U.S. patent application number 12/316169 was filed with the patent office on 2009-06-18 for multifunction abrasive tool with hybrid bond.
Invention is credited to Robert F. Corcoran, JR., Richard W. J. Hall, Lynn L. Harley, Thomas Puthanangady, Srinivasan Ramanath, Rachana D. Upadhyay.
Application Number | 20090151267 12/316169 |
Document ID | / |
Family ID | 40524782 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090151267 |
Kind Code |
A1 |
Upadhyay; Rachana D. ; et
al. |
June 18, 2009 |
Multifunction abrasive tool with hybrid bond
Abstract
Abrasive tools and techniques are disclosed that can cut hard,
brittle materials to relatively precise dimensions. The tools,
which can include a hybrid bond of metal or metal alloy and a resin
matrix together with fine abrasive grits, can be employed, for
example, in mirror finish cutting applications, thereby enabling
`1.times.` or `single-pass` multi-function abrasive processes. The
specific selection of resin and metal or metal alloy types is such
that the tool is sufficiently brittle for the purpose of
manufacture and durability, but ductile enough to withstand the
grinding and handling stresses (an exemplary hybrid bond includes
bronze and polyimide). Numerous tool types and applications will be
apparent in light of this disclosure, including abrasive products
for electronic device manufacturing such as thin 1A8 blades (single
blade or multi-blade configuration).
Inventors: |
Upadhyay; Rachana D.;
(Shrewsbury, MA) ; Ramanath; Srinivasan; (Holden,
MA) ; Corcoran, JR.; Robert F.; (Holden, MA) ;
Puthanangady; Thomas; (Shrewsbury, MA) ; Hall;
Richard W. J.; (Southborough, MA) ; Harley; Lynn
L.; (Worcester, MA) |
Correspondence
Address: |
SAINT-GOBAIN CORPORATION
1 NEW BOND STREET, BOX 15138
WORCESTER
MA
01615-0138
US
|
Family ID: |
40524782 |
Appl. No.: |
12/316169 |
Filed: |
December 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61007417 |
Dec 12, 2007 |
|
|
|
Current U.S.
Class: |
51/298 |
Current CPC
Class: |
B24D 18/0009 20130101;
B23D 61/028 20130101; B24D 3/02 20130101; B24D 5/12 20130101 |
Class at
Publication: |
51/298 |
International
Class: |
B24D 3/00 20060101
B24D003/00; B24D 3/10 20060101 B24D003/10; B24D 3/30 20060101
B24D003/30 |
Claims
1. A multifunction abrasive tool, comprising: a hybrid bond of a
bronze and a polyimide; and a plurality of fine abrasive grits
blended with the hybrid bond; wherein the tool has a substantially
uniform thickness of 250 microns or less.
2. The multifunction abrasive tool of claim 1, wherein the tool is
a 1A8 type wheel or a 1A1 type wheel, having a thickness of about
100 microns or less.
3. The multifunction abrasive tool of claim 1, having a
substantially uniform thickness of about 65 microns or less.
4. The multifunction abrasive tool of claim 1, wherein the tool
includes about 1 to 50 volume percent (vol %) of polyimide, about
40 to 85 vol % of bronze, and about 5 to 40 vol % of fine abrasive
grits.
5. The multifimction abrasive tool of claim 4, wherein the tool
includes about 10 to 40 vol % of polyimide, about 45 to 75 vol % of
bronze, and about 10 to 25 vol % of fine abrasive grits.
6. The multifunction abrasive tool of claim 5, wherein the tool
includes about 11.25 vol % of polyimide, about 70 vol % of bronze,
and about 18.75 vol % of fine abrasive grits, with each component
having a tolerance of .+-./-20%.
7. The multifunction abrasive tool of any one of claim 1, wherein
the bronze consists essentially of 60/40 to 40/60 by weight of
copper and tin.
8. The multifunction abrasive tool of claim 1, wherein the
polyimide consists essentially of particles having an average
diameter of about 40 microns or less.
9. The multifunction abrasive tool of claim 1, wherein the bronze
consists essentially of particles having an average diameter of
about 40 microns or less.
10. The multifunction abrasive tool of claim 1, wherein the fine
abrasive grits consist essentially of diamonds having an average
diameter of about 40 microns or less.
11. The multifunction abrasive tool of claim 10, wherein the
diamonds have an average diameter of about 1 to 12 microns.
12. The multifunction abrasive tool of claim 11, wherein the
diamonds have an average diameter of about 1 to 3 microns.
13. The multifunction abrasive tool of any one of claim 1, wherein
the polyimide is Vespel.RTM. SP1 polyimide.
14. The multifunction abrasive tool of claim 1, wherein the
polyimide is Meldin 7001.RTM. polyimide.
15. The multifunction abrasive tool of claim 1, wherein the tool is
included in a multi-blade configuration that includes a plurality
of such tools in a gang-like configuration.
16. An abrasive tool, comprising: a hybrid bond of a metal or metal
alloy and a resin associated with a softening temperature less than
500.degree. C., wherein the metal or metal alloy has a liquid phase
or transient liquid phase at the softening temperature of the resin
and a fracture toughness between 1 and 5 MPa.m.sup.0.5 at room
temperature,; and a plurality of fine abrasive grits blended with
the hybrid bond; wherein the tool has a substantially uniform
thickness of 250 microns or less.
