Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR INFRARED
WELDING OF THERMOPLASTIC PARTS
This invention relates to the joining of thermoplastic parts through the
application of infrared energy to one or all of the parts to be joined and
wherein the
source of the infrared energy is an incandescent lamp whose output rays are
directed
toward a defined target area by means of one or more reflectors.
It is well known that thermoplastic parts can be joined by heat welding. A
common application of this knowledge is found in the construction of
automobile
interior panels and components such as sun visors which are constructed
largely of
thermoplastic components. Heat welding can be achieved by any of several
technologies or methods including hot plate welding, hot air j et welding,
laser welding
and ultrasonic welding.
Hot plate welding, generally speaking, involves the application of a heated
metal
plate to the thermoplastic parts to be joined. A significant disadvantage in
hot plate
welding is the fact that thermoplastic material often sticks to the hot plate,
resulting in
filaments or streamers of material being drawn from the thermoplastic parts.
This
requires secondary cleanup operations to both the parts and the hot plate
welder. Hot
plate welding is also difficult or impossible to apply to small areas.
Hot air heating for thermoplastic fusion suffers the disadvantage of imprecise
application; i.e., the hot air flows not only over the target area but also
over surrounding
areas and components which are undesirable to heat.
Laser heating suffers a number of disadvantages including high expense and the
dangers which are inherently associated with stray laser radiation.
Ultrasonic welding is technically complex and requires not only an
electroacoustic transducer but also a properly dimensioned horn which can be
resonated.
One aspect of the present invention is a method of welding or joining two or
more thermoplastic parts by first heating a well-defined area of one or more
of the parts
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through the application of infrared energy generated from an incandescent
source and
directed toward the area by one or more reflectors. In the simplest form, the
method
involves the steps of locating the incandescent source at the focal point of a
parabolic
reflector thereby to produce a collimated output which is directed toward a
target area to
soften the thermoplastic material throughout the target area to produce
contemporaneous or subsequent fusion.
In a more typical application, the method involves placing an incandescent,
infrared source at or near the focal point of an imaging reflector which, at
least in one
cross-sectional plane, is parabolic so as to direct rays from the source in a
substantially
collimated pattern, collecting the rays in or by a second reflector which is
joined to and
substantially contiguous with the first reflector but which is of a non-
imaging character,
so as to direct substantially all of the output rays through an aperture
formed in the
second reflector, the size and shape of which substantially conforms to the
size and
shape of the target area in the thermoplastic material or materials to be
welded. The
first and second reflectors are preferably but not necessarily made of a metal
such as
aluminum and is plated with a material such as gold which is highly reflective
to
infrared energy so as to reflect substantially all of the infrared energy from
the source to
and through the aperture to the target area. In the preferred method, the area
ofinetal in
the body forming the second reflector and surrounding the aperture is flat
such that it
may be pressed against the thermoplastic material forming the target area to
add
joining or welding pressure and to cool the area or volume of thermoplastic
material
immediately surrounding the target area which conforms to the shape and size
of the
output aperture in the secondary reflector. In one embodiment hereinafter
disclosed, the
flat area has two non-coplanar portions to fit into an inside corner.
30
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In accordance with the inventive methodology, the shape and size of the output
aperture may take any of several forms from simple circular spots to straight
lines,
curved lines and angled corners.
According to a second aspect of the invention, an apparatus is provided for
generating and directing infrared energy from a source such as an incandescent
halogen lamp or series of such lamps to a target area. In the simplest form,
the
apparatus of the present invention comprises a broadband source such as a
halogen
lamp and parabolic reflector which receives illumination from the source and
directs it
toward a defined target area in a collimated fashion.
