GB2231288A - Thread-grinding machine for relief grinding of thread-cutting tools - Google Patents

Description

t b :2:;z-:3 a.:5a a a The present invention relates generally to

thread-cutting devices, more specifically to metal-cutting uachine tools employed for thread-cutting by means of a grinding wheel, and has particular reference to a threadbrinding machine.

The herein proposed thread-gr-inding machine can find application for cutting teeth in multipoint cutting tools, such as taps, gear hobs, disktype or form milling cutters, in which the teeth having relieved profile surfaces are confined between flutes and can be located along a helix or circumference. There can be at least one tooth on one thread of the helix or on one cizcumference, while the flutes can be either st--al.-ht or helical.

As commonly known, relieving the teeth Profile surfaces in multipoint tools allows the cutting tool tooth profile and the tooth relief " anGle to be maintained constant after repeated tool regrinding. With relieved tooth profiles, the projection of tooth outer edge on a plane perpendicular to the cutting tool axis is most often shaped as an Archimedean spiral. To obtain relieved surfaces behind the cutting edges of a multipoint tool, grinding machines are provided with a relievinG mechanism. The relieving mechanism comprises a cam having a profile shaped as an Archimedean spiral and kinematically associated with a drive adapted to rotate it. With every full turn of the reli-ievin,; mechanisL cam, a required relieved zooth profile is generated on each-of the workpiece sumfaces confined betiveen the fluze edges. The number of surfaces to be relieved is eqa-s:1 to the number of flutes. In the case of only one flute, the,,-ur.-7ace to be machined Y.1111 be located between the flute edges. If the number of 'Llutes is -reater, the surfaces to be relieved will be disposed between the edges of the adjacent flutes.

In relieving the teeth profile surfaces. it is of primary importance that the relieving mechanism be engaged in proDer tirme. VJith the relievins mechanism cam in the initial position, it is essential that, as the machining coramences, the cam rotation drive be engaged at the instant nhen the Grinding, wheel is brought in contact with one of the workpiece surfaces confined between the flute edges. As this takes place, the grinding Y,,heel has to come in contact with the surface to be relieved at a point in the immediate vicinity of the flute edge on the side of the relief or rake faces of the tooth in a multipoint cutting tool depending on the sense of rotation of the workpiece to be machined. If the rotary drive of the r'lieving mecharlisr, cam fails to be enga-,.ed at the right e;D time, as the grinding Y;heel is brou-ht in contact with other surfaces of the workpiece to be machined, the relieved tooth profile surface may be substantially changed, with attendant reduction in the yield per cent of sound finished products.

In thread-.-rindiny machines, there are incorporated various devices and arran-ements adapted to enable the r,o.rkpiece surfaces disposed between the flute edges, to be DrOPerlY oriented with respect to the grinding wheel, as they come to contact it.

Enown in the present state of the art is a threadgrindinG machine used for machining thread in taps having at least two flutes. The machine comprises a base mountino. a table with tvo supports f or the work iece to be 0 p machined, at least one of the supports being kinematically associated vith a i,.,ox"'-piece rotation drive rhich in turn is kinematically associated with a mechanism for table reciprocation lengthwise the axis of rotation of the workpiece to be machined, and a theelhead incorporating a grinding wheel and a drive for rotating it, the wheelhead being kinematically associated with a drive adapted to effect its translational movement in a direction perpen--;icular with the axis of rotation of the woxkpiece to be machined, and a relieving mechanism whi.ch is associated.

via a clutch, with the workpiece rotation drive and comprises a cam which can be turned to predetermine a relieved profile of each of the workpiece surfaces confined between the flute ed-es. The machine is also provided with a means 0 for orienting the woxkplece to be machined as it comes to contact the grinding wheel surface at the beginning of the machining process when the relieving mechanism cam is in the initial position. Tap blanks have at least two 1 flutes and a shank provided with flats, the surfaces of the flats being parallel in pairs. Specifically, the shank has a square cross-section. For a batch of taps to be machined, one of the shank flats is strictly oriented in relation to one of the flutes.

The means for orienting the workpiece to be machined i...hen it comes in contact with the grinding- wheel surface at the beginning of the machining process, is made in the form of a holder adapted to be fitted in the loading device of the thread-gr-inding machine. The holder is shaped as a rod having square cross-sectional sockets provided lengthwise its axis and adapted to receive the shanks of tap blanks. Proper orientation of tap blanks is attained due to their being loaded in the holder in a similar manner so that the flats and flutes be disposed similarly with respect to the rod axis. Such a means for orienting the workpieces demands accurate orientation of the shank flats in relation to the flutes for every blank in a batch of tap blanks to be machined. Besides. the ad- ditional operation of loading the blanks into holders increases the tap manufacturing costs.

