US3440774A - Diamond tool - Google Patents

Description

April 29, 1969 F. URN 3,440,774

DIAMOND TOOL Filed oct. 12, 196e sheet ,8 of 2 INVENZCOR. Fran f/eff zu'zz "Y www United States Patent Oiice 3,440,774 DIAMOND TOOL Frantisek Cum, Prague, Czechoslovakia, assignor to Naradi, narodni podnik, Prague, Czechoslovakia Continuation-in part of application Ser. No. 445,863,

Mar. 31, 1965. This application Oct. 12, 1966, Ser.

Claims priority, application Czechoslovakia, May 13, 1963, 2,704/63 Int. Cl. B24d 5/00, 7/00; C04b 31/16 U.S. Cl. 51-206 8 Claims ABSTRACT F THE DISCLOSURE This application is a continuation-in-part of my copending application Ser. No. 364,239, tiled May 1, 1964, now abandoned, and Ser. N0. 445,863, filed Mar. 31, 1965, now Patent No. 3,288,580, dated Nov. 29, 1966.

This invention relates to diamond tools, such as abrasive tools, for the shaping of very hard materials to exacting specifications.

Diamond grinding wheels are conventionally employed for shaping very hard materials, such as sintered carbides. The usual diamond grinding wheel has a narrow edge portion which is held substantially in point contact with the object to be shaped and is moved over the surface of the object for working each point of the surface. The movements of the grinding wheel are guided by a copying attachment in which a pattern of the desired surface is sensed by a stylus, or by an electronic or other equivalent of such an attachment.

The working edge of most conventional diamond grinding wheels consists of a binder matrix in which diamond grains are embedded. The dimensions of the wheel and its shape change as the diamond grains are worn down and torn from the binder. The shape of the working edge can be restored only by removing a layer of binder with the diamonds embedded therein, and diamonds which never performed their grinding function are lost during restoration of the wheel shape.

The known diamond grinding wheels are limited in their application to relatively simple shapes, and they work slowly since they are in contact with a work piece substantially in one point only. The limitations of the available diamond tools have heretofore made it impractical to use sintered or cemented carbides in many dies or similar applications for which they would be suitable otherwise.

The shortcomings of conventional diamond grinding wheels are also inherent in hand files which employ diamond grains as a cutting medium and are prepared in an analogous manner.

The working surface of a conventional diamond tool, in which diamond grains are embedded in a binder matrix, is occupied to a significant part by the binder which does not produce a signiiicant cutting elfect.

Attempts were made heretofore to avoid the shortcomings of the aforedescribed abrasive compositions by a carrier with a single layer of diamond grains. Diamond 3,449,774 Patented Apr. 29, 1969 grains, however, are normally of different shapes and sizes, but even if all grains in the single layer are of identical shape and size, and they never are, their cutting points are normally not in a common plane. The grains of the known single-layer diamond tools are more or less randomly oriented, and not all diamond grains make contact with a workpiece until the points of the farthest projecting grains are worn away. It is evident that very close dimensional tolerances cannot be` maintained with such a tool.

It is an object of the invention to provide a diamond tool that may be employed in extended area contact with the workpiece to be shaped, thereby sharply reducing the time required for shaping.

Another object is the provision of a contoured diamond tool with which the shape to be produced may be directly reproduced, thereby avoiding the need for a copying attachment.

With these and other objects in view, as will hereinafter become apparent, the invention in one of its aspects resides mainly in a tool in which a single layer of closely packed diamond grains is partly embedded in a face of a carrier, from which the diamond grains partly project. The cutting points of the projecting portions of the grains are directed outwardly from said layer and lie in the desired common working surface.

If the tool is a grinding wheel, the common working surface of the cutting points is a surface of revolution and forms an annulus about the axis of the grinding wheel. The contour of the surface may be chosen at will and may include axially offset annular ribs and grooves of angular or arcuate section, concave or convex. Most diamond grains of the layer are in abutting contact with at least one other grain of the layer. The innermost portion of the grains are embedded in the carrier face to different depths depending on the sizes of the individual grains.

