Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TECHNICAL DISCLOSURE
The invention relates to masonary cutting tools such as
diamond and cubic boron nitride saw blades, core drills and drill
bits comprised of one or more metal bonded abrasive cutting
elements or segments securely joined to a metal core by an
intense high energy laser beam fusion welding process that resist
higher temperature of and thus enhances the dry cutting ability
of the cutting tool.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to rotary masonary saw blades,
core drill and drill bits having at least one metal bonded
diamond or cubic boron nitride abrasive cutting element or
segment welded to a metal support center core, or shank.
2. Description of the Prior Art
The prior art discloses a variety of cutting tools
having one or more metal bonded abrasive cutting elements
fastened to a metal support, center, core, or shank. One well
known and most widely used attachment method is to braze the
segment to a metal support center wherein the strength of the
joint depends on the brazing material, how well it is applied,
! and how much of it bridges the visible joint or seam at each side
of the support. In most instances the brazing material is not as
strong, has a lower melting point and is softer than the
materials of the segment and support joined thereby. Thus, the
brazing material is subjected to erosion by both excess heat and
abrasion produced during the cutting process. This is especially
true when cutting dry and without the use of coolant that
normally reduces the temperature and washes away the abrasive
swarf and aggregates in the kerf or cut.
Dry cutting of hard materials without the application
of coolant or water to the cutting tool is increasing worldwide
because in some instances the coolant or water will contaminate
the materials, is undesirable and will freeze in cold weather.
Hence, during prolonged use the erosion causes each
side layer or bead of the brazed joint to become progressively
softer, thinner and weaker and at some critical point the segment
under the stress of centrifugal and operating force is no longer
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held to the support by a sufficient amount of brazing material.
The Applicant's invention has solved this weakness by
laser beam fusion welding the adjoining material of the segment
and support together into a seamless integral mass without the
use of additional welding, brazing or soldering material.
Although high energy laser beam welding is known for other
applications, the Applicant is unaware of any analogous prior art
in which preformed cutting elements containing abrasive particles
and a metal bonding material of one composition is laser beam
fusion welded to a metal support of a different metallic
composition as disclosed and claimed hereinbelow.
S~MMARY OF THE INVENTION
A cutting tool for cutting hard materials has one or
more preformed metal bonded abrasive cutting elements, each
comprising a molded matrix of known abrasive, diamond or cubic
boron nitride cutting particles and metal bond materials high
energy laser beam fusion welded to a metal support, center, core,
or shank. The cutting particles held in place by the metal bond
material are dispersed in an outer cutting portion of each
cutting element and adjacent an inner non-cutting metal portion
free of cutting particles. The inner non-cutting metal portion
has an inner surface adapted for and held in locating mating
engagement with an outer mating support surface of the metal
support, center, core, or shank during laser beam fusion welding
of the adjoining mating portions of the metal support, center,
core or shank, and the inner metal portion together into a strong
integral unitized and seamless cutting tool. Thus, the invention
also provides a method for making unitary cutting tools such as
rotary saw blades, core drills and drill bits with metal bonded
abrasive cutting elements fusion welded to a drivable metal
support, center, core or shank by a fusion welded phase of
adjoining metal portions without visible seams and the use of
additional welding material and which can withstand the higher
temperature dry cutting conditions.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a fragmentary side view of a $egmental
abrasive saw blade constructed according to the invention;
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Figure 2 is a perspective view of a cutting element
fusion welded to a portion of the metal support center of the saw
blade in Figure 1;
Figure 3 is a perspective view of another embodiment of
a cutting element having an integral backing portion fusion
welded to the metal support;
Figure 4 is a view partly in section of a core drill
constructed according to the invention; and
Figure 5 is a perspective view of a cutting element
fusion welded to the tubular metal support of the core drill in
Figure 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTtS)
Referring to Figure 1, a segmental rotary abrasive saw
blade or cutting tool 10 has a preformed metal support, center or
disc 12 including a wall of predetermined diameter and wall
thickness usually made of AISI 4130 steel. The steel center 12
has a central hole 14 adapted for receiving a drive means or
shaft of a machine on which it will be mounted and rotatably
driven. Extending radially inwardly from the outer peripheral
surface of the support center 12 are a plurality of radial slots
16 and intervening cutting element support sections 18 of the
! wall including cutting elements 20 thereon angularly spaced
about the axis of the center.
Each cutting element support section 18 has an outer
peripheral surface initially adapted for locating mating
engagement with an inner surface of the preformed cutting element
20 during laser beam fusion welding thereof to the support
section 18 of the metal support wall. Each preformed cutting
element 20 comprises an outer cutting portion 22 including a
plurality of suitably hard abrasive cutting particles 24
dispersed in and held in place by a matrix of metal bonding
material 26 extending inwardly to and may include an inner
non-cutting metal portion 28 with an inner mating surface.