0 Another prior-art universal thread-rinding machine intended for machining the blanks of most diverse multipoint toolsy such as taps. gear hobs or special-purpose milling cutters having at least one flute. is known to comprise a base mounting a table with two supports for the -5 to be Machined, at least one of the supports being kinematically asiociated with a worlepiece rotation drive which in turn is kinematically associated with a mechanism for table reciprocation lenz- bthviise the axis of rotation of the workpiece to be machined, and a wheel head incorporating. a grinding, wheel and a drive for rotating it, the wheelhead being kinematically associated with a drive adapted to effect its translational movement in a direction perpendicular with the axis of rotation of the workplece to be machined, and a relieving mechanism v.!.--ich is kinematically associated with the ijoxkDiece rotation drive through the agency of a clutch linked with a means for orienting the workpiece to be machined as it comes to contact the grinding wheel surface at the beginning of the machining process when the relieving mechanism cam in in the initial position, the cam being rotatable to predetermine the shape of relieved profile of each of the workpiece surfaces confined between the flute edges.

The means for orienting the workpiece to be machined is fashioned in the form of a faceplate secured on the extension of the spindle of the workpiece rotation drive, and serves as a clutch for the relieving, mechanism and the workpiece rotation drive. The faceplate has a base, a rotary member and a driveplate and enables the spindle, the workpiece and the relieving mechanism carA to be kinematically linked to each other by means of a driver dog secured'on the workpiece to be machined.

Proper o--iencp,-uior. of the vorkpiece is a preparatory techno'Lot,ical Drocedure which is intended to be carried out manually by the 0Derator and v..hich involves bringing t-he grinding wheel surface in contact with the flute edge, while the relieving mechanism cam is kelpt in its initial position, by changing the ang ulax position of the rotary member of the faceplate relative to its base, the position oil the workpiece being checked visually.

Angular position of the vjox',,.plece to be machined can be 10 adjusted by turning it with respect to the driver dog v.ithout dist-arbing the position of the rotary member of the faceplate as related to its base.

In actual practice, the workpiece orientation time may vary from two to five minutes depending upon the operator's professional skill. For every new batch of cutting tools to be machined, the orientation means has to be reset and the initial workpiece datum settings 0 have to be established. Fuxthe=ore, the accuracy of viorkpiece orientation Is also dependent on the operator's skill. As a result, the operating efficiency of the threadgrinding machine is considerably reduced.

It-is therefore an object of the present invention to increase the operating efficiency of the thread-grinding machine owing to reduced time required for setting the workpiece to be machined in a desired position preparatory to machining.

With the foregoing and other objects in view the present invention thus resides in the fact that in a thread-rinding machine intended for machining the blanks of multipoint cutting tools having at least one flute, comprising a base mounting a table with two supports for the i,.,orL-piece to be machined and a wheelhead; at least one of the supports is kinematically associated with a workpiece rotation drive which in turn is kinematically associated with a mechanism for table reciprocation lengthwise the axis of rotation of the workpiece to be machined; the v.,heell.iead incorporates a grinding Y.heel and a drive for rotatinj it, v.hile the wheelhead is kinematically associated with a drive adapted to effect its translational movement in a direction perpendicular with the axis of rotation of the workpiece to be machined; the workpiece rotation drive is kinematically associated v.ith a relieving mechanism through the agency of a clutch linked with a means for orienting the workpiece to be machined as it comes to contact the grinding wheel surface at the beginning of the machining process when the relieving mechanism cam is in the initial position, the cam being rotatable to predetermine the shape of relieved profile of each of the morkpiece surfaces confined between the flute edges; the means for orienting the workpiece to be machined as it comes to contact the grin- 2.5 ding wheel surface at the beginnin,.,7 of the machining process, comprises a pickup of grinding wheel end position at preset feed, v.,hich Dickup is electrically associated with the v-.,orkpiece rotation drive, a grinding v..ieel-to-workpiece contact pickup, the outputs of both of the pickups being connected to the inputs of a controlled clutch engagement control unit which has its output electrically associated with the controlled clutch and adapted to generate a control pulse in response to a pulse produced by the grinding mheel-to-viorkpiece contact pickup, and delivered to its input after a pulse sent by the pickup of grinding mheel end position at weset feed.

