Note: Descriptions are shown in the official language in which they were submitted.
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ULTRASONI C IMPACT MACHINING OF BODY SURFACES
TO CORRECT DEFECTS AND STRENGTHEN WORK SURFACES
RELATED PATENTS
This application is a PCT International
application claiming benefit of U.S. Application Serial
No. 10/207,859 f fled July 31, 2002; which in turn in a
continuation-in-part of U.S. Application Serial Nos.
09/273,769 filed March 23, 1999, now U.S. Patent No.
6,289,736, and U.S. Application Serial No. 09/653,987
filed September 1, 2000, now U.S. Patent No. 6,458,225
Bl; the 1 atter application in turn being a continuation-
in-part of U.S. Application Serial No. 09/288,020 filed
April 8, 1999, now U.S. Patent No. 6,338,765 B1; which in
turn is a continuation-in-part of U.S. Application Serial
No. 09/14 5,992 f i led September 3, 1998, now U.S. Patent
No. 6, 171, 415 Bl .
FIELD OF INVENTION
This invention relates to methods of ultrasonic
impact machining of manufactured metallic bodies of
various shapes t o strengthen the surfaces and correct
external and int a rnal manufacturing defects and in-
service-generated fatigue defects, and related apparatus,
ultrasonic transducers and treated metallic bodies.
More particularly, the invention relates to
applicat ion of ultrasonic impact energy at various
external surface zone treatment configurations of a
metallic workpiec a with sets of ultrasonically driven
impact needles in an ultrasonic transducer configuration
relatively movabl a to scan the external working surface
of a workpiece body, such as a propeller, bearing or
other machine part, wherein small diameter, freely-moving
impact needles provide enough energy to modify parameters
and properties of the surface, and deform and compress
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impacted surface areas and adjacent sub-surface regions
to significant depths.
BACKGROUND OF INVENTION
The parent applications, which are incorporated
herein in entirety by reference, relate to some of the
ultrasonic system and method features herein disclosed.
Published background technology for the
application of ultrasonic impact energy to the surface of
polypropylene and thermoplastic materials for welding or
riveting, is evidenced by U.S. Patent No. 5,976,31 4
issued November 2, 1999, by Manfred Sans for DEVICE FOR
ULTRASONIC TREATMENT OF WORKPIECES. However, this
teaching does not disclose a feasible system for the
reworking of machined metal workpieces by ultrasonic
impact machining methods wherein the machined metal
surface and sub-surface thereunder is deformed to control
surface texture and workpiece hardness, as does tha
pre sent invention.
The application of ultrasonic energy to metal
weld joints, as disclosed by S. E. Jacke in U.S. Patent
No _ 3, 274, 033 issued September 20, 1966 for ULTRASONICS,
involves contacting an. ultrasonically oscillating
transducer horn directly upon a welded seam between
abutting thin titanium alloy panels to process welding
defects. However, this transducer horn system cannot
w de 1 fiver enough-power to a massive metal workpiece body to-
ef festively penetrate any considerable distance into sub-
surface areas for deforming and compressing the surface
and adjacent sub-surface regions and increasing the
strength of massive metal bodies, such as cast iron used
in various tool embodiments for compressive confrontation
of mating surfaces.
Various specialty ultrasonic metal working
impact tools, including hand operated transducers, are
disclosed in the prior art for surface deformation and
sub-surface plastici~ation of explicit shapes and
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contours, typically cylinders, rot ating surface segments
and planar sheets by direct mechanical interfacing of an
ultrasonically vibrating head with a metallic surface
work site. Typical disclosures are found in Russian
Inventor's Certificates including: SU 1447646 A1,
published December 30,1988; SU 126 3510 A2, published
October 15, 1986; SU 1756125 A1, published August 23,
1992; SU 1255405 Al, published September 7, 1986; SU
1576283 A, published July 7, 1990; SU 998104, published
January 5, 1981; SU 1214396 A, pub lished February 28,
1986; SU 1481044 A, published Sept ember 28, 1987; and
SU 1703417 A1, published January 7, 1982 relating to
direct mechanical contact between an oscillating
ultrasonic transducer head oscillating at the prescribed
ultrasonic frequency and the treat ed metallic object
surface. These ultrasonic transducers in general dispose
a..single directly driven impact e1 ement coupled to a
driving oscillator surface, which vibrates at a periodic
ultrasonic frequency as applied to treatment of a welded
structure to reduce welding defect s.
French Patent No. 2,662,180 filed May 7, 1991
relates to a system for applying ultrasonically impulse
energy for the special purpose of inducing plastic
surface deformation at weld sites to correct welding
defects in plastic materials. Thi s prior art system,
however, does not disclose satisfactory ultrasonic
machining methods or systems or an ultrasonic-transducer
structure as afforded by the present invention or any
structure or methods that could successfully develop and
control ultrasonic energy intensity sufficient for
general purpose ultrasonic impact machining by deforming
both surface and sub-surface structure to a significant
depth in a variety of working rote rface surface shapes of
massive metallic bodies for compre ssively confronting
mating surfaces .
Statnikov et al publishe d documents IIW XIII-
1617-96 and IIW XIII-1609-95 relat a to the state of the
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art of hand held tools for applying ultrasonic impact
energy directly from an oscillating transducer head at
the impacting resonant frequency of the driving .
oscillator. These transducers are special purpose
transducers with single impacting needles adapted to a
system configuration for achieving the particular
functional treatment of welded structure defects.
These prior art ultrasoni c transducer systems
have not provided satisfactory tools, systems or methods
for reworking and machining metalli c work interface
surfaces of various shapes employed in frictional
compressive and sliding cont act, such as presented in
rotary bearing surfaces, brake drums as well as sliding
and reciprocating engine cylfinders or wedges, propellers
and the like, thereby to deform surface and sub-surface
structure, hardness and texture for producing longer work
life while bearing increased compre s sive work loads.
In general, the prior art ultrasonic transducer
systems have not been able to provi de high enough readily
controlled impact power over .work interfaces of
considerable surface area on metallic workpiece
interfacing surfaces to precisely control both the
surface hardness and texture and the adjacent sub-surface
structure at significant working depths exceeding normal
wear tolerances. The prior art has produced ball peening
and ultrasonic transducer impacting systems with enough
power to .reach the material's yield points for
deformation treatment in the molten or plasticized state.
However, this invention produces enough ultrasonic impact
power to effectively reach the ultimate material strength
of the body, and thus modify, the surface layer.
Thus, such prior art systems and methods do not
provide substantially universal u1t rasonic transducer
systems and methods suitable in siz e, power and control
for achieving work functions, such as desirable for the
repair or manufacturing of metallic work interfacing
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surfaces for compressive confrontation with mating
surfaces. Nor is the prior art capable of plastically
deforming and compressing surface and adj acent sub-
surface regions to sufficient depths particularly for
machining a variety of different surface configurations
on massive metallic bodies thereby to attain specif zed
end structure in both surface and sub-surface regions of
a treated metallic workpiece. High power ultrasonic
transducers also must be confined in size to machine
internal cylindrical working surfaces of bearings,
keyways and t he 1 i ke .
Also, the ultrasonic transducer must be of a
nature to ultrasonically impact machine metallic obj ects
of various interacting surface shapes to greater depths .
For example, consider the problems of manufacturing
and/or repairing a propeller having critical surface
characteristics at blades, hubs and fillets of different
shapes and masses, and being subject to various kinds of
sub-surface defects, such as cavitation, corrosion, wear,
cracl~s and welding stresses, which would deteriorate the
reaction of marine propeller blade working surfaces in
underwater compressive and sliding interface with
saltwater. There has been no known successful multi-
function system or method for ultrasonic impact machining
of such diverse sets of conditions as incurred in the
manufacture and in-service repairs of marine propellers.
The typical prior art manufacture and repair of
marine propellers is expensive and complex and must
employ a series of incompatible treatment methods, such
as heat treatment of the metall is workpiece in a furnace,
which. cause defects which deteriorate the desired service
as a marine propeller. Propellers are conventionally
cast and left with sub-surface pores, cavities, cracks
and geometric deviation from design shape. Manufacturing
defects are detected by ultrasonic, X-ray, metric and
other non-destructive tests. Conventional repairs are
made by heat treatments and controlled cooling cycles,
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grinding, machining, welding depositions, and the like,
which in turn introduce new stresses, fatigue and
corrosive characteristics and are expensive and time
consuming. In particular, the heat treatments are
critical in the presence of transition surfaces, blade
thickness variations, uneven mass distributions, etc.
which tend to leave unevenly distributed thermal
deformations and unfavorable residual tensile stresses
that speed up corrosion, fatigue and wear failures in
service, particularly in salt water environments.
