US2647348A - Feed mechanism for internal grinding machines - Google Patents

Description

Aug. 4, 1953 s, N 2,647,348

FEED MECHANISM FOR INTERNAL GRINDING "AQHINES Filed Feb. 20, 1952 2 Sheets-Sheet l I ROBERT 5. .1, Kim

Aug. 4, 1953 R. s. HAHN FEED MECHANISM FOR INTERNAL GRINDING MACHINES Filed Feb. 20, 1952 2 Sheets-Sheet 2 i120 121 m il 1150:

Rosem- 5. HAHN as, 4W

Patented Aug. 4, 1953 [TED STATES TNT OFFICE FEED MECHANISM FOR INTERNAL GRINDING MACHINES Application February 20, 1952, Serial No. 272,570

10 Claims.

This invention relates to feed mechanisms for internal grinding machines, particularly those in which the position of a cross slide determines the size of the work.

It has been the usual practice to arrange such machines so that in bringing the work and wheel together, the cross feed mechanism causes the wheel rapidly to approach the surface to be ground, and at a predetermined point to slow down and feed at an intermediate rate known as the rough grinding feed rate. The bulk of the material is removed during this rough grinding period. Commonly, rough grinding continues until the cross slide reaches a contact which causes separation of the wheel and work for trumg.

Grinding is then resumed at a slower feed rate of the cross slide, which is termed the finish grinding feed rate, until the cross slide'reaches a second contact which terminates the grinding cycle. At this point the workpiece is presumed to be ground to the proper size.

Quite accurate sizing might be obtained if the active surface of the wheel could be kept in an invariant position relative to the cross slide.

In practice it is found, however, that some fluctuations in workpiece size occur, especially if an attempt is made to increase the grinding rates. These size fluctuations are undesirable in many industries where it is desired to grind quickly large quantities of parts, all to exactly the same size.

These fluctuations in size which become pronounced at high grinding rates are due to variations in the amount of original stock to be ground out of each successive workpiece, to inherent variations in the rate of cutting exhibited by the wheel, and also to variations in the hardness of each successive workpiece. The force between wheel and work causes lateral and angular deflection of the parts, especially the wheel spindle which may be comparatively flexible, and the variations mentioned cause changes in these deflections. Hence the position of the wheel changes relative to the cross slide causing size variations.

Accordingly, this invention provides means for feeding the wheel against the workpiece in such a manner that the size fluctuations caused by varying deflections in the machine are reduced to a very low magnitude even under relatively high rates of grinding. The force-velocity characteristics of the cross slide feed are manipulated in such a way as to accomplish the desired results,

In previous machines of this general type the cross feed rate is essentially independent of the force acting between the wheel and work, i. e., a constant feed rate is established. This is highly desirable in order to round up and generally true the bore of the workpiece, but it is very undesirable for the purpose of controlling size, since the grinding force may fluctuate considerably as the wheel is fed into the workpiece and thereby cause variable deflections of the machine'and consequently size variations.

I have found it desirable to control the cross slide so as to maintain between wheel and work a constant force which is essentially independent of feed velocity. Under some conditions of grinding, I may use a predetermined constant force for the rounding up or roughing part of the operation and a lower predetermined constant force for finishing to size. I may also find it preferable to use the constant rate type of feed for roughing and the constant force type for finishing. My invention is adapted to use either combination. By using a predetermined force independent of feed rate, the deflections in the machine may be kept uniform from piece to piece, the active surface of the wheel is in a definite position relative to the cross slide, close size control may be attained even at high grinding rates, and the angular position of the wheel support maybe so fixed as to compensate for deflections and bring the active surface of the wheel parallel to the finished work surface.

I find it desirable, during the rounding up part of the operation, to hold one of the supports in such an angular relation to the path of reciprocation as to compensate for angular deflection in the supports.

In another embodiment of my invention I arrange the cross feed mechanism to apply to the cross slide a force which increases rapidly with any tendency for the slide to move in the direction to separate the wheel and work, but which is essentially independent of velocity in the feeding direction.

In the drawings:

Fig. 1 is a front elevation of a machine which embodies the invention.

Fig. 2 is a plan view of the portion of a machine of the invention including a wiring and fluid pressure diagram.

Fig. 3 is a view of switches and operating mechanism in one operative position.

