Abstrict A method is provided for manufacturing a segmented diamond blade.
The method includes the steps of placing a core into a mold and
pouring a metal mixture into a mold cavity surrounding the core.
The metal mixture is cold pressed to the core to form a blade having
a continuous outer rim. Thereafter, the core and outer rim are suspended
in a free-sintering furnace which is heated to an initial diffusion
bonding temperature. The core and outer rim are heated for an initial
bonding time period. Thereafter, the furnace is heated to a final
diffusion bonding temperature and the core and outer rim are maintained
at this temperature for a final diffusion bonding time period. After
the blade cools, it is placed in a cutting tool and segmented. During
segmentation, a plurality of radially aligned notches are cut through
the outer rim and a corresponding plurality of gullets are cut in
the core. During cutting, an inert gas, such as helium, argon or
the like, is blown under high pressure directly onto the cutting
point. The present method facilitates diffusion bonding and segmentation
by using an optimal combination of metal particles to form the outer
rim.
Claims What is claimed is:
1. A method for producing a cutting blade having a core and a segmented
outer rim comprising the steps of:
introducing a bond powder mixture onto said core to form a continuous
uninterrupted outer rim, said bond powder mixture including metal
particles and hardened cutting particles;
after said introducing step, bonding said core to said continuous
uninterrupted outer rim by heating said continuous uninterrupted
outer rim and said core to a preselected temperature; and
after said bonding step, forming notches through said continuous
uninterrupted outer rim to remove portions of said outer rim and
portions of said core to form a segmented outer rim.
2. A method for producing a cutting blade according to claim 1
further comprising the step of:
forming a bond powder comprising first and second metals which
bond to form a bronze or brass compound, a third metal which functions
as a wetting agent, and a fourth metal which bonds to said bronze
compound and said wetting agent.
3. A method for producing a cutting blade according to claim 1
further comprising the step of:
forming a bond powder comprising at least three types of metal
that will bond with one another and with said core.
4. A method for producing a cutting blade according to claim 1
further comprising the step of:
forming a bond powder comprising at least two types of metal that
will bond with one another and with said core, and at least one
type of hardened particles for cutting.
5. A method for producing a cutting blade according to claim 1
further comprising the step of:
forming a bond powder comprising at least one type of metal that
will bond with one another and with said core, and diamond particles
for cutting.
6. A method for producing a cutting blade according to claim 1
wherein said bonding step further includes the steps of:
heating said core and outer rim to an initial bonding temperature
for an initial bonding time period, and
thereafter, heating said core and outer rim to a final bonding
temperature for a final bonding time period.
7. A method for producing a cutting blade according to claim 1
wherein said bond powder comprises at least first and second metals
and said bonding step further includes the step of:
bonding said first and second metals to one another by heating
said core and outer rim to an initial bonding temperature which
is above a melting point of said first metal and below a melting
point of said second metal during an initial bonding time period.
8. A method for producing a cutting blade according to claim 1
wherein said bond powder comprises at least first and second metals
bonded to one another to form a bonded alloy and a third metal,
said bonding step further includes the step of:
bonding said bonded alloy and said third metal with one another
by heating said core and outer rim to a final bonding temperature,
which is above a melting point of said bonded alloy and below a
melting point of said third metal, during a final bonding time period.
9. A method for producing a cutting blade according to claim 7
wherein said bond powder comprises at least a third metal and wherein
said bonding step further comprises the step of:
bonding said third metal and a diffusion bonded alloy formed by
said first and second metals by heating said core and outer rim
to a final bonding temperature, which is above said initial bonding
temperature, during an initial bonding time period.
10. A method for producing a cutting blade according to claim 9
wherein said final bonding temperature is below a melting point
of said third metal.
11. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
centering said core within a mold and pouring said bond powder
mixture into a void surrounding said core; and
cold pressing said bond powder mixture to obtain approximately
65% compression thereof with respect to a maximum compression.
12. A method for producing a cutting blade according to claim 1
wherein said bonding step is free-sintering while densification
and bond shrinkage occur.
13. A method for producing a cutting blade according to claim 1
wherein said bond powder includes at least two metals and wherein
said core and outer rim are heated during said bonding step to a
temperature between melting points of said two metals.
14. A method for producing a cutting blade according to claim 1
wherein said bonding step includes the steps of:
initially heating said core and outer rim to a temperature between
1400.degree. F. and 1600.degree. F. to effect initial bonding; and
finally heating said core and outer rim to a temperature between
1600.degree. F. and 2000.degree. F. to effect final bonding.
15. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
hot pressing said bond powder mixture to obtain partial compression
thereof.
16. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
performing rapid solidification of said bond powder mixture to
obtain partial compression thereof and adhesion to said core.
17. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
sintering of said bond powder mixture to obtain partial compression
thereof and adhesion to said core.
18. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
microwave sintering of said bond powder mixture to obtain partial
compression thereof and adhesion to said core.
19. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
hot isostatically pressing said bond powder mixture to obtain adhesion
to said core.
20. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
coining said bond powder mixture to obtain adhesion to said core.
21. A method for producing a cutting blade according to claim 1
wherein said introducing step further comprises the step of:
forging said bond powder mixture to obtain adhesion to said core.
22. A cutting blade having a circular core with an outer periphery
having gullets formed thereabout and with a continuous outer rim
thereon, said continuous outer rim having notches therein proximate
said gullets, said blade being formed by a method comprising the
steps of:
introducing a bond powder mixture onto said core to form a continuous
uninterrupted outer rim, said bond powder mixture including metal
particles and hardened cutting particles;
after said introducing step, bonding said core to said continuous
uninterrupted outer rim by heating said continuous uninterrupted
outer rim and said core to a preselected temperature; and
after said bonding step, forming notches through said continuous
uninterrupted outer rim to remove portions of said outer rim and
portions of said core to form a segmented outer rim.
23. A cutting blade formed by the method of claim 22 further comprising
the step of:
forming a bond powder comprising first and second metals which
bond to form a bronze compound, a third metal which functions as
a wetting agent, and a fourth metal which bonds to said bronze compound
and said wetting agent.
24. A cutting blade formed by the method of claim 22 further comprising
the step of:
forming a bond powder comprising at least three types of metal
that will bond with one another and with said core.
25. A cutting blade formed by the method of claim 22 comprising
the step of:
forming a bond powder comprising at least two types of metal that
will bond with one another and with said core, and at least one
type of hardened particles for cutting.
26. A cutting blade formed by the method of claim 22 further comprising
the step of:
forming a bond powder comprising at least one type of metal that
will bond with one another and with said core, and diamond particles
for cutting.
27. A cutting blade formed by the method of claim 22 wherein said
bonding step further includes the steps of:
heating said core and outer rim to an initial bonding temperature
for an initial bonding time period, and
thereafter, heating said core and outer rim to a final bonding
temperature for a final bonding time period.
28. A cutting blade formed by the method of claim 22 wherein said
bond powder comprises at least first and second metals and said
bonding step further includes the step of:
bonding said first and second metals to one another by heating
said core and outer rim to an initial bonding temperature which
is above a melting point of said first metal and below a melting
point of said second metal during an initial bonding time period.
29. A cutting blade formed by the method of claim 22 wherein said
bond powder comprises at least first and second metals bonded to
one another to form an alloy and a third metal, said bonding step
further includes the step of:
bonding said bonded compound and said third metal with one another
by heating said core and outer rim to a final bonding temperature,
which is above a melting point of said alloy and below a melting
point of said third metal, during a final bonding time period.
30. A cutting blade formed by the method of claim 22 wherein said
bond powder comprises at least a third metal and wherein said bonding
step further comprises the step of:
bonding said third metal and a bonded compound formed by said first
and second metals by heating said core and outer rim to a final
bonding temperature, which is above said initial bonding temperature,
during an initial bonding time period.
31. A cutting blade formed by the method of claim 30 wherein said
final bonding temperature is below a melting point of said third
metal.
32. A cutting blade formed by the method of claim 31 wherein said
introducing step further comprises the step of:
centering said core within a mold and pouring said bond powder
mixture into a void surrounding said core; and
cold pressing said bond powder mixture to obtain approximately
65% compression thereof with respect to a maximum compression.
33. A cutting blade formed by the method of claim 22 wherein said
bonding step is free-sintering while densification and bond shrinkage
occur.
34. A cutting blade formed by the method of claim 22 wherein said
bond powder includes at least two metals and wherein said core and
outer rim are heated during said diffusion bonding step to a temperature
between melting points of said two metals.
35. A cutting blade formed by the method of claim 22 wherein said
bonding step includes the steps of:
initially heating said core and outer rim to a temperature between
1400.degree. F. and 1600.degree. F. to effect initial bonding; and
finally heating said core and outer rim to a temperature between
1600.degree. F. and 2000.degree. F. to effect final bonding.
36. A method for producing a cutting blade according to claim 22
wherein said introducing step further comprises the step of:
hot isostatically pressing said bond powder mixture to obtain adhesion
to said core.
37. A method for producing a cutting blade according to claim 22
wherein said introducing step further comprises the step of:
coining said bond powder mixture to obtain adhesion to said core.
38. A method for producing a cutting blade according to claim 22
wherein said introducing step further comprises the step of:
forging said bond powder mixture to obtain adhesion to said core.
39. A method for producing a cutting blade according to claim 1
wherein said harden cutting particles include diamond particles.
40. A cutting blade according to claim 22 wherein said hardened
cutting particles include diamond particles.