17. The abrasive tool of claim 16, wherein the softening
temperature is a Heat Deflection Temperature as measured by ASTM
standard D648, and is in the range of 160 to 400.degree. C.
18. The abrasive tool of claim 16, wherein the resin has a
ductility in the range of about 3% to 25%.
19. The abrasive tool of claim 16, wherein the metal or metal alloy
is a bronze
20. The abrasive tool of claim 16, wherein the resin is a
polyimide.
Description
FIELD OF THE DISCLOSURE
[0001] The disclosure relates to abrasives technology, and more
particularly, to abrasive tools suitable, e.g., for simultaneously
performing multiple functions, such as dicing and polishing of hard
brittle materials.
BACKGROUND
[0002] Resin-metal or so-called "hybrid" bonds are generally known
in the superabrasives industry. The first resin bonds for diamond
tools were based on phenolic systems. It was soon found that the
resin itself was not optimum, on its own, for some applications.
Thus, tool makers introduced secondary fillers to modify the
properties of the resin and enable the performance of tools in
various applications to be improved. In particular, silicon carbide
powder was introduced where a more brittle, friable bond was
needed, and copper powder was introduced when a stronger, tougher
bond was required (e.g., copper metal bond tools were used in
antiquity with natural diamond powder for cutting gemstones). These
fillers are still used in many conventional phenolic resin bond
systems.
[0003] During the 1970's it was thought that, in some applications,
the properties of hybrid resin-metal bonds might enhance
performance. In more detail, if the diamond could be distributed in
a continuous metal phase (for wear resistance and long life), and
if a continuous resin phase could be incorporated into the
microstructure (for lower wear resistance and free-cutting
properties), then the benefits of both systems might be available.
This technique was first successfully employed in the Resimet.RTM.
bonding system, in which the primary component is a cold-pressed
and sintered metal porous structure that firmly secures diamond or
CBN grains. The secondary bond component is a vacuum cast resin
which completely impregnates the porosity in the metal bond
structure. The result is a microstructure with two interpenetrating
continuous metal (bronze) and resin (epoxy) phases. Great Britain
Patent No. 1,279,413 describes details of such bonding systems.
Typical applications for this type of hybrid bond are in grinding
of carbide cutting tools, particularly when good corner-holding
ability is required, and typical grit sizes are in the mesh range
FEPA D46 and coarser (i.e., 325 Mesh and coarser, or 44 microns and
coarser).
[0004] Phenolic resin has good thermal resistance, but polyimide is
even better, so when these types of resins were introduced in the
late 1970's by DuPont, one of the first applications was in diamond
tools. U.S. Pat. Nos. 4,001,981 and 4,107,125 describe polyimide
bonded superabrasive tools. As in phenolic resin tools, various
fillers are used to modify the properties of the bonds, and copper
and bronze powders are used as well. Such polyimide based bonds are
typically used in situations where a lot of heat is generated
(i.e., where the bond must be resistant to high temperatures). The
primary example application is in fluting of round, cemented
carbide tools, such as drills and end-mills.
[0005] More exacting applications calling for greater precision and
cut quality have historically used different tool configurations
and bond types. For example, and as is known, a hard disk drive
(HDD) is a commonly used storage mechanism used in numerous
consumer electronic applications, including computers and game
consoles, mobile phones and personal digital assistants, digital
cameras and video recorders, and digital media players (e.g., MP3
players). HDD designs generally include a circular magnetic
`platter` (onto which data are recorded) that spins about a
spindle. As the platter spins, a read-write head is used to detect
and/or modify the magnetization of the platter storage location
directly under it. The read-write head itself is attached to a
`slider,` which is an aerodynamically shaped block that allows the
read-write head to maintain a consistent `flying height` above the
platter. The slider is connected to an actuator assembly (e.g.,
motor and arm) that operates to move the read-write head to any
storage location on the platter. Manufacturing of the slider
component presents a number of challenges. For instance, as the
form factor of the electronic devices that employ HDDs decreases,
so does the size of the components that make up the HDD, including
the slider (which can be about 1/50.sup.th to 1/100.sup.th the size
of a penny). As such, the slider must be cut to fairly precise
dimensions. Exacerbating this manufacturing complexity is the fact
that sliders are typically made from hard brittle materials (e.g.,
Al.sub.2O.sub.3--TiC, see for example U.S. Pat. No. 4,430,440),
which are difficult to cut without incurring problems such as
chipping and excessive kerf.
[0006] There remains a continuing need, therefore, for new abrasive
tools that can cut hard, brittle materials to precise
dimensions.
