U.S. patent number RE32,380 [Application Number 06/320,089] was granted by the patent office on 1987-03-24 for diamond tools for machining.
This patent grant is currently assigned to General Electric Company. Invention is credited to William A. Rocco, Robert H. Wentorf, Jr..
United States Patent |
RE32,380 |
Wentorf, Jr. , et
al. |
March 24, 1987 |
**Please see images for:
( Certificate of Correction ) ** |
Diamond tools for machining
Abstract
Diamond tools and superpressure processes for the preparation
thereof are described wherein the diamond content is present either
in the form of a mass comprising diamond crystals bonded to each
other or of a thin skin of diamond crystals bonded to each other.
In each instance the diamond content is supported on and directly
bonded to an extremely stiff sintered carbide substrate in order to
provide mechanical support therefor to more effectively utilize the
high elastic modulus of the diamond. The questions raised in
reexamination request No. 90/000,610, filed Aug. 15, 1984, have
been considered and the results thereof are reflected in this
reissue patent which constitutes the reexamination certificate
required by 35 U.S.C. 307 as provided in 37 CFR 1.570(e).
Inventors: |
Wentorf, Jr.; Robert H.
(Scotia, NY), Rocco; William A. (Scotia, NY) |
Assignee: |
General Electric Company
(Schenectady, NY)
|
Family
ID: |
26907113 |
Appl.
No.: |
06/320,089 |
Filed: |
November 10, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
26660 |
Apr 8, 1970 |
|
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Reissue of: |
212408 |
Dec 27, 1971 |
03745623 |
Jul 17, 1973 |
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Current U.S.
Class: |
407/119;
76/115 |
Current CPC
Class: |
B01J
3/062 (20130101); B23B 27/148 (20130101); B23B
27/20 (20130101); B23P 5/00 (20130101); B23P
15/30 (20130101); B24D 3/06 (20130101); C04B
37/021 (20130101); E21B 10/46 (20130101); E21B
10/5673 (20130101); C04B 35/645 (20130101); Y10T
407/27 (20150115); B01J 2203/0635 (20130101); B01J
2203/0655 (20130101); B01J 2203/0685 (20130101); C04B
2235/6567 (20130101); C04B 2237/363 (20130101); C04B
2237/401 (20130101); C04B 2237/567 (20130101); C04B
2237/704 (20130101); B01J 2203/062 (20130101) |
Current International
Class: |
B01J
3/06 (20060101); B24D 3/04 (20060101); B24D
3/06 (20060101); B23B 27/14 (20060101); B23B
27/20 (20060101); B23P 5/00 (20060101); B23P
15/30 (20060101); C04B 37/02 (20060101); E21B
10/46 (20060101); E21B 10/56 (20060101); B26D
001/00 () |
Field of
Search: |
;407/119 ;76/11A
;148/1.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Patent Bulletin from Japanese Classification of the Japanese Patent
Office Re: Japanese Patent No. 1969-78-18-announced Apr. 12,
1969-Entitled "Method of Manufacturing Diamond Dispensed Superhard
Alloy." .
Diamond-Impregnated Carboloy-G. F. Taylor, General Electric
Review-Feb., 1934 ed..
|
Primary Examiner: Vlachos; Leonidas
Attorney, Agent or Firm: Leydig, Voit & Mayer
Parent Case Text
BACKGROUND OF THE INVENTION
This is a continuation-in-part of U.S. Pat. application Ser. No.
26,600 -- Wentorf, Jr. et al., filed Apr. 8, 1970, now abandoned
and assigned to the assignee of the instant invention.
Claims
What we claim as new and desire to secure by Letters Patent of the
United States is:
1. In a tool for machining with diamond wherein the diamond
crystalline material for machining is held by a support material
and said diamond crystalline material and said support material
comprise a tool insert, which tool insert is in turn to be held by
a tool shank adapted to be held in a machine tool, the improvement
in tool insert construction in which:
a. the diamond crystalline material comprises a concentration of
diamond in excess of 70 percent by volume in which .Iadd.the
.Iaddend.diamond crystals are .Iadd.disposed in random fashion and
substantially all of the diamond crystals are .Iaddend.directly
bonded to adjacent diamond crystals,
b. the support material is a mass of cemented carbide considerably
larger in volume than the volume of the concentration of said
diamond crystalline material and
c. said diamond crystalline material and said cemented carbide
being joined at an interface, said interface consisting solely of
cemented carbide.Iadd., or its elements .Iaddend.and diamond
crystals, the bond therebetween being stronger than the
.[.tensile.]. .Iadd.fracture .Iaddend.strength of the diamond.
2. The improvement in claim 1 wherein the tool insert is
indexable.
3. The improvement in claim 1 wherein the diamond crystalline
material is present as a sheet having a thickness of about 30 mils
or less.
4. The improvement in claim 1 wherein at least one exposed face of
the diamond crystalline material contains crystals from the group
consisting of titanium carbide and zirconium carbide.
5. The improvement in claim 1 wherein the concentration of diamond
in the diamond crystalline material is in excess of 90 percent by
volume.
6. The improvement in claim 1 wherein the diamond crystalline
material is composed of diamond and cemented carbide uniformly
distributed therein.
