US3457678A

US3457678A - Grinding apparatus

Info

Publication number: US3457678A
Application number: US515022A
Authority: US
Inventors: Wilfred Keith Temple
Original assignee: Newall Engineering Co Ltd
Current assignee: Newall Engineering Co Ltd
Priority date: 1965-12-20
Filing date: 1965-12-20
Publication date: 1969-07-29
Anticipated expiration: 1986-07-29
Also published as: GB1053140A

Description

July 29, 1969 w. K. TEMPLE GRINDING APPARATUS 2 Sheets-Sheet 1 Filed Dec. 20, '1965 A .EN s

July 29, 1969 w. K. TEMPLE GRINDING APPARATUS 2 Sheets-Sheet 2.

Filed Dec. 2O,V 1965 United States Patent O U.S. Cl. 51-5 3 Claims ABSTRACT OF THE DISCLOSURE A grinding apparatus comprising a grinding wheel, a dressing tool operable to dress the grinding wheel, and automatic control means for controlling operation of the dressing tool as a function of three quantities viz. the time in the grinding life of the grinding wheel, the radial feed transmitted to the dressing device at each dressing operation, and the time interval between successive dressing operations, not more than one of the last two mentioned quantities being maintained constant. According to a preferred feature of the invention the automatic control means comprises means for advancing the dressing tool a constant or substantially constant effective feed distance at each dressing operation, and means for initiating a dressing operation of the dressing tool after a grinding time interval which reduces as the diameter of the grinding wheel decreases with use.

This invention relates to grinding apparatus and is concerned more particularly with the periodic dressing operation performed on the grinding wheel by a dressing tool for sharpening or re-shaping the cutting surface or for removing the surface layer, which may become impregnated or loaded with particles cut from the workpiece or workpieces.

According to this invention there is provided grinding apparatus comprising a grinding wheel, a dressing tool operable to dress the grinding wheel, and automatic control means for controlling operation of the dressing tool as a function of three quantities viz, the time in the grinding life of the grinding wheel, the radial feed transmitted to the dressing device at each dressing operation, and the time interval between successive dressing operations, not more than one of the last two mentioned quantities being maintained constant.

According to a preferred feature of the invention the automatic control means comprises means for advancing the dressing tool a constant or substantially constant effective feed distance at each dressing operation, and means for initiating a dressing operation of the dressing tool after a grinding time interval which reduces as the diameter of the grinding wheel decreases with use.

The automatic control means may comprise a device for producing a response directly proportional to the diameter of the wheel and connected to control the initiating means to initiate a dressing operation of the dressing tool after a grinding time interval which is directly proportional to thel diameter of the grinding wheel at the time of the prece-ding dressing operation. Alternatively the automatic control means may comprise a counter which counts the number of articles machined by the grinding wheel so as to provide a measure of the progress of the life of the grinding wheel, and which is set to initiate each successive dressing operation of the dressing tool in depedence on the number of articles machined by the wheel since the preceding dressing operation, and means for varying the setting of the counter such that the number of articles machined by the Wheel between suc- "ice cessive dressing operations is reduced as the diameter of the wheel decreases.

In other preferred arrangements according to the invention, the automatic control means comprises means for initiating a dressing operation by thel dressing tool at constant or substantially constant grinding time intervals, and means for controlling the effective forward feed of the dressing tool in inverse ratio to the diameter of the grinding wheel at the time of initiating the dressing operation. In one such construction said means for controlling the effective forward feed of the dressing tool in inverse ratio to the diameter of the grinding wheel at the time of initiating the dressing operation comprises a feedscrew controlling said forward feed of the dressing tool which feed-screw has a variable pitch. The apparatus in this construction may further comprise a workpiece support and means for adjusting the relative positions of the grinding wheel and workpiece support in a direction normal to the axis of the grinding wheel for compensating for the increased rate of radial consumption of the wheel with reduction of the grinding wheel diameter.

Some embodiments of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIGURE 1 shows a fragmentary partly-sectioned side View of a grinding machine,

FIGURE 2 shows an enlarged View of a detail of FIG- URE 1, and

FIGURE 3 shows a second embodiment of the invention.