SUMMARY
[0007] One embodiment of the present disclosure provides a
multifunction abrasive tool suitable, e.g., for dicing and
polishing hard brittle materials in a single pass. The tool
includes a hybrid bond of metal/metal alloy and resin, and a
plurality of fine abrasive grits blended with the hybrid bond. The
metal alloy can be bronze which may, for example, consist
essentially of 50/50 by weight of copper and tin, and the resin can
be a polyimide such as, for instance, Vespel.RTM. SP1 polyimide,
available from E. I. du Pont de Nemours and Company, Meldin
7001.RTM. polyimide, available from Saint-Gobain Performance
Plastics Corporation, or a comparable polyimide. The tool can be
substantially straight and have a substantially uniform thickness
of 250 microns or less. In specific example cases, the tool is a
1A8 type wheel or a 1A1 type wheel, and has a thickness of about 65
microns or less (other wheel types will be apparent in light of
this disclosure). In one particular configuration, the tool
includes about 1 to 50 volume percent (vol %) of resin, such as
polyimide, about 40 to 85 vol % of metal/metal alloy, such as
bronze, and about 5 to 40 vol % of fine abrasive grits. In another
more specific configuration, the tool includes about 10 to 40 vol %
of resin, such as polyimide, about 45 to 75 vol % of metal/metal
alloy, such as bronze, and about 10 to 25 vol % of fine abrasive
grits. In another more specific configuration, the tool includes
about 11.25 vol % of polyimide, about 70 vol % of bronze, and about
18.75 vol % of fine abrasive grits, with each component having a
tolerance of .+-.20%. The polyimide may, for example, consist
essentially of particles having an average diameter of about 40
microns or less, and the bronze may consist essentially of
particles having an average diameter of about 40 microns or less,
and the fine abrasive grits may consist essentially of diamonds in
a 50 to 75 concentration, and having an average diameter of about
40 microns or less. In a more specific such configuration, the
bronze consists essentially of particles having an average diameter
of about 10 microns or less. The tool may be included in a
multi-blade configuration that includes a plurality of such tools
in a gang-like arrangement (either distinct tools formed
individually and coupled together, or formed as a monolithic
structure).
[0008] Another embodiment of the present disclosure provides an
abrasive tool suitable, e.g., for dicing and/or polishing hard
brittle materials. The tool is configured similar to the tool
discussed above, but has a substantially straight and substantially
uniform thickness in the range of 30 to 125 microns.
[0009] Another embodiment of the present disclosure provides an
abrasive tool suitable, e.g., for dicing and/or polishing hard
brittle materials. The tool includes a hybrid bond of a metal or
metal alloy, and a resin associated with a Heat Deflection
temperature (e.g., as measured by ASTM standard D648) or other
comparable processing temperature parameter (where the resin
softens without melting, generally referred to as a "softening
temperature") less than 500.degree. C. (e.g., in the range of about
100.degree. C. to 450.degree. C., or even more specifically, in the
range of about 160.degree. C. to 400.degree. C.). The metal or
metal alloy (e.g., bronze) has a liquid phase or transient liquid
phase at the Heat Deflection or softening temperature of the resin,
and a fracture toughness between 1 and 5 MPa.m.sup.0.5 at room
temperature. The resin (e.g., polyimide) can have a ductility in
the range of about 3% to 25%. The tool further includes a plurality
of fine abrasive grits blended with the hybrid bond. In various
alternative embodiments, the tool can have a substantially straight
and substantially uniform thickness of 250 microns or less. In one
particular case, the tool is a multifunction tool capable of both
slicing and polishing hard brittle materials in a single pass.
Various other abrasive tool parameters as discussed herein can be
equally applied to such alternative embodiments.
[0010] Another embodiment of the present disclosure provides a
method for making abrasive tools suitable, e.g., for dicing and/or
polishing hard brittle materials. The method includes providing
pre-selected proportions of particulate ingredients including
abrasive grains, a polyimide, and a pre-alloyed bronze (e.g., about
50 by weight % of copper and about 50 weight % of tin). The method
continues with mixing the particulate ingredients to form a
substantially uniform composition, placing the substantially
uniform composition into a mold of desired shape, and compressing
the mold to a pressure in the range of about 25-200 MPa for a
duration effective to form a molded article (e.g., 5 to 30
minutes). The method continues with heating the molded article to a
temperature less than 500.degree. C. (e.g., in the range of about
100.degree. C. to 450.degree. C., or even more specifically, in the
range of about 160.degree. C. to 400.degree. C.) for a duration
effective to sinter the bronze and soften the polyimide, thereby
integrating the abrasive grains and sintered bond into a composite
of substantially continuous metal alloy phase, with a substantially
continuous or substantially discontinuous polyimide phase, and then
cooling the composite to form the abrasive tool. The method may
continue with lapping or otherwise finishing sides of the abrasive
tool to provide desired degree of straightness and thickness (e.g.,
double-sided lapping, where opposing sides of the tool are
simultaneously lapped to provide substantially uniform thickness of
about 250 microns or less). In an alternative embodiment, the
method includes forming multiple thinner tools from the initial
abrasive tool, where each thinner tool has a substantially uniform
thickness of 250 microns or less, thereby providing a multi-blade
abrasive tool (ganged-like configuration). In one such case,
forming multiple thinner tools from the initial abrasive tool is
accomplished using electro-discharge machining (EDM).
[0011] The features and advantages described herein are not
all-inclusive and, in particular, many additional features and
advantages will be apparent to one of ordinary skill in the art in
view of the drawings, specification, and claims. Moreover, it
should be noted that the language used in the specification has
been principally selected for readability and instructional
purposes, and not to limit the scope of the inventive subject
matter.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
[0012] Abrasive tools and techniques are disclosed that can cut
hard, brittle materials to relatively precise dimensions. The
tools, which include a hybrid bond of metal or metal alloy (e.g.,
bronze) and a resin (e.g., polyimide) matrix together with fine
abrasive grits, can be employed, for example, in mirror finish
cutting applications, thereby enabling `1.times.` or `single-pass`
multi-function abrasive processes. Numerous tool types and
applications will be apparent in light of this disclosure,
including abrasive products for electronic device manufacturing
such as thin 1A8 blades (single blade or multi-blade configuration)
and other such cutting blades.