Other features and many of the a-ttendant advantages of this invention will be readily appreciated as the same becomes better understood from the following detailed specification, when considered with the annexed drawing inl which: f

FIG. l shows the working portion of a diamond grind ing wheel of the invention in axial section;

FIG. 2 shows a detail of the wheel of FIG. greatly enlarged scale;

FIG. 3 illustrates a mold, in a fragmentary axial section, for making the wheel of FIG. 1;

FIGS. 4 land 5 illustrate the making of a diamond grinding wheel by means of the mold of FIG. 3; and

FIG. 6 shows the nished wheel on a smaller scale than that employed in FIG. 1.

Referring now to the drawing in detail, and initially to FIG. 1, there is seen a working portion of a grinding Wheel having a partly Seen central carrier portion 1 which is a generally circular metal disc whose circumference 2 is knurled for conforming engagement with a backin-g 3. The outer face 5 of the backing 3 has an annular shape and is contoured corresponding to the shape that it is intended to produce in the workpiece. The outer face 5 is corrugated, two annular ribs being separated by a groove. One of the ribs is convexly rounded Whereas the other rib has a sharp edge. The groove has an exposed face of concave curvature.

A representative portion of the surface 5, indicated by a circle A in FIG. 1, is shown on a larger scale in FIG. 2. The outer surface 5 is studded with closely packed diamond grains 4. A majority of the grains is disposed in such a manner that their greatest dimension or longitudinal axis is transverse to the corresponding portion of the surface 5. The exposed minor part of practically each grain 4 tapers in a direction away from the surface 5 to an annular point or cutting edge 4a. The embedded major lona parts flare from the surface inward of the backing member 3 in such a manner that the portion of each grain which has the greatest cross section perpendicular to the aforementioned axis and the inwardly flaring portion of the major grain part are embraced by the material of the backing member 3. All cutting points or edges 4a lie in a common working surface defined by a single set of circles about the wheel axis.

The diamond grains 4 are so closely packed that each grain touches or almost touches at least one laterally adjacent grain. There is no gap where an additional grain of a size comparable to that of the illustrated grains 4 could be inserted in the surface 5 of the backing member 3. When the backing member 3 is made of transparent plastic, it is seen that the projection of practically each grain 4 into the corresponding portion of the surface 5 is contiguous to or overlaps the corresponding projection of at least one adjacent grain, and that a continuous pattern is formed by the projections of practically all the grains 4 in the surface 5, or in the aforementioned working surface, which closely duplicates the shape of the surface 5. The term projection, as employed herein, refers to orthogonal projection.

The diamond grains 4 vary somewhat in their length. A layer of a thickness n somewhat beneath the surface 5 (see FIG. 2) is, therefore, partly occupied by diamond grains 4. The grains form an irregular pattern in the layer n due to the different dimensions of the grain bottom portions extending into the bonding material, not relevant to the working properties of the tool illustrated.

When the wheel partly shown in FIG. 1 is rotated about its axis, and a workpiece is radially urged against the wheel, a recess conforming to the shape of the surface 5 is ground into the workpiece. Since all diamond grains 4 make simultaneous contact with the surface of the workpiece, the grinding pressure and other stresses are uniformly distributed over all grains 4. Because the diamond grains are closely packed, they cannot tilt under the grinding stresses even if the backing member 3 is made of very soft material. The diamond grains wear relatively slowly, and individual grains are not readily dislodged `from the backing 3 because the embedding material axially extends beyond the portion of each grain whose cross section is greatest. The relatively large contact area between the diamond points and the workpiece sharply reduces the time required for removal of workpiece material as compared with a conventional wheel in which diamond grains are distributed in the binder matrix in three dimensions and are relatively widely spaced from each other.

