Abstract:
An apparatus of asynchronous electric discharge machine for wire cut adopted for use in machine industries employs a first electric discharge machine unit and a second electric discharge machine unit to provide electric energy to a cutting wire to generate alternate ignition and discharge on a work piece. The asynchronous operation uses two different discharge circuits in two different time sequences to reduce the probability of occurring discharge at the same spot and effectively reduce pause time, and prevent the cutting wire from rupturing, thereby to reduce production cost and improve operation efficiency.

Description:
FIELD OF THE INVENTION 
   The invention relates to an apparatus of electric discharge machine for wire cut adopted for use in machinery industries, particularly to an apparatus of asynchronous electric discharge machine for wire cut that performs machine operations alternately. 
   BACKGROUND OF THE INVENTION 
   Electric discharge machine is an indispensable machine method nowadays. Its basic principle is explained briefly as follows. The problems occurred at present also will be discussed. 
   In principle, electric discharge machine is a thermal machine method that converts electric energy to thermal energy of work pieces and rapidly melts the work pieces. In other words, in electric discharge machine an electric arc discharging phenomenon occurs through a machine liquid in a very close gap formed between the electrode and the work piece, and a heating effect takes place on the work piece to result in melting of the work piece. The work piece forms an electric discharge trace due to electric discharging. The process is repeatedly performed to fabricate a product forming a desired shape. 
   Refer to  FIG. 1  for a conventional wire cut electric discharge machine apparatus. First, an ignition power supply device  11  provides the required power and connects to an upper machine guide  12  and a lower machine guide  13  in a parallel connection, and also connects to a work piece  14 . A cutting wire  16  has two ends connecting respectively to the upper machine guide  12  and the lower machine guide  13  to establish electric connection. The upper machine guide  12  (or the lower machine guide  13 ), work piece  14  and cutting wire  16  form an ignition circuit. A main power supply device  15  is located between the upper machine guide  12  (or lower machine guide  13 ) and the work piece  14  to form a discharge circuit. An ignition switch  17  is provided to activate the ignition power supply device  11 , for supplying electric power. Through the ignition circuit, an electric arc is generated between the cutting wire  16  and the work piece  14 . Once the electric arc occurs, the ignition switch  17  is turned off and a main discharge switch  18  is activated. Through the main discharge circuit, the main power supply device  15  provides electric power, to produce an electric discharge machine phenomenon between the cutting wire  16  and the work piece  14 . As a result, the work piece  14  generates heat and melts partially to form a required shape. Finally the main discharge switch  18  is turned off and pauses for a selected time period. 
   Refer to  FIG. 2  for the time sequence of a conventional wire cut electric discharge apparatus. As shown in the drawing, electric power is supplied concurrently to the upper machine guide and the lower machine guide. The ignition time A of the upper machine guide and the ignition time B of the lower machine guide are synchronously activated at the ignition time E 1 . The discharge time C of the upper machine guide and the discharge time D of the lower machine guide also synchronously occur at discharge time E 2 . Then the process is stopped for a preset off time E 3 . After the work piece is insulated from the cutting wire, the foregoing machine process is repeated. Operation energy is simultaneously generated from the upper machine guide and the lower machine guide as follows:
 
 E   1 =(11+12)× Vg 
 
where E 1  is energy,  11  is the electric current of the upper machine guide,  12  is the electric current of the lower machine guide, Vg is the voltage in the gap between the work piece and the cutting wire. Discharge power is as follows:
 
  P   1 = E   1 × F   1 
 
where P 1  is the discharge power, F 1  is the discharge frequency.
 