7. The process for preparing a diamond-tipped tool insert
comprising the steps of:
a. placing within an enclosure of protective metal a mass of
carbide molding powder and contiguous thereto a smaller mass
containing diamond particles in greater than 70 percent by volume
concentration, the carbide being selected from the group consisting
of tungsten carbide, titanium carbide, tantalum carbide and
mixtures thereof and the bonding metal being selected from the
group consisting of cobalt, nickel and iron,
b. simultaneously heating said enclosure and the contents thereof
to temperatures in the range of 1,400.degree.-1,600.degree. C and
applying pressures in excess of about 45 kilobars for at least 3
minutes,
c. ceasing the input of heat to said enclosure,
d. removing the pressure applied to said enclosure, and
e. removing protective metal from the unified mass produced.
8. The process recited in claim 7 wherein the carbide molding
powder is a mixture of tungsten carbide powder and cobalt
powder.
9. The process recited in claim 7 wherein the diamond particles are
disposed in a layer over at least one flat surface of the mass of
carbide molding powder, said layer being about 30mils or less in
thickness.
10. The process for preparing a diamond-tipped tool insert
comprising the steps of:
a. placing within an enclosure of protective metal a body of
cemented carbide and contiguous thereto a mass smaller in volume
containing diamond particles in greater than 70 percent by volume
concentration, the carbide being selected from the group consisting
of tungsten carbide, titanium carbide, tantalum carbide and
mixtures thereof bonded together with metal selected from the group
consisting of cobalt, nickel and iron,
b. simultaneously heating said enclosure and the contents thereof
to temperatures in the range of 1,400.degree.-1,600.degree. C and
applying pressures in excess of about 45 kilobars for at least 3
minutes,
c. ceasing the input of heat to said enclosure,
d. removing the pressure applied to said enclosure, and
e. removing protective metal from the unified mass produced.
11. The process of claim 10 wherein the cemented carbide body is
tungsten carbide cemented with cobalt.
12. The process of claim 10 wherein the diamond particles are
disposed in a layer over at least one flat surface of the cemented
carbide body, said layer being about 30 mils or less in
thickness.
13. A tool insert consisting of a sintered carbide mass supporting
at least one mass, smaller in volume, of harder abrasive material,
said harder abrasive material comprising a concentration of diamond
in excess of 70 percent by volume and a material selected from the
class consisting of metals able to function both as sintering
agents for carbide powders and as catalyst-solvents for the
conversion of graphite to diamond at temperatures and pressures in
the diamond-stable region and carbides thereof, said diamond being
in the form of crystals .Iadd.disposed in random fashion with
substantially all of the diamond crystals being .Iaddend.directly
bonded to adjacent diamond crystals, said at least one mass of
harder abrasive material and said sintered carbide mass being
joined along .Iadd.an .Iaddend.interface area consisting solely of
cemented carbide .Iadd.or its elements .Iaddend.and diamond, the
bond therebetween being stronger than the .[.tensile.].
.Iadd.fracture .Iaddend.strength of diamond.
14. The tool insert of claim 13 wherein the at least one mass of
harder material is present as a sheet having a thickness of about
0.030 inch or less.
15. The tool insert of claim 13 wherein the class recited consists
of cobalt metal, nickel metal and iron carbide.
16. The tool insert of claim 15 wherein the material selected is
cobalt.
17. The tool insert of claim 13 wherein the at least one mass of
harder material also contains cemented carbide uniformly
distributed therein.
18. The tool insert of claim 13 wherein the product is an indexable
tool insert. .Iadd.
19. A diamond tipped tool insert made according to a process
comprising the steps of:
a. placing within an enclosure of protective metal a mass of
carbide molding powder and contiguous thereto a smaller mass
containing diamond particles in greater than 70 percent by volume
concentration, the carbide being selected from the group consisting
of tungsten carbide, titanium carbide, tantalum carbide and
mixtures thereof and the bonding metal being selected from the
group consisting of cobalt, nickel and iron,
b. simultaneously heating said enclosure and the contents thereof
to temperatures in the range of 1,400.degree.-1,600.degree. C and
applying pressures in excess of about 45 kilobars for a period of
time sufficient to bond substantially all of the diamond crystals
directly to adjacent diamond crystals,
c. ceasing the input of heat to said enclosure,
d. removing the pressure applied to said enclosure, and
e. removing protective metal from the unified mass produced.
.Iaddend. .Iadd.20. A diamond-tipped tool insert made according to
a process comprising the steps of:
a. placing within an enclosure of protective metal a body of
cemented carbide and contiguous thereto a mass smaller in volume
containing diamond particles in greater than 70 percent by volume
concentration, the carbide being selected from the group consisting
of tungsten carbide, titanium carbide, tantalum carbide and
mixtures thereof bonded together with metal selected from the group
consisting of cobalt, nickel and iron,
b. simultaneously heating said enclosure and the contents thereof
to temperatures in the range of 1,400.degree.-1,600.degree. C and
applying pressures in excess of about 45 kilobars for a period of
time sufficient to bond substantially all of the diamond crystals
directly to adjacent diamond crystals,
c. ceasing the input of heat to said enclosure,
d. removing the pressure applied to said enclosure, and
e. removing protective metal from the unified mass produced.
.Iaddend.
Description
Both diamond impregnated wheel dressers and diamond cut-off wheels
have been constructed employing as the abrading medium various
mixtures of cemented carbide and diamond grit. Neither of these
types of tools is used to directly produce an ultimate component
and, therefore, these are not considered machining tools nor are
such tools constructed with the capability to withstand the great
stress imposed by direct machining.
