US1914647A - Method for finish grinding and polishing - Google Patents

Description

Patented June 20, 1933 PATENT OFFICE CLIFFORD T. BAULE, OF BROOKLINE, PENNSYLVANIA METHOD FOR FINISH GRINIDING AND POLISHING Application filed July 16,

My invention relates to a method for polish grinding and finds particularly wide application in the internal or external grinding of ball races, piston pins, pistons and the like.

A purpose of my invention is to use a cutting wheel for obtaining a polish finish to exact dimension by speed adjustment of the wheel or speed adjustment of the work if the work be rotating, either or both, using vthe same wheel for rough cutting and for polishing, in a single chucking.

A further purpose is to eliminate any unevenness such as chatter marks on the ground surface of rotating work before finish polishing h v changing (preferably increasing) the speed of the work or by upsetting any synchronism of vibration between the wheel and work.,

A\ further purpose is to produce polish by reducing the speed of a cutting wheel below iis effective cutting speed after grinding to size.

Further purposes will appear in the specilicai'ion and in the claims.

Figures 1 and 2 are diagrammatic profile views of the same piece of work preparatory to finish grinding, in Figure 1 illustrating in great exaggeration cyclic unevennesses of surface that have in Figure 2 been removed by my new method.

Figures 3 and 4 are diagrammatic views illust-rating developed surfaces as obtained respectively by the usual method of grinding and by my new method.

ln the drawing similar numerals indicate like parts.

In the prior art, grinding wheels are run at a cutting speed, (peripheral) that is,'usu allv about. 100 feet per second. This speed has been maintained both for rough cutting and during finish grinding, the rate of feed of' the wheel into thel revolving work being reduced as theoperation approaches finish grinding to obtain a smoother surface and a more accurate grinding to size.

-I have discovered that the character of the finish surface may be grea`tly improved by making changes for finish grinding in the speed of turning the work or in the speed of 1926. Serial No. 1225801.

turning theI wheel, either and usually more desirably both.

lNhen a piece of rotating work after rough cutting is ready for finish grinding, its ground surface frequently has cyclic unevennesses, indicated in profile grossly exaggerated at 5 of Figure 1. T he unevennesses may comprise chatter marks quite apparent to the eye, but vmore frequently in good practice any individual marks are too small to be perceived either by eye or touch.

These cyclic unevennesses are generally due to vibrations between the Wheel and work, too complex for definite analysis but determined-by lack of absolute dynamic balance of the wheel,`lack of absolute dynamic balance of the work and by elastic and dimensional characteristics of the supporting structure, and therefore are a resultant of superimposed vibrations having frequencies respectively corresponding to the very rapid speed of rotation of the wheel, to the much slower speed of rotation of the work and to i. elastic and dimensional characteristics of supporting structure, the latter vibrations being the slowest of all.

I have found that these cyclic unevennesses may be eliminated to a great extent by changing the speed of rotation of the work, and that they are eliminated more rapidly by speeding up the work than by slowing it down. h

This elimination of cyclic unevennesses is evidenced by disappearance of chatter marks when these were present, and when chatter marks are notl present, which is usually the case in good practice, by a materially smoother surface.

The cause of this corrective result from changing the speed of the Work appears to be due to a number of factors.

y First, any change in the speed of the work upsets the synchronism of the vibrations with respect to the position of the high and low parts of the vibrations upon the work surface, so that when the synchronism is upset the high parts ofthe unevennesses-are taken off. If the change of speed of the work is maintained a new set of oscillatory unevennesses will doubtless form, but in practice the change should not be long enough for this to take place.

Another factor lies in the mere change in speed of the Work irrespective of its effect upon the synchronism with existing vibrations. The speed of Work that is best for cutting is not that which is best for polishing and I increase the speed of the work from that found best for cutting into that better for polishing.

It is probable that a gradual change from one speed to another is more effective than an abrupt change but in practice it is almost impossible to have anything but a more or less gradual change, so that any change is more or less gradual.

I find that a polish cannot be obtained by merely changing the speed of the work if the Wheel is still running at a cutting speed. Changing the speed of the work takes out cyclic unevennesses and greatly improves the finish and I have further discovered that a polish can be obtained by slowing down the wheel below its cutting speed.

I find that slowing the wheel from its cutting speed into what I call its polishing speed gives a polish finish that has hitherto been considered unattainable by means of a cutting wheel.

The reduction of speed of the wheel from cutting speed to polishing speed for finishing is usually far more important than changing the speed of the work as in many cases the cyclic unevennesses are too small to matter or so small that they appear t0 be lost during able c the polishing by slowin down the wheel.

In many other cases, owever, the work should be changed, preferably speeded up to take out these unevennesses before the wheel is slowed down as otherwise there are low portions of the surface that are not reached by the wheel polishing, and in every case the polishing operation will be upon a more even surface if speed of the work has been changed before slowing down the wheel.

The speed of the work should be changed while the wheel is still runninv at cutting speed, as the wheel has' to cut off t e high portions of the unevennesses.

In that method permits rough cutting and polishing with the same wheel and with one chucking it is particularly well adapted to use with automatic` grinders used for quantity production of internally or externally ground parts suchv as the ball races, piston pins, pistons, etc.

It will be understood that it is the relative speed between the engaging surfaces of the wheel and work that determines whether the wheel cuts or polishes. This reduction in relative speed is best effected by reducing the actual speed of the wheel which is usually many times greater than that of the work, but optionally it may be obtained by a suitange in the speed of'the work piece.

