GB2255303A

GB2255303A - Circuits for electrical discharge machining.

Info

Publication number: GB2255303A
Application number: GB9109481A
Authority: GB
Inventors: Ya-Chien Chung; Huann-Jen Yang
Original assignee: Industrial Technology Research Institute ITRI
Current assignee: Industrial Technology Research Institute ITRI
Priority date: 1991-04-30
Filing date: 1991-05-02
Publication date: 1992-11-04
Anticipated expiration: 2011-05-02
Also published as: GB2255303B; GB9109481D0; GB2255303A8

Abstract

A discharging circuit generates a triangular discharging current waveform; the ascending section of the triangular waveform being determined by means of a voltage and an inductance of the circuit, whilst the variation rate of a descending section of the waveform is determined by means of an inductance, a peak current and a resistance in the circuit so as to generate a negative and descending current variation rate. <IMAGE>

Description

1 1.

2 2 S 5 5 -"I'S A Discharging circuit arrangement for An Electrical Discharging Machine This invention relates to a discharging circuit for an electric discharging machine.

During using a discharging machine since the wire-cuttin- wave width electric of current waveform in an electric discharging machi.ne is too longr ( >1.0 tks), it would cause the breakage of the wire and a coppersticking phenonmenon; therefore, the wave width of etil-1.eil L waveform in an electric discharging machine for wire cii tt ip., is usually limited within 10,0s. In order to e I- c va I e the cutting speed, a considerable higher energy has to be 0 in the discharging gap within the -:xfores,-ii.(] perjod or t-..i ill e n 1 C5 i.e., to increase the value of peak 1) 11 r!I-) C, discharging, the wire electrode is under Iligh tellsi 1 c.

condition, and therefore the wire electrode is often hroken on -e f orm as a result of consumption. A triangular dischni-ling r piece from f as t can prevent the wire electrode and working consumption ratio; in other words, it can increase the cutting speed.

Although a capacitor type of discharging circuit can control the width of waveform by means of a proper inductance circuit, the to generate a triancruar :5 capacitance discharging value and an circuit is unable 1 1 1 discharging waveform, which Call be Oilly wIL11 a transistorized discharging circuit. Accordiii,--r Lo Lhe invention, a discharging machine including a discharging circuit and a dischargecontrolling circuit can tl:renerate a triangular section of determined discharging current waveform; the ascending the triangular discharging waveform is to be by means of a voltage and an inductance of the discharging circuit, while the variation rate of the,ing waveform is descending section of the triangular discharg to be determined by means of an inductance, a peak current and a resistance in the discharge- controlling circuit; the current in the descending section is controlled with a sharpe negative slope.

ZD An embodiment of this invention is described by way example with reference to the drawings, in which:

FIG.1 is a conventional capacitor type of discliar,,-,,-in,:, circuit.

FIG.2 is an equivalent discharging circuit diagram.

FIG.3 is a conventional storage capacitor type of dischargingr circuit diagram.

FIG.4 is a transistor type of discharging circuit diagram.

FIG.5 is a snubber circuit diagram which is added in the switch device as shown in FIG.4.

FIG.6 is an equivalent current circuit jiagram upon 2 the diode 14 becoming conductive as shown in FIG.4.

2 FIG.7 is an embodiment of the discharging circuit diagram according to the present invention.

FIG.8 is an equivalent circuit diagram as shown in FIg.7 upon the switch element being turned off.

FIG.9 illustrates a waveform in a capacitor type of' discharging circuit.

FIG.10 illustrates a triangular curretit underdamping condition.

Referring to FIG.1, a capacitor type of cliseliargi.iil,-circuit diagram comprises a direct current (D.C.) POWEPt SUPPLY 1, a resistor 2, a chopping dek-ice swiLch 3, a control-and-driving signal 4, a capacitor 5, aii(l a sjorlcpj.e 6.

During discharging, the power is mainly stipplied wi I b the g capacitor 5. Referring to Fig.2 (an e.qui,,-aleiit discli<ii,,-,,iii=. circuit diagram), the circuit diagram comprises a capacitor 5 which has a voltage of "Vc", an inductance L 8 which is unavoidable by wiring, and a gap voltage Vg 9. The current wave is an index form as shown in FIG.9, and the width of current waveform can be obtained with the following 11:1 equation:

tp= 7LAJLC The peak value of current:

Ip=(VC-Vg) / ic The peak value of current are closely related to and 3 the voltage across the capacitor during discharging; A t t5 peak value of a discharging current may be obtained with a storage capacitor type of discharging circuit as shown in FIG.3, which comprises a charging circuit switch 10 and a discharging circuit switch 11.

