Abstract:
Provided are an eccentric electrode for an electric discharge machining apparatus, a method of manufacturing the same, and a micro electric discharge machining apparatus including the same that are capable of generating a micro cylindrical shape on a workpiece with simple operations. The electrode for an electric discharge machining apparatus having a machining head is provided. The electrode includes a first member rotatably attached to the machining head and having a rotation axis, and a second member mounted on the first member, eccentrically disposed with respect to the rotation axis of the first member, and having an inverse tapered shape facing away from the machining head. Accordingly, a conveyance path for machining the object being processed can be simplified to increase its efficiency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application Nos. 10-2013-0131234, filed on Oct. 31, 2013, and 10-2013-0151177, filed on Dec. 6, 2013, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The present disclosure relates to an eccentric electrode for electric discharge machining to machine a micro shape in a workpiece, a method of manufacturing the same, and a micro electric discharge machining apparatus including the same. 
     Research on technology of high functional ultra-micro parts in optic digital communication technology, medical environments, and the electronic home appliance industry has been widely performed. Sizes, performance, functions, and so on, of advanced products are restricted by sizes of parts to be machined and machining technologies. Accordingly, a mechanical technology is gradually being varied toward miniaturization, functionalization and diversification. 
     Presently, a method of machining a micro tool is classified as mechanical machining of physically cutting and machining a workpiece or electric discharge machining using a physical/electrical action. Since mechanical machining involves machining the workpiece through mechanical contact, it is difficult to perform drilling or milling using a large tool. Meanwhile, since micro electric discharge machining has an advantage in that a desired micro hole or shape is machined because there is no physical force applied to a tool to remove stiffness restriction, micro electric discharge machining is used to extremely precisely machine a turbine engine nozzle or an inkjet nozzle, an orifice for a gas or liquid used in aerospace engineering or the medical field, a nuclear fusion measurement apparatus, an X-ray electron gun, a micro connecting section of a high speed computer, fine holes and shapes of a micro turbine, an aircraft engine, and so on. 
     SUMMARY 
     The present disclosure is directed to an eccentric electrode for electric discharge machining, a method of manufacturing the same, and a micro electric discharge machining apparatus including the same that are capable of generating a micro cylindrical shape on a workpiece with simple operations. 
     According to an aspect of the present disclosure, there is provided an eccentric electrode for electric discharge machining rotatably attached to a machining head, the eccentric electrode for electric discharge machining including: a body section attached to the machining head; and an eccentric section eccentrically provided at the body section and having an inversely tapered shape. 
     The body section may have a cylindrical shape, and the eccentric section may be formed at a position spaced a certain distance from a center of the body section. 
     In the eccentric section having the inversely tapered shape, a diameter of a cross-section adjacent to the body section may be larger than that of a cross-section opposite to the body section. 
     A method of manufacturing an eccentric electrode for electric discharge machining includes causing a non-machined tool electrode to approach a plate electrode having a hole to perform electric discharge machining; and performing the electric discharge machining to form the tool electrode having an inversely tapered shape while rotating the tool electrode along a trajectory to increase a trajectory radius when a portion of the tool electrode enters the hole. 
     The method may further include providing the non-machined tool electrode and the plate electrode in an electric discharge bath; and applying power to both of the non-machined tool electrode and the plate electrode to perform the electric discharge machining. 
     According to another embodiment of the present disclosure, there is provided a micro electric discharge machining apparatus including: a machining head, a tool electrode attached to the machining head, a conveyance unit configured to support the machining head and perform movement and rotation operations, an electric discharge bath filled with a processing liquid, a work table provided in the electric discharge bath and on which a workpiece is placed, a power supply configured to supply power to the electric discharge bath and the tool electrode, and a control unit configured to generally control the above-mentioned components, wherein the tool electrode is an eccentric electrode for electric discharge machining including a body section attached to the machining head and an eccentric section concentrically formed at one side of the body section, and the eccentric electrode for electric discharge machining has an inversely tapered shape to machine a micro cylindrical shape on a workpiece. 