In the herein proposed thread-grindinG machine. the controlled clutch engagement control unit adapted to generate a control pulse in response to a pulse produced by the grinding vjheel-to-workpiece contact pickup and delivered to its input after a pulse sent by the pickup of grinding wheel end position at preset feed, provides for engagement of the controlled clutch and for starting the relieving mechanism at the instant when the workpiece is in a required position irrespective of the position it assumed initially mhen secured between the supports. viz., in a position when the grinding wheel is in contact xvith the edge of the workplece flute on the side of rake or relief surface of the tooth in a multipoint cutting tool, depending on the sense of rotation of the workplece to be machined.

As the grinding wheel is advanced for the amount of preset feed towards a stationary workpiece, two different kinds of their mutual position can be encountered: one position when the advanced---rinding wheel is brought in contact with the workpiece at any arbitrary point located between the flute edges, and the other position when the advanced grinding wheel fails to come in contact with the workDiece to be machined, that is after feed motion is completed, part of the grinding theel is arranged between the flute edges of the viorkpiece to be machined.

Mien the grinding wheel and the workpieoc are in the former position described above, the grindint; wheelto-wo.rkpiece contact pickup will operate first, while the controlled clutch engagement control unit produces no pulse to be sent to the controlled clutch. Next, as soon as the grinding wheel assumes its end position, the pickup of grinding wheel end position at preset feed will operate whereupon the workpiece rotation drive is engaged and the workpiece is brought in rotation in the direction of working motion.

At the instant when, in the oDurse of workpiece rotation, a flute occurs opposite the grinding wheel face, no pulse is produced at the output of the grinding wheel- 25to-workpiece contact pickup, but pulses will be produced again when the grinding wheel strikes the flute edge and rill be awlied to the inDut of the controlled clutch engagement control unit which senerates a control C) c) ---alse to effect en-a-ement of the controlled clutch and 0 0 starting of the relieving mechanism.

-,.hen the workpiece to be machined and the grinding wheel are in the lat c;er position mentioned hexeinbefore, the pickup, of grinding %,..heel end lposition at preset feed operates first to produce a pulse to be applied to the innut of the controlled clutch enf-a--ement control unit, with the result that the viorkD-iece rotation drive is engaGed and a control pulse is -enercted to entSa--e the controlled clutch in exactly the same sequence as that described for the former of the mutual positionsdescribed above. The clutch is engaged, thus settinG the-relieving mechanism cam in motion. In such a manner, at the instant 'when the relieving mechanism is engaged, the blank of any multipoint cutting tool will find itself in a required position.

This allows the total workpiece machining time to be considerably reduced due to reduced time required for the technological procedure involving orienting the workpiece preparatory to machining, thus improving the operating efficiency of the tb--ead- grindinj machine. The workpiece orientation accuracy and time are no longer dependent on the cutting tool, the number or arrangement of the flutes, or operator's skill.

o additional resettins an' of the d torkriece orientation means is required in machining the blanks of various kinds af multipoirlu cuttiti6: tools usin,:,,, the same feed at the first pass.

Versatility of the herein proposed workpiece orientino, =cans enables use of simple constructional arrangements for the v.,,orkpicce loading devices.

The expenditures involved in ea, in-ing both universal tl-,read-griuding machines an-J automatic machine tools with the herein proposed orienting means are minimized.

In what follows the preser.-u invention will now be disclosed in a detailed descripzion of an illustrative embodiment thereof with reference to the accompanying drawinGs, wherein:

FIG. 1 is a view of a simplified kinematic diagram of a thread-grinding machine incorporating a controlled clutch engageaent control unit, according to the invention; FIG. 2 is a view of a functional block diagram of the controlled clutch engagement control unit; FIG. 3 is a view of a workpiece to be machined and the grinding wheel shown fragmentarily to still further illustrate their mutual position at the instant i,.,hen the grindinG wheel is broujht in contact Y,.ith the work piece to be machined; FIG. 4 is a view of FIG. 3 showing the grinding wheel positioned opposite the flute; -rIG. 5 is a view of FIG. 3 sho".in zhe grinding -,.heel brought in contact i.iiu-h the flute edge disposed on the side of the tooth rake surf ace of the cutting tool.

