Note: Descriptions are shown in the official language in which they were submitted.
~ ~74~
ULTRASONIC SPOT WELDING ASSEMBLY AND METHOD
Technical Field
This invention relates to an ultrasonic welding
apparatus. More particularly, this application relates
to a spot welding tip for an ultrasonic welding
apparatus.
~rt
Ultrasonic welding has been used for bonding in a
number of materials. Most commonly, ultrasonic bonding
is utilized in thermoplastic material~. Recently, it
has been discovered that ultrasonic spot welding could
be accomplished. See, for 0xample, the November-
December 1980 issue of Plastics Design Forum,
page 86. This publication describes techniques of
ultrasonic spot welding as well as the advantages in
producing a clean appearance on the surface opposite the
weld. This article describes a process for welding two
thermoplastic sheets together wherein a standard welding
tip penetrates one sheet and extends halfway through the
second. The article further addresses the possibility
of inverse spot welding, that is, fitting the welding
tip to a moun~ing fixture or anvil, and utilizing a
flat-faced horn to provide ultrasonic energy.
The use of ultrasonic spot welding is further
described in an article entitled "Ultrasonic Assembly,~
by R.A. Clarke published in the 1980-81 Modern Plastics
Encyclopedia, page 447-450. In this article, Clarke
discloses the general advantages of an annular ring
design in the horn or tip for ultrasonic spot welding.
30None of the above-referenced ultrasonic welding tip
configurations or methods provide a suitable means for
permitting the free flow of melted thermoplastic
material away from the weld joint and tip therein during
~`
44V~:i
--2--
the welding process. The accumulation of melted
material in this region may interfere with the continued
melting of the unmelted material at the weld joint (it
absorbs ultrasonic enexgy) and so lends itself to
thermal degradation which may result in a weld joint of
insufficient strength. Furthermore, this melted
material may cause overheating of the weld tip
configuration, which can damage the welds and
surrounding sheet material.
The present invention discloses a welding tip which
includes a plurality of conical projections interspersed
with a plurality of reservoir portions. The conical
projections are placed in contact with the material to
be welded and ultrasonic energy is applied to the
material. The ultrasonic energy is concentrated and
the melt is dispersed by the conical projections and
heats the sheet material adjacent to these projections
to thereby soften the material. The softened material
is displaced by the conical projections and is gathered
in reservoir portions of the tip which are provided for
accumulation of the displaced material. The material
continues to be softened and displaced until the conical
projections are substantially fully inserted into the
sheet material. The conical projections in the preferred
embodiments are right circular conical, right circular
frusto-conical or pyramid in shape or are configured so
as to allow self-release of the sheet material
therefrom. The reservoirs are constructed with a volume
significantly greater than the volume of the conical
projection in order to allow for expansion in the
displaced material.
The present invention provides a system for spot
welding a plurality of sheets of thermoplastic material
together comprising:
(a) welding tip assembly adjacent to an
obverse face of juxtaposed sheets of said thermoplastic
material including an anvil, at least one welding tip
extending therefrom, said welding tip having a base
~ 7~
attached to said anv~l and an apex spaced apart from
said anvil at a predetermined height above said anvil;
(b) means for inserting said welding tip into
an obverse face of said juxtaposed sheets a sufficient
distance to at least paxtially penetrate each sheet of
material being welded, said distance being less than the
height of said welding tip to thereby provide a
reservoir space between said anvil and the obverse face
of sheet material; and
(c) means for applying ultrasonic energy to
said thermoplastic ~heet material adjacent said welding
tip;
whereby melted thermoplastic material may
freely flow into said reservoir space.
A plurality of weld tip configurations are provided
on a common support and the welding tips on the anvil of
each are selectively removable to provide different weld
tip configurations depending on the characteristics of
the materials being welded.