[0013] In one exemplary application, the disclosed tools can be
used in the mirror finish dicing of read-write head sliders.
Typically, read-write head sliders made of hard, brittle materials
such as alumina titanium carbide (Al.sub.2O.sub.3--TiC) are
manufactured in a two-step process involving a dicing step that
uses a metal-bonded tool and a subsequent discrete polishing step
that uses a resin-bonded tool. A tool configured in accordance with
an embodiment of the present disclosure is capable of performing
both slicing and polishing in a single pass (also referred to as a
"1.times. process" herein). As will be appreciated in light of this
disclosure, note that such embodiments may also be used in
multiple-pass or "2.times." processes, if so desired.
[0014] In more detail, the blade of this example embodiment
includes a metal/metal alloy, such as bronze, and a resin, such as
polyimide resin, with fine diamond abrasive grit for
dicing/polishing of hard and brittle material such as
alumina-titanium carbide. The metal alloy can be substantially
continuous or discrete in nature, although substantially continuous
can have certain performance benefits associated with kerf quality
and tool wear, and can be sintered in solid or liquid phase at
process temperatures of the polyimide. In addition, the metal alloy
can transfer the stiffness to the tool (i.e., no interfacial
sliding between metal alloy and polyimide), and its hardness can be
less than that of the work material. A suitable polyimide (or other
comparable resin) generally has low elongation % and high thermal
stability. As will further be appreciated in light of this
disclosure, the present disclosure is not intended to be limited to
bronze and polyimide. Rather, the bronze can be replaced, for
example, by any metal or metal alloy that has a liquid phase or
transient liquid phase at the softening temperature (e.g., Heat
Deflection temperature as measured, for instance, by ASTM standard
D648) of the resin and a fracture toughness between 1 and 5
MPa.m.sup.0.5 at room temperature. Alternatively, the polyimide can
be replaced, for example, by any resin or polymer that has a
softening temperature less than 500.degree. C. (e.g., in the range
of about 160.degree. C. to 400.degree. C.) and a ductility in the
range of about 3% to 25%. In general, the specific selection of
resin and metal alloy types is such that the tool is sufficiently
brittle for the purpose of manufacture and durability, but ductile
enough to withstand the grinding and handling stresses (i.e.,
overly stiff tools are susceptible to breakage).
[0015] The content of resin may range, for example, from about 1 to
50 volume percent (vol %), while the content of metal/metal alloy
may range, for example, from about 40 to 85 vol %. The metal alloy
can be bronze with, for example, 60/40 to 40/60 copper/tin by
weight (e.g., 50/50 by weight %). The diamond content (or other
suitable abrasive grain) may range, for example, from 10 to 30 vol
%, at a concentration ranging from about 40 to 100 concentration.
The diamond grit particles may have an average diameter, for
instance, of not more than 40 microns in diameter, preferably in
the range of 1 micron to 12 microns, and more preferably in the
range of 1 micron to 3 microns. The bronze powder and polyimide
particles may have an average diameter, for instance, of not more
than 40 microns and more preferably 30 microns or less. The actual
composition will vary depending on factors such as desired
straightness and rigidity/ductility, as well as self-dressing
capability and allowable degree of chipping along the kerf (if
any). Such tools perform well in 1.times. slicing/polishing
processes for hard brittle workpieces, such as in manufacturing of
microelectronic wafer components (e.g., silicon wafers and
Al.sub.2O.sub.3--TiC sliders).
[0016] The abrasive is not intended to be limited to diamond, and
can be essentially any suitable abrasive such as CBN, fused
alumina, sintered alumina, silicon carbide, or mixtures thereof.
The selection of abrasive depends on factors such as the material
being cut and desired tool cost. As is known, the abrasive grains
may be provided with a coating which will vary in its nature,
depending on the specific abrasive used. For instance, if the
abrasive is diamond or CBN then a metal coating on the abrasive
(e.g. nickel) can be used to improve grinding properties.
Similarly, fused alumina's grinding quality is enhanced, in certain
grinding or cutting applications, if the grain is coated with iron
oxide or a silane such as gamma amino propyl triethoxy silane.
Likewise, sintered sol gel and seeded sol gel alumina abrasive
exhibit enhanced grinding properties when they have been supplied
with a silica coating, or in some cases, improvement may result if
the sintered abrasive is silane treated. The operable abrasive grit
size can also vary depending on the desired performance, and in
accordance with some embodiments of the present disclosure, the
grit size is 40 microns or finer.
[0017] In various alternative embodiments, tools of the present
application can have a thickness of 250 microns or less, preferably
100 microns or less, more preferably 70 microns or less, and even
more preferably 65 microns or less. Although the tool type and its
dimensions can vary as well (depending on the target application),
one such example tool is a type 1A8 wheel, having a thickness of
about 30 to 130 microns (e.g., 65 microns or less), an outside
diameter of about 50 to 150 millimeters (e.g., 110 mm), and inside
diameter of about 35 to 135 mm (e.g., 90 mm). The abrasive section
of the multi-function blade generally extends from the outside
diameter to the inside diameter of the wheel, although partial
abrasive sections that extend from the outside diameter to some
distance from the inner diameter can be used as well, when
suitable.
[0018] The tool can be manufactured, for example, from a powder
blend at around 300 to 420.degree. C. In one such embodiment, the
selection of the metal alloy is such that at least one of the
phases present in the alloy melts at such a temperature, resulting
in improved sinterability of the tool, better diamond retention,
enhanced tool stiffness, and a path for extraction of the heat
generated in slicing/polishing process. Polyimide generally does
not possess a melting point at the process temperatures, but only
softens. High pressures can be used to ensure that the
densification is complete during the formation process (e.g.,
molding).