41. A cutting blade formed by the method of claim 22 wherein said
hardened cutting particles include diamond particles.
42. A method for producing a cutting blade having a core and a
segmented outer rim comprising the steps of:
introducing a bond powder mixture onto said core to form a continuous
outer rim;
bonding said core to said continuous outer rim by heating said
continuous outer rim and said core to a preselected temperature,
wherein said bonding step includes the steps of,
heating said core and outer rim to an initial bonding temperature
for an initial bonding time period; and
thereafter, heating said core and outer rim to a final bonding
temperature for a final bonding time period; and
forming notches through said continuous outer rim to remove portions
of said outer rim and portions of said core to form a segmented
outer rim.
43. A method for producing a cutting blade having a core and a
segmented outer rim comprising the steps of:
introducing a bond powder mixture onto said core to form a continuous
outer rim;
bonding said core to said continuous outer rim by heating said
continuous outer rim and said core to a preselected temperature;
and
forming notches through said continuous outer rim to remove portions
of said outer rim and portions of said core to form a segmented
outer rim, wherein said bond powder includes at least two metals
and wherein said core and outer rim are heated during said bonding
step to a temperature between melting points of said two metals.
44. A cutting blade comprising:
a circular core having an outer periphery with a continuous outer
rim press molded thereon, said outer rim being formed from a bond
powder mixture including at least two types of metal particles and
at least one type of hardened cutting particles, said at least two
types of metal particles being bonded to one another, said continuous
outer rim having an innermost region proximate said outer periphery
of said core in which said at least two types of metal particles
are bonded to said outer periphery of said core, said continuous
outer rim having a plurality of radially aligned notches cut therethrough
to segment said continuous outer rim, wherein said two types of
metal particles are bonded to one another by heating said outer
rim to an initial bonding temperature which is between melting points
of said two types of metal particles.
45. A cutting blade comprising:
a circular core having an outer periphery with a continuous outer
rim press molded thereon, said outer rim being formed from a bond
powder mixture including at least one type of metal particles and
at least one type of hardened cutting particles, said at least one
type of metal particles being bonded to one another, said continuous
outer rim having an innermost region proximate said outer periphery
of said core in which said at least one type of metal particles
are bonded to said outer periphery of said core, said continuous
outer rim having a plurality of radially aligned notches cut therethrough
to segment said continuous outer rim, wherein bonded metal particles
in the outer rim form a substantially non-porous homogeneous alloy
compound which, when cut, substantially evenly melts along a cut
kerf to form the said notches.
46. A cutting blade having a circular core with an outer periphery
having gullets formed thereabout and with a continuous outer rim
thereon, said continuous outer rim having notches therein proximate
said gullets, said blade being formed by a method comprising the
steps of:
introducing a bond powder mixture onto said core to form a continuous
outer rim;
bonding said core to said continuous outer rim by heating said
continuous outer rim and said core to a preselected temperature;
and
cutting notches through said continuous outer rim to remove portions
of said outer rim and portions of said core to form a segmented
outer rim, wherein said bond powder includes at least two metals
and wherein said core and outer rim are heated during said bonding
step to a temperature between melting points of said two metals.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method for manufacturing
a cutting blade having a hardened outer rim that is initially formed
as a continuous outer rim diffusion bonded to a core which is then
cut to produce a segmented blade.
2. Description of the Related Art
Cutting blades have been proposed that have hardened particles
embedded in the outer rim to cut extremely hard surfaces, such as
concrete, masonry and the like. These saw blades are rim typically
formed with a steel core and a continuous or segmented rim embedded
with the hardened particles, such as diamonds, tungsten carbide,
polycrystalline diamond and the like (hereafter collectively referred
to as "diamond particles").
In the past, methods have been proposed for manufacturing diamond
blades which were dependent upon the configuration and function
of the blade. These blades are separable into two primary types,
blades formed with a continuous outer rim and blades formed with
a segmented outer rim. Continuous rim blades are used in applications
where chipping is critical, but blade speed is not, such as when
cutting tile. Segmented rims are used in applications where chipping
is not critical, but blade speed is critical, such as when cutting
concrete. As the blade speed increases, typically, the operating
temperature increases. If heated sufficiently, the outer segments
will expand. The segments expand into the notches therebetween.
To construct a continuous rim blade, one method (U.S. Pat. No.
3369879) has been proposed in which an annular grinding member
is affixed to a copper ring which is affixed to a steel core of
the blade. The steel core is centered within a mold, the core's
perimeter is coated with solder, the copper ring is pressed onto
the core and bonded thereto with the solder. Next, a mixture containing
diamond particles is poured into a cavity in the mold surrounding
the copper ring. The mold is closed and heat and pressure are applied
to the mixture to "hot press" the rim. This combination
of heat and pressure forms a rigid grinding rim and secures the
outer rim to the copper ring.
