US1931363A - Grinding wheel - Google Patents

Description

Oct. 17, 1933. E. STUBBS 1,931,363 I GRINDING WHEEL Filed Dec. 31, 1932 grwwwto'v WITNESSES EVERARD d-ruass Zr. R. w fl Patented Oct. 11, 1933 v UNITED STATES Gnmnmc WHEEL Everard Stubbs, Springfield, vs, assignor to Norton Company, Worcester, Mass, at corporation of Massachusetts Application December 31, 1932 Serial No. 649,671

4 Claims.

the work to be ground back and forthin a path.

transverse to the grinding wheel axis, as the work rotates, in order that the grinding surface of the wheel may continuously engage the work throughout the entire surface contour. In such a construction, this reciprocating motion is ordinarily effected by mounting the work on a swinging frame and automatically rocking the frame relative to the grinding wheel, which isi lxedly mounted thereto, by means of a rotatingpattern on the frame in contact with a fixed follower; However, the use of this type of construction has not been very satisfactory and it has involved many difllculties owing to the complex movement utilized through which the I 2 work must be cyclically moved during the grinding operation, the complicated form of machine construction required to effect such movement without variation in the grinding results, and the additional requirement that certain narrow limits of diameter must be adhered to within which the grinding wheel may be used if satisfactory grinding results are to be obtained. Such a procedure has also resulted in a departure from the true pattern to be ground and so is highly objectionable.

In accordance with the invention as set forth in my copending application Serial No. 612,232, filed May 19, 1932, I have thereillustrated and described a grinding machine construction and {o a method particularly adapted for forming bodies of various irregular and non-circular contours which does not involve any relative reciprocating motion between the grinding wheel and the work to present the work surface to be ground continuously to the grinding surface of the wheel during the grinding operation. In that construction, it has been found feasible to employ a specially shapedgrinding wheel, vin- 5o stead of the prior reciprocating arrangement heretofore practiced, and this wheel is shaped as the conjugate of the work to be ground and is adapted to be rotated in angular synchronism with the work rotation during the grinding op- 65 eration, in which case the wheel-and work are arranged to remain in a proper grinding phase relation at all times.

In the art of grinding cams or other irregularly shaped bodies involving a change in surface curvature, it is necessary that. the grinding 'wheel cut and wear away at substantially the same rate over its entire cutting surface to produce results true to pattern. However, it is found .in practice that the. grinding action of this shaped cutting wheel has not been uniform and i that certain portions of the grinding face of the wheel, particularly those portions in contact with thesides of the cam leading from the heel portion to the toe, tend to wear away/faster than does the remainder of the wheel, this being due principally to the small, narrow arc of the wheel surface which is required to traverse rapidly across the more extensive sides of a cam and thereby is subjected to the greater wear. This excessive wear of the peripheral portions of the grinding face necessitates frequent truing of the grinding wheel to bring it back to its correct' form, thus involving a large loss of grinding time and wasting the substance of the wheel.

It is accordingly the primary object of my invention to overcome these difliculties expe-' rienced in conjugate grinding and to provide a grinding wheel which is not only of the desired shape'and cutting condition, but is also of a5 non-uniform grinding characteristics throughout the grinding face and which will more efficiently grind work pieces' of various irregular contours than will a wheel of uniform" grinding properties throughout its periphery.

A further object is to provide a grinding whee for forming bodies of irregular contour in which the grinding characteristics of the grinding surface vary in'a peripheral direction, the portion of the wheel corresponding to the position of greatest wear being adapted to compensate for such wearing tendencies and so retain the wheel wear substantially uniformly throughout the wheel periphery.

With these and other objects in view, as will be apparent from the following disclosure, my invention resides in the subject matter described in the specification and set forth in the claims appended hereto.

