GB2029291A - Compact dressing tool - Google Patents

Abstract

Prior art dressing tools have not been able to provide both free cutting and smooth surface finish. Dressing tool (10) does this by incorporating two abrasive members (16) and (18), one of which (16) is positioned to crush when the tool is applied to a rotating grinding wheel, while the other (18) shears the wheel. Preferably one abrasive member (16) contacts the grinding wheel tangentially, the other member (18) being placed normal to the grinding wheel at a rake angle ranging from positive to negative. <IMAGE>

Description

SPECIFICATION Compact dressing tool This invention relates to methods for dressing grinding wheels and, more particularly, relates to dresser tools of abrasive compacts.

Dressing may be defined as any operation performed on the face of a grinding wheel that improves its cutting action. Trueing is a dressing operation but is more precise, i.e., the face of the wheel may be made parallel to the spindle or made into a radius or special shape. Regularly applied trueing is also needed for the accurate size control of the work, particularly in automatic grinding.

Opening is another dressing operation and refers to the breaking away 9f the bond material from around the abrasive particles In a wheel thereby exposing them for grinding. A new wheel is initially opened and may have to be periodically opened thereafter to expose new particles when the previously exposed particles have been dislodged or dulled and to remove grinding swarf, which may accumulate during grinding, from around the abrasive particles.

Reference can be made to Machinery's Handbook (20th Ed. 1976) pp. 1992 to 1994 for a listing of commonly used dressing tools and methods for their use. One common type is a single point diamond tool having a granular shaped diamond mounted at one end of a tool shank. Dressing is performed with such a tool by engaging the periphery of a rotating wheel with the cylindrical handle of the tool disposed at a negative angle of 100 to 190 relative to a line drawn perpendicular to a tangent to the wheel periphery at the point of engagement of the tool with the wheel. This is equivalent to a negative back rake angle of about 550 to 600. The tool is also occasionally rotated about its longitudinal axis to prolong diamond life by limiting the extent of the wear facets and also to produce a pyramidal shape of the diamond tip.

It is also common to use a dresser having a plurality of individual diamond mounted in an army e.g., straight line, across the nib of the dresser.

These dressers are generally referred to as multipoint or cluster type. In use, the dresser is canted at an angle of 30 to 100, bringing two to five individual diamond points into contact with the grinding wheel. The multiple points often permit faster cross feed rates than the single point dresser.

While the prior dresser tools are generally considered to be satisfactory, manufacturers are always concerned with improving the grinding process, such as by improving the wheel life, wheql cutting speed, surface finish on the workplece produced by the grinding wheel, dressing tool life and dressing speeds.

Present dressing techniques "glaze" the grinding wheel slightly to produce a smooth surface finish. This produces a poor cutting wheel that "burns" the object during grinding. It is desirable that the grinding wheel be both "free cutting" and capable of producing a smooth surface finish. "Free cutting" refers to a grinding wheel's capability of rapidly removing material from a workpiece and requiring low cutting energy input from the grinding machine. But the present technology has not been able to meet the two fold criteria of free cutting and smooth surface finish because of the trade off inherent in the prevent dresser tools.

Accordingly, this invention seeks to provide a dressing action which 'enhances and improves the grinding process in these areas.

Another object of this invention is to provide an improved dressing tool particularly applicable for dressing grinding wheels which will grind workpieces and improve both free cutting and smooth surface finish characteristics.

The present invention provides a double action dressing tool comprising a body having at least a first abrasive means having a working edge and a second abrasive means having a working edge, said first means being positioned on said body such that, when said tool is applied to a rotating grinding wheel, said first abrasive means working edge crushes the wheel, and said second abrasive means working edge shears the wheel. The first and second abrasive means preferably present working edges in substantially orthogonal relationship.

With this structure, two action dressing is accomplished. The order of application of shearing and crushing across the wheel may be varied depending upon the results desired. The second abrasive means or compact may be disposed at a negative, positive or zero räke angle.

The invention further provides a method of dressing a grinding wheel comprising the steps of: rotating the grinding wheel about its axis; contacting the wheel with the working edge of an abrasive member aligned substantial parallel to the direction of wheel rotation and moving said working edge across the wheel to cause a crushing action; and contacting the wheel with the working edge of an abrasive member aligned substantial perpendicular to the direction of wheel rotation and moving the working edge across the wheel surface to cause a shearing action.