In a more typical application, the apparatus of the present invention
comprises a
first reflector of an imaging type; e.g., a parabolic reflector with an
infrared source
mounted at the focal point to produce a collimated output. The apparatus
further
comprises a second reflector which is joined to the first reflector in such a
fashion as to
form one or more essentially contiguous surfaces. The second reflector, unlike
the first
reflector, is a non-imaging reflector such as a Winston cone which has no
focal point and
simply directs received energy through an output aperture at the converging
end wherein
the size and shape of the aperture at least approximates the size and shape of
the target
area toward which the infrared radiation is directed. In a preferred form, the
second
reflector is formed of metal such as aluminum and is constructed to have a
pressing
surface area immediately surrounding the output aperture which surface area
can be
brought into physical engagement with the thermoplastic material of at least
one part to
be welded. The pressing surface area can be planar or curved or lie in several
planes to
fit the welded part or parts. Alternatively, the second reflector may be
maintained in
closely spaced relationship with the thermoplastic part or parts to be welded.
As it is hereinafter described in greater detail, the first and second
reflectors may be
configured as surfaces of revolution wherein the overall apparatus takes on an
essentially
elongated cylindrical shape. Alternatively, the first and second reflectors
may be
configured in such a way as to produce a line of illumination, either
straight, angled, or
curved. In other forms, the reflectors are configured to produce a"corner" of
illumination such that the weld head formed by the second reflector may be
inserted
into an inside corner and welding illumination is directed to both of the
converging
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surfaces of the inside corner. In all cases described immediately above, the
reflector
combination comprises a first imaging reflector which is parabolic in at least
one cross
section and a second non-imaging reflector such as the Winston cone or
compound
parabolic concentrator (CPC) which is fully described in the literature.
Other applications of the present invention will become apparent to those
skilled in
the art when the following description of the best mode contemplated for
practicing the
invention is read in conjunction with the accompanying drawings.
The description herein makes reference to the accompanying drawings wherein
like reference numerals refer to like parts throughout the several views, and
wherein:
Fig. 1 is a cross-sectional view of a first device embodying the invention;
Fig. 2 is a plan view in cross section of cylindrical components in the device
of
Fig. 1;
Fig. 3 is a cross-sectional view of a detail in the device of Fig. 1;
Fig. 4 is an exploded view of the device of Fig. 1;
Fig. 5 is a cross-sectional view of a device similar to the device of Fig. 1
but
illustrating the manner in which light rays are reflected by the reflectors
and further
illustrating one manner of using the device;
Fig. 6 is a sectional view of a device similar to the structure of Fig. 1 and
with a
spacer illustrating a second mode of operation;
Fig. 7 shows a first alternative construction;
Fig. 8 illustrates a second alternative construction using multiple sources to
produce a straight line weld area;
Fig. 9 is a partly broken away view of a device for creating an angled line of
weld area;
Figs. 10 and 11 illustrate another alternative construction using multiple
sources
to create a weld area in an inside corner;
Figs. 12 is a section through the CPC portion of the device of FIG. 11; and
Fig. 13 is a side view of another alternative device including an external
punch
head.
Referring now to Figs. 1-3, a first embodiment of the invention is shown to
comprise a generally cylindrical infrared spot welder 10 poised a small
distance above
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layered thermoplastic materials 12 and 14, the upper layer 14 having a small
hole 16
punched or otherwise formed therein to admit in.fiared rays from the welder 10
to the
lower layer 12 so that the two layers can be effectively fused together in an
area
approximating the size and shape of an aperture 32 in the lower end of the
welder 10.
5 Hole 16 is not required in cell materials, especially those which are thin
and transparent,
or nearly so, to infrared radiation.
As shown in the figures, the welder comprises a cylindrical body 20 with
passages (not shown) to carry conductors from an outside 110-volt AC source to
a
broadband source of illumination in the form of a 100-watt halogen lamp or
source 26
the output of which contains a substantial percentage of illumination in the
infrared
range. In actual practice, the lamp of choice is a 12V, 100-watt lamp which
requires
conversion of the 110V AC to 12V DC. Various power sources can be used
depending
on the number and type of lamps required. The lamp 26 is mounted in a holder
assembly 22 which fits telescopically into the body 20 of the welder 10 and
has formed
at its lower end a parabolic surface, or primary reflector, 24 having a
deposited layer 25
of gold thereon to preferentially reflect infrared rays from the lamp 26. The
lamp 26 is
mounted in the holder 22 in such a way that the source of illumination is
essentially at
the focal point of the parabolic surface 24 whereby the rays of illumination
which are
emitted from the lamp 26 and reflected off of the gold surface 25 of the
parabolic
reflector 24 are collimated and travel downwardly along the longitudinal or
vertical axis
of symmetry of the welder 10 as shown in Fig. 1, this axis of symmetry also
carrying
the reference character 34 in Fig. 3.
