WORKPIECE GRINDING APPARATUS

Abstract: Method and apparatus for workpiece grinding comprising rough grinding using an abrasive wheel and finish grinding by means of an abrasive belt wherein the workpiece remains within the grinding station throughout the grinding process. The apparatus consists of a grinding wheel (10) and an abrasive belt (26) whereby the wheel and belt are movable towards and away from the workpiece so as to allow for rough and finish grinding without removal of the workpiece. In an alternative embodiment a grinding wheel (50) is mounted on a wheelhead (92) together with a belt grinding facility and rotation of the wheelhead (92) about an axis (108) causes the grinding belt (72) or the wheelhead (50) to be presented to the workpiece. Another embodiment allows for a grinding belt and wheel to be adjacent, alternative wheel and belt operation being achieved by use of a supporting arm (116) which alters the belt position. A final embodiment allows for a belt (120) and wheel (122) on separate supports (124 and 126), on opposite sides of the workpiece and independently movable from opposite sides thereof into contact with the workpiece.

Description: Title: Workpiece grinding apparatus Field of Invention This invention relates to improvements in or relating to workpiece grinding apparatus. Background to the Invention When grinding (abrasive machining) the profile of a cam lobe, as on a camshaft for an automotive engine, it is normal to use an abrasive wheel. However, when the cam profile has a re-entrant form, the size of the abrasive wheel to grind into the re-entrant section may be so small as to preclude this method of grinding. The grinding of re-entrant forms has been performed hitherto by using an abrasive belt which is pulled round a guide shoe the curved end of which produces a small known radius on the abrasive surface of the belt, which can therefore produce not only the non re-entrant parts of the forms, but also the re-entrant parts. Unfortunately abrasive belts tend to wear rapidly when removing large amounts of stock. Objects of the Invention It is one object of the present invention to provide an improved method of grinding a workpiece which incorporates belt grinding. It is another object of the present invention to provide an improved workpiece grinding machine which includes the step of belt grinding. Summary of the Invention According to one aspect of the present invention there is provided a method of workpiece grinding comprising the steps of: (1) rough grinding to form a modified profile (herein defined), using an abrasive wheel, and (2) finish grinding the profile by means of an abrasive belt. By modified profile is meant an approximation to the final profile obtained using a grinding wheel so that a minimum of stock is left on non re-entrant parts of the profile but more stock may be left in regions of re-entrant parts of the profile. The abrasive belt is employed in accordance with the invention to remove the remaining stock from the parts of the workpiece having the modified profile including the stock in any re-entrant parts of the profile which cannot be removed- by a grinding wheel. In a conventional grinding machine for grinding a workpiece such as a camshaft by a grinding wheel, the workpiece is mounted between a headstock and a footstock which define a grinding station. The headstock and/or tailstock also rotate the workpiece in a conventional and controlled manner about an axis through the workpiece. A wheelhead mounts the grinding wheel and controls a reciprocating wheelhead feed to provide an action which puts the grinding wheel in the correct position during the rotation of each section of the workpiece being ground, to thereby generate the desired profiles therealong and to remove the grinding wheel therefrom. By superimposing a feed onto the reciprocation of the wheelhead, a profile is reduced in size in a controlled manner towards its finished size. In a conventional abrasive belt grinding machine, the belt is similarly advanced and retracted in a reciprocal manner with a feed, to finish the workpiece as required. In accordance with the invention, apparatus for grinding a workpiece comprises a grinding station having a grinding wheel mounted for rotation and reciprocal movement as aforesaid for producing a modified profile on the workpiece and associated therewith is an abrasive belt grinding facility adapted to finish grind the modified profile to the final profile whilst the shaft is still located between the same headstock and footstock in the grinding station. The belt grinding facility may be mounted for grinding with movement along the same abrasive axis as the grinding wheel at the grinding station, or along a different abrasive axis, which may be laterally spaced from the wheel abrasive axis, or opposite to but aligned with the abrasive axis of the wheel or in the same plane as the wheel but angled relative to the wheel abrasive axis. Where the headstock and footstock are mounted on a carriage which can be moved relative to the abrasive axis or axes of the wheel and belt, to present different regions of a workpiece in succession to the grinding station, the whole workpiece may be finished by way of a succession of separate wheel and belt grindings in the same machine. Typically the grinding wheel and abrasive belt grinder and their respective drives and controls are incorporated in the wheelhead. In one embodiment of the invention the grinding wheel and abrasive belt assembly are both mounted on the wheelhead in such a manner that by rotating the wheelhead, typically through 180° about a vertical axis, either the grinding wheel or the abrasive belt can be presented