As is pointed out in the article "Diamond-Impregnated Carboloy" by
George F. Taylor (General Electric Review, Vol. 37, No. 2 February,
1934, pages 97-99) in column 2 on page 98 "The adhesive bond
between the Carboloy and the diamond is so strong that when the
mass is fractured the grains lying along the fracture are split
through, each part adhering to its Carboloy matrix." In the process
disclosed for producing a wheel dresser the powdered metallic
ingredients for the Carboloy cemented carbide are mixed with
crushed diamond and heated to normal sintering temperatures for
producing cemented carbide.
In U.S. Pat. No. 2,818,850 -- Schwarzkopf et al. arcuate cutting
segments used in cut-off blade construction are prepared using
powder mixtures of tungsten carbide plus cobalt alone and with
diamond dust. Each segment is composed of a larger portion
(initially a mixture of tungsten carbide plus cobalt plus diamond)
and a smaller portion (initially a mixture of tungsten carbide plus
cobalt). The smaller portion is located radially inward of the
larger portion (a) so that the segment can be ground to fit
perfectly onto the metal wheel and (b) in order to provide a
surface free of diamond particles for ease of brazing (or otherwise
uniting) the cutting segment to the steel disc. A hot pressing
sequence is employed (1,400.degree.-1,650.degree. C and 1,000-4,000
psi) to convert the tungsten carbide/cobalt mixture to cemented
carbide.
A similar construction of arcuate abrasive sectors for cut-off
wheel construction is disclosed in U. S. Pat. No. 2,796,706 --
Anderson with the additional teaching that the carbide molding
powder may contain carbide selected from the group consisting of
tungsten carbide, titanium carbide and tungsten carbide and
mixtures thereof. Although nickel or iron can be used as the
bonding metal for sintered carbide, cobalt is preferred. The
initial material mix employed in preparation of the abrasive
sectors differs from the Taylor article and Schwarzkopf et al in
that the mixture includes some previously sintered carbide.
In each of the aforementioned constructions, since the adhesive
bond between the cemented carbide and the diamond is relied upon to
hold the diamonds in the structure, the diamond content must
necessarily be less that that percentage at which there would be
substantial diamond to diamond contact.
In the text "Industrial Applications of the Diamond" by Norman R.
Smith (Hutchinson and Co., First Edition 1965) on page 119 et seq.
it is stated that "Diamond tipped tools are also used for the
direct machining of non-ferrous metals and other materials." On
page 120 a description is set forth of how such tools are made and
there is a statement near the bottom of the page that diamond
tipped machining tools "can be used for practical purposes only on
the non-ferrous metals, plastics, carbon and hard rubber."
As is described in the Smith text on page 120 first the diamond
(usually 1/2 to 1 carat) must be carefully selected; next the
diamond must be properly positioned in the tool to assure certain
grain orientation and thereafter, the tool is set in a powder metal
insert of rectangular form. This powder metal insert serves to
locate the diamond in relation to jigs that are used to shape the
diamond to its cutting form. After proper shaping of the diamond,
the insert is brazed in a slot in the tool shank. This tool shank
is then machined to proper size while simultaneously correctly
positioning the working surface of the diamond in relation to the
tool shank.
The development of tools for machining plastics, reinforced
plastics, ceramics, graphite composites and non-ferrous metals,
which have a lower initial cost than the aforementioned
diamond-tipped tools and which do not have the susceptibility of
these single-point diamonds to fracture and destruction would be of
great benefit to the art.
SUMMARY OF THE INVENTION
The instant invention by the application of high pressure, high
temperature technology provides a solution to the aforementioned
problem enabling the preparation of diamond tipped machine tools in
which in place of utilizing a single diamond, the working diamond
content is present (a) in the form of a mass of diamond crystals
bonded to each other or (b) in the form of a thin skin of diamond
crystals bonded to each other. In order to fully utilize the
machining capabilities of the diamond content in machining
operations in which the diamond working edge may be subjected to
pressures as high as 1,000,000 psi, the diamond content is
supported on and directly bonded to a mass of extremely stiff
cemented carbide substrate significantly larger in size than the
diamond material being supported thereon.
BRIEF DESCRIPTION OF THE DRAWING
This invention will be better understood from the following
description and drawing in which:
FIG. 1 illustrates one exemplary high pressure, high temperature
apparatus useful in the preparation of the product of this
invention;
FIG. 2 illustrates in section one form of charge assembly
configuration for use within the apparatus of FIG. 1 in the
practice of the instant invention;
FIG. 3 is a three dimensional view illustrating a composite diamond
machine tool insert;
FIG. 4 is a section taken through the insert of FIG. 3 either on
line X--X or on line Y--Y;
FIGS. 5 and 6 are each three dimensional views of composite
diamond/sintered carbide machine tool inserts prepared according to
this invention;
FIG. 7 is a sectional view showing a combined liner/charge assembly
for preparing the structures of FIGS. 3, 5 and 6;
FIG. 8 is a three-dimensional view of a cutting tool assembly with
an indexable tool insert of this invention shown in place and
FIGS. 9 and 10 are photomicrographs (about 250X magnification) of
polished surfaces of the layer of diamond fines prepared as part of
a composite tool insert by the process of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
One preferred form of a high pressure, high temperature apparatus
in which the composite tool insert of the instant invention may be
prepared is the subject of U.S. Pat. No. 2,941,248 -- Hall
(incorporated by reference) and is briefly illustrated in FIG. 1.
