A wire-cut electroerosion apparatus

Abstract: In a wire-cut EDM apparatus for cutting a workpiece (2) submerged in a processing tank (3) filled with a machining fluid (15), an opening (24) is made in the side wall of the tank through which an arm unit passes. A slide plate (14) also has an opening for passage of the arm unit and also prevents leakage from the space between the opening (24) and the arm unit. A low frictional member may be placed between the arm unit and the slide plate for axially sealing the arm unit. Frictional resistance from movement of the lower arm unit is reduced and machining accuracy improved.

Description: Field of the Invention The present invention relates generally to a wire-cut electroerosion apparatus. More specifically, the present invention relates to a wire-cut electrical discharge machining ("EDM") apparatus for performing submerged machining. Background of Invention In wire-cut EDM, electrical discharge machining may be performed with the workpiece submerged in a processing tank that is filled with a machining fluid. A wire electrode runs between an upper guide head and a lower guide head with the two guide heads mounted on an upper arm unit and a lower arm unit, respectively. In such machines, an opening is made in the processing tank for inserting the lower arm unit with the lower guide head into the tank. Positioning of the workpiece relative to the wire electrode is accomplished by moving the processing tank in two orthogonal directions in a plane parallel to its base. One direction is parallel to the axis of the lower arm unit and the other direction is parallel to the tank wall having the opening. In this type of wire-cut EDM apparatus, the space between the opening and the lower arm unit must be sealed to prevent leakage of the machining fluid from the processing tank. Various configurations for sealing proposed in the past are illustrated in U.S. Patent No. 4,565,915 to Girardin, U.S. Patent No. 4,918,279 to Babel et al., U.S. Patent No. 4,647,747 to Goto, U.S. Patent No. 4,808,786 to Shinkai, et al., and U.S. Patent No. 4,992,640 to Tanaka, et al. As shown in Figure 11, some of these conventional arrangements use a sealing plate 4 provided between the opening 3 and the lower arm unit 1. Sealing members are then placed between the sealing plate 4 and the wall of the processing tank 2 and also between the wall and the lower arm unit 1. The positioning of sealing members between the sealing plate 4 and the lower arm unit 1, however, creates a problem in terms of frictional resistance, also called the sealing resistance. Among other problems, the sealing resistance may cause the lower arm unit to deform thereby degrading machining accuracy. From EP-A-0 133 160 it is known to have the lower arm tightly pass through a plate which is linearily moveable in parallel to the wall of the processing tank. This plate is slidingly guided in an also fluid-tight manner with respect to the wall of the tank. This latter sealing necessitates a significant force to overcome the friction. The friction forces created by this sealing provisions tend to bend the lower arm. Furtheron, the seal between lower arm and plate has to withstand the forces needed to move the plate with respect to the tank without leaking. According to EP-A-0 304 882, the moveable plate is separately connected to a part immovable with respect to the lower arm. This connection may be a sleeve surrounding the lower arm or a rigid connection to the support of the electroerosion cutting apparatus. Hence, these additional means for the suppression of any force exerted by the moveable plate on the lower arm render the device at least more complicate and consequently move expensive. Summary of the Invention An object of the present invention is to provide an electroerosion apparatus which reduces the sealing resistance to the arm unit and also improves the machining accuracy. Another object of the invention is to provide a tank sealing system for an electroerosion apparatus which seals the arm unit when power is not supplied to the sealing system. A further object of the present invention is to seal the arm unit without introducing unwanted bubbles into the machining area of the processing tank. Another object of the present invention is to seal the arm unit without agitating the machining fluid at the machining location. A further object of the present invention is to provide an effective means for collecting machining fluid escaping from the tank and returning it to the processing tank. Another object of the present invention is to provide an electroerosion apparatus in which a space between the arm unit and an adjacent member is maintained precisely. Another object of the present invention is to provide an electroerosion apparatus in which the sliding resistance of the axial seal for the arm unit is minimized. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. The present invention generally relates to a wire-cut electrical discharge machining apparatus ("EDM") in which an opening is formed in the wall of the processing tank for passage of a lower arm unit. The processing tank is filled with a machining fluid for performing submerged machining operations on the workpiece. In accordance with a preferred embodiment of the present invention, and in accordance with its objects and purposes, the wire-cut electrical discharge machining apparatus may also comprise a processing tank having an opening for the passage of a lower arm unit. A covering member, placed around the arm unit, covers the opening by sliding side-to-side with the arm unit. Machining fluid flows in the space between the covering member and the arm unit. A sub-tank may be provided for catching and recirculating the fluid flowing between the arm unit and the covering member. Also, the covering member may have a recessed portion connected to an aspirator for drawing in machining fluid. The sealing resistance between the slide plate and arm unit is reduced and machining fluid flow controlled. In accordance with a further aspect of the present invention, and in accordance with its objects and purposes, a wire-cut EDM apparatus is provided comprising a processing tank having an opening for passage of a lower arm unit. A covering member is positioned around the arm unit and covers the opening by sliding side-to-side with the arm unit. A contact member may be connected to the covering member for contacting the arm unit. Advantageously, the contact member has a low coefficient of friction and supplies a low frictional axial seal with respect to the arm unit. Brief Description of the Drawings The accompanying drawings, which are incorporated in and form a part of the specification, illustrate various embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: FIGURE 1 is a cross-sectional view of one embodiment of the wire-cut EDM apparatus of the present invention; FIGURE 2 is a cross-sectional view of a first embodiment of the invention; FIGURE 3 is a cross-sectional side view of the first embodiment of the invention; FIGURE 4 is a cross-sectional view of a second embodiment of the invention; FIGURE 5 is a cross-sectional view of a third embodiment of the invention; FIGURE 6 is a side view of the third embodiment of the invention; FIGURE 7 is a cross-sectional view of a fourth embodiment of the invention showing the use of "mudguard" packing; FIGURE 8 is a side view of the fourth embodiment of the invention; FIGURE 9 is an enlarged view showing the positioning plate in the fourth embodiment of the invention; FIGURE 10 is an enlarged cross-sectional view of the sealing arrangement in the fourth embodiment of the invention; FIGURE 11 is a cross-sectional view of a conventional sealing apparatus for an EDM machine. Detailed Description of the Preferred Embodiments Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Figure 1 illustrates a cross-sectional view of one embodiment of the wire-cut EDM apparatus. In this embodiment, a workpiece 2 is submerged into a processing tank 3 filled with a machining fluid 15. A wire electrode 1 is guided from an upper guide unit 8 (schematically shown), to a lower guide unit 9 (schematically shown), to a pulley 11, and then through the inside of a pipe 6. The processing tank 3 is supported by a table 4A and a saddle 4B that sits on a bed 7. The table 4A moves along an X-axis, which is in a direction parallel to the wall of the processing tank 3 having an opening 24, and the saddle 4B moves along a Y-axis, which is in a direction parallel to the axis of the pipe 6. This enables two-dimensional positioning of the processing tank 3 with respect to the workpiece 2. The machining fluid 15 may be drained through the drain outlet 23 by the release of a drain valve 27. Each of the guide units 8 and 9 has an associated fluid flushing nozzle 10 (illustrated schematically). The upper guide unit 8 is supported by an upper arm (not illustrated) and the lower guide unit is supported by a lower arm unit 5. The lower arm unit 5 is positioned inside the cylindrical pipe 6 and both pass into the processing tank through the opening 24 in the wall of the tank 3. Hereinafter, the term "arm unit" will be used to refer to both the lower arm unit 5 and the pipe 6. A slide plate 14 is positioned between the opening 24 of the processing tank 3 and the arm unit. Slide plate 14 may advantageously be generally rectangular in shape, having an opening at or about its center for passage of the arm unit. The slide plate 14 covers the opening 24 and serves as a sealing means. An outside edge of the slide plate 14 is attached to a plate holding guide 12 by a seal member 13. The plate holding guide 12 is connected to the inside wall