A thread-grinding, machine comprises a base 1 (FIG. 1) mounting a table 2 with two supports 3 and 4 in which a multipoint cutting tool blank 5 is scoured. Te blanks 5 of multipoint cutting tools such as taps, gear hobs, disk-type or form milling cutters, have cylindrical or conical surfaces provided with at least one flute either parallel to the blank axis or disposed alorV, a helix. Depending upon the application of the cutting. tool, the number of flutes can vary from one to twenty four or more.

The support 3 is made in the form of a machine headstock incorporating a spindle 6 accommodating a centre 7 provided with a collet chuck 8. The support 4 is in fact the machine footstock where a centre 9 is held. At least one of the supports 39 4 is kinematically asso- ciated with a drive 10 fox rotatin; the v.oxkpicce to be machined.

According to the herein described embodiment of the thread-grinding machine, the workpiece rotation drive is associated with the support 3.

The workpiece rotation drive 10 comprises an electric motor 11 which is installed on the base 1 and has a shaft zhereo'L linked, via a belt drive 12, to a spline shaft 13 associated with the 06 of the SUPPort 3.

The table 2 is installed on the base 1 so as to be free to reciprocate lengthwise the axis of rotation of the workpiece 5 and it is linked with a mechanism 14 for table reciprocation, that is the longitudinal feed mechanism.

The table reciprocation mechanism 14 comprises a leadscrev; 15 thich is rotatably mounted on the tajle 2 10 parallel with the axis of rotation of the blank 5 and en.,aZes.with a nut 16 secured on the base 1.

The workplece rotation drive 10 is kinematically associated mith the table reciprocation mechanism 14 by means of a ch3nge-gear quadrant 17 intended for presetting the required thread pitch. The constructional arrangement of the change-gear quadrant 17 used in the threadgrinding machine, is comLnonly known. One gear 18 of the change-gear quadrant 17 is made fast on one extension of the leadsc-rew 15, while another gear 19 is installed on the spline shaft 13 of the viorkpiece rotation drive 10.

The base 1 mounts a vjheelhead 20 which is kinematically associated with a drive 21 adapted to effect Its translational movement in a direction perpendicular mith the axis of rotation of the workpiece 5 to be machined. The wheelhead translational movement drive 21 comprises an electric motor 22 whose shaft carries a gear 23 engaging with a gear 24 which is rigidly connected to a L nut 25 installed on the wheelhead 20 so as to be free to rotate about its axis. The nut 2.5 engages with one extension of a cross feed leadscrew 26. The axis of the cross feed leadscrew 26 is disposed in a plane perpendicular to the axis of rotation of the vorkpiece 5. The other extension of the cross feed leadscrew 26 is traver- sably mounted in a support 27 scoured in the base 1. AccordinG to the herein described embodiment of the threadgrinding machine, the mheelhead translational movement 1 C) drive 21 is kinematically associated with a relieving mechanism 28. The relieving mechanism 28 comprises a roller 29 rigidly connected to the cross feed leadscrew 26. The roller 29 is continuously kept in contact with a cam 30 of the relieving mechanism 28. The cam 30 is ro- tatably mounted on a shaft 31 and has a profile most com;2only shaped as an Archimedean spiral. Every full turn of the cam 30 of the relieving mechanism 28 enables a required relieved tooth profile to be generated on each of the workpiece surfaces confined between the adjacent flute edges. According to another prior-art em- bodiment of the thread-grinding machine, the relieving mce,IianisL can be kinematically associated with one or two supportus for mounting the workpiece to be machined.

To provide for continuous contact between the rol- ler 29 and the cam 30 of the relieving mechanism 28$ the wheelhead 20 is held against the base 1 by means of S tel'.sl on s-urilig 32 installed in such a mariner -hat its 3-xis is suos-lkl$all.-,j-ial!Y parallel to the cross feed leadscrew 26.

The relieving mechanism 28 is ally asso- ciated with the vjoxlr,.Dicce rotation drive 10 throu-Sh a clutch made in the form of a controlled clutch 33 having one of its members installed. on the shaft 319 whereas the other its member is mounted or. one extension of a shaft 34 of a change-gear quadrant 35 of the relieving mechanism 28, the gear quadrant being comprised of a number of change gears, one gear 36 being installed on the other extension of the shaft 34. Another gear 37 of the change-gear quadrant 35 is mounted on the spline shaft 13 of the workpiece rotation drive 10.

The change-gear quadrant 35 of the relieving mechanism 28 is set up in such a manner that for every full turn of the workpiece 5 to be machined, the number of full revolutions of the cam 30 of the relieving mechanism 28 be equal to the number of -wojkpicce surfaces confined between the flutes.