The process employed in the practice of this invention is described
in U. S. Pat. No. 3,609,818 -- Wentorf, Jr. (incorporated by
reference).
Apparatus 10 includes a pair of cemented tungsten carbide punches
11 and 11' and an intermediate belt or die member 12 of the same
material. Die member 12 includes an aperture 13 in which there is
positioned a reaction vessel 14. Between punch 11 and die 12 and
between punch 11' and die 12 there are included gasket/insulating
assemblies 15, 15', each comprising a pair of thermally insulating
and electrically nonconducting pyrophyllite members 16 and 17 and
an intermediate metallic gasket 18.
Reaction vessel 14 in one preferred form, includes a hollow salt
cylinder 19. Cylinder 19 may be of other material, such as talc,
which (a) is not converted during high pressure-high temperature
operation to a stronger, stiffer state (as by phase transformation
and or compaction) and (b) is substantially free of volume
discontinuities occurring under the application of high
temperatures and pressures, as occurs, for example, with
pyrophyllite and porous alumina. Materials meeting the criteria set
forth in U. S. Pat. No. 3,030,662 (column 1, lines 59 through
column 2, line 2, incorporated by reference) are useful for
preparing cylinder 19.
Positioned concentrically within and adjacent cylinder 19 is a
graphite electrical resistance heater tube 20. Within graphite
heater tube 20 there is in turn concentrically positioned the
cylindrical salt liner 21. The ends of liner 21 are fitted with
salt plugs 22, 22', disposed at the top and bottom, respectively.
As will be described hereinbelow liner 21 may have a cylindrical
hollow core to receive one large charge assembly containing
sub-assemblies or the liner may consist of a series of mold
assemblies arranged in a stack for the preparation of a plurality
of composite tool inserts, e.g. as shown in FIGS. 3, 5, and 6.
Electrically conductive metal end discs 23 and 23' are utilized at
each end of cylinder 19 to provide electrical connection to
graphite heater tube 20. Adjacent each disc 23, 23' is an end cap
assembly 24 and 24' each of which comprises a pyrophyllite plug or
disc 25 surrounded by an electrical conducting ring 26.
Operational techniques for simultaneously applying both high
pressures and high temperatures in this apparatus are well known to
those skilled in the super-pressure art. The foregoing description
relates to merely one high pressure, high temperature apparatus.
Various other apparatuses are capable of providing the required
pressures and temperatures that may be employed within the scope of
this invention.
FIG. 2 illustrates an arrangement for producing a plurality of
disc- or pill-shaped composites (sintered carbide substrate with a
layer of sintered diamond formed thereover). Charge assembly 30,
although not illustrated in proportion, fits within space 31 of the
apparatus of FIG. 1.
Charge assembly 30 consists of cylindrical sleeve 32 of shield
metal selected from the group consisting of zirconium, titanium,
tantalum, tungsten and molybdenum. Within cylindrical shield metal
sleeve 32 are disposed a number of sub-assemblies protected above
and below by shielding discs 33 made of titanium or zirconium. Each
sub-assembly so protected on all sides consists of larger mass 34
and smaller mass 36. Each mass 36 is largely or completely made up
of diamond powder (in the size range from about 0.1 micrometer to
500 micrometers in largest dimension).
Each mass 34 consists of a carbide molding powder, preferably a
mixture of tungsten carbide powder plus cobalt powder.
Unexpectedly, whether or not the carbide molding powder is
initially separate from the diamond powder as shown in FIG. 2 or
whether some carbide molding powder is mixed with the diamond, the
cobalt content makes itself available to function both (a) as the
metal bond for sintering the carbide and (b) as a diamond-making
catalyst required for conversion of graphite to diamond. It is well
known in the art of preparing cemented carbides that the reason
cobalt is able to accomplish the requisite cementing action is
because of its strong tendency for dissolving carbides. It was not
expected that the cobalt mixed in the carbide molding powder would
look to a source of carbon other than the nearby carbide or (in
view of the dissolution of carbide therein) that the cobalt would
retain capability to dissolve elemental carbon and be able to
function as a diamond-making catalyst. On the contrary it has been
found that the cobalt is able to conduct both functions admirably
and based upon the results with cobalt, it is expected that nickel
and iron and mixtures of any of cobalt, nickel and iron should
perform the same functions.
The mass 36 may, therefore, contain minor quantities of graphite
powder or carbide molding powder in addition to the diamond powder.
Also, instead of arranging masses 34 and 36 with a sharp transition
from the carbide-cobalt powder mix to the diamond powder layer, a
transition layer (not shown) may be provided between the
carbide-cobalt mass and the diamond layer. This transition layer
would contain both carbide-cobalt powder and diamond grit in a
gradated mix to minimize stress concentrations.
Even with mass 36 completely composed of diamond crystals the
capability for diamond growth is still required in order to
reconvert to diamond (a) such graphite as is formed during the
conduct of the consolidation process and (b) such diamond as may
dissolve in the catalyst-solvent metal in regions of high free
energy and regions of high temperature.
