US3327432A

US3327432A - Grinding machine

Info

Publication number: US3327432A
Application number: US374404A
Authority: US
Inventors: George H Lockwood
Original assignee: Heald Machine Co
Current assignee: Heald Machine Co
Priority date: 1964-06-11
Filing date: 1964-06-11
Publication date: 1967-06-27
Anticipated expiration: 1984-06-27
Also published as: GB1105972A; DE1502448A1

Description

J1me 1967 G. H- LOCKWOOD 3321432 GRINDING MACHINE Filed June 11. 1964 INVENTOR Cjeorqe H. Joell/food Unitcd States Patent 3,327,432 GRINDING MACHINE George H. Lockwood, Worcester, Mass, assignor to The Heald Machine Company, Worcester, Mass., at corporation of Delaware Filed June 11, 1964, Ser. No. 374,404 7 Claims. (Cl. 51165) This invention relates to a grinding machine and, more particularly, to apparatus arranged to produce finished surfaces of revolution by the abrasion process.

In the art of finishing surfaces of revolution by grind ing, there are two methods which have generally been used for determining the final dimension of the finished surface. One of these methods is that of terminating the grinding operation when the wheelhead which carries the abrasive wheel reaches a predetermined position relative to the workhead which carries the workpiece; in using this method it is common practice to dress the abrasive wheel from time to time and, at the time of dressing, to compensate for the amount of wheel material removed by wear during grinding and by the dressing operation by moving the final size position. The second method is to use an ,in-process gage which measures the size of the surface to be finished during the grinding operation and terminates the operation when the proper size has been reached. In both of these processes the wheel can be dressed either during each grinding cycle or after a predetermined number of grinding cycles have gone by. The difiiculty with doing this is that abrasive wheels differ in quality from one another and any given wheel may vary in its prediliction to wear from time to time. This means that at one time the dressing operation may remove a considerable part of the wheel, while at another time it may remove very little, due to variations in wear of the wheel. Since the dressing or passage of the diamond over the abrasive wheel determines the smoothness of the surface of the wheel as well as its geometry, variations in the amount of wheel removed by the diamond will vary the quality of the dress as well as the geometry of the wheel; this can greatly affect the finished size and shape, particularly when precision work is being done. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine in which substantially equal amounts of the abrasive wheel are removed during successive dressing operations.

Another object of this invention is the provision of a grinding machine in which the surface of the wheel after each dressing is of a standard quality both with regard to smoothness and to geometry.

A further object of the present invention is the provision of a grinding machine in which it is possible to finish surfaces of revolution to a consistent quality of finish and geometry.

It is another object of the instant invention to provide a grinding machine in which the abrasive wheel is dressed only when such a dressing operation is necessary, thus providing a saving in the number of wheels used fora given amount of work.

It is a further object of the invention to provide an internal grinding machine in which the abrasive wheel is dressed only when it i necessary.

It is a still further object of the present invention to provide an internal grinding machine in which feed compensation and dressing operations will take place in a non-predetermined manner to make the most efficient use of the abrasive wheel.

With these and other objects in view, as will be apparcut to those skilled in the art, the invention resides in the 3,327,432 Patented June 27, 1967 Ice combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

The single figure of the drawings is a somewhat schematic view of a grinding machine embodying the principles of the present invention.

Referring to the single figure of drawings, it can be seen that the grinding machine, indicated generally by the reference numeral 10, comprises a workhead 11 supporting a workpiece 12 and a wheelhead 13 supporting and rotating an abrasive wheel 14. For the purposes of illustration, the workpiece 12 is shown as consisting of a bearing race of a ball bearing whose internal bore is to be finished. The wheel 14 is, therefore, dressed to a cylindrical surface and mounted on a spindle 15 extending from the wheelhead 13. The wheelhead is mounted on a wheelhead table 16 which, in turn, is mounted on an intermediate table 17 for movement thereof transversely of the wheel axis. For this purpose, the upper surface of the intermediate table 17 is provided with transverse ways 18 on which the wheelhead table 16 is mounted. Furthermore, the intermediate table 17 is capable of transverse sliding motion over the surface of a base 19 on which the elements of the grinding machine are mounted and this motion is facilitated by transverse ways 21 mounted on the upper surface of the base 19.