The ivheelhead 20 has a spindle 38 adapted to carry a grinding wheel 39 which is kinematically associated vith a drive 40 for rotating it. The grinding wheel drive 40 comprises an electrio motor 41 connected to the spindle 38 of the grinding wheel 39 through a belt drive 42.

The controlled clutch 33 is associated vith the viork.icce orientation means at 'the initial instant of machininG Y.,hen the viorkpicce is broujht in contact with t-he surface of the grindinZ wheel 39, rhile the cam 30 of the relieving mechanism is in its initial position.

The controlled clutch 33 can be made in the form of any controlled clutch, such as electromagnetic friction clutch or hydraulic-op"rated friction clutch, or any prior-art controlled clutch provi-ding for the shafts to be connected substantially in any arbitrary position. The means 'Cor omienting the v,,or':.-ricce at the initial instant of machining when the torkpiece is brought in contact with the grinding wheel surface, comprises a controlled clutch engagement control unit 43 which is elect- rically associated with the centrolled clutch 33.

The workpiece orientation means comprises a grinding v.,heel-to-vjoxkDiece contact pickup 44 mhose output is con nected to an input 45 of the controlled clutch engagement control unit 43.

The grinding ivheel-to-viorkpicce contact pickup 44 is in fact a piezoelectric transducer installed imme diately on the centre 9 of the support 4. Use can be made of any other prior-art pickup capable Of DrOdUCin a pulse at its output mhen the grinding wheel is broujht in contact with the workplece.

-,1 11 I- The work-Diece orientation means also comprises a:icup 46 of grinding wheel end position at preset feed which is connected to an inDut 47 of the controlled clutch engagement control unit 43. The pickup, 46 can be made in the form of an ordinary limit switch installed on the base 1 and adapted to inmeract with a cam made fast on the mheelhead 20 whose position predetermines the amount of preset feed of the grindi ng wheel 39.

The pickup 46 is electrically associated with the viorkpicce rotation drive 10.

The thread-grinding machine also comprises a pIckup 48 of initial position of the cam 30 of the relieving mechanism 28. The pickup 48 of initial DOSition of the relieving mechanism cam can be made in the form of a contact sT.,itch mounted on the base 1.

The drive for rotating the cam 30 of the relieving mechanism 28 is made in the form of the workpiece rotation drive 10. Use can also be made of a separate drive (not shown in FIG. 1) for bringing the cam 30 of the, relieving mechanism 28 in the initial position.

The controlled clutch engagement control unit 43 is electrically associated mith the controlled clutch 33 and is adapted to -enerate a control pulse in response to a pulse produced by the grinding rheel-toijorkpiece 2.5 contact pickup 44 and delivered to Its input after a pulse sent by the pickup, 46 of grinding wheel end position at preset feed. An embodiment of the funct-ional block 17 dia--raru of the controlled clutch engagement control unit 43 is represented in FIG. 2. It co-prises a twoinput AND gate 49 whose one input serves as the input 45 of the controlled clutch enGagement control unit 43 and is connected to the grinding wheel-to-workpiece contact pickup 44. The other input of the two-input AND gate 49 serves as the input 47 of the controlled clutch engagement control unit 43, and is connected to the pickup 46 of grindine, wheel end position at preset feed. The o-atput of the two-input AIM gate 49 is connected to one of the inputs of a two-input AND gate 5U 'which is connected i,,.ith its output to the input of an OR gate 51. The output of the OR gate 51 is connected to one of the inputs of an AIM gate 52. The input and the output of the OR gate 51 are interconnected. The AND gate 52 is connected with Its output to the input of an OR gate 53. The output of the OR gate 53 is connected to one of the inputs of a two- input AND gate 54. The input.and the output of the OR gate 53 are inter conne cted - The two-input A17D gate 54 is connected with its output to the input of an OR gate 55. The second input of the two-input AND gate 54 is connected to the first input of the two-input AND gate 49. The f ixst input of the AND gate 49 is also connected to the inputs of NO gates 56. 57, as well as to one of the in- 1-5 2.5 Duts tylo-iriput A11D -ate 58. The:'.0 gate 56 is con nected rith its output to the second Input of the two input AND G.at-e 52 ijhich is connected -,..ith its first inDut to the input of a NO gate 59. The N^J gate 57 is connected with its output to one of the inputs of a two input AND gate 60 which is connected its other input to the second input of the two-input AND gate 49, and Y.1th izs output, to one of the inputs of a two-input AND gate 61. The other input of the two-input AIM gate 61 is connected to the output of the 1,70 gate -':.c,. The output of the two-input AND gate 61 is connected to the input of an OR gate 62 whose output is connected to its input. The output of the OR gate 62 is connected to the other input of the two-input AND gate 53 and to the input of a NO gate 63 whose output is connected to the other input of the two-input AND gate 50.