The parabolic reflector 24 diverges; i.e., flares outwardly toward an open end
where it abuts and meets the open or larger end of a second reflector 30
formed by an
end cap 28 having a cylindrical collar portion 29 which fits around the
cylindrical body
20 of the welder 10 to bring a shoulder 38 into abutment with the lower end
surface of
the parabolic reflector 24. The inside surface or reflector portion 30 of the
end cap 28
has deposited thereon a layer 31 of gold which is preferentially reflective to
infrared
radiation. The lower end of the reflector 30 converges toward aperture 32
which, in the
3 0 embodiment in Figs. 1-3, is circular and at least approximates the size
and shape of the
area of the layered materials 12 and 14 to be welded or fused together.
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Reflector 30 is a non-imaging reflector; i.e., it has no focal point and
simply
causes the collimated rays of illumination from the primary reflector 24 to be
directed
through the aperture 32 after one bounce off of the deposited gold layer 31.
Accordingly, illumination from the halogen lamp 26 is essentially uniformly
spread
over the area of the aperture 32 and over the area of the layers of materials
12 and 14 to
be welded. As stated above, the secondary reflector 30 is a surface of
revolution with
a curved shape designed to collect the radiation from the halogen lamp 26 and
the collimated radiation from the primary reflector 24 and direct the
radiation through the aperture 32. In the preferred form, the shape of the
secondary
reflector 30 is known as a Winston cone or a compound parabolic concentrator
(CPC)
and has the effect of maximizing the collection of incoming radiation within a
particular field of view. Unlike the reflector 24, the reflector 30 is a non-
imaging-like
concentrator designed to funnel all illumination directed from the primary
reflector 24
in the lamp 26 through the aperture 32.
The welder 10 is shown in an exploded view in Fig. 4. In this view, the
welder 10 comprises three subunits, the body 20, the holder 22 and the end cap
28.
The holder assembly 22 includes the primary reflector 24, the halogen lamp 26,
a
lampholder 40 and lampholder electrical connectors 42. In the welder 10, it
was
found that a part was needed for firmly holding the halogen lamp 26 and for
positioning and orienting the lamp 26. As such, the lampholder 40 was
developed for the welder 10. In addition, the lampholder 40 provides good
electrical connection between the leads from the halogen lamp 26 to the
electrical
connectors 42. The lampholder 40 includes a circuit stamp 44 formed by traces
positioned between a first lampholder part 46 and a second lampholder part 48.
Parts 46 and 48 are fabricated from high-temperature plastic formed with
apertures to admit electrical leads for contacting with the circuit stamp 44.
The
lampholder 40 is made from three separate pieces but, alternatively, can be
formed
as a single piece.
The leads from the lamp 26 are inserted into the apertures in the lampholder
so
as to be firmly held. The lampholder 40 is positioned on the end of the holder
assembly 22 most distant from the primary reflector 24. 'The lampholder 40 in
the
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assembly 22 holds the lamp 26 in such a way that the lamp filament is
positioned
substantially at a focal point of the parabolic primary reflector 24.
Electrical connectors
42 are inserted into the lampholder 40 on the side opposite the lamp 26.
The body 20 as shown in Fig. 4 is generally cylindrical with a hollow bore
through the length of the body and having first and second ends. The body
includes a
cylindrical bore having a receptacle 50 at the first end sized to receive the
assembly 22.
The body 20 includes a detent pin 52 for meeting with a detent 54 in the
assembly 22.