It is also necessary to introduce various
surface treatments after internal heat treatments, such
as to supply protective coatings on propeller blades and
the like, which in turn introduce surface imperfect ions
that interfere with work surface operation. For example,
required surface characteristics may range from in-
service optical smoothness to specified degrees of
surface roughness necessary to anchor an outer smoothing
layer, and there has been no known prior art ultrasonic
machining method or system for achieving this.
Thus, it is an object of this invention to
ultrasonically machine workpiece working interface
surfaces to achieve designated smoothness, hardness,
surface deformation, surface relief, compressive
stresses, friction, reflectivity and corrosion resistance
and to remove surface and sub-surface defects.
It is a primary objective of the invention to
employ ultrasonic impact surface and sub-surface plastic
deformation tools, systems and methods for improving
metallic workpiece surface strength while substantially
reducing manufacturing procedures and costs.
Improvements of propeller reliability using
ultrasonic impact machining is achieved by directing
aperiodic force impulses on the workpiece surface with a
freely axially moving impacting needle element driven
from a primary ultrasonic energy delivery surface
vibrating at the specified ultrasonic frequency.
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It is critical in such operations to produce
enough power for deforming surface and sub-surface
regions of a workpiece to necessary depths . The present
invention greatly increases output power by operation of
a transducer driven from a periodic ultrasonic frequency
energy source through a series of energy concentratiori
s tapes operable at interfacing higher harmonic resonarice
frequencies operable at a Q-factor increase and
significantly higher velocity imparted to needle-like
freely axially moving impacting elements.
OBJECTS OF THE INVENTION
It is, therefore, a primary object of this
invention to introduce novel multi-functional ultrasonic
impact machining methods, transducers and systems for
restructuring metallic workpiece working surfaces of
various configurations during manufacture or repair.
It is a concurrent obj ect of this invention to
treat metallic workpieces in final stage manufacturing
steps by replacing awkward and expensive furnace heating
treatments with ambient temperature ultrasonic impact
energy treatments at a workpiece surface, and to prepare
with an improved transducer array metallic workpiece
surfaces of different surface shapes for manufacturing'
steps for establishing specified modifications of surf ace
texture and adj acent sub-surface regions introduced of ter
conventional manufacturing procedures on metall 1c
workpieces, such as grinding, weld depositions, alloying
and deposition of protective coatings, etc.
Other objects, features and advantage s of the
present invention will be found throughout the follows.ng
descriptions, drawings and claims.
BRIEF DESCRIPTION OF THE INVENTION
Novel ultrasonic impact machining methods and
systems comprehensively treat both regularly-shaped,
planar and irregularly-shaped metallic workpiece world ng
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surfaces by subj eating the machined surfaces to
ultrasonic impact energy from high velocity, small
diameter needle-shaped impacting members . Thus, critical
working surface and adjacent sub-surface regions of
metallic workpieces, including marine propellers, are
plastically deformed to produce specified surface
textures and hardness and associated sub-surface
structural changes induced by surface impact . An
ultrasonic transducer provides a periodically osci llating
energy transfer interface to a set of small diameter
impacting needles that freely axially move into impact at
high velocity into the machined surface to release
sufficiently high energy to deform the workpiece ~to
greater depths than heretofore feasible. The impact
needles of the set are individually impelled from a
transducer oscillating surface operating at a single
specified ultrasonic frequency to impact the working
surface in a kinetic energy transfer relationship and
rebound in an aperiodically controlled mode or randomly.
Impact power of small diameter needles moving
independently from the driving transducer to the
workpiece in a free axial mode of movement permits very
high velocities and high energy derived from the
transducer periodic ultrasonic power source . This
results in enough impact power for both plastic surface
and sub-surface structural reconfiguration of heavy
metallic objects to significant depths. Because of the
small impact area, short impact time, duty cycle and the
heat absorbing characteristics of the metallic worl~piece,
surprisingly, during ultrasonic impact, the workpiece is
rapidly heated and cooled at a localized area at the
point of the impact and machined at ambient temperatures .
The workpiece after machining remains then at an ambient
temperature.
A transducer to workpiece interface is
established by operation of sets of impacting needles
which rebound from the work surface to the periodically
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ultrasonic oscillating driving anvil. This in effect
produces a broad-band work interface characteristic that
maximizes , working power output transferred by the
separate very high velocity needles instantaneously
impacting the surf ace from the periodically oscill ating
ultrasonic power generating source in accordance with the
advantageous kinet is energy impact relationship (W=mv2/2 )
utilized by this invention. Thus, the kinetic energy
delivered from the high velocity of the free flying
impact needle, being a function of v2, is much larger
than possible with the direct impact of the transducer
horn taught by Jacke and other direct transducer t o
workpiece interfacing systems of the prior art mentioned
above.
The mult iple increase of the oscillation
velocity of impact needles at the instant of impact is
due to the nonlinear relation between the oscillat ion
velocity and the gap between the needle butt and the
transducer head impact surface. Here the mass, "m",
which determines the impact energy at a certain velocity,
includes above all the mass of the transducer and the
mass of the needle reduced to the butt of the needle .
Moreover, the impact includes the ultrasonic
oscillations of the impact needle in the surface layer of
the material being treated together with the ultrasonic
transducer head impact surface during individual
ultrasonic impact . Such ultrasonic oscillations in turn
initiate in the treated material power ultrasonic waves
propagation of whi. ch creates individual ef f ects of
reduction in deformation resistance and relaxation in the
material being treated.
Thus, the depth of the ultrasonic impact
treatment in this case is determined by energies of
controlled ultrasonic impacts, ultrasonic deformations
and ultrasonic waves that are initiated in the wor3cpiece
during interface of the ultrasonic transducer, impact
needle and the workpiece .
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Critical to the output power delivery is a
series of mechanically interconnected serial stages in
the working transducer assembly, which is small in size
for portabl a and manual operations and thus adaptable to
use in rest rioted spaces, for providing excellent power
transfer efficiency from a basic periodic ultrasonic
source of power. A series of interconnected transducer
stages exhi biting respective mechanical resonances
harmonically related to the primary ultrasonic
oscillation frequency so that a much greater multiple of
that primary ultrasonic frequency thereby imparts a very
high velocity to the freely moving impact needles and
further produce a Q-factor amplification of the
oscillating system contributing to greater output power
from the available oscillator input power. Also, for
efficient transfer of power from the respective operating
stages of t he transducer, matched instantaneous
resistances are provided at the instantaneous loading
moment of operation when the freely axially movable
impact needle elements are driven by the transducer
oscillating surface vibrating at the primary ultrasonic
frequency aperiodically into the surface of the
workpiece .
This mode of operation provides the novel
thermal treatment to the workpiece to plasticize the
surface and sub-surface metal for the impact machining
improvement of the workpiece work surface strength and-
operating performance in the presence of working
compressive forces. Thus, the thermal machining in the
plastic state with impact forces compressing the
workpiece ( a . g. a propeller) metal surface layer produces
increased compressive working force capacity expended by
compressive 1y interfacing saltwater with mechanically
moving surf aces e.g. propeller blade surfaces, and the
operating life is lengthened.
A scanning system employing a lathe, surface
scanning system, or the like, for systematically scanning
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a movable transducer head over a prescribed scanning
pattern thus uniformly and in any specified way
distributes the individual impacts from the impacting
elements over select ed worl~piece surface zones, which may
have different interconnected surface shape
configurations depending upon the individual workpiece.
Accordingly, thi s invention provides novel
ultrasonic oscillating elements and operating methods and
novel ultrasonic impact machining modes for machining
interfacing working surfaces of various kinds of metallic
workpieces to effect plastic surface and sub-surface
deformation resulting in structural changes, and
increasing material hardne s s and service life.
These and other features and advantages of the
invention will be set forth with particularity throughout
the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings, similar reference
characters found in the several views represent similar
features to facilitate comparison.
FIGURE 1 is a block circuit diagram of the
ultrasonic impact surface treatment system of the
invention.
FIGURE 2 i s a diagrammatic sketch of the manner
of inducing compressive stresses at a working surface and
immediate sub-surface region in response to a set of
impacting elements.