[0019] One commercially available abrasive tool consists of cobalt
metal, resin, and fine diamond grits. However, the use of cobalt
can pose a number of issues. Specifically, a cobalt-based product
is typically very brittle and tends to break in handling and use.
In addition, use of cobalt leads to a structure that is
under-sintered and possesses poor grit retention (this is because
cobalt doesn't flow very well at process temperatures associated
with suitable resins). Depending on context, cobalt can be
environmentally unfriendly. Furthermore, the high stiffness of
cobalt may not be transferred to the tool due to sliding at the
cobalt-resin interface. Other factors, such as the choice of resin
type and fillers used, and process temperature also play a role in
tool performance (e.g., beneficial qualities of resin deteriorate
when subjected to excessive temperature).
[0020] Another subtle but significant issue associated with using
cobalt is related to magnetic properties. In particular, cobalt is
known as a hard ferro-magnetic material which will readily
magnetize. To this end, it is believed that the cobalt in a
cobalt-based blade may upset the magnetic properties of the sliced
and polished workpiece (e.g., Al.sub.2O.sub.3--TiC sliders). This
could be due either to residual cobalt contamination picked up on
the surface of the workpiece during cutting (e.g., as the tool
wears, cobalt is released from the tool and some of it sticks to or
is embedded in the workpiece), or to the effect of cobalt in the
tool influencing the local magnetic field around the grinding zone,
which subsequently interacts with the workpiece.
[0021] In contrast to such conventional cobalt-based products, a
tool configured in accordance with an embodiment of the present
disclosure has shown superior ability to withstand handling and
high grinding forces by maintaining a suitable degree of ductility,
and can be used to grind at higher depths of cut. In addition, the
exemplary metal alloy does not include any cobalt, and sufficiently
flows at process temperatures associated with polyimide to provide
excellent sinterability, grit retention, stiffness, and ductility.
Moreover, a metal alloy of bronze is non-magnetic and thus does not
influence the local magnetic field around the grinding zone, or
contaminate the workpiece surface with magnetic particles. U.S.
Pat. Nos. 5,313,742, 6,200,208, and 6,485,532 provide additional
details relevant to conventional abrasive tools capable of cutting
hard brittle materials. Each of the '742, '208, and '532 patents is
herein incorporated by reference in its entirety.
[0022] Thus, abrasive tools configured in accordance with such
embodiments can be used in simultaneous 1.times. dicing and
polishing operations performed in the manufacture of
Al.sub.2O.sub.3--TiC sliders and other such components made from
hard brittle materials. In a more general sense, abrasive tools
configured in accordance with such embodiments can be used to
perform 1.times. processes involving the combination of cutting and
polishing to a fine finish workpieces that are traditionally sliced
or otherwise cut with one tool and polished with another. Such
tools may be used in non-1.times. applications (e.g., 2.times.) as
well, if so desired. The disclosed tools provide improved tool
life, better edge quality (good perpendicularity and no or low
degree of chipping), and better finish relative to conventional
tools (no or fewer scratches). In addition, the tools effectively
reduce manufacturing costs associated with time, labor, and power,
by enabling a two-in-one process.
[0023] Example Tool Configuration #1
[0024] In one specific abrasive tool configuration according to an
embodiment of the present disclosure, the tool is a type 1A8 wheel,
having a thickness of about 65 microns, an outside diameter of
about 110 millimeters, and an inside diameter of about 90 mm, and
the blade composition is as follows: 31.25 volume percent
Vespel.RTM. SP1 polyimide (with the powder particles having an
average diameter of about 30 microns), 50 vol % bronze (50/50 by
weight of copper and tin, with the powder particles having an
average diameter of about 30 microns), and 18.75 vol % of diamond
(at 75 concentration, and having an average diameter of 1 to 3
microns). The diamonds can be, for instance, 1 to 3 .mu.m (-8
.mu.m) RB Amplex.RTM. diamond, or 1 to 2 .mu.m (-8) RVM CSG Diamond
Innovations.RTM. diamond. Other suitable diamond types and sources
will be apparent in light of this disclosure. The tolerances on the
tool dimensions and composition may be, for example, .+-.10
percent, although looser tolerances (e.g., .+-.20 percent or more)
or tighter tolerances (e.g., .+-.5 percent or less) can be used as
well, depending of the particular application and desired precision
and performance.
[0025] The thinness of the tool reduces wasted work material, yet
has a straightness that allows for precision slicing and edge
quality (low kerf loss with substantially perpendicular kerf wall,
such as within 15 degrees of the perpendicular plane or better).
Straightness refers to the axial thickness of the wheel being
substantially uniform at all radii from the radius of the arbor
hole to the outer radius of the wheel. In one embodiment, this
thin, straight tool thickness is achieved by double-sided lapping
the tool down to 65 microns. Single-sided lapping may be used as
well, but care must be given so as to not distort the tool (e.g.,
using cooling techniques and allocating additional manufacturing
time).