The detent pin 52 limits the depth that the reflector assembly 22 is inserted
into the
body 20 and orients the reflector assembly 22 to a desired position within the
body 20.
Detent pin 52 is inserted through a hole that extends through the wall of the
body 20 to
the interior bore.
The body 20 includes an aperture for affixing an air fitting 56 to the body 20
for
cooling purposes. The air fitting 56 provides for attachment to an air source.
The air
provided via the air fitting 56 is used to cool the lamp 26 and to cool the
welded plastic
following heating by the infrared welder. The air flows through the bore in
the body 20,
through the air apertures in the lampholder 40 and around -the lamp 26. Air
enters the
chamber encompassed by the primary reflector 24 and the secondary reflector 30
and
exits through pores or apertures 58 in the end cap 28 of the secondary
reflector. The
pores 58 are added to the end cap 28 to permit the exit of the air when the
aperture 32 is
blocked by the object being welded which occurs whenever the distal end
surface; i.e.,
the surface surrounding the aperture 32, is brought into contact with the
material being
welded, a strategy which is shown in Fig. 5. The body 20 includes a cover 60
for
sealing the second end of the body 20. The cover prevents air from exiting the
second
end of the body. Optionally, a pneumatic cylinder (not shown) may be attached
for the
purpose of driving a press used to force plastic pieces together.
The body 20 has a circumferential detent where an 0-ring 62 is positioned. The
0-ring 62 mates with a complementary detent situated in a collar 29 of the end
cap 28.
The 0-ring provides for a secure fit of the end cap 28 over the end of the
body 20. The
body 20 includes a pin 64 on the exterior of the body 20 for aligning the end
cap 28 and
securely holding the end cap 28 to the body 20.
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The welder 10 is assembled by inserting the assembly 22 into the receptacle
region 50 of the body 20. The assembly 22 is positioned by aligning the detent
54 with
the detent pin 52. The end cap is then fitted over the first cap of the body
such that the
outer rim of the primary reflector 24 is seated on the shoulder 38 of the
secondary
reflector 30. The end cap 28 and body 20 fit together such that the 0-ring 62
is
positioned in a circumferential groove in the body and a complementary detent
in the
end cap 28. The position of the end cap 28 is oriented by the pin 64 situated
in the side
of the body 20. The use of the pin 64 permits an end cap 28 having an
asymmetrical
shape when required by design criteria.
Alternatively, a variation in the design for fitting the end cap 28 on the
body 20
may use threads on the exterior of the first end and the end cap may have
complementary threading on the interior of the end cap collar 29.
Fig. 5 illustrates a cross-sectional drawing of the welder 10 in an altemative
use wherein the planar end surface 37 of the welder; i.e., the surface
immediately
surrounding the output aperture 32, is brought into contact with the upper
layer 14' of
layered thermoplastic materials 12' and 14'. As shown in Fig. 5, the rays
emanating
from the halogen lamp 26 at the largest angle contact the parabolic surface
bearing the
gold plating 25 and are collimated so as to be directed in essentially axial
fashion
toward the aperture 32. Those rays which contact the plating 31 of the
secondary
reflector 28; i.e., the CPC, are directed in one bounce through the aperture
32. In this
illustration, substantially like the illustration of Fig. 1, the aperture
defines the size and
shape of the weld area. In addition, it has been found that the gold plating
25, 31 on the
reflective surfaces is so efficient that the metal making up the body of the
secondary
reflector 28 remains quite cool and, when the annular end surface 37 thereof
is pressed
against the upper layer 14' as shown in Fig. 5, it serves as a heat sink to
ensure that the
weld occurs only in the circular conforming essentially to the size and shape
of the
aperture 32 in the secondary reflector 28. This is particularly useful where
precisely
defined weld areas are desired.
Fig. 6 illustrates the welder 10 with an additional accessory in the form of
an
adjustable spacer 83 which can be used to precisely control the spacing
between the
output aperture 32 and the top surface of the layered materials 12' and 14'.
