron beam.

The present invention directly detects temporal vertical vibrations in the focal position of the electron beam that occur due to ripples included in the high voltage power supply circuit of an electron beam welding machine. By continuously vibrating the electron beam at a high frequency and substantially weakening the power density of the electron beam, that is, the drilling effect, defects such as spikes that occur at the penetration tip during partial penetration welding can be prevented or complete welding can be achieved. This is intended to improve the back wave bead during welding.

Electron beam welding is a welding method that utilizes the perforation effect of an electron beam, particularly in the high power density part at the center.

Therefore, a weld bead with deep penetration and a very narrow fusion width can be obtained.

On the other hand, this perforation action tends to cause unique welding defects.

Typical of these defects are spikes, cold shuts, porosity, etc. that occur at the penetration tip during partial penetration welding, or irregularities in the underwave bead during full penetration welding.

Conventionally, the method used to prevent these defects was to widen the electron beam diameter and weaken the drilling force during partial penetration welding, but this method results in shallower penetration and wider fusion width, which is a characteristic of electron beam welding. are canceled out.

In addition, when performing full penetration welding, the electron beam power is increased more than necessary, and the welding is performed by penetrating the central high part of the power density distribution and utilizing the phenomenon of melting of the welded object due to the peripheral part where the piercing force is weak. However, this method requires a large amount of electric power and cannot be used particularly when the thickness of the workpiece increases and exceeds the electron beam power rating.

Therefore, there is currently no method to essentially prevent welding defects.
At present, the precision weldability that is an excellent feature of electron beam welding is not exhibited, and the use of this welding method is currently severely limited.

The present invention is based on research on the microscopic metal melting mechanism during electron beam welding, detects the metal melting state during electron beam welding, feeds this back, vibrates the electron beam for an appropriate time, and substantially By weakening the power density of the beam, the purpose is to prevent the occurrence of various welding defects and improve the bead shape, thereby improving the reliability during precision welding of electron beam welding.

In an electron beam welding machine, the high voltage power supply circuit contains ripple, regardless of the amount.

According to this ripple variation, the focal position of the electron beam oscillates vertically over time.

Defects such as spikes that occur at the penetration tip are likely to occur when the focus of the electron beam is close to the penetration tip.

At the same time, the occurrence of defects is closely related to the behavior of the molten metal at the penetration tip, and when these two conditions overlap, sharp spikes are generated due to the drilling action of the electron beam, and there are cold shuts and An accompanying porosity defect remains.

Furthermore, when the electron beam penetrates the object to be welded, the uranami bead tends to become rough due to the discontinuous and violent movement of the molten metal due to the perforation effect.

The present invention detects vertical movement of the electron beam focus by measuring ripples included in a high voltage power supply circuit, feeds back this detection signal, and detects when the electron beam focus approaches the penetration tip. , the electron beam is deflected and oscillated at a high frequency to substantially weaken the power density of the beam, thereby suppressing the extra puncturing force of the electron beam.

Next, details of the present invention will be specifically explained with reference to the drawings.

FIG. 1 shows an embodiment of an electron beam welding machine and a high voltage ripple detection method of the present invention.

FIG. 2 also shows an embodiment of the control circuit.

An electron beam 2 produced by a high voltage power supply 5 and an electron gun 1 is focused by a converging lens 3 and collides with a workpiece 9 to melt it.

This molten metal moves and solidifies as the object to be welded 9 moves (toward the left in the figure) and becomes a weld bead 9A.

The focal point of the electron beam 2 oscillates vertically over time due to ripples included in the high voltage power supply 5.

A high resistance 6 and a low resistance 7 are inserted in series on the negative side and positive (ground) side of the high 1 voltage circuit, the voltage 7B across the low resistance 7 is detected, and this is applied to a bandpass filter 10iIc to generate the main ripple component. Separate 10B.

Generally, when the high voltage decreases, that is, when the output 10B becomes a negative value, the focus of the electron beam moves far away, that is, toward the back side of the object to be welded.

When performing deep penetration welding, the focal point (average value) is generally set near the surface of the workpiece, so a negative value of waveform 10B means that the electron beam mainly melts the penetration tip.

The output 10B is applied to the comparator 11, and when the voltage becomes less than a predetermined negative value, the comparator 11 generates a constant voltage.

This output 11B is applied to the gate circuit of the oscillator 12, and when the comparator 11 is generating a voltage, the oscillator 12
oscillates and generates an alternating current voltage.

