Abrasive tool making process – material – or composition – With carbohydrate or reaction product thereof
Patent
1991-01-22
1992-04-07
Rachuba, M.
Abrasive tool making process, material, or composition
With carbohydrate or reaction product thereof
5116587, 51 33W, 51105EC, 51281C, B24B 4900
Patent
active
051016010
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of and to an apparatus for grinding a circumferential surface on a workpiece. In particular the invention is applicable to the grinding of a circumferential surface on a workpiece where the workpiece is being rotated about an axis, but the surface to be ground is not concentric with that axis. Examples of such applications are the grinding of cam profiles on camshafts (where the surface being ground is non-circular) and the grinding of crank pin journals on crankshafts (where the surface being ground is circular but is offset from the crankshaft axis).
It is known to grind crankshafts by using a "master blank" as a template and to set up the grinding machine to copy the profile of the blank to the workpiece. This technique suffers from inaccuracy through the need for a number of pivoted linkages and supports between the blank and the workpiece, and also as a result of wear on the blank.
Such machines which effectively copy the shape of an accurately dimensioned blank have now been largely replaced by CNC (computer numerically controlled) grinding machines where the movement cycle of the grinding wheel or of the workpiece is programmed into the machine.
It is also known to grind crankshaft journals (which each have a circular circumference but are located on different axes) by mounting the crankshaft so that it rotates about the axis of the journals being ground. This requires careful setting up, and the crankshaft has to be remounted at least three times for all the journals to be ground.
According to a first aspect of the invention there is provided a method of grinding a circumferential surface on a rotating workpiece where the surface is not concentric with the axis of rotation of the workpiece, the method comprising mounting a grinding wheel on a first axis, mounting the workpiece for rotation about a second axis, rotating the grinding wheel and the workpiece about their respective axes so that the grinding wheel makes grinding contact with the surface to be ground and, during each workpiece revolution, moving the grinding wheel axis backwards and forwards in a first plane and moving the workpiece axis in a second plane which is inclined to the first plane, with the movement of both axes being under computer numerical control.
In theory, the second plane can be at any angle from 1 up to and including 90 degrees to the first plane. It is important that the movement of the axis in the second plane be capable of resolution into components, one of which makes an angle of 90 degrees to the first plane. Practical reasons are however likely to limit the possible angles of inclination, and it is preferred that an angle of about 45 degrees be chosen.
The workpiece axis preferably performs simple harmonic motion in the second plane.
The reason for moving the workpiece axis in addition to the grinding wheel axis is to ensure that the point of contact between the grinding wheel and the surface being ground always lies on the same line, this line preferably lying in the first plane. For circular parts, this results in the surface velocity at the grinding wheel/workpiece interface remaining constant at all times. For noncircular surfaces, a good approximation to constant surface velocity is achieved. The grinding conditions are thus optimised and all parts of the circumference are treated evenly.
The invention also provides computer numerically controlled apparatus for grinding a circumferential surface on a workpiece, the apparatus comprising a grinding wheel mounted for rotation on a first axis and a rotatable workpiece support defining a second axis about which a workpiece can be supported and rotated, characterised in that the first axis is reciprocable along a first path, and the workpiece support with the second axis is reciprocable along a second path at an angle to the first path.
The angle which the second path makes to the first linear path is preferably of the order of 45 degrees, but may vary between 90 degrees and about 20 degrees. It is not essential for the second pa
REFERENCES:
patent: 3886693 (1975-06-01), Tajnafoi et al.
patent: 4077302 (1978-03-01), Staebler
patent: 4238205 (1980-12-01), Geiger et al.
patent: 4485592 (1984-12-01), Kawaguchi et al.
Ford Motor Company
Malleck Joseph W.
Rachuba M.
Sadler Clifford L.
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