The workhead 11 is mounted on a workhead table 22 which is capable of sliding motion over the upper surface of the base 19 in a direction extending longitudinally of the axis of the wheel 14, there being ways 23 mounted on the upper surface of the base to permit this motion. The workpiece 12 is mounted on suitable shoes forming part of the workhead 11 and the workpiece is rotated by a rotating platen 24 which is driven by a motor 25 mounted on the workhead table 22. The motor is connected to the platen through pulleys and belts in the usual manner. Located in the workhead is an in-processgage 26 mounted on the end of an elongated spindle 27, which spindle is actuated by a hydraulic linear actuator 28 mounted on the table 22. The motion of the table 22 and all of its accessory elements longitudinally of the axis of the wheel 14 is brought about by a hydraulic linear actuator 29 mounted on the upper surface of the base 19 and having a connecting rod connected to the table 22. A dressing element such as a diamond holder 31 is mounted on the table 22 in such a manner that the diamond lies between the workhead and the wheelhead and protrudes transversely to a position somewhat forward of the rearwardmost point on the periphery of the bore of the workpiece 12. Mounted on the table 22 beside the spindle 27 of the gage is a microswitch 32 whose actuating finger is in a position to be engaged by a disc 33 mounted on the spindle 27.

Mounted on the upper surface of the base 19 forwardly of the wheelhead 13 is a hydraulic linear actuator 34 having its piston rod connected to the forward edge of the wheelhead table 16 and capable of moving the wheelhead rearwardly to bring about contact of the abrasive wheel 14 with the surface of the bore of the workpiece 12. Also mounted on the upper surface of the intermediate table 17 is a backoff stop 35 which, for the purposes of illustration, is shown as a threaded shaft extending through an abutment on the table and operated by an electric motor 36 to produce incremental rotation and forward and rearward motion of the stop 35. The outboard side of the wheelhead table 16 is provided with a finger 37 and on the upper surface of the table 17 are mounted a first switch 38 and a second switch 39. The operating fingers of these two

switches

38 and 39 are in line for engagement by the finger 37 on the table 16 as the wheelhead is moved transversely of the wheel axis.

Mounted on the upper surface of the base 19 is a compensation mechanism including a threaded shaft 41 mounted in suitable bearings and abutinents on the 'surface and engaging a nut 41A on the underside of the intermediate table 17 so that, by its rotation, the shaft produces transverse motion of the intermediate table 17 over the base 19. A pinion 42, which includes a ratchet mechanism, is mounted on the shaft and this pinion is operated by a rack 43 which is capable of to and fro movement under the operation of a hydraulic linear actuator 44 whose operating fluid reaches it through

conduits

45 and 46 leading to a servo valve 47.

The grinding machine, which has been described above, is basically similar in nature to the internal grinding machine described in the patent application of Frederick A. Hohler et al. Ser. No. 217,683, filed Aug. 17, 1962, now Patent No. 3,197,921, dated Aug. 3, 1965; for the details of the construction of the machine, reference may be made to this patent application.

The control elements are shown as connected to two

power lines

48 and 49. The gage switch 32 is connected on one side to the line 48 and on the other side to the coil 51 of a relay 52. The other side of the coil 51 is connected directly to the power line 49. Forming part of the relay 52 is a normally-open contactor 53 connected on one side to the line 48 and on the other side through a normally-closed cont-actor 54 to one side of the motor 36 forming part of the backofi stop 35. The other side of the armature of the motor is connected to the power line 49 through a coil 73 of a relay 72. One side of the first switch 38 is connected to the power line 48, while the other side is connected through the coil 55 of a relay 56 which operates the normally-closed contactor 54. The other side of the coil 55 is connected directly to the line 49. The hold-in circuit for the relay 56 is formed by a line 57 leading from the power line 48 to one side of a normally-open contactor 58, the other side of which is connected between the switch 38 and the coil 55. The second switch 39 is connected on one side to the line 48 and on the other side through a coil 59 of'a relay 61, the other side of the coil being connected directly to the line 49. The common point shared by the switch 39 and the coil 59 is connected on one side to a normally-open contactor 62 forming part of the relay 52 and having its other side connected to an actuating coil 63. This actuating coil operates on the plunger of the servo valve 47 and, when energized, serves to introduce hydraulic fluid into the actuator 44. The other side of the coil 63 is connected through a coil 64 to the line 49. The coil 64 operates on the plunger 65 of a counter 66, which counter serves to register the number of times that the coil 64 is energized and, after a predetermined number has been counted, to close a switch 67 mounted on its interior. The hold-in circuit for the coil 59 is formed by a normallyopen contactor 68, one side of which is connected to the line 48 and the other side of which is connected between the switch 39 and the coil 59. The switch 67 on the interior of the counter 66 is connected on one side to the line 49 and on the other side through a dresser coil 69 back to the line 48, the coil 69 serving to set in motion a dressing cycle in the well-known manner. Connected around the switch 67 is a normally-open contactor 71 forming part of the relay 72.