[0026] In this particular example embodiment, the tool includes a
substantially continuous metal alloy phase (pre-alloyed bronze),
with either a substantially continuous or substantially
discontinuous polyimide phase. This 1A8 tool design can be used,
for example, in 1.times. applications where simultaneous slicing
and polishing is desired. The substantially continuous metal alloy
phase of bronze improves the stiffness of the tool (high aspect
ratio of exposed tool, so stiffness is helpful in controlling
kerf), and the polyimide adds a degree of compliance to the tool
structure so that, during cutting, the diamond on the tool sides
are pressed back slightly into the bond, thereby limiting the depth
of cut which they take, and thus improving edge finish on the
workpiece.
[0027] When compared to a cobalt-based polyimide tool of similar
configuration, this example multifunction tool performed comparably
with respect to edge straightness and chip thickness proximate the
edge. However, the tool configured in accordance with this
embodiment was relatively harder than the cobalt-based tool, and
exhibited both lower tool wear and smaller kerf relative to the
cobalt-based tool. In addition, AFM (atomic force microscope)
analysis showed that this tool provided a better workpiece edge
finish Ra of 27 .ANG., compared to the workpiece edge finish Ra of
43 .ANG. provided by the cobalt-based tool.
[0028] Table 1 summarizes performance parameters of this
comparative analysis between the Example 1 embodiment and the
cobalt-based tool. These data are based on the first row or pass of
the tool through the workpiece. For additional passes (rows), the
difference in wear rate became further pronounced. For instance,
after 15 rows (24 slots), the tool wear was about 36 microns for
the cobalt-based tool and about 28 microns for the Example 1
embodiment. The comparative testing was done at a table speed of
about 100 mm/min and tool speed of 9000 RPMs.
TABLE-US-00001 TABLE 1 Performance Comparative Data Cobalt-based
Parameter Tool Embodiment #1 Tool Wear 4 0 .mu.m Straightness 2 2
.mu.m Kerf 74 67 .mu.m Chips 1 1 .mu.m Surface Finish 43 27 Ra,
.ANG.
[0029] In addition, it is noted that increasing tool speed of the
Example 1 embodiment from 9000 RPMs to, for instance, 11000 to
18000 RPMs (depending on upper limit of machine) improved edge
straightness and reduced need for tool dressing. On the other hand,
lower tool speeds can be used, if performing intermediate tool
dressing operations (e.g., in between each row or sub-set of rows)
is acceptable.
[0030] With respect to particle sizes, there is generally no
specific requirement. Commercially available sizes of the various
tool components have been used as described herein, with acceptable
results (as also described herein). However, it is generally
believed that finer particle sizes of bronze may operate to improve
diamond distribution and tool performance. Thus, in some
embodiments described herein, bronze particles in the range of 10
microns or less are used (e.g., to improve distribution of the 1 to
3 micron diamond). However, and as will be appreciated in light of
this disclosure, larger bronze particles (e.g., in the 30 micron
range) are effective as well.
[0031] Example Tool Configuration #2
[0032] In another specific abrasive tool configuration according to
an embodiment of the present disclosure, the tool is a type 1A8
wheel, having dimensions as previously described, and a blade
composition as follows: 21.25 volume percent Vespel.RTM. SP1
polyimide (with the powder particles having an average diameter of
about 30 microns), 60 vol % bronze (50/50 by weight of copper and
tin, with the powder particles having an average diameter of about
30 microns), and 18.75 vol % of diamond (at 75 concentration, and
having an average diameter of 1 to 2 microns). Previous discussion
with respect to tolerances is equally applicable here.
[0033] This example multifunction tool provided a workpiece surface
finish Ra of 42 .ANG., with other performance parameters remaining
comparable to the Example 1 embodiment.
[0034] Example Tool Configuration #3
[0035] In another specific abrasive tool configuration according to
an embodiment of the present disclosure, the tool is a type 1A8
wheel, having dimensions as previously described, and a blade
composition as follows: 11.25 volume percent Vespel.RTM. SP1
polyimide (with the powder particles having an average diameter of
about 30 microns), 70 vol % bronze (50/50 by weight of copper and
tin, with the powder particles having an average diameter of about
5 to 8 microns), and 18.75 vol % of diamond (at 75 concentration,
and having an average diameter of 1 to 3 microns). Previous
discussion with respect to tolerances is equally applicable
here.
[0036] This example multifunction tool provided a workpiece surface
finish Ra of 48 .ANG., with other performance parameters remaining
comparable to the Example 1 embodiment. However, this tool provided
improved straightness, better entry and exit geometry (scratch-free
entry and exit of cut) relative to Example 1 embodiment, and
reduced dressing operations between rows.
[0037] Example Tool Configuration #4
[0038] In another specific abrasive tool configuration according to
an embodiment of the present disclosure, the tool is a type 1A8
wheel, having dimensions as previously described, and a blade
composition as follows: 30.25 volume percent Vespel.RTM. SP1
polyimide (with the powder particles having an average diameter of
about 30 microns), 57.25 vol % bronze (50/50 by weight of copper
and tin, with the powder particles having an average diameter of 5
to 8 microns), and 12.5 vol % of diamond (at 50 concentration, and
having an average diameter of 1 to 2 microns). Previous discussion
with respect to tolerances is equally applicable here.
[0039] This example multifunction tool exhibited performance
parameters comparable to Example 1 embodiment.
