Electric heating – Metal heating – Cutting or disintegrating
Patent
1986-04-07
1988-11-29
Pellinen, A. D.
Electric heating
Metal heating
Cutting or disintegrating
B23H 102
Patent
active
047883995
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electrical circuit for electro-discharge machines, machining a workpiece by electro-erosive discharges in a dielectric medium with a machining gap between the electrode-tool and the workpiece, this last constituting itself an electrode, comprising means delivering erosive discharges through terminals supplying respectively said electrodes with the electrical erosive energy pulses and means for preignition supplying in the beginning of each erosive pulse a preignition pulse of higher voltage and lower energy than said erosive pulses, which ignite or ionize in the dielectric medium inside the machining gap each time a channel through which travels then the erosive discharge.
A circuit according to this generic definition is already known, namely in the description of the U.S. Pat. No. 3,893,013 in the name of the present inventor.
Besides, the description of the U.S. Pat. No. 3,604,885, mentioned as a "technical background", proposes a circuit nearing also the above mentioned generic description.
Nevertheless, formerly it has never been proposed means for regulation of the preignition voltage to a value considered as favourable, the inconstancy of the preignition peak voltage being a source of perturbations lowering the efficiency and the quality of the machining. The risk of the indesireable preignition peak voltage fluctuations is particularly great if the preignition energy is borrowed from the element such as the machining capacitor which temporarily and repeatedly accumulates the electrical erosive discharge energy. The document PCT/CF 84/00108 (priority here claimed, publication 1985) exposes, in its first fourteen pages, the general and detailed technical considerations regarding the electro-discharge machining. These fourteen pages are considered as included in the present specification by way of reference.
In a general way, the present invention aims to improve the electro-discharge machining systems with preignition previously known, the purpose of the present invention being particularly to provide an electrical circuit for an electro-discharge machine, working according to the preignition principle, in which the drawbacks of the previous systems can be avoided and especially in which the parameters conditioning the channel ignition as well as that of the electro-discharge machining could be adequately mastered.
According to the invention, the circuit for electrical discharge machining following the abovementioned generic description, realizes performances aimed by one or another independent claims statements. It should be pointed out that the characteristics stated in each independent claim intervene respectively for different problems of preignition stabilization.
Dependent claims define different embodiments of the invention which are particularly advantageous especially as regards the voltage stability, an easy detection of the tendency of the preignition energy rise, the constitution of the circuit allowing the preignition energy stabilisation manually or automatically, the simplicity and efficiency of preignition pulse generation, etc. . .
Regarding the particularity of the invention, it should be pointed out that the mentioned means of clamping can have either a voltage limiting characteristic, without a voltage stabilisation (for example, a Zener diode in series with a not negligible resistor), or having a really current stabilizing characteristic (for example a Zener diode without an ohmic resistance in series).
The machining gap being supposed to present an electro-disruptive characteristic, a parallel connection of a clamping circuit also supposed to be electro-disruptive, may seem paradoxical. In fact, everything being well considered, this paradox does not exist, since on the one hand, the machining gap is not equivalent to a classical electro-disruptive element and, on the other hand, there are means allowing to control the gap according to the preignition pulse parameters, which maintain equal both voltage values "apparently electro-disruptive" (but in wh
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Evans Geoffrey S.
Pellinen A. D.
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