The weld tip support is disposed along a weld line
and the ultrasonic energy is applied by a welding horn
extending along the weld line. The welding horn tends
to generate weaker ultrasonic energy in peripheral
regions, such as those adjacent the distal ends of the
welding horn. Accordingly, to compensate for the weaker
ultrasonic energy in these regions, the tips may be made
slightly longer than in intermediate regions or the tips
may be disposed in more shallow counterbores in the
associated anvils to engage a greater diameter of the
tip therefore displacing more material. An alternative
approach would be to employ a welding horn of greater
length than the weld line to avoid edge effects.
In a first preferred embodiment of the present
invention, the welding tips are right circular cones
with heights A above the anvil and base diameters B at
the anvil. An ideal ratio of A/B is 1.2 in a first
preferred embodiment and 0.76 in a second preferred
44~
embodiment. With these ratios, the tips are
self-releasing and also penetrate sheet material with a
minimum of energy.
It is an object of an aspect of the present
invention to provide an improved ultrasonic welding
apparatus and method.
It is an object of an aspect of the present
invention to produce improved ultrasonic spot welds in
sheet thermoplastic material.
It is an ob~ect of an aspect of the present
invention to providP these welds along a relatively
lengthy weld line and to produce these welds with a
welding tip configuration which is self-releasing from
the sheet material upon completion of the weld due to
its full tapered symmetry.
It is an object of an aspect of the present
invention to provide a welding tip of a sufficient
height to provide a natural reservoir between the
support base of the welding tip configuration and the
weld tips per se.
It is an object of an aspect of the present
invention to provide removable weld tips and means for
changing the number of welding tips and/or the size of
the tips used in order to facilitate optimum weld
strength along the line of the weld with varying
materials and varying thicknesses to be welded.
It is an object of an aspect of the present
invention to provide optimally dimensioned and shaped
weld tips to create optimum strength weld joints and
smooth self-release of the tips from the melted sheet
material.
It is an object of an aspect of the present
invention to provide a welding tip which may be used for
inverse spot welding in thermoplastic material and which
may be removed from contact with the sheet material by
displacement only in a direction parallel to the line
along which the spot welds are produced.
Other aspects of this invention are as follows:
~. ~74~t3'ti
4a
A method of spot welding a plurality of sheets of
thermoplastic material together comprising the steps of:
(a) providing a plurality of welding tips adjacent to an
obverse face of juxtaposed sheets of said thermoplastic
material, each of said welding tips extending from an anvil
and having a base attached to said anvil and an apex spaced
from said anvil at a predetermined height above said anvil,
said plurality of welding tips extending along a weld line
to be formed in said juxtaposed sheets;
(b) inserting said welding tips into an obverse face of
said juxtaposed sheets a sufficient distance so that each
welding tip at least partially penetrates each sheet of
material being welded, said distance being less than the
height of said apex of said each welding tip above the
15 anvil from which said each welding tip extends, to thereby
provide a reservoir space between said anvil and the
obverse face of said sheet material; and
(c) applying ultrasonic energy to said thermoplastic
sheet material adjacent to said welding tips, said
20 ultrasonic energy being applied by a welding horn extending
along the entire length of said weld line and the
ultrasonic energy applied adjacent to the distal ends of
said weld line being slightly weaker than at intermediate
positions along said line, the welding tips adjacent to the
25 distal ends of said weld line having heights slightly
greater than the heights of the welding tips intermediate
the distal ends of said weld line.
4~
.4b-
A system for spot welding a plurality of sheets of
thermoplastic material together comprising:
(a) a plurality of welding tips adjacent to an obverse
face of juxtaposed sheets of said thermoplastic material,
each of said welding tips extending from an anvil and
having a base attached to said anvil and an apex spaced
from said anvil at a predetermined height above said anvil,
said plurality of welding tips extending along a weld line
to be formed in said juxtaposed sheets;
(b) means for inserting said welding tips into an
obverse face of said juxtaposed sheets a sufficient
distance so that each welding tip at least partially
penetrates each sheet of material being welded, said
distance being less than the height of said apex of said
each welding tip above the anvil from which said each
welding tip extends, to thereby provide a reservoir space
between said anvil and the obverse face of said sheet
material; and
(c) means for applying ultrasonic energy to said
thermoplastic sheet material adjacent to said welding tips,
said ultrasonic energy being applied by a welding horn
extending along the entire length of said weld line and the
ultrasonic energy applied adjacent to the distal ends of
said weld line being slightly weaker than at intermediate
positions along said line, the welding tips adjacent to the
di.stal ends of said weld lines having heights slightly
greater than the heights of the welding tips intermediate
thQ distal ends of said weld line.