Alternative methods have been proposed for bonding the abrasive
rim to the central core (U.S. Pat. Nos. 2189259; 2270209 and
Reissue 21165). In the method of the '259 patent, the core and
the outer rim are separately poured into respective central and
outer cavities of a mold. These cavities are separately closed and
then aligned with one another and heated and compressed to hot press
to the outer rim onto the core. In the method of the '209 patent,
a steel central core is centered in the mold and the outer rim mixture
is poured into a cavity surrounding this steel core. The mixture
is hot pressed directly onto the core. In the method of the '165
reissue patent, the abrasive rim is welded or soldered to the central
core.
The '879 patent, '209 patent, and '165 reissue patent are incorporated
by reference.
As to the second type of blades, previous methods (U.S. Pat. No.
3590535) have been proposed to construct segmented outer rims.
In the method of the '535 patent, a plurality of diamond bearing
outer segments are formed from a mixture of diamond dust, copper
powder and tin powder. Each outer segment is separately press molded
onto a corresponding steel underlying segment. The steel underlying
segments are machined to fit the contour of the core and subsequently
welded thereto.
In an alternative method (U.S. Pat. No. 3048160) a blade for
cutting hard materials is formed by initially molding a plurality
of abrasive cutting segments. As originally formed, each segment
includes a serrated bottom surface which is welded to the perimeter
of the core by heating, and applying radial pressure against an
outer surface of, each segment. An alternative method (U.S. Pat.
No. 2818850) has been proposed in which the cutting segments are
hot pressed such that the included diamond dust is concentrated
near the outer surface of the cutting segment. Once hot pressed,
an inner surface of the cutting segments are ground to provide a
curved surface thereon which substantially corresponds to the outer
arc of the blade core. Next, each segment is brazed to the disc
core.
However, each of the above methods has only met with limited success.
As to the latter group of methods, which separately fasten multiple
segments to the core, each of these methods require separate and
repeated handling of each segment. More specifically, each segment
must be separately hot pressed. Next, each segment must be debarred
along its outer surface and ground along its inner surface to form
a concave surface thereon, the radius of which substantially corresponds
to that of the steel core. Then, each segment must be separately
bonded to the core.
Further, this latter group of methods experience extreme difficulty
in bonding each segment to the steel core. The diamonds within each
segment interfere with this bonding process. To overcome this problem,
the '535 patent uses an underlying diamond face or backing layer
molded to the diamond section and welded to the core. The '160 patent
forms a serrated surface on each segment to effect bonding. The
'850 patent utilizes a special molding technique to concentrate
the diamond segments proximate the rim's outer surface.
The outer rims also create problems during welding steps since
the welders are highly sensitive to the copper and diamond particles
within the outer rim. When a welding beam contacts a copper particle,
it is partially reflected and consequently less effective at heating
the region of the abrasive segment surrounding the copper particle.
Also, if the temperature of the welding beam is excessive and the
beam contacts a diamond particle, the beam causes carbonization
of the diamond particle. Ultimately, the carbonized diamond particle
detaches from the segment. Diamond particles within the back side
of each segment inhibit the radiusing process in which the concave
surface on each segment is machined to match the core. To minimize
the effects of the diamond particles upon the grinding and welding
processes, a bonding or backing material is formed along the back
side of the diamond segment. This backing material is easily ground
to the desired radius and easily welded to the core.
Further, diamond blades formed by methods within the former group
are void of notches within the core. These notches reduce heating
of the blade and help clear foreign particles from the cut during
operation. Consequently, blades formed by methods within the former
group have more limited applications. If overheated, the continuous
rims expand and often fail. Heretofore, it has been impossible to
construct a segmented diamond blade without separately forming and
securing each diamond segment to the core. The need remains in the
industry for an improved method for manufacturing segmented diamond
blades. The present invention is intended to meet this need, and
to overcome drawbacks previously experienced.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for
manufacturing cutting blades having a hardened segmented outer rim
which removes the need to handle each segment separately and which
reduces the number of steps within the manufacturing process.
It is another object of the present invention to provide a method
for manufacturing diamond blades in which a continuous outer rim
is diffusion bonded to a blade core and thereafter cut into segments.
It is another object of the present invention to facilitate the
diffusion bonding process through which the outer rim is bonded
to the core by utilizing at least one type of metal particles which
undergoes densification.
It is another object of the present invention to eliminate the
need to machine the inner surface of the diamond rim to conform
to the outer curve of the core.
It is another object of the present invention to provide a method
for manufacturing diamond blades which are easily cut with a cutting
tool to cleanly cut notches through the outer rim and into gullets
in the core.
It is another object of the present invention to provide a method
for manufacturing diamond blades which uses a laser cutting beam
having a narrow width and which utilizes an inert gas blown into
the cut to avoid air oxidation therefrom.