In accordance with this invention, I propose to provide a conjugate grinding wheel for use in grinding work of irregular contour, with a uniformly wearing grinding surface. by making appropriate variations in the grinding characteristics in those portions of the wheel surface 110 which are subject to excessive wear, the location of which is dependent upon the character of the work to be ground. That is, .that portion of the wheel which is subjected to the heavier grinding action and which will, therefore, be worn away more rapidly than other sections of the wheel is preferably made harder in its grinding characteristics or more resistant to vwear than is another portion which is not called upon to do such severe grinding. For example, if the work piece to be ground is a cam of the automotive type having a circular heel portion M and sloping sides leading to the toe, then that .face.

portion of the wheel which is intended to grind these sides and in which only a small arc of the grinding face will necessarily traverse across the more extensive surface of the cam'slope is preferably made to have different grinding characteristics from that of the remainder of the wheel, in order to make the wheel wear. substantially uniform. Hence, for grinding a cam as thus described, this are of the wheel substance should be made soas to be harder acting in its grinding characteristics. In practice, I provide the wheel with a hard, wear-resisting grinding portion, such as an abrasive section or sector, located on the grinding face of thewheel at the points which are required to grind the slopes of the cam or in other positions of excessive wear.

This hard wheel section may be made in vari-' ous ways, such as by varying the size and kind of the abrasive grains used or by varying the amount of bond employed and, therefore, thevgrade of hardness of the wheel, or by varying the structure of the wheel, 1. e.', the relative relationship of the abrasive, bond and pores. However, the essential condition in each case is to have that, portion of the wheel which is called upon to do the more severe work well adapted to stand up under the grinding operation and not wear away too rapidly, and so will not require the remainder of the grinding surface to be trued down to the .extent of the worn sur- Moreover, it is desirable that this particular sector or are of the wheel be of such characteristics that-it will grind the work surface contacting therewith with satisfactory results. Also, it will be understood that the sectors or sections of the wheel which are to be made of different grinding characteristics from the remaining portions will have their length of arc determined by the work shape so that the harder 'acting sector will extend throughout the desired extent of work surface to be ground thereby.

One embodiment of my invention is shown in the accompanying drawing,- in which the figure comprise an irregularly shaped contour which is the-conjugate of the work to be ground. The grinding surface 11 is provided with several peripheral portions 01 sections 13 and 14 of vitrifled ceramic bonded abrasive grains having a harder grade of hardness on the Norton scale and different grinding characteristics thanthe remaining portions 15 an 16 of the annulus integrally united therewith and composed of abrasive grains bonded with a vitrified ceramic bond and having a softer grade than the other portions. The harder bonded sections 13 and 14, which may be of the same or different grades of hardness and grinding characteristics, extend circumferentially around thegrinding periphery and preferably in a radial direction inwardly to the spindle aperture 12, and they are separated by the portions 15 and 16 which are subjected to the lesser wearing tendencies. However, the extent and location of these harder bonded sections 13 and 14 are necessarily determined by the character and position'of the work contour to be ground.

The wheel materials may be combined and shaped into a grinding wheel by suitable means and methods. For example, the vitrified grinding wheel may be made according to well-known methods employed in the art by molding in the desired form granular abrasive material, such as crystalline alumina or silicon carbide, mixed with a suitable ceramic bonding medium, such as a suitable mixture of ball clay, slip clay and feldspar, as is known in the art, after which the wheel is baked at a temperature to use or vitrify the bond.

As an illustration of one particular method of making a wheel having the grinding characteristics above described, which may be utilized for grinding a cam, I may first provide a moldable mixture for the hard portionsby selecting the proper quantity of crystalline alumina grains of a suitable size, such as one which will just 'pass through. a screen having 50 meshes per linear inch, and a raw ceramic bonding material ness when the bond has been matured. This material is placed in a mold at the proper angular location with respect to the points of excessive wear, so as to form the sections or sectors 13 and 14 extending across the mold from the central coregto the outer peripheral band and curved in shape where it contacts with the walls of the mold band. The spaces between the sections 13 and 14 of this harder acting wheel composition are then filled with a mixture of crystalline alumina grains of the same grit size and type of bond, in which the ingredients are so proportioned as to produce sections 15 and 16 of grade N or other desired grade. The

mass isthen subjected to pressure in a standard pressing operation in order to compact the green material of the sections and cause it to cohere and become united into an integral mass in which the lines of demarkation between the 185 harder acting sections13 and 14 respectively and the adjacent sections 15 and 16 thereto are not pronounced, owing to the abrasive grains of one section being pressed into the bond in the adjoining section and the intermingling of the bonds at the junction planes. The wheel is then fired to vitrify the bond, in accordance with standard practice.

