Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2000-06-12
2001-10-30
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069110, C219S069160
Reexamination Certificate
active
06310313
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in an electrical discharge apparatus, and more particularly to improvements in an electrical discharge apparatus capable of maintaining for long periods of time the effect of lubricating balls or rollers used in sliding portions of mechanically driven parts, and improvements in an electrical discharge apparatus capable of preventing a decline in the operating efficiency due to a condition such as a machining stop during an abnormality of a lubricant supplying unit for supplying a lubricant to the mechanically driven parts.
2. Description of the Related Art
In an electrical discharge apparatus for machining a workpiece by supplying working electric power to a gap between the workpiece and an electrode provided in a working fluid, it is well-known that unless machining debris produced in the machining gap is eliminated by some method, the insulation between the electrode and workpiece and the repetition of electric discharge cannot be maintained in proper states, and that a state of arc discharge occurs, producing adverse effects such as a decline in the machining efficiency and the deterioration of characteristics of the machined surface.
As a technique used in conjunction with the injection, ejection, and suction of a working fluid to discharge the machining debris from the machining gap, the so-called electrode jumping operation is known in which the electrode is intermittently made to undergo reciprocating motion at a high speed. In the case of a machining configuration for which fluid processing, such as the injection, ejection, and suction of the working fluid to discharge the machining debris, cannot be physically used, the electrode jumping operation is the only method of discharging the machining debris and is generally regarded as one of the machining conditions.
An example of this electrode jumping operation is shown in
FIG. 12
, in which the ordinate shows the position of the electrode, while the abscissa shows the time. Parameters of the electrode jumping operation include an amount of rise of jump,
201
, jump time
202
, machining time
203
, and a jump speed. For example, in a case where the machining depth is large, by securing a sufficiently large amount of rise of the jump, the discharge of the machining debris from the deep machined hole is made possible. Further, the jump speed affects the jump time (wasteful time) which does not contribute to machining as well as the machining-debris discharging efficiency. Thus, the setting of the parameters of the electrode jumping operation is very important to improve the machining rate by discharging the machining debris with high efficiency.
In addition, to improve the machining efficiency, it is the general practice to repeat the electrode jumping operation at a high speed and a high acceleration. For example, the conditions of the electrode jumping operation in which the amount of rise of the jump is 0.2 mm and the maximum rate of arrival reaches 1,000 to 5,000 mm/min are set values which are commonly used frequently, and the speed and the acceleration are very large. Under such conditions of the electrode jumping operation, the load applied to mechanically driving parts, such as a ball screw and guides, which are generally used in the electrical discharge apparatus is very large, and it is difficult to form and maintain oil films of a lubricant on their sliding surfaces.
Further, in the electrical discharge apparatus in which positional changes during machining are very small and machining is carried out for long periods of time as compared with general machine tools, the wear of sliding surfaces of the mechanically driving parts is sometimes accelerated locally. If the wear of the sliding surfaces continues to be accelerated locally, a decline in the machining accuracy, in particular, constitutes a problem in the electrical discharge apparatus for which working accuracy on the order of microns is required. Therefore, to avoid the occurrence of such wear, it is extremely important to supply the lubricant constantly or intermittently to the mechanically driving parts such as the ball screw and the guides.
If the lubricant fails to be supplied to the mechanically driven parts due to the shortage of the lubricant or a failure of a lubricator, an advance in the wear of the mechanically driven parts is acceleratedly promoted, and the dust of wear produced continues to bite into the sliding surfaces, with the result being that the mechanically driven parts are subjected to further damage.
Furthermore, with the electrical discharge apparatus, since the time of performing unmanned operation is long, and high-accuracy machining is required, it is necessary to provide some protective function or other in preparation for such a situation in which the supply of the lubricant is stopped. Accordingly, a protective function is provided for forcibly terminating a machining program in progress in the event that the supply of the lubricant is stopped during the operation of the electrical discharge apparatus. However, if such a protective function is operated, since the time of performing unmanned operation is long in the electrical discharge apparatus as described above, the decline in the operating efficiency due to the stoppage of the scheduled machining in its course has presented a large problem.
SUMMARY OF THE INVENTION
The present invention has been devised to overcome the above-described problems, and its primary object is to obtain an electrical discharge apparatus capable of maintaining for long periods of time the effect of lubricating balls or rollers used in sliding portions of mechanically driving parts during the electrode jumping operation.
In addition, a secondary object is to obtain an electrical discharge apparatus which has the function of monitoring the state of operation of a lubricant supplying unit for supplying a lubricant to the mechanically driving parts, and which is capable of preventing a decline in the operating efficiency due to the stoppage of scheduled machining in its course upon detection of an abnormality in the remaining amount of the lubricant in the lubricant supplying unit or an abnormality of the lubricant supplying unit.
To attain these objects, the electrical discharge apparatus in accordance with the invention comprises: first electrode jumping means whereby the electrode is caused to jump with respect to the workpiece and in which an amount of rise of jump (an amount of rise of a first electrode jump) is set as one machining condition aimed at discharging machining debris produced during electric discharge; second electrode jumping means whereby the electrode is caused to jump with respect to the workpiece and in which is set an amount of rise of jump (an amount of rise of a second electrode jump) with which balls or rollers used on a sliding portion of a mechanically driving part of the electrical discharge apparatus undergo one revolution or more; and a unit for determining the jumping operation for making a comparison between the amount of rise of the first electrode jump and the amount of rise of the second electrode jump, wherein in a case where the amount of rise of the first electrode jump is smaller than the amount of rise of the second electrode jump, the second electrode jumping operation is effected in addition to the first electrode jumping operation.
In addition, the electrical discharge apparatus comprises: a lubricant supplying unit for supplying a lubricant to a mechanically driving part; a lubricant-remaining-amount monitoring unit having a function of detecting an abnormality in a remaining amount of the lubricant supplying unit or a remaining amount therein and outputting the same to a controller; and a lubricant-supplying-unit operation monitoring unit having a function of detecting an abnormality of the lubricant supplying unit and outputting the same to the controller, wherein machining is stopped after a program being executed is terminated in at least any one of a
Akune Mitsuaki
Kanaya Takashi
Ogawa Hajime
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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