The present invention relates to an apparatus for conveying a wire electrode to a workpiece in wire electric discharge machining, i.e., a wire electrode supplying apparatus for a wire electric discharge machine.
FIG. 5 illustrates an example of a conventional wire electrode supplying apparatus disclosed in, for instance, Japanese Patent Publication No. 10130/1981 or 47135/1987. In this example, a wire electrode, while being constrained by a jet of working fluid such as water, is conveyed from a wire electrode feeding-side wire guide section to a wire electrode receiving-side wire guide section that are arranged with a workpiece placed therebetween. In the drawing, reference numeral 1 denotes a workpiece; 2, a machining start hole formed in the workpiece 1; 3, a wire electrode which discharges electricity between the same and the workpiece 1; 4, a wire electrode feeding-side wire guide section, and 5, a support member. An upper wire guide 6 has at its head a dies guide 7 having a smaller clearance with respect to the wire electrode 3. Numeral 8 denotes guide dies, and numeral 9 denotes a power supplying element which is fitted in the upper wire guide 6 formed into a cylindrical configuration. The wire electrode 3 is supported by the guide dies 8 and the dies guide 7 on the upper and lower sides of the power supplying element 9, respectively, so as to be held along a longitudinal center line of the wire electrode feeding-side wire guide section 4. Accordingly, the wire electrode 3 is squeezed by and is brought into contact with notched surfaces of the power supplying element 9. Numeral 10 denotes a jet nozzle. A small-diameter opening is provided in the center of a bottom plate of the jet nozzle 10 coaxially with the wire electrode 3, and the jet nozzle 10 is arranged in such a manner as to be vertically slidable inside the support member 5. Numeral 11 denotes a compression spring which is disposed in such a manner as to surround the jet nozzle 10 inside the support member 5. Normally, the compression spring 11 keeps the jet nozzle 10 pressed to its upper limit, in which case an inner bottom surface of the jet nozzle 10 and a lower end surface of the upper wire guide 6 are spaced apart from each other with a small clearance. Numeral 12 denotes a working fluid injection nozzle, and numerals 13, 14, 15 denote working fluid introducing passages. When the working fluid flows in through the working fluid introducing passage 13, the working fluid is filled in a chamber partitioned by an inner wall of the support member 5 and an inner wall of the jet nozzle 10, and downward pressure is applied to an upper surface of a flange of the jet nozzle 10 and an inner bottom surface thereof. Furthermore, when the jet nozzle 10 is thereby lowered against the compression spring 1, the working fluid is jetted through the opening at the bottom plate of the jet nozzle 10. The wire electrode 3 is thus constrained and conveyed to the workpiece 1 by this jet. When the working fluid flows in through the working fluid introducing passage 14, the working fluid is filled in a chamber partitioned by an inner wall of the support member 5 and an outer wall of the jet nozzle 10. The working fluid is then filled in the interior of the working fluid injection nozzle 12 through the working fluid introducing passage 15, and is injected toward the workpiece 1 through the opening of the working fluid injection nozzle 12 so as to effect wire electric discharge machining. Numeral 20 denotes a wire electrode receiving-side wire guide section, and 21 denotes a support member. Numeral 22 denotes a lower wire guide which has, at its head, dies having a small clearance with respect to the wire electrode 3. Numeral 23 denotes power feeding dies; 24, guide dies; and 25, a working fluid injection nozzle. Numeral 30 denotes a mounting plate for supporting the apparatus from its rear; 31, guide dies; and 32, a capstan roller. A wire feed motor 33 rotatively drives a capstan roller 32, and in this example a DC motor is used as the feed motor 33. A pinch roller 34 is openably fixed to the mounting plate 30 via a support arm 35 and a mounting shaft 36. The pinch roller 34 is constantly pressed against the capstan roller 32 by means of a compression spring 37 interposed between the support arm 35 and the mounting plate 30. The compression spring 37 is accommodated in and fixed to an accommodating block 38 provided on a front surface of the mounting plate 30. Numerals 40, 41 denote guide pipes; numeral 42 denotes a guide pipe holder; and 43, a cylinder block. The guide pipe 40 is secured to the cylinder block 43 via the guide pipe holder 42. An upper portion of the guide pipe 41 is formed into a flange, the guide pipe 41 being disposed in such a manner as to be vertically slidable inside the cylinder block 43 by means of this flange. The guide pipe 40 is coaxially inserted in the guide pipe 41 such the guide pipes 40, 41 overlap with each other over a substantial length in a longitudinal direction with a fixed clearance between an outer peripheral surface of the guide pipe 40 and an inner peripheral surface of the guide pipe 41. Air introducing passages 44, 45 are provided in the cylinder block 43, and the arrangement is such that air used for the lifting and lowering of the guide pipe is supplied by an unillustrated air supplying device to the interior of the cylinder block 43.