FIGURE 3 i s a diagrammatic sketch illustrating
generation of ultrasonic impacts from a free flying
impact member obtaining one-sided impact driving energy
by abutment from an oscillating ultrasonic transducer
head to drive the impact member at high velocity as a
freely moving object for impacting a working surface
being ultrasonically machined.
FIGURE 4 is a diagrammatic representation of a
typical magnetostrictive u1 trasonic impact transducer
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assembly embodiment interfacing the exterior working
surface of a metallic workpiece.
FIGURE 5 is a representative diagrammatic
sketch of a cross-section of a multiple stage transducer
terminating in a set of impacting elements, which are
axi ally free to move at high velocity into a workpiece
surface in response to periodic impact by the transducer
int erf ace .
FIGURE 6 is a diagrammatic sketch illustrating
the impact interface of the freely moving needle
impacting elements of a typical set with the periodically
vibrating transducer driving surface to receive
oscillation energy for delivery to and impacting the
worl~piece surface in a controlled and random aperiodic
mode of operation.
FIGURE 7 is a diagrammatic sketch in cross-
section of a workpiece surface being scanned by impact
needles and deformed while in a plant is state by impact
tips of the needles during direct contact with an
ultrasonic impact transducer head and after impact of the
transducer head upon the needle in accordance with the
invention in the process of plastically deforming and
restructuring the workpiece surface.
FIGURE 8 is a sketch of a scanning mechanism
for moving the ultrasonic transducer and accompanying set
of impact elements over a selected workpiece zone in a
manner producing a uniform pattern over the surface (the
heat treatment of the workpiece not being shown) .
FIGURES 9A-9E illustrates a set of typical
worl~pieces having working surfaces of varied surface
configurations for providing compressive forces to mating
surfaces that require ultrasonic impact machining in
accordance with this invention for increasing work load
capacity and reducing manufacturing defects.
FIGURE 10 is a side view cross-section sketch
of a propeller blade workpiece to be ultrasonically
macYlined in accordance with this invention.
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FIGURE 11 is a side view cross-section sketch
of a propeller blade diagrammatically illustrating
regions to be subj ected to ultrason.i.c impact plastic
deformat ion to correct for manufacturing or service
defects, in accordance with one embodiment of the
invention .
FIGURE 12 diagrammatically explains the effect
on the material strength of a workp z ece body during work
under di f ferent temperatures .
FIGURE 13 is a diagrammat is representation of a
typical stress-strain curve for metallic components under
stress.
FIGURE 14 is a diagrammat is representation of
the various levels of deformation introduced into the
working surface of a workpiece as a result of the
ultrasonic machining process of the invention. This
represents two mating surfaces of a work body, the upper
body treated to a certain depth by ultrasonic impact
showing the effects of zones I, II and III, while the
lower body is not treated.
FIGURE 15 diagrammatically depicts the process
of the impacting needle elements on the working surface
of the workpiece during the machining process of this
invention .
FIGURE 16 shows the flow of a medium across a
smooth surface such as a propeller .
FIGURE 17 graphically dep scts the relationship
between the velocity of flow of a medium over a smooth
surface versus the distance from the surface.
FIGURE 18 graphically shoves the effect of the
velocity of flow on the distance between the local
surface vortex flow at the surface .
FIGURE 19 is a graphical representation showing
the dependence of cavitation erosion intensity on the
distance between the local surface vortex flow at the
surface
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FIGURE 20 is a graphical depiction of the
influence of velocity of flow at the surface on the
c avitation erosion intensity.
FIGURE 21 shows the effect of the macro - relief
alteration of the flow pattern over the surface of_ a
propeller after ultrasonic impact machining.
FIGURE 22 shows the effect of the micro - relief
alteration on the flow pattern across the surface of the
propeller after ultrasonic impact machining.
FIGURE 23 is a top view of the effect of the
f low of the liquid across the ultrasonic impact machined
surface taking into effect the altered surface profile
and micro- and macro-relief surface effects on tha flow
pattern.
DETAILED DESCRIPTION OF
THE PRESENTLY PREFERRED EMBODIMENTS
With reference to FIGURE 1 of the drawings,
this block system diagram identifies the ultrasonic
impact operating system for treating metallic worl~piece
surfaces, shown as work surface 13, by employing a set of
ultrasonically movable impacting elements 12, pre s ented
typically as sets of three or four spaced members , for
impacting the work surface 13 under control of the
ultrasonic transducer head 11. The periodic pulse energy
source 10, typically operable at ultrasonic frequencies
up to 100 kHz, induces oscillations into the transducer
head 11, preferably subject to feedback frequency and
phase control 14 processing feedback from the working
t ransducer head 11 to aid in matching resonance
characteristics of the head when working on the work
surface 13 in the manner more particularly set forth in
the parent applications.
In FIGURE 2 , the impacting element set 12 '
creates at the work surface 13 and extending into the
sub-surface region 17 of a metallic work body 15,
plasticized metal permitting the surface texture to be
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machined and sub-surface structural modifications in the
work body 15 material to be retained. This effec t is
diagrammatically shown at sub-surface region 17 a s
separate working regions for the three impacting elements
of the set 12' deforming the sub-surface metal to a depth
determined by the impact power of the individual impact
elements in the set 12'. The resulting deformati on,
typically compressive stress patterns, are merged over
the entire workpiece surface being treated by appropriate
scanning of the transducer across the selected workpiece
surface by a scanning mechanism, such as a lathe or a
scanning mechanism of the nature described below and
shown in FIGURE 8.
The scanning device 20 in FIGURE 8 comprises a
"universal joint"-type of mechanism for carrying a
transducer with the set of impact elements 12 arranged to
forcefully contact and scan a two or three dimens i onal
workpiece surface treatment zone 21 in a regular pattern.
The delivery heads of impact elements 12 deliver the
required impact energy from the individual impact
elements of the set to plastically deform increments of
the metal workpiece which are integrated into a
substantially uniform ultrasonic impact machining pattern
across the scanning area for producing a predetermined
combination of specified internal residual deformations,
typically compressed sub-surface metal strengthens ng the
metal for accomplishing its interfacing work funs t ion at
a confronting work surface and tailored surface texture
finishing characteristics. Those skilled in the art may
automate the scanning procedure and provide selec t ed
scanning patterns depending upon the workpiece shape or
functional operation in interfacing with a corresponding
work surface or medium.
It is seen therefore that at ultrasonic
frequencies up to 100 kHz with relative scanning of the
impacting element set 12 about the work surface 1 3, at
appropriate scanning rates, substantially uniform
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compressed surface structure and texture will be induced
over the entire scanned treatment zone 21 (see FIGURE 8) ,
and the sub-surface metal will be .compressed to a depth
that exceeds the maximum wear expectations of the
workpiece being processed _ In this process, the
ultrasonic impacts result in instantaneous high
temperature with a rapid heating and cooling effect at
the point of impact from s ndividual impacting elements
that plastically deform the surface to establish a
surface texture and sub-surface compression layer that
hardens in place uniforml y across the work surface of the
workpiece as the scanner moves and thus distributes the
impacting energy over the workpiece work surface to
machine the workpiece whi 1 a in the plasticized state.
This impact treatment zone 21 is characterized by
residual compression stresses at the surface and in the
adjacent sub-surface region, which are readily controlled
to comply with the working specifications of various
workpieces or workpiece regions by choices of oscillator
energy and frequency, impact duty cycle, needle mass and
velocity, and the like, thereby to produce specified
surface texture and sub-surface deformation typically
during reworking of cast and previously conventionally
machined metallic workpie ces in final manufacturing
stages and repair or maintenance procedures encountered
during the working life o f the workpieces.
For achieving substantially greater transducer
11 to work surface 13 energy transfer and to control or
randomize the time of impacts of individual impacting
elements 12 on the work surface 13, the free axial
movement mode of operation with freely axially moving
impact member 12" characterized by the diagrammatic view
of FIGURE 3 is of significance in the present invention .
Thus, the free flying impact member 12" , by abutting the
ultrasonically oscillating transducer head 11 impact
surface 18, is impacted t o receive kinetic energy and
propel the impact member 1 2" at high velocity toward the
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work surface 13 as a free flying member to convert its
kinetic energy upon the work surface 13, thereby
releasing enough energy upon the work surface 13 to
texture and compress that surface and adjacent sub-
surface regions while the metal workpiece, is in its
plastic state. The impact member after delivering its
energy to the workpie ce work surface 13 then rebounds off
work surface 13 for a further energy receiving impact
cycle with the transducer head impact surface 18. This
results in controlled or random aperiodic impacts of the
free flying impact member 12" , which respond
aperiodically to surf ace characteristics of the workpiece
as the impact member 12" rebounds and contacts the
transducer head impact surface 18 at various phases
during the periodic oscillations of transducer 11.
