U.S. patent application number 15/368725 was filed with the patent office on 2018-06-07 for eddy current vibration absorber assembly for cutting tool.
This patent application is currently assigned to Kennametal Inc.. The applicant listed for this patent is Kennametal Inc.. Invention is credited to Shi Chen, Samuel Eichelberger, Igor Kaufmann, Tony Schmitz.
Application Number | 20180154453 15/368725 |
Document ID | / |
Family ID | 62240335 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180154453 |
Kind Code |
A1 |
Eichelberger; Samuel ; et
al. |
June 7, 2018 |
EDDY CURRENT VIBRATION ABSORBER ASSEMBLY FOR CUTTING TOOL
Abstract
A cutting tool includes a cutting insert mounted to a head
attached to a collar at a first end of the cutting tool. A shank is
located at a second, opposite end of the cutting tool. A central
cavity extends inwardly from the first end toward the shank. An
eddy current vibration absorber assembly is disposed within the
central cavity. The eddy current vibration absorber assembly
includes an absorber mass made of an electrically conductive
material, a magnetic material proximate the absorber mass, and a
support member for supporting the absorber mass within the central
cavity. The eddy current vibration absorber assembly is tuned by
selectively adjusting a distance between the absorber mass and the
magnetic material.
Inventors: |
Eichelberger; Samuel;
(Trafford, PA) ; Schmitz; Tony; (Matthews, NC)
; Chen; Shi; (North Huntingdon, PA) ; Kaufmann;
Igor; (Nuemberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kennametal Inc. |
Latrobe |
PA |
US |
|
|
Assignee: |
Kennametal Inc.
Latrobe
PA
|
Family ID: |
62240335 |
Appl. No.: |
15/368725 |
Filed: |
December 5, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23B 2260/10 20130101;
B23B 2250/16 20130101; B23B 2260/004 20130101; F16F 15/14 20130101;
F16F 7/104 20130101; F16F 7/1011 20130101; B23B 29/022 20130101;
F16F 2222/06 20130101; B23B 27/002 20130101 |
International
Class: |
B23B 29/02 20060101
B23B029/02; F16F 15/03 20060101 F16F015/03 |
Claims
1. A cutting tool, comprising: a cutting insert mounted to a head
attached to a collar at a first end of the cutting tool; a shank
located at a second, opposite end of the cutting tool; a central
cavity extending inwardly from the first end toward the shank; and
an eddy current vibration absorber assembly disposed within the
central cavity, the eddy current vibration absorber assembly
comprising an absorber mass made of an electrically conductive
material proximate a magnetic material, and a support member for
supporting the absorber mass within the cavity, wherein the eddy
current vibration absorber assembly is tuned by selectively
adjusting a distance between the absorber mass and the magnetic
material.
2. The cutting tool of claim 1, wherein the absorber mass is made
of copper.
3. The cutting tool of claim 1, wherein the absorber mass is made
of two different materials.
4. The cutting tool of claim 1, wherein the magnetic material
comprises a plurality of permanent magnets.
5. The cutting tool of claim 1, wherein the magnetic material
comprises an electromagnet.
6. The cutting tool of claim 1, wherein the support member is made
of titanium.
7. The cutting tool of claim 1, wherein one end of the support
member is secured within a cavity of the collar and an opposite end
of the support member is secured within a cavity of the absorber
mass.
8. The cutting tool of claim 1, wherein the cutting tool comprises
a boring bar.
9. An eddy current vibration absorber assembly, comprising: an
absorber mass made of an electrically conductive material; a
magnetic material proximate the absorber mass; and a support member
for supporting the absorber mass within a central cavity of a
cutting tool, wherein the eddy current vibration absorber assembly
is tuned by selectively adjusting a distance between the absorber
mass and the magnetic material.
10. The eddy current vibration absorber assembly of claim 9,
wherein the absorber mass is made of copper.
11. The eddy current vibration absorber assembly of claim 9,
wherein the absorber mass is made of two different materials.
12. The eddy current vibration absorber assembly of claim 9,
wherein the magnetic material comprises a plurality of permanent
magnets.
13. The eddy current vibration absorber assembly of claim 9,
wherein the magnetic material comprises an electromagnet.