During charging, the charging circuit switch 10 is turned on, while the discharging circuit switch 11 is turned off. When the capacitor 5 is charged to a desired voltage level the charging circuit switch 10 will be turned off, while the discharging circuit switch 11 will be turned on to be ready for discharging; the aforesaid circuit can obtain a consistent result between the width of and the waveform crest; the major advantage current thereof a large current switching may not take place during current moment, but the drawback is that discharging waveform is unable to generated, drawback can be improved by using a discharging circuit as shown in FIg.4.

waveform is that the high a triangular The aforesaid transistorized In the transistorized discharging circuit, if the value of the limiting resistor 2 is relatively small- or zero, the ascending rate of current, upon the carrier-wave switch 3 being turned on, would be Sr=(Vs-Vg)/L in which Vs is the level of the D.C. power supply 1, and Vg is the gap voltage during dischargii-i-,,.

4 When the current is ascended to a desired value, the switch 3 has to be turned off; however, a directly turning off would damage the switch 3. If a snubber circuit such as a the aforesaid circuit, the aforesaid damage would be avoided. FIG.5 includes a resistor 12, a diode 14, and a capacitor 15; after the switch 3 is turned off, a current would first flow through the capacitor 15 on the output end of the switch 3, and the diode 14. An equivalent circuit of FIGS is shown in FIGS, which is substantially a LC circuit Lo receive a given current upon the Ip being increased; however, such a circuit is unable to generate a triangular discharging waveform in the descending section of the waveform.

RCD circuit as shown in FIG.5 is added ir According to the present invention, adischarging circuit is so designed that when the switch element is turned off, a negative current variation is to be generated by means of an equivalent circuit having a current to flow.

FIG.7 is an embodiment of a discharging circuit diagram according to the present invention, which comprises a resistor R1 1G, a resistor R2 17, a capacitor Cl 18, and a diode 19. When the current is increasing, the aforesaid circuit has an ascending rate of current, i.e., Sr= (Vs-Vg P P)/L in which Vs stands for the level of the D.C. power % 25 supply 1, Vg stands for the gap voltage, M stands for the j 1 1 inductance in the circuit. As soon as the current reaches the peak value Ip, the switch 3 will be turned off, while the diode 19 is turned on; an equivalent circuit thereof is shown in FIG.8; the variation curve of the current is shown as follows:

R1.IP + Sf.L=0 and then Sf=-Rl. Ip/L; likewise, the resistance of R1 16 can be obtained with the known reducing rate of current, Ip and L, i.e., Rl=isfi.L/IP.

In order to obtain an approximate triangular discharging waveform, the value of the capacitor Cl 18 must be designed properly. The aforesaid equivalent circuit is a RLC circuit with an underdamping function so as to obtain a better result as shown in FIG.10. The critical damping conditions of the RLC circuit may be satisfied with the following:

R I C 1 - 4 L= 0; under the condition of underdampin,g,,, 1 Cl < (4L / R 1) according to the above equation, ti-ie valuo of Cl 18 can be selected.

In FIG.7, the value of resistor R2 1.7 is designed in accordance with the value of Cl so as to let Cl 18 store 6 1 1 Z:

v energy during a charging period, and discharge cenipletely during the rest time of the discharge gap. A triangular discharging waveform may be obtained by means of the aforesaid circuit with a proper selection on the values of Rl, R2 and Cl so as to increase the cutting speed.

p Q 7

Claims

1.A discharging circuit for an electric-discharging machine, in which a discharging circuit controls a triangular discharging current waveform of said electric discharging machine so as to increase a cutting speed; and said discharging connected in 2 5 circuit comprising a switch element series with a voltage of a power supply being a wire electrode, a working piece, and a discharge-controlling circuit being connected between said wire electrode and said working piece; and said discharge-controlling circuit including a diode connected in parallel with a resistor R2, a capacitor Cl, and connected in series with a resistor R1; and by means of said discharge-controlling circuit, a current waveform in an ascending section of said discharging waveform being determined by means of a 1:)os,;el.supply voltage, a gap voltage during discharging, and ail inductance in said circuit, and the ascending rate of current being equal to an equation (i. e., said power-supply voltage minus said gap voltage, and then being tli,. ided ifith said inductance of said circuit); and s!he.n said currei-it ascending to a peak value Ip, said switch elenient ill said circuit being cut off so as to have a diode in said discharge-controlling circuit become conduct_ive, and to have said triangular discharging current waveform become a descending rate variation, i.e., (-Rl.1p/L), in which Rl 8 discharge C1 triaii5u]-ar j 1 1 being Rl in said discharge controlling circuit, lp being a peak current, and L being an inductance in said circuit.

2. A discharging circuit for an electric discharging :Y machine as claimed in claim 1, wherein said R1 value in said i discharge-controlling circlitit=JSfi.L/Ip, and a capacitance of said Cl being less than (4L/R1); and a valve of R2- being determined with (R2.Cl < resting time) so as to lia-sre an energy stored in said Cl fully discharged at said resting time; and Sf being a current variation rate, L beiii,.,r, an inductance of said circuit, while Ip being a peak current.

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