Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2000-04-14
2002-06-25
Rachuba, M. (Department: 3724)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S008000, C451S011000, C451S051000, C451S065000, C451S249000, C451S251000
Reexamination Certificate
active
06409573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a combination grinding machine adapted to sequentially grind a plurality of axially separated portions to be machined (hereinafter, called merely object portions) of a rotatably supported workpiece by means of a pair of cooperative grinding wheels which are controlled independently of each other to be fed in the axial and radial directions of the workpiece.
2. Description of the Related Art
A combination grinding machine of this kind; particularly, that for grinding a crankshaft includes a pair of wheel heads which each include a grinding wheel and which can be numerically controlled independently of each other to be fed in the axial and radial directions of the crankshaft, which serves as the rotatably supported workpiece. The pair of grinding wheels are controlled so as to efficiently and cooperatively grind a plurality of crank pins two at a time according to a machining program stored in a numerical control unit.
During grinding, the crankshaft is rotated about the axis of journals, so that the crank pins revolve around the axis of journals. The wheel heads advance and retreat synchronously with crankshaft rotation so as to advance and retreat according to the angular positions of the corresponding revolving crank pins.
Conventionally, in order to improve the profile irregularity of ground portions, a crankshaft which has undergone grinding undergoes lapping. The thus-completed crankshaft is attached to, for example, a cylinder block of an internal combustion engine for automotive use. For lapping, a separate lapping machine is employed. In the lapping machine, ground surfaces of the crankshaft are lapped by means of tape-shaped sand paper or polishing film.
Since grinding and lapping are performed by use of different machines, a crankshaft must be transported from a grinding station to a lapping station. Also, idle time consumed, for example, for positioning on a lapping machine is involved, thus impairing machining efficiency. Because of intensive wear of sandpaper or polishing paper, lapping involves a problem of the sandpaper or polishing paper breaking. Therefore, lapping itself is not highly efficient.
Further mover, although conventional lapping can improve surface roughness, the conventional lapping has the following drawback. That is, in the conventional lapping, sandpaper or polishing film is merely pressed against a crank pin via a floating mechanism without accurate control of the spatial relationship (i.e., relative position) between the sandpaper or polishing film and a crank pin. As a result, the lapping process impairs high roundness and cylindricity of crank pins which have been accomplished in the preceding grinding process.
SUMMARY OF THE INVENTION
A primary object of the present invention is to solve the above-mentioned problem involved in the conventional machining in which grinding and lapping are performed separately from each other.
Another object of the present invention is to prevent an impairment in geometrical accuracy of object portions in a lapping process subsequent to a grinding process.
Still another object of the present invention is to efficiently grind and superfinish a plurality of object portions of a workpiece.
A further object of the present invention is to prevent unfavorable events involved in grinding—such as deflection of a workpiece derived from a mechanical contact between a grinding wheel and an object portion and vibration of the workpiece and machine—from having an adverse effect on final finishing performed on ground portions.
An additional object of the present invention is to perform highly efficient grinding without involvement of deflection of a workpiece in a grinding process, which involves a relatively heavy machining load, and to perform highly accurate final-finishing without involvement of rubbing of a ground surface against a mechanical member other than contact with a final-finishing tool in a final-finishing process, which involves a relatively light machining load.
A still further object of the present invention is to supply a sufficient amount of grinding solution to a region of grinding during grinding so as to prevent the occurrence of burning on a ground surface, and to eliminate an adverse effect of a dynamic pressure of grinding liquid supplied to a region of grinding during superfinishing so as to attain high finishing accuracy.
A still further object of the present invention is to enable efficient grinding and superfinishing of a plurality of journals and crank pins of a crankshaft through a single setup of the crankshaft on a grinding machine.
To achieve the above objects. the present invention provides a combination grinding machine comprising a first wheel head and a second wheel head, which can be controlled independently of each other to be fed in the axial direction of a rotatably supported workpiece and in a direction perpendicular to the axial direction. The first wheel head includes a grinding wheel, and the second wheel head includes a superfinishing wheel. Axially separated object portions of the workpiece which have been ground by means of the grinding wheel are superfinished by means of the superfinishing wheel, while the workpiece is continuously supported on the grinding machine without the manner of support being changed. In this way, grinding and superfinishing are combined.
Grinding and superfinishing are performed on a single machine, while the workpiece is supported by means of a workpiece support mechanism without the manner of support being changed, so that transfer of the workpiece from a grinding station to a superfinishing station becomes unnecessary. The position of a contact point of the grinding wheel with respect to the workpiece is varied together with the second wheel head, which can be advanced and retreated in an accurately controlled manner. Thus, the surface roughness of the object portion which has been ground by means of the grinding wheel of the first wheel head can be improved while the geometrical profile of the object portion, such as roundness and cylindricity, is maintained as finished accurately by means of the grinding wheel. Thus, machining can be performed intensively, and superfinishing accuracy is improved. Preferably, each of the grinding wheel and the superfinishing grinding wheel comprises a layer of CBN grains or diamond grains, which features a long grinding life. Preferably, the grinding wheel and the superfinishing wheel are disposed on the first and second wheel heads, respectively, in such a manner so as to face each other.
Preferably, a numerical control unit for controlling the grinding machine is programmed in the following manner. The grinding wheel of the first wheel head, which has its home position at one end of a common path, initially grinds the object portion which is located far from the home position; i.e., the object portion which is located near the other end of the common path, at which the home position of the second wheel head is located. Subsequently, the grinding wheel sequentially grinds the remaining object portions while the first wheel head is returning to its home position. The superfinishing wheel of the second wheel head sequentially superfinishes the object portions which have been ground by means of the grinding wheel, while the second wheel head is moving toward the home position of the first wheel head, and in parallel with grinding which is performed by means of the grinding wheel. Grinding and superfinishing are performed in parallel with each other on at least a portion of object portions, thereby shortening machining time per workpiece. Preferably, the grinding wheel starts grinding from the object portion which is located nearest to the home position of the second wheel head, and then grinds the remaining object portions while the first wheel head is returning to its home position. Also, the superfinishing wheel superfinishes the object portions which have been ground by means of the grinding wheel, while moving after the fi
Katsuta Mamoru
Machida Kazuo
Mukai Ryohei
Sano Shoichi
Terahara Goro
Rachuba M.
Toyoda Koki Kabushiki Kaisha
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