The foregoing and other objects of the present invention
will become more fully apparent with reference to the
4~r;
--5--
following specification, drawings and claims which
relate to the preferred embodiments of the present
invention.
The present invention will become more fully
understood from the detailed description given
hereinbelow and the accompar.ying drawings which are
given by way of illustration only and wherein:
Figure 1 is a perspective of a por~ion of a welding
tip of the present invention;
Figure 2 is a schematic perspective of the use of
the welding tip of the present invention in welding
sheet material in an inverse spot welding process;
Figure 3 is a perspective of a portion of the
welding tip of the present invention illustrating the
provision of cooling passages therein; and
Figure 4 is a perspective of a portion of a welding
tip according to the teachings of the present invention
in which the semi-spherical reservoirs are replaced by
troughs disposed adjacent the cylindrical projections
and parallel to the weld line.
Figure 5 is a perspective of a welding tip
configuration of a first preferred embodiment of the
present invention;
Figure 6 is an enlarged frontal view of a single
welding tip of the first preferred embodiment of the
present invention;
Figure 7 is a schematic si~e view of the operation
of a single welding tip of the type illustrated in
Figure 6 for welding sheet material in an inverse spot
welding process utilizing a positive stop for the weld
horn;
Figure 8 is a top planar view of an anvil support
bar illustrating a plurality of weld tip groups
extending along a weld line and
Figure 9 is a second preferred embodiment of a weld
tip according to the present invention for welding sheet
material in an inverse spot welding process which
4~ 3
--6--
permits the elimination of the positive stop of
Figure 7.
Best Mode(s) for Carrying Out the Invention
Referring to figure 1, the welding tip of the
present invention IgenerallY indicated as 10) includes a
plurality of conical projections 12 altexnately
interspersed with a pluxality of reservoirs 14 along a
tip base 16. The conical projections 12 serve to
concentrate ultrasonic energy where they contact the
sheet material at their respective apices 18. While the
conical projections may be formed in any shape suitable
for concentrating the ultrasonic energy and facilitating
self-release which will be described hereinbelow,
figure l illustrates one form of cone. It should be
noted, that the term cone is intended to encompass its
broadened meaning and is not intended to limit the
present application to the right circular cone which is
merely one embodiment of cone utilizable in the welding
tip of the present invention.
In a welding tip such as that illustrated in
figure l, the distance between cone apex and base should
be configured to equal approximately one and one-half
times the thickness of the sheet material to be welded.
Further, the cone base is desirably constructed with a
width of approximately ~wice the cone's height or about
three times the thickness of the sheet material to be
bonded.
Figure 2 of the present application illustrates the
use of the tip lO of figure 1 in an inverse ultrasonic
spot welding process. To facilitate inverse ultrasonic
spot welding, the welding tip lO is securely fastened to
an anvil or mounting bar 20 which is positioned on one
side of two sheets of material to be welded 30, 40.
Figure 2 further illustrates the placement of an
ultrasonic transducer or horn 50 on the other side of
--7--
the sheets of material to be bonded by spot ~elding
according to the teachings of the present invention.
The spot welder schematically illustrated in
figure 2 functions as follows. The material to be
bonded is supported by a support 60 with the first and
second sheets 30, 40 juxtaposed along the desired lines
to be welded. The tip 10 of the present invention is
presented into contact with one side of the juxtaposed
first and second sheets of material 30, 40 by movement
of the anvil 20 upon which it is disposed.