It is another object of the present invention to facilitate the
cutting of notches through the outer diamond rim by forming the
outer rim from a mixture of metal bonding agents and diamond particles
which is easily cut with a laser beam.
Other and further objects of the invention, together with the features
of novelty or pertinent thereto, will appear in the detailed description
set forth below.
In summary, a method is provided for manufacturing a blade having
a diamond impregnated outer rim. The method includes the steps of
placing a core into a mold and pouring a metal diamond mixture into
a mold cavity surrounding the core. The metal diamond mixture is
cold pressed to the core to form a blade having a continuous outer
rim. Thereafter, the core and outer rim are stacked in a free-sintering
furnace which is heated to an initial diffusion bonding temperature.
Thereafter, the furnace is heated to a final diffusion bonding temperature
and the core and outer rim are maintained at this temperature for
a final diffusion bonding time period. After the blade cools, it
is placed in a cutting tool and segmented. During segmentation,
a plurality of radially aligned notches are cut through the outer
rim and a corresponding plurality of gullets are cut in the core.
During cutting, oxygen gas is used. The present method facilitates
diffusion bonding and segmentation processes thereafter.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following description of the drawings, in which like reference
numerals are employed to indicate like parts in the various views:
FIG. 1 is a side elevational view of a diamond blade
resulting from the inventive method;
FIG. 2 is a side elevational view of a diamond blade at
an intermediate step within the present method, after the
diamond rim has been diffusion bonded onto the core; and
FIG. 3 illustrates a side sectional view along line 3--3
in FIG. 1 of a diamond blade formed by the present method.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a diamond blade generally designated by the
reference numeral 1 which is produced by the present method. The
diamond blade 1 includes a disc-shaped core 2 formed of a hard material,
such as steel and the like. The core 2 is surrounded by an outer
rim 4 that is separated into a plurality of segments 6 having notches
8 therebetween. The notches 8 extend radially toward the center
of the blade 1 and are formed with circular gullets 10 at an innermost
end thereof. Optionally, the gullets 10 could be formed with another
shape, such as a U-shape, V-shape, and the like. The blade 1 is
produced in accordance with the following process. As the inventive
method utilizes conventional machines to perform the molding, heating
and cutting operations, these machines are not illustrated specifically.
According to the preferred embodiment, a mold is used to cold press
a continuous outer rim 14 (FIG. 2) onto the core 2. The mold includes
a base having a centering pin thereon for receiving a central hole
18 of the core 2. The centering pin centers the core 2 within the
mold such that an outer periphery 20 of the core 2 is positioned
proximate a circular void within the mold. The mold includes a bottom
support which supports the core 2 and a top support which is received
upon the core 2. The bottom and top supports include outer peripheries
which substantially aligns with the outer periphery 20 of the core
2. Once the core 2 and the top support are inserted into the mold,
they cooperate to form the circular void which is filled with a
bond powder.
The bond powder is formed from a mixture of metal particles and
hardened particles. The hardened particles may be diamonds, tungsten
carbide, polycrystalline diamond and the like. The metal particles
may be phosphorus, zinc, antimony, iron, nickel, cobalt, silver,
copper, tin and the like which interact to form alloys. The composition
of the bond powder may be varied so long as it remains compatible
with the methods explained hereafter. These metals are chosen to
serve a variety of goals, including the provision of a dense hard
outer rim, a strong bond between the outer rim and core and an outer
rim that is evenly cut. To maximize the results of the instant method,
the composition of the metal powder must be compatible with desired
diffusion bonding and cutting techniques.
The bond powder may include first and second metals which diffusion
bond with one another to form bronze, brass or a similar alloy (e.g.,
copper and tin or zinc and tin) and a third metal (e.g., nickel,
cobalt) that diffusion bonds (sinters) with the bronze or brass
to form an extremely dense composite alloy. Also, the bond powder
may include a fourth metal (e.g., silver or nickel alloy) which
serves as a "wetting agent" to facilitate diffusion bonding
between the outer rim and the core. In the following example, a
particular bond powder composition is discussed only by way of example.
A bond powder is formed which may, by way of example only, comprise
diamond, tin, copper, silver and nickel particles. The tin, copper,
silver and nickel have melting points of approximately 450.degree.
F., 1980.degree. F., 1760.degree. F. and 2600.degree. F., respectively.