The manner in which the diamond grinding wheel of FIG. l is prepared is illustrated in FIGS. 3 to 6. A mold 6 is made rst. As shown in FIG. 3, the mold 6 has a cavity 7 of circular cross section which conforms to the diamond wheel that is to be made. The circumferential wall 9 of the cavity 7 is a replica of the shape in which the layer of diamond grains 4 is to be deposited on the nished wheel. The mold 6, furthermore, has a wide cylindrical locating bore 8 which is contiguously coaxial with the cavity 7.

The mold 6 is preferably machined from an inexpensive wrought aluminum alloy containing copper and magnesium as primary alloying elements together with minor amounts of iron, nickel, and titanium. A forming tool of high-speed steel having a rake angle of 3 on the side and from to 25 on the face may be employed for shaping the critical contour of the wall 9 on an accurate toolmakers lathe. The tool may be used over and over again in the relatively soft aluminum alloy. As is evident from FIG. 3, the aluminum alloy blank from which the mold 6 is made has about twice the axial thickness of the wheel to be prepared.

The diameter of the locating bore 8 should be about four fifths of the diameter of the cavity 7, but this relationship is not critical, as will be readily apparent.

An insert 10 of generally stepped cylindrical shape is prepared next. As seen in FIG. 5, the insert has one portion 11 which precisely lits the bore 8 and constitutes a broad locating pin, and another portion 12 whose axial height is substantially equal to that of the cavity 7, and whose diameter is approximately 5 to 10% smaller than that of the cavity. The insert 10 is made of the same aluminum alloy as the mold 6 by turning on a precision lathe. The outer curved face of the portion 12 is knurled.

When proper t of the insert 10 in the mold 6 is established, the insert is withdrawn, and both the mold and the insert are carefully degreased. The mold, moreover, is immersed in dilute, lukewarm sodium hydroxide solution for 60 seconds while in an inverted position so as to etch the circumferential wall 9 of the cavity 7 without etching the locating bore 8, rinsed in water, and dried.

A thin but `continuous layer of adhesive is next applied to the circumferential cavity wall 9 by brushing or spraying the wall carefully with an adhesive solution, such as an aqueous 5 percent solution of gum arabic. The layer should not be more than a few microns thick and is not visible on the scale of the drawing.

The mold 6 is then tilted until the axis of the cavity 7 is approximately horizontal, and diamond powder of the desired grain size is heaped on the lowermost portion of the circumferential cavity wall 9 while the adhesive is still moist. It is essential that the amount of diamond powder applied be much larger than that required for covering the diamond grinding wheel to be prepared. For example, if the wheel will eventually carry 7 carats of diamonds, the amount of powder supplied should be 35 carats. The mold 6 is slowly turned once about its axis. This can be done simply by hand or while holding the mold in a suitable support. The entire, adhesive-coated cavity wall 9 thus is contacted with diamond powder. The weight of the excess powder forces the bottom layer of diamond grains into and through the adhesive into abutting engagement with the wall 9 of the mold 6.

The individual grains are driven through the adhesive layer in the direction of their longitudinal axes and come to rest against the wall 9 of the mold 6 with their terminal points abutting against the wall. This readily observed fact is believed due to the pressure of other grains, which acts from all directions except from the direction of the wall. The rotation of the mold 6 produces a tumbling action in which the diamond grains align themselves to move longitudinally as they slide downward along the surface of the tumbling body of diamond grains, and their points impinge first upon the adhesive layer.

The loose diamond grains continue tumbling as the mold is further rotated, but a layer of diamond grains is held in the thin adhesive layer whose thickness must not be more than a fraction of the average length of the diamond grains. The retained grains are densely packed, almost every grain making abutting contact with at least one adjacent grain, and the direction of their longitudinal axes is more or less perpendicular to the mold wall 9.