The two-input AIM gate 58 is connected with its output to the input of the OR gate 55 whose output serves as an output of the controlled clutch engagement control unit 43.

0 Z.) Illustrated in FIGE 39 49 5 is the tap blank 5 having three flutes 64 and three surfaces 65 of the blank 5 each of which is confined between edges 0606 and 67 of the flutes 64. The edge 66 is disposed on 'he side of the tooth rake surface of the cutting tool to be machined, while the edge 67, on the side of the tooth relief surface. Arrows v and w indicate the sense of rotation of the work- -2j- Diece 5 and the -rinding,,,,heel 399 respectively, Y;hereas e denotes feed of the i,.,heel 39.

The thread-Grinding machine operates as follows.

First, according to the number of flutes provided on the blank 5 (FIG. 1) of the multipoint cutting tool to be machined, the change-gear quadrant 35 of the relieving mechanism 28 has to be set up in such a manner that t- he number of full revolutions of the cam 30 of the relieving mechanism be equal to the nu mber of surfaces of the 'workpiece 5 confined between the flute edges. Next, with the 'controlled c"'Lu-.ch 33 engaged, the cam 30 of the relieving mechanism 28 is brought in the initial position using the workpiece rotation drive 10. The initial position of the cam 30 of the relieving mechanism 28 corresponds to a vjheelhead position when the grinding wheel is spaced away from the axis of rotation of the workpiece, a distance substantially equal to the maximum or minimum cutting tooth radius depending on the sense of rotation of the workplece drive. In determining the initial position of the cam 30 of the relieving mechanism 28, time of response of the controlled clutch 33 has to be taken into consideration. The instant when the cam 30 of the relieving mechanism 28 arrives at the initial position is registered by the initial position pickup 48 of the cam 30 of the relieving mechanism 28, and a pulse is produced to stop the motor 11 of the work- 11 piece rotation drive lU and to disengaGe the controlled clutch 33. For bringing the relieving mechanism cam in the initial 'Dosition, use can be made of a separate relieving mechanism cam actuation drive (not shown in FIG.1).

Next, the torkpiece 5 is installed in any arbitrary position in the suPPorts 3 and 4 and held between the centres 7 and 9. The amount ofpreset feed e of the grinding wheel 39 is then established. The drive 21 for translational movement of the wheelhead 20 is engaged whereby the 'wheelhead is set in motion.

As the wheelhead 20 moves towards the stationary workpiece, but before it reaches its end position at preset feed,the grinding wheel 39 may come in contact with the surface of the workpiece 5. If this is the case, the pickup 44 installed on the support 4 will register its vibration and will send a pulse to the input 45 of the controlled clutch engagement control unit 43 which, how- LJ ever, produces no pulse to engage the controlled clutch 33. The grinding wheel 39 (FIG. 3) bites into the workpiece 5 for the amount of preset feed e. As soon as the grinding wheel 39 reaches its end position, the pickup 46 of grinding wheel end Position at Dreset feed mill operate and deliver a pulse to engage the workpiece rotation drive 1c). Besides, the pulse produced by the pickup 46 is transmitted to the input of the controlled clutch engagement control unit 43. The controlled clutch 33 is disengaged. If, in the course of rotation of the workpiece 5, the flute '04 occurs opposite the grinding wneel 39 (FIG. 4)s there will be no pulse at the output of the grinding vjheel-to-v,,orkpiece contact pickup 44 (FIG. 1), and, correspondingly, no pulse at the input 45 of the unit 43. V.7hen the edge 66 (FIG. 5) of the flute 64 comes in contact with the grinding wheel 39. the pulse will appear again and will be transmitted to the inDUt 45 of the controlled clutch engagement control unit 43. In response to the pulse produced by the pickup 44 and delivered after the pulse produced by the pickup 46, the controlled clutch engagement control unit 43 which generates a control pulse to engage the controlled clutch 33 and to start the relieving aechanism 28.

