 |
Description  |
|
|
BRIEF SUMMARY OF THE INVENTION
This invention refers to a method for securing thermoplastic parts to other
parts. More specifically, this invention refers to a method for securing a
thermoplastic part to another part by means of the application of
ultrasonic energy.
It is often desired to secure a part formed of a thermoplastic material to
another part which may or may not also be of a thermoplastic material.
The use of high frequency vibratory energy for securing parts together is
well known in the art. For instance, U.S. Pat. No. 3,367,809, entitled
"Sonics" issued to Robert S. Soloff, dated Feb. 6, 1968 and U.S. Pat. No.
3,499,808, entitled "Method and Apparatus for Securing Parts together by
Sonic Energy" issued to Edward G. Obeda, dated Mar. 10, 1970, disclose a
method and apparatus for securing a thermoplastic part to another part by
applying sonic energy to a projection of the thermoplastic part and
causing deformation thereof, such as peening over. One or more upstanding
projections in the form of bosses or studs of a thermoplastic part are
placed through corresponding apertures in another part, which is to be
fastened to the thermoplastic part, and subseqently sonic energy is
coupled to the protruding free end of the projections. By virtue of the
dissipation of sonic energy, the thermoplastic projections soften and the
tool or horn which provides the sonic energy and is in contact with the
free end of the projection flattens the softened thermoplastic projection,
obtaining a peening over effect. In both of these prior art methods and
devices the vibratory energy is applied in a direction parallel to the
longitudinal axis of the upstanding thermoplastic projection.
The present invention concerns the securing together of parts by means of
the application of high frequency vibratory energy in a direction
substantially normal to the longitudinal axis of the upstanding
thermoplastic projection. In order to achieve the securing together, a
horn adapted to undergo ultrasonic vibrations at a frequency in the range
between one and 100 kHz is provided and includes a cavity disposed in a
side wall of the horn in a direction normal to the longitudinal axis of
the horn. The cavity further is disposed substantially at an antinodal
region of longitudinal motion of the horn.
In the present method, the parts are placed into juxtaposition with the
projection extending from the thermoplastic part. The free end of the
projection is urged by a static force into the cavity in a direction
normal to the direction of longitudinal motion of the horn. The horn is
then caused to vibrate at a high frequency thereby causing a softening and
flowing of the thermoplastic material in the cavity concomitantly with the
projection being urged into the cavity. The ultrasonic energy, therefore,
is applied to the free end in a direction substantially normal to the
longitudinal axis of the upstanding thermoplastic projection. Upon ceasing
the high frequency vibratory motion of the horn, the softened and flowed
material solidifies and conforms to the shape of the cavity. The present
invention generally encompasses frequencies in the range between one and
100 kHz, preferably frequencies in the range between 16 and 60 kHz. The
advantage of using ultrasonic energy in the forming and securing process
arises from the fact that ultrasonic vibrations aid in the deforming of
thermoplastic material by causing a softening and flowing of the
thermoplastic material. The material solidifies soon after the application
of ultrasonic energy is stopped. Moreover, as is known when using high
frequency vibratory energy, the elastic recovery of thermoplastic material
when the applied forming force is removed is greatly reduced, see the book
"Ultrasonic Engineering" by Julian R. Frederick, John Wiley & Son, Inc.,
New York, NY, 1965, page 170.
A principal object of this invention is, therefore, the provision of a new
improved method for securing parts together.
Another important object of this invention is the provision of a method for
securing a thermoplastic part to another part by applying high frequency
vibratory energy to the free end of a projection in a direction
substantially normal to the longitudinal axis of the projection extending
through an opening in the other part.
Further, and still other objects of this invention will be more clearly
apparent by reference to the following description when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of an apparatus useful for practicing the
present invention;
FIG. 2 is an elevational view, partly in section, of the cavity and horn
providing the vibratory energy to the projection;
FIG. 3 is an elevational view, partly in section, of the upstanding
projection of a thermoplastic part being urged into a cavity disposed in
the horn prior to the application of the ultrasonic energy, and
FIG. 4 is a cross-sectional view of the parts after the present method for
securing has been practiced.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the figures and FIG. 1 in particular, numeral 22 refers to
an ultrasonic energy transducer or converter which is fed from an
electrical generator 24 via a conductor 23. The transducer 22, which
includes either piezoelectric or magnetostrictive means for converting
electrical energy applied to acoustic vibrations, is provided with a horn
14 which acts as an impedance transformer and is used generally for
increasing the amplitude of longitudinal vibrations apparent at the
frontal surface 32 of the horn. The horn 14 is dimensioned so that at the
predetermined frequency supplied by the transducer 22 the horn will act as
a half wavelength resonator for the sound traveling longitudinally
therethrough, thereby causing the output surface 32 to be located at an
antinodal region of longitudinal motion. The horn 14 includes an open
cavity 16 which is disposed in the side of the horn in a direction
substantially normal to the direction of travel of the longitudinal
vibrations through the horn 14 when the horn is rendered resonant; the
direction of travel of the longitudinal vibrations is shown by the double
headed arrow in FIG. 2. The cavity 16 further is disposed substantially at
an antinodal region of longitudinal motion of the horn 14, i.e. near the
output surface 32. The shape of the cavity, for example, may be concave
hemispherically domed and preferably provides a limited slip fit for an
upstanding projection urged therein.