Simultaneously, the ultrasonic transducer or horn 50 is
moved in a line perpendicular to the plane of the
respective sheets of materials in order to engage the
other side of the sheets. Ultrasonic energy is applied
to the sheets of material to be bonded via the
ultrasonic horn 50. ~s the conical projections 12 of
the welding tip 10 contact the sheet material at
alternating spots therealong, the ultrasonic energy is
concentrated at these spots. The sheet material is
thereby softened and displaced by contact with the
conical projections 12. The sheet material which is
softened is accumulated in reservoirs 14 to remove the
material from the area of ultrasonic energy
concentration to avoid overheating of the softened
material and to concentrate the ultrasonic energy on
unsoftened material.
When the spot welds have been completed to their
desired depth with the conical projections fully
inserted into the sheet material, the ultrasonic energy
is withdrawn. Cooling of the sheet thermoplastic causes
shrinkage thereof. The configuration of the conical
projections 12 is such that the welding tip
self-releases from the sheet material. Thus, the
configuration of the welding tip of figure l facilitates
3S self-release of the tip from the sheet material after
welding and produces improved welds ~y providing
0r~:
--8--
reservoirs for accumulating the softened sheet material
juxtaposed to the conical projections 12.
While the figure 2 embodiment of the present
invention illustrates the technique known as inverse
spot welding, it is possible to utilize the welding tip
of the present invention in normal spot welding by
affixing the tip to the ultrasonic horn 50.
The reservoirs 14 of the figure l welding tip are
semi-spherical in shape and are typically sized to
accumulate about 1.5 times the volume displaced by an
associated conical projection. The volume of each
reservoir should be at least 1 and 1/3 times the volume
of an associated conical projection.
When the system of the present invention is
utilized in automated production, residual heat buildup
within the welding tip can be troublesome. Without
adequate precautionary measures, the termperature of the
welding tip can become sufficient to cause the sheet
material to melt to the welding tip. Referring to
figure 3, where like numerals designate like parts with
figure 1, cooling passages may be provided within the
welding tip 10 in order to control the temperature
thereof. The temperature may then be controlled by
controlling the flow rate of the coolant or by other
means in order to maintain the welding tip to the
desired temperature. With polyethylene, it is desirable
to maintain the temperature at about 90 Fahrenheit.
When the welding tip reaches 130 to 140 Fahrenheit,
the polyethylene begins to stick to the tip. The weld
tip 10 of the present invention may be either made
integral with the anvil 20 or may be made replaceably
fixable thereto.
In the specific application for which the system of
the present invention is utiliz0d, it is necessary to
move the anvil 20 and weld tip 10 into place by moving
the anvil in a direction parallel to the weld line
produced. ~o signiflcant movement perpendicular to the
(16
g
plane of the sheet materials is therefore permitted in
this embodiment. Therefore, it is desirable to
configure the weld tip so as to easily slide away from
the completed weld along a direction parallel to the
weld line.
In figure 4~ where like elements are also
designated by like numerals, a modified weld tip is
illustrated wherein the semispherical reservoirs of
figure 1 are replaced by a pair of peripheral troughs
22, 24 arranged on either side of the alternately
arranged conical projections 12. These trough~ 22, 24
are fed by a plurality of feeder trough reservoir
portions 26 which direct the molten sheet material into
troughs 22, 24 for collection. Upon completion of the
weld, the weld tip of figure 4 may be more easily
removed from juxtaposition with the sheet material in a
direction parallel to the mold line as there is no
significant accumulation of material between the
interspersed conical projections 12 in the area where
the reservoirs 14 of the figure 1 embodiment would
otherwise accumulate material. Therefore, the lateral
movement of the weld tip may be more easily facilitated.