As later discussed with reference to FIGURE 6,
the transducer and it s set of freely axially moving
impact needles indivi dually driven from a periodically
ultrasonically vibrating transducer driving surface
produces great er needl a kinetic energy than prior art
transducers and transfers power to the independent impact
member 12" randomly and aperiodically from the
periodically vibrating ultrasonic frequency of the
workpiece driving surface.
The multipl a increase of the oscillation
velocity of impact needles at the instant of impact is
due to the nonlinear relation between the oscillation
velocity and the gap between the butt of the needle 12
and the head of the transducer 11. Here the mass, "m",
which determines the impact energy at a certain velocity,
includes above all the mass of the transducer 11 and the
mass of the needle 12 reduced to the butt of the needle.
Moreover, the impact includes the ultrasonic
oscillations of the impact needle 12 in the surface layer
of the material being treated 13 jointly with the
ultrasonic transducer head 11 during individual
ultrasonic impact. Such ultrasonic oscillations in turn
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ini t late in the treated material power ultrasonic waves
propagation which creates individual effects of
deformation resistance reduction and relaxation in the
material being treated.
Thus, the depth of the ultrasonic impac t
treatment in this case is determined by an energy of
controlled ultrasonic impacts, ultrasonic deformations
and ultrasonic waves that are initiated in the workpiece
during periodic controlled or random contact of the
ultrasonic transducer 11, impact needle 12 and workpiece
13 .
This method of treatment of metallic working
surface 13 thus permits work surfaces of diverse shapes,
masses and surface characteristics with an ultrasonic
transducer head 11 supplied with a set of ultrasonic
impact members 12" impacting the workpiece at ext a rnal
surface locations then efficiently induces ultrasonic
surface impact machining by deforming the surface and
adj acent sub-surface region for achieving specified
surface and sub-surface conditions including compression
of the workpiece material for inducing greater hardness
and longer life expectancy for subj ecting the worl~piece
work surfaces to surface resistance, medium contact and
wear encountered in designated work environment
conditions of encountering mating surfaces in a
compressive embrace .
The plan view transducer configuration o f
FIGURE 4 looks downwardly toward the metallic three
dimensionally-shaped workpiece 25, which typically
pre s ents a conventionally ground or machined surface
texture and is retained in a suitable mechanical holder
26. The portable and free axially moving transducer 27
oscillates at a prescribed ultrasonic frequency from a
remote oscillator energy source (10 in FIGURE 1) by way
of the magnetostrictive converter 28 with energizing
coi 1 s 29, comprising a first sequential operating stage
I. The intermediate stage II is preferably a re-
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placeable waveguide 30 for concentrating the incoming
ultrasonic energy vibrations of a particular frequency to
impact and drive the indenter element (s) 31 of the third
stage III, which in turn ultrasonically plasticizes and
compresses the metallic workpiece 25 (stage IV) .
Preferably the indenter element (s) are sets of needles
operating in the mode illustrated in FIGURE 3 for
assuring sufficiently high velocity impact energy to
control sub-surface workpiece structure to significant
enough depths to improve the output strength of the
particular worl~pieces being processed.
Thus, this invention comprises a multi-stage
transducer array terminating in an impact delivery head
driven by an ultrasonically oscillating transducer power
delivery stage through an abutting intermediary waveguide
transformation stage. The impact producing stage
elements, preferably comprise a set of freely axially
movable impacting elements which individually randomly
and in a controlled aperiodic mode convert the
instantaneous periodic delivery of energy from the
ultrasonic energy driving system to impact individual
elements in the set when striking the workpiece surface
to deliver their energy derived from the oscillating
transducer power source. These impacting elements then
rebound to engage the transducer for delivery of a
subsequent energy stroke from an abutting periodically
oscillating transducer energy delivery interface surface
in a random or controlled phase of its oscillation cycle.
In view of different lengths of movement of the freely
axially movable impacting needle elements of a set
between the transducer energy delivery interface surface
and the workpiece surface to occur at different
oscillation phases, and subj ect to the topography of the
workpiece surface, the individual striking needles of a
set act independently and not in periodic unison for
delivery of the transferred energy from the impacting
elements to the workpiece surface.
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The efficiency of the transducer devices as
referenced in FIGURES 4 and 5, and their methods of use
for achieving necessary energy to plasticize and compress
metallic workpieces i s dependent upon ef f icient and
coordinated interfacing of several transducer stages to
transmit ultrasonic oscillations between the energy
producing ultrasonic generator and to concentrate
available oscillator energy onto the impact needle
elements for striking and plasticizing the metallic
workpiece at an external surface work zone . Thus, the
transducer configuration is critical.
For example , the structures of the transducer
assembly multiple stages I+II, III, and IV in FIGURE 4
and equivalent stages 2 , 4 and 1 in FIGURE 5, a1 1 have
inherent natural mechanical resonance response
characteristics . Thus, in accordance with this
invention, the various transducer stages are tai lored to
present resonance frequencies related to the fundamental
ultrasonic oscillation frequency produced at the
magnetostrictive converter 28. In this respect, the
natural frequency of stages II, III and IV of the FIGURE
4 transducer assembly and corresponding stages 2 , 4 and 1
of the FIGURE 5 transducer assembly are individually
tuned to a natural resonance frequency which is a
multiple of the fundamental ultrasonic oscillation
frequency. This concentrates the oscillating velocity to
the impacting elements and vibrates them at a much higher
speed so that the energy of oscillation transferred to
the ~..mpacting needles is maximized. Consider that when
the resulting working frequency of the impact needles is
at harmonic frequencies much higher than the basic
ultrasonic oscillator frequency this imparts a higher
impact needle velocity v, and makes the v2 kinetic energy
component of the impacting element deliver enough energy
to plasticize the surface material of the workp.iece to a
significant working depth below the impact surface and
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compresses the workpiece body at an energy level equal to
or above the ultimate material strength.
Further, the transducer stages are designed
with the instantaneous acting resistance of the separate
stages at the instant of contacting an indenter element
for a power impact cycle which is related to both the
instantaneous stresses in the various stages (U) and the
instantaneous oscillating velocities (V) reduced to the
contact points of the indenter elements by the ratio U/V,
which is equal for each stage. This assures effective
maximum power transfer of the energy of oscillation from
stage to stage .
With reference to FIGURE 5, the resistance of
the various stages are equalised as expressed in the
fol 1 owing equation: R=U1/V1=U2/V2=U3/V3=U4/V4. This
invention, therefore, contemplates establishing an
instantaneous active resistance R when the impact energy
delivery head contacts an indenter element substantially
equal to the instant active resistance at the respective
individual multiple stages.
In FIGURE 5, the oscillating system presented
thereat includes : tool 3 with transducer and oscillating
velocity transformer 2, indenter elements 4 and
workpiece 1. An energy balance in such a system is
determined by the equality of kinetic energy at the
output of the system and the potential energy stored by
the workpiece due to plastic deformation of its treated
surface, ultrasonic deformations and relaxation of the
workpiece material in the ultrasonic wave as described
above . Generally and functional ly, the equation of the
energy bal ante can be written as follows:
M3 (V3 ) 2/2 + M4 (V4 ) 2/2 + M1 (V1 ) 2/2 = C1 (X1) 2/2 ,
where
M (1, 3 and 4) are the respective equivalent
masses of the workpiece, tool and indenter elements
reduced to the impact points on the workpiece surface;
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V (1, 3 and 4) are the respective maximum
oscillating velocities of the workpiece, tool and
indenter elements in the impact points on the workpiece
surface ;
C1 is the equivalent elastic factor of the
workpiece reduced to the impact points on the workpiece
surface ;
X1 is the equivalent elastic deformation of the
workpiece caused by equivalent plastic deformations of
the worl~piece, ultrasonic deformations and relaxation of
the worl~piece material in the ultrasonic wave initiated
in the workpiece by the ultrasonic impact.
