Abstract:
An apparatus for electrode charge machining includes a T-shaped quill movable in the vertical direction, at least two linear motor yokes attached to the quill symmetrical about the fixed point of the piston rod of a counter balance device and moving in parallel, at least two linear motor permanent magnets facing the yokes, an electrode mounting device fixed at the lower end of the quill, the counter balance device for balancing a gravitational force acting on the quill and the tool electrode. The gravity balance device consists of an air cylinder with the piston rod. And the air cylinder is fixed with a support frame, with the piston rod extending down into the quill and fixed with a level plate in the quill in the coaxially with the quill.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for electrodischarge machining to form holes of desired shapes in a workpiece, by moving a tool electrode vertically down to make a very small gap between the workpiece and the tool electrode and causing repeated electric discharge of over 60V for a long period of time between the workpiece and the tool electrode. 
     Electrodischarge machining is widely applied to a conductive workpiece, especially for manufacturing molds and sophisticated components. A workpiece to be processed is fixed on a table, and a tool electrode is made of conductive materials such as copper or graphite, and cut into a needed shape and then is held movable in a vertical direction by a quill above the table. Then the tool electrode is moved very close to the workpiece, separated by a very small gap of 10-100 μm. Then if power pulse of over 60V and 1 A is applied between the electrode and the workpiece during the ON time, dielectric liquid of insulation flowing in the gap breaks down and electric discharge (or called electric avalanche) occurs. The electric discharge is a process of energy transmission and energy distribution, producing a very high heat shock to give rise to vaporizing and melting so that the insulation fluid vaporizes and inflates. After electric discharge comes to an end, sudden cooling occurs to let inflated air press inward to form microscopic crater-shaped cavities remained in the surface of the workpiece. The surface roughness of the cavities depends on the pulse-on time and peak current of the power used in the machining process. The quill has to be adjusted in its position for removing debris out of the workpiece, and the gap between the electrode and the workpiece has to be kept proper for continuing the process. Besides, the debris and air bubbles have to be exhausted out at the same time during machining in order to maintain safety. 
     Flushing operation during the discharging process is effected by the flowing of dielectric fluid caused by pressure difference in the gap between the electrode and a workpiece being machined. There are three kinds methods for removing waste debris: 
     1. A suckling mouth or nozzle is placed through the electrode or a workpiece, needing the cost for the added component and its route. But it is not easy to obtain balanced smoothness. 
     2. Flushing oil on the sidewall of the workpiece cavity: this is easy to perform, but pressure of the flushed oil may be not enough to remove the debris in a deep hole, causing secondary discharge in the deep cavity, greatly affecting the precision and surface uniformity of a workpiece. 
     3. Utilizing a jump motion operation of the electrode: if a low moving speed is used in this method, the electrode may only jump for a short distance, and its speed is very slow, less than 3 m/min, so working time has to be prolonged, wasting much time in waiting, and too frequent jumping may spend too much time to obviously lower efficiency. 
     It is preferable to use only the third method for improving accuracy of the shape of the cavity in a workpiece, because it can easily acquire balanced flushing pressure. As to accuracy and speed, it is important to design a high-speed movement method and mechanism. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an electric discharge machining apparatus that can effectively performing vertical movement to a horizontal level, and at the same time to provide a weight balancing device and a positioning device so as to alleviate the whole structure, rigidifying and exposing the structure. Then the apparatus becomes profitable in accommodating, adjusting, completely eliminating necessity of taking apart the device in maintaining and operating. 