It is obvious that this invention is not limited in its application to the specific materials mentioned. One may select the various abrasives, such as silicon carbide, crystalline alumina, boron carbide, tungsten carbide or such other abrasive materials as are well known in the grinding art, of such grain sizes as are deemed I50 best for the particular operation to be performed. Various other types of bond may also be employed which are standard knowledge in the industry,- depending upon the character of the material to be cut and the service and production desired. For example, one may utilize, in place of the vitrified ceramic wheel bonds, such bonding materials as shellac, rubber, sodium silicate or various resinoid materials, particularly those of the phenolic resinoid type. It is also within the scope of this invention to utilire different sizes of abrasive grains in the different sections 13, 14,15 and 16 respectively,

either coarse in the hard sectors 13 and 14 or fine in the other portions 15 and 16 or vice versa. The abrasive material may be used in a variety of sizes of grain, which is sometimes advantageous to obtain the required grinding characteristics, or. the particles may be uniform in; size. It is essential, however, that the bond ofthe harder actingsectors 13 and 14 be materially harder than that of the portions less subjected to excessive wear. It is furthermore within the scope of my invention to vary the grinding characteristics of the hard sectors 13 and 14 of the wheel by changing the grain size; that is, by employing grains of the finer sizes, so that the wheel portions containingthis material will act harder in their grinding action, and so will not wear away as rapidly as would one embodying grains of a coarser size. Also, by using fine grains and properly proportioning the bond accordingly, the abrasive content of these sectors 13 and 14 may .be materially increased to produce a harder grinding action. Likewise, -the structure of these particular sectors may be made to a variety of abrasive packings so that they will be of a more dense nature and will,

which are successively placed in grinding con-.

tact with the particular sections of the grinding wheel there shown. It will be observed that this particular representation indicates six welldefined stages of the grinding operation. It

will, therefore, be seen that if the rotation of the cam and the grinding wheel, on their respective axes, is assumed to be in a counter-'- clockwise direction and in angular synchronism with each other, as indicated in the drawing, then during the grinding operation, the grind-'- ing of the various portions of the cam contour there shown will take place as follows: The sloping side surface of the cam included between the angle a willbe ground by the grinding wheel section 14 of harder acting characteristics; next, the cam are included between the angle b'! will, be operated on by the extensive wheel section 16 of lesser grinding properties; then, the sloping side surface included between the cam angle 0 will be subjected to the grinding action of the harder acting section 13; and lastly, to conclude the grinding operation, the portion included between the angle d", which comprises the'toe portion of the cam, will be ground by the remaining wheel section 15 of a softer grade of hardness than the preceding section.

In order to insure having the various wheel sections inexact angular relationship at all times with the respective cam contour portions, as indicated in the drawing, I preferably so proportion and locate these wheel sections that the central angle formed by two radial planes and the included are of the respective wheel contour will be substantially equal to the angle formed by two radii and the included arc of 'the cam of which the respective wheel section is the conJugate shape. It, of course, is to be under-'- stood that a high degree of mathematical accuracy is not required in fixing the length of arc of the sections, as the amount and location of such portions depend on the nature of the work to be ground and that, if desired, the portions of harder and softer grades may merge gradually into-one another in order that there may be no sharp lines of division between the various sections of the wheel. It, of course, will be understood that this invention relates equally well to grinding wheels for grinding all kinds of bodies of irregular shape, such as splined shafts, which have peripheral surfaces of such shape, that one portion of the wheel is required to have different grinding characteristicsfrom another.