It should be noted that each indenter element
of Figure 5 excites oscillations of a new "added" mass in
the wor7~piece, thereby increasing the equivalent mass M1,
and hence the kinetic energy is reduced to the point
(points ) of the impact (impacts) . According to the
energy balance equation, increase in kinetic energy of
the impact (impacts) results in the increase of the
energy induced to the surface and the material of the
workpiece, which in turn is equivalent to the potential
energy stored by the workpiece during ultrasonic impact.
The results obtained from the given process include
increas a of treatment depth, increase of induced
compres live stresses and their level in the region of the
material ultimate strength, optimization of the phase and
crystal- - structure of the workpiece material, a spatial
component of regular macro- and micro-relief of the
treated surface.
Now with further reference to FIGURE 5,
identifying the overall movable transducer casing 3,
including the force of the spring urging the transducer
into the work surface, the transducer assembly 2, the
indenter elements 4 and the workpiece 1, the various
coordinated oscillating systems are employed to attain
appropriate designated ultrasonic impact of the surface
of the vuorkpiece 1 uniformly over a scanning pattern
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while achieving controllable surface smoothness,
hardness, compressive stresses and surface shaping as
well as corresponding sub-surface removal of defects
including the replacement of residual tensile stresses
with compressive stresses and corrective machining, etc.
as achieved in the plasticization procedure induced by
the impact treatment.
Thus, by establishing in a mufti-stage
transducer array of a set of interfacing stages having
respective natural resonance characteristics harmonically
related to the ultrasonic frequency from the driving
energy from said energy driving system, massive metallic
worl~pieces can be plasticized below the surface to
achieve designated specifications, particularly with
respect to the repair of manufacturing tool marks and
other residual defects. This invention provides improved
ultrasonic impact methods for plastically deforming the
sub-surface metal, preparing the workpiece surface zone
texture for such tasks as receiving a protective coating,
or for introducing specific surface and sub-surface
macro-relief and micro-relief surface texture patterns,
plastically deforming the sub-surface metal to eliminate
inter-granular irregularities, plastically deforming and
compressing the sub-surface metal to conform the surface
conf.zguration of the workpiece to selected
specifications, plastically deforming the sub-surface
metal to compress a workpiece surface layer to a
significant depth and to preserve residual compressive
forces introduced by such treatment, to increase
dimensional stability, fatigue, dynamic and thermocyclic
life and other induced modifications of massive metallic
worl~pieces of the nature hereinafter set forth in
specific examples.
In FIGURE 6, the diagrammatic showing of the
indenter elements 4 of FIGURE 5 encompasses the freely
axial ly moveable impact members 12 " discussed in
connection with FIGURE 3. The manner in which these sets
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of indenter elements achieve random or controlled
aperiodic energy delivery impacts upon the workpiece
surface 1 when indenter elements are driven by a
transducer impact surface 36 and can oscillate between
the impact surface 36 and the workpiece surface 1 at a
periodic ultrasonic frequency much higher than the basic
ultrasonic power oscillation frequency is illustrated.
Thus, a selected individual indenter element 35 is shown
in its freely movable axial mode for receiving l~inetic
energy during the impacting operation induced by the
abutting oscillating transducer surface 36, which
vibrates between the upper two horizontal lines as the
workpiece i.s scanned by the transducer head in the
direction of treatment 37. The indenter element 35 is
shown in various phase positions relative to the periodic
driving source as the transducer travels to the right in
the direction of treatment 37 along the workpiece surface
1 in response to the various positions of the transducer
surface 36 and the topography of the workpiece surface 1.
At 38 the indenter element is shown in free flight after
contact with the workpiece surface 1 to deliver its
kinetic energy of ter its excursion induced by contacting
the transducer surface 36, at a phase between vibrating
limits 39 and 40 for different vibrating positions or
phases of the transducer abutment surface 36. In
abutment with the oscillating transducer, the indenter
element 35 at vibrating limit 39 receives energy transfer
from the ultrasonic energy source driving transducer. It
is, therefore, seen that the indenter element 35 ,
depending on the boundary conditions on the surface 36,
may vibrate both controllably and randomly, but
aperiodically even though the transducer driving output
surface only periodically vibrates . In this manner, the
indenter element 3 5 strikes the workpiece surface 1
randomly or controllably to deliver its energy and
thereafter rebounds from the workpiece surface 1 at
instants determined by relative positions respectively of
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the oscillating transducer surface 36 and the macro- or
micro-relief pattern exhibited on the workpiece surface
1 . This feature thus introduces a novel mode of
ultrasonic impact machining of heavy metallic workpieces,
which is controllable in nature and therefore applicable
to diverse workpiece surfaces and different workpiece
masses, surface characteristics and wor7~piece shapes as
ultrasonic impact energy is delivered by individual
indenter elements 35, etc. within the sat of indenter
a 1 ement array 4 .
Now with reference to the diagrammatic view of
the workpiece surface 1 in the machining' process of the
invention as exemplified in FIGURE 7, the ripples 45
represent an initial state presenting tool marks on the
surface being treated before ultrasonic impact machining
plasticizes and smooths the surface 1 of the workpiece,
typically carrying residual tool mark defects encountered
in manufacturing steps, such as tooling or grinding the
workpiece surface. The resulting plasticized workpiece
surface 1 in the ultrasonic impact treatment process of
the invention displays a micro-relief or macro-relief
pattern provided by plasticizing the workpiece metal on
the surface at a selected contact zone and extending into
its associated sub-surface region respectively resulting
in either plastically smoothed or roughened workpiece
surfaces and a compressed sub-surface workpiece layer
extending to a depth greater than the designated wear
depth of the workpiece surface being machined.
It is significant here that the resulting
workpiece will be hardened above its yield point and
substantially to its ultimate strength extending through
the sub-surface depth being treated, as more specifically
set forth in the parent application Ser.zal No. 09/653, 987
directed to the specific embodiment of drum braking
systems. Also it is significant that the workpiece is
machined at ambient temperatures, made possible by the
instantaneous nature of the impact by the impact needles
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over a small surface of the workpiece body area at a duty
cycle such that the thermal energy is quickly absorbed in
the worl~piece body as a heat sink, to thereby permit
ultrasonic machining of a workpiece at substantially
ambient temperatures .
In FIGURES 9A-9E, various typical metallic
workpiece surface shapes for mechanically interfacing in
a designated work function with other surfaces and media
in operation are shown. These workpiece working surfaces
are typically subjected to surface resistance; medium
contact ; fatigue and wear when exposed to designated work
environment conditions as machine elements, structural
elements and the like; and compressive forces when
interfacing with a mating surface . The ultrasonic impact
deformation machining method as provided by the invention
for achieving a provides the required level of local
thermomechanical effect on the material structure
necessary to establish specified levels of resistance to
frictional wear, contact fracture, cyclic failure,
thermocyclic fatigue, corrosive fatigue, magnetization
and undesirable shape deformation. This is realized by
achieving specified and improved hardness , roughness,
residual stresses, contact strength, fatigue limits,
friction factors, reflectivity and corrosion resistance.
The employed technical operations of the present
invention include thermal processing, plasticization, and
compression of an outer wo-rkpiece metal layer by these
ultrasonic machining impact procedures for heat
treatment, surface alloying or other changes of texture
and characteristics of surface materials, for example,
establishing protective coatings with specified surface
texture including polishing and burnishing, and removal
of resident defects. We have determined that the
ultrasonic impact machining methods of this invention
provide ~ through plasticization of the workpiece metal in
response to ultrasonic impact surface treatment and
compression, a novel surface layer and adjacent sub-
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surface region extending to greater depths to
substantially realize the ultimate workpiece body
strength, and thus significantly improve service life
over the prior art methods, such as ball peeving, which
cannot realize a workpiece body strength greater than the
y.zeld point at which the metal is plasticized.
Thus, this invention provides improved methods
of treating metallic workpiece working surfaces of
diverse shapes and masses, such as shown in FIGURES 10
and 11, with a set of ultrasonic impact elements treating
the workpiece at external surface zones to induce surface
and sub-surface modifications, thereby removing
structural defects and achieving specified surface zone
conditions, work interface surface hardness and longer
life expectancy of the workpiece under service conditions
of forceful surface to medium or surface to mating part
compressive forces in either static or sliding contact
conditions and interfacing with other external
deterioration forces including corrosion and thermo-
mechanical fatigue, for example.
