Patent Application
20120312787
The present invention relates to an electrical discharge machining apparatus that removes or cuts a part of a workpiece at a plurality of locations at the same time by generating electrical discharge between the workpiece and a machining electrode opposed to the workpiece at a plurality of locations, and also relates to an electrical discharge machining method.
In a conventional electrical discharge machining apparatus, electrical discharge machining pulses are applied between a workpiece and each of a plurality of machining electrodes, which are opposed to the workpiece and are not electrically connected to each other, thereby performing electrical discharge machining at the same time (for example, Patent Literature 1). Moreover, when performing electrical discharge machining by causing one machining electrode to oppose to a workpiece at a plurality of locations, the impedance with the adjacent opposing section of the machining electrode is increased by increasing the distance from the adjacent machining electrode or coiling the machining electrode (for example, Patent Literature 2).
Patent Literature 1: Japanese Patent Application Laid-open No. H09-248719
Patent Literature 2: Japanese Patent Application Laid-open No. 2000-107941
However, because the above-described conventional electrical discharge machining apparatus is composed of a plurality of machining electrodes that are not electrically connected to each other, a machining electrode running system becomes complicated, therefore, it is difficult to realize multiple-parallel (for example, equal to or more than 10 in parallel) and narrow-gap (for example, 1 mm or less) machining.
Moreover, in a system in which one machining electrode is opposed to a workpiece at a plurality of locations and a section between the machining electrode and an adjacent machining electrode is coiled, space needs to be reserved for coiling the section, therefore, it is difficult to realize multiple parallel (for example, equal to or more than 10 in parallel) and narrow gap (for example, 1 mm or less). Moreover, in these systems, a machining preparation process for routing the machining electrode becomes complicated. Furthermore, the apparatus becomes larger as the parallel number becomes larger.
This invention is achieved in view of the above and has an object to avoid disconnection of the machining electrode and degradation of the quality of the machined surface by suppressing short-circuit current and to obtain a multiple-parallel and narrow-gap electrical discharge machining apparatus. Moreover, this invention has an object to shorten a machining preparation process and reduce the size of the apparatus.
In order to solve the aforementioned problems, an electrical discharge machining apparatus according to one aspect of the present invention is configured to include: a machining electrode that is one wire and includes a plurality of opposing sections with respect to a workpiece by being wound around a plurality of guide rollers; a driving unit that changes a relative distance between the workpiece and the opposing sections; and a plurality of pulse generating units that apply electrical discharge machining pulses between the workpiece and the opposing sections, respectively, wherein the pulse generating units are controlled such that application start times of electrical discharge machining pulses for adjacent opposing sections do not coincide with each other.
According to the present invention, abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface can be avoided by suppressing the concentration of the electrical discharge machining current, which flows largely immediately after the start of the application of an electrical discharge machining pulse, in a short-circuited portion. Moreover, abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface can be prevented while maintaining the machining speed regardless of the rate of the application time or the pause time of electrical discharge machining pulses. Moreover, because the gaps can be narrowed, the apparatus can be reduced in size. Furthermore, an effect is obtained in which the preparation process before the start of the machining is shortened.
Exemplary embodiments of an electrical discharge machining apparatus according to the present invention will be explained below in detail based on the drawings. This invention is not limited to these embodiments.
The workpiece 1 is fixed to a driving table 6 and the relative distance between the opposing sections 2a to 2j of the machining electrode 2 and the workpiece 1 can be changed by driving the driving table 6 by a motor 3. A pulse control unit 5 transmits a control signal that causes pulse generating units 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, and 4j to generate an electrical discharge machining pulse. Electrical discharge machining pulses generated in the pulse generating units 4a to 4j are fed to the opposing sections 2a to 2j of the machining electrode 2 via power feed contacts 9a, 9b, 9c, 9d, 9e, 9f, 9g, 9h, 9i, and 9j, respectively.
Moreover, the pulse control unit 5 instructs the pulse generating units 4b, 4f, and 4j to start applying an electrical discharge machining pulse at time 0.5, stop the application at time 1.5, and apply an electrical discharge machining pulse again at time 2.5. Moreover, the pulse control unit 5 sends an instruction to the pulse generating units 4c and 4g to apply an electrical discharge machining pulse from time 1 to time 2 and an instruction to the pulse generating units 4d and 4h to apply an electrical discharge machining pulse from time 1.5 to time 2.5.