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Fig. 7 illustrates another alternative embodiment of the invention comprising
two side-by-side halogen lamps 126a and 126b in a holder defining adjacent
parabolic
reflective surfaces, or primary reflector, 124 which may or may not be coated
with gold
as previously described. A secondary reflector 130 is mounted to the primary
reflector
124 to receive the collimated radiation from both of the sources 126a and 126b
and
directed outwardly through an aperture 32' which essentially defines the shape
and size
of the weld area to be formed between the materials 12 and 14. As was the case
with
respect to the embodiment of Fig. 6, an adjustable spacer 83 is mounted to the
device to
establish the correct spacing.
Looking now to Fig. 8, a still further embodiment of the invention is
illustrated.
The purpose of the device of Fig. 8 is to produce a straight line weld area.
Referring to
Fig. 8, a reflector assembly 65 is shown to comprise left and right mirror
image portions
65a and 65b fabricated such as by machining from aluminum stock. An interior
volume
66 is machined out of the assembly to accommodate eight halogen lamps of which
only
68a, 68b and 68c are numbered. The lamps have suitable holder assemblies 74a,
74b
and 74c corresponding generally to the structure shown at 40 in Fig. 4. The
halogen
lamps 68a, 68b and 68c, when properly installed, are uniformly spaced along
the linear
volume 66 with the lamps 68a, 68b and 68c projecting into a reflective
interior formed
by surfaces 80, 82, 84 and 86. The surfaces 80 and 82 are formed in the upper
interior
portion of the reflector assembly portions 65a and 65b to form a linearly
distributed
parabolic reflector; i.e., a reflector which is parabolic in cross-section
perpendicular to
the linear axis. Once again, the halogen lamps 68a, 68b and 68c are located
within the
structure of Fig. 8 so as to occupy essentially the focal point of the
linearly distributed
parabola formed on the surfaces 80 and 82.
The surfaces 80 and 82 are contiguous with the lower surfaces 84 and 86 in the
reflector portions 65a and 65b, respectively, to form a non-imaging or Winston
cone
reflector which operates in the fashion described above. With reference to
Fig. 8, a
linear aperture 85 defining the shape and size of the weld area is formed
between the
two opposed legs of the lower reflector assembly where the surfaces 84 and 86
terminate. As is the case with respect to the structures of Figs. 1-5,
surfaces 80, 82, 84
and 86 are preferably plated with gold so as to reflect substantially all of
the infrared
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wavelength radiation from the lamps 68. A side plate 88 is fastened such as by
machine
screws to the side surface of the reflector assembly 65. Alternatively, the
reflector
assembly 65 may be joined to another similar reflector assembly to produce an
even
longer line of infrared weld illumination. End surfaces 87 and 89 are coplanar
straight;
5 parallel lines which can be pressed against the parts to be fused as was
described with
reference to Fig. 5. A lampholder assembly 92 is provided to make electrical
contact
between a support structure 94 and lamps 74a,74b,74c. Fastener assembly 96
cooperates with an aperture in siructure 94 to mount the reflector assembly 65
in position.
In using the device of Fig. 8, it is common to press the flat end surfaces of
the
10 opposed legs of the lower reflector assembly against the part or parts to
be welded.
However, a slight spacing may also be used as explained above. The mirror
image
opposed portions of the reflector assemblies 65a, 65b in Fig. 8 are held
together by
means of machine screws placed through suitably formed and threaded apertures
90
in those structures.
Referring now to Fig. 9, another embodiment of the invention is shown for
producing a curved line of infrared welding illumination. The embodiment of
Fig. 9
comprises a reflector assembly 100 having a base 100a, an outside component
100b
and an inside component 100c. Parabolic surfaces 104 and 106 are formed in a
curved
line on the base component 100a to define a primary reflector for halogen
lamps 102
located in a distributed fashion along the apex of the parabolic surface. It
will be
understood that the base component 1 OOa is machined out to provide a location
volume
for the lamps 102 in a manner similar to that shown in Fig. 8. The base 100a
may be
made in two parts as shown or as a single piece. The surfaces 104 and 106 are
parabolic
in a cross-section plane orthogonal to the axis of symmetry which runs along
the center
line of the curved volume. Again, the lamps 102 are located at the focal line
of the
parabolic reflector formed by surfaces 104 and 106.