to the workpiece. The abrasive belt may be driven independently by its own drive means or from the grinding wheel drive means. The drive means may to advantage be electronically and/or microprocessor controlled to control speed, direction of rotation, acceleration and deceleration as may be required to control the abrasive action of the wheel and belt. Where a single drive means is employed provision may be made to disconnect the drive to the grinding wheel and/or the belt by for example, a clutch such as an over-running clutch, or simply by controlled belt slackening. Conveniently the wheelhead is separate from but mounted on an underslide which supports and guides the mechanism which determines the reciprocating axis of the wheel and belt, and indexing means is provided by which the wheelhead may be rotatably indexed to present one grinding device or the other and means is provided for locking the wheelhead when in either grinding position. Preferably the indexing is incremental to allow for fine positioning of the wheelhead. As applied to the production of a camshaft the sequence of grinding in accordance with the invention comprises rough grinding consecutively all the camshaft lobes on a workpiece using the grinding wheel to produce modified cam profiles at each cam position, indexing the wheelhead through the appropriate angle to present the abrasive belt to the workpiece and finish grinding consecutively all the modified profiles along the camshaft to the required size and shape. The finished component can be unloaded and a new workpiece put in place whilst the wheelhead indexes to present the grinding wheel to begin again the sequence as described above. In another embodiment, the abrasive belt is mounted alongside the grinding wheel and the belt and wheel are movable towards and away from the workpiece so that when the abrasive belt is grinding the grinding wheel is clear of the parts of the workpiece being ground by the belt and when the grinding wheel is to be engaged, the abrasive belt can be retracted so that the grinding wheel can be presented to the workpiece without the abrasive belt making contact with the workpiece. In this embodiment the grinding sequence typically involves rough grinding a component using the grinding wheel and then finish grinding the same part of the component using the abrasive belt before the wheelhead assembly is moved to the next region of the component to be ground. In a further embodiment the abrasive belt is adapted to be engaged with the workpiece to finish grind a modified profile whilst the grinding wheel is actively rough grinding another axially spaced region of the workpiece. In this way workpieces can be finish ground in virtually the same time as would be required to rough grind it prior to a finish grinding sequence. Although of particular application to grinding workpieces having re-entrant features such as complex cam lobes on a camshaft, the method and apparatus of the invention can be applied to non re-entrant component grinding. The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1a is a schematic view of a cam lobe adjacent to a grinding wheel for rough grinding in accordance with the invention and Figure 1b is a cam lobe adjacent to an abrasive belt for finish grinding in accordance with the invention, Figure 2 is an elevation and plan of a combined grinding wheel and abrasive belt machine tool showing the grinding wheel presented to the workpiece, Figure 3 is an elevation and plan view of a combined grinding wheel and abrasive belt machine tool showing the abrasive belt presented to the workpiece, Figure 4 is an elevation and plan view of a combined grinding wheel and abrasive belt machine tool showing the grinding wheel and belt fitted alongside each other, and Figure 5 is an elevation and plan view of a combined grinding wheel and abrasive belt showing the grinding wheel and abrasive belt incorporated in separate grinding heads. Detailed description of the illustrated embodiments Figure 1a shows a section of a grinding wheel 10, rotating in the direction of arrow 22 about an axis of rotation (not shown) and reciprocably. in the direction of arrows 13 to move wheel 10 and its grinding surface towards and away from a cam lobe 14 to be ground. The surface of wheel 10 engages the surface of lobe 14 at an imaginary plane 12 diametrically passing through the axis of rotation of wheel 10 and the base circle axis of lobe 14 at a variable point 24 of cam lobe 14. Lobe 14 is rotating in a controlled manner around an axis 18 in the direction of arrow 16. The cam lobe 14 has a modified profile 20 which remains after the rough grinding step. Cam lobe 14 is rotated about axis 18 to facilitate its grinding. The controlled angular rotation of the cam lobe 14 is complemented by a controlled reciprocal movement of the grinding wheel in the direction of arrow 13 so that it is in the correct position relative to the angle position of the cam lobe. Figure 1b shows a section of an abrasive belt 26 moving in direction of arrow 28 over cylindrically curved shoe. face 30 of fixed guide shoe 32. Alternatively, as indicated in broken line, the fixed shoe may be replaced by a roller 33 driven by passage of the abrasive belt over its periphery. The belt assembly is selectably securable along axis 34, in the direction of the arrow 36. Belt 26 and its grinding surface is also movable in the direction of arrow 36 to move its grinding surface towards and away from the surface of the cam lobe 40 to be ground. When the grinding surface of moving belt 26 engages the surface of cam lobe 40 at location 38, along a diametric plane passing through the base circle of lobe 40 and the longitudinally