If all normal factors associated with the grinding process such as peripheral speeds of work and wheel, amount of material to be removed from the work, the rate of this removal, the homogeneity and hardnesses of work and wheel and the cooling uid remain sensibly constant throughout the life of the wheel, then within reasonable limits there is a constant relationship between the volume of material removed from the work and the volume of grinding wheel consumed due to that which is broken away during the grinding process added to that which is removed by the dressing or forming process. Thus a wheel of large diameter can be expected to be capable of grinding more workpieces between successive wheel dressing or forming operations than can one of smaller diameter operating under the same conditions. Alternatively, if the number of workpieces produced between dressing operations is maintained constant, then, within certain limitations, it will be possible to dress a less amount off the larger wheel than off the smaller one at each dressing operation. One limitation is that the amount dressed off the larger wheel should be sufficient to remove the impregnated or loaded layer if this be the factor which determines the need for redressing, or that the amount removed from the larger wheel should be suiiicient to restore completely the original geometrical form of the wheel if this be the determining factor.

In the case of a grinding machine which is entirely under the control of a skilled operator, the latter will instinctively perform or initiate the dressing operation at intervals which take account of the condition of the wheel Iand of its diameter at that time. In the case of grinding ymachines which operate fully automatically, semiautomatically, or under the control of other than skilled operators, then to achieve maximum efficiency it is desirable to have automatic means for controlling the oper-ation of the dressing device.

Referring now to FIGURES l and 2 of the drawing there is shown diagrammatically a grinding machine according to the invention in which a dressing operation of the grinding wheel is initiated at constant or substantially constant intervals in the grinding life of the grinding wheel, the radial feed transmitted to the dressing device being a predetermined minimum, having regard to the factors described above, when the grinding wheel is new but increasing as the diameter of the grinding wheel increases. T he grinding machine comprises a base having lengthwise extending guideways 11 on which a support 12 for a workpiece is slidably mounted. Second guideways are formed on top of the 'base and extending at rightangles to the guideways 11 and are engaged by the guide ribs 13 of a grinding wheel carrier 14. A motor driven grinding wheel 15 is mounted on a shaft 16 in journals in the carrier 14 and is thus movable at rightangles to its own axis towards and away from the workpiece support 12. A feed screw 17 which is slidably keyed at one end in a shaft 18 and journaled in a piston 19a at its other end is engaged by a follower 14a on the carrier 14 to control the movements of the grinding wheel towards and away from the workpiece support 12. The piston 19a is slidably mounted in a cylinder 19b on the base 10 and serves to transmit to the feed screw 17 and carrier 14 rapid inward and outward movements of the grinding wheel 15 relative to the workpiece support 12. Shaft 18 is supported in a journal 10a in the base 10 and carries at its opposite end a gear wheel 20 which meshes with a pinion 21 on a gear hub 22. Hub 22 carries, coaxially with gea-r 21, a gear 23 engageable by a plunger 24 secured on a handwheel 25. Handwheel 25 is secured on a shaft 26 mounted on the base 10 and extending through the hub 22. Increments of feed movement are imparted to the grinding wheel by mea-ns of handwheel 25, or automatically by means (not shown) connected to the shaft 18.

A dressing device for the grinding wheel 15 is mounted on the carrier 14. The dressing device comprises a diamond-tipped tool which is mounted on a sleeve 31 y slidingly keyed in a slide 32 for movement towards and away from the axis of the grinding wheel. The slide 32 is in turn slidably mounted on a guideway 34 which is formed in a guide plate 33, so that the slide is constrained to slide parallel to the axis of the grinding wheel. A hydraulic piston and cylinder motor 35 is connected Fbetween the carrier 14 and the slide to move the slide 32 along the guideway 34 and thus traverse the diamond dressing tool 30 across the face of the grinding wheel. A cam screw 36 is disposed within the sleeve 31 and is mounted in a journal in the slide 32 and xed against endwise movement relative to the slide. The cam screw is engaged by a follower 37 on the inner surface of the sleeves 31. Thus, rotation of the cam screw causes the diamond tool 30 to move towards and away from the periphery of the grinding wheel. The shaft of the cam screw projects from the slide 32 and has secured thereon a ratchet 38 and a pinion 39. Ratchet 38 is engageable by a pawl 40 operated by a control device 41 of known kind. Actuation of device 41 is initiated in the present instance by a counting mechanism 42 having an actuating arm 43. The arm 43 is operated by each article 44 which has been machined by the grinding wheel -as the finished article leaves the machine. When a predetermined number of articles 44 have operated the actuating arm 43 of the counting device 42 an actuating impulse is transmitted to the device 41 which then moves pawl 40 to rotate ratchet wheel 38 and move the diamond tool 30 a predetermined distance towards the axis of the grinding wheel 15 and subsequently initiates a movement of the motor 35 to traverse the diamond tool 30 across the periphery of the grinding wheel to perform a dressing operation. Thus Where the machine is operating automatically or semiautomatically, a dressing action is initiated by the counting device 42 at constant or substantially constant intervals in the grinding life of the wheel. The number of articles machined constitutes a parameter of the extent of wear of the wheel. To provide for an increasing amount to be dressed off the wheel as the wheel diameter decreases, the cam screw 36 has, as is shown more clearly in FIGURE 2 a pitch which increases steadily towards the end of the cam screw nearer the grinding wheel, such that the diameter of wheel 15 after each dressing operation is related in a predetermined manner to the distance of the tool from the centre of wheel 15, and hence to the diameter of the wheel, at the time of the preceding dressing operation. The amount dressed off the wheel is thus controlled in relation to the diameter of the Wheel.