By virtue of the above-described arrangement, when the wire electrode 3 is automatically supplied, air is made to flow into the cylinder block 43 through the air introducing passage 44 so as to apply pressure to the upper surface of the flange of the guide pipe 41. When the guide pipe 41 is lowered to its lower limit by this pressure, the space between a lower end of the guide pipe 40 and an upper surface of the guide dies 8 is shut off from the outside, so that an enclosed space is formed along the wire electrode 3 inside the guide pipe 41. Simultaneously, if the working fluid is allowed to flow into the support member 5 from an unillustrated working fluid supplying device via the working fluid introducing passage 13, the jet nozzle 10 receives the hydraulic pressure of the working fluid on its flange surface, with the result that the jet nozzle 10 is pressed down. In consequence, a sufficient gap is produced between the opening at the bottom plate of the jet nozzle and the upper wire guide 6. Consequently, the working fluid jetted through the opening at the bottom plate of the jet nozzle 10 advances straightforward to a far distance without being scattered. The wire electrode 3 is constrained and conveyed to the wire electrode receiving-side wire guide section 20 by the working fluid thus jetted. At this time, the wire electrode 3 has already been cut by an unillustrated known wire electrode cutting mechanism disclosed in, for instance, Japanese Patent Laid-Open No. 80528/1985, and its tip is located in the guide pipe 41 above the guide dies 8. After the guide pipe 41 is lowered, the feed motor 33 is started to rotate the capstan roller 32 and the pinch roller 34, the wire electrode 3 is then fed to the wire electrode feeding-side wire guide section 4 where it passes consecutively through the guide dies 8, the upper wire guide 6, and the jet nozzle 10. The wire electrode 3 while being constrained by the jet continues to be fed and passes consecutively through the machining start hole 2, the lower wire guide 22, the power feed dies 23, and the guide dies 24, and is conveyed by an unillustrated wire collecting mechanism using a fluid, a belt, a roller, or the like. Then, the wire electrode 3 is taken up below the guide dies 24, or accommodated in a specific container. As a result of the above-described operation, the wire electric discharge machine is set in a state in which it is capable of effecting wire electric discharge machining.
However, the following problems have hitherto been encountered with the conventional wire electrode supplying apparatuses for wire electric discharge machines.
First, as shown in FIG. 6, in a state in which the jet nozzle 10 has been lowered after the influx of the working fluid through the working fluid introducing passage 44, the distance between the dies guide 7 and the opening of the jet nozzle 10 is large. Moreover, the wire electrode 3 is inherently liable to bend, and the tip of the wire electrode 3 has a certain degree of freedom to move. Therefore, after passing through the dies guide 7 with the jet nozzle 10 lowered, when the tip of the wire electrode 3 is further fed toward the opening of the jet nozzle 10, the tip of the wire electrode 3 can deviate from a vertical line and become unable to pass through the opening by being caught on the inner bottom surface of the jet nozzle 10. In this situation, as the feed motor 33 further rotates, the wire electrode 3 is forced out through a gap formed between the capstan roller 32 and the pinch roller 34 on the one hand, and the guide pipe 40 on the other. This results in the serious drawback of rendering the proper feeding of the wire electrode 3 impossible.
Secondly, as shown in FIG. 7, if the wire electrode 3 is fed by a greater length from the working fluid injection nozzle 12 without being properly constrained by the jet, the wire electrode 3 is unable to pass through the machining start hole 2 and deviates substantially therefrom for the same reason as that mentioned above. Even if the working fluid is subsequently jetted, it is impossible for the tip of the wire electrode 3 to be inserted into the machining start hole 2.
Thirdly, at the time when the wire electrode 3 passes through the upper wire guide 6 or the lower wire guide 22, the tip of the wire electrode 3 receives load when the tip passes through the wire guide with a small clearance in the advancing direction. In particular, in order to improve the accuracy of wire electric discharge machining, it is desirable to make the clearance of the dies guide 7 as small as possible, but the smaller the clearance, the greater the load entailed in the passage of the wire electrode 3. In addition, the greater the speed of feeding the wire electrode 3, the greater the load applied to the wire electrode 3. As the load applied to the wire electrode 3 with respect to the direction of its feed increases, the wire electrode 3 is pressed against the inner peripheral surfaces of the pipes 40, 41 and the upper wire guide 6. With a further increase in the load, the wire electrode 3 is even forced out through the gap between the pinch roller 34 and the capstan roller 32 on the one hand, and the guide pipe 40 on the other, with the result that the subsequent proper feeding of the wire electrode 3 becomes impossible. Accordingly, in the case of the conventional apparatus, a sequence is adapted in which until the tip of the wire electrode 3 reaches the unillustrated wire collecting mechanism from a wire cutting position, the speed of feeding the wire electrode 3 is set to a low speed, e.g., 5 mm/sec., and after the tip of the wire electrode 3 reaches the wire collecting mechanism and becomes conveyable by the wire collecting mechanism, the speed of feeding the wire electrode 3 is changed to a high speed, e.g., 50 mm/sec. The arrival of the wire electrode 3 at the wire collecting mechanism is detected by a means (not illustrated) for detecting the passage of the wire electrode 3, which includes a timer or a sensor provided on, for instance, the wire recovering mechanism, a detection signal being sent by the detecting means to a numerical controller for a determination of the arrival. Consequently, as for the duration of low-speed operation, if the distance between the two wire guides is, for example, 250 mm, it takes as much as 50 seconds for the wire electrode 3 to pass between these wire guides alone. Hence, the duration of passage of the wire electrode 3 becomes substantially long, thereby rendering the operation inefficient.