If, as the wheelhead 20 moves to its end position, the grinding wheel 39 fails to come in contact with the v..,orkpiece 5, then in the end position the grinding wheel 39 (FIG. 4) will be positioned opposite the flute 64. In this case, the pickup 46 (FIG. 1) of grindin- wheel, end position at preset feed will be the first to operate by producing, a pulse delivered to the input 47 of the controlled clutch engagement control unit 43. In response to a pulse produced by the piG]pup 46, the workpiece rotation drive will be started. The i,,ioxkpiece is set in rotation and, as soon as the edge 66 (FIG. 5) of the flute 64 comes 1 in con-wact with the Srindinj Y;heel 39, a pulse produced by the rickup 44 will be delivered to the input 45 of the controlled clutch engagement conzrol unit 43. In res-onse to the Dulse roduced by the -rinding wheel- to- k' - p 0 0 wo.-klece contact pickup 44 and delivered after the pulse produced by the pickup 45 o.- v.heel end position at preset feed, to the input 45 of the controlled clutch enga-ement control unit 43, the latter generates a control pulse to enbac;e the controlled clutch 33 and to start the relieving mechanism 28. After the conzrolled clutch 33 is engaged, if the amount of preset feed aGrees to the amount of machining allowance to be removed at a parti cular pass, the workpiece 5 keeps rotatirk-,. in the direc tion of ijorkin,.-,,, movement. If the amount of preset feed is found to be less than that of machinin,-,-, allowance, it is. recommendable to stop the workpiece _rotatbion d^rive 10 and to move the grinding wheel 39 in the direction of feed for the amount remaining from the machining allowance. If this amount is large enough as to cause undercutting of the workpiece to be machinedg it is reasonable to reverse the workpiece, the reversal to be effected in response to the pulses produced by the grinding vjheel-to-,workpiece contact pickup, 44 when the grindin,,- wheel 39 (FIG. 5) is brjught in contact with the edges 66 and 67 of the flute 64 25 to receive. the grinding. wheel 39.

As a result of-engagement of the controlled clutch 33, the kinematic train of the relievinG r-ecl"-anism 28 is com leted and the cam 30 predetermines motion of the p U rheelhead 20 to effect relieving of each surface con ined betmeen the flutes. The controlled clutch 33 remains en-aged in the course of entire cycle of machining of the v,,orkD!ece 5. Thus, the herein proposed means for orienting the morkpiece at the initial instant of machininG mhen the grinding rheel is brou.,-ht in contact vith 'It-#he morkpiece in the initial position of t-he relieving mechanism cam, automatically maintains a correct position of the v.. oxkpiece 5 of any multipoint c-a-utin- tool %%,,ith respect to the grinding vjheel 39, -Which substantially increases the operating efficiency of the thread-grinding ma chine The controlled clutch engagement control unit 43 operates in the folloving manner.

A pulse first produced by the grinding wheel-to-viorkpiece contact pickup 44 and delivered to the input 45 (FIG. 2) of the unit 43 is then applied to the inputs of AND gates 49 and 54 and to the inputs of NO gates 56, 57. Next, as the pickup 46 of grinding wheel end position at preset feed operates, a pulse is applied from the input 47 of the unit 43 to the other input of the AND gate 49 and to the other input of the An., gate 60. If pulses are applied to both of the inputs, the AND gate 49 operates to send a pulse f rom its output to one of the in- 1 Dut S L of the AND gate 5U whose other input receives a pulse f rom the output of the NO gate 03, since there is no pulse applied to the in-out of the NO gate 63. The AND gate 50 operates to send a pulse from its output to the input of the OR gate 51 which responds by sending a pulse from its output to the input of the OR gate 51.

Such a feedback loop provides for presence of a Dulse at the output of the OR gate 51 when there is no pulse at the output of the AlTD gate 5c). Besides, the pulse from the OUtDUt Of the OR gate 51 is applied to the input of the AND gate 52 and to the input of the NO gate 53. There is no pulse at the other input of the AND gate 52 since the pulse applied to that input from the NO gate 56 is zero.

1.5 There is no pulse at the output of the NO gate 53 connected to the input of the AND gate 61, thich prevents operation of the AND gate 61.

In the case of absence of pulses at the input 45 of the unit 43, no pulse is applied to the input of the NO gate 56 which sends from its output a pulse to the second output of the AND gate 52 so that the latter operates to deliver a pulse from its output to the input of the OR gate 53. As soon as the OR gate 53 operates, a pulse from its output is applied to the input of the AND gate.54 as well as to its own input to provide for presence of a pulse at its output if no pulse is applied from the output of the AND game 52.