The abrasive of the abrasive means or member may be diamond, cubic or wartzitic boron nitride composite compacts or cluster compacts, a made diamond or cemented carbide compacts.

in order that the invention may be clearly understood, preferred embodiments thereof will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a double action dressing tool in accordance with a preferred embodiment of the present invention: Figures 2A, 2B and 2C are fragmentary crosssectional views, typically taken along line AA in Figure 1, showing the shearing compact set at zero, positive, and negative rake angles, respectively; Figure 3 is a schematic view ofllie double action dresser tool applied to a rotating grinding wheel; and Figure 4 is alternative embodiment of an oscillatory, double action dressing tool.

A dressing tool 10 of an embodiment of this invention is shown in Figure 1. Tool 10 includes a shank or handle portion 123and a head nib 14.

Two composite compact blanks 16 and 18 are carried or embedded or otherwise attached to the nib 14 and extend therefrom.

The configuration of the shank 1 2 and head nib 14 are illustrative and other shapes well known in the art are also useful as well.

A cluster compact is defined as a cluster of abrasive particles bonded together either (1) to a self-bonded relationship, (2) by means of bonding medium disposed between the crystals, (3) by means of some combination of (1) and (2).

Reference can be made of U.S. 3,136,615; U.S.

3,141,746 and U.S. 3,233,988 for a detailed disclosure of certain types of compacts and methods for making same.

A composite compact is defined as a cluster compact bonded to a substrate material such as cemented tungsten carbide. A bond to the substrate can be formed either during or subsequent to the formation of the cluster compact. Reference can be made to U.S.

3,745,623; U.S. 3,745A89 and U.S. 3,767,371 for a detailed disclosure of certain types of composite compacts and methods of making same.

The term cemented carbide as used herein means one or more transitional carbides of a metal of Groups IVb, Vb, and Vlb of the Periodic Table cemented or bonded by one or more matrix metals selected from the group iron, nickel and cobalt. A typical cemented carbide contains WC in a cobalt matrix or TiC in a nickel matrix.

Each of the composite blanks 1 6 and 18 can include a laminar substrate 116A and 18A of cemented carbide and an abrasive mass or layer 16B and 188. Abrasive Layer 16B may be comprised of an abrasive selected from the group consisting of diamond, cubic boron nitride (CBN), wurtzite boron nitride (WBN, and mixtures of two or more of the foregoing. Examples of suitable composite compacts sold by the General Electric Company under the designations: COMPAX~ Industrial Diamond Tool Blanks (polycrystalline diamond on a cemented carbide substrate) and BZN Compacts (CBN crystals on a cemented carbide substrate).

Composite blank 16 is a relatively long blank and is positioned with its abrasive layer 16B in a generally vertical orientation, as viewed in Figure 1, whereas blank 18 is shorter and positioned with its abrasive layer 1 8B in a generally horizontal orientation.

The functions of the blanks 16 and 18 may be best understood with reference to Figure 3 which shows the typical application of tool 10 to the surface of grinding wheel 20 which is rotating in the direction indicated. Tool 10 is moved in two directions, namely, into and laterally across the surface of the wheel 20. Blank 1 6 functions to crush the grinding wheel and blank 18 shears the wheel.

The long blank 16 extends beyond the wheel contact region as shown in Figure 3. The action of the long blank 16, because of contact angles, crushes the grinding wheel. This function breaks bond posts in bonded wheels, exposing new grains of abrasives and fractures existing exposed grains.

The short blank 18 is positioned substantially near the grinding wheel contact radius. The short blank 18 shears the wheel grains establishing exact grinding wheel diameter and a "free cutting" state. The short blank rake angle may be zero, positive or negative as shown in Figures 2A, 2B and 2C, respectively. Rake angle refers to the angle of engagement of dresser tool with the grinding wheel as measured from the tool table as a plane of reference. A table of a dressing tool is the tool surface against which chips of the grinding wheel bear as they are severed. In any rake orientation the leading abrasive edge of blank 1 8 is essentially orthogonal to the leading abrasive edge of blank 16.

In this manner the working edge of compact 16 engages the wheel surface aligned substantially parallel to the direction of wheel rotation and compact 18 engages the wheel surface with its working edge substantially transverse to the direction of wheel rotation. The working edge of compact 18 should engage the wheel surface at a position adjacent to the point of tangency of the working edge of compact 16 to the wheel surface.