The bond powder is poured into the circular void, the mold is closed
and the circular void is compressed upon itself and toward the core
2. The mold cold presses (e.g., no heat is applied) the void to
compact the bond powder into an outer rim having a density of approximately
65% of its maximum attainable density. The cold pressing technique
also momentarily secures the bond powder to the core 2. At this
stage, the blade includes a core 2 surrounded by a continuous outer
rim 14 which is illustrated in FIG. 2. A variety of alternative
methods exist for initially forming the outer rim upon the core,
prior to achieving densification through diffusion bonding. For
instance, the outer rim may be formed by hot pressing, rapid solidification,
injection molding and free sintering, hot isostatic pressing (e.g.,
application of pressurized gas), coining, forging, and the like,
so long as the method provides a continuous rim which may be diffusion
bonded to the core. Alternatively, the outer rim may be extruded
onto the core, cold pressed and then hot pressed, hand filled and
then hot pressed, microwave centered, hand-filled and then infiltrated
with liquid metal and the like.
In the preferred embodiment, the cold pressed blade is removed
from the mold and placed in a furnace for free (pressureless) sintering
to achieve further densification. Densification can be achieved
by hot pressing the powder bond to the core to produce diffusion
bonding internally within the outer rim between the metal particles
therein. Optionally, the blade may be placed in a hot press sintering
(pressurized) furnace, and the like. Densification through diffusion
bonding also occurs between the outer rim 14 and the core 2 thereby
mounting the outer rim 14 permanently upon the core 2. The blade
1 is furnaced between 2 and 8 hours at a temperature preferably
not to exceed 2000.degree. F. The sintering time and temperature
varies based on the single metal or combination of metals within
the bond powder. During an initial stage of sintering the furnace
is heated to a temperature, at which the first and second metals
(e.g., tin, zinc, copper, etc.) combine to form a bronze or brass
alloy. The melting point of copper or zinc is then reduced to a
point between 1400.degree. F. and 1600.degree. F., which will vary
depending upon the percentage of tin and copper, tin and zinc, etc.,
within the bond powder.
After the initial sintering phase, if metals such as nickel, cobalt,
silver and similar alloys are present, the furnace temperature is
increased to 1600.degree. F.-2000.degree. F., at which it is maintained
for a final densification process of soaking such as for 2 hours.
When heated to this higher temperature, silver, nickel, cobalt and
similar alloy metals melt and flow through the bond powder to increase
densification. These alloys are chosen for their characteristics
as a "wetting agent" to facilitate diffusion bonding between
the bond powder and the outer periphery of the core. As the partially
liquid bronze or brass and silver elements interact with other metals
(e.g., iron, cobalt, nickel, etc.) densification of the entire system
is achieved through liquid phase sintering. This allows the shrinkage
of metal around diamond particles as gullet as the ring around the
metal disc. While the diamond containing rim section is shrinking
over the disc, the diffusion enhanced metallurgical bonding process
further strengthens the rim to core interface.
Throughout the diffusion bonding process, the hard particles (e.g.,
diamonds) remain evenly distributed through the bond powder and
the outer rim. The diffusion bond within the bond powder and between
the bond powder and the metal core varies in depth and density depending
upon the time, temperature and pressure. The atoms within the bond
powder and metal core move and interlock during diffusion bonding.
The amount of movement determines the depth of the bond. Thus, as
the temperature and pressure within the furnace vary, so does the
depth of the diffusion bond. The depth and density of the diffusion
bond into the core also dependent upon the diffusion coefficients
of the core and each metal within the metal powder. Thus, the longer
that the blade is held within the furnace, the denser the diffusion
bond.
The furnace temperature must be carefully selected and maintained
throughout diffusion bonding to prevent the formation of localized
pockets or voids within the outer rim. The number of voids within
the bond powder is referred to as its porosity.
Further, if the furnace temperature is raised too high during the
final diffusion bonding phase, this heat will detrimentally effect
the diamond particles within the outer rim, such as through graphitization
and the like.
Diffusion bonding may be achieved through a variety of methods,
such the interstitial mechanism, the vacancy mechanism, substitutional
and the like. These and other diffusion bonding techniques compatible
with the present method, are disclosed in a text book entitled "Diffusion
in Solids" by Paul G. Shewmon of the Carnage Inst. of Tech.,
Dept. of Metallurgical Engineering, McGraw Hill Book Co., 1963
which is incorporated by reference. Similarly, a variety of devices
may be used to achieve diffusion bonding, such as a hot press sintering
(pressurized furnace) and the like. The use of a free-sintering
furnace is by way of example only. Further, the furnace may be heated
to a single temperature and maintained therethrough, so long as
diffusion bonding is achieved. The type of device used to achieve
diffusion bonding will also depend on the type and number of materials
in the bond powder.
By way of example, a hot sintering press may be used to achieve
a diffusion bond, which is heated to a single temperature and is
induced with a single pressure. The heat time and pressure may be
varied so long as a diffusion bond is achieved.
To facilitate the diffusion bonding process, it is also preferable
to use materials (e.g., bronze, copper, silver and nickel) within
the bond powder having close melting points. Alternatively, a single
material may be used for the bond powder, such as nickel or cobalt.