At the initial Instant v,,hen a second pulse is deli vered at the input 45 of the unit 43, the unit sends a pulse to the second input of the A nx gate 54 which operates to deliver a pulse to the input of the OR gate 55 which in turn produces at its output a pulse sent to the controlled clutch whereby it is engaged.

If the first pulse, is applied -to the input 47 of the controlled clutch engagement control unim 43, it is delivered to one of the inputs of the AUD gate 49 and to one of the inDuts of the AND -ate 60. Since there is no pulse at the output of the NO gate 57, a pulse f Tom its output will be applied to the other input of the AND gate 60. The AND gate 60 operates to- produce a pulse at its output which is applied to one of the inputs of the AND ga-'u-e 61 r. hose other input receives a pulse from the output of the NO gate 53 'which has no pulse at its input.

The AND gate 61 operates to send a pulse from its output to the input of the OR gate 62. As soon as the OR gate 62 operates a pulse from its output is applied to its ovin input and to the input of the AND gate 58 as vell as to the input of the NO gate 63.

There is no pulse at the output of the NO gate 63, which prevents operation of the AND gate 50.

The application of a pulse f rom the output of the OR gate 62 to its own input provides for presence of a pulse 1 1 at its outpuz when there is no pulse at t-he output of the AND Gate 61.

W ,hen a DUlse is applied to the input 41- it is also appi-ied to the input of the AIM gate 58 Y;hich operates to produce a pulse at its output and deliver it to the input of the OR gate 55 which in turn produces a pulse at its output and sends it to the controlled clutch 33 whereby it is en-.

a.ed.

Thus, the controlled clutch 33 is engaged in response to the first pulse sent to the input 49 of the unit 43 by the grindinG -c. .heel-'vo-vjorú'-piece conzact pickup 441 if the pulse is received after the pulse froa the pickup 46 of grinding wheel end position at preset feed, applied to the input 47 of the unit 43; or in response to the second Dulse from the contact lpickup 44, LE its first pulse was received earlier than the pulse from the pickup, 46 of grinding wheel end position at preset feed.

Thus, the controlled clutch 33 will be engaged if the pulse applied from the grinding rheel-to-vjorkpiece contact pickup 44 to the input of the controlled clutch engagement control unit 43 was received after the pulse from the pickup 46 of grindinG wheel end Position at r)reset feed.

Claims (2)

1. --8Y.EAT Y.E CLAI11,1 IS

   I. A thread-grinding machine intended for machining the blanks of multipoint cutting tools having at least one 'lute, comprising a base mounting- a table with two supports for the ivoxkpiece to be machined and a rheelhead; at least one of the supports is kinema-vically associated with a workpiece rotation-drive which in turn is kinematically aseociated with a mechanism for table reciprocation lenGthwise the axis of rotation of the i,.,orkpiece to be machined; the wheelhead incorporates a grinding wheel and a drive for rotating it, while the theelhead is kinematically associated with a drive adapted to effect its translational movement in a direction perpendicular with the axis of rotation of the workpiece to be machined; 1.5 the workpiece rotation Qrive is kinematically associated with a relieving mechanism through the agency of a clutch linked with a means for orienting the workpiece to be machined as it comes to contact the grinding wheel surface at the beginning of the machining process when the relieving mechanism cam is in the initial position, the cam being rotatable to predetermine the shape of relieved profile of each of the workpiece surfaces confined between the flute edges; the means for orienting the workpiece to be machined as it comes to contact the grinding wheel surface at the beginning of the machining process, comprises a pickup of grinding wheel end position at A preset feed, nhich is electrically associated with the rorkiDiece rozation drive, a grindinG Y;heel-to-vjorkplece contact Dickup, the out. uts of both of the rickups being connected to the inputs of a controlled clutch engagement control unit T,,hich has its output electrically associated with the controlled clutch and is adapted to generate a control pulse in response to a pulse produced by the grinding wheel-to- workplece contact Dickup and delivered to its input after a pulse sent by the pickup of grinding 10 rheel end position at preset feed.
2. 2. A tuh-"ead-grindin&. machine made substantially as described above with reference to the accompanying draviings.

   Published 1990 at The Patent Offtce. State House,6671 High Holborn, LondonWC1R 4TP. Further copiesmaybe obtained &om The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray. Kent, Con. 1187