extending line of movement 34, a finish grinding of a modified profile such as that shown in Figure 1a, is achievable. The point of engagement between cam lobe 40 and the belt 26 on axis 34, is denoted by 38. The controlled angular rotation of the cam lobe 40 is complemented by a controlled backwards and forwards reciprocatory movement of belt 26 along axis 34, so that the locus of the belt/lobe engagement at 38 accurately facilitating the grinding of the final shape that the cam lobe is to possess. Figure 2 shows an elevation 46 and plan view 48 of a dual purpose grinding machine wherein a grinding wheel 50 is conventionally mounted on a spindle (not shown) which rotates in the direction of arrow 51 in a wheel housing 52 about an axis 54 and is driven by a drive motor 56. The grinding surface of grinding wheel 50 is in contact with the surface of a cam lobe 58 of a cam shaft 60, which is fixed between a headstock 64 and a footstock 62. Headstock 64 rotates cam shaft 60 in a conventionally controlled manner about an axis -66 and is in turn driven by an electric motor (not shown) housed in headstock 64. An approximate cam profile can thus be produced by advancing the grinding wheel surface towards cam lobe 50 until the approximate cam profile is achieved. Footstock 62 is slidable and securable along axis 66 in the directions indicated by arrow 68. Adjacent to the headstock 64 is a conventional truing or dressing device 70 which is manoeuvred by sliding headstock 64 across the face of grinding wheel 50 or belt 72 with device 70 in contact therewith for truing the grinding wheel 50 or abrasive belt 72 prior to use. When truing is complete, headstock 64 is slid back and secured so as to secure workpiece 60 in position, so that truing device 70 is free of the grinding wheel 50 and belt 72. A wheelhead 92 also incorporates the abrasive belt assembly 76 which includes the belt 72. Conventional rotational indexing of the wheelhead through 180° about an axis 108 presents abrasive belt 72 instead of wheel 50 to workpiece 60. Wheelhead 92 is mounted on an underslide 106 which supports and guides wheelhead 92 for rotation about axis 108, so that wheelhead 92 can be rotatably indexed and rigidly locked (by locking means not shown) when in either grinding position. Wheelhead 92 is mounted on underslide 106 and driven backwards and forwards on slide 134 by a feed member 107 so that the abrasive belt 72 or grinding wheel 50 can be advanced or withdrawn from the workpiece as required at the beginning and ending of a grinding step and reciprocated so as to respond to the changing component profile during rotation of the latter and to readjust position for the next workpiece. Slide 134 is conventionally supported on the machine tool base 136. Figure 3 shows the grinding machine of Figure 2 with the abrasive belt in contact with the cam lobe. The belt mechanism comprises an abrasion belt tensioning pulley 78 attached by means of arm 80 to a securing member 84. The arms are attached to the securing member by means by pivot bearings 81, and to the body of the wheelhead 92 by means of a pneumatic cylinder 200. The pneumatic cylinder is retractable allowing the arm to swing down for fitting new belts. The pneumatic cylinder can then be extended at a controlled rate and pressure to correctly tension the abrasive belt 72. The abrasive belt is driven around a larger pulley 86 which is rotated by a belt drive 90 via drive motor 88. The larger pulley 86 is carried by the securing member 84 and the abrasive belt drive motor 88 is secured to the body of the wheelhead 92 via a vibration absorbing platform 94. The abrasive belt 72 also passes around two belt guide pulleys 96 and 98 which are also carried by securing member 100 so that they are equidistant from the guide shoe 102 and shoe supporting grooved member 104. The guide pulleys are located behind the guide shoe 102 so that the belt passing over the guide shoe protrudes forward of the guide mechanism enabling grinding of the workpiece 105 by the abrasive belt. Figure 4 shows plan 112 and elevation 114 of an embodiment of the machine wherein the abrasive belt mechanism and grinding wheel mechanism are adjacent to each other and wherein the abrasive belt extends forwardly of the abrasive wheel when the abrasive belt supporting grooved arm 116 has been lowered into the position shown in Figure 4(a). Alternation between abrasive mechanisms is by retraction of the abrasive belt shoe by rotation of supporting arm 116 around axis 118, so that the abrasive belt mechanism is now displaced behind the grinding wheel surface when viewed from the side. Thus, rotation of the arm 116 allows alternative abrasive wheel rough grinding and abrasive belt finish grinding operations, without the non grinding device interfering with the workpiece while the other is active. The other constructional features are similar to those of the previous examples shown in the drawings except that there is no need for any rotatable indexing means as both mechanisms are functional on the same side of the wheelhead as each other. In Figure 5 the abrasive belt 120 and the abrasive wheel 122 are located on separate wheelheads 124 and 126 on either side of the machine tool mounting 128. Both wheelheads are slidable over respective support members 130 and 132 and the abrasion mechanism is essentially as hereinbefore described except that in this embodiment it is possible to grind a workpiece from both sides. After rough grinding, one part of the grinding wheel 122 is retracted and the abrasive belt 120 is advanced and engaged for finish grinding the same part, before the workpiece is axially advanced to present another region for rough grinding.