     The eccentric section may be eccentrically disposed at a position spaced a certain distance from a center of the body section, and the eccentric section may be vertically lowered and rotated by the conveyance unit to form a micro cylindrical shape on a workpiece. 
     The control unit may control any one of an operation mode in which a micro cylindrical shape of a workpiece is machined, and an eccentric electrode forming mode in which the tool electrode is machined by the eccentric electrode for electric discharge machining. 
     The control unit may move the machining head downward in a vertical direction in the operation mode, and rotate an eccentric tool electrode attached to the machining head to form a micro cylindrical shape on the workpiece. 
     The control unit may machine the eccentric electrode for electric discharge machining having the inversely tapered shape while causing a non-machined tool electrode to approach a plate electrode having a hole and disposed in the electric discharge bath at a certain speed and performing trajectory rotation to increase a trajectory radius as time elapses in the eccentric electrode forming mode. 
     According to one embodiment of the present disclosure, an electrode for an electric discharge machining apparatus having a machining head is provided. The electrode includes a first member rotatably attached to the machining head and having a rotation axis, and a second member mounted on the first member, eccentrically disposed with respect to the rotation axis of the first member, and having an inverse tapered shape facing away from the machining head. The first member has a cylindrical shape, and the second member is disposed away from the rotation axis of the first member at a predetermined distance. 
     The inverse tapered shape has a first diameter of a first cross-section adjacent to the first member being smaller than that of a second cross-section facing away from the first member. 
     According to another embodiment of the present disclosure, a method of manufacturing an electrode for electric discharge machining is provided. The method includes approaching a tool electrode to a plate electrode having a hole to perform the electric discharge machining, and when at least a portion of the tool electrode enters the hole, rotating the tool electrode with respect to a rotation axis along a trajectory on a plane normal to the rotation axis while performing the electric discharge machining for shaping the tool electrode into an inverse tapered form, wherein the trajectory increases a trajectory radius in response to a time. 
     The method further includes providing the tool electrode and the plate electrode in an electric discharge bath, and applying a power to both of the tool electrode and the plate electrode to perform the electric discharge machining. 
     According to the other embodiment of the present disclosure, an electric discharge machining apparatus having a machining head, a tool electrode coupled to the machining head, a conveyance unit configured to support the machining head and perform movement and rotation operations of the machining head, an electric discharge bath filled with a processing liquid, a support disposed in the electric discharge bath and configured to accommodate an object being processed, a power supply configured to supply a power to the electric discharge bath and the tool electrode, and a control unit configured to control the electric discharge machining apparatus is provided. The electric discharge machining apparatus includes the tool electrode having, a first member attached to the machining head and having an axis; and a second member eccentrically disposed with respect to the axis of the first member and having an inverse tapered shape, wherein the electrode is configured to form a micro cylindrical shape on the object being processed. 
     The second member is eccentrically disposed away from the axis of the first member at a predetermined distance, and the second member is configured to be moved downward in a vertical direction and is configured to be rotated by the conveyance unit to form a micro cylindrical shape on the object being processed. 
     The control unit is configured to control one of a first operation mode in which the micro cylindrical shape is formed on the object being processed, and a second operation mode in which the tool electrode is machined so that the second member is eccentrically disposed with respect to the axis of the first member. The control unit in the first operation mode is configured to move the machining head downward in a vertical direction, and is configured to rotate the tool electrode attached to the machining head to form a micro cylindrical shape on the object being processed. 