14. The eddy current vibration absorber assembly of claim 9,
wherein the support member is made of titanium.
15. The eddy current vibration absorber assembly of claim 9,
wherein one end of the support member is secured within a cavity of
the collar and an opposite end of the support member is secured
within a cavity of the absorber mass.
16. A method of tuning an eddy current vibration absorber assembly
disposed within a central cavity of a cutting tool, the eddy
current vibration absorber assembly comprising an absorber mass
made of an electrically conductive material; a magnetic material
proximate the absorber mass; and a support member for supporting
the absorber mass within the central cavity, the method comprising
selectively adjusting a distance between the absorber mass and the
magnetic material.
Description
FIELD OF THE INVENTION
[0001] In general, the invention relates to a cutting tool and,
more particularly, to a cutting tool, such as a boring bar, with a
tunable dynamic vibration absorber assembly that utilizes eddy
currents for vibration suppression.
BACKGROUND OF THE INVENTION
[0002] During a metal cutting operation, any vibratory motion
between a cutting tool and workpiece may lead to undesirable
cutting performances such as poor workpiece surface finish and
out-of-tolerance finished workpieces. Furthermore, such vibration
may cause the cutting tool or the machine tool to become
damaged.
[0003] To reduce these vibrations, the metal removal rate can be
decreased. However, this approach interferes with production and
only minimally reduces the amount of vibration.
[0004] Instead of decreasing metal removal rates, tuned boring bars
have been manufactured using a heavy mass supported by rubber
elements. The rubber elements are responsible for providing the
stiffness and damping for the dynamic absorber system. Stiffness
and damping are material specific properties. Therefore, it is
impossible to design the dynamic absorber package to specified
stiffness and damping parameters for optimum performance using
rubber elements alone. Another method to introduce damping that has
been employed is the addition of a viscous fluid in the dynamic
absorber cavity within the boring bar shank. While this method does
increase damping, the rubber elements and viscous fluid must be
chosen carefully to ensure compatibility. Otherwise, the viscous
fluid can deteriorate the rubber elements and alter the performance
of the boring bar. Therefore, there is a need to provide a dynamic
absorber that solves the above-mentioned problems.
SUMMARY OF THE INVENTION
[0005] The problem of using rubber elements to suppress vibration
in a cutting tool is solved by providing an eddy current dynamic
absorber. The eddy current effect arises from the interaction of a
magnet that produces a strong magnetic field and a mass made of a
highly electrically conductive material. The relative motion
between the magnet and the conductive material causes the
conductive material to experience a change in the magnetic flux
(i.e. varying magnetic field strength) that is described by
Faraday's law of induction, thereby creating a flow of electrons
within the conductive material. As the current flows, it creates
small loops, which are referred to as eddy currents. The direction
of the eddy current obeys Lenz's law, which states that an induced
current always flows in the direction opposite to the source that
produced the induced current. Due to the direction of rotation of
the eddy currents, a magnetic field is produced that is opposite in
direction to the relative motion that created them. This opposite
magnetic force resists the relative motion and provides damping of
vibrations during a cutting operation. The amount of damping that
can be produced is determined by the conductivity of the conductive
material, the magnetic strength of the magnet, the thickness of the
conductive material, the surface area of the magnet, and the
distance between the conductive material and the magnet. These
factors can be used to mathematically predict the amount of damping
obtainable which will make it possible to build a dynamic absorber
to the specified damping parameters needed to optimize the
performance of the tuned eddy current vibration absorber
assembly.
[0006] In one aspect of the invention, a cutting tool comprises a
cutting insert mounted to a head attached to a collar at a first
end of the cutting tool. A shank is located at a second, opposite
end of the cutting tool. A central cavity extends inwardly from the
first end toward the shank. An eddy current vibration absorber
assembly is disposed within the central cavity. The eddy current
vibration absorber assembly comprises a magnetic material proximate
an absorber mass made of electrically conductive material, and a
support member for supporting the absorber mass within the cavity,
wherein the eddy current vibration absorber assembly is tuned by
selectively adjusting a distance between the absorber mass and the
magnetic material.