   In conventional techniques for high speed machine, the detected discharge frequency is about 80 kHz, if the off time is set at 8 us. As every discharge must be followed by a waiting off time to recovery the discharge gap insulating again, shortening the off time can effectively increase the discharge frequency and improve machine efficiency. 
   SUMMARY OF THE INVENTION 
   The invention effectively reduces discharge off time and provides an apparatus of asynchronous electric discharge machine for wire cut, that alternately supplies electric power to the upper machine guide and the lower machine guide, for a significant reduction of discharge off time, an increase of discharge frequency, and for a higher cutting speed. 
   The invented apparatus of asynchronous electric discharge machine for wire cut mainly includes an ignition power supply device to provide electric energy required in the operations of the apparatus, a first electric discharge machine unit and a second electric discharge machine unit connecting to the ignition power supply device. The first electric discharge machine unit and the second electric discharge machine unit have respectively an upper machine guide and a lower machine guide connecting to a cutting wire. Through the ignition of an independent first ignition module and a second ignition module, the first electric discharge machine unit and the second electric discharge machine unit alternately generate electric arc discharge to the work piece, to melt the work piece and form a desired shape. The circuits for the two electric charges are different. Possible discharge at the same spot is greatly reduced. Machine off time shortens to 3 us is possible, and discharge frequency may increase to 133 Khz. Thus discharge frequency increases nearly 1.6 times. Because the invention adopts asynchronous discharge, and the current paths of the two discharges are different, the problems of conventional techniques that have the same discharge spot and a repeated electric arc discharge phenomenon may be prevented, and machine frequency greatly increases. 
   Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a schematic view of a conventional electric discharge apparatus for wire cut. 
       FIG. 2  is a schematic view of the timing chart of a conventional electric discharge apparatus for wire cut. 
       FIG. 3  is a schematic view of the asynchronous electric discharge machine apparatus for wire cut, according to the invention. 
       FIGS. 4A and 4B  are process flow charts of the method of the asynchronous electric discharge machine apparatus for wire cut, according to the invention. 
       FIG. 5  is a time sequence control chart of the method of the asynchronous electric discharge machine apparatus for wire cut, according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 3 , the invented asynchronous electric discharge machine for wire cut has an ignition power supply device  10  to provide electric energy required for ignition, for activating electric discharge. It may be an AC or DC power supply device. There are a first electric discharge machine unit  100  and a second electric discharge machine unit  200  including respectively an upper machine guide  20  and a lower machine guide  30 , connecting to the ignition power supply device  10  in a parallel connection. A cutting wire  40  is provided with two ends connecting respectively to the upper machine guide  20  and the lower machine guide  30 , to establish a good electric connection. The cutting wire  40  generally is a copper wire or copper alloy wire with excellent conductivity. The first electric discharge machine unit  100  further includes a first ignition module  110  which has one end connecting to the upper machine guide  20 , another end connecting to the ignition power supply device  10 , and a first ignition switch  60 . There is also a first main discharge module  120  which has one end connecting to the upper machine guide  20 , another end connecting to a work piece  50 , and a first discharge switch  61 . There is a first power supply device  62  between the upper machine guide  20  and the work piece  50 . 
   The second electric discharge machine unit  200  is constructed like the first electric discharge machine unit  100 . It includes a second ignition module  210  with one end connecting to the lower machine guide  30 , another end connecting to the ignition power supply device  10 , and a second ignition switch  70 . There is a second main discharge module  220  which has one end connecting to the lower machine guide  30 , another end connecting to the work piece  50 , and a second discharge switch  71 . There is a second power supply device  72  between the lower machine guide  20  and the work piece  50 . 
   Refer to  FIGS. 4A and 4B  for the process of the invention. First, activate the first ignition switch (step  100 ) to enable the ignition power supply device to provide a first ignition energy to the upper machine guide (step  110 ), and to generate ignition between the upper machine guide and the work piece (step  120 ); turn off the first ignition switch after the ignition has taken place (step  130 ); activate the first discharge switch (step  140 ); provide electric energy through the first power supply device and generate discharge between the cutting wire and the work piece through the connection of the upper machine guide, and process cutting machine on the work piece for a selected time period (step  150 ); immediately turn off the first discharge switch and stop operation for a preset time period (step  160 ); then stop the operation of the first electric discharge machine unit, and the second electric discharge machine unit takes over and continues the operation. First, activate the second ignition switch (step  200 ) to enable the ignition power supply device to provide a second ignition energy to the lower machine guide (step  210 ), and to generate ignition between the lower machine guide and the work piece (step  220 ); turn off the second ignition switch while the ignition takes place (step  230 ); activate the second discharge switch (step  240 ); provide electric energy through the second power supply device and generate discharge between the cutting wire and the work piece through the connection of the lower machine guide, and process cutting machine on the work piece for a selected time period (step  250 ); turn off the second discharge switch and stop operation for a preset time period (step  260 ). Repeat the processes from step  100  to step  260  until the product is formed in the desired shape. 
   Refer to  FIG. 5  for the time sequence control of the method of the asynchronous electric arc machine apparatus for wire cut according to the invention. Comparing  FIG. 2  with  FIG. 5 , it shows that the ignition time A 1  of the upper machine guide is executed for a period of the first ignition time F 1  (this time period is to initiate the discharge, the time duration cannot be precisely controlled); next, proceed the discharge time A 3  of the upper machine guide for a preset duration of the first discharge time period F 2 ; then stop the operation for a preset duration of the first off time period F 3 . Then immediately, the ignition time A 2  of the lower machine guide is proceeded for a selected time period after the second ignition time G 1  is activated, and the discharge time A 4  at the lower machine guide proceeds for a preset duration of the second discharge time period G 2 ; finally, stop the operation for a preset duration of the second off time period G 3 . The aforesaid steps are repeatedly executed for machine operations on the work piece. The invention is an asynchronous process that is different from the conventional process of synchronous ignition and discharge. Furthermore, the energy supplied by the invention is as follows:
 
 E   3 = I   3 × Vg 
 
I 3  is the electric current of the upper machine guide or the lower machine guide, or may be adjusted as the sum of the electric current of the conventional upper machine guide and lower machine guide. Therefore, the energy obtained is the same as the energy obtained by a conventional one. The operation power is:
 
 P   3 = E   3 × F   3 
 
P 3  is the discharge power, F 3  is the discharge frequency.
 
   The invention aims to provide alternate and asynchronous discharge for the upper machine guide and the lower machine guide. Hence the current paths of the first discharge and the second discharge are different. As a result, the off time is shorter than the off time of conventional techniques. It prevents discharge at the same spot or a repetitive arc discharge effectively, and avoids rupture of the cutting wire. 
   In summary, the invented method and apparatus of asynchronous electric discharge machine for wire cut employs independent ignition modules and main discharge modules to generate ignition discharge alternately, for melting the work piece, processing cutting machine. The current paths of two discharges are different. Thus the off time is much shorter than the off time used by conventional machine, and operation efficiency increases greatly. In addition, continuous discharge on the same spot is avoided, rupture of the cutting wire is prevented, and the service life of the cutting wire increases. 
   While the preferred embodiment of the invention has been set forth for the purpose of disclosure, modifications of the disclosed embodiment of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments not departing from the spirit and scope of the invention.