     The control unit in the second operation mode is configured to approach the tool electrode to a plate electrode having a hole therein disposed in the electric discharge bath, and the control unit in the second operation mode is configured to rotate the tool electrode along a trajectory that increases a trajectory radius in response to a time at a predetermined speed so as to shape the tool electrode into an inverse tapered form. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a conceptual view of a micro electric discharge machining apparatus according to an embodiment of the present disclosure; 
         FIGS. 2A to 2C  are views for describing a shape and an operation of the eccentric electrode for electric discharge machining according to the embodiment of the present disclosure; 
         FIGS. 3A to 3C  are views for describing a method of manufacturing an eccentric electrode for electric discharge machining according to an embodiment of the present disclosure; 
         FIG. 4  is a view showing that a micro cylindrical shape is formed on a workpiece using an eccentric electrode  20  for electric discharge machining manufactured through the method of  FIGS. 3A to 3C ; 
         FIG. 5  is a view showing an eccentric electrode for electric discharge machining according to another embodiment of the present disclosure; 
         FIGS. 6A to 6C  are views showing a method of manufacturing an eccentric electrode for electric discharge machining according to another embodiment of the present disclosure; 
         FIG. 7  is a view showing that a micro cylindrical shape is formed by machining a workpiece using the eccentric electrode for electric discharge machining manufactured by the method shown in  FIG. 6 ; and 
         FIG. 8  is a view showing a plurality of micro cylindrical shapes formed on the workpiece manufactured by the method of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. While the present disclosure is shown and described in connection with exemplary embodiments thereof, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the disclosure. Throughout the drawings, like elements are designated by like reference numerals. 
       FIG. 1  is a conceptual view of a micro electric discharge machining apparatus according to an embodiment of the present disclosure. 
     First, electric discharge machining by a micro electric discharge machining apparatus  100  will be described, and then a configuration thereof will be described in detail. 
     The electric discharge machining is a machining method using an electric discharge phenomenon, i.e., a machining method in which a voltage having a high frequency pulse waveform is applied between an electrode and a workpiece to perform electric discharge to remove a surface layer of the workpiece in a desired shape. In other words, the electric discharge machining is a machining method in which a tool electrode and a workpiece are immersed in an insulating processing liquid and an arc electric discharge is continuously generated to remove a portion of the workpiece, and a voltage having a high frequency pulse waveform is applied between the electrode and the workpiece to perform the electric discharge to remove a surface layer of the workpiece. 
     The micro electric discharge machining apparatus  100  can machine a workpiece with relatively high precision with no restriction in machining, provide a uniform machining surface, and perform a machining operation with no necessity of post processing. The micro electric discharge machining apparatus  100  inserts the electrode and the workpiece into the processing liquid, maintains a small gap between the electrode and the workpiece, and then applies a voltage to the electrode and the workpiece. Accordingly, the electric discharge starts between the electrode and the workpiece, and here, the gap between the electrode and the workpiece is referred to as an electric discharge gap or an electric discharge interval. Here, an extremely large number of pulse waveforms are generated between the electrode and the workpiece by a high frequency pulse power supply, the generated pulse waveforms flow to the shortest point of the workpiece, and electricity having a high current density heats and melts the workpiece. This point is referred to as an electric discharge point. A temperature is rapidly increased at the electric discharge point to generate a high pressure between the electrode and the workpiece to generate an evaporation phenomenon and a vaporization phenomenon. The melted metal of the workpiece can be converted into small grains and can be removed by a flow of the processing liquid. 
     The micro electric discharge machining apparatus  100  may include a machining head  10  configured to perform the above-mentioned operations, a tool electrode  20  attached to the machining head  10 , a conveyance unit  30  configured to support the machining head  10 , movable along X, Y and Z axes and rotatable in A, B and C directions, an electric discharge bath  40  filled with a processing liquid, a work table  50  disposed in the electric discharge bath  40  and on which a workpiece is placed, a power supply  60  configured to supply power to the electric discharge bath  40  and the tool electrode  20 , and a control unit  70  configured to entirely control the micro electric discharge machining apparatus  100 . 
     The machining head  10  can perform position and posture control of the tool electrode  20  according to a posture control configuration of six degrees of an X axis and a Y axis for controlling a position in a horizontal direction of the tool electrode  20 , a Z axis for controlling a position in a vertical direction, and A, B and C axes for controlling rotational angles of the X, Y and Z axes. The machining head  10  is provided with a spindle (not shown) disposed therein to be rotatable by a motor (not shown). 
