BACKGROUND ART An inert gas tungsten arc welding (TIG) suitable for welding base metals having thickness ranging from 0. 6mm to 3mm and an inert gas metal arc welding (MIG) for welding base metals having thickness of 3mm or higher have been widely used as an inert gas arc welding.

Such inert gas arc welding in which an electric arc is generated between the base metals and a tungsten rod or a metal wire electrode under an atmosphere of the inert gas which has been known to show no reaction with metals at even a high temperature is widely used in manufacturing aircrafts, rockets, automobiles, machineries related to a low temperature, and railway vehicles, etc.

As shown in Fig. 1, one of the prior art inert gas arc welding systems is provided with a power supply 1, a gas bottle 2 charged with inert gas such as argon gas, a gas pressure regulator 3, an electrode wire supply device 5 for supplying an electrode wire to a welding torch 7, a hose connected between the gas bottle 2 and the electrode wire supply device 5 for supplying the inert gas within the gas bottle 2 to the electrode wire supply device 5, a connection line 6 connected to the welding torch 7, and a current adjustment (not shown) electrically connected to the power supply 1 for allowing the welder to adjust the current level.

Meanwhile, as for the prior art inert gas tungsten arc welding system, it is further provided with a high frequency generating device or an air-cooled or a water- cooled cooling device (not shown).

In this inert gas arc welding system, the electric arc generated between the base metal and the electrode wire supplied through the welding torch 7 melts the electrode wire and, at the same time, the inert gas provided to the welding torch 7 isolate the welding zone and the electric arc from surrounding air.

As shown in Fig. 2, the welding torch 7 has a conductive member 7b inside a nozzle 7a and is supplied with the electrode wire through an inner diameter of the conductive member 7b. The inert gas 9a isolates the electric arc 9 from the surrounding air. At this time, a direct-current or an alternating current is applied to the conductive member 7a and the base metal 8 connected to the power supply 1 and beads are formed around the welding zone 8a.

Figs. 3 and 4 give views showing base metals welded using the prior art welding system, respectively. As shown, when a tomography is conducted, very coarse cracks 8b are found at several portions of a weld zone 8a. It can be seen that weld junctions 8c, 8d are not connected to each other well. The weld junctions 8c, 8d have a problem that their vertical sectional surfaces are not uniform. Accordingly, the base metal having such weld junctions 8c, 8d, experiences breaking at cracks 8b and the junction line 8c, 8d, which may occur due to an external shock or aging.

In addition to the breaking, the base metal welded by the prior art inert gas arc welding has different conditions of the surface thereof. For example, in a case that helium gas is used, the surface of weldment is not uniform and has a defected shape. Further, in a case of argon gas having a good cleansing function of removing an oxidation layer, it is easy for many bubbles to be generated.

Further, in the prior art arc welding system, a direction in which ions of the inert gas is supplied and a direction in which electrons of the electrode wire is supplied are different from each other depending upon the polarity of the applied current and this significantly affects the condition of the weldment.

DISCLOSURE OF THE INVENTION It is, therefore, a primary object of the invention to provide an apparatus for alternately supplying more than one kinds of inert gases to a welding torch in a periodic manner, thereby considerably increasing conditions of weldments, and achieving a uniform vertical sectional surface of a weld junction.

Another object of the invention is to provide a method for alternately supplying different inert gases according to kinds and size of a base metal, thereby increasing a quality of the results by welding.

The above and other objects of the invention are accomplished by providing an apparatus for an alternate supply of inert gases comprising : an electronic controller provided with a plurality of control circuits for alternately supplying an electric power from a power supply to a plurality of solenoids at frequency determined based on input values input via an input key pad in order to alternately supply the different kinds of inert gases to a main body ; and a gas mixer having a tubular member provided between the plurality of solenoids in an axial direction, and a gas opening/closing device inserted into the tubular member tube so as to move to and fro within the tubular member to optionally open and close a first gas inlet tube and a second gas inlet tube by using magnetic force caused by the solenoids.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of the instant invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which : Fig. 1 illustrates a schematic view of a prior art inert gas arc welding system ; Fig. 2 depicts a sectional view showing principles of the welding system shown in Fig. 1 ; Figs. 3 and 4 give views showing base metals welded using the prior art welding system shown in Fig. 1, respectively ; Fig. 5 presents a schematic view of a welding system therein incorporating an apparatus for an alternate supplying of inert gases in accordance with one embodiment of the present invention ; Fig. 6 represents a block diagram showing a configuration of the inventive apparatus for the alternate supplying of the inert gases ; Fig. 7 offers a circuitry of major parts of the inventive apparatus shown in Fig. 6 ; Fig. 8 discloses a partially cut-away sectional view of the major parts of the inventive apparatus shown in Fig. 6 ; Fig. 9 sets forth a sectional view of the inventive apparatus shown in Fig. 8, when taken along a line D-D ; Figs. 10 and 11 represent views showing base metals welded using the inventive apparatus shown in Fig. 6, respectively ; and Fig. 12 depicts a block diagram showing an inventive method for an alternate supply of inert gases using the inventive apparatus shown in Fig. 6.