Fig. 4 is a view similar to Fig. 3 with the switches in another position.

In the drawings, Figs. 1 and 2, grinding tool I is shown mounted on a spindle 2 which is supported and driven by suitable power means such as a motor in a wheel head 3. The wheel head is adjustably fastened to a swivel plate 5 by gibs I and 8 and the swivel plate 5 is pivoted at Iii to a slide I2. The gibs I and 8 permit the wheel head 3 to be adjusted toward or away. from its pivot I for a purpose to be described. The wheel head 3 may swivel horizontally around the pivot I0 on the slide I2 within limits determined in a clockwise direction by an adjusting screw I3I ,.threaded.in an extension I4 of the slide I2 and i'n'a'countcr. clockwise direction by a similar screw I36 threaded in a slide extension I6; Afislidable plug I8: loaded with a spring I33 int-he slide-extension IB'. urges the wheel head in a clockwise direction against the screw I3I and a piston-ZQ-intheslide extension I4 is arranged to urge the wheel head in a counterclockwise direction against the-screw I36 and plug I8 when fluid under pressure is introduced to itscylinder I35. v 1'. The slide I2 moves in ways-I.3:on a'.base;.II;in-a direction. (upwardly; in Fig. 2') to-allow-cross feed motionito be imparted to theewheel relative; tot-he work. A nut 22 attached-under theslide- I2: is engaged-bya lead screw I25inthe. base Mr and rotation of the lead screw I25; by an electric motor I23. through a pinion I26: and gear .IQ'I advancesand retracts the wheel headeand'wheel. The workpiece M is held ina chuck IIlIl onaspindle IBI journalled in a work. head 43; and driven'by any'convenient means, notshown; The workhead 43. ismounted on a slidable traverse table 42- arrangedto be moved-right. andwleftvas: viewed to cause the wheel I to. entertheworki l t in the usual: manner so that it can then be fed against the worksurface by the mechanism of: the present invention. The workpiece I-4-is-..traversed-toward and away from the'wheel I: by suit-- able means such as fiuid'pressureiromza pump;- 45, line -3 and reversing.valve -ifiacting ima-cyl. inder. 47: variously on either side oizai piston 418* connected to the traverse table 42-. througm a piston. rod'49, the fluid on theoppositesideaofi the piston 48 exhausting through thevalve-dfii and alineEO to a sump 52.

Fig..2.shows the parts inrough grinding, poshtion with the wheel head 3 swivelled. clockwise about. the pivot II) under force of the spring i3.I i,. so. as to compensate for angular deflections, in. the. wheel spindle and other. parts duetotheforce between wheel and workand'thereby, topresent. the cutting surface ofv thewheel.paral1el.to:the desired grinding line. Adjustmentof. the desired. amount. of swivelling is obtained by; the settingof. thescrewliii in this position.

' Means are provided for controlling. and. limiting to a predetermined value the amountLoi. normal force exerted bythe wheel against the work.

during grinding and, according to this invention, this is accomplished by measuring adefleotibn caused by the force and using this measure. to. control the feeding of the wheelagainst' the work so as to maintain the predetermined force on the wheel.

The measuring is accomplished'by a gage and the gage used to measure deflection may be of the non-contacting type, in which case'it isconvenient to measure the deflection of a rotating part such as the wheel spindle; work spindleor" close to the cylindrical periphery of the chuck I00 with air gaps IE4 and I05 between the chuck and the gages. The coil Hi6 and a rheostat I88 in series with it form one leg of a conventional bridge circuit indicated at H3. The coil I0? and a rheostat I09 in series with it form another leg. The other two legs are impedances Iii) and III.

The bridge circuit II! is supplied with alternating current from a power source 89 through a transformer H2. The output of the bridge is connected to=an amplifier H3 through a wire M4,. the upper leg of switch I42, contacts I I5 and H5 of a switch 90, and also through a wire Iil, the lower'leg of switch I42, contacts H8 and H8 of a; switch I31; a wire la and contacts I29 and I2'I of switches I56 and I45 and a wire Mfia.