The operation of the invention will now be readily understood in view of the above description. First of all, most of the elements in the grinding machine operate in the conventional manner. The motor 25 ope-rates to rotate the drive platen 24 which rotates the workpiece 12 about the axis of the surface of revolution which is to be finished. In a similar manner, the wheelhead 13 rotates the spindle and the abrasive wheel 14 at high speed. All longitudinal motions between the wheel 14 and the workpiece 12 are brought about by use of the actuator 29 sliding the table 22 over the ways 23. Furthermore, all transverse motion between the wheel 14 and the workpiece 12 takes place over the ways 18 and the ways 21. The main feed motion takes place in the cylinder 34 while a compensating motion takes place by means of the screw 41 operated by the actuator 44 through therack 43 and the pinion 42. Assuming that the wheel 14 is dressed and all elements are properly geometrically related to one another, the workhead 11 is advanced in the direction of the wheel 14 by the actuator 29 until the wheel 14 lies within the bore in the workpiece. Then, the movement of the table 22 and the workhead 11 is stopped (with the exception of the usual reciprocation) and oil is introduced into the cylinder 34 advancing the wheel 14 against the back surface of the workpiece bore. The pressure of the oil in the actuator 34 is limited so that this, in effect, limits the amount of force or pressure brought by the rotating wheel 14 against the rotating surface of the workpiece 12. Feeding in this manner is known as controlled force feeding in contrast to the so-called feed rate feeding in which .t-hewheel is advanced at a predetermined rate and the force varies. In the present case, the force is kept below a constant predetermined value and the rate of motion of the wheel into the workpiece varies with the amount of work encountered in grinding the surface. While the grinding is taking place, the actuator 29 is producing a slight reciprocation of the table 22 and the workhead 11 along the ways 23 with the effect that the ends of the wheel 14 emerge from one side of the bore in the workpiece or the other. When. the mot-ion takes place so that the end of the bore adjacent the gage 26 is exposed, the gage 26 measures the bore. For instance, if it is a plug gage, as shown, it will try to. enter the bore. If the bore is still too small, the plug will not be able to enter and conditions remain as before. The plug is advanced toward the bore by the actuator 28. Eventually, the grinding will take place until the bore is exactly the right size in which case the gage 26 will enter the bore. This will cause the disc 33 on the.

gage spindle 27 to engagethe switch 32 and close it. This terminates the grinding operation, causes the actuator 34 to reverse its motion and withdraw the wheel 14 away from the surface of the workpiece. After the wheel has been withdrawn radially, the actuator 29 causes.

the workhead 11 to move longitudinally away from the wheel. As the workpiece is drawn axially away from the wheel, the diamond passes over the surface of the wheel, on occasion, and dresses it so that it is ready for the next cycle. It will be understood that the grinding cycle is oversimplified; in most cases there will be a rough grind followed by a finish grind. The forces introduced.

by the actuator 34 are different in the two cases. When the actuator 34 withdraws the wheelhead 13 forwardly on the occasion of a dressing cycle, the table 16 on which the wheelhead is mounted is backed off until it strikes the back-off stop 35. Then, longitudinal motion of the workhead 11 will causes the diamond to remove a portion of the surface of the wheel 14. On occasion, due to wear of the wheel, it will be necessary to advance the wheel toward the work surface and this is accomplished by the compensating mechanism of which the screw shaft 41 is the principal element and the actuator 44 is the instigator.

Now, in setting up the machine, the first switch 38 is set up so that, when the wheelhead table 16 is against the backoff stop 35 and the wheel 14 is dressed by the diamond holder 31 in this position, the cycle will cause the bore to be exactly the right size at the time that the finger 37 strikes the switch 38. As a practical matter, this switch is set so that the part would be ground slightly nndersize in its diameter by approximately .001 inch if the cycle were terminated when the switch 38 is closed. Of course, in the cycle itself, the grinding will continue for another .001 inch of diameter until the gage 26 enters the bore and terminates the cycle. The second switch 39 is located on the table 17 so that, when it is closed by the finger 37 the grinding has progressed about .001 inch further on the diameter. Theoretically, this is the time when the gage 26 should enter the bore. Now, due to the wear on the wheel, the gage 26 will enter the bone and terminate the cycle at various times relative to the closing of the