This means that, although there is a timing at which a voltage is applied to a plurality of the opposing sections of the pulse generating units 4a to 4j at the same time (for example, the opposing sections 2a, 2d, 2e, 2h, and 2i at time 0.25 in
According to the present embodiment, power feeding is not started simultaneously to the opposing section 2e of the machining electrode that is in contact with the workpiece 1 and the opposing sections 2d and 2f adjacent to the opposing section 2e. Therefore, in a time period during which the peak current occurs, the impedance from the opposing section to the closest opposing section to which power feeding is started simultaneously increases by four times as much as the case of starting power feeding simultaneously to all the opposing sections of the machining electrode 2. Therefore, even when a short circuit occurs, the energy caused by electrical discharge machining pulses fed to the other opposing sections flowing into a short-circuited portion through the machining electrode can be suppressed considerably.
As a result, it is possible to provide a high-speed electrical discharge machining apparatus that generates electrical discharge at a plurality of locations at the same time while avoiding disconnection of the machining electrode and degradation of the quality of the machined surface. Moreover, the machining electrode 2 is supplied from one machining electrode bobbin 8 and there are only guide rollers 7a to 7d between the mutually adjacent opposing sections of the machining electrode, therefore, multiple parallel (for example, 10 or more) and narrowed gap (for example, 1 mm or less) can be easily realized.
Furthermore, it becomes possible to control pulses in the electrical discharge machining at the same time in the adjacent opposing sections 2a to 2j at a plurality of locations regardless of whether it is the time for which an electrical discharge machining pulse is applied or the time for which an electrical discharge machining pulse is paused, therefore, it is possible to provide a high-speed electrical discharge machining apparatus that generates a discharge in a plurality of non-adjacent opposing sections at the same time while suppressing energy flowing through the machining electrode 2 without reducing the discharge frequency.
Moreover, because the path of the machining electrode 2 does not need to be made long between each of the opposing sections 2a to 2j of the machining electrode 2, the apparatus can be reduced in size. Furthermore, because it is sufficient to wind the machining electrode around each of the guide rollers 7a to 7d only once in order, the preparation process before the starting of the machining can be shortened.
In the present embodiment, an example is given where the machining electrode 2 and the workpiece 1 are opposed to each other at ten locations, however, a similar effect can be obtained even with an electrical discharge machining apparatus that includes a machining electrode opposed to the workpiece at M locations (M is 2 or larger). The effect becomes greater as M becomes larger. Moreover, in the present embodiment, an equal difference is provided between the application start times of an electrical discharge machining pulse to be applied to adjacent opposing sections of the machining electrode, however, a similar effect can be obtained even if the difference is not uniform as long as the difference is made equal to or longer than the peak time (for example, 0.1 μsec) of current is provided.
Particularly, the electrical discharge machining apparatus according to the present embodiment can avoid abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface by suppressing the concentration of the electrical discharge machining current, which flows largely immediately after the start of the application of an electrical discharge machining pulse, in a short-circuit portion. Moreover, abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface can be avoided while maintaining the machining speed regardless of the rate of the application time or the pause time of electrical discharge machining pulses. Moreover, because the gaps can be narrowed, the apparatus can be reduced in size. Furthermore, the preparation process before the start of the machining can be shortened.
Moreover, the electrical discharge machining apparatus according to the present embodiment is particularly useful in a case where a large machining current flows immediately after the start of the application of an electrical discharge machining pulse, as in a system in which an electrical discharge machining pulse is applied between the workpiece and the machining electrode by electrically connecting a capacitor in which charge has been stored in advance to the workpiece and the machining electrode.
In the present embodiment, one machining electrode 2 is caused to oppose the workpiece 1 at the opposing sections 2a to 2j at a plurality of locations. However, even when each of a plurality of machining electrodes, which are electrically insulated from each other, is opposed to the workpiece in deionized water, if the intervals between the machining electrodes are narrowed (for example, 1 mm or less) and the machining electrodes are made parallel to each other over a long distance (for example, 150 mm or more), the resistance between opposing sections of adjacent machining electrodes becomes about a few hundred ohms or less, therefore, an effect similar to the present embodiment can be obtained.
