Abstract:
An electrochemical machining (ECM) system for machining a workpiece includes a plurality of ECM stations. A first ECM station machines a first region of the workpiece. A second ECM station machines a second region of the workpiece separate from the first region. Additional ECM stations may also be utilized. Each ECM station includes a stationary electrode for delivering electric current for eroding material from the workpiece. Each ECM station also includes an ultrasonic transducer for determining a width of electrolyte between the stationary electrode and the workpiece. Machining of the workpiece in each ECM station is completed when the width of electrolyte reaches a predetermined width.

Description:
[0001]     This invention claims priority to U.S. Provisional Patent Application No. 60/655,846, filed Feb. 24, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The subject invention relates generally to an electrochemical machining system for shaping and forming metallic workpieces.  
         [0004]     2. Description of the Related Art  
         [0005]     Methods and systems for electrochemical machining are well known in the prior art. One example of a multiple station electrochemical machining system is disclosed in U.S. Pat. No. 3,414,501 (the &#39;501 patent).  
         [0006]     The system disclosed in the &#39;501 patent machines a continuous strip of razor blade stock. The stock is conveyed through a machining chamber. The chamber includes a series of electrodes immersed in an electrolyte. The electrodes are separated from one another by insulating spacers. The stock passes close to each electrode as it is conveyed through the chamber. An electric current passes through the electrodes, the electrolyte, and the stock, thus eroding a portion of the stock away from one region of the stock.  
         [0007]     Although the &#39;501 patent may provide an effective system for machining the one region of the stock to manufacture razor blades, there remains an opportunity to provide an electrochemical machining method and system for machining workpieces with complex machining needs.  
       SUMMARY OF THE INVENTION  
       [0008]     A method of machining a workpiece according to the invention includes providing an electrochemical machine tool having a plurality of discrete work stations that are each fitted with dedicated electrode tooling of a prescribed shape and size that differs from station to station for performing successive electrochemical machining operations on the workpiece. The workpiece is introduced to a first of the stations and is supported in a fixed relation relative to the electrode of the first station to define a starting gap between the workpiece and the electrode which is caused to widen during the electrochemical machining operation without physical movement of either the workpiece or electrode. The widening of the gap is monitored until the gap reaches a predetermined increased gap condition and thereafter the machining operation is discontinued at the first station. The workpiece is then advanced to at least a second successive ECM station where the process is repeated until such time as a final workpiece size and shape is achieved.  
         [0009]     The invention further contemplates an ECM tool which includes a plurality of discrete ECM stations each having a dedicated electrode machine tool of predetermined configuration that differ among the stations and being supported in fixed position during a machining operation. A device is provided for supporting a workpiece to be machined in fixed position at each station relative to the fixed electrode to define a starting gap therebetween which widens during the course of machining at each station.  
         [0010]     The invention has the advantage of enabling complex shapes to be electrochemically machined on a workpiece in a step-wise efficient manner.  
         [0011]     The invention has the further advantage of carrying out the ECM process using stationary ECM tooling and multiple ECM stations such that a certain amount of machining of a workpiece takes place at one station having fixed ECM tooling, and is then advanced to a subsequent station ECM station or stations at which further machining takes place relative to fixed ECM tooling. In this way, the process avoids the need for movable tooling and reduces the time a workpiece spends at any one station, since only part of the machining is carried out at any one station and can be controlled to optimize efficiency such that the maximum number of workpieces can be cycled through the stations to maximize production rate. By controlling the amount of machining that occurs at any station relative to the fixed ECM tooling, it minimized the time that the fully machined surfaces of a workpiece spend at the first station while awaiting the machining of other regions of the workpiece. Instead, once the desired optimal amount of machining is completed at the first stations, the workpiece is advanced to at least a second station for further machining in the other areas, and then from there to subsequent station(s), if necessary, for additional machining in further regions of the workpiece.  
         [0012]     The subject invention also provides an ECM system for machining the workpiece comprising the first ECM station including the first stationary electrode and the electrolyte to form the first gap of electrolyte between the workpiece and the first stationary electrode for eroding material from the first region of the workpiece by passing the electric current through the first stationary electrode, the first gap of electrolyte, and the workpiece. The ECM system also comprises the second ECM station including the second stationary electrode and the electrolyte for forming the second gap of electrolyte between the workpiece and the second stationary electrode for eroding material from a second region of the workpiece, by passing the electric current through the second stationary electrode, the second gap of electrolyte, and the workpiece. The subject invention further comprises a workpiece handling system for moving the workpiece from the first machining station to the second machining station.  