The speed at which the mold is being rotated must be high enough to produce the aforedescribed tumbling action. At lower speeds, the entire body of diamond grains may slide as a unit along the mold wall, and the desired result is not achieved. The necessary speed of rotation can readily be determined by inspection in any particular `case and varies with specific conditions. The size of the diamond grains is the most important variable in this respect. With dry diamond grains of to 150 mesh, the mold should be rotated about its axis once in 20 to 30 seconds, and not more.

The excess diamonds which are not retained by the adhesive are poured out, and the coated mold is permitted to stand in air for about 5 to 15 minutes, thereby permitting the adhesive to set fully. The mold is then set up, as shown in FIG. 4, the insert 10 is placed in the mold, and the annular space between the insert portion 12 andthe diamond layer on the axial mold wall 9 in the cavity 7 is filled with `a binder materal.

It is preferred to use a mixture of higher melting metal particles and a low melting alloy as a binder. Aluminum alloy chips produced in machining the mold 6 and the insert 10 may be comminuted and screened, and the fraction passing through a 0.22 mm. screen, but retained on a 0.20 mm. screen may be mixed with one half part by weight of coarse antimony powder having a particle size of 0.15 to 0.22. mm. The mixture is loosely packed in the annular mold space. The small solid metal particles are then bonded to each other, to the insert portion 12 and to the diamond grains 4 on the mold wall 9 by a low melting alloy which is preferably applied under pressure to avoid air pockets. The mold 6, the insert 10, the loose powder in the annular mold space, and the diamond grains on the mold wall are preferably inserted in a conforming diecasting mold, and the low melting alloy is injected into the annular space in a manner conventional in diecasting.

A preferred casting alloy consists of 65 percent of a conventional zinc diecasting alloy containing copper and aluminum as the principal alloying elements, about 32 percent cadmium, and about 3 percent of a commercial silver solder, mainly consisting of silver, copper, zinc, and cadmium, but other alloys having a lower melting point than the aluminum alloy and the antimony powder may be employed.

The mixture of aluminum chips and antimony powder prevents the diamond grains from being displaced by the impact of a stream of molten metal. It also strengthens the cast alloy after solidifcation. The powder may be omitted entirely in small grinding wheels and gravity casting may be resorted to.

After solidication of the cast material and removal of sprues and gates, there is obtained the structure shown in FIG. 5 in which the annular gap between the diamond grains and the knurled surface of the insert 10 is filled by the backing 3 of metal which conformingly envelops the bottom portions of the grains 4 which project from the adhesive layer in a radially inward direction.

Next, the mold 6 is removed from the partially finished wheel, the bulk of the mold is cut away on a lathe, some of the remainder may be ground olf, and the thin remaining shell may be stripped from the layer of diamond grains 4 which are firmly embedded in the backing 3. Such stripping is greatly facilitated by the preliminary etching of the mold 6 in sodium hydroxide solution.

The locating pin 11 is machined away from the remainder of the insert 10, thereby leaving the central wheel portion 1 which is then axially bored to provide a chucking hole 13. The radial faces of the wheel may be further iinished, and the adhesive may be removed, if so desired, by wet cleaning with or without pumice.

The point 4a of each grain 4 thus projects from the surface 5 of the backing 3 over a distance which corresponds to the thickness of the initial adhesive layer. All points 4a lie in a common surface parallel to the surface 5.

If a at surface or any other surface that is not of circular cross section, for instance, the surfaces of a blocktype dresser or a hand file, is to be coated with a layer of diamonds according to this invention, a mold with a corresponding flat or other surface defined by a single set of parallel lines is coated lwith adhesive, and a large excess of diamonds is heaped on the adhesive coating. The aforedescribed tumbling action then is produced by rocking the mold until a dense layer of aligned diamond grains is partly embedded in the adhesive layer. The diamond layer if backed with a binder, such as a low-melting alloy, in a manner evident from the more detailed description of the making of a grinding wheel. All ponits of the diamond grains lie in the aforementioned plane when the tool is nished and are therefore capable of area contact with a workpiece during relative movement of tool and workpiece in the direction of the parallel lines which define the surface.