~ eferring to figure 5, a single group of welding
tips (generally indicated as 10) includes a plurality of
staggered conical projections 82 removably mounted
within the anvil body 90 or support plate 90. A
plurality of optional drill-formed well reservoirs R may
be provided between projections 82. A plurality of such
welding groups would typically be disposed along a
welding line. The conical projections 82 serve to
concentrate ultrasonic energy and disperse the melt
where they contact the sheet material at their respective
apices 88. While the conical projections 82 may be
formed in any shape suitable for concentrating the
ultrasonic energy and facilitating self-release, which
will be described hereinbelow, figure 5 illustrates one
form of cone. It should be noted that the term "cone"
~ ;~7~
--10--
is intended to encompass its broadened meaning and is
not intended to limit present application to a right-
circular cone which is merely one embodiment of cone
usable in the welding tips of the present invention.
For example, a pyramid also falls within the generic
definition of a cone.
Figure 6 is an enlarged diagrammatic illustration
of a single welding tip of a first preferred embodiment
of the present invention. Welding tip 11 is a single
unit comprising a shank 83, a base portion 84 having a
diameter B and a conical projection 82 of a height A
extending upwardly from this base portion. In a welding
tip such as that illustrated in figure 6, the distance
of height A between cone apex 88 and its junction with
based portion 84 should be configured to equal
approximately three times the thickness of a single
sheet of material of two equal thickness sheets to be
welded together. Further, the tip is preferably
constructed such that the ratio of height A to width B
of base portion 84 equals approximately 1.2.
Figure 7 is a diagrammatic side elevational view
illustrating the operation of a single welding tip 11 of
the present invention for welding sheet material in an
inverse spot welding process. To facilitate inverse
ultrasonic spot welding, the welding tip 11 is fastened
to a stationary anvil or mounting bar 90, which is
positioned on one side of two substantially equal
thickness sheets of material 100, 110 to be welded
together. Figure 7 further illustrates the placement of
a movable horn 120 on the opposite side of the sheets of
material to be bonded by spot welding according to the
teachings of the present invention. A positive stop 86A
mounted on the horn 120 is operatively associated with a
stationary stop 86~ to limit the downward stroke of the
horn. As horn 120 is lowered, it pushes sheets 100 and
110 again~t welding tip 81, causing cone 82 to pierce
sheet 110 and penetrate sheet 100 ~y approximately half
its thickness. The degree of pentration is, of course,
44~
--11--
controlled by the positions of stops 86A, 86B.
Therefore, approximately 1.5 sheet thicknesses A1 are
penetrated by cone 82. Cone 82 has a height of
approximately 3Al (3 times the sheet thickness).
Accordingly, a free reservoir space 89 of a thickness B
results between sheet 110 and anvil 90.
Ultrasonic energy is applied to the sheets of
material to be bonded via the ultrasonic horn 120. As
the plurality of conical projections 82 of the
ultrasonic welding tips 81 penetrate the sheet material
along the weld line, the ultrasonic energy is
concentrated and the melt is dispersed at these spots.
The sheet material is thereby softened, forming melt
pools 92 between the sheets. Molten material, as at 94
is also accumulated in the free space 89 between
anvil 90 and sheet 110. As stated hereinbefore,
space 89 is created by stops 86A and 86B which allows
the cones 82 to be inserted only through sheet 110 and
approximately half the sheet thickness into sheet 100.
The back flow of molten material produced by the
ultrasonic welding action literally hangs at 94 from the
sheets 100, 110 above the anvil 90. The free flow of
the molten sheet material effectively removes a
substantial portion of molten material from the region
of the ultrasonic energy concentration and avoids
overheating of the molten material so removed. Thus,
ultrasonic energy can be better concentrated on
unsof~ened material to continue the welding process.
When the spot welds have been completed to their
desired depth (1.5 times the thickness of the bottom
sheet 110, the positive stops 86A, 86B controlling this
distance), the application of ultrasonic energy is
terminated. Cooling of the sheet thermoplastic causes
shrinkage thereof. The configuration of the conical
projections 82 is ~uch that the cone 82 of welding
tip 81 self-releases from the sheet material.