MODES OF CARRYING OUT THE INVENTION Preferred embodiments of the inventive apparatus and a method for alternately supplying different inert gases to a welding torch will now be described with reference to the accompanying drawings.

The inventive apparatus to be explained hereinafter can be applied to special arc welding systems using normal inert gases or other systems operated under a periodically alternate supply of the inert gases.

Fig. 5 presents a schematic view of a welding system therein incorporating an apparatus for an alternate supply of inert gases in accordance with one embodiment of the present invention.

Fig. 6 represents a block diagram showing a configuration of the inventive apparatus for the alternate supplying of the inert gases. Fig. 7 offers a circuitry of major parts of the inventive apparatus shown in Fig. 6, Fig. 8 discloses a partially cut-away sectional view of the major parts of the inventive apparatus shown in Fig. 6, Fig. 9 sets forth a sectional view of the inventive apparatus shown in Fig. 8, when taken along a line D-D, Figs. 10 and 11 represent views showing base metals welded using the inventive apparatus shown in Fig. 6, respectively, and Fig. 12 depicts a block diagram showing an inventive method for an alternate supply of inert gases using the inventive apparatus shown in Fig. 6.

In Fig. 5, the inventive apparatus for an alternate supply of inert gases which is designed to be widely applied to various different arc welding systems is operated by a separate power source and has a volume of 170mm x 170mm x 60mm and a 1. 5kg weight which enable the apparatus to be mounted at any place which the welder wants.

A main body 100 of the inventive supply apparatus is connected to a plurality of gas bottles 20 and 30 for periodically alternately supplying different inert gases such as argon gas (Ar) or helium gas (He) to a welding torch in inert gas arc welding systems. Each of the gas bottles 20 and 30 is provided with a pressure regulator 23 or 33 which is well known in the art and communicates with an inlet hose 41 or 42 and a discharge hose 43 for supplying the gases to a welding torch 7. Further, the inert gas arc welding system is provided with a core wire supply device 5 for a supply of a wire electrode, a connection line 6 for connecting the welding torch 7 to the core wire supply device 5, and a power source 1 for supplying electricity required for a welding process.

As shown in Fig. 6, the main body 100 of the inventive apparatus for a periodically alternate supply of the different inert gases from the gas bottles 20 and 20 described above includes an electronic controller 110, a display panel 120, an input key pad 130, a power supply 140, and a gas mixer 150 for a mixing of the gases and a pressure regulation.

The power supply 140 receives an approximately 220V AC voltage and provides both an output voltage of an approximately 36V AC or DC voltage and an output voltage of an approximately 5V DC voltage. The 36V voltage is for operating a plurality of solenoids of the gas mixer 150 under control of the electronic controller 110, whereas the 5V voltage is for a circuit within the electronic controller 110, a LCD indicator of the display panel 120, and a circuit for the input key pad 130.

The input key pad 130 which is configured in a same manner as that of the conventional key input device is used to input information for selecting a control mode, e. g., a kind and thickness of the base metal, a welding process or the use of cutting.

The display panel 120 allows the welder to confirm the control mode selected by the electronic controller 110 based on the input date and the conventional"LCD" or"FND Display"may be used for the display panel 120.

The electronic controller 110 is constituted with a plurality of electronic devices for performing control functions (to be described later) serves to perform alternately applying and cutting-off the 36V voltage to/from the solenoids of the gas mixer 150 at frequency ranging from about 2Hz to 20Hz. Under control of the electronic controller 110, the gas mixer 150 properly mixes the gas introduced through a first gas inlet tube 101 with the gas introduced through a second gas inlet tube 102 and allows the mixed gas having relatively high pressure (caused by pulsation pressure) kept in a constant level to be supplied to the welding torch of the inert gas arc welding system via a mixed gas exhaust tube 103. Such electronic controller 110 selects the control mode (e. g., an operative frequency of the solenoid is differently given according to the selected control mode) by receiving key entries through the input key pad 130, and displays the selected control mode.

As shown in Fig. 7, the electronic controller 110 which controls the input key pad 130, the display panel 120, the gas mixer 150 by using power from the power supply 140 is provided with a key input connector 115a, a display connector 116a, a key input port 115b, a display output port 116b, a microprocessor, a program memory 112, a control output port 114 for the gas mixer 150, a first gas opening/closing output port 118, a second gas opening/closing output port 119, a first transistor 117a, and a second transistor 117b.