It will be understood that under conditions of semiautomatic or automatic operation, the steady reduction in the size of the grinding wheel would lead to progressively increasing errors in the sizes of the articles being produced if nothing were done to introduce appropriate corrections. In the present arrangement, these corrections are made automatically by the arrangement of the screw 17 and follower 14a. Screw 17 has a pitch which increases from one end of the screw to the other such that the nearer the grinding wheel approaches the work table the greater is the pitch of the screw. This increase in pitch is matched to the increase in pitch of the cam screw 36 so that screw 17 compensates for the increasing rate of radial removal, by wear and dressing operations, of the material of the grinding wheel as the wheel radius decreases by feeding the Wheel forward an increasing amount.

The pitch of screws 36 and 17 is very much exaggerated in the drawings.

Referring now to FIGURE 3 of the drawings, a second embodiment is shown diagrammatically in which a constant radial feed is transmitted to the dressing device at each dressing operation but in which the time interval between successive dressing operations is governed in dependence on the diameter of the grinding wheel. The apparatus is to be applied to a grinding machine similar to that illustrated in FIGURE 1 except that the cam screw 36 and feed-screw 17 are replaced by constant pitch screws, and that device 42 is replaced by a modified counting device. The apparatus comprises a counting mechanism 50 having an actuating arm 51 which is disposed so as to be operated by each finished article 52 as it leaves the machine. Mechanism 50 has output terminals connected in circuit with device 41 and transmits an electrical pulse thereto to actuate the initiation of a dressing operation when a counted number of machined articles has operated arm 51. The number is adjusted by a photoelectric device 53 which extends round the edge of wheel 15 `and which is responsive to the diameter of the wheel. The device 53 produces a response directly proportional to the diameter of the wheel 15 and sets the counter 50 in accordance with said diameter. Since the wheel diameter decreases during the lifetime of the grinding wheel, the setting of the counter willlikewise be reduced between successive dressing operations and thus there is a progressive reduction in the number of articles which must operate arm 51 before a dressing operation is initiated by mechanism 50.

In yet another arrangement (not illustrated) the feed screw 17 and cam screw 36 may be replaced by constant pitch screws which are rotated through an angle which is increased progressively as the diameter of the wheel decreases. This may be accomplished by a pulseoperated electric motor connected to drive the screws, the pulses being supplied to the motor under the control of a photoelectric device similar to device 53, which is responsive to the diameter of the grinding wheel. Alternatively the sleeve may be advanced a gradually increasing distance by a motor-driven cam which is rotated through a constant angle in response to signals transmitted from a counting device 42.

I claim:

1. Grinding apparatus comprising a grinding wheel, a dressing tool operable to dress the grinding wheel and automatic control means for controlling operation of the dressing tool, said automatic control means comprising means for initiating a dressing operation by the said dressing tool at substantially constant grinding time intervals, and automatic means for controlling the effective forward feed of the dressing tool in inverse ratio to the diameter of the grinding wheel at the time of initiating the dressing operation, said means for controlling the effective forward feed of the dressing tool in inverse ratio to the diameter of the grinding wheel at the time of initiating the dressing operation comprising a feed-screw controlling said forward feed of the dressing tool which feedscrew has a variable pitch.

2. Grinding apparatus as claimed in claim 1, further comprising a workpiece support and means for adjusting the relative positions of the grinding wheel and workpiece support in a direction normal to the axis of the grinding wheel for compensating for the increased rate of radial consumption of the wheel with reduction of the grinding wheel diameter.

3. Grinding apparatus as claimed in claim 2, wherein the grinding wheel is mounted on a support table and .References Cited UNITED STATES PATENTS 3,079,906 3/1963 Thompson 125-11 3,113,405 12/1963 schneider 51-i425 2,946,162 7/1960 Mader 51-165 HAROLD D. WHITEHEAD, Primary Examiner U.S. Cl. X.R. 51-165; 12S-l1