Note: Descriptions are shown in the official language in which they were submitted.
1 3 ~ 9 ~ 5
--1--
~i OF PIASTIC AMD PIASTIC M~RTx CoMPC61l~ MaISRIAIS
FIELD OF lNv~llc~/laL~hUUWU OF ~ lNV~NllUN
Ihe present invention relates to methods and a~ya~aL~s for
the fuse melting or binding of plastic materials and plastic
matrix ccmposite materials.
A composite is a resin or resin-like crystalline,
amorpbous or sem1-crystalline matrix in which is embedded wires,
fibers, whiskers or flakes typically of c~rhsn, graphite,
fiberglass or boran. Reinforcing materials can be long, short,
layered, ~ , orderly or randcm. Typically, layers cccposed
of parallel fibers are oriented and laminated in dirre~
dlrP~t;~nc to p m duce a stress-free, l;ght~ ht, uniform sheet
of unusual ~LL~
Reinforced polymer composites can maintain material
strength and integrity at cont;nllollc source temperatures
typically at 400 deg. F. and higher and have s~L~I~rl;~l usage in
the fields of aircraft, automotive structures, construction
materials, machine parts and a variety of ccnsu=er product
~t;~nc as a replacement for me*21 and wcod.
A major problem which has plA~l~P~ the plastic and plastic
matrix composite industry is the lack of a~ iate ter~un~l~gy
for joining of these composites. Present state-of-the-art
bonding methods are unSa~;~r~ ; these ;nrll~P A~hPcives~
resistance welding, ultrasonic ho~;ng, vibration welding,
~ rt;~ bcnding, high frequency welding, mPrhA~;cAl fasteners
and ilr~o~d radiant heat. Each method has i~t~ problems
which this invP~t;~ cvcrco5e5.
- 13~9~5
It is an object of the invention to provide
a quick and effective method of bonding plastic matrix
composites and melt fusing monolithic thermoplastics
and elastomers which overcomes virtually all of the
problems inherent in present state-of-the-art bonding
processes and results in bonds and fusions which
consistently test in excess of 2,000 psi in lap shear,
1,000 psi or more in flat pull strength, and over 5
lbs. in peel.
It is a further object of this invention to
provide a uniform bond which avoids the discontinuity
introduced by adhesives; avoids the vibration and
tearing inherent in ultrasonic bonding; avoids the
ferrous residue inherent in induction bonding; avoids
the thinning and weakening produced by high frequency
welding; solves the problem of material puncture which
is a problem with mechanical fastening; and eliminates
the installation of high resistance wire that remains
in the seam during resistance welding.
It is an object of this invention to provide
a strong, stress-free bond of any geometric
configuration.
It is an object of this invention to provide
a leak-proof homogenous bond line without any
reduction of the composite sheet's or part's thickness
by means of molecular bonding within the resin of the
joined thermoplastic composites such that the bond is
as strong as the resin itself.
It is a further object of this invention to
provide a method of bringing together the surfaces to
be bonded immediately on the cessation of heating
which result in bond strengths up to and in excess of
2,000 psi in lap shear on a l"xl" bond line, and over
1339~05
1,000 psi in a flat tensile pull, and more than 5 lbs
in a test peel on the same l"xl" bond specimen.
It is a further object of this invention to
provide non-contact heating of bond line material
without reducing the thickness of the pre-joined
sheets or parts in substantially reduced times of
approximately 30 seconds to 10 minutes.
It is a further object of this invention to
provide intermittent focused radiant heat means to
both surfaces to be bonded prior to bonding and to
provide heat means to the enriching matrix prior to
bonding whereby only the outermost layers of the
designated bonding areas on surfaces to be bonded are
heated, leaving the internal temperature and fiber
structure of the material essentially unaffected, and
leaving the adjacent surface material unheated.
SUMMARY OF THE INVENTION
According to the invention, intermittent
focussed infrared radiant energy is focussed
simultaneously on the designated bonding areas on
surfaces of multiple parts to be joined. A bonding
agent consisting of a "neat" layer (i.e., essentially
free of reinforcement or other foreign infusion) of
the matrix material may be applied to one or both
designated areas of the surfaces to be bonded. The
surfaces are then brought into immediate bonding
contact with sufficient pressure to accomplish the
bonding without distorting the material.