This output 12B is applied to the power amplifier 8, which excites the electron beam deflection lens 4 and deflects the electron beam. When the focus of the electron beam approaches the penetration tip, the electron beam oscillates. The power density of the electron beam is substantially reduced.

The present invention is not limited to the example illustrated above, and various modifications can be made without departing from the spirit of the present invention.

The bead shape of electron beam welding obtained by the method of the present invention is achieved by oscillating the electron beam intermittently and at a time when the electron beam mainly melts the penetration tip and does not directly affect the penetration depth. The penetration depth hardly decreases, and the bead width also does not increase significantly.

Furthermore, since the power density of the electron beam on the surface to be welded during vibration is weak, it can be expected to have an effect of improving surface beads such as decorative embellishments.

Therefore, reliable welding results can be obtained without impairing the deep penetration and precision weldability that are the characteristics of electron beam welding, and the range of application of electron beam welding can be expanded.

An example of the present invention is shown.

Table 1 shows an example of the results of partial penetration welding using an electron beam welding device having the control system shown in Figures 1 and 2.
Shown below.

Acceleration voltage 40KV, beam current 270mA.

Welding speed 76.2 cm/min *Y deflection (direction perpendicular to the welding line) Bead 1 in the table is the result of normal welding without beam deflection;
Bead 2 is the result of welding with continuous beam vibration of 10 KHz, and bead 3 is the result of welding with feedback control according to the present invention.

As shown in Table 1, in the welding results according to the present invention, the generation of pores can be greatly reduced while maintaining the penetration depth.

This means that the sharpness of each spike has become softer, and of course defects such as cold shut have not occurred.

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Next, an example of the results of full penetration welding of a thick plate is shown in FIG. 3 and Table 2.

30 lengths of 5M50 steel *Y deflection Figure 3 is a side view and cross-sectional view of a typical fully fused weld bead under the conditions shown in Table 2.

In Table 3, beads L 2 and 3 are the results obtained by normal welding, bead 4 is the result of welding with continuous beam vibration of 10 KHz, and bead 5 is the result of welding by the control method of the present invention.

When a 5M50 steel plate with a thickness of 30 mm is welded under the conditions of bead 1, it becomes an uranami bead in which molten metal periodically hardens in the form of droplets, as shown in Figure 3a.

Furthermore, as shown in bead 2, when the beam current is increased, the droplets become smaller (but the Uranami bead becomes larger (Fig. 3b)).

Furthermore, when the current is increased as in bead 3, the electron beam penetrates through the center where the power density is high and welds at the periphery where the punching force is weak, resulting in a good underwave bead as shown in FIG. 3C.

However, this requires considerably more power.

Continuously vibrating the electron beam produces good results as in bead 4, but requires extra power and also increases the front bead width considerably, as shown in FIG. 3C.

- If the method of the invention is adopted, good results can be obtained with the same minimum power as bead 1, and the bead width does not become too wide.

In this way, welding thick plates does not require more power than necessary, so it is particularly effective for welding machines that actually have an upper limit on their rating.

Further, even if the beam diameter is expanded to some extent under these conditions and a burn-through bead is formed, burn-through can be prevented by welding according to the method of the present invention due to the effect of the above-mentioned embellishment.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electron beam welding device and a method for detecting the electron beam focal position, FIG. 2 is a diagram showing the principle of the control method of the present invention, and FIG. 3 is a bead shape during full penetration welding. 1 is an electron gun, 2 is an electron beam, 3 is a converging lens, 4 is a deflection lens, 5 is a high voltage power supply, 6 is a high resistance, 7 is a low resistance,
8 is a power amplifier for the polarizing lens, 8A is the input terminal of the amplifier 8, 9 is the object to be welded, 9A is the welding bead, 7B is the voltage waveform at the resistor 7, 10 is the bandpass filter, and 10B is the filter 10's input terminal. Output, 11 is comparator, 11B is comparator output, 12 is oscillator, 12B is oscillator output, a
. bs c and C' are bead shapes.

Claims (1)

[Claims] 1. In electron beam welding, the main component of the ripple components included in the high voltage power supply circuit is detected, and the appropriate phase of the ripple component is determined when the focus of the electron beam approaches the tip of the welded object. An electron beam welding method characterized by vibrationally deflecting an electron beam in phase for a duration of half a cycle or less of the current component and within a range that does not change the overall melting form.