The 5V voltage from the power supply 140 is supplied to a connection line between the key input connector 115a and the key input port 115b in a parallel connection therewith, via a first input line 141, whereas the 36V voltage is connected to the first and the second transistors 117a, 117b via a second input line 142. The key input port 115b and the display output port 116b are connected to a bus for a signal processing of the microprocessor 111 in a parallel relationship therewith.

The data memory 113 keeps therein reference data, e. g., the kind and the thickness of material of which the base metal is made, the use of welding, the use of cutting, in a form of, e. g., data sheet, on which determining or selecting the operative frequency (about 2Hz to 20Hz) of the solenoid is based.

The microprocessor 111 is operated based on a control logic stored in the program memory 112 and generates a first gas opening/closing control signal 114a and a second gas opening/closing control signal 114b alternately.

Such control signals 114a and 114b are amplified by the first transistor 117a and the second transistor 117b, respectively, and are sent to the first gas opening/closing output port 118 and the second gas opening/closing output port 119, respectively, via a rectifier circuit. Accordingly, the microprocessor 111 of the electronic controller 110 can allow a first solenoid 151 and a second solenoid 152 provided in the gas mixer 150 to be in opposite states of ON or OFF to each other, by using such the first gas opening/closing output port 118 and the second gas opening/closing output port 19.

As shown in Figs. 8 and 9, the gas mixer 150 is provided with the first solenoid 151, the second solenoid 152, and a T-shaped tube 153 inserted between the solenoids.

The first solenoid 151 and the second solenoid 152 generate magnetic forces which are exerted in an opposite direction to each other and serve to move a gas opening/closing device 154 back and forth within the T- shaped tube 153, when electricity is alternately applied to the solenoids 151 and 152 via the first and the second gas opening/closing output ports 118 and 119.

The T-shaped tube 153 which communicates with the first gas inlet tube 101, the second gas inlet tube 102 and the mixed gas discharge tube 103 is provided with therein a centered main chamber 158 and gas chambers 159 positioned on both lateral portions of the main chamber 158, respectively. Partitions each of which has a through hole through which the gas opening/closing device 154 is moved divide the T-shaped tube into such gas chambers 159 and the main chamber 158. Heads 155 of the gas opening/closing device 154 are inserted into the. partitions, respectively.

The gas opening/closing device 154 is constituted with a center rod and the heads 155 integrally formed with both ends of the center rod. Further, the heads 155 have guide bars 157 formed on outward ends of the heads 155, respectively, which can be inserted into the first gas inlet tube 101 and the second gas inlet tube 102, respectively, so that the gas opening/closing device 154 can alternately closing inner diameters of the first gas inlet tube 101 and the second gas inlet tube 102, moving back and forth within the T-shaped tube.

Further, each of the heads 155 of the gas opening/closing device 154 has a conic shape at its outward end, which is convergent in a direction toward the first gas inlet tube 101 or the second gas inlet tube 102, and a plurality of slits 156 formed on its peripheral surface. The slits 156 which can be formed in a linear form or a helical form serve to change vortex flow of the gas into linear flow, which may easily occur in opening/closing portions of the first and the second gas inlet tubes 101 and 102 and the gas chambers 159.

Accordingly, in the main chamber 158 of the T-shaped tube 153, irregular flow of the gas caused by an occurrence of the pulsation pressure is minimized during passing through the slits 156 of the heads 155. Further, the mixed gas having relatively high pressure due to the occurrence of the pulsation pressure is supplied to the welding torch of the inert gas arc welding system via the mixed gas discharge tube 103. Such mixed gas having as its components different kinds of inert gases, e. g., Argon gas (Ar) or Helium gas (He) causes a good condition of the result by the welding process since different componential inert gases each of which has its own welding characteristic are alternately emitted from a nozzle of the welding torch and applied to a weld zone, by the inventive apparatus.

That is, the applicant has found that, in the base metal welded by the inert gas arc welding system equipped with the inventive apparatus for the alternate supply of the different inert gases, when a tomography is conducted, only fine cracks 81 are found on rare occasions at the weld zone 80 having relatively reduced bubbles. It has been also found that a weld junction 82 connects the base metals in a form of substantial straight lines. Further, a vertical sectional surface of the weld junction 82 which has been found uniform can minimize breaking which may easily occur due to an external shock or aging.

Table 1 shown below represents the comparison between the inert gas arc welding system equipped with the inventive apparatus described above and the conventional welding system.

Table 1 Automatic Prior art apparatus Inventive apparatus welding . Aluminum Steel Aluminum Steel plate plate plate plate Thickness (mm) Welding current 400 160-250 280 110-170 (A) Gas flow rate 12 9 8. 4 4 (L/min) Percentage of 0. 3 or 0. 1 or 0. 09 or 0. 02 or impurity higher higher lower lower content zu As shown in Table 1, the alternate supply of argon gas and helium gas has a reduced power consumption by 30% than that in the prior art arc welding using same kinds of gases. The inventive apparatus has not only a better weld result but also a welding accuracy increased by 15% to 20% than those in the prior art. Further, the weldment obtained by inventive apparatus has impurity content reduced by three times to five times than that by the prior art. In addition, the inventive apparatus has a more reduced consumption of the inert gases which are known as expensive by 30% to 50% than that of the prior art apparatus.

