Gear cutting – milling – or planing – Milling – Process
Reexamination Certificate
2001-04-09
2003-03-18
Howell, Daniel W. (Department: 3722)
Gear cutting, milling, or planing
Milling
Process
C082S001110, C409S200000
Reexamination Certificate
active
06533508
ABSTRACT:
TECHNICAL FIELED
The present invention relates to a machining apparatus and a machining method for machining a workpiece by rotating a tool and the workpiece relatively and, more particularly, to an apparatus and a method for rotating and revolving either the tool or the workpiece.
BACKGROUND ART
In a so-called contouring operation or a machining operation, a cutting tool having a cutting blade is revolved around a work material (workpiece) while the cutting tool is rotated on its own axis. This machining method is typically exemplified by an end milling operation, an example of which is described in Japanese Patent Laid-Open No. 63-212442 (JP-A-63-212442). According to the contouring method described in this publication, before the workpiece is machined by rotating and revolving an end mill, a turning diameter of an edge of the rotating and revolving end mill is measured with a laser beam, and a tool diameter of the end mill is compensated by means of tool diameter compensation function of a numerical control unit on the basis of the result of the aforementioned measurement. In an actual cutting operation, on the other hand, the end mill is at first inserted in the center of a bore to be cut and moved therefrom to a position where the edge of the end mill contacts with the inner surface of the hole to be cut, more specifically, to a position corresponding to a machining diameter, and thereafter moved along the inner face of the bore to be cut. In short, the end mill is revolved by rotating the end mill, as mounted on a spindle of a machine tool, on its own axis and by moving the spindle in a circular motion in a so-called X-Y plane.
In addition to the aforementioned apparatus, there is known an another type of apparatus using a mechanism of a polar coordinate system. More specifically, on a leading end of a main arm, which is rotated or given an oscillatory rocking motion by a motor, there are mounted a motor for the spindle and a tool shaft arm. On a leading end of the tool shaft arm, there is mounted a tool shaft which is rotated by the motor for the spindle. In this kind of apparatus, the tool shaft is moved in a circular motion, that is, revolved either by giving the main arm associated with the tool shaft arm a rocking motion or by rotating the main arm. Radius of revolution of the tool shaft are changed by varying relative angles of the tool shaft arm to the main arm.
There is known a still another type of apparatus which is constructed such that a tool shaft is so mounted on a first axis as to move in the radial direction thereof. This tool shaft is rotated with the first axis, resulting in the tool shaft revolving. The revolution radius of the tool shaft is changed by varying positions of the tool shaft in the radial direction of the first axis.
In the aforementioned contouring operation, a relative speed of the cutting blade to the work material, that is, a cutting speed corresponds to the sum of a circumferential speed of the cutting blade moving in response to rotation of the tool and a speed of a circular motion performed by the cutting blade moving in response to revolution of the tool. According to the aforementioned conventional contouring operation, however, the tool is revolved by giving the spindle having the tool mounted thereon a circular motion, so that the speed of revolution is far lower than the speed of rotation. Therefore, the cutting speed is substantially determined by the speed of rotation of the tool, that is, the number of rotation of the spindle.
In a conventional apparatus using a mechanism of the so-called X-Y coordinate system, the tool is revolved by coordinating the feeds of the spindle in the bisectional directions in the X-Y plane. This restriction of control makes it difficult to revolve the machine tool at a higher speed. When the spindle is moved in the bisectional direction, moreover, a spindle head is vertically moved along a column, and simultaneously with this, the column is horizontally moved on a bed. Thus, the members to be moved have so large mass that the spindle cannot be revolved at a higher speed.
On the other hand, the same problem may occur in an apparatus employing polar coordinate system, in which a reciprocating motion of the main arm is transmitted via its leading end to the tool shaft arm to cause the tool shaft to revolve. Specifically, the main arm is reciprocated with a motor imparting a reciprocating motion to the tool shaft arm and a motor rotating the tool shaft, and the tool shaft is revolved by driving these two motors cooperatively, as in the aforementioned apparatus employing the X-Y coordinate system. Therefore, it is difficult to increase the speed of revolution of the tool shaft.
In still another type of apparatus, too, the tool shaft is revolved with a motor for rotating the tool shaft, so that the overall mass to be revolved is increased, which makes it difficult to revolve the tool shaft at a higher speed. In an apparatus constructed to revolve the tool shaft, the motor for rotating the tool shaft changes its position according to a change of revolution radius of the tool shaft, so that a position of the center of the gravity of a rotating member as a whole changes. As the speed of revolution of the tool shaft is raised, therefore, its vibration may be increased.
In the prior art, in short, it is impossible to increase the speed of revolution of the tool shaft or the cutting tool mounted thereon, and a ratio of revolution speed of the spindle to the cutting speed is not more than 2 to 3%, so that the feed rate per revolution of the tool is lowered. To enhance the working efficiency, therefore, the working operation has to be performed by increasing the speed of rotation of the tool or increasing the width of the cutting blade.
If the cutting width is increased, however, the area where chips contact with the cutting blade is broadened, so that friction and heat is remarkably generated, thereby shortening the tool life. This results in the disadvantage that the working efficiency is greatly restricted. The aforementioned contouring work is the so-called intermittent cutting operation, in which the cutting blade bites into the work material repeatedly. In the method of the prior art as described above, on the other hand, the tool is revolved at a low speed and at a small feed rate, that is, the tool is rotated on its own axis at a high speed, thus increasing the number of times that the cutting blade bites into the work material repeatedly. When this cutting operation is performed, in other words, many wide and long chips are produced. Therefore, an impact force more frequently acts on the cutting blade. Moreover, this impact force is strong, so that the possibility of shortening the tool life is increased, which restricts the working efficiency.
The present invention has been made in consideration of the actual state of art as described above, and has an object to provide an apparatus and a method capable of improving a working efficiency in a machining operation performed by rotating a tool and a workpiece relatively to each other.
Another object of the invention is to provide an apparatus and a method capable of improving a working efficiency and a working accuracy by making it possible to vary a ratio between a number of rotation of the tool or the workpiece and a number of revolution of the tool or the workpiece.
Still another object of the invention is to provide a machining apparatus capable of raising a speed of revolution of the tool or the workpiece at a high level.
Another object of the invention is to provide a machining apparatus capable of changing a radius of revolution of the tool or the workpiece while rotating and revolving the tool or the workpiece.
Another object of the invention is to provide an apparatus and a method capable of improving the working efficiency without shortening the life of the tool.
DISCLOSURE OF THE INVENTION
The machining apparatus of the invention is provided with a spindle rotating while mounting a tool or a workpiece and a revolution shaft rotating on its ce
Howell Daniel W.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Toyota Jidosha & Kabushiki Kaisha
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