In accordance mth this invention, I have thus provided a grinding wheel which has its various portions normally exposed to excessive wear in grinding work of irregular contour which 'is the conjugate of the grindingwheel surface and which is so made that the life of these portions will be increased and the contour of the grinding surface of thewheel will be maintained for a longer period of life than does the surface of the standard wheel. Sucha wheel is intended, moreover, to give a more satisfactory grinding operation on those portions of the work surface which are not properly ground by the standard wheel employing a uniform mixture throughout the wheel periphery. For certain types of grinding operations, it is also within the scope of this invention to have a particular section in the wheel, such as the sector 15 which serves to grind the toe portion of a cam, made, of a softer grade on the Norton scale and, therefore, a material of different grinding characteristics than the other portions 13, 14 and 16 respectively of the grinding face 11, to better accomplish a desired result. It will also be apparent that the grinding wheel may grind on either the periphery or,

the side faces, the grinding surface in either case being shaped to conform with the work surface as a conjugate thereof.

,It is to be understood that the term conjugate as used in thisspecification and in the so related as to be produced by the rotation of the connecting surfaces of the cutting wheel on the work about fixed axes with their angular velocities equal or in a simple ratio where these surfaces are in part irregular in shape and their peripheries are of unequal extent. If the work and wheel were rotated in opposite directions and their circumferences were the same in length and their angular velocities were the same, the two surfaces would (have a pure rolling contact;

but with the dissimilarity of length of the two.

peripheries, a slippingv or cutting action between the wheel and work serves to grind the latter to size. If the wheel and the work are rotated in the same direction, the cutting conditions are the same as in a normal cylindrical grind- 1 8 operation. They may be rotated in opposite I directions if desired. It is essential; however, that the work and the grinding wheel rotate 130- claimsis associated with those curveswhich are 1 in fixed angular synchronism and that the wheel be soshaped that for each revolution thereof, it will reproduce a conjugate shape on the work. The work and the wheel are said to be in angular synchronism when their angular velocities are in'simple ratio of one to one, two to one, three to one, etc. In other words, the wheel and work are always rotated to a proportionate angular displacement.

It is to be understood that the wheel covered by the present invention may be applied tq forming eccentrically revolved cylindrical surfaces, such as crankpins, as well as non-circular peripheral surfaces, the cross-section or contour of which does not form geometric circles, such as cams, and to the forming of irregular surface contours on the side faces of rotary bodies;

hence the expression work of non-circular.

contour and similar wordings found in the claims are to be interpreted as covering such shapes. The invention applies equally to grinding holes of an irregular shape-by forming the grinding wheel so that when it rotates in synchronism with the work blank, it will produce a conjugate surface in the inner peripheral surface of the work. Various other applications of this invention are clearly within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A grinding wheel comprising a body of bonded abrasive grains having a preshaped grinding surface of non-circular contour which is the conjugate of the work 'face to be finished, said wheel having a grinding surface portion of definite grinding characteristics adapted to grind a definite portion of the work, and a further abrasive portion of different grinding characteristic" which is adapted for grinding another portion of the work as. the work and the wheel are revolved in angular synchronism.

2. A grinding wheel comprising a body of bonded abrasive grains, the grinding periphery of which is shaped as the conjugate of the contour of the finished work piece, said wheel having a section made of abrasive grains and bond adapted for grinding a definite portion of the grind another section of the .work surface as the grinding wheel and the work are rotate in angular synchronism.

3. A grinding wheel comprising a body of 4. A grinding wheel of the type covered by claim 1 in which the grinding body has a plurality of spaced sections of a definite grade adapted to contact with the opposed portions of the work surface, said parts being separated by sections of abrasive material which are of harder grinding characteristics and which subtend such arcs of wheel surface as to contact-with those parts of the work surface which are tobe ground thereby.

EVERARD STUBBS;

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