The double action (crush-shear) tool 10 can be used two ways, depending upon which blank 16, 18 crosses the wheel 20 first during dressing. If the long blank 16 precedes the short one 18, crushing and then shearing, a smooth, stable, freecutting wheel surface will be produced. The action of the short blank 1 8 will dimensionally stabilize the wheel 20 and open it a bit, especially if the blank is used at a positive rake.

If the tool 10 is used with the short blank 18 preceding the long blank 16, shearing is the predominant dressing mode. However, tool wear is greater for the short blank, exposing more of the long blank to the wheel and causing a crushing action. Dimensional control is excellent, but dimensional stability drops due to broken bond posts during the crushing action.

Figure 4 shows an alternative tool 1 0' which is especially useful for surface grinders and other machines where the tool 10' oscillates making several dressing passes across the grinding wheel.

Tool 10' employs two crushing blanks 26 and 28 and one shearing blank 30. Composite compact blanks 26, 28 and 30 are embedded in or attached to nib 24 and include respectively, substrate 26A, 28A, 30A and abrasive 26B, 28B, 30B, as described above. The structure of tool 10' assure that a crushing blank 26 or 28 will always precede the shearing blank 30 as the tool is oscillated across the face of the grinding wheel.

The orientation of blanks 26 and 30 may be rotated 1 800 from that shown in Figure 4. Blank 26 should be oriented as shown. Blank 30 may, of course, have a positive, zero, or negative rake angle as shown in Figures 2A-2C.

While the invention has been described in terms of illustrative tools, it is clear that in its broadest aspects the invention also includes a method of dressing wherein an abrasive is passed in a controlled orientation in successive passes across a grinding wheel to crush and shear. Thus, while this method may be conveniently practised with the use of a pair of blanks, Figure 1, or three blanks, when oscillation is used, Figure 4, it is possible to practise the method with a single blank.

The single blank method would include contacting the grinding wheel with the blank oriented substantially parallel to the direction of wheel rotation to crush during the first pass (as blank 16, Figure 1).

The second pass would subject the wheel to a shearing action by rotating the abrasive 900 about the tool handle axis and moving it across the wheel surface. As discussed previously, the order of the first and second pass may be reversed.

The abrasive may be of a cluster compact or composite compact of diamond, cubic boron nitride, or wurtizitic boron nitride or a made diamond (a thin, triangular shaped natural diamond in combination with a long needleshaped crystal), or cemented carbide compacts.

Claims (12)

1. A double action dressing tool comprising a body having at least a first abrasive means having a working edge and a second abrasive means having a working edge, said first means being positioned on said body such that, when said tool is applied to a rotating grinding wheel, said first abrasive means working edge crushes the wheel and said second abrasive means working edge shears the wheel.

2. A dressing tool according to claim 1, wherein said first and second abrasive means present working edges in substantially orthogonal relationship.

3. A dressing tool according to claim 1 or claim 2, wherein said abrasive means comprise abrasives in the form of cluster compacts selected from the group consisting of diamond, cubic boron nitride, wurtzite boron nitride and mixtures thereof.

4. A dressing tool according to claim 3, wherein said compacts are composite compacts.

5. A double action dressing tool for dressing a grinding wheel comprising a body defining a nib; said nib having first, second and/or third composite compacts extending therefrom, said first and/or third compact presenting an elongate abrasive working edge to tangentially contact and crush the grinding wheel periphery and said second composite compact presenting a working edge to shear the grinding wheel, said compacts having an abrasive selected from the group consisting of diamond, cubic boron nitride, wurzite boron nitride and mixtures thereof.

6. A dressing tool according to any one of claims 1-5, wherein said second abrasive means or compact is set at a positive rake angle.

7. A dressing tool according to any one of claims 1-5, wherein said second abrasive means or compact is set at a negative rake angle.

8. A dressing tool according to any one of claims 1-5, wherein said second abrasive means or compact is set at a zero rake angle.

9. A method of dressing a grinding wheel comprising the steps of: rotating the grinding wheel about its axis; contacting the wheel with the working edge of an abrasive member aligned substantial parallel to the direction of wheel rotation and moving said working edge across the wheel to cause a crushing action: and contacting the wheel with the working edge of an abrasive member aligned substantial perpendicular to the direction of wheel rotation and.moving the working edge across the wheel surface to cause a shearing action.

10. A method according to claim 9, wherein said shearing action step is performed prior to said crushing action step.

11. A double action dressing tool substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

12. A method of dressing a grinding wheel substantially as hereinbefore described with reference to and as shown in the accompanying drawings.