switches

38 and 39 and the present apparatus makes changes in the relationship of the parts in accordance with the time when this gage determines that the bore is exactly the right size. Now, if the gage 26 enters the bore in the workpiece and closes the switch 32 before the finger 37 on the table 16 reaches the first switch 38 on the table 17, this condition is an indication that the wheel surface is larger than is ideal. The backoff stop is moved forwardly to make the wheel smaller and, at the same time, a dress operation is called for. Electric-ally, the closing of the switch 32 causes the coil 51 of the relay 52 to be energized, which closes the normally-open contactor 53. This completes the circuit from the power line 48 through the contactor 53, through the normally-closed contactor 54, through the incremental motor 36 (connected to the back-off stop 35) and through the coil 73 .to the power line 49, so that an increment of back-01f stop adjustment forward takes place. The energization of the relay 52 also causes the closing of the normally-open contactor 71 and causes current to pass through the coil 69 bringing about a dressing operation.

If, when the gage 26 enters the bore and closes the switch 32, the finger 37 has already arrived at the switch 38, nothing happens. This is because the closure of the switch 38 causes the energization of the coil 55 of the relay 56. The first thing that this relay does is to close the normally-open contactor 58 which operates through the line 57 to hold in the relay. At the same time, it opens the normally-closed relay 54 which prevents the back-off stop from being adjusted. This also prevents the current from passing through the coil 73 of the relay 72, so that the contactor 71 is not closed and a dressing operation does not take place.

Now, if the gage 26 enters the bore when the finger 37 has arrived and closed the switch 39 (the switch 38 having been previously closed and re-opened by passage of the finger), then a difierent situation prevails. First of all, the closing of the switch 32 causes the energization of the relay 52 as before. Part of this relay includes the normally-open contactor 62 which is then closed. The closing of the switch 3? energizes the relay 61 and locks in that relay through the normally-open contactor 68. If the gage switch 32 later causes the closing of the normally-open contactor 62, then current passes through the coil 63 and operates the servo valve 47. This causes oil to fiow to the actuator 44, which actuator operates through the rack 43 and the pinion 42 (as well as the ratchet mechanism) to rotate the screw shaft 41 and cause a compensation motion of the wheelhead 13 toward the portion of the bore which is to be ground and toward the diamond holder 31. At the same time that the coil 63 is energized, so is the coil 64 which operates on the operating lever 65 of the counter 66 which records the fact that a single compensation action has taken place. A predetermined number of counts has been previously set in the counter 66 in the usual way and, when this number is reached, the switch 67 is closed, which causes current to pass through the coil 69 and produce a dressing operation. In all cases, after the grinding cycle has been completed, it is presumed that there are other contacts that cause various operations to take place, as is normal practice; among these is the opening of a normally-closed contactor 101 whose opening serves to drop out any relays that have previously been locked up, with the exception of the internal circuits of such devices as the counter 66.

In a general way, then, compensation through the screw shaft 41 takes place by a predetermined amount only when sufiicient wear takes place so that the gage 26 enters the bore late by a certain amount, this amount being determined by the setting of the

switches

38 and 39. Furthermore, a dressing operation takes place only after a certain number of compensation movements. Now, compensation takes place only because the measuring apparatus indicates that more than a predetermined amount of wear has taken place on the wheel. If, then, at the same time dressing takes place, only after a certain number of compensation movements, this means that dressing takes place after a predetermined amount of wheel wear also.

In the preferred embodiment, the two switches are set approximately .0005" apart which represents .001" on the diameter of the workpiece. Furthermore, the increment of compensation introduced by the screw shaft 41 is approximately .0002 inch. It should be pointed out that the gage entering the bore in the workpiece early (that is to say, before the finger 37 contacts the first switch 38) is due usually to diamond wear or, perhaps, even a chipping of the diamond. This means that the back-01f stop 35 is advanced toward the rear of the machine and this causes the wheel 14 to advance closer to the diamond when dressing takes place.

Although the present invention is illustrated in connection with a machine which uses the controlled force method of feeding, it will be understood that it can be used also with a feed rate type of feeding operation.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. An internal grinding machine, comprising (a) a base on which are mounted a workhead having a workpiece-holding means, a wheelhead having a rotatable abrasive wheel, and a dresser,

(b) means bringing about relative movement transversely of the wheel axis between the wheelhead and the workhead to produce grinding cycles on successive workpieces,

(c) means bringing about a compensating transverse movement on occasion,

(d) means making a determination of the total amount of wheel wear which has taken place since the last compensating movement at the end of each grinding cycle and causing a compensating transverse movement when the wheel wear exceeds a predetermined amount, and

(e) means bringing about a dressing operation after a predetermined number of compensating movements have taken place since the last dressing operation.