Hereunder, an inventive method for alternately supplying the inert gases using the inventive apparatus for the alternate supply of the inert gases described above will be described.

As shown in Fig. 12, the main body of the inventive alternate gas-supply apparatus is connected to the inlet hoses of the gas bottles which are charged with argon gas and helium gas, respectively (S10). Then, the main body is switched on and the inert gas arc welding system is also switched on at the same time. At the moment, electricity is applied to the electronic controller and the display panel, thereby bringing the gas mixer into a stand-by state for its operation, which will apply a mechanical stimulation and pressure to the base metal depending upon the kind of the base metal.

At this time, the welder or the operator inputs information on, e. g., the kinds and the size of the base metal to be welded by using the input key pad (S20) and confirms the control mode determined by the input information through the display panel (S30).

Next, in the inventive apparatus for the alternate supply of the inert gases, the power is alternately applied to the first solenoid and the second solenoid, i. e., while one is powered on, the other is powered off or vice versa, at the frequency corresponding to the determined control mode to operate the gas opening/closing device. (S40) That is, when the electronic controller outputs the first gas opening/closing control signal, the 36V voltage is applied to the first solenoid (while the line for the second gas opening/closing control signal is shorted out) to allow the first solenoid to attract the gas opening/closing device by the magnetic force caused by the applied power. For this reason, the first gas inlet tube is closed, while the second gas inlet tube being opened to cause the argon gas to be introduced into the main chamber of the T-shaped tube. After time interval determined by the operative frequency for the solenoid, the electronic controller outputs the second gas opening/closing control signal, the 36V voltage is instantly applied to the second solenoid (while the. line for the first gas opening/closing control signal is shorted out) to allow the second solenoid to attract the gas opening/closing device by the magnetic force caused by the applied power. For this reason, the second gas inlet tube is closed, while the first gas inlet tube being opened to cause the helium gas to be introduced into the main chamber of the T-shaped tube. The argon gas and the helium gas sequentially and alternately introduced into the main chamber of the T-shaped tube are properly mixed with each other and discharged through the mixed gas discharge tube of the gas mixer under a constant level of pressure.

The different kinds of inert gases introduced into the gas mixer by the operation of the gas opening/closing device in the above described manner are alternately supplied to the nozzle of the welding torch.

(S50) After that, the welder can perform the welding process by positioning the welding torch near the base metal (S50), confirming the condition of the welding (S60).

The method for the alternate supply of the inert gases performed in this manner may be applied to the development of an aviation and space instrument and machines made of aluminum alloy having a higher strength which are normally accompanied by complicated technical problems and may be used in manufacturing conventional machineries in combination with accelerated welding technologies.

As described above, the inventive apparatus and the method for the alternate supply of the inert gases has a reduced power consumption by 30% than that in the prior art arc welding system, a better weld result, a welding accuracy increased by 15% to 20% than that in the prior art, and a more reduced consumption of the expensive inert gases by 30% to 50% than that of the prior art apparatus.

Further, since the inventive apparatus for the alternate supply of the inert gases is designed to use a separate power source, it can be applied to various different types of inert gas arc welding systems as a separate equipment therefor.

Further, the inventive apparatus for the alternate supply of the inert gases is designed to permit both advantages of the argon gas having an outstanding cleansing function and the helium gas causing an even weld surface, to be exerted by alternately supplying both gases, thereby resulting in a remarkably evened weld surface.

Furthermore, the inventive apparatus for the alternate supply of the inert gases can minimize the occurrence of the crack and the breaking of the weld and result in the uniform vertical sectional surface of the weld junction.

Moreover, the inventive apparatus for the alternate supply of the inert gases provides a convenient user interface by employing the display panel and the input key pad.

In addition, the inventive apparatus for the alternate supply of the inert gases may be applied to all of the welding systems as far as it is intended that they alternately supply different inert gases.

If the inventive apparatus for the alternate supply of the inert gases has an arc sensor equipped in the welding torch, the input data can be automatically determined based on the measurements by the arc sensor.

The inventive apparatus for the alternate supply of the inert gases may be applied to an automated inert gas arc welding system.

The inventive apparatus for the alternate supply of the inert gases can result in stable arc maintenance by uniformly supplying the inert gases.

Finally, the inventive apparatus for the alternate supply of the inert gases can increase the quality of the weld and, hence, productivities.

Although the inventive apparatus and method for an alternate supply of inert gases has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.