Once the densification process is complete, the furnace is shut
down and left to cool. During the cooling process the densified
diamond rim section contracts. As it contracts the outer rim provides
an enhanced mechanical/physical interlocking mechanism with the
peripheral portion of the core which has undergone diffusion bonding.
The density may increase/change by 30-40% (during the densification
process) from its original cold pressed density. Hence, the dimensions
of the outer rim will shrink. If the height of the outer rim, when
cold pressed, is approximately 0.200", its final height, after
diffusion bonding, will equal roughly 0.180". Similarly, if
the width of the cold pressed outer rim equals 0.8", it will
contract to roughly 0.7" after diffusion bonding. The diffusion
bonded region which includes the metal powders and steel particles
from the core represents the strongest portion of the blade. However,
all pores or voids must be removed from this region (also referred
to as the bonding interface) to prevent premature failure.
However, if the outer rim is formed with localized pockets of non-bonded
metal particles, these pockets are less dense than the diffusion
bonded regions.
Once the blade is cooled, it is transferred to a cutting tool,
such as laser cutter, water beam cutter, plasma arc cutter, electron
beam cutter and the like. Alternatively, the blade may be transferred
to a punch tool for punching out the segment notches and/or gullets
or slots. The tool cuts or punches out each notch 8 through the
outer rim 4 and/or each gullet 10 within the core 2 (FIG. 1). Here
again, the types of metals, and percentages thereof, must be selected
to ensure that the tool is able to perform a smooth and fast cut
or punch.
By way of example, the cutting tool may constitute a laser beam
cutter of the type disclosed in an article entitled "Investigations
in Optimizing The Laser Cutting Process" by F. O. Olsen, which
is incorporated by reference. The laser beam cutter includes a lens
for focusing a laser beam onto the blade. Below the lens, is formed
a gas chamber into which pressurized gas is introduced and directed
onto the blade. The laser beam cutter includes a bale located on
a bottom side thereof to define a lower region of the gas chamber.
The bale includes a nozzle tip having a thickness N.sub.a and an
outer diameter N.sub.d. The nozzle tip includes a nozzle aperture
therethrough and in the center thereof having an outer diameter
N.sub.d. The nozzle tip is located a distance N.sub.h from the region
of the blade being cut.
During operation, the nozzle height N.sub.h is continuously adjusted
to maintain an optimal height between the cutting tool and the blade.
For best results, the diameter N.sub.d of the nozzle aperture is
maintained large in comparison to the nozzle distance N.sub.h between
the nozzle and the blade. This is preferable to direct the gas beam
into the cut curve. When the ratio N.sub.d N.sub.h is large, the
gas pressure decrease from the nozzle tip down to the cut curve.
Further, when this ratio is large, it allows pressure variations
along the distance between the nozzle tip and the diamond blade.
These pressure variations may cause lensing effects which may disturb
the laser beam. Hence, it is preferable that the ratio N.sub.d N.sub.h
remain large, such as N.sub.d N.sub.h .gtoreq.2. This ratio maintains
a negligible pressure variation between the nozzle tip and the diamond
blade, thereby avoiding lensing effects and increasing the gas pressure
within the cut curve. When the ratio N.sub.d N.sub.h is large, the
nozzle tips outer diameter N.sub.d effects the gas flow. When this
outer diameter N.sub.d increases for a given nozzle height N.sub.h,
the gas flow along the outer surface of the diamond blade and the
nozzle tip decreases.
The laser beam utilized in the preferred embodiment is polarized
and directs a stream of pressurized gas onto the cut kerf, in order
to obtain maximum cutting efficiency from the cutting tool. By way
of example, the beam may be polarized in a direction parallel to
the cutting direction. The polarization of the laser beam effects
the cutting rate of the laser and causes variations in the geometry
of the cut curve. When the cutting tool is used to cut materials
with a low reflectivity for normally incident light, the effects
of the laser polarization are not noticeable. Hence, it is preferable
to use metals which diffusion bond to one another to form a composition
having low reflectivity. Compositions which are highly reflective
reflect the laser beam away from the cut kerf and inhibit its propagation
through the blade.
Adjusting the gas pressure also varies the cutting rate and quality.
At extremely low pressures, high quality cuts are difficult to obtain
while maintaining a desired cutting rate. The cutting rate may be
increased when the beam pressure is increased to an intermediate
level. At extremely high pressure values, burning effects are encountered
in the bottom of the cut which impede the quality of the cut. Optionally,
if a desired pressure is unattainable, the outer diameter N.sub.d
of the nozzle tip may be increased to achieve the same effect as
high pressures within the cutting zone. The dynamic behavior of
the laser beam cutter causes the formation of striations (e.g.,
grooves or rough surfaces) within the cut curve.