2. An internal grinding machine as recited in claim 1, wherein means is provided to produce a fixed amount of transverse movement of the wheelhead towards the dresser when the wheel wear is less than another predetermined amount.

3. An internal grinding machine, comprising (a) a base on which are mounted a wheelhead, workhead, and dresser,

(b) feed means for bringing about movement between the workhead and the wheelhead to produce grinding cycles on successive workpieces,

(c) an in-process gage terminating the operation of the feed means when each workpiece reaches final size,

(d) location means determining a precise relationship of the wheelhead relative to the workhead,

(e) means determining the distance between a first point where the gage operates and a second point where the location means operates,

(f) compensation means operative when the first point is reached a distance greater than a predetermined distance after the second point is reached,

(g) a counter registering the number of times that the compensation means is operative since the last dressing operation, and

(h) means operative after a predetermined number has been reached to bring about a dressing operation.

4. An internal grinding machine as recited in claim 3,

wherein a back-off stop is provided to locate the relationship of the wheelhead and workhead during the dressing operation, and wherein an incremental movement of the stop is made if the first point is reached before the second point.

5. A grinding machine, comprising (a) abase,

(b) a workhead having a workpiece-holding means mounted on the base,

(c) a wheelhead having a rotatable abrasive wheel mounted on the base,

(d) a dresser operative to dress the wheel on occasion,

(e) means bringing about relative movement longitudinally and transversely of the Wheel axis between the wheelhead and the workhead to produce grinding cycles on successive workpieces,

(f) means making a determination of wheel wear, the said means consisting of apparatus measuring the dimensional relationship between a first locus at which finish size is reached and a second locus at 8 which a fixed point in the movement between the wheelhead and the workpiece is reached,

(g) an in-process gage for determination of workpiece finish size, and

(h) means bringing about a dressing operation of the dresser on the wheel when the said determination reaches a predetermined amount.

6. A grinding machine as recited in claim 5, wherein, when the first locus is reached before the second locus, the position at which dress takes place will be changed and wherein, when the first locus is reached after the second locus and the dimensional relationship exceeds a predetermined amount, a compensation movement between the wheelhead and the diamond takes place.

7. A grinding machine as recited in claim 6, wherein a counter registers the number of compensations that have taken place since the last dressing operation and, when a predetermined number of compensations have taken place, to bring about a dressing operation.

References Cited UNITED STATES PATENTS 1,684,485 9/1928 Guild et a1. 5l50 2,897,638 8/1959 Maker 5l-50 X- 2','932,130 4/1960 Blood et a] M 5150 3,003,293 10/1961 Gluchowicz 5l165 3,167,891 2/1965 Coes etal 5l281 X LESTER M. SWINGLE, Primary Examiner.

Claims

1. AN INTERNAL GRINDING MACHINE, COMPRISING (A) A BASE ON WHICH ARE MOUNTED A WORKHEAD HAVING A WORKPIECE-HOLDING MEANS, A WHEELHEAD HAVING A ROTATABLE ABRASIVE WHEEL, AND A DRESSER, (B) MEANS BRINGING ABOUT RELATIVE MOVEMENT TRANSVERSELY OF THE WHEEL AXIS BETWEEN THE WHEELHEAD AND THE WORKHEAD TO PRODUCE GRINDING CYCLES ON SUCCESSIVE WORKPIECES, (C) MEANS BRINGING ABOUT A COMPENSATING TRANSVERSE MOVEMENT ON OCCASION, (D) MEANS MAKING A DETERMINATION OF THE TOTAL AMOUNT OF WHEEL WEAR WHICH HAS TAKEN PLACE SINCE THE LAST COMPENSATING MOVEMENT AT THE END OF EACH GRINDING CYCLE AND CAUSING A COMPENSATING TRANSVERSE MOVEMENT WHEN THE WHEEL WEAR EXCEEDS A PREDETERMINED AMOUNT, AND (E) MEANS BRINGING ABOUT A DRESSING OPERATION AFTER A PREDETERMINED NUMBER OF COMPENSATING MOVEMENTS HAVE TAKEN PLACE SINCE THE LAST DRESSING OPERATION.