     The tool electrode  20  receives power from the power supply  60 , and can perform electric discharge machining of the workpiece using the supplied power. The tool electrode  20  is formed in an eccentric shape and can be attached to the machining head  10 . When the tool electrode  20  having the eccentric shape (hereinafter referred to as “an eccentric electrode for electric discharge machining”) is attached to the machining head  10 , the micro cylindrical shape can be formed on the workpiece only by rotation of the machining head  10  and movement in the vertical direction (movement in the Z-axis direction). 
     The conveyance unit  30  may include an X-axis conveyance frame  30   a  configured to enable X-axis conveyance, a Y-axis conveyance frame  30   b  configured to enable Y-axis conveyance, and a Z-axis conveyance frame  30   c  configured to enable Z-axis conveyance. The X-axis conveyance frame  30   a , the Y-axis conveyance frame  30   b  and the Z-axis conveyance frame  30   c  provided at the conveyance unit  30  may have rotational angles that can be controlled in the A, B and C directions. 
     The processing liquid is supplied into the electric discharge bath  40 , and the workpiece mounted therein can be machined through the electric discharge machining. While not shown, the electric discharge bath  40  has a hole formed in one corner thereof and configured to discharge the processing liquid. 
     The work table  50  may be disposed in the electric discharge bath  40  such that the workpiece can be placed thereon. While a workpiece  5  may be directly placed on the horizontally formed work table  50 , the workpiece  5  may be placed a certain distance from the work table  50  using a predetermined jig. 
     The power supply  60  may supply a certain amount of power to the electric discharge bath  40  and the tool electrode  20  when the workpiece is worked on. 
     The control unit  70  can entirely control the micro electric discharge machining apparatus  100 . The control unit  70  can differently control the micro electric discharge machining apparatus  100  in an operation mode in which a micro cylindrical shape of the workpiece is machined, and an eccentric electrode forming mode in which the eccentric electrode  20  for electric discharge machining is formed. 
     The control unit  70  controls the Z-axis conveyance frame  30   c  to vertically lower the machining head  10  when the micro columnar shape is formed on the workpiece  5 , and rotates a spindle (not shown) disposed in the machining head  10  to rotate the eccentric electrode  20  for electric discharge machining. When the machining head  10  is moved downward, the eccentric electrode  20  for electric discharge machining connected to the machining head  10  approaches the workpiece  5 . When the eccentric electrode  20  for electric discharge machining approaches the workpiece  5 , the electric discharge machining is performed, and the micro cylindrical shape can be formed according to rotation of the eccentric electrode  20  for electric discharge machining. According to an aspect of the present disclosure, since the eccentric electrode  20  for electric discharge machining is eccentrically provided, movement along the X axis and the Y axis is not performed when the micro columnar shape is formed, and only movement along the Z axis and rotation in the C direction of the tool electrode  20  according to rotation of the spindle (not shown) provided in the machining head  10  are performed. 
     The control unit  70  controls formation of the eccentric electrode  20  for electric discharge machining according to an electric discharge action between the two electrodes by connecting the non-machined tool electrode  20   a  to the machining head  10  and installing a plate electrode  80  in the electric discharge bath  40  when the eccentric electrode  20  for electric discharge machining is formed. The control unit  70  can form an eccentric section in a trapezoidal shape as well as a rectangular shape when the eccentric electrode  20  for electric discharge machining is formed, and a specific method thereof will be described below. 
       FIGS. 2A to 2C  are views for describing a shape and an operation of the eccentric electrode for electric discharge machining according to the embodiment of the present disclosure. 
     Referring to  FIG. 2A , the eccentric electrode  20  for electric discharge machining may include a body section  24  inserted into and attached to the machining head  10  and an eccentric section  28  eccentrically attached to the body section  24 . The body section  24  is connected to the spindle (not shown) in the machining head  10  to be rotatable. The eccentric section  28  is attached to a side surface of the body section  24  rather than a center thereof to machine the workpiece  5 . 