One-half of a CPC surface 108 is formed in the upper outside structural
component 100b along with a first anvil or clamping surface 112. The opposite
side of
the Winston cone or CPC secondary reflector surface 110 is formed in the
component
100c along with an interior clamping or anvil surface 114.
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One-half of a CPC surface 108 is formed in the upper outside structural
component 100b along with a first anvil or clamping surface 112. The opposite
side of
the Winston cone or CPC secondary reflector surface 110 is formed in the
component
100c along with an interior clamping or anvil surface 114.
In practice, the device of Fig. 9 works the same as the device of Fig. 8,
except
that the line of welding illumination is curved rather than straight or
linear. The lamps
102 are uniformly distributed along the length of the reflector surface and
end plates 109
are used to prevent the loss of IR energy through the open ends. The weld line
may be
extended from the curved portion on one side as shown, or on both sides.
Referring now to Figs. 11 and 12, another device 120 is shown for projecting a
line of welding illumination into an inside corner. The device is again
preferably made
in several pieces which are machined and screwed together and includes a base
122 for
receiving three halogen lamps 125 within a linear volume having a cross-
sectional area
defined by parabolic reflective surfaces 128. Again, the structure is such
that the lamps
125 are located along the distributed focal line of the parabolic reflector.
The reflective
surface is essentially linear and is contiguous with a secondary CPC surface
130 which
is compound as shown in Fig. 12; i.e, it extends outwardly from the junction
line with
the parabolic reflector to a right-angled end surface 131 of the structure 120
so as to fit
into and clamp against the inside surfaces of a 90 degree interior corner of a
structure
134 to be welded together. The CPC surface 130 varies as shown in Fig. 12 to
provide a
uniform output intensity along the entire length of the aperture 129 which
defines the
corner weld. End plates 127 such as shown at 88 in Fig. 8 are used to confine
the
illumination.
Referring now to Fig. 13, the device 10 of Fig. 1 is shown combined with an
anvil 132 mounted on a swing arm 134 attached to an actuator 136 having an
extensible
arm 138 for swinging the arm 134 and the anvil 132 between the operative
position
shown in Fig. 13 and a home position wherein the anvil 132 and the arm 134 are
rotated
counterclockwise so as to be out of the way of the device 10 during the
heating stage.
The typical operation of the device in Fig. 13 is to bring the device 10 very
close
to or in contact with the layers 12 and 14, whereupon the incandescent lamps
126 are
actuated to heat the parts' and begin the fusing process. The device 10 may
then be
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raised and the actuator 136 operated to bring the arm 134 and the anvil 132
into the
position shown. The device 10 is then further advanced toward the workpiece to
perform a pressing operation.
The anvil may also be mounted on a frame which is located within the
reflectors
24 and 30 and advanced through the aperture 32 to perform the pressing
operation after
the heating step. However, the internal location of the frame and anvil within
the
reflector structure interferes to some degree with the transmission of
illumination from
the lamp 26 thus favoring the structure shown in Fig. 13 thereover.
It will be appreciated that in all of the embodiments described and shown
there
is a primary reflector which is parabolic in at least one cross-sectional
plane. All such
reflectors have a focus and all collimate the rays from the source. In some
embodiments, the focus is a point; in others it is a line. In every
embodiment, the rays
are directed to a well-defmed target area.
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be
understood
that the invention is not to be limited to the disclosed embodiments but, on
the contrary,
is intended to cover various modifications and equivalent arrangements
included within
the spirit and scope of the appended claims, which scope is to be accorded the
broadest
interpretation so as to encompass all such modifications and equivalent
structures as is
permitted under the law.