[0007] In another aspect of the invention, an eddy current
vibration absorber assembly comprises an absorber mass made of an
electrically conductive material; a magnetic material proximate the
absorber; and a support member for supporting the absorber mass
within a cavity, wherein the eddy current vibration absorber
assembly is tuned by selectively adjusting a distance between the
absorber mass and the magnetic material.
[0008] In yet another aspect of the invention, a method of tuning
an eddy current vibration absorber assembly, the assembly
comprising an absorber mass made of an electrically conductive
material; a magnetic material proximate the absorber; and a support
member for supporting the absorber mass within a cavity, the method
comprising selectively adjusting a distance between the absorber
mass and the magnetic material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] While various embodiments of the invention are illustrated,
the particular embodiments shown should not be construed to limit
the claims. It is anticipated that various changes and
modifications may be made without departing from the scope of this
invention.
[0010] FIG. 1 is a top view of a cutting tool with an eddy current
vibration absorber assembly according to an embodiment of the
invention;
[0011] FIG. 2 is an end view of the cutting tool of FIG. 1;
[0012] FIG. 3 is a cross-sectional view of the cutting tool with
the eddy current vibration absorber assembly taken along line 3-3
of FIG. 2;
[0013] FIG. 4 is an end view of an eddy current vibration absorber
assembly according to an embodiment of the invention;
[0014] FIG. 5 is a graph of real data as a function of the distance
between the absorber mass and the magnetic material; and
[0015] FIG. 6 is a graph of imaginary data as a function of the
distance between the absorber mass and the magnetic material.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring now to FIGS. 1-3, a cutting tool 10, such as a
boring bar, is shown according to an embodiment of the invention.
Although the present invention is directed to a boring bar 10 for
boring deep holes in work pieces, the principles of the invention
can be applied to any cutting tool that produces vibrations when
cutting a work piece.
[0017] A cutting tool, such as a cutting tool 12, such as a cutting
insert, may be mounted in a conventional manner to a head 14
attached to a collar 16 at one end 18 of the boring bar 10. A shank
20 is located at the opposite end 22 of the boring bar 10. The
boring bar 10 has a central cavity 24 extending inwardly from the
end 18 toward the shank 20. In the illustrated embodiment, the
boring bar 10 includes a coolant tube 26 extending along a central,
longitudinal axis 28 of the boring bar 10 for providing coolant
proximate the cutting insert 12. It will be appreciated that the
coolant tube 26 is optional and can be omitted. For example, the
coolant tube can be replaced with a threaded stud or a solid stud
with threaded ends. In another example, the shank 20 can be
manufactured without the central cavity 20 as a solid shank.
[0018] Use of the boring bar 10 in a metalworking operation will
produce vibrations that travel through the boring bar 10, thereby
affecting the stability of the cutting process. For this reason,
the boring bar 10 is provided with an eddy current vibration
absorber assembly, shown generally at 30, according to an
embodiment of the invention that will dampen the vibrations
traveling through the boring bar 10.
[0019] In general, Faraday's law of induction is a basic law of
electromagnetism predicting how a magnetic field will interact with
an electric circuit to produce an electromotive force (EMF), which
is a phenomenon called electromagnetic induction. It is a
fundamental operating principle of transformers, inductors, and
many types of electrical motors, generators and solenoids.
[0020] Faraday's law states that the EMF is also given by the rate
of change of the magnetic flux:
= .differential. .PHI. .differential. t ( Eq . 1 ) ##EQU00001##
where .epsilon. is the electromotive force (EMF) and .PHI. is the
magnetic flux. The direction of the electromotive force is given by
Lenz's law, which states that the direction of current induced in a
conductor by a changing magnetic field due to Faraday's law of
induction will be such that it will create a field that opposes the
change that produced it. Lenz's law is shown by the negative sign
in Faraday's law of induction:
= - .differential. .PHI. .differential. t ( Eq . 2 )
##EQU00002##
which indicates that the induced voltage (.epsilon.) and the change
in magnetic flux (.delta..PHI.) have opposite signs. It is a
qualitative law that specifies the direction of induced current,
but says nothing about its magnitude. Lenz's law explains the
direction of many effects in electromagnetism, such as the
direction of voltage induced in an inductor or wire loop by a
changing current, or why eddy currents exert a drag force on moving
objects in a magnetic field.