A schematic diagram of the main part of an electrical discharge machining apparatus according to the second embodiment of the present invention is illustrated in
In this manner, the pulse control unit 5 according to the present embodiment does not apply an electrical discharge machining pulse to adjacent opposing sections (for example, the opposing section 2a and the opposing section 2b) at the same time, i.e., the pulse control unit 5 controls the pulse generating units 4a to 4j so as not to provide a time period during which an electrical discharge machining pulse is applied to adjacent opposing sections at the same time.
As a result, it is possible to provide a high-speed electrical discharge machining apparatus that generates electrical discharge at a plurality of locations at the same time while avoiding disconnection of the machining electrode and degradation of the quality of the machined surface. Moreover, the machining electrode 2 is supplied from one machining electrode bobbin 8 and there are only guide rollers 7a to 7d between the mutually adjacent opposing sections of the machining electrode, therefore, multiple parallel (for example, 10 or more) and narrowed gap (for example, 1 mm or less) can be easily realized.
Moreover, because the path of the machining electrode 2 does not need to be made long between each of the adjacent opposing sections 2a to 2j of the machining electrode 2, the apparatus can be reduced in size. Furthermore, because it is sufficient to wind the machining electrode around each of the guide rollers 7a to 7d only once in order, the preparation process before the starting of the machining can be shortened.
In the present embodiment, an example is given where the machining electrode 2 and the workpiece 1 are opposed to each other at ten locations, however, a similar effect can be obtained even with an electrical discharge machining apparatus that includes a machining electrode opposed to the workpiece at M locations (M is 2 or larger). The effect becomes greater as M becomes larger. Moreover, in the present embodiment, an equal difference is provided between the application start times of an electrical discharge machining pulse to be applied to adjacent opposing sections of the machining electrode, however, a similar effect can be obtained even if the difference is not uniform as long as the electrical discharge machining pulse is not applied to adjacent opposing sections at the same time.
In the electrical discharge machining apparatus according to the present embodiment, no electrical discharge machining pulse is applied to an adjacent machining electrode, therefore, this is equivalent to the fact that the impedance between machining electrodes opposed to the workpiece increases by at least twice or more and thus it is possible to prevent abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface. Moreover, because the gaps can be narrowed, the electrical discharge machining apparatus can be reduced in size. Furthermore, the preparation process before the start of the machining can be shortened. The electrical discharge machining apparatus according to the present embodiment is particularly useful in the case of using a pulse generating unit that uses a resistor and a transistor (including a field-effect transistor) and applies rectangular electrical discharge machining pulses.
In the present embodiment, one machining electrode 2 is caused to oppose the workpiece 1 at the opposing sections 2a to 2j at a plurality of locations. However, even when each of a plurality of machining electrodes is opposed to the workpiece in deionized water, if the intervals between the machining electrodes are narrowed (for example, 1 mm or less) and the machining electrodes are made parallel to each other over a long distance (for example, 150 mm or more), the resistance between opposing sections of adjacent machining electrodes becomes about a few hundred ohms or less, therefore, an effect similar to the present embodiment can be obtained.
The pulse generating units 4a to 4j are divided into groups, each including, for example, five pulse generating units in the order starting with the pulse generating unit 4a, and the pulse pattern storing unit 16 stores therein the order of applying an electrical discharge machining pulse in each group. Specifically, for example, the following order pattern is stored.
First→Third→Fifth→Second→Fourth→(thereafter, repeat from the First)
The pulse control unit 5 that has read the order of an electrical discharge machining pulse from the pulse pattern storing unit 16 instructs the pulse generating units 4a, 4b, 4c, 4d, and 4e to start applying an electrical discharge machining pulse in the following order.
4
a→4c→4e→4b→4d→(return to 4a)
In a similar manner, the pulse control unit 5 instructs the pulse generating units 4f, 4g, 4h, 4i, and 4j to start applying an electrical discharge machining pulse in the following order.
4
f→4h→4j→4g→4i→(return to 4f)
Moreover, the pulse control unit 5 instructs the pulse generating units 4b and 4g to apply an electrical discharge machining pulse between times 0.6 and 1.2 and times 1.6 and 2.2, instructs the pulse generating units 4c and 4h to apply an electrical discharge machining pulse between times 0.2 and 0.8 and times 1.2 and 1.8, instructs the pulse generating units 4d and 4i to apply an electrical discharge machining pulse between times 0.8 and 1.4 and times 1.8 and 2.4, and instructs the pulse generating units 4e and 4j to apply an electrical discharge machining pulse between times 0.4 and 1.0 and times 1.4 and 2.0.