Claims: Claims 1. A method of workpiece grinding comprising the steps of: (1) rough grinding to form a modified profile (herein defined), using an abrasive wheel, and (2) finish grinding the profile by means of an abrasive belt, without removing the workpiece from a machine. 2. Apparatus for performing the method of Claim 1 for grinding a workpiece comprising a grinding station having a grinding wheel mounted for rotation to produce a modified profile on a workpiece and associated therewith an abrasive belt grinding facility adapted to finish grind the modified profile to a final profile whilst the workpiece is still within the grinding station. 3. Apparatus as claimed in claim 2 wherein the belt grinding facility is movable for grinding along the same abrasive axis as the grinding wheel at the grinding station. 4. Apparatus as claimed in claim 2 wherein the belt grinding facility is movable for grinding along a different abrasive axis from that of the grinding wheel. 5. Apparatus as claimed in claim 4 wherein the said different axis is laterally spaced from the abrasive axis of the grinding wheel. 6. Apparatus as claimed in claim 2 wherein the said different axis is opposite to but aligned with the abrasive axis of the grinding wheel. 7. Apparatus as claimed in claim 2 wherein the said different axis is in the same plane as the wheel but angled relative to the abrasive axis of the grinding wheel. 8. Apparatus as claimed in claim 2 or 3 wherein the headstock and footstock are mounted on a carriage which is movable, relative to the abrasive axis or axes of the wheel and belt, to present different regions of a workpiece in succession at the grinding station, so that a whole workpiece may be finished by way of a succession of separate wheel and belt grindings in the same machine. 9. Apparatus as claimed in claim 2 or 3 wherein the grinding wheel and abrasive belt assembly are both mounted on the wheelhead such that by rotating the wheelhead, either the grinding wheel or the abrasive belt can be presented to the workpiece. 10. Apparatus as claimed in claim 9 wherein the wheelhead is rotable about a vertical axis. 11. Apparatus as claimed in claim 10 wherein the wheelhead is rotable through 180° about the said vertical axis. 12. Apparatus as claimed in any of claims 2 to 11 wherein the drive means is electronically and/or microprocessor controlled to control some or all of speed, direction of rotation, acceleration and deceleration to control the abrasive action of the wheel and the belt. 13. Apparatus for performing the method of claim 1, wherein the abrasive belt is mounted alongside the grinding wheel, and the belt and wheel are movable towards and away from the workpiece so that when the abrasive belt is grinding, the grinding wheel is clear of the parts of the workpiece being ground by the belt and when the grinding wheel is to be engaged, the abrasive belt is retracted so that the grinding wheel can be presented to the workpiece without the abrasive belt making contact therewith. 14. Apparatus for performing the method of claim 1 wherein the abrasive belt is adapted to be engaged with the workpiece to finish grind a modified profile whilst the grinding wheel is actively rough grinding an axially spaced region of the workpiece. 15. Apparatus and method for grinding substantially as herein described in Figures 1, or 2-3, or 4 or 5 with reference to and as illustrated in the accompanying drawings.

Inventors: COVERDALE STEPHEN ROGER, GRAYSTON GRANVILLE, COVERDALE, STEPHEN, ROGER, GRAYSTON, GRANVILLE
Applicants: COVERDALE STEPHEN ROGER, GRAYSTON GRANVILLE, WESTERN ATLAS UK LTD, COVERDALE, STEPHEN, ROGER, GRAYSTON, GRANVILLE, WESTERN ATLAS UK LIMITED
Application year: 1993
Main classification: B24B19
IPC codes: B24B19, B24B21, B24B27