In order to retain the benefits of mechanically unstable
structuring of the charge assembly, discs 37 are made of the same
material as cylinder 19 to provide necessary "follow through"
action to occupy reduced volume within each sub-assembly during the
process.
In the preparation of tool inserts by the instant process the
charge assembly 30 is placed in the apparatus 10, pressure is
applied thereto and the system is then heated. The temperatures
employed are in the range from about 1,300.degree.-1,600.degree. C
for periods of time in excess of about 3 minutes in order to sinter
the carbide/cobalt mixture while at the same time the system is
subjected to very high pressure e.g. of the order of 55 kilobars to
insure thermodynamically stable conditions for the diamond content
of the system. At 1,300.degree. C the minimum pressure should be
about 50 kilobars and at 1,400.degree. C the minimum pressure
should be about 52.5 kilobars. At the temperatures employed, of
course, the cobalt component of the system is melted making some of
the cobalt available for displacement from mass 34 into mass 36,
where it functions as a catalyst-solvent for diamond growth.
Thus, at the same time (a) the carbide is converted to the sintered
state, (b) the diamond crystals in mass 36 become consolidated into
a mass of sintered diamond and (c) an excellent bond develops at
the interface between diamond-rich mass 36 and cemented carbide
mass 34 to produce a truly integrated mass. When pressure is
applied to the system, some diamond grains are crushed, but because
of the presence of diamond catalyst, these grains consolidate and
heal under diamond-stable pressures and temperatures. At the
interface between masses 36 and 34 any small spaces between diamond
crystals accommodate intrusions of sintered carbide, which is
somewhat plastic at the operating temperatures. Thus, at the
interface the diamond particles are firmly interlocked with and
bonded to the sintered carbide.
The direct bonding relationship created in situ between the very
high strength diamond material and the significantly larger mass of
underlying stiff support material obviates any need for the
interposition of any bonding layer therebetween, as for example,
would result from brazing or soldering. By providing stiff,
non-yielding support material in direct contact with the
diamond-rich machining edge region, the incidence of fractures in
the diamond material is greatly minimized.
Further, the diamond-rich region is primarily a cluster of diamond
crystals bonded together in self-bonded relationship with the
diamond particles disposed in random fashion. In order for an
incipient fracture to produce cleavage of the diamond mass (or
layer) the cleavage plane would have to follow a tortuous course
dictated by the random disposition of the cleavage planes of the
individual particles. Thus, any fracture which is initiated will be
unable to extend very far into the diamond compact.
The preparation of diamond compacts for use as the abrading
elements in cutting and grinding tools wherein at least 50 percent
by volume of the compact consists of diamond crystals is disclosed
in U. S. Pat. No. 3,141,746 -- De Lai (incorporated by reference).
The compact so prepared is then attached to some support. There is
no teaching in De Lai leading the technician to the in situ
creation of a composite tool insert in which a diamond compact when
formed is integrated with a sintered carbide support mass as in the
instant invention nor is there any indication that cobalt present
either in a carbide molding powder (or in cemented carbide) will
make itself available as a catalyst to the diamond-forming
reaction.
The material for mass 34 is preferably a tungsten carbide molding
powder (mixture of carbide powder and cobalt powder) commercially
available in grit sizes of from 1 to 5 microns. The tungsten
carbide may, if desired, be replaced in whole or in part by either
or both of titanium carbide and tantalum carbide. Since some use of
nickel and iron has been made in the bonding of carbides, the
material for providing the metal bond in the cemented carbide may
be selected from the group consisting of cobalt, nickel, iron and
mixtures thereof. Cobalt, however, is preferred as the metal bond
material. All three of the aforementioned metals function as
catalyst-solvents for diamond synthesis and, therefore, any of
these three metals can exercise the dual functions required in the
practice of this invention. The composition of carbide molding
powders useful in the practice of this invention may consist of
mixtures containing about 80-97 percent carbide and about 3-20
percent cobalt by weight.
The preferred diamond content of mass 36 will range from 90 to 99+
percent by volume. However, a somewhat lower content of diamond
grit may be employed, the lowest diamond content being about 70
percent diamond (by volume).
If desired, a thin sheet of catalyst-solvent may be disposed
between any or all of masses 34 and the masses 36 adjacent thereto
to supplement the carbide-bonding/catalyst-solvent metal. The
useful catalyst-solvent materials are disclosed in U.S. Pat. No.
2,947,609 -- Strong and U.S. Pat. No. 2,947,610 -- Hall et al.,
both of which are incorporated by reference. This disposition of
catalyst metal is compatible with a mechanically unstable
structural system. However, it has been found that the additional
catalyst metal is not required and ordinarily not preferred.
Referring now to the composite tool inserts shown in FIGS. 3, 5 and
6, direct preparation of these non-symmetrical shapes requires a
modified construction of salt liner 21 and plugs 22, 22'. However,
non-symmetrical shapes (e.g. the insert shown in FIG. 6) and
symmetrical shapes can also be made by first preparing a
pill-shaped composite (as would result from the arrangement of FIG.