7~4~f~i
-12-
Thus, the configuration of the welding tip of
figures 5, 6 and 7 facilitates self-release of the tip
from the sheet material after welding and produces
improved welds by providing a natural reservoir pace
for accumulating a substantial portion of the softened
or molten sheet material flowing from positions
juxtaposed to the conical projections 82.
Further, the pointed and elongated tip portion 82
with a height-to-base ratio of approximately 1.2, as
illustrated in figure 6, allows for an enhanced piercing
action through the sheet material which requires less
load on the power supply during the welding process and
still provides adequate weld strength.
Still further, the taper on the conical
projection 82 is about 45, resulting in less displaced
melted sheet material and provides a cosmetically more
acceptable weld.
While the figure 7 embodiment of the present
invention illustrates the technique known as inverse
spot welding, it is also possible to utilize the tip of
the present invention in normal spot welding hy affixing
the tip to the ultrasonic horn 120.
The outer zones of an ultrasonic welding horn 120,
typically generate lower amplitude ultrasonic energy and
therefore produce weaker welds at the outer peripheral
zones of the horn. In accordance with the present
invention as illustrated in figure 8, weld tip groups Wl
and W7 in the peripheral outer zones of an anvil support
bar AB have a counterbore depth ~85, figure 7) for
placement of the base of the removably mounted tips
which is about 0.010 inches shallower than the
counterbores of the remaining tip groups W2 to W6 on the
anvil support bar along the weld line. Thus, cones 82
in tip groups Wl and W7 penetrate further into
sheets 100, 110. This compensates for the inherent
feature of lower power output at outer zones of the
ultrasonic horn 120~
~,, Fd 7 4 4 ~
-13-
The shanks 83 and bases 84 of welding tips ll are
removably mounted in the anvil body 90 in counterbore
sockets, as illustrated in figure 7, for ease of
maintenance and replacement. More importantly, the
number of tips in each grouping and the size of the tips
in each grouping on the anvil may be easily changed to
vary the optimum weld strength along a weld line. This
permits the welding of a wider variety of polymer
materials and/or a wider range of varying sheet
thicknesses even though generally more melt pools per
grouping will result in a higher tensil strength per
group.
In the preferred embodiment, the welding tips of
the present invention are utilized to spot weld
high-density polyethylene sheets. However, any suitable
material may be welded utilizing the welding apparatus
of the present invention.
Similarly, in the present invention, the welding
horn could be made of any suitable material as can the
welding tips of the present invention. In the preferred
embodiments, the welding tips 81 are manufactured of
aluminum and are then hard-coat anodized for better
abrasion resistance. The tip is then treated with
polytetrafluorethylene, known under the trademark
"TEFLON", to prevent surface sticking. Further, the
welding tips 81 can also be manufactured from other
materials such as carbonized steel with proper heat
treatment.
Previously, the use of this type system in
automated production resulted in residual heat buildup
within the welding tip. Cooling passages had to be
provided within the anvils in order to control the
temperature of the welding tips. In the present
invention proper tip geometry and number of tips per
group along the weld line reduce residual heat buildup
as disclosed hereinabove. Still further, since the
~ ~74~4()r~;
anvil never contacts the molten material or sheets being
welded, less heat is applied to the anvil.
Figure 9 is an enlarged diagrammatic illustration
of a single welding tip of a second preferred embodiment
of the present invention as utilized in an inverse
welding process. Welding tip 81 is a single unit
comprising a shank 83, a base portion 84 having a
diametex B and a frusto-conical projection 82 of a
height A extending upward from this base portion. It
should be understood that the welding tip of figure 9
may be substituted for the welding tip of figure 6 in
the illustrations of figures 5 and 8 according to the
present invention. In a welding tip such as that
illustrated in figure 9, the distance of height A
between the distal end cone and its junction with base
portion 84 should be configured to equal approximately
one and one-half times the thickness of a single sheet
of material of two equal thickness sheets to be welded
together. Further, the tip is prefer~bly constructed
such that the ratio of height A to width B of base
portion 84 e~uals approximately 0.76.