The metal bond 26 and portion 28 comprises material
selected from a group consisting of cobalt, iron, bronze, nickel
alloy, tungsten carbide, chromium boride and mixtures thereof.
In Figure 3 there is shown another embodiment of a
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cutting element 20' in which the inner non-cutting metal portion
is an additional integrally formed backing strip or layer 28' of
metal totally free of abrasive particles and of a different
metallic composition than the metal bonding material 26 and 26'
holding the abrasive particles 24 and 24', in outer cutting
portions 22 and 22' of the cutting elements 20' and 20'. The
metallic backing layer 28' of a different composition is
provided when the metallurgical composition of the metal bond 26'
is undesirable for obtaining the desired strong fusion or
welding of the segment to the metal support. Preferably the
composition of the backing layer 28' is selected from a group
consisting of iron, nickel alloy, bronze, and mixtures thereof,
when the metal bond 26' is cobalt, tungsten carbide, or a mixture
thereof.
Typically, an abrasive cutting element or segment 20'
will have a metal bond composition 26' consisting by volume of
80% cobalt and 20% tungsten carbide holding 1.1 carats of diamond
particles dispersed therein and a metal backing layer 28'
simultaneously formed therewith consisting of 65% iron, 25%
nickel alloy, and 10% bronze by volume.
The metal support, center, core, or shank to which the
cutting elements 20 and 20' are fused or welded to is usually
made of a steel alloy consisting of 0.3% carbon, manganese,
silicon and the balance iron.
A typical cutting tool in the ~orm of a rotary abrasive saw
blade 10 and about 14" (35.6 cm) in diameter has a steel center
12 initially of about 13.5" (34.3 cm) in diameter, is .095" ~2.38
mm) thick, a 1" (2.54 cm) arbor hole 14, twenty (20) equally
spaced radial slots 16 and cutting elements support sections 18
to each of which a cutting element 20 or 20' is laser beam fusion
welded.
A typical preformed cutting element or segment 20 or
20' for attachment to the center 12 has an arcuate shape
including a convex outer surface, an inner concave mating
surface of a radius equal to 1/2 the diameter of the mating
convex peripheral surface of the steel center 12, a chord length
of 1.937" (4.91 cm), a radial depth between outer and inner
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surfaces of 1/4" (6.35 mm) and an axial thickness of .125"
(3.17 mm) that is greater than the wall of the steel center to
which it is to be fused. The outer cutting zone or portion
containing the abrasive cutting particles has a radial depth
sufficiently less than the total radial depth of the cutting
segment to provide either the abrasive free inner non-cutting
zone or portion 28 or the additional clear backing layer 28' of
sufficient radial depth of at least 1/32" (0.8 mm) to prevent the
high energy or laser beam from contacting an abrasive particle
and hence producing a weaker fused or welded phase WP of the
adjoining metals.
When encountered by the heat of the beam the abrasive
particles will boil causing the evolution of gas, and hence,
porosity and poor alloying of the welded or fused metal and
thereby degrading the strength and performance thereof.
Another embodiment of the invention is disclosed in
Figure 4 in the form of a rotary core drill 30 comprising a
preformed tubular metal or steel support core or shank 32 which
may be substantially the same composition as the steel center 12
or AISI 1020 steel and of predetermined axial length adaptable
for driving attachment to the drive means of a conventional core
drilling motor or machine.
At the opposite end, the steel support tube 32 has an
annular wall including an end surface 34 initially adapted for
mating locating engagement and fusion welding of one or more
cutting elements or segments 40 of arcuate shape thereto.
It is obvious that the preformed cutting elements 20,
20' and 40 may be made in the form of a single continuous
annular cutting element not shown but are preferably arcuate
segments angularly spaced around the rotational axis and end of
the steel center or tube and interrupted by radial or axial slots
therebetween.
An arcuate preformed cutting element or segment 40
adapted for fusion welding to the support tube 32 has, as shown
in Figure 5, portions constructed in the same manner and of
substantially the same material as are the saw blade segments 20
and 20'. Each cutting element 40 comprises an outer cutting
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portion 42 including an outer end surface in which a plurality of
suitable hard abrasive particles 44 are dispersed and held in
place by a matrix of metal bonding material 46 extending axially
inwardly to an inner non-cutting metal portion 48 including an
inner mating surface.
The metal bonding material holding the hard cutting
particles of abrasive in place is formulated from the same
materials disclosed above with respect to either the segments 20
and 20'. Likewise, the inner non-cutting portion 48 may be of
the same metallic composition as the metal bond 46 or an
additional integrally formed clear backing layer of a different
metallic composition as taught above with respect to the cutting
elements 20 and 20'.