1 The-output. from the amplifier H3 is fed to a standard electronic motor controller I22. The controller I22 is connected to the armature and field of the D. C. feed motor I23, by wires 2 I0, 2| I,

242 and1213; the latter two. being connected through 'aireversing switch I'M;

'Theibridgeicircuit 'IILis initially unbalanced- SO that when there is no defiectionof'the chuck I 89 and its spindle: IGI' the output. of the bridge is high; and the wheeli'i': is fed rapidly towardthe worlcMu. After'the: wheel and work are iniconta'ct,. the deflection: of the chuck Hi8 caused: by theforce. between" wheel. and work reduces the air gap lflfl andiincreasesathe air gap I85, changing the reluctance'of thegages I32 andv I 83, which tends to balance the bridge circuit I0; reducing its output to the amplifier I13 and reducing i the speedotieedmotor I23: The deflection caused by the force between 'wheel and work is "thus. held to a preset value during the roughing operation.

It itis desiredlto employ a constant rate insteadiof; aconstant force for the roughing opera-- tion, the switch I42 may be moved by handor other means-into-its upper position, connecting the. amplifier I I3- througlrthe contacts 5 I5 I and H5 to one side of.' the power source 82, and throughthe. 1ine-I45a, the contacts I2I, I29,=the wire II-Iaand-contacts H9 and I18 to'a potentiometer. I41 across the line 82. Roughing feed will then be at a fixedrate substantially independent ofthe force. betweenwheel'and work, instead of at. a constant. force, andasdetermined by the setting'of the potentiometer I I'I.

A'tl the-conclusionof the roughing operation a switch I 32" is. closed'by any conventional means,

controlled, for example, as by a gage entering the.

Work or as in Fig. 2, b the slide I2. reaching a preset position. A'n adjusting. screw 37- on an extension of theslide I2 is.preset to allow. the.

switch. I32 to close at the desired'pointl Closure of'th'e switch. I32 energizes a solenoid I33 from ap'ower. source BI'lifting a valve I34, which disconnects thecylinder I35 from an exhaust line 59" and connects it to a pressureline 53from the fluid' pressure pump 45;. swivelling the headl2 tacts- I40 and- I43 and disconnectsthe contacts. H8 and H9, which interrupts'the input to the amplifier I I 3' and stops the feed for truing.

A -the'table 42"is-moved"to'the'left toseparate the wheel and work axially in the conventional manner fortruing, a table dog it moves the switch I45 counterclockwise to disconnect the amplifier circuit through the wire I45a temporarily and a swinging dog I55 moves the switch I56 clockwise, as shown in Fig. 3.

As the table returns to grinding position, the dog I44 restores'the switch M to clockwise position, completin a connection from the bridge circuit to the amplifier ilt'through the line H! across the contacts Mb, I43, through a wire M311 and across the contacts I66 and I2I and the wire I45a. This starts the finishing feed, but as the rheostats I O6 and I G9 are now short-circuited, a relatively small deflection is suflicient to slow down the feed motor I23. Consequently the force applied to the wheel while finish grinding may be relatively light.

When the conclusion of the finishing operation is signalled in the usual way, either by the entry of a gage or, as shown, by the movement of the to its extreme left, or loading position. As grindin is finished a switch I43 is allowed to close by the movement of an adjusting screw 38 to energize a solenoid I49 from the power source 8i which closes a switch I 5B and establishes holding circuit through a switch I5I, and also lifting the switch I24 and reversing the feed motor I23, retracting the slide I2 until it opens the switch I5 I, allowing the switch I24. to drop into the feeding position shown. Retraction of the slide I2 again opens the switch I32, allowing the switch I3! to drop into rough feed position, as shown, and the valve I34 to drop into its lower position,

connecting the cylinder I 35 to exhaust and allowing the spring I30 to swivel the head 2 back into roughing position against the screw it I.

Movement of the table 42 further out to the loading position moves the switch I 45 to its counterclockwise or off position, and the switch I to its counterclockwise, or roughing position (Fig. 4). When the table is next moved into grinding position, the dog I55 rides over the switch I56, but the dog I moves the switch I to its clockwise position and feeding is resumed.

The wheel head 3 may be adjusted in the gibs I and 8 toward or away from its pivot Iii until the radial movement of the wheel I, when the head 3 is swivelled from roughing to finishing position, approximately equals the deflection set up during the roughing operation. Then when the wheel and work are brought into overlapping relation after truing, only a minimum feeding motion is required to resume grinding. The screws Il-BI and I36 are adjusted to make the ground surface truly cylindrical, or with the desired taper, both at the end of the roughing and the end. of the finishing operations.