Figure 9 also illustrates the operation of the
second preferred embodiment of a single welding tip 81
of figure 9 for welding sheet material in an inverse
spot welding process. To facilitate inverse ultrasonic
spot welding, the welding tip 81 is fa~tened to a
stationary anvil or mounting bar 90, which is positioned
on one side of two substantially equal-thickness sheets
of material 100, 110 to be welded together. Figure 9
further illustrates the placement of a movable horn 120
on the opposite side of the sheets of material to be
bonded by spot welding according to the teachings of the
present invention.
With the welding tip of figure 9, the positive
stop 86A of figure 7 may be eliminated or, if desired,
it may be retained. As horn 120 is lowered, it pushes
sheets 100 and 110 against weld tip 81, causing
~ ~744()~i
frusto-conical tip 82 to pierce sheets 110 and penetrate
sheet 100 by more than half its thickness. The degree
of penetration is, of course, controlled by the height
of the frusto-conical tip 82 above the shoulder 84S of
base 84 of the welding ~ip 81. Therefore, more than 1.5
sheet thicknesses A1 are penetrated by frusto-conical
tip 82. The height of frusto-conical tip 82 plus the
extension of base 84 above the top of anvil body 20 is
approximately 3.5 Al (3.5 times the sheet thickness).
Accordingly, a free reservoir space 89 of a thickness B
results between sheet 110 and anvil 90.
Ultrasonic energy is applied to the sheets of
material to be bonded via the ultrasonic horn 120. As
the plurality of conical projections 82 of the
ultrasonic welding tips 82 penetrate the sheet material
along the weld line, the ultrasonic energy is
concentrated at these spots. The sheet material is
thereby softened, forming melt pools 92 between the
sheets. Molten material, as at 94, is also accumulated
in the free space 89 between anvil 90 and sheet 110. As
stated hereinbefore, space 89 is created by the
extension of base 84 and shoulder 84S above the top of
anvil 90, which allows the frusto-conical tips 82 to be
inserted to the controlled depth of the tips' height
into sheets 100, 110. As in the figure 7 embodiment,
the back flow of molten material produced by the
ultrasonic welding action literally hangs at 94 from the
sheets 100, 110 above the anvil 90. The free flow of
the molten sheet material effectively removes a
substantial portion of molten material from the region
of the ultrasonic energy concentration and avoids
overheating of the molten material so removed. Thus,
ultrasonic energy can be better concentrated on
unsoftened material to continue the welding process.
When the spot welds have been completed to their
desired depth (the shoulder 84S of base 84 controlling
this distance), the application of ultrasonic energy is
~4~ci
-16-
terminated. Cooling of the sheet thermoplastic causes
shrinkage thereof. The configuration of the
frusto conical tips 82 is such that the tip 82 of
welding tip 11 self-releases from the sheet material.
5Further, the shoulder 84S of base 84 as it extends
a distance Bl above the top of the anvil body 90 also
disburses evenly and radially the molten material
between the juxtaposed sheets, pxoducing a uniform, and
therefore stronger, weld due to the pressure exerted on
10the sheets 100 and 110 by the horn 120 against the
shoulder 84S of base 84.
Still further, the taper on the frusto-concial tip
82 has an included angle of approximately 45, resulting
in less displaced melted sheet material and provides a
cosmetically more acceptable weld.
Industrial Applicability
The present invention can be used to spot weld
sheet thermoplastic material.
It should become apparent to one of ordinary skill
in the art that various changes and modifications may be
made in the device of the present invention which are
within the contemplation of the inventor. Thus, the
scope of the present application should not be construed
as limited by the specification or drawings thereof, but
must be determined from review of the claims included
herewith.