of the processing tank 3. A first embodiment of the invention, shown in Figures 2 and 3, includes a processing tank 3 having an opening 24 in one of its walls. In this embodiment a non-loading, axial sliding seal is used. The opening 24 is closed by a covering member 114. The covering member 114 comprises a plate-like member having a through hole for passage of a lower arm unit 112. The lower arm unit 112 is supported by the column C and extends into the processing tank 3. The covering member 114 fits inside a guide frame 141, which is secured to the wall of the processing tank 3, for example by screws. Two seals, 143A and 143B, seal the covering member 114 with respect to the guide frame 141 while allowing the covering member 141 to move in the X axis direction as indicated in Figure 2. An annular member 116A is secured to one end of the covering member 114. The member 116A creates an annular space 118 with respect to the arm unit 112. Preferably, the space 118 is on the order of about 0.05 to 0.1 mm. A sub-tank 119 is positioned beneath the processing tank 3 and covering member 114. The sub-tank 119 collects machining fluid passing through the annular space 118. While its capacity will vary depending on the size of the tank 3 and other factors, for a typical wire-cut EDM installation the capacity of the sub-tank 119 is preferably on the order of about 3 liters. A shield plate 120 is positioned behind the covering member 114 and moves along the X axis with the arm unit 112. The shield plate 120 moves along a guide member 121, which is fastened to a guide rail 119' positioned at the bottom of the sub-tank 119. The shield plate 120 has an opening through which the arm unit 112 passes. A seal 122 is used to prevent the machining fluid from flowing to the column side of the shield plate 120. The seal 122 preferably only applies a very slight contact pressure against the arm unit 112 to avoid applying a load to the arm unit 112 during motion of the processing tank 3. As best seen in Figure 3, the guide frame 141 is preferably rectangularly shaped and includes sides 141A, 141B, 141C, and 141D which surround the opening 24 in the processing tank 3. The annular member 116A, discussed above, is concentrically disposed with respect to the lower arm unit 112, thereby forming the annular space 118. The operation of the embodiment of Figures 2 and 3 is as follows. Because the annular member 116A does not seal against the arm unit 112, when the tank 3 is full, machining fluid will flow through the space 118. The shield plate 120 directs the machining fluid into the sub-tank 119. From the sub-tank 119, the machining fluid is recycled into the processing tank 3 through a suitable hose or duct. This sealing device 122 provides a low-frictional resistance to the arm unit 112 when it is moved axially. As a result, the arm unit 112 may be smoothly positioned and working accuracy improved. Figure 4 illustrates a second embodiment of the invention and represents a variation on the embodiment of Figures 2 and 3. In this embodiment, an annular member 116B is secured to the covering member 114. The annular member 116B is configured to form a space 118A between it and the arm unit 112. An elbow unit 124 positioned at a drain opening at the lower end of the annular member 116B at a recessed portion 123 thereof feeds into pipe 125. The elbow unit 124 and pipe 125 form part of an aspirator unit. Machining fluid flowing through the space 118 into the space 118A is aspirated through the elbow unit 124 and pipe 125. A sub-tank 119, described above with respect to Figures 12 and 13, may also be provided in case the flow through the spaces 118 and 118A is greater than the intake capacity of the aspirator. Machining fluid aspirated through the pipe 112 or drained from the sub-tank 119 may then be returned to the processing tank 3 or other fluid reservoir. Since the machining fluid is allowed to freely flow through the spaces 118 and 118A, axial sliding resistance on the arm 112 is reduced and the machining accuracy improved. Figures 5 and 6 illustrate a third embodiment of the invention which represents a variation of the embodiment of Figures 2 and 3. In this embodiment, the covering member 114 includes a recessed portion 126 in which an elastic tube 127 is positioned. A slide sheet 129 is fastened to the covering member 114, preferably by a holding plate 130. As will be understood by one of skill in the art, the slide sheet 129 should have a low coefficient of friction and may, for example, comprise a layer of polytetrafluoroethylene on the order of 0.5 mm in thickness. The pressure inside the elastic tube 127 may be controlled by use of a pipe 128 to ensure minimal sliding resistance between the arm 112 and slide sheet 129 consistent with adequate sealing. A supply of compressed air or pressurized fluid may be supplied