     Referring to  FIG. 2B , the machining head  10 , to which the eccentric electrode  20  for electric discharge machining is attached, moves in the Z-axis direction, and operates the spindle (not shown) disposed therein to rotate the eccentric electrode  20  for electric discharge machining upon movement in the Z-axis direction. Specifically, the machining head  10  gradually moves downward in the vertical direction to rotate the eccentric electrode  20  for electric discharge machining. When the machining head  10  vertically moves downward, an extremely large number of pulse waveforms are generated by the high frequency pulse power supply by the eccentric electrode  20  for electric discharge machining attached to the machining head  10 , and the generated pulse waveforms flow toward the shortest point of the workpiece to heat and melt the corresponding position. 
     Referring to  FIG. 2C , since the eccentric electrode  20  for electric discharge machining is inserted into the workpiece  5  while performing the electric discharge machining, it is possible to check formation of the micro cylindrical shape on the workpiece  5 . 
       FIGS. 3A to 3C  are views for describing a method of manufacturing the eccentric electrode for electric discharge machining according to the embodiment of the present disclosure. 
     Referring to  FIG. 3A , the plate electrode  80  is previously prepared in the electric discharge bath  40 , and the non-machined tool electrode  20   a  is mounted on the machining head  10 . The plate electrode  80  is placed on the work table  50  while being spaced a certain distance from the work table  50  using a jig  55  provided at one side. The plate electrode  80  has a hole  85  having a certain size and disposed at one side thereof. The hole  85  formed in the plate electrode  80  has a diameter corresponding to a width of the eccentric electrode  20  for electric discharge machining. 
     Referring to  FIG. 3B , the control unit  70  controls movement of the non-machined tool electrode  20   a  along the Z axis, and application of power to both of the non-machined electrode  20   a  and the plate electrode  80 . 
     Referring to  FIG. 3C , when a certain time elapses while the non-machined tool electrode  20   a  moves along the Z axis, the eccentric section  28  is formed to a size of the hole of the plate electrode  80 . When the above-mentioned method is used, the eccentric electrode  20  for electric discharge machining including the body section  24  and the eccentric section  28  eccentrically provided at the body section  24  is formed. 
       FIG. 4  is a view showing that the micro cylindrical shape is formed on the workpiece using the eccentric electrode  20  for electric discharge machining manufactured through the method of  FIGS. 3A to 3C . 
     When the eccentric electrode  20  for electric discharge machining is rotated in the C direction while moving in the Z axis, which is a direction of the workpiece, the micro cylindrical shape is formed. However, the micro cylindrical shape has a frustoconical shape (a tapered shape) due to a reaction with the eccentric electrode  20  for electric discharge machining as shown in  FIG. 4 . This is caused because a machining time of the eccentric electrode  20  for electric discharge machining that machines a side surface of the micro cylindrical shape is entirely irregular. That is, a diameter of a cross-section of the micro cylindrical shape is smallest (reacted for a longest time) at an initial reaction position (the uppermost cross-section of the workpiece) and largest (reacted for a shortest time) at a reaction termination position (the lowermost cross-section of the workpiece), and thus a micro cylindrical shape having an abnormal form (a tapered shape) is formed. Accordingly, according to the aspect of the present disclosure, the eccentric electrode  20  for electric discharge machining of the micro electric discharge machining apparatus  100  has an inversely tapered shape (a conical shape having a diameter larger at the upper end cross-section than the lower end cross-section), and thus the tapered shape of the micro cylindrical shape of the workpiece can be guided to a cylindrical shape. For example, the inversely tapered shape of 50:1 means that a diameter increases to 1 mm larger than that of a starting point of the cylindrical shape in 50 mm. When the eccentric electrode  20  for electric discharge machining has the inversely tapered shape, it is possible to prevent the micro cylindrical shape of the workpiece  5  from being machined in the tapered shape. 
       FIG. 5  is a view showing an eccentric electrode for electric discharge machining according to another embodiment of the present disclosure. 