Usually the engaging surfaces of work and wheel move in opposite directions so that when the work is speeded for taking out cyclic unevennesses the relative speed between the engaging surfaces (and therefore the effective cutting speed of the work) is also increased. However if the engaging surfaces move in the same instead of opposite directions any increase in the speed of the work will reduce the relative speed of the engaging surfaces, from that in which the Wheel cuts to that in which it polishes if the change 0f wheel speed has been of the requisite amount.

In operation, after rough cutting, the unevennesses of surface, indicated at 5 upon the interior and 5 upon the exterior in Figure l and there grossly exaggerated, are removed by changing the synchronism of vibrations, preferably by increasing the Speed of the work. Usually a very small portion of the grinding time will suffice to greatly improve the surface, which may now be as represented at 6 and 6 of Figure 2. The surface in Figure 3 will be true equally of the exterior or interior.

The effective speed of the wheel is now reduced from cutting speed to polishing speed and the even but unpolished surface indicated as 6 and also as 6 in Figure 3 becomes the polished surface 7 of Figure 4.

Every grinding wheel has a reco nized grinding peripheral speed below whic 1 it is noticeably ineffective for grinding purposes. Part of the benefit of my invention will be secured by the polishing effect of any speed sufficiently below this effective grinding speed for the polishing effect to be large as compared with the grinding but for the best results the speed must be so far reduced that the grinding effect is negligible and the size is not substantially affected by the polishing operation. This will of course differ with different wheels and different materials or surfaces ground but can very readily be determined by trial for any given character of work.

It will be evident that the broader aspects of my invention in so far as polishing is concerned apply to finishing the grinding of plain surfaces and surfaces of irregular contour or which for any other reason are not revolved, as well as to the polishing of revolving surfaces, though there is additional advantage in the case of the rotating work in the interrelation between the revolving surface and the wheel rotating at a speed below its proper cutting speed. In my illustration I have applied the method to rotating work in order to explain the more complex a plication of the method and that application which, moreover, has the greatest utility, recognizing that the more simple applications 'of the method to work which does not rotate are included within this illustration.

I am aware that the application of my iny vention may be widely variant according to I in finish grinding for a brief period with the circumstance, need and preference and claimall such variations in so far as they fall within the spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. In using an automatic grinding unit comprising a work holder adapted to hold a metal Work piece and a grinding Wheel adapted to rotate at cutting speed While engaging the Work, the method of .smoothing the ground surface which consists in grinding vthe Work at one Work speed, in reducing the speed of the wheel after finish grinding to a speed below its effective cutting speed and in polishing the ground surface with the grinding wheel rotating at the reduced speed. Y 2. In using an automatic grinding unit comprising a work holder adapted to hold and rotate a metal Work piece and a. grinding Wheel adapted to rota-te at cutting speed while engaging the Work, the method of smoothing (the ground surface which consists in 'grinding the work at one work speed, in changing the speed of the work to eliminate uncvenesses of surface, and in finish grinding the ground surface for a brief interval with the work rotating at the changed speed.

3. In using an automatic grinding unit comprising a. work holder adapted to hold and rotate a metal work piece and a grinding Wheel adapted to rotate at cutting speed While engaging the Work, the method of grinding, smoothing and polishing the ground surface A which consists in grinding the Work at one work speed, 'in changing the speed of the work to eliminate unevennesscs of surface, in finish grinding for a brief period with the work rotating at the changed speed, and in polishing with a wheel rotating at a speed below its effective Vcutting speed.

4. In using an automatic grinding unit comprising a work holder adapted to hold and rotate a metal work piece and a grinding wheel adapted to rotate at cutting speed While engaging the work, the method of smoothing and polishing the ground'surface which consist-s in grinding the work at one Work speed, in changing the speed of the work to s eliminate unevennesses of surface, in finish grinding for a brief period with the Work rotating at the changed speed, in reducing the relative speed of the engaging surfaces of the wheel and Work, and in polishing at the reduced speed.

5. In using an automatic grinding unit comprising a work holder adapted to hold and rotate a metal Work piece and a grinding wheel adapted to rotate at cutting speed while engaging the work, the method of smoothing the ground surface which consists in grinding the work at one work speed, in increasing the speed of the Work as compared with the Work speed at which it was ground to eliminate unevennesses on the ground surface, and

Work rotating at increased speed.

6. In using an automatic grinding unlt comprising a. work holder adapted to hold and rotate a metal work piece and a grinding wheel adapted-to rotate at cutting speed while engaging the work, the method of smoothing the ground surface which consists in grinding the work at one work speed, in increasing the speed of the work to eliminate unevennesses on the ground surface, in finish grinding for a brief eriod with the work rotating at the increased speed, in reducing the relative speed of the engaging surfaces of the Wheel and work and in polishing at the reduced speed.

7 The method of rotarily grinding and finishing al piece of metal work, which consists in grinding off the ortion to be removed from the work at an e ective cutting speed forthe grinding wheel and in polishlng the surfaces left at a low grinding wheel speed,

below the effective cuttin speed of the grinding wheel which is used or polishing.

8. The method of grinding, finish grinding and polishing a rotary metal work piece to smooth the ground surface and the finish, which consists in grinding the work at one Work speed, in changing the speed of work for the finish grinding as compared with the grinding Work speed so as to eliminate unevenness of the surface and in polishing the work at a wheel speed below the effective cutting speed of the wheel used for'polishing.

CLIFFORD T. RAULE.

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