     The invention includes a T-shaped quill movable in the vertical direction to move a tool electrode toward a workpiece while repeatedly producing electric discharge between the workpiece and the tool electrode. The T-shaped quill consists of a square column and a rectangular cubic member provided with two rectangular through holes coaxial with the quill and a T-shaped through hole coaxial with the quill, and the square column has a hole communicating with the T-shaped hole. The invention further includes an electrode mounting device fixed under the square column for fixing a tool electrode, and a gravitation force balancing device for balancing the quill and the electrode mounting device consists of an air cylinder fixed on a support frame moving in parallel to the quill. The air cylinder has a piston rod extending down in the T-shaped through hole and fixed with a level fix plate in the square column. The invention further includes at least two linear motors, which respectively have a yoke fixed in the rectangular through holes of the cubic member and located symmetrical about the balance device and the connect point of the level fix plate in the square column. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     This invention will be better understood by referring to the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a first embodiment of an apparatus for elect rod is charge machining in the present invention; 
     FIG. 2 is another perspective view of the first embodiment of an apparatus for electrodischarge machining in the present invention&#39; 
     FIG. 3 is a front view of the first embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 4 is a perspective view of a T-shaped quill in the present invention; 
     FIG. 5 is a side view of a linear motor in the present invention; 
     FIG. 6 is a front cross-sectional view of the first embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 7 is a left cross-sectional view of the first embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 8 is an upper cross-sectional view of the first embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 9 is a perspective view of a second embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 10 is an upper cross-sectional view of the second embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 11 is a perspective view of a third embodiment of an apparatus for electrodischarge machining in the present invention; 
     FIG. 12 is a front cross-sectional view of the third embodiment of an apparatus for electrodischarge machining in the present invention; and, 
     FIG. 13 is an upper cross-sectional view of the third embodiment of an apparatus for electrodischarge machining in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of an apparatus for electrodischarge machining in the present invention, as shown in FIGS. 1,  2  and  3 , includes a column  11  fixed with a rear side of a bed  1 , a frame  2  positioned at a front side of the column  11 , a T-shaped quill  4  disposed in the frame  2 , a slidable member  12  sliding in the Y axis direction, a saddle  13  positioned on the slidable member  12  and moving in the X axis direction vertical to the Y axis direction, a workpiece hole  14  formed in the saddle  13  and filled with insulation liquid, a tool electrode  31  connected to an electrode mounting device  3  connected coaxially to a lower straight portion of the T-shaped quill  4 . 
     The T-shaped quill  4  shown in FIG. 4 has a rectangular cubic member  41  formed in the upper portion, and the rectangular cube member  41  has an upper and a lower surface in parallel, two rectangular holes  42  and a T-shaped hole  43  positioned between the two holes  42 , and all the three holes  42 , and  43  are vertical in the same axis. 
     The frame  2  has two straight rectangular posts  21  respectively in a front left side and a front right side and respectively passing through the two rectangular holes  42  so that the T-shaped quill  4  may move up and down with the acceleration more than 10 m/s in the Z axis direction with the holes  42  moving along the two posts  21 . This force is supplied by two linear motors  5 . 
     Next, as shown in FIG. 5, each linear motor S has a stator consisting of a plurality of permanent magnets  51  and a magnetic plate  52  with the permanent magnets  51  fixed spaced apart thereon, positioned vertical at an outer side of each rectangular parallel post  21 , and an armature coil  54  and a yoke  53  of each motor  5  are positioned vertically to face in parallel the permanent magnets  51  and the magnetic plate  52 , fixed firmly in the two rectangular holes  42  of t he rectangular cubic member  41 . 
     As the level cross-sectional surface of the rectangular cube member  41  has four circumferential walls of different thickness, so rigorously speaking, the T-shaped quill  4  has no true geometrical center axis, and at the same time the gravitational axis of the T-shaped quill  4  is eccentric to the geometrical axis of the rectangular cube member  41  or the square column  44 . 
     Further, the upper and the lower surface of the rectangular holes  42  of the rectangular cubic member  41  respectively have a blocker  46 ,  47  to limit the largest stroke of the rectangular cubic member  41 . When the blockers  46  and  47  respectively collide with the stoppers  25 ,  26  of the frame  2 , they function as elastic components of shock force. Further, limiters  48  and  49  are provided at an upper side and a lower side of the sidewall of the frame  2  behind the stoppers  25 ,  26 , restricting the rising position of the rectangular cubic member  41 , as shown in FIGS. 1,  2 ,  3  and  7 . 