[0040] Example Tool Configuration #5
[0041] In another specific abrasive tool configuration according to
an embodiment of the present disclosure, the tool is a type 1A8
wheel, having dimensions as previously described, and a blade
composition as follows: 20.25 volume percent Vespel.RTM. SP1
polyimide (with the powder particles having an average diameter of
about 30 microns), 67.25 vol % bronze (50/50 by weight of copper
and tin, with the powder particles having an average diameter of 5
to 8 microns), and 12.5 vol % of diamond (at 50 concentration, and
having an average diameter of 1 to 2 microns). Previous discussion
with respect to tolerances is equally applicable here.
[0042] This example multifunction tool exhibited performance
parameters comparable to Example 3 embodiment.
[0043] In addition to the performance testing previously described,
wear test data were measured for a number of samples having varying
amounts of abrasives content, as well as bronze-polyimide ratio, to
determine the effect of such variations on tool wear. While there
was no significant change in tool wear attributed to varying
diamond concentration (e.g., from 60 to 75 concentration), a
significant change in tool wear can be achieved by increasing the
bronze content (e.g., from 65 vol % to 70 vol % or 75 vol %
corresponded to decrease in tool wear).
[0044] Example Tool Configuration #6
[0045] In another specific abrasive tool configuration according to
an embodiment of the present disclosure, the tool is a type 1A8
wheel, having a thickness of about 65 microns, an outside diameter
of about 110 millimeters, and an inside diameter of about 90 mm,
and the blade composition is as follows: 26.5 volume percent Meldin
7001.RTM. polyimide (with the powder particles having an average
diameter of about 10 microns), 54.8 vol % bronze (50/50 by weight
of copper and tin, with the powder particles having an average
diameter of about 8 microns), and 18.7 vol % of diamond (at 75
concentration, and having an average diameter of 1 to 2 microns).
The diamonds can be, for instance, 1 to 2 .mu.m (-8 .mu.m) 1 to 2
.mu.m (-8) RVM CSG Diamond Innovations.RTM. diamond. The tolerances
on the tool dimensions and composition may be, for example, .+-.10
percent, although looser tolerances (e.g., .+-.20 percent or more)
or tighter tolerances (e.g., .+-.5 percent or less) can be used as
well, depending of the particular application and desired precision
and performance. The tools are manufactured in a manner similar to
the tools in Example 1.
[0046] The thinness of the tool reduces wasted work material, yet
has a straightness that allows for precision slicing and edge
quality (low kerf loss with substantially perpendicular kerf wall,
such as within 15 degrees of the perpendicular plane or better).
Straightness refers to the axial thickness of the wheel being
substantially uniform at all radii from the radius of the arbor
hole to the outer radius of the wheel. In one embodiment, this
thin, straight tool thickness is achieved by double-sided lapping
the tool down to 65 microns. Single-sided lapping may be used as
well, but care must be given so as to not distort the tool (e.g.,
using special cooling techniques and allocating additional
manufacturing time).
[0047] In this particular example embodiment, the tool includes a
substantially continuous metal alloy phase (pre-alloyed bronze),
with either a substantially continuous or substantially
discontinuous polyimide phase. This 1A8 tool design can be used,
for example, in 1.times. applications where simultaneous slicing
and polishing is desired. The substantially continuous metal alloy
phase of bronze improves the stiffness of the tool (high aspect
ratio of exposed tool, so stiffness is helpful in controlling
kerf), and the polyimide adds a degree of compliance to the tool
structure so that, during cutting, the diamond on the tool sides
are pressed back slightly into the bond, thereby limiting the depth
of cut which they take, and thus improving edge finish on the
workpiece.
[0048] When compared to a cobalt-based polyimide tool of similar
configuration, this example multifunction tool performed comparably
with respect to edge straightness and chip thickness proximate the
edge.
[0049] Table 2 summarizes performance parameters of this
comparative analysis between the Example 6 embodiment and the
cobalt-based tool. In this example, tool performance was determined
after allowing sufficient cuts for it to reach a steady state. The
tool wear for example, is determined over 35 cuts after reaching
the steady state. The comparative testing was done at a table speed
of about 100 mm/min and tool speed of 9000 RPMs.
TABLE-US-00002 TABLE 2 Comparative Performance Data Cobalt-based
Parameter Tool Embodiment #6 Tool Wear over 10-11 12-14 35 cuts,
.mu.m Straightness 2 2 .mu.m Kerf 74 67 .mu.m Chips 1 1 .mu.m
[0050] Methods of making abrasive tools as described herein can
include one or more of the following steps:
[0051] (a) providing pre-selected proportions of particulate
ingredients including superabrasive grains (e.g., fine diamond
having average diameter of 1 to 2 microns), a polyimide, and a
pre-alloyed bronze consisting essentially of about 40 to about 60
weight % of copper and about 40 to about 60 weight % of tin;
[0052] (b) mixing the particulate ingredients to form a
substantially uniform composition, which can be formed using any
suitable blending apparatus (e.g., double cone tumblers, twin-shell
V-shaped tumblers, ribbon blenders, horizontal drum tumblers, and
stationary shell/internal screw mixers);
[0053] (c) placing the substantially uniform composition into a
mold of desired shape (e.g., 1A8 tool);
[0054] (d) compressing the mold to a pressure in the range of about
25-200 MPa for a duration effective to form a molded article;
[0055] (e) heating the molded article to a temperature less than
500.degree. C. (e.g., in the range of about 100.degree. C. to
450.degree. C., or even more specifically, in the range of about
160.degree. C. to 400.degree. C.) for a duration effective to
sinter the bronze and soften the polyimide, thereby integrating the
abrasive grains and sintered bond into a composite of substantially
continuous metal alloy phase, with a substantially continuous or
substantially discontinuous polyimide phase (e.g., higher content
such as 30 vol % or more of polyimide tends to provide a
substantially continuous phase, while lower content such as less
than 30 vol % tends to provide a substantially discontinuous phase;
note, however, that either phase is acceptable and provides
acceptable results);
[0056] (f) cooling the composite to form the abrasive tool; and
[0057] (g) lapping sides of the tool to provide desired degree of
straightness and thickness (e.g., an axial thickness of the tool
being substantially uniform at all radii from the radius of the
arbor hole to the outer radius of the tool, with the final
thickness being, e.g., about 65 microns). This lapping can be
implemented as double-sided lapping, so as to further improve
straightness.