2) and then cutting and shaping the unit. For the preparation of
non-symmetrical shapes the structure fitting within heater tube 20
may be formed as a series of cylindrical blocks in stacked
cooperating arrangement to provide molds to be filled with the
powder constituents of carbide molding powder (CMP) and diamond
fines (D). By way of example, in FIG. 7 salt block 21a has formed
therein a recess 72 replicating the shape of the desired tool
insert allowing for the thickness of the protective metal sheath
73. Recess 72 is lined with metal 73 as shown and powdered masses
CMP and D are properly located therein. Cover salt block 21b has
recesses therein to accommodate cover sheet 74 completing the
protective metal enclosure for the powders and, preferably, a
back-up block of sintered carbide SC to minimize puncturing of the
protective metal layer 74. A number of such cooperating pairs of
salt blocks such as 21a, 21b may be employed with the contents
described.
In the tool insert construction 40 of FIG. 3 both faces 41 and 42
of the cemented carbide 43 and diamond compact 44 are formed with a
rake (FIG. 4) to facilitate presentation of the diamond cutting
edges of diamond compact 44 to the work piece.
In forming the thin layers 51, 61 of consolidated diamond in the
tool insert constructions 52, 62 shown in FIGS. 5 and 6, the layer
of diamond fines bonded to cemented carbide bodies 53, 63,
respectively, is limited to a maximum thickness of about 30 mils
(0.75 mm) and a minimum thickness of about 1/2 mil (0.012 mm)
although the capability exists for preparing such layers in
thicknesses as great as about 80 mils. The purpose of deliberately
making these layers 51, 61 very thin is in order (a) to present the
diamond layers 51, 61 as chip breaker faces and (b) to make it
easier to sharpen the tool inserts 52, 62. Ideally, the
relationship between the properties of the diamond layer to the
cemented carbide will be such that the edge of the diamond will
wear away slightly less rapidly than the cemented carbide. When
this condition prevails a small amount of the diamond layer will
continue to project beyond the cemented carbide support body to
provide a cutting edge and the amount of diamond utilized will be
commensurate with the life of the tool.
The layer of material placed in the mold over the carbide molding
powder may be diamond grit, or a thin layer of graphite to be
converted to diamond during high pressure, high temperature
exposure under diamond-stable conditions using the bonding metal of
the carbide molding powder as the catalyst. Mixtures of graphite
and diamond may also be used. However, a basic requirement is that
the consolidated diamond-rich region of any of the completed
composite tool inserts must have a concentration of diamond therein
greater than 70 percent by volume and, preferably, in excess of 90
percent by volume.
After completion of the high temperature, high pressure process,
which simultaneously achieves (a) sintering of the carbide powder,
(b) creation of a strong consolidated mass of diamond crystals (or
thin sheet of consolidated diamond crystals) and (c) the creation
of an extremely effectively interface bonding the diamond to the
sintered carbide, first the temperature and then the pressure are
reduced. Upon recovery of the tool insert masses, the protective
sheath metal remains strongly affixed to the outer surfaces
thereof. Exposure of the desired surfaces of the composite tool
insert is accomplished by simply grinding away the protective
sheath.
Since some of the protective sheath is converted to the carbide,
the alternative is available whereby by not grinding away all of
this covering material a thin outer layer of titanium carbide or
zirconium carbide can be left over the chip breaker face of the
diamond-rich regions 43, 51, 61. Greater amounts of carbide may be
introduced in the surface of the chip breaker face by adding a
small amount of titanium carbide (or zirconium carbide) powder in
the layer of diamond fines D in filling cavity 72 or by using
synthetic diamond or graphite which contain titanium. By having the
exposed surface of the compacted diamond-rich region contain small
crystals of titanium carbide incorporated therein, for example, the
life of the chip breaker face should be increased and should
minimize the deleterious effect on the tool insert of the hot metal
being removed from the workpiece.
FIG. 8 shows an assembled cutting tool comprising a shank portion
81, a head portion 82, and a ridge 83 having a vertical shoulder
83a defining the rear boundary of the head portion. Indexable
cutting insert 84 in the shape of a triangular prism with
diamond-rich layer 84a bonded to sintered carbide support block 84b
is firmly retained by cutter bit clamp 86. Insert 84 is releasably
held so that its cutting surface is exposed slightly beyond cutter
bit seat 87 made of any hard metallic substance (e.g. cemented
carbide). Cutting insert 84 may be tightened into position or
removed for repositioning (indexing) or replacement by turning a
set screw (not shown) in aperture 88. Various configurations of
cutting insert may be employed, e.g. cylindrical, rectangular
solid, etc.
FIGS. 9 and 10 together show the effect of increased consolidation
on the extent of diamond-to-diamond bonding in the polycrystalline
diamond-rich layer of the composite tool insert. Increasing
consolidation is favored by exposure to the high pressures and high
temperatures according to the method of this invention for longer
times during preparation of the composite tool insert. Thus, FIG. 9
shows the polished surface of a diamond-rich layer of a composite
tool insert wherein the area (or volume fraction) of bonded diamond
grains 91 is about 90 percent of the total. The exposure time to
high pressure and temperature was 15 minutes. Interfaces 92 are
representative of diamond-to-diamond bonding between adjacent
crystals. These same diamond crystals 91 seen in the polished
surface of FIG. 9 are bonded in the third dimension to adjacent
diamond crystals (not seen). Although regions 93 between crystals
91 may be cobalt metal, nickel metal or iron carbide, depending
upon what metal bond material is employed for the carbide powder,
in this particular composite regions 93 are mostly cobalt metal.