     The magnetic plate  52  and the armature coil  54  of the linear motor  5  face each other with a gap extremely tiny and accurate, and possible to be adjusted in their positions by adjusting screws  55 , enabling the two linear motors  5  provided with a same function. Because the linear motors  5  have a direct load of the T-shaped quill  4  and the tool electrode  31  and a high speed for moving them, the motors  5  produce extremely large driving force, generally involving much heat at the same time so that a circulating cooling system has to be used for exhausting the heat produced by a machine shaft, guaranteeing precise positioning of the machine axis. The circulating cooling system is commonly applied to industrial products, by providing an inlet (not shown in the Figures) of an air or liquid cooling tube at the edge of the yoke  53  near the armature coil  54  of the linear motors  5 . Further, a linear optical scale  7  as shown in FIG. 2 is fixed on one side of the frame  2 , and a position sensor  71  is fixed at one side of the rectangular cubic member  41  for facing the linear optical scale  7  in order to read the moving position of the T-shaped quill  4 . 
     Next, at least two linear roller bearing rails  22  are provided in order to accurately guide the T-shaped quill  4  in its operation, as shown in FIGS. 4 and 6, respectively fixed at a front side of the two rectangular posts  21  of the frame  2  in the same axis of movement, and with two parallel upper bearing blocks  56  fixed in the two rectangular holes  42  of the cubic member  41  (or on the front inner wall of the two rectangular holes  42 ), matching closely with the linear roller bearing rails  22 . Further, a fixing plate  57  is fixed at an intermediate portion of the T-shaped quill  4 , and two lower bearing slideable blocks  58  are fitted in two recesses in an inner sidewall of the fixing plate  57  to match with the linear roller bearing rails  22 , for strengthening bending stiffness of the square column  44 . 
     Further, in order to reduce the load continually added on the linear motors  5 , as shown in FIGS. 6,  7 ,  8  an air cylinder  6  is provided to support the weight so as to complete symmetrical force for controlling the motor driver. A comparatively slender piston rod  61  in the air cylinder  6  is used to take less space in the T-shaped quill  4  so as to reduce the dimensions of the quill  4 . Then the projection edge  23  and the supporting frame  24  of the frame  2  are used to fix the rear end of the air cylinder  6 , which is positioned in parallel to the moving axis, having the piston rod  61  extending down and passing through a brake  62  and having its outer end located in the square column  44  and connected firmly to a level fixing plate  45  positioned in the square column  44 . The brake  62  clamps the piston rod  61  in the power-off time to prevent the tool electrode  31  from accidental falling. The other end of the piston rod  61  is located in the cylinder  6 , reciprocating therein. A pressure gauge (not shown in the Figures) is provided to measure the inner pressure of the cylinder  6 , with a pressure servo-controller controlling the inner pressure to let the inner pressure shore up the gravitational weight, reducing the electricity loading needed for the linear motors  5  during operation stopped. 
     Next, a second embodiment of an apparatus for electrodischarge machining is shown in FIGS. 9 and 10, having the same structure as the first embodiment except the linear motors  5 , which have moving components of a yoke  53  and an armature coil  54  shaped as rectangular and contained in the two rectangular holes of the rectangular cubic member  41 , and stationary components (or the stator) of a permanent magnet  51  and a magnet post  52 . The yoke  53  has a center hole for the round permanent magnet  51  and the round magnet post  52  to fit therein, and the permanent magnet  51  and the magnet post  52  have their upper and their lower ends connected to the frame  2  in the same moving axis as the cubic member  41 . 
     In the second embodiment, the stator of the linear motor  5  has its upper and its lower end directly connected to the frame  2  so that the T-shaped quill  4  may slide up and down smoothly, saving the two rectangular posts  21 , the level fixing plate  57  and the lower bearing slide block  58  in the first embodiment. 
     Next, a third embodiment of an apparatus for electrodedischarge machining is shown in FIGS. 11,  12  and  13  , having the same structure as the first embodiment except the frame  2 , which has a square block  27  with an inner square hole and two rectangular posts  21  positioned vertically in the inner square hole. The square block  27  further has a nearly θ-shaped member added to the lower end for reinforcing supporting force of the frame. 
     While the preferred embodiment of the invention have been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications that may fall within the spirit and scope of the invention.