A typical 3" core drill 30 with a 14" (35.56 cm) core
length has a steel tube or blank about 14-l/4" (36.22 cm) long
with an outside diameter of 3" (7.61 cm), an inside diameter of
2.834" (7.2 cm) and a wall thickness of about .083" (2.1 mm) to
the end surface of which four cutting elements 40 are fusion
welded to provide the entire cutting crown with an outside
diameter of 3.052" (7.74 cm) and an inside diameter of 2.78"
(7.07 cm). Each of the kerf cutting segments 40 has a radial
wall thickness of .135" (3.17 mm) an axial length of about 1/4"
(6.35 mm), a chordal length of 1.575" (4 cm), an outer cutting
portion and an inner non-cutting portion of substantially the
same axial length as the radial depth of the cutting elements 20
and 20'.
The hard cutting particles 24, 24' and 44 of the
respective cutting elements 20, 20', and 40, may be of any known
abrasive material but are preferably natural or synthetic diamond
or cubic boron nitride particles of from 20 to 60 grit size (840
to 250 microns~ with or without a metal coating.
Each of the cutting elements 20, 20' and 40, are
preformed by placing a first bottom layer of a mixture of the
desired cutting abrasive particles and the metal bonding
material in powder form of predetermined depth to form the outer
cutting portion in a suitably shaped cavity of a mold designed to
produce the desired size and shape of cutting element. A second
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top layer of either the same metal bonding or a different
metallic powdered material, or a preformed metal strip, of
sufficient depth to form the inner non-cutting portion of the
cutting element is then spread or placed on top of the bottom
layer. The mold is then closed and the contents hot pressed at
about 1850F (1010 C) for 3 minutes and under 1.5 ton/in2 (20.7
MPa), a temperature sufficient to sinter or fuse the metal strip
or powders together and which, upon cooling, provides an integral
preformed cutting element or segment of the desired configuration
ready for attachment to the support center, core tube, or shank.
One or more of the preformed cutting elements of the
desired configuration and the appropriate steel support center,
tube core, or shank, are then placed in a fusion welding
fixture. The fixture aligns, holds and presses the cutting
elements arranged in the desired position so that the inner
mating surface of each cutting segment is pressed against an
outer mating surface of the steel support center tube, core, or
shank. Rotation of the fixture, cutting segments and steel
support relative to a stationary laser beam heat source means is
begun. Alternatively the fixture, steel support and cutter
element, may be held stationary and the laser beam heat source is
moved relative thereto.
In either arrangement the high energy laser beam of
the heat source is focused on a focal point FP near the mating
interface or surfaces of the segment and steel support, and
midway through the wall thickness of the steel support.
Typically, the focal point FP may be 0.005 inches radially inward
of the steel periphery, and 0.040 inches below the surface (from
the incident beam side) of a typical 0.095" (2.4 mm) thick steel
core. Exact parameters varies widely with the geometry and
chemistry of the steel core and of the cutting segment. The
intense heat melts and fuses together the entire thickness of the
adjoining inner non-cutting metal portion of the cutting element
and the outer portion of the steel support contacted thereby, and
the molten volume of the adjoining materials fused together
alloys and freezes to a fusion welded phase WP as the beam makes
contact with other areas thereof to be fusion welded.
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When joining segments to steel greater than 0.095" (2.4
mm) in thickness, and after completion of the welding on one
side of the cutting tool, the fusion welding may be repeated on
the opposite side of the cutting tool whereby the fusion of the
adjoining materials extends substantially through the entire
wall thickness of the steel support. Hence, the initial visible
seam or line of demarcation between the adjoining inner locating
mating surfaces of the cuttlng segment and the steel support,
present prior to fusion welding, is substantially eliminated and
no longer visible to the naked eye.
In its place is left a narrow band of strong, coherent
fusion welded phase WP of the adjoining materials able to resist
higher temperatures produced during dry grinding applications and
thus prevent loss of cutting elements.
Alternatively, both sides of the cutting tool may be
simultaneously fusion welded by placing laser beam heat source
means on each side of the cutting tool and focusing each of the
beams to penetrate substantially to one half (1/2) the wall
thickness of the steel support and thus simultaneously fusion
weld opposing side portions of the adjoining materials of the
same segment and steel support. One beam may be directed to
fusion weld one side of the steel support to one segment and the
other beam on the opposite side directed to simultaneous fusion
weld a different nonopposing opposite side portion of the steel
support and the same cutting element or of another cutting
element together.
Following the completion of the fusion welding process
the cutting tool may be relieved of stresses produced therein
during the fusion welding process. The cutting tool can be
stress relieved by the usual process of slowly rotating the
cutting tool under a radiant or induction heating coil to anneal
the stresses and improve the strength and performance of the
fusion welded area.
In comparison to the prior art brazed cutting tools,
the cutting tools of the invention have up to three (3) times
greater joint strength and withstand higher stresses and
temperatures than brazed cutting tools.
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As many other embodiments of the invention are possible
it is to be understood that the embodiments disclosed in the
drawings and described hereinabove are for illustrative purpose
only and that the invention includes all modifications and
embodiments thereof falling within the scope of the appended
claims.
