Note: Descriptions are shown in the official language in which they were submitted.
Z~
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 opexation 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 of the bond material from around the
abrasive particles in a wheel thereby exposing them for grinding.
new wheel is initially opened and may have to be period-
ically 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 10 to 15 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 55 to 60. 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.
- 1 -
~2~;~8
It is also comn~Dn to use a dresser having
a plurality of individual diamon~smounted in an array,
e.g., straight line, across the nib of the dresser.
These dressers are generally referred to as multi-point
or cluster type. In use, the dresser is canted at
an angle of 3 to 10, 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, wheel cutting
speed, surface finish on the workpiece produced by
the grinding wheel, dressing tool life and dressing
speeds.
Present dressing techniques "gla~e" 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 no-t been able to meet the two
~' J - 2 -
2'~8
~old criteria o~ free cutting and smooth surface finish
because of the trade off inherent in the present dresser tools.
Accordingly, it is a feature of this invention to
provide a dressing action which enhances and improves the
grinding process in these areas.
Another feature 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 dresser tool of the present invention includes at
least two composite compacts which are positioned on the tool
nib to contact the rotating surface of the grinding wheel
tangentially to crush the wheel and substantially normal to
shear the wheel. 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 shearing compact may be disposed at a
negative, positive or zero rake angle.
In its broader aspect the present invention involves
a method of dressing wherein an abrasive body is used in
succession to crush and shear. The abrasive body may be
w ~tzi tic
' diamond, cubic or ~iar-~itic boron nitride composite compacts
or cluster compacts, a macle diamond or cemented carbide
compacts.
Figure 1 is a perspective view of a double action
dressing tool in accordance with the present invention;
Figures 2A, 2B and 2~ are fragmentary cross-
sectional 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 of the double action
dresser tool being applied to a rotating grinding wheel; and
1129Z~8
Figure 4 is alternative embodiment of an
oscillatory, double action dressing tool.
While this invention is susceptible of embodiment
in many di~ferent forms there is shown in the drawings and
will hereinafter be described in detail a preferred embodiment
of the invention, and modifications thereto, with the
understanding that the present disclosure is to be considered
as an exemplification of the principles of the invention and
is not intended to limit the invention to the embodiments
illustrated.
A dresser tool 10 of this invention is shown in
Figure 1. Tool 10 includes a shank or handle portion 12 and
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 configurations of the shank 12 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) in 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. Patent No. 3,136,615 -
dated June 9l 1964 - Bovenkerk et al; U.S. Patent No. 3,141,746
- dated July 21, 1964 - DeLai and U.S. Patent No. 3,233,988 -
dated February 8, 1966 - Wentorf Jr. et al 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 b~ made to U.S. Patent No. 3,745,623 - dated
July 17, 1973 ~ ntorE Jr. et al; and U.S. Patent No.
3,~
,4~-~ - dat~d ~uly 10, 1973 - Cristal and U.S. Patent No.
3,767,371 - dated October 23, 1973 - Wentorf Jr. et al 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 VIb 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 16 and 18 can include
a laminar substrate 16A and 18A of cemented carbide and an
abrasive mass or layer 16B and 18B. Abrasive layer 16B may be
comprised of an abrasive selected from the group consisting
of diamond, cubic boron nitride (CBN), wurtzite ni-tride (WBN,
and mixtures of two or more of the foregoing. Examples of
suitable compo~ite 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 cemen-ted
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 18B 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 xotating in the direction indicated. Tool 10 is
moved in two directions, namely, into and laterally across
l~Z~Z~B
the surface of the wheel 20. Blank 16 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, 2s 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 18 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 o~ the working edge of compact 16
to the wheel surface.
The double action (crush-shear) tool lU 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 shearin~, a smooth, stable,
free~cutting wheel surface will be produced. The action of
3LlZ~ 8
the short blank 18 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 10' 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,
A 28B, 30B, as described above. The structure of tool 10' assureS
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
180 from that shown in Figure 4. Blank 28 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 discribed in terms of
illustrative tools, it is clear that in its broadest aspects
the invention also includes a method of dressing wherein a
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
-- 7 --
1129~8
is used, Figure 4, it is possible to practise the method with
a single blank.
The single blank method would include contac-ting 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 90 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 macle diamond (a thin, triangular shaped natural
diamond in combination with a long needle-shaped crystal), or
cemented carbide compacts.
These and other modifications may be made by these
skilled in the art without departing from the scope and spirit
of the present invention as pointed out in the appended claims.
-- 8 --