[0021] Eddy currents (also called Foucault currents) are loops of
electrical current induced within conductors by a changing magnetic
field in the conductor, due to Faraday's law of induction. Eddy
currents flow in closed loops within conductors, in planes
perpendicular to the magnetic field. They can be induced within
nearby stationary conductors by a time-varying magnetic field
created by an AC electromagnet or transformer, or by relative
motion between a magnet and a nearby conductor. The magnitude of
the current in a given loop is proportional to the strength of the
magnetic field, the area of the loop, and the rate of change of
flux, and inversely proportional to the resistivity of the
material.
[0022] According to Lenz's law, an eddy current creates a magnetic
field that opposes the magnetic field that created it, and thus
eddy currents react back on the source of the magnetic field. For
example, a nearby conductive surface will exert a drag force on a
moving magnet that opposes its motion, due to eddy currents induced
in the surface by the moving magnetic field. This effect is
employed in eddy current brakes, which are used to stop rotating
power tools quickly when they are turned off. The current flowing
through the resistance of the conductor also dissipates energy as
heat in the material.
[0023] Referring now to FIG. 3, the eddy current vibration absorber
assembly 30 comprises a generally cylindrical absorber mass 32
adjacent a magnetic material 34. In the illustrated embodiment, the
magnetic material 34 comprises one or more permanent magnets 34
disposed within the cavity 24 proximate the shank 20 of the cutting
tool 10. However, it will be appreciated that the invention is not
limited by the type of magnetic material, and that the invention
can be practiced with any desirable magnetic element that produces
a magnetic field, such as an electromagnetic field, and the
like.
[0024] At least a portion of the absorber mass 32 is made of highly
electrically conductive material, such as copper, aluminum, and the
like. In the illustrated embodiment, the absorber mass 32 has two
portions: a first portion 32a made of a highly electrically
conductive material, such as copper, aluminum, and the like; and a
second portion 32b made of a different material with a relatively
higher density, such as tungsten, and the like. The second portion
32b is provided in the illustrated embodiment so that the absorber
mass 32 has an adequate amount of total mass to adequately dampen
vibrations in the cutting tool 10. However, it will be appreciated
that the absorber mass 32 can be made of a single piece of
electrically conductive material, so long as the mass of the
absorber mass 32 is sufficient to provide adequate dampening of
vibrations in the cutting tool 10. The first portion 32a can be
secured to the second portion 32b by press fitting, brazing,
welding, and the like. In the illustrated embodiment, for example,
the first portion 32a is press fit to the second portion 32b.
[0025] As seen in FIG. 3, the absorber mass 32 has a first end 36
proximate the magnetic material 34, and a second, opposite end 38
proximate the collar 16. In the illustrated embodiment, the
absorber mass 32 has a total length of about 5.0 inches (127 mm),
wherein the exterior surface of the first portion 32a has a length
of about 4.0 inches (101.6 mm) and the exterior surface of the
second portion 32b has a length of about 1.0 inches (25.4 mm).
Thus, there is about a 4:1 ratio in the relative length between the
first portion 32a and the second portion 32b.
[0026] The absorber mass 32 is supported within the cavity 24 by a
support member 40. In the illustrated embodiment, the support
member 40 is made of a suitable material to provide some stiffness
or rigidity, but allow the absorber mass 32 to move within the
cavity 24. For example, the support member 40 can be made of a
relatively strong, lightweight material, such as titanium, and the
like. In the illustrated embodiment that includes the coolant tube
26, the support member 40 is annular in shape to allow the coolant
tube 26 to pass through the support member 40. In another
embodiment in which the coolant tube 26 is omitted, the support
member 40 can be a solid member. One end 40a of the support member
40 is secured within a cavity 42 of the collar 16 and the opposite
end 40b of the support member 40 is secured within a cavity 44 of
the absorber mass 32. The support member 40 can be secured to the
collar 16 and the absorber mass 32 by press fitting, brazing,
welding, and the like. In the illustrated embodiment, the support
member 40 is press fit into the collar 16 and the absorber mass
32.