Referring also to FIGS. 2 and 3, a support plate 30 supports a workpiece 10
which comprises a polymeric theremoplastic material and is provided with
one or more upstanding projections 11 to be deformed. The projection,
typically, is of circular cross section and is molded integrally with the
thermoplastic workpiece 10. A second workpiece, such as a plate 12, is
placed in juxtaposition with the workpiece 19 so that a respective
aperture 13 of the plate 12 encircles the projection 11. The projection 11
should emerge from the top surface of the second workpiece which is to be
secured to the underlying workpiece 10. The free upstanding end of the
projection 11 is adapted to be contacted by the surface of the cavity 16
of the horn 14 by suitable force means, for example, a hydraulic jack 31
containing a piston 33 coupled to the support plate 30. Jack 31,
transducer 22 and horn 14 are supported by base 18 as shown in FIG. 1.
Transducer 22 and horn 14 are supported by base 18 by means of supports 26
and 28 in a manner well known in the art.
The apparatus shown schematically in FIG. 1 is described in greater detail
in U.S. Pat. No. 3,752,380, issued to Andrew Shoh, dated Aug. 14, 1973,
entitled "Vibratory Welding Apparatus." The design of resonators or horns
is described in Frederick supra, pages 87 to 98.
The free or exposed end of the projection 11 to be formed or shaped is
urged by the force means into the cavity 16 in a direction normal to the
direction of longitudinal motion of the horn 14. The amount of force is
not critical. The horn 14 is then rendered resonant along its longitudinal
axis at a predetermined frequency while the projection concomitantly is
urged into the cavity to thereby cause a softening and flowing of the
thermoplastic material to conform to the shape of the cavity 16. When the
desired degree of shaping has been obtained, the vibratory motion of the
horn 14 is stopped. However, the projection 11 for a brief dwell time is
urged further toward the horn 14 thereby effecting solidification and
formation of the thermoplastic material. The shaped end 18 of the
projection 11 is then withdrawn from the cavity 16 and the parts are
secured together as shown in FIG. 4.
Description of the Operation
The operation of the apparatus from FIG. 1 can now be visualized from the
following description. The free end of the upstanding projection 11 is
urged by the piston 33 into the cavity 16 in a direction normal to the
direction of longitudinal motion of the horn 14. The generator 24 is
energized and provides high frequency electrical energy via a cable 23 to
the converter unit 22, causing the horn 14 to become resonant and vibrate,
typically at 20 kHz. Concomitantly with the vibrations of the horn 14, the
upstanding projection 11 of the workpiece 10 is urged further into the
cavity 16 thereby causing a softening and flowing of the thermoplastic
material which conforms to the shape of the cavity. When the desired
degree of shaping has occurred, the generator 24 is deactivated thereby
ceasing the vibrations of the horn 14. Following a brief dwell period, the
projection 11 is withdrawn from the cavity 16 and the parts are secured
together as is shown in FIG. 4.
When securing together parts utilizing a 3/16 inch diameter projection
urged into a 1/4 inch concave hemispherical cavity machined into a horn
which vibrates at 20 kHz with a peak-to-peak amplitude of vibration of
0.005 inch to 0.008 inch maximum, the time for securing the parts together
is approximately one second.
Moreover, it will be appreciated by those skilled in the art that the parts
to be secured may be manually held and the projection 11 urged into the
cavity 16 of the horn 14 coupled to the converter unit 22 supported by a
suitable stand.
While there have been described and illustrated certain specific embodiment
of the present invention, it will be apparent to those skilled in the art
that various further changes and modifications can be made without
deviating from the broad principle of the invention which shall be only
limited by the scope of the appending claims.
* * * * *
|
|
 |
|
 |
Description |
|