The representative surfaces illustrated in
FIGURES 9A through 9E show several examples of the work
interface surfaces for encountering mating surfaces in a
compression and sliding mode of action that are addressed
by this invention, including cylindrical surfaces, such
as rotary bearing surfaces 50, fillets 51 and flat spots
52 representing clutching surfaces, which may be
superimposed adjacent to or upon the cylindrical surface
shapes . Flat surfaces with tapered edges 53 as found in
wedges, dowels and gibes and flat sheets 54 representing
other types of surface structures used, for example, as
structural gs.rders encountering static residence
compressive forces such as vibration, loading and
corrosion. The working surface encounters local thermo-
mechanical plasticization to modify the surface texture
and to extend into compression layers to produce greater
surface strength induced by ultrasonic impact machining
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methods of this invent s. on. Also workpieces of complex
shapes , such as machine parts, guideways 55 and
propellers as shown in FIGURES 10 and 11, offer different
curvatures, masses and angular projections at interfacing
work surfaces, which may be subj ected to thermal
plasticization and ultrasonic machining by the improved
ultrasonic transducer and impact methods of this
invent ion .
The propeller workpiece of FIGURES 10 and 11 is
presented as a workpiece embodiment of the invention
exhibiting various surface configurations which are
subjected to illustrate various initial conventional
machining operations in initial manufacturing steps,
which are machined in the final manufacturing stages by
the ultrasonic impact methods of this invention. This
type of metallic workpiece object is machined by
ultrasonic impact surface machining that induces surface
and sub-surface plasticization and compressive forces to
control the surface and sub-surface texture and interface
strength beyond the yie 1d strength of the workpiece body
metal approaching the ultimate metal strength. The
machined workpiece surfaces are characterized by a
distributed pattern of compressed indentations at the
impact element contact areas .
Referring now to FIGURE 10, the propeller 60,
which constitutes a metallic casting, is shown diagram-
matically in cross-sects.onal view with blades 61
extending from the hub 62. The fillets 63, 64 that
appear on the rear surface are identified by the
respective dotted line pairs. The main blade portion is
shown in FIGURE 11. The alternative dotted hatching
pattern 66 represents areas reworked in the manufacturing
process where defective portions are removed by grinding
before heat treatment and weld repairs 71 and surface
coatings 69 are introduced, for example in .prior
manufacturing steps. Residual defective and weak
portions are, in accordance with this invention, machined
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by ultrasonic local thermomechanical surface impact
treatment of superior magnitude, which plasticizes and
compresses an outer layer of the workpiece metal surface
including adj acent sub-surface areas .
The improved methodology of this invention thus
is employed, for example, to rectify defects caused by
weld repairs, internal voids and cracks, thermal and
corrosive deformation gradients of the base metals and
propeller blade, by machining fillet and hub shapes and
surface configurations to replace conventional
manufacturing steps and heat treatment operat ions. The
ultrasonic impact thermal treatment of this invention is
attained at ambient workpiece temperatures to
redistribute compression stresses and eliminate tension
stresses incurred in rectification of the above-mentioned
defects by welding, grinding and shaping of the propeller
surfaces while reforming the surface texture and
compressing the metal in an outer layer of considerable
depth to provide greater strength and longer life. The
stress gradients at welds and boundaries between
propeller structural components of different
configuration imposed by manufacturing impact treatment
steps to localized thermomechanical treatment thus are
processed to rectify propeller defects and increase
operational strength. Propeller reliability is increased
by the methodology of this invention by decreasing motion
resistance strength-in water, reducing cavitation defects
and increasing fatigue resistance, maximizing' corrosion
fatigue strength and equalizing the strength between
propeller components, such as the blades and the hub.
Also the surface treatments afforded by this invention
improve corrosion resistance in the presence of saltwater
and reduce parasitic blade oscillations under variable
amplitude hydrodynamic loading conditions. The metal
strength of the work interface is substantially increased
to withstand compressive forces up to the u1t imate
workpiece metal body strength. Furthermore, this
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methodology when introduced in the final manufacturing
stages reduces manufacturing complexity and tooling
costs, thus significantly decreasing propeller
manufacturing and repair costs over the conventional
processing methods of the prior art.
This prior state of the art for solving
propeller endurance problems, including heat treatment
processes, has been outlined, for example, by N _ N.
Sokolov et al, Stainless Steel Propellers, Sudpromgiz,
Leningrad 1960; Solokov et al, Propellers in Aluminum
Bronze, Sudostroenie, Leningrad, 1971; and I. I _ Bogoraz
et al, Propeller Manufacture Reference Book,
Sudostroenie, Leningrad, 1978. Strain hardening methods,
such as hammer and shot peening, applied to the surface
of blades, fillets and a hub are found in I. I. Bogoraz
et al, Propeller Manufacture Reference Book,
Sudostroenie, Leningrad, 1978; and E. V. Zvyagintsev et
al, Controllable Pitch Marine Propellers, Sudostroenie,
Leningrad, 1966. These methods produce compressive
stresses on the propeller surface. However, by their.
physical nature are devoid of treatment ~ parameter control
technology, which can give a specified surface smoothness
so important on the propeller propulsion surface .
This invention using the ultrasonic impact
technology set forth in my document IIW Doc. XI=I-1857-
99, Lisbon, 1999 is based on the improvement of
transforming harmonic oscillations of an ultrasonic
transducer into controlled aperiodic impulses of force on
the surface being treated. This can be accomplished with
low energy intensity not more than 2000W, high specific
power, not lower than 300W/cm2 with mobile equipment,
with a tool weight depending upon transducer frequency
and power, between 200 g to 2.5 kg in the frequency range
from 44 to 27 kHz. These improvements also permit fine
adjustments and automated controls of treatment
parameters, impact intensity and treated surface quality.
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Some of the main characteristics of propellers,
as primarily governed by condi dons and propert ies of
surfaces of the blades, hub and fillets, when intended to
operat a in an aggressive and harsh saltwater environment
include : motion resistance in water, cavitation strength,
fatigue resistance, corrosion control, equalized strength
of blades and hub, reasonable costs for manufacture and
repair, etc. The range of defects to be treated and
repaired include : sub-surface pores, shrinkage and
blowholes, inter-granular cracks and hairlines, geometric
deviations from the design shapes and size of blades
fillet s , hubs, etc . Well -known conventional prior art
techniques remove the above defects by machining, arc
welding, subjecting to machining followed by furnace heat
treatment at the thermal tempering temperature of no
lower than 600 °C for not less than 6 hours . Thi s
invention rectifies all of those defects of machining
followed by welding using ultrasonic impact treatment .
In this case, the furnace heat treatment step is omitted
and energy saving of no less than 10, 000 kW per each
propeller is achieved with a blade diameter more than 3
m. Propellers ranging from spans of 300 mm to 12, 000 mm
or larger need to be handled. Defects in the vicinity of
fillets and sharp direction changes are ideally treated
with 1 fight mobile impact transducer tool assembl ies such
as set forth in FIGURE 5. Mechanized scanning means such
as shown in FIGURE 8 assure uniform ultrasonic impact
treatment of selected treatment zones and are adaptable
by those skilled in the art for associated automated
timing and energy control systems responsive to the
workpiece nature, shape and obj ectives of the thermal
treatment, which is successfully replaced by ultrasonic
impact treatment.
Now,. as will be seen by specific reference to
the propeller in FIGURE 11, wherein defects have been
determined by ultrasonic, X-ray, fluorescent and/or other
non-destructive and introscopy tests following
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conventional manufacturing steps of coating, heating,
grinding, machining, welding and removal or deposition of
propeller body metal, the usually portable ultrasonic
impact transducers are employed for ultrasonic local
impact thermomechanical plastification of the surface and
sub-surface regions of a treatment zone to remove
defects, produce specified surface texture and strength
and improve performance life of the propeller in service _
The conventional prior art heat treatments of
the entire propeller body in a furnace subj ects the
various masses, shapes and region boundaries encountered
in a propeller to different residual stresses and thermal
deformations which impair the propeller performance in
both long time and short time desired service functions .