     The eccentric electrode  20  for electric discharge machining may include the body section  24  attached to the machining head  10 , and the eccentric section  28  attached to the body section  24  and having the inversely tapered shape. 
     Since the eccentric section  28  has the inversely tapered shape, when the machining head  10  vertically moves downward and the eccentric electrode  20  for electric discharge machining is inserted into the workpiece  5 , a region of the eccentric electrode  20  for electric discharge machining having a relatively large diameter is disposed at the lowermost end of the micro cylindrical shape formed on the workpiece  5  to further cause the electric discharge machining, and a region of the eccentric electrode  20  for electric discharge machining having a relatively small diameter is disposed at the uppermost end of the micro cylindrical shape to cause less of the electric discharge machining, preventing generation of the tapered micro cylindrical shape. 
       FIGS. 6A to 6C  are views showing a method of manufacturing an eccentric electrode for electric discharge machining according to another embodiment of the present disclosure. 
     Referring to  FIG. 6A , like  FIG. 3A , the plate electrode  80  is previously prepared in the electric discharge bath  40 , and the non-machined tool electrode  20  is mounted on the machining head  10 . The plate electrode  80  is placed on the work table  50  while being spaced a certain distance from the work table  50  using the jig  55  provided at one side thereof. 
     Referring to  FIGS. 6B and 6C , the control unit  70  controls movement of the tool electrode  20  along the Z axis, and application of power to both of the tool electrode  20  and the plate electrode  80 . The control unit  70  rotates the tool electrode  20  along a trajectory thereof while moving the tool electrode  20  along the Z axis. The control unit  70  performs the trajectory rotation with reference to an eccentric section  28 , which is to be generated using the X-axis conveyance frame  30   a  and the Y-axis conveyance frame  30   b  upon rotation of the tool electrode. Here, the trajectory rotation with reference to the eccentric section  28  includes performing the trajectory rotation using a center of the hole  85  of the plate electrode  80  as a reference axis. The control unit  70  controls gradual increase of a trajectory radius upon the trajectory rotation. When the trajectory diameter of the trajectory rotation of the non-machined tool electrode  20   a  is gradually increased in this way, since the electric discharge action is generated relatively less at the region adjacent to the plate electrode  80  (the lowermost region) of the non-machined tool electrode  20   a  and the adjacent region further approaches an inner wall of the hole of the plate electrode  80  as the diameter of the trajectory rotation is gradually increased, the eccentric electrode  20  for electric discharge machining having the inversely tapered shape having a small diameter of the upper end of the eccentric electrode  20  for electric discharge machining (a portion near the body section) and a large diameter of the lower end (a portion far from the body section) is formed. 
       FIG. 7  is a view showing that the micro cylindrical shape is formed by machining the workpiece using the eccentric electrode for electric discharge machining having the inversely tapered shape manufactured by the method shown in  FIG. 6 , and  FIG. 8  is a view showing that a plurality of micro cylindrical shapes are formed on the workpiece by the method shown in  FIG. 7 . 
     The eccentric electrode  20  for electric discharge machining may include the body section  24  attached to the machining head  10 , and the eccentric section  28  eccentrically attached to one side of the body section  24  through the above-mentioned method. Since the eccentric section  28  has the inversely tapered shape, the micro cylindrical shape of the workpiece can be machined in a cylindrical columnar shape. Specifically, when the eccentric tool electrode  20  having the inversely tapered shape approaches the workpiece  5  to cause the electric discharge action, the upper surface of the workpiece becomes farther from the eccentric tool electrode  20  having the inversely tapered shape as time elapses, and thus further generation of the electric discharge action at the upper end of the workpiece having a relatively longer contact time can be minimized. 
     As can be seen from the foregoing, since the micro cylindrical shape is formed on the workpiece using the eccentric electrode for electric discharge machining, a conveyance path for machining can be simplified, and time can be saved to improve machining efficiency. 
     It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present disclosure without departing from the spirit or scope of the disclosure. Thus, it is intended that the present disclosure cover all such modifications provided they come within the scope of the appended claims and their equivalents.