         [0013]     The ECM system and method of the present invention allow for more complex electrochemical machining than is available in the prior art. Several portions of the workpiece can be machined to produce elaborate machined parts, such as, but not limited to, pistons, connecting rods, and camshafts. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:  
         [0015]      FIG. 1  is a perspective view of an electrochemical machining (ECM) system.  
         [0016]      FIG. 2A  is a cross-sectional view of the first ECM station before a workpiece is machined.  
         [0017]      FIG. 2B  is a cross-sectional view of the first ECM station after the workpiece is machined.  
         [0018]      FIG. 3A  is a cross-sectional view of the second ECM station before the workpiece is machined.  
         [0019]      FIG. 3B  is a cross-sectional view of the second ECM station after the workpiece is machined.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     Referring to the Figures, where like numerals indicate like parts throughout the several views, an electrochemical machining (ECM) system for machining a workpiece is shown generally at  10  in  FIG. 1 . A method of an associated ECM process is also described herein.  
         [0021]     The ECM system  10  comprises a plurality of ECM stations numbering at least two, but including three or more stations contemplated by the invention. For purposes of illustration only, the process will be described with respect to two ECM stations, but it is to be understood that the description is applicable to and the invention contemplates having a third, a forth or more ECM stations as may be required by a particular application or workpiece. Referring to the drawings, the system  10  is shown to include a first ECM station  12 , a second ECM station  14 , and a workpiece handling system  16 . Preferably, the workplace handling system  16  is an automated device for moving and manipulating the workpiece into and out of the first and second ECM stations  12 ,  14  and through other components of the system  10 . The workpiece handling system  16  may comprise a robot, a gantry, conveyors, grippers, or other apparatus well know to those skilled in the art. A controller  18  is operatively connected to the workpiece handling system  16  for controlling operation and movement of the workpiece handling system  16 .  
         [0022]     The ECM stations  12 ,  14  both function to erode material from the workpiece  20 . However, the first ECM station  12  erodes material from a first region of the workpiece  20 , while the second ECM station  14  (and any subsequent ECM stations) erodes material from another region of the workpiece  20 . The locations of the first and second regions on the workpiece  20  depend on a number of factors, including rough dimensions of the workpiece  20 , desired finished dimensions of the workpiece  20 , an amount of stock to be removed from the workpiece  20 , etc. The first and second regions may be at different positions on the workpiece  20 . Alternatively, the first and second regions may be at the same or overlapping positions on the workpiece  20 .  
         [0023]     Referring now to  FIG. 2A , the first ECM station  12  comprises a first stationary electrode  22  immersed in an electrolyte  24  or flushed with a flow of electrode to be effectively immersed. The position of the first stationary electrode  22  is fixed, meaning the stationary electrode  22  does not move at any time during the ECM process. The first ECM station  12  further comprises a first part holder  26 . The first part holder  26  retains the workpiece  20  stationary during the ECM process.  
         [0024]     The workpiece handling system  16  moves the workpiece  20  into the first ECM station  12  and places the workpiece  20  in the first part holder  26 . The first region of workpiece is immersed (or flushed) in the electrolyte  24 . This forms a first gap of electrolyte  28  between the first stationary electrode  22  and the workpiece  20 . The gap is maintained at about 50-400 microns.  
         [0025]     A power supply  30  is operatively connected to the first stationary electrode  22  and the workpiece  20 . In the illustrated embodiment the power supply  30  is electrically connected to the first part holder  26 , which is in turn electrically connected to the workpiece  20 . The power supply  30  produces electric current that passes through the first stationary electrode  22 , the first gap of electrolyte  28 , and the workpiece  20 . This application of electric current causes material from the first region of the workpiece  20  to be eroded away from the workpiece  20 , as shown in  FIG. 2B . The electrolyte  24  flows through the first gap of electrolyte  28  to flush the eroded material away.  
         [0026]     The first ECM station  12  further includes a first ultrasonic sensor  32  operatively connected to a measurement apparatus  34 . The first ultrasonic sensor  32  and measurement apparatus  34  determine the width of the first gap of electrolyte  28 . It is preferred that the first ultrasonic sensor  32  is embedded within the first stationary electrode  22 . However, those skilled in the art realize that the first ultrasonic sensor  32  may be located in a variety of positions to adequately determine the width of the first gap of electrolyte  28 .  
