Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2001-03-12
2003-06-17
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069170
Reexamination Certificate
active
06580049
ABSTRACT:
TECHNICAL FIELD
This invention relates to improvements in an electric discharge machining method and apparatus for performing machining (rocking machining) while rocking an electrode with respect to a workpiece in a plane vertical to a machining feed direction.
BACKGROUND ART
Rocking machining is intended for efficiently ejecting work scrap with stirring by performing electric discharge machining to a workpiece while moving an electrode relatively with respect to the workpiece in a plane vertical to a machining feed direction. Also, simple shapes such as circle or rectangle are generally used as a rocking shape, and the shape similar to an electrode shape is obtained as the shape after machining the workpiece.
Such rocking machining includes means for performing constant-speed rocking with a constant swing speed, means for controlling the amount of electrode transfer according to an interelectrode voltage between an electrode and a workpiece as disclosed in JP-A-6-126540, means for controlling the amount of electrode transfer by the amount of residual machining calculated from a difference between an electrode position and a target machining shape as disclosed in JP-A-2-212026, and so on.
Also, there is means for dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether a target machining shape is attained every each division shape and completing the rocking machining when the rocking movement completion determination is made in all the division shapes, and such a machining method is disclosed in JP-A-2-212026, JP-A-6-126540, JP-A-10-166224, and so on.
In a method using an interelectrode voltage for a change in a swing speed, it is necessary to detect the interelectrode voltage during machining and predetermine the amount of electrode transfer based on interelectrode voltage data. Thus, an apparatus for detecting and calculating the interelectrode voltage and data of the amount of electrode transfer based on the interelectrode voltage data must be provided. Also, in constant-speed rocking, in the case of dividing a rocking shape and making a rocking completion determination, it becomes a constant swing speed even within the division shape in which a target shape has been attained and the rocking completion determination has been made, so that waste time increases. Further, in the constant-speed rocking, when a factor which deteriorates properties of a machined surface of abnormal electric discharge due to an electric discharge concentration or a short circuit etc. or secondary electric discharge performed through work scrap and so on occurs, the rocking is performed at the constant swing speed, so that continuous time of abnormal electric discharge etc. is the same at all the positions and it is difficult to break the continuation of the abnormal electric discharge etc. by rocking movement, with the result that machining tends to become unstable.
FIG. 7
is a diagram showing rocking paths, and as shown in
FIG. 7A
, there is a rocking path for performing machining by a predetermined amount of rocking after movement from the rocking coordinate origin to the X-axis positive direction and as shown in
FIG. 7B
, there is a rocking path for performing machining by a predetermined amount of rocking after movement from the rocking coordinate origin to a direction of 45° (for example, it is assumed that a counterclockwise direction is positive.) with respect to the X-axis positive direction. Also,
FIG. 8
is a diagram showing dividing examples of a rocking shape, and since a division is started on the X-axis of the rocking coordinates in the division of a conventional rocking shape, when the rocking shape is equally divided into n portions, there are a case of dividing one quadrant into an even number as shown in
FIG. 8A and a
case of dividing one quadrant into an odd number as shown in
FIG. 8B. A
division expression of such a division is given by N=&thgr;/360×S (where digits to the right of the decimal point are discarded) when it is assumed that the number of the division shape is N (N=0, 1, 2. . . , n−1) and an angle of an electrode position viewed from the rocking coordinate origin is &thgr; (the X-axis positive direction is &thgr;=0°) and the number of divisions of the rocking shape is S. In the case of making a completion determination every each division shape, depending on the number of divisions (for example, the case of equally making an even-numbered division in multiples of 8), when the completion determination is made at A
1
and A
2
of adjacent division shapes in a corner portion of a target machining shape of a workpiece as shown in
FIG. 9
, a large left section occurs in this corner portion and shape accuracy becomes worse. Also, in rocking machining of an elongated electrode shape as shown in
FIG. 10A
, a difference in a machining area per each division shape becomes large and as shown in
FIG. 10B
, two division shapes are used in the center of each side of a target machining shape of a workpiece, so that a large left section occurs and shape accuracy becomes worse when a completion determination is made, for example, at A
3
and A
4
as shown in FIG.
10
B.
FIG. 11
is an illustration showing a division example of a rocking shape in rocking machining capable of switching a swing speed every division shape, and in such rocking machining, the swing speed is determined on the basis of the amount of residual machining calculated from a difference between a target machining shape and the present electrode position and a high swing speed (for example, V
1
of
FIG. 11
) is given when a left section is small and a low swing speed (for example, V
2
of
FIG. 11
) is given when a left section is large. Also, in the case that an electrode moves from a division shape in which the high swing speed V
1
is given to a division shape in which the low swing speed V
2
is given, when the speed difference between the high swing speed V
1
and the low swing speed V
2
is large, the electrode reaches the inside of the division shape in which the low swing speed V
2
is given at the high swing speed V
1
due to a delay etc. of calculation time. Therefore, in such a case, a left section tends to occur, so that shape accuracy becomes worse and further machining time becomes long.
DISCLOSURE OF THE INVENTION
This invention is implemented to solve the problems described above, and an object of the invention is to obtain an electric discharge machining method and apparatus capable of improving machining shape accuracy and reducing machining time in the electric discharge machining method and apparatus with high machining stability of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes.
With an electric discharge machining method according to a first invention, in the electric discharge machining method of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all the division shapes, the rocking shape is divided so that either one or both of each corner and the center of each side of the target machining shape is located on a bisector or substantially a bisector of a division angle.
With an electric discharge machining method according to a second invention, in the electric discharge machining method of dividing a rocking shape for a change in a swing speed and a rocking movement completion determination and determining whether or not a target machining shape is reached every each division shape and completing rocking machining when the rocking movement completion determination is made in all
Katougi Hidetaka
Nakagawa Takayuki
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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