to the elastic tube 127. Figures 7 through 10 illustrate a fourth embodiment of the invention which represents yet another variation of the embodiment of Figures 2 and 3. In this embodiment, a packing 131, preferably formed of a low coefficient of friction material such as polytetraflouroethylene-soaked fibers in the form of a piece of cloth or felt, is contained in a recess in a cap 135. The cap 135 is preferably positioned in a notch provided in the covering member 114. The cap 135 is also preferably of a low friction material such as polytetrafluoroethylene. An elastic member 136 positioned between the covering member 114 and the cap 135, preferably around the entire perimeter of the cap, to bias the cap 135 and packing 131 against the arm unit 112. The member 136 should be selected to exert minimal bias to seal while minimizing sliding resistance on the arm unit. A mudguard packing or dam 132, is positioned on the arm unit 112 between the processing tank 3 and the packing 131. The mud guard packing 132 inhibits any particles deposited on the arm unit 112 from reaching the packing 131. Another dam, in the form of drain packing 133 may be advantageously positioned on the arm unit 112 behind the packing 131 to prevent any machining fluid passing the packing 131 from contacting the column C. As shown in Figure 8, a plurality of binding members 150 may be secured to the covering member 114 for supporting the first dam, i.e., mudguard packing 132 and the second dam, i.e., drain packing 133. Positioning plates 134 may also be secured to the covering member 114. As best seen in Figure 9, the positioning plates 134 maintain the spacing between the covering member 114 and the arm unit 112. The positioning plates 134 may also be used in the first through third embodiments described above. This embodiment allows the arm unit 112 to move from side to side and also axially while maintaining a axial seal which has a low coefficient of friction. The foregoing description of preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. For example, in a power cut off situation, a shield plate may be provided in the rear of the slide plate 14 so that any fluid that leaves the opening 24 may be led to a supplemental tank as quickly as possible Various modifications may also be made to the power cut off sealing embodiments. Also, the invention is not intended to be limited to the described structures for collecting and recirculating fluid from the work tank as other devices may also advantageously be used. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims: A wire-cut electroerosion apparatus including a processing tank for containing machining fluid and having at least one side wall (3) with an opening (24) therein, a column (28, C) placed on the outside of said tank, an arm unit (112) which is supported on said column at one end and extends into said tank through said opening, said arm unit having a longitudinal axis, said tank being moveable with respect to said arm unit in two orthogonal directions, one of which is in a direction parallel to said one side wall and the other of which is in a direction parallel to the axis of said arm unit, and a plate member (114) having a passageway sized to freely pass said arm unit, for covering said opening (24), characterized by at least two plates (134) each of which are secured to said plate member and extend to said arm unit to maintain a generally constant spacing between said plate member and said arm unit; and a seal member (129; 131) of a low friction coefficient connected to said plate member (114), for providing a generally fluid-tight seal in said generally constant spacing. The wire-cut electroerosion apparatus of claim 1, characterized in that said seal member (129) comprises a thin sheet (129) having a polytetrafluoroethylene impregnated surface. The wire-cut electroerosion apparauts of claim 1 or 2, characterized by an inflatable tube (127) positioned to elastically hold said thin sheet (129) against said arm unit (112). The wire-cut electroerosion apparatus of claim 1, 2 or 3, characterized in that said seal member (131) comprises a packing (131) formed of polytetrafluoroethylene-soaked fibers. The wire-cut electroerosion apparatus of claim 4, characterized by a mud guard (132) positioned on said arm unit (112) between the other end of said arm unit and said packing (131). The wire-cut electroerosion apparatus of claim 4 or 5, characterized by an annular member (133) positioned around said arm unit (112) between said packing (131) and said one end of said arm unit (112).

Inventors: HORI HIDEHITO, HOSAKA AKIO, ITOH GEN, WATANABE YOSHIHIRO, HORI, HIDEHITO, HOSAKA, AKIO, ITOH, GEN, WATANABE, YOSHIHIRO, Watanabe, Yoshihiro, c/o Sodick Co.Ltd.
Applicants: SODICK CO LTD, SODICK CO., LTD.
Application year: 1991
Main classification: B23H7
IPC codes: B23H7