         [0027]     The measurement apparatus  34  generates an ultrasonic wave that is transmitted by the first ultrasonic sensor  32 . The ultrasonic wave propagates through the first stationary electrode  22  and the first gap of electrolyte  28  to the workpiece  20 . The wave reflects off the workpiece  20  and is received by the first ultrasonic sensor  32  and sent back to the measurement apparatus  34 . The measurement apparatus  34  then computes the width of the first gap of electrolyte  28  based on the time delay between the sending and receiving of the ultrasonic wave.  
         [0028]     This measurement of the first gap of electrolyte  28  is performed continuously during the ECM process. As the electric current is applied and material is eroded from the workpiece, the width of the first gap  28  will increase. The measurement apparatus  34  is operatively connected to the controller  18 . The measurement of the first gap  28  is sent to the controller  18  in real-time.  
         [0029]     In addition to the workpiece handling system  16  and measurement apparatus  34 , the controller  18  is also operatively connected to the power supply  30 . The controller  18  sends commands to the power supply  30 . These commands are used to turn the power supply  30  on an off and adjust the properties of the electrical current produced by the power supply  30 . These properties include voltage, amperage, pulse width, etc. Preferably, the power supply  30  returns feedback of its operation back to the controller  18 .  
         [0030]     In a first embodiment, the controller  18  analyzes the current measurement of the first gap  28  provided by the measurement apparatus  34 . When the first gap  28  of electrolyte reaches a first predetermined width, the controller  18  stops the flow of electric current produced by the power supply  30 . Stopping the flow of electric current is accomplished using a switch, relay, or other appropriate device (not shown). The controller  18  than commands the workpiece handling system  16  to remove the workpiece  20  from the first ECM station  12  and transfer the workpiece  20  to the second ECM station  14 .  
         [0031]     In a second embodiment, the controller also analyzes the current measurement of the first gap  28  provided by the measurement apparatus  34 . The workpiece handling system  16  is commanded to remove the workpiece  20  from the first ECM station  12  when the first gap  28  of electrolyte reaches the first predetermined width. The electric current is not stopped, but the electrical circuit is interrupted as the workpiece  20  is removed by the workpiece handling system  16 . No switch or relay is required to stop the flow of electric current. The controller  18  then commands the workpiece handling system  16  to transfer the workpiece  20  to the second ECM station  14 .  
         [0032]     As stated above, the second ECM station  14  functions in a similar manner to the first ECM station  12 . Referring now to  FIG. 3A , the second ECM station  14  comprises a second stationary electrode  36  and the electrolyte  24 . The second ECM station  14  may share the electrolyte  24  from the first ECM station  14 , or may have its own separate supply of electrolyte  24 . Preferably, the second ECM station  14  also comprises a second part holder  38  to secure the workpiece  20  during the ECM process. A second gap  40  of electrolyte is formed between the workpiece  20  and the second stationary electrode  36  after the workpiece handling system  16  has placed the workpiece  20  in the second part holder  38 . A second ultrasonic sensor  42 , preferably embedded within the second stationary electrode  36 , is operatively connected to the measurement apparatus  34  to determine the width of the second gap  40  of electrolyte. Electric current is applied and material is eroded from a second region of the workpiece  20 , as shown in  FIG. 3B . An independent power supply or the power supply  30  used in the first ECM station  12  may supply the electric current.  
         [0033]     Of course, as mentioned additional ECM stations could also be added to the ECM system  10 . Furthermore, additional stationary electrodes could be added to any of the ECM stations. The number of ECM stations and stationary electrodes per ECM station will vary depending on the type, size, and complexity of the machining requirements of the workpiece  20 .  
         [0034]     The ECM system  10  also comprises at least one electrolyte delivery system  44 . The electrolyte delivery system  44  supplies the electrolyte  24  to the first and second ECM stations  12 ,  14 . The electrolyte delivery system  44  includes pumps, hoses, and other related devices to maintain a certain pressure and flow of electrolyte  24  to the ECM stations  12 ,  14 . The electrolyte delivery system  44  also includes at least one electrolyte filtering device  46 . The electrolyte filtering device  46  filters material eroded from the workpiece  20  and other debris from the electrolyte  24  while maintaining the temperature, salt concentration, cleanliness, and pH level of the electrolyte  24 .  
         [0035]     Preferably, the controller  18  is operatively connected to the workpiece handling system  16 . This allows the controller to coordinate the machining and moving of the workpiece  20  to maximize throughput of a plurality of workpieces  20  through the ECM system. Accordingly, the ECM system  10  is designed to equalize a first time necessary to erode material from the first region of the workpiece  20  to a second time necessary to erode material from the second region of the workpiece  20 .  
         [0036]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.