The steps to accomplish the bonding are as
follows:
1~394~
- 4
Step One: Abrade or clean (e.g. with
solvent) the bonding areas to be jointed (optional)
and/or enrich the bonding areas with a "neat" layer of
thermoplastic resin, compatible with the matrix of
each part.
Step Two: Apply with heat a pellet of neat
resin or an extruded monolithic tape of neat resin to
the bond line of one or both bonding surface areas of
each interface of the material to be bonded.
(Alternatively, the resin tape may contain dispersed
fibers or other reinforcement in some embodiments).
Step Three: Heat the tape (if any) and
bonding area quickly without heating the inner layers
of the plastic matrix material.
Step Four: As soon as the upper and lower
interfaces and bonding tapes or pellets have been
softened sufficiently to be reformed as a single
fusion, the press is brought together quickly. A
mechanical stop prevents the upper and lower press
parts from crushing the material; however, sufficient
pressure between 10 psi and 300 psi is applied to
provide the pressure necessary to fuse the bonding
material together.
Other objects, features and advantages of
the invention will appear from the following detailed
description of preferred embodiments thereof,
reference being made to the accompanying drawing, in
which:
BRIEF DESCRIPTION OF THE DRAWING
Fig. la is a schematic vertical cross
section showing a preferred method and apparatus
according to the invention of heating the bonding
1339~5
- 5
matrix in the bonding zones by means of a robotically
activated, reciprocating, non-contact, focussed,
intense, infrared heat source disposed between the two
press parts.
FIG. lb is a schematic prospective view of
FIG. la.
FIG. 2 is a schematic view of the press
parts being brought together immediately after the
heating cycle with sufficient pressure, typically
between 20 psi and 300 psi, to accomplish the bonding.
FIG. 3 is a schematic vertical cross section
taken transverse to the materials to be bonded showing
the advantage of using a non-fibrous, neat, monolithic
thermoplastic resin to enhance the bonding area.
FIG. 4 shows a schematic view of a preferred
manner of applying an extruded monolithic tape of the
same matrix resin on the bond line of each interface
of the joining sheets or parts.
FIG. 5 is an alternative embodiment of FIG.
3 showing the application of a preferred tape directly
from an extruder onto the sheet or formed part to be
bonded.
FIG. 6 is a schematic vertical cross section
taken transverse to the materials to be bonded showing
an optional method of abrading the fusion side of the
bonding areas prior to heating.
FIG. 7 is a schematic vertical cross section
showing a preferred method and apparatus according to
the invention illustrating the stepped increase in
surface temperature of the bonding zone with each
stroke of the focussed infrared heat source.
FIG. 8a through 8e are schematic cross
sections showing a sample of the wide variety of joint
configurations possible with this invention.
- 6 13~ S
FIG. 9a, 9b and 9c are schematic vertical
cross sections showing joint configurations of various
multi-dimensional structures.
FIG. 10 is a schematic vertical cross-
sectional view of the robotic arm with affixedparabolic elliptical infrared reflectors illustrating
adjustment of the focal lengths of said heat sources.
FIG. 11 is a schematic perspective view
illustrating the use of this invention for fusing
parts of pre-molded elastomeric or composite
thermoplastics.
FIGs. 12 and 12a are schematic vertical
cross-sectional views of point focus parabolic
elliptical infrared heat sources mounted back to back
on a robotic arm which can be preprogrammed to trace
on a circular or elliptical path.
FIGs. 13a, 13b and 13 are alternate
embodiments of this invention showing the use of
focussed parabolic elliptical infrared spot beams at
various angles mounted on a robotic armature which can
be programmed to move in any geometric configuration.
FIGs. 14-15 and 17 are schematic
representations of another preferred embodiment at
various positions of operation, as described.
FIG. 16 is a temperature-time trace
applicable to operation of the FIGS. 14-15 and 17
apparatus.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
There is shown in FIG. 1 an apparatus 10,
according to a preferred embodiment of the present
invention for bonding two thermoplastic objects,
comprising press platens, 12 and 14, heating means, 22
13~3~
- 7
and 24, mounted on a robotic armature, 26, the
respective support and activating means, 32, 34 and
36.