I claim:

1. In an internal grinding machine, a work support, a wheel support having a grinding tool, said supports being relatively movable to feed the tool against a workpiece in said work support, feed means to feed said tool against the workpiece, gage means to measure the deflection in one of said support resulting from the force between tool and work, and rate control means for said feed means responsive to gage means whereby said defiection is maintained substantially constant during a part of the grinding operation.

2. In an internal grinding machine, a Work support, a wheel support having a grinding tool, said supports being relatively movable to feed the tool against a workpiece in said work support, feed means to feed said tool against the work- 2.0 slide I2 to a preset position, the table 42 is moved piece with a predetermined force substantiallyindependent of the feed rate, and control means for said feed'means, said control means being constantly responsive to a deflection of one of said supports resulting from the force between tool and work during grinding.

3. In the combinationas' set forth in claim 2,

one of said supports being pivotally movable relative to the other and means automatically to change the pivotal relation of said supports at a predetermined point during grinding thereby compensating for deflections in said supports caused by the force between said grinding tool and work.

4. In the combination as set forth in claim 2, one of said supports bein arranged for reciprocation relative to the other, a member controlling the angle between One of said supports and the path of said reciprocation, stops for said member, one of said stops having a fine adjustment, means to press said member against one of said stops, and means responsive to the position of one of said supports for pressing said member against another one of said stops thereby compensating for deflections in said supports caused by the force between said grinding tool and work.

5. In the combination as set forth in claim 2, said constant force feed means being operable during a part of said cycle, and means operating during another part of said cycle to feed said tool against the workpiece at a predetermined rate substantially independent of the force between said tool and said work.

6. In an internal grinding machine, a work support, a wheel support having a grinding tool, said supports being relatively movable to feed the tool against a workpiece in said work support, feed means including a motor to feed said wheel against the workpiece, a gage to measure defiections in one of said supports caused by the force between the tool and the workpiece and speed control mechanism for said motor, said speed control mechanism being responsive to said gage.

7. In combination as set forth in claim 6, means automatically to vary the response of said speed control means to said gage at a predetermined point whereby the feed rate changes for a given deflection in said support.

8. The method of grinding an internal surface of revolution in a workpiece, comprising the steps of rotating the workpiece in a support, rotating a grinding tool in a support, feeding one of said supports at a rate substantially independent of the force between tool and work for a rounding operation, then feeding one of said supports with a feed controlled by the deflection of one of said supports for a finishing operation thereby maintaining said deflection constant, and terminating the grinding when one of said supports reaches a predetermined position while said constant deflection is maintained.

9. The method of grinding an internal surface of revolution in a workpiece, comprising the steps of rotating the workpiece in a support, rotating a grinding tool in a support, feeding one of said supports at a rate substantially independent of the force between tool and work for a rounding operation, then feeding the tool into the work with a force substantially independent of the feed rate for a finishing operation thereby maintaining a constant force between said supports, and terminating the grinding when one of said supports reaches a predetermined position while said constant force is maintained.

;.1Q. .-In an,interna1 grinding machine, a work support a wheel support having a grinding tool, ;one of said supports being arranged to move in ;a -,path of reciprocation-relativeto the other to enter the wheel in the work and said supports beingrelativelymovableto feed the tool against iagworkpiece in the work support, feed means to .ieed-the toolagainst the workpiece with a predetermined force substantially independent of thefeed rate, gagemeans to measure the deflec- -,.tion inrone of said supports resulting from the z force between tool and work, rate control means for said feed means responsive to said gage means ,maintaining said deflection substantially con- .stant .during a part of the grinding operation, and means operating in response to said deflection to; change the angular relation between one of ,thesupports-and said path of reciprocaition thereby compensating for said deflection. ROBERT S. HAHN.

References Cited in the file of this patent UNITED I STATES PATEDTIS Number Number Name Date Morey et'ai Feb. 16, 1932 Mershon Sept.'27, 1932 Buvier et a1 May 10, 1938 Pyne Nov. 16, 1943 'Styberg 1- Jan. 9, 1945 'Wessman Nov. 20, 1945 Mennesson Oct. 10, 1950 Hathaway Mar. 6, 1951 FOREIGN PATENTS Country Date France Nov. 21, 1929

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