[0058] The abrasive grits (e.g., diamonds) are generally present in
both the bronze and polyimide phases, but predominantly in the
bronze phase. The polyimide phase is more elastic than the bronze
phase, and imparts a degree of elasticity to the abrasive tool,
which is believed to control the depth of cut taken by the abrasive
grits on the cutting edge, and possibly the sidewall of the tool
(assuming a wheel configuration), so as to reduce the chip size
taken due to the intended abrasion process and thus generate the
surface finish required.
[0059] The abrasive tools described herein can be produced by a
densification using cold-press or hot-press techniques. In a
cold-press process, sometimes referred to as pressureless
sintering, a blend of the composite components is introduced into a
mold of desired shape and a high pressure is applied at room
temperature to obtain a compact but friable molded article. The
high pressure can be, for example, in the range of 25-200 MPa.
Subsequently, pressure is relieved and the molded article is
removed from the mold then heated to sintering temperature. The
heating for sintering can be done, for instance, while the molded
article is pressurized in an inert gas atmosphere to a lower
pressure than the pre-sintering molding pressure (e.g., less than
about 100 MPa, or even more specifically, less than about 50 MPa).
Sintering can also take place under vacuum. During this low
pressure sintering, the molded article (e.g., thin abrasive wheel
of the 1A8 type) can be placed in a mold and/or sandwiched between
flat plates, to help maintain its straightness during sintering. In
a hot-press process, the blend of particulate bond composition is
put in the mold, typically of graphite, and compressed to a high
pressure as in the cold-press process. However, an inert gas is
utilized and the high pressure is maintained while the temperature
is raised, thereby achieving densification while the tool preform
is under pressure.
[0060] Note that this method may be used to fabricate a single
blade or multi-blade configuration. With respect to a multi-blade
configuration made up of individually fabricated tools (gang
configuration), there is an additional consideration of suitable
tolerancing on each member tool of the gang. In more detail, while
tolerances in a single blade embodiment may be acceptably higher,
such high tolerances in a gang configuration may stack up to
provide undesirable results (e.g., lack of desired precision).
Thus, and in accordance with one embodiment of the present
disclosure, tolerances of the individual tools included in the gang
are such that any resulting stacking falls within an acceptable
range. The ganged tools can be separated, for example, by spacers
of a material such as alumina or steel. Alternatively, another
embodiment is a multi-blade tool that is fabricated by forming a
monolithic multi-blade structure from a thicker tool. The thicker
tool can be made using the previously described manufacturing steps
(a through f, and optionally g), with the initial tool thickness
being sufficient to allow the desired number of individual tools to
be formed therefrom (e.g., 3600 microns or thicker). Each of
individual tools formed within that initial tool thickness can be,
for example, under 125 microns (or less) and separated by the inner
structure itself whose diameter is smaller than the thin outer
tool. Such a monolithic structure effectively provides a built-in
spacer between individual tools, thereby reducing tolerancing
variables. A ganged assembly of individual tools having a thick
inner section and thin outer section for cutting is described in
the previously incorporated U.S. Pat. No. 5,313,742. This principle
(thick inner section and thin outer section) can be adopted into a
monolithic structure as described herein. The forming of individual
tools from the initial thicker tool can be accomplished, for
instance, by electro-discharge machining (EDM), although other
suitable machining techniques can be used (e.g., milling, wire
sawing, etc). Finishing techniques such as lapping can be used to
further refine parameters (thickness and straightness) of the
individual tools.
[0061] The foregoing description of the embodiments of the
disclosure has been presented for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Many modifications and
variations are possible in light of this disclosure. For instance,
Vespel.RTM. SP1 polyimide is noted as acceptable for use in
embodiments, but other comparable polyimides or polymers having
qualities that suitably interact with the metal alloy and abrasive
can be used as well. Likewise, the wheel types may vary (e.g., 1A1,
1A8, or any relatively thin abrasive wheel configuration). It is
intended that the scope of the invention be limited not by this
detailed description, but rather by the claims appended hereto.
[0062] The Abstract of the Disclosure is provided solely to comply
with U.S. requirements and, as such, is submitted with the
understanding that it will not be used to interpret or limit the
scope or meaning of the claims. In addition, in the foregoing
Detailed Description, various features may be grouped together or
described in a single embodiment for the purpose of streamlining
the disclosure. This disclosure is not to be interpreted as
reflecting an intention that the claimed embodiments require more
features than are expressly recited in each claim. Rather, as the
following claims reflect, inventive subject matter may be directed
to less than all features of any of the disclosed embodiments.
Thus, the following claims are incorporated into the Detailed
Description, with each claim standing on its own as enabling and
describing discretely claimed subject matter.
* * * * *