The prior art step of grinding of propeller surfaces, not=
only creates undesirable surface roughness
characteristics and also establishes unwanted surface
tensile stresses thus causing natural surface damage,
which invites corrosion under action of variable
amplitude hydrodynamic loading in the presence of
saltwater. This deficiency is corrected by the present
invention by producing a plasticized controllable surface
condition by ultrasonic thermomechanical impact of sets
of impacting elements controllably as well as randomly
and aperiodically striking the surface as it is scanned
over a given treatment pattern in a given treatment zone _
Thus, in FIGURE 11, the propeller 60 presents
blade 61, hub 62 , and fillet (63, 64, FIGURE 10) surfaces
of different masses and shapes that may be subjected to
ultrasonic impact treatment both in surface and sub-
surface regions of the blade using the above-mentioned
transducer (tool ) and in accordance with the methodology
of this invention. The propeller 60 thus, is also
representative of other metallic workpiece bodies having
various shapes and mass distributions and displaying
surface zones presented for forceful interfacing with
other media or metallic bodies of the nature set forth in_
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FIGURE 9, for example, thereby to establish specified
levels of resistance to frictional wear, cracks, fatigue
failure, corrosion, tensile stresses and surface
irregularities . The surface zones of these metallic
bodies are thus scanned with sets of impact needle
indenters having freedom of individual relative axial
movement over a specified range of movement in response
to abutment with an oscillating ultrasonic transducer
energy driving surface to induce the increased magnitude
of kinetic energy necessary for plasticizing and
compressing surface and sub-surface regions of the
metallic body to significant depths thereby to control
surface shape, roughness, hardness, compressive stresses,
contact strength, fatigue limits, grain structure,
corrosion resistance and to eliminate sub-surface
defects. These needle impact elements thus operate in
the mode of operation illustrated by FIGURE 6.
Thus, the present methods of ultrasonic impact
plasticization of a metallic workpiece body produce the
required energy to metallic body surface from an energy
producing ultrasonic oscillating system thus to
forcefully abut a set of impacting elements onto a
workpiece surface zone at high velocity. The translated
energy is readily controlled to meet specified results
with appropriate masses and velocities of the impacting
needles, the ultrasonic frequency and amplitude, etc _
The preferred embodiment is characterized by an
interfacing energy transducer presenting a physically
interconnected series of coordinated serially disposed
interfacing sub-systems as hereinbefore described. These
sub-systems each have individual natural resonant
characteristics chosen as a multiple of the specified
single primary ultrasonic frequency from a pulse energy
driving source thus by action of induced natural resonant
OSC111ations from the available ultrasonic energy source
significantly increasing and concentrating the output
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energy available for delivery to the set of impact ing
elements at the surface of the workpiece being machined.
Individual indenter elements with axial freedom of
movement located in the transducer head indenter set,
when thus oscillating in response to abutment with a
transducer energy driving surface oscillating at the
primary ultrasonic frequency, thereby impact the surface
of the workpiece in a controlled and random asymmetric
pattern with enough energy to plasticize sub-surface
metal regions in the workpiece bodies . This treatment of
the workpiece surface in a novel manner produces either
smoother or rougher surface characteristics as desired
during the plasticization phase of operation. Sub-
surface treatment , followed by hardening of the
plasticized workpiece treatment zones, preserves
important compression force characteristics and presents
a compressed metallic surface layer for encountering
forces exceeding the yield strength. of the workpiece
metal, such as cast iron. Different elements of the
workpiece, joined for example by fillets, are compatibly
treated to reduced stress conditions for improving the
workpiece performance and life.
These features and advantages of the invention
are related in particular to the specific propeller 60 of
FIGURE 11, wherein the "as-cast" main section 70 of the
propeller blade 61 has been filled with added metal 71,
such as- by weld deposition 72. This leaves undesirable
internal tension stresses near the weld joint interfaces
which are alleviated by the ultrasonic plasticizati.on
impact machining methodology of this invention applied to
selected propeller blade surface zones after the welding
and grinding operations are performed in a conventional
manner.
As mentioned above, this invention allows
omitting propeller heat treatment applied after welding
areas of removed defects, provides for relaxation and
reduction of welding residual stress level, propeller
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dimensional stability in service, geometrical accuracy
specified by the drawing, and increases fatigue and
corrosion resistance .
Blowhole defects 73 appearing in the
restructured original casting are eliminated by machining
followed by welding and treatment of the deposited metal
by the ultrasonic plasticization impact machining
methodology of this invention. Similarly, pore clusters
74, inter-granular cracks and interface defects 75,
welding seam defects 76, and integration of casting
interface surfaces with added material 77, are machined
by the plasticization of sub-surface regions with
surface-induced ultrasonic impacts delivered randomly by
a set of individual freely axially movable impact
needles. Thus, residual welding stresses are relaxed by
the surface impact of the set of controlled and randomly
striking freely axially movable indenters in the vicinity
of the welded zones , as provided by this invention.
Also, the interfaces of blade, hub and fillet surfaces
are treated to relax residual manufacturing stresses and
to produce a requisite more corrosive resistant surface,
f or example by producing a higher strength compressed
surface and sub-surface outer layer.
Now the more general nature of the machining
process of this invention and of the machined product
produced thereby is set forth. Thus, reference i.s made
to the- strength-strain diagram of FIGURE 12 representing
the dependence of the plastic zone upon temperature for
cast iron metal wor7~pieces when loaded during their
designated service, for example, during compression for a
rotatable bearing, and when the base metal of the
workpiece is processed by the ultrasonic machining
methods of the invention. The material yield strength S
for different temperatures are shown on the curve. Thus,
at 100°C, the yield strength of the working material
decreases to 73% of the material yield point at ambient
temperature (20°C) . It is then of significant advantage
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to machine the workpiece metal at ambient temperatures as
achieved by this invention, to be addressed in more
detail later with reference to FIGURE 15.
With reference to FIGURE 13, the classical
stress-strain curve for workpiece material is illustrated
with stress force F indicated on the vertical axis and
deformation indicated on the horizontal axis. The curve
represents three zones of deformation (I, II, and III)
that are pertinent to the machining and service operation
of the workpiece surfaces subj ected to compressive and
sl iding forces when interfacing mating surfaces . This
ultrasonic machining process imparts deformation to the
surface in the zone closest to the ultimate strength of
the metal material which is depicted as zone III on the
curve by compressing the metal , whereas prior art
methods, such. as peening, work at the plastic state of
the working piece metal , namely the zone I I lower
magnitude yield point .
In FIGURE 14, two mating surfaces 78 and 79 of
a metallic workpiece are depicted wherein the various
levels of deformation introduced into the workpiece
surface 78 following treatment under the ultrasonic
impact machining process of tha invention are
diagrammatically shown. The mating surface area or
abutment area 87 is placed under load during the
designated service of the workpiece. Accompanying sub-
surface layers are indicated by the zones I; II and III.
It is significant here that the work surface of the
treated metal is compressed and therefore resides in zone
II2 approaching the ultimate strength of the base metal
of the workpiece body. Beneath this outer protective
high strength layer of compressed material is a layer of
material deformed at its yield point in the deformation
zone II of FIGURE l3. The elastic region of the
workpiece body remains in zone I of FIGURE 13.
Thus, as diagrammatically set forth in FIGURE
14, a compressing force applied by the high kinetic
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energy needle indenters of the invention produces a
surface strength in the maximum material strength zone
III during machining of the workpiece, and conforms the
cast iron workpiece, obtained in the plastic state I2 , to
a work surface having a stronger compressed surface layer
for confronting the workpiece mating part in a
compressive and usually sliding contact mode. This
results in higher bearing forces and longer life
workpieces.
To achieve this result, as depicted in FTGURE
15, a small area impacting needle element striking and
compressing a work surface at a high velocity is employed
in the ultrasonic impact machining methods of the
invention.
From the deformation characteristics of FIGURE
13, the first plateau is formed when impacting forces
reach the material yield point of zone II forming plastic
indentations of the workpiece material.
Contrast that with the zone III area where the
ultrasonic impact machining method of this invention
introduces deformation on the workpiece surface layer
resulting in a strengthened compressed workpiece work
surface layer up to 2 mm deep at a point close to the
range 0.9 to 0.95 of the maximum cast iron material
strength to achieve a substantial improvement in
compressive work forces feasible, and results in
elimination of pri or stress concentrations at that
surface and the reduction of crack development in
service. Here the total depth of the layer, which
includes the above-mentioned strengthened layer, elastic
compressive stress layer and the layer relaxed by the
impulse and ultras onic stresses, extends to a depth in
the order of at least 12 mm thus to afford extended life
over expected wear depths specified for the workpiece
such as a bearing or brake drum. When the ultrasonic
impacts are applied by scanning the entire work surface
of the workpiece with the impact needles, this improved
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method assures a uniform surface texture on the surface
ranging from a surface slightly roughened with a micro
texture for adhering to a coating material to one of
substantially optical smoothness, as desired for
propeller blade workpieces for example . The prior art
peening methods of surface treatment form areas of
plastic deformation with induced compressive stresses not
greater than material yield strength to depths of about 2
mm and, therefore, cannot significantly improve the wear
life of the workpieca at the level obtained by the
combined effect of the ultrasonic impact and a wave with
induced compressive stresses equal to the ultimate
strength of the treated material, their elastic and
relaxation influence on the material condition up to 12
mm from the surface in accordance with this invention.
