Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2002-05-06
2004-03-30
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06713706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an electric discharge shaping/profiling machine such as a die sinking electric discharge machine, an electric spark machine or the like for shaping or profiling (i.e., machining in more general terms) a workpiece by applying a pulse-like voltage across an electrode and the workpiece between which a processing liquid or solution such as a dielectric liquid intervenes. More particularly, the present invention is concerned with a jump control apparatus for the electric discharge shaping/profiling machine, which apparatus is designed for improving the precision of machining (or machining precision) while allowing the time taken for the machining process to be shortened essentially without being influenced by geometrical factors such as shape or profile to be finally imparted to the workpiece.
2. Description of Related Art
In the electrical discharge shaping/profiling machine such as the die sinking electric discharge machine or the like employed heretofore for shaping or profiling a workpiece such as a die or the like, a high-frequency electrical spark is discharged from a metal tool serving as a tool electrode to disintegrate electrically conductive materials from a workpiece such as of hardened steel or the like. The tool electrode and the workpiece are immersed in a dielectric liquid (processing liquid), and a feed mechanism maintains a spark gap between the tool electrode and the workpiece. As spark discharges melt the materials of the workpiece, the particles are flushed away, and the tool electrode advances. The process is accurate and is used for machining dies, molds, holes, slots, and/or cavities of almost any desired shape.
In the electric discharge shaping/profiling machine of this type, the tool electrode and the workpiece are immersed in the processing liquid so that the liquid intervenes between the tool electrode and the workpiece. This is for the purpose of suppressing temperature-rise at a location where the electric discharge takes place to thereby prevent occurrence of accident such as misfire due to the discharge spark.
In the course of the electric discharge machining, sludge (i.e., pulverized materials or particulates) is produced from a surface of the workpiece being machined. If the sludge should be left as it is, performance of the electric discharge taking place between the tool electrode and the workpiece will be lowered, involving degradation in the precision of machining. For this reason, it is required to remove or discharge the sludge as speedily and timely as possible.
Such being the circumstances, there has heretofore been proposed a jump control apparatus for moving upwardly and downwardly the tool electrode of the electric discharge shaping/profiling machine in succession to the pulse-like electric discharge to thereby remove or discharge the sludge produced during the machining process substantially on a real time basis.
With this type of the jump control apparatus for the electric discharge shaping/profiling machine, when the tool electrode is moved downwardly relative to the surface of the workpiece being machined, the dielectric liquid or processing liquid intervening between the tool electrode and the workpiece is caused to forcibly flow onto the surface of the workpiece being machined, whereby the sludge is caused to be flushed away from the surface of the workpiece being machined.
In this conjunction, it is however noted that in case the jumping velocity of the tool electrode is smaller than the optimal value, the amount of the processing liquid which is displaced from the surface of the workpiece being machined will decrease. As a result of this, when the tool electrode is moved upwardly, the liquid containing the sludge again flows back onto the surface of the workpiece being machined, rendering it difficult or impossible to remove the sludge.
Such being the circumstances, in order to allow the sludge to be removed speedily and effectively, it is required to set optimally the so-called jump conditions (e.g. jump-up quantity and jumping velocity) for the tool electrode by taking into consideration not only the properties of the processing liquid such as viscosity but also mechanical factors (e.g. mechanical strength) of a main spindle employed for driving the tool electrode.
As the hitherto known jump control apparatus for the electric discharge shaping/profiling machine, there may be mentioned those disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 309630/1998 (JP-A-10-309630) and Japanese Patent Application Laid-Open Publication No. 200 1-9642 (JP-A-2001 -9642), respectively.
In the case of the jump control apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 309630/1998, the jump-up quantity is determined on the basis of the area of the workpiece being machined, depth thereof and the like factors, whereon the jumping velocity is automatically set through a fuzzy logic or inference on the basis of the area being machined and the spark gap in precedence to initiation of the jump control.
However, in the case of the jump control apparatus described just above, it is noted that upon setting the jump conditions, no consideration is paid to the change or variation which may occur in the distance (spark gap) between the tool electrode and the workpiece in dependence on the conditions for the electric discharge as well as in the machined-surface length between the machining surface defined at the tip end of the tool electrode (i.e., bottom surface of the tool electrode) and the top surface of the workpiece.
Consequently, when the distance between the tool electrode and the workpiece (i.e., one of the conditions for the electric discharge) is set to be large and/or when the shape or profile resulting from the machining presents a tapered portion and/or a curved surface, it is difficult or impossible to remove the sludge by flushing with the processing liquid.
As a result of this, such situation may arise that the machining process for the workpiece does not proceed speedily and smoothly. Besides, the desired machining precision may not satisfactorily be achieved.
Further, in the jump control apparatus described above, the jump conditions are set or established through the fuzzy logic inference. Consequently, in the case where the tool electrode is of a rib-like form (i.e., when the desired finished shape of the workpiece is of a rib-like form), which means that the area subjected to the machining process is large, the jump-up quantity of the tool electrode may be estimated or inferred to be smaller than the demanded or desired value.
However, for discharging or removing the sludge by flushing with the processing liquid carrying the sludge, a large jump-up quantity is ordinarily demanded. Accordingly, with the small jump-up quantity such as mentioned above, there may arise such unwanted situation that the sludge can not adequately be removed.
On the other hand, in the jump control apparatus for the electric discharge shaping/profiling machine disclosed in Japanese Patent Application Laid-Open Publication No. 2001-9642 (JP-A-2001-9642), the feeding speed for the jump motion of the tool electrode is set to 20 m/min at the lowest, while the tool electrode feeding acceleration/deceleration is set to be not lower than 1.0 G.
In this case, however, since the moving speed of the tool electrode may be set to a value greater than a permissible value, there may take place a region of negative pressure at or along the bottom surface of the tool electrode when it moves upwardly, as a result of which mechanical damage and degradation of the machining precision may unwantedly occur due to deformation of the main spindle, giving rise to a problem.
It is further noted that in the apparatus disclosed in both the publications cited above, a feed-back control system is adopted for controlling optimally the jump conditions stepwise progressively in the course of the machining process. As a consequence, a lot of tim
Akiyoshi Masao
Yuzawa Takashi
Evans Geoffrey S.
Leydig , Voit & Mayer, Ltd.
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