The cutting rate is primarily dictated by the rate at which the
cutting tool is able to penetrate and progress through the entire
thickness of the blade (e.g., the outer rim and core). The cutting
rate may not exceed the rate at which the cutting tool is able to
cut the densest and hardest metal compound within the outer rim.
The smoothness of the cut will be dictated by the uniformity of
the bond powder and the pores therein (i.e., percentage of voids).
This is due partially to the fact that when a laser beam encounters
a void or pore in the material being cut, the laser erratically
jumps this void. Also, the voids typically contain gas pockets.
When the laser beam encounters the gas pocket, the gas is turbulently
discharged from the pocket. The uneven laser jumping motion and
the gas discharges create uneven regions along the kerf of the cut
(also referred to as "blow holes). Therefore, as the densification
and uniformity of the bond powder is increased and the porosity
decreased, the smoothness of the cut kerf is increased.
However, when complete diffusion bonding occurs, the outer rim
exhibits a somewhat homogeneous bronze-nickel-silver alloy composition
throughout. This alloy composition melts substantially evenly. Every
region within the alloy composition does not melt at exactly the
same instant since partial or localized melting is controlled by
the percentage of the content of the lower melting point elements
within the local region of the alloy. However, the diffusion bonded
particles within a localized region of the alloy composition melts
proximate one another and within a substantially small temperature
and time range. Thus, if the alloys are uniformly formed along the
cutting surface within the cut kerf, it will melt at approximately
the same time as it is exposed to the cutting beam. Hence, the cutting
beam is able to melt the alloys along the entirety of the cutting
surface within a short period of time, blow the melted alloy composition
from the cut kerf and move the beam while the alloy composition
is still molten.
However, the cutting operation is not as smooth when the metal
particles through out the outer rim are not properly diffusion bonded.
Cutting quality is related to the ratio of the bronze or brass content
to that of other alloys. When the copper/bronze/brass content is
greater than 20%-50% of the overall composition, then the cutting
quality is reduced. As noted above, when executed improperly, localized
regions of copper and nickel are formed within the outer rim during
diffusion bonding. The melting point of copper is somewhat less
than that of nickel. When the cutting tool encounters a copper region,
it melts this region quite rapidly, much faster than it is able
to melt any surrounding nickel regions. Thus, the cutting tool must
remain at a particular location while it melts the nickel. As the
cutting tool remains focused on the nickel region, it continues
to transmit heat to the neighboring copper region. Hence, copper
along side the cut kerf is melted. This copper ultimately flows
away from the cutting tool, cools and solidifies. The region of
displaced copper or bronze leaves a void or recess in the outer
rim which is wider than the surrounding cut kerf. Also, the large
region of displaced copper solidified on the surface of the outer
rim or within the cut kerf thereby forming an irregularity on the
blade (referred to as a "bubble"). Also, the pocket of
liquid copper may surround a diamond particle. Thus, as the copper
is displaced, it weakens the support for the diamond which may also
become dislodged and create an even bigger void (referred to as
a "blow hole").
Thus, to avoid bubbles and blow holes, it is important that the
diffusion bonding step form a dense, non-porous and somewhat homogeneous
metal alloys throughout the outer rim.
Further, to maximize the use of a laser beam as the cutting tool,
the diffusion bonded alloys within the outer rim must be relatively
non-reflective. When the laser beam contacts reflective materials,
a portion of the beam is reflected which reduces the effective cutting
power of the laser. Copper is highly reflective, while the bronze-silver-nickel
composition is less reflective. Therefore, when localized pockets
of copper are formed within the outer rim, these pockets reflect
a large portion of the laser beam. This reflection reduces the effective
cutting power of the laser.
Also, the bronze-nickel-silver alloy composition has a lower melting
point than the nickel. Thus, the temperature necessary to cut the
bronze-nickel-silver alloy composition is less than that necessary
to cut nickel. Thus, the compositional uniformity impacts the cutting
temperature.
While the above example discusses the use of tin, copper, silver
and nickel, it will be understood that the present invention is
not limited to use with these materials. Instead, any materials
may be used so long as they form a composition that is compatible
with the cutting tool. Further, a single type of metal may be used
to construct the bond powder. A bond powder formed of a single type
of metal may be hot pressed around a core that is plated with copper,
tin, and zinc (e.g., bronze or brass) to achieve diffusion bond
of the powder metal to the core while densifying the bond powder.
In an alternative embodiment, the core 2 is initially formed with
the circular gullets 10 therein spaced about its circumference.
The core 2 with the gullets 10 therein is placed in the cold press
and then in the bell furnace as explained above. Thereafter, the
cutting step merely needs to cut the notches 8 through the outer
rim 4 into the core 2 to the circular gullets 10. The circular gullets
10 which may be formed as pre-existing holes, serve as heat sinks
to avoid cracking during use.
The following examples illustrate the percentages of metals which
may be used, the heating temperatures and the heating times.
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