Gear cutting – milling – or planing – Milling – Machine frame
Reexamination Certificate
2001-07-17
2004-09-07
Wellington, A. L. (Department: 3722)
Gear cutting, milling, or planing
Milling
Machine frame
C409S137000, C409S211000, C029S03300H, C029S563000
Reexamination Certificate
active
06786686
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a numerically controlled machine tool for machining a large workpiece such as an aircraft part mounted on a workpiece support unit by moving a spindle having a tool mounted thereon in the directions along an X-axis, a Y-axis and a Z-axis with respect to the workpiece.
BACKGROUND ART
In production of an airframe of an aircraft, a method has been conventionally employed in which component parts of the airframe are divided into a plurality of segments and the segments are machined and joined with each other with bolts and rivets. In recent years, however, the trend is toward integrating these parts as far as possible and thereby reducing the jointed portions. As a result, the parts to be machined have increased in size and have become complicated in shape, thereby giving rise to the demand for a novel machine tool for machining such parts.
The unique performance requirements of such a machine tool include the provision of a table on which a large workpiece can be mounted, the provision of a sufficient long stroke in feed axes to machine a large workpiece and the possibility of machining a large part having a complicated shape at any points and in any kind of shapes by a single setup. Further, such parts are required to be machined efficiently, at high speed and with high accuracy. Also, in view of fact that a desired size of a workpiece to be machined varies from one machine tool user to another, the machine tool of a size required by each user can preferably be produced and installed in the factory quickly and at an appropriate time.
For the purpose of fixedly mounting a large workpiece, the table of the machine tool must be large, and it is necessary to take into consideration that the movability of the large table in the directions along three orthogonal linear feed axes, i.e., an X-axis, a Y-axis and a Z-axis, or in the directions along three rotational feed axes, i.e., an A-axis, a B-axis and a C-axis, is disadvantageous from the viewpoint of ensuring the high-speed, high-accuracy machining. Therefore, a machine tool for machining a large part, unlike normal machine tools, is required to have a fixed table and also requires that the spindle rotating with the tool held thereon is provided with orthogonal linear feed units and rotational feed units and is thereby movable in the directions along orthogonal linear feed axes and in the directions along rotational feed axes.
In addition, since a large workpiece is liable to deteriorate an efficiency of a workpiece setup process, the table for fixedly mounting the workpiece thereon is required to include means for automatically changing the workpiece for improving an efficiency of the setup process and an operating rate of the machine tool.
It is noted that the X-axis and the Y-axis are orthogonal to each other in a vertical plane, and extend horizontally and vertically, respectively, while the Z-axis extends in a horizontal direction perpendicular to both the X-axis and the Y-axis. It is also noted that the directions along the A-axis, the B-axis and the C-axis are defined as the directions of rotation about the X-axis, the Y-axis and the Z-axis, respectively.
A first prior art available for satisfying these requirements is a symmetric multiaxial linear motor machine tool described in Japanese Unexamined Patent Publication (Kokai) No. 8-318445. The machine tool includes a vertical gantry movable in a direction along the X-axis on vertically opposed frames, a saddle movable in a direction along the Y-axis on the vertical gantry, a ram adapted to be movable in a direction along the Z-axis on the saddle, a spindle head disposed at the front end portion of the ram for rotatably supporting a spindle having a tool mounted thereon, and a table fixed on the front portion of the frame for mounting a workpiece thereon. The X-, Y- and Z-slides are driven in the feed directions along the X-, Y- and Z-axes by linear motors. The vertical gantry is guided on two sides, upper side and lower side, with respect to the frame and driven by the linear motors. The arrangement of a stator (static element) and a mover (moving element) of the linear motor is symmetrical on the upper and lower sides of the frame so that the attraction forces of the stators acting on the movers, in both the upper and lower linear motors, are vertically offset from each other.
A second available prior art is a machine tool described in Japanese Unexamined Patent Publication No. 9-262727. The machine tool includes a vertical bed in the shape of a rectangular frame having a through opening at the center thereof in front view, an X-slide in the shape of a rectangular frame movable in a direction along the X-axis on the front side of the vertical bed and having a through opening at its center in front view, a Y-slide adapted to be movable in a direction along the Y-axis while being supported and guided in the through opening of the X-slide, a Z-slide adapted to be movable in a direction along the Z-axis while being supported and guided by the Y-slide, a spindle head disposed at the front end portion of the Z-slide for rotatably supporting a spindle having a tool mounted thereon, and a table fixed on the front portion of the vertical bed for mounting a workpiece thereon. The X-, Y- and Z-slides are guided by a pair of rail-shaped guides and driven in the feed directions along the X-, Y- and Z-axes by a pair of linear motors.
Further, a third available prior art is a workpiece pallet exchange method described in Japanese Unexamined Patent Publication No. 60-29261. The machine tool with a pallet changer disclosed in this patent publication includes a machine body for machining a workpiece by relative movement in directions along the X-, Y- and Z-axes between a spindle head for rotatably supporting a spindle having a tool mounted thereon and a table for mounting the workpiece thereon, and a pallet changer disposed adjacent to the machine body for giving and receiving the pallets to/from the table to exchange them. The pallet changer has a plurality of surfaces for mounting pallets thereon and is so structured to rotate about a horizontal rotational axis and thereby to index a w pallet change position, a standby position or a workpiece cleaning position.
As described above, a large machine tool for machining a large part such as a machine tool for machining aircraft parts is generally provided with a fixed, immovable table for mounting a large workpiece thereon, and a rotating spindle thereof having a tool held thereon is provided with an orthogonal linear feed units and/or rotational feed units, thereby allowing for the movement of the spindle in the directions along the X-, Y- and Z-axes and the rotation thereof in the directions along the A-, B- and C-axes. In addition, such machine tool generally has a horizontal spindle, which can move in a relatively long stroke along the X- and Y-axes. Therefore, a tall, large column is moved by being guided on the bed in the horizontal direction along the X-axis while the spindle head moves on the column in the direction along the Y-axis.
As described above, the larger workpiece results in an increased time for the setup process including operations of mounting the workpiece on the table and removing chips from the workpiece or demounting the workpiece from the table after machining. Therefore, during the setup process, the operation of the machine tool is inevitably stopped, thereby resulting in the problem of a low machine operating rate. Further, a movable body (for example, the spindle head and the column) moved in the direction along the X-axis is unavoidably larger and heavier. This makes it difficult to feed the movable body at high speed and also causes another problem of making it difficult to maintain a high positional accuracy in direction along the X-axis due to friction resistance caused by the weight of the movable body moved in the direction along the X-axis.
A method for solving the problem of the reduced working efficiency and the low machine operating rate due to the longer t
Makino Milling Machine Co., Ltd.
Paul & Paul
Ross Dana
Wellington A. L.
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