According to the present embodiment, it is possible to store the appropriate order of starting the application of electrical discharge machining pulses to increase the difference between the application start times of an electrical discharge machining pulse for adjacent opposing sections of the machining electrode 2, therefore, the effect of electrical discharge machining pulses applied to the other opposing sections of the machining electrode 2 can be eliminated. Consequently, it becomes possible to provide a high-speed electrical discharge machining apparatus that generates electrical discharges at a plurality of locations at the same time while preventing abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface.
If the application time is longer, five adjacently arranged opposing sections are controlled so that the application of electrical discharge machining pulses is not started simultaneously in a similar manner to the third embodiment. If the unit of the number of the opposing sections, for which the application of electrical discharge machining pulses is not started simultaneously, is defined as N, then N is five.
Then, the application of electrical discharge machining pulses is started in the following order (Step S2) while providing a difference D that is one fifth of the sum of the application time and the pause time (Step S5) in the groups, each including five pulse generating units, in a similar manner to the third embodiment.
First→Third→Fifth Second→Fourth→(thereafter, repeat from the First)
As described above, in Step S5, a minimum interval D of the difference between the application start times of each electrical discharge machining pulse for different opposing sections when the application start times do not coincide with each other is determined by the following equation.
D=(application time+pause time)/N
On the other hand, in Step S1, when it is determined that the application time of an electrical discharge machining pulse is equal to or shorter than the pause time, N′ is calculated, which is given by (rounding down of (pause time/application time) after the decimal point) (Step S3). Then, N is defined as N′+1 and the second embodiment is selected (Step S4). When N=2, D=(application time+pause time)/2 in Step S5, therefore, the application of electrical discharge machining pulses for adjacent opposing sections of the machining electrode is started while providing a difference that is a half of the sum of the application time and the pause time in a similar manner to the second embodiment.
As described above, in the present embodiment, for example, the pulse control unit 5 determines the number N of continuously adjacent opposing sections of the machining electrode 2 whose application start times of an electrical discharge machining pulse do not coincide with each other, the minimum interval D of the difference between the application start times of an electrical discharge machining pulse when the application start times do not coincide with each other, and a pattern of the order of applying an electrical discharge machining pulse by the pulse generating units on the basis of the application time and the pause time of a given electrical discharge machining pulse pattern.
Moreover, the third embodiment selected in Step S1 is not limited to a case where N=5 and the embodiment selected in Step S1 is not limited to the above. Accordingly, it is obvious that various variations can be considered with respect to the present embodiment including changes in the pattern of electrical discharge machining pulses without being limited to the above embodiment.
According to the present embodiment, a pulse generation pattern can be controlled in accordance with discharge energy and an oscillation frequency, therefore, abnormal consumption and disconnection of the machining electrode and degradation of the quality of the machined surface can be prevented by preventing discharge energy from flowing from an adjacent opposing section of the machining electrode. Because a user does not need to examine and set a pulse generation pattern, an unskilled person can easily perform the machining and the automation.
Furthermore, the present invention is not limited to the above-described embodiments and various modifications can be made in the execution phase without departing from the scope of the invention. Moreover, in the embodiments described above, inventions in various phases are included, therefore, various inventions can be extracted by an appropriate combination of a plurality of disclosed components. For example, even when some components are removed from all the components illustrated in the embodiments, if the problems described in the Technical Problem section can be solved and the advantages described in the Advantageous Effects of Invention section can be obtained, then the configuration without the removed components can be extracted as an invention. Furthermore, components in different embodiments may be appropriately combined.
As described above, the electrical discharge machining apparatus and the electrical discharge machining method according to the present invention are useful in a system in which an electrical discharge machining pulse is applied between a workpiece and a machining electrode by electrically connecting a capacitor, in which electrical charge is stored in advance, to the workpiece and the machining electrode, and is particularly suitable to a case where large machining current flows immediately after the start of the application of an electrical discharge machining pulse.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-090902 | Apr 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP11/57841 | 3/29/2011 | WO | 00 | 8/20/2012 |