FIG. 10 shows the polished surface of a diamond-rich layer wherein
the initial concentrations of materials, the pressure and the
temperature were substantially the same as for the layer of FIG. 9,
but was subjected to these conditions for 45 minutes longer than
the composite of FIG. 9. The numerals employed in FIG. 10 represent
the same characteristics as in FIG. 9. The effect was to almost
completely consolidate the diamond grains 91 so that most of the
diamond grains 91 are in intimate contact with each other over most
of their peripheries, the area (or volume fraction) of diamond
being over 95 percent of the total.
A fragment of a composite tool insert consolidated as shown in FIG.
10 was placed in a warm mixture of HF, HCL and HNO.sub.3. The
sintered carbide portion dissolved in less than 1 hour, but the
diamond portion (initially individual grains) of the fragment
remained intact and strong after 4 hours of this exposure. The
diamond fragment was then placed in a fresh batch of this acid
mixture for 60 hours at 27.degree. C and 6 hours at 100.degree. C
with no change occurring. No metal was visible in examining the
fragment under the microscope (36X), but the fragment still
responded to a strong magnet. Apparently, some small quantity of
cobalt was trapped within the structure where it could not be
reached by the acid. Similar acid treatment of less dense
diamond-rich layers (e.g. 70 to 90 percent diamond by volume) was
able to remove all metal so that the compacted diamond mass, which
remained intact because of the direct diamond-to-diamond bonding,
was no longer affected by a magnet. The high tensile strength
(estimated to be about 20,000 psi) of the mass of compacted diamond
grains indicates the extent of diamond-to-diamond bonding. Broken
masses were examined and no metal could be seen on the broken
surfaces at 36X magnification.
If desired, another variation that may be made in the process of
preparation of the tool inserts of this invention is the use of
cemented carbide in place of the carbide molding powder. In such a
process metal-lined cavity 22 receives a pre-formed cemented
carbide body contiguous with a diamond-rich region to form the
desired chip breaker face. Even under these conditions the bonding
metal in the solid cemented carbide body will be effective as
catalyst-solvent for the diamond compaction and/or conversion.
Regardless of whether the composite tool insert of this invention
is prepared using carbide molding powder or previously cemented
carbide, the requisite diamond-to-diamond bonding and the
carbide/diamond interface bonding both occur, when greater than 70
percent by volume of diamond is employed in the abrasive mass
adjacent the cemented carbide. In both instances the interface bond
between the diamond material and the cemented carbide components is
stronger than the .[.tensile.]. .Iadd.fracture .Iaddend.strength of
diamond, because of the high pressure, high temperature process
employed.
Thus, by the practice of the instant invention the less expensive
diamond material obtained from nature or synthetically prepared
(e.g. diamond grit ranging from 60 mesh to 325 mesh [U. S. Sieve];
poorly crystallized and other reject material) may be embodied into
a product useful in the direct machining of metals, because of the
improved strength and resistance to shock and wear thereof. The
indexable composite tool inserts of this invention are of value in
turning, boring and milling operations on non-ferrous metals such
as copper, brass, bronze, silver, gold, platinum and alloys of
aluminum, magnesium, titanium and zinc. These tool inserts are of
particular interest in the machining of non-metallic materials,
such as plastics, composites, and ceramics and have been
successfully tested on flame-sprayed alumina, graphite,
glass-impregnated plastic materials, ceramics and ablative
materials for re-entry nose cones.
EXAMPLE 1
A uniform mixture of 58 volume % diamond (60 to 80 mesh) and 42
volume % of carbide molding powder (87 weight % tungsten carbide/13
weight % cobalt) were placed in a cylindrical mold lined with
zirconium metal (as mass 34 in FIG. 1). A layer (about 0.5 mm
thick) of the same diamond fines was spread over the top (as layer
36). This system fully enclosed in zirconium was subjected to a
pressure of about 57 kilobars and 1,500.degree. C for 10 minutes.
After the temperature and pressure were reduced, the resultant
composite body was recovered and used successfully to shape an
aluminum oxide grinding wheel as one would use a cutting tool.
EXAMPLE 2
A lined mold similar to that used in EXAMPLE 1 was partly filled
with 75 mg of 325 mesh diamond powder mixed with 25 mg of graphite
powder. On top of this first layer was placed a metal disc (10 wt %
Al, 90 wt % Fe) about 0.1 mm thick. A second layer was placed over
this disc consisting of 87 wt % tungsten carbide powder/13 wt %
cobalt powder. This system fully enclosed in protective zirconium
metal was subjected to a pressure of about 56 kilobars and
1,500.degree. C for 30 minutes. After the temperature and pressure
were reduced a monolithic cylindrical body was recovered. The
diamond layer was sintered together and was strongly bonded to the
sintered carbide adjacent thereto. This body was later brazed into
a suitable strong holder and the diamond layer was shaped to form a
cutting tool. This tool was successfully used to machine Rene 41
alloy.
EXAMPLE 3
The process of EXAMPLE 2 was repeated without the Al-Fe disc. A
similar monolithic body was recovered with the sintered layer of
diamond strongly bonded to the sintered carbide. This cylinder was
also mounted in a holder by brazing and shaped for use as a cutting
tool.