[0027] As noted above, the absorber mass 32 is suspended within the
cavity 24 only by the support member 40 and the absorber mass 32 is
allowed to move within the cavity 24. It is noted that the coolant
tube 26 (if included) does not provide any additional support for
the absorber mass 32. In addition, the absorber mass 32 has an
outer diameter that is smaller than the inner diameter of the
cavity 24 that enables the absorber mass 32 to freely move in two
directions perpendicular to the longitudinal axis 28 of the cutting
tool 10 (i.e. in the y- and z-directions). Further, the second end
38 of the absorber mass 32 is separated from the collar 16 by a
small distance 46 to allow clearance between the collar 16 and the
absorber mass 32. Thus, the support member 40 acts as a cantilever
beam and the absorber mass 32 acts as a point mass on a tip of the
support member 40 (i.e. cantilever beam). It should be noted that
the absorber mass 32 is fixed in the x-direction, and that the
absorber assembly 30 can be tuned by adjusting the distance 48
between the absorber mass 32 and the magnetic material 34.
[0028] Referring now to FIG. 4, a schematic representation of the
cantilever of the eddy current vibration absorber assembly 30 is
described. The eddy current vibration absorber assembly 30 has a
natural frequency, Wn, that can be defined by the following
equation:
Wn = K M ( Eq . 3 ) ##EQU00003##
where, Wn=natural frequency (rad/s), K=stiffness (N/m), and M=mass
(kg).
[0029] The stiffness, K, is given by the following equation:
K = 3 EI L 3 ( Eq . 4 ) ##EQU00004##
where, E=modulus of elasticity (N/m.sup.2), I=second moment of
inertia (m.sup.4), and L=length (m).
[0030] The mass, M, is given by the following equation:
M=(33/140)M.sub.b+M.sub.t (Eq. 5)
where, M.sub.b=mass of beam (kg), M.sub.t=mass at tip (kg),
[0031] The amount of the highly electrically conductive material
32a of the absorber mass 32 is determined by how much damping is
required. If the amount of damping is met by the amount of material
32a and the mass requirement is not met, then the material 32b
having the relatively higher density is added until the mass
requirement is met. The length, L, outer diameter (OD) and inner
diameter (ID) of the support member 40 is selected to meet a
specific stiffness requirement.
[0032] Referring back to FIG. 3, the electrically conductive
material 32a of the absorber mass 32 is separated from the magnetic
material 34 by a very small distance 48 when the eddy current
vibration absorber assembly 30 is mounted within the central cavity
24 of the cutting tool 10. The distance 48 can be in a range
between about 0.001 inches (0.025 mm) to about 0.100 inches (2.54
mm). In the illustrated embodiment, the distance 48 is about 0.01
inches (0.25 mm). The small distance 48 allows the eddy current
vibration absorber 30 to be tuned by selectively adjusting the
distance 48 between the absorber mass 32 and the magnetic material
34.
[0033] FIGS. 5 and 6 shows test results for the eddy current
vibration absorber assembly 30 of the invention. Specifically, FIG.
5 shows a graph of real data (m/N) as a function of the distance 48
between the absorber mass 32 and the magnetic material 34, and FIG.
6 shows a graph of imaginary data (m/N) as a function of the
distance 48 between the absorber mass 32 and the magnetic material
34. In FIGS. 5 and 6, the distance 48 was selectively adjusted
between about 0.50 inches (12.7 mm) and 0.010 inches (0.25 mm). As
seen in FIGS. 5 and 6, the distance 48 of about 0.50 inches (12.7
mm) provided the least desirable damping, while the distance 48 of
about 0.010 inches (0.25 mm) provided the most desirable
damping.
[0034] As described above, the cutting tool 10, such as a boring
bar, includes an eddy current vibration absorber assembly 30 that
utilizes eddy currents to dampen vibrations of the cutting tool 10.
The method of using eddy currents for suppression of vibrations
generated by the cutting tool provides for superior damping
capability, as compared to conventional damping methods using an
absorber mass with rubber elements.
[0035] The patents and publications referred to herein are hereby
incorporated by reference.
[0036] Having described presently preferred embodiments the
invention may be otherwise embodied within the scope of the
appended claims.
* * * * *