The ultrasonic impact machining methods of the
invention thus enhance frictional wear properties,
performance and life of rotary bearing surfaces, which
can be readily machined by transducer driven impacting
elements and machining systems afforded by this invention
to improve the life expectancy of particular workpieces .
The ultrasonic impact energy is applied at an intensity
level sufficient to induce a surface and sub-surface
deformation pattern that produces increased strength in
the surface layer and balanced distribution of forces in
the zone I elastic volume of the basic workpiece body
material (FIGURE 14) that together with an outer textured
surface suitable for the workpiece in its specified
service decreases tharmomechanical fatigue and scuffing
or heat checking under conditions of dry sliding contact
and frictional loading at the work surface.
FIGURES 16 through 23 depict the flow
improvement properties of a liquid 80 across an
ultrasonic impact machine treated surface 81. It is
known that the flow of liquid across a smooth surface has
a dampening layer 82 of medium thickness at the surface
81 where the speed is close to zero, and the speed of
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flow increases as you move further from the contacting
surface ( FIGURE 17 ) . The graph in FIGURE 17 shows the
relative speed of the liquid 80 flowing across the
surface 81 as a function of distance from the area of
contact between the liquid 80 and the surface 81. As a
result at the contact point of the surface 81 this flow
is turbulent with vortex 84 cavitation property. These
vortexes 84 are relatively evenly distributed depending
on the properties of the liquid 80. This is shown in
FIGURE 16. These vortexes 84 lead to a rippling effect
in each vortex 84 of the flow with a high degree of
surface cavitation. This breakdown and reforming of the
vortex 84 at the surface 81 leads to pockets of high
concentration of surface erosion cavitation 85 and
corrosiori . These areas attack the surface 81 and lead to
severe surface erosion and corrosion fatigue . This is
shown on the surface 81 by means of pitting that
eventually leads to cracking and premature failure. The
size between the centers of two consecutive vortexes,
which is directly related to the size of the vortex 84,
is shown in FIGURE 18 as a function of the velocity of
flow of the liquid 80 over the surface 81. As the speed
of flow increases so the distance between the centers of
each vortex 84 decreases. This leads to an increase of
concentration of surface erosion cavitation 85 on the
surface 81.
The specific force of cavitation explosion
(SFCE) is a function of size or frequency of the vortexes
which determine the space between adjacent vortexes as
shown in FIGURE 19. The larger the distance between the
centers of the vortexes the lower the amount of SFCE.
The smaller the distance between the centers of the
vortexes the higher the SFCE. Thus, since the distance
between the vortexes is dependent on the speed of flow
(FIGURE 18) the SFCE is a function of the speed of flow
as shown in FIGURE 20. It is shown in FIGURE 20 that as
the flow velocity increases, the erosion cavitation
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activity on the flow surface is increased . These
relationships and observations are true f or conditions of
a smooth surface. This turbulent effect also affects the
ability of the body to move through the medium. As a
body moves through a turbulent flow, additional energy is
consumed to overcome the medium resistant e. This is
traction resistance. The turbulence disturbs the
movement stability and produces unfavorable, and
potentially dangerous, resonant oscillat i on in the moving
body. In addition, the Bernoulli effect of the velocity
gradient within the associated vortexes at the surface
results in an uneven distribution of pres sure across the
moving body. In liquid, such fluctuations of pressure
cause cavitation. With. a certain relationship between
velocity and pressure in the flow, cavit ation, in turn,
causes erosion of the flow surface, disturbs the hydro-
dynamic characteristics of the body around which the
liquid is flowing and with time produces concentrators on
the surface, which in turn give rise to dynamic and
fatigue failures. An example of such a moving body
through a liquid medium is a ship propeller or hull of
the ship.
As shown at FIGURES 21-23, the altered surface
macro- and micro-relief as a result of ultrasonic impact
machining such a body alters the f low characteristics of
the liquid 80 at the boundary of contact between the
surface 81 of the body and-the liquid 80. Ultrasonic
impact machining results in a superpositi on of a macro-
and micro-relief on the surface 81 of the body such that
the geometry of this relief overlaps with the possible
combination of the spacing between the centers of the
vortexes. This effect is shown in FIGURE S 21, 22 and 23.
The new surface relief of the surface 81, as defined in
this invention, results in a geometry at the surface 81
that appropriately corresponds with the surface vortex
flow over the surface 81. Using FIGURES 17, 18, 19, and
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20 it 1s possible to forecast the phase shift and size of
vortexes and their overlapping.
Further to this, the lsquid 80 fills the
indentations on the surface 81 as a result of the
ultrasonic impact machining and is basically held there .
In doing so, the liquid layer where the velocity is
almost zero at the surface 81 (shown earlier in FIGURE
16) is not in direct contact with the surface 81 of the
moving body as shown in FIGURES 21, 22 and 23 resulting
in a laminar flow 86 across the surface 81 and providing
a protective shield to the moving body. This new
condit zon radically decreases the velocity gradient,
eliminates the prerequisites for the curl formation of
the vortex and, hence the possible formation of turbulent
flow formation. This as a result provides for a stable
prerecsuisite for laminar flow 86 across the surface 81.
As a result of the laminar flow 86, the
phenomena of instability in movement, which is
unfavorable and present in turbulence, is not present.
As a result there is no resonant oscillations of the body
being flowed around and no energy loss as a consequence
of medium resistance as there is with turbulence . Hence,
the cavitation and surface damage that is present in
turbulence is eliminated and there is no danger of
unpredictable dynamic and fatigue failure .
Accordingly, this invention provides a new
method f-or enhancing the life, reliability and durability
of bodies subj ected to intense f low of medium and
currents. This invention results in a new principle of
fluid dynamics and surface geometry and shape. The
possibility exists of new bodies that can be subj ected to
severe fluid flow. The invention generates a result that
allows bodies to travel through a fluid medium with a
condition of laminar flow which otherwise would have
suffered premature failure due to the severing action of
turbulent flow. This results in a new method for
decreasing resistance in the flow, improving the fluid
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dynamics of the body through the medium, and a new method
of surface protection in aggressive medium.
This invention provides the treatment of a
metallic workpiece to plasticize the workpiece surface
and adjacent sub-surface regions by ultrasonic impact
from a set of freely axially movable impacting elements
driven by an oscillating energy transfer transducer
surface oscillating at a single ultrasonic frequency
thereby to randomly or controllably and forcefully impact
a working interface surface of the metallic workpiece
with impacting elements in a set producing enough kinetic
energy to plasticize the worl~piece surface and the
adj acent sub-surface region to a considerable depth with
the workpiece residing at an ambient temperature.
The novel transducer of the invention includes
features such as a multi-stage transducer with a
plurality of serially connected stages having different
related residual resonance frequency characteristics
harmonically related to the s ingle ultrasonic energy
source frequency and characterized by a set of impacting
elements having freedom of axial movement arranged for
being driven by the single ultrasonic operating energy
source frequency to randomly (asynchronously) or
controllably impact a workpiece surface. A scanning
device moves the transducer set of impact elements
forcefully in contact with a workpiece surface over a
designated treatment zone on the workpiece surface for
uniform thermal treatment generated throughout the
treatment zone by the randomly impacting elements thus
serving to plasticize the metallic workpiece surface and
adj acent sub-surface region.
Thus, the novel impacting element array
arranged to axially move impacting elements freely over a
striking path between an energy supplying contact with
the transducer oscillating abutment surface and an energy
conversion at impact at the workpiece surface provides a
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novel operation mode driving impacting elements of the
set randomly into the workpiece surface .
Those novel features descriptive of the nature
and spirit of the invention are set forth with
particularity in the appended claims. As will be
apparent to one skilled in the art, various modifications
can be made within the scope of the aforesaid
description. Such modifications being within the ability
of one skilled in the art form a part of the present
invention as embraced in these claims.