EXAMPLE 4
A system was prepared wherein a solid disc of cemented carbide (94
wt % tungsten carbide/6 wt % cobalt) is used as a pressure back-up
member. This piece of cemented carbide was placed in a
zirconium-lined mold and covered with a thin sheet of zirconium
metal. A layer of diamond powder (30 mg of 100 mesh diamond) about
0.4 mm thick was spread over the zirconium sheet and a second disc
of the cemented carbide 0.13 inch thick was placed over and in
contact with the diamond layer. This entire assembly together with
the protective zirconium metal, was exposed to about 57 kilobars
pressure and a temperature of about 1,500.degree. C for 60 minutes.
The diamond layer of the composite cylinder recovered had been
consolidated, with the diamond crystals firmly bonded together and
also bonded to the cemented carbide body. After polishing the
diamond layer to form a cutting tool, microscopic examination
revealed extensive bonding between adjacent diamond grains and
healing or re-joining of diamond grains which had been broken
during initial cold compression of the specimen. In a dry cutting
test on Rene 41 alloy moving at 50 feet per minute this tool was
used to remove a chip 0.090 inch wide and 0.010 inch thick and the
chip separated from the metal at red hot temperature. This tool
performed better than a standard sintered carbide tool by showing
less wear and producing better chip and surface finishes. There was
no cracking off or spalling of the diamond layer as it wore
away.
A round bar of steel 4.5 inches in diameter and 40 inches long was
coated with aluminum oxide by a high temperature spray process to
produce a hard, dense coating about 0.030 - 0.035 inch thick having
a hardness of about 70 Rockwell "C." This coated bar was mounted in
a lathe and various tools described below were used to machine the
oxide surface thereof. Cutting speed was 100 feet/minute and the
feed and depth of cut were both about 0.005 inch. After the
indicated cutting time, the tools were removed and examined for
wear, etc. The results are set forth in the following table.
TABLE 1 ______________________________________ Totals Cut- ting
Time Total Wear Type Item Description (min.) (inches) of Wear
______________________________________ 1 Sintered tungsten 3 0.065
abrasive carbide 97WC3Co 2 0-30 ceramic tool 3 0.125 abrasive
(Al.sub.2 O.sub.2 base) 3 Natural diamond 1 30.006 chipping single
crystal 4 Composite tool insert 30.000 none as shown in FIG. 6
detected (sintered dia./ 94WC6Co) corner 1 5 Brown natural 60.008
chipping diamond-single crystal 6 Yellow natural 60.004 chipping
diamond-single crystal 7 Cont'd. use of item 90.001 abrasive 4 -
corner 1 8 Corner 2 of item 4 300.0005 abrasive 9 Corner 2 of item
4 600.0015 abrasive 10 Corner 2 of item 4 900.0025 abrasive 11
Corner 2 0f item 4 1200.0035 abrasive
______________________________________
After a few minutes of use, each of the single diamond tools failed
to perform satisfactorily, because of the edge chipping. Such tools
are known to be sensitive to chipping. The sintered diamond/carbide
composite tool insert of this invention does not appear to be
sensitive to chipping in the machining of refractory non-metals and
hence has a longer useful life. Tool No. 1 was made of the hardest
grade of cemented carbide commercially available but, like the
aluminum oxide tool, is not hard enough to prevent rapid wear in
the cutting of refractory non-metals.
Aluminum oxide coatings of the kind used in this test are employed
as sealing surfaces on rotating parts in aircraft gas turbines, for
example. The mechanical properties of the coating tested are
comparable to those of many ceramics (e.g. borides, nitrides,
carbides, etc.) -- bodies used for a wide variety of purposes,
often as parts having precise shapes and dimensions. A long-lasting
diamond tool that can machine such materials has considerable
utility.
EXAMPLE 5
Item No. 4 (Table 1) was made as follows: a base block of 94WC6Co
of sintered carbide received a layer (0.130 gram) of 100/120 mesh
manufactured diamond thereover. The combination was enclosed in a
zirconium sheath. A second block of 94WC6Co was located over the
diamond layer (outside the Zr sheath) and the system was subjected
to 55 kb and 1,500.degree. C for 1 hour.
EXAMPLE 6
A tool insert was prepared by enclosing a mixture of 100/200 mesh
manufactured diamond and 94WC6Co powder (70 volume % diamond and 30
volume % carbide powder) in a cylindrical Zr cup and subjecting the
combination to 55 kb and 1,500.degree. C for 30 minutes. The
cylindrical tool insert formed was 0.240 inch in diameter and about
0.1 inch thick.
This tool insert was tested by machining the Al.sub.2 O.sub.3
coating on the shaft used in Table 1. The cutting speed used was 50
feet/minute at a feed of 0.005 inch for a period of 3 minutes. The
wear was measured to be 0.0055 inch and slight chipping was
observed. This tool insert did not perform as well as the insert of
Example 5, but was markedly superior to both Item No. 1 and Item
No. 2 of Table 1.
Continued research may well result in the identification of other
metals and/or alloys able to function as bonding agents in the
sintering of carbide molding powders. Any such metals or alloys
that are also included among the catalyst-solvents disclosed in the
aforementioned U.S. Pat. No. 2,947,609 and U.S. Pat. No. 2,947,610
should, when used in effective amounts, be able to exercise the
dual functions required for the practice of this invention; namely,
sintering of the carbide powder and converting of the graphite to
diamond at temperatures and pressures in the diamond stable
region.
* * * * *