Obviously, the steps of supporting a layer of diamond grains, produced according to the invention, with a supporting material which also acts as a binder for the diamond grains may be carried out in diiferent Ways.

The annular space between the diamond grains and the insert 10 may be lled with an amalgam, such as bronze amalgam, which is put in position with a spatula. The radial forces to which such a grinding wheel may be subjected are, of course, limited by the strength of the amalgam.

A plastic backing is adequate for small grinding wheels, and the mold 6 described hereinabove may be used for casting a wheel of thermosetting synthetic resin under heat and pressure after the internal mold wall has been coated with diamond grains in the manner described. The product formed is a plastic wheel in the surface of which the diamond grains are embedded in the manner illustrated in FIG. 2.

When the diamond grinding tools of the invention engage a workpiece, the piece has simultaneous bearing contact with a multiplicity of diamond particles embedded in the surface of the tool in the area of engagement, so that all the diamond particles participate in the cutting action, and the load is evenly distributed, no one diamond point being overloaded.

Very complex contours are readily ground on the workpiece by merely feeding the piece in a straight path against the working surface of a diamond wheel of the invention. The ribs and grooves of the 'working surface produce a complementary contour on the workpiece.

The diamond tools of the invention therefore permit a grinding technique commonly applied to steel to be extended to workpieces made of very hard and abrasive materials, such as hintered carbides, cermets, ferrites, corundum, and the like. The diamond tools of the invention are prepared in a simple manner and at low cost. The invention is not limited to grinding Wheels, but is equally applicable to diamond-faced les, block-type and roller dressers, and other tools.

The tools of the invention cannot be restored to operating condition after having been worn down, but their useful life is very long because of the uniform distribution of stresses among all diamond grains of the surface layer. The rate at which very hard materials'may be ground away with the tools of the invention has never been achieved heretofore. The prevailing orientation of the diamond grains with their longest axes approximately perpendicular to the working surface permits the close packing of the grains which is necessary for the rapid cutting action.

What is claimed is:

1. A tool comprising, in combination:

(a) carrier means having a face; and

(b) a single layer of closely packed diamond grains,

(1) a major part of each grain being embedded in said face and the remaining minor part projecting from said face,

(2) said minor part tapering in a direction outward of said carrier means substantially to a cutting point,

(3) said major part flaring from said face in .a direction inward of said carrier means and having a portion of greatest cross section transverse of said direction, said portion of greatest cross section being inwardly spaced from said face,

(4) said cutting points lying on a common working surface, and

(5) the projections of substantially each grain overlapping the projection of one other grain in said working surface.

2. A tool as set forth in claim 1, wherein said carrier means has an axis, and said working surface is a surface of revolution about said axis.

3. A tool as set forth in claim 1, wherein substantially every diamond grain in said layer is in abutting contact with at least one other grain in said layer.

4. A tool as set for in claim 1, wherein said face and said surface are substantially parallel and spaced from each other.

5. A tool as set forth in claim 1, wherein each grain of at least a majority of said grains has a greatest linear dimension transverse of said working surface and of said face.

6. A tool as set forth in claim 1, wherein said carrier means has an axis, the cutting points of all grains located in a common radial plane relative to said axis being equidistant from said axis.

7. A tool as set forth in claim 6, wherein said working surface is a surface of revolution and includes a plurality of axially spaced annular ribs, said ribs defining therebetween at least one annular groove.

8. A tool as set forth in claim 7, wherein substantially every diamond grain in said layer is in abutting Contact with at least one other grain in said layer, and each grain of at least a majority of said grains has a greatest linear dimension transverse of said working surface and of said face.

References Cited UNITED STATES PATENTS ROBERT C. RIORDON, Primary Examiner.

D. G. KELLY, Assistant Examiner.

U.S. Cl. X.R.

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