The timing and closure pressure of the press
is controlled by the press. Plastic materials to be
bonded, 2 and 4, are affixed to the respective press
platens by vacuum suction devices (not shown) integral
to the platens.
During the heating phase the press remains
in its open position. When the heating cycle is
complete, the upper and lower press parts are brought
quickly and forcefully together into the closed
position, as shown in FIG. 2.
The heating sources 22 and 24, fixedly
mounted on the robotic arm 26, are movable into or out
of a work zone between parts 12 and 14, and are
capable of reciprocal and pivotable movement within
such zone. Each of the heat sources 22 and 24 are
elongated perpendicularly to the cross-sectional plane
shown in FIG. 1.
The focal vector of the upper heat source 22
is pointed upward essentially normal to the surface of
the first plastic material 2 to be heated. The focal
vector of the lower heat source 24 is pointed downward
essentially normal to said second plastic material 4
to be heated. The heat sources 22 and 24 consist of
commercially available parabolic/elliptical infrared
lamps. The displacement, velocity, periodicity,
temperature and focal lengths and path of said heat
sources are independently controlled.
Prior to the heating of the plastic
materials to be bonded, 2 and 4, bonding zones 42 and
44 of said materials to be fused are enriched with
resin identical to the resin which forms the matrix of
1339~0~
the thermoplastic composite FIG. 3). To accomplish
the placing of the resin enrichment pellet 50 or tape
52 which must be preheated prior to the heating of the
plastic matrix composite materials, a robotic feeding
arm is utilized (not shown). In alternative
embodiments, extruded monolithic tape 52 is applied,
as shown in FIG. 4, or preformed tape 54 is applied
directly by an extruder (FIG. 5). An optional step,
as shown in FIG. 6, is the abrading of the surfaces to
be joined.
The incremental temperature of the surfaces
of the bonding zones increases 80 with each stroke 82
of the reciprocating robotic armature with affixed,
focussed heat sources, as shown in FIG. 7. Because
plastic has a low coefficient of heat conductivity,
during each brief cooling phase 84 of the oscillating
focussed heat application the heat is radiated away
from the surface to the air rather than to the
interior material. Thus the internal temperature 86
remains virtually unaffected while the surface
temperature increases to the melt fusion point as
shown at 88 in FIG. 7. It is this alternative
"endothermic/exothermic" process which is essential to
the present invention. Alternatively, the heat
sources can remain stationary and the materials can be
reciprocated.
A multitude of joint configures is possible,
as shown in FIGS. 8a through 8e. Three-dimensional
preformed plastic objects can be bonded together as
shown in FIGS. 9a, 9b and 9c. For example, any size
corrugated board may be constructed by bonding flat
sheets on either side of a stamp pressed board, as
shown in FIG. 9c.
9 1333~
The focal lengths of the lamps can be
adjusted to coincide with the surface of the material
to be heated as shown in FIG. 10. This means that the
heat is at maximum intensity at the bonding zone.
Indeed, if such intense heat were applied
continuously, the plastic would melt or burn.
In an alternative embodiment this invention
can be used to melt-fuse two halves of a preformed
bulb as shown in FIG. 11. The two lamps 22 and 24 are
mounted back to back on the reciprocating robotic
armature 26 while the halves of the preformed
elastomeric bulb 60 and 62 are placed on the upper and
lower press parts 12 and 14. The focussed heaters 22
and 24 are then reciprocated and when the melt fusion
temperature is reached, the robotic arm is removed and
the two press parts 12 and 14 brought together. The
result is a completely fused bulb 64.
In an alternative embodiment the heat
sources are point-focus, parabolic elliptical,
infrared reflectors 70, 72 mounted back to back on a
robotic armature 26 which rotates in a circle or
ellipse thus tracing out a circular or elliptical path
on the materials to be bonded, as shown in FIG. 12.
This embodiment allows the intermittency of heat
application to be accomplished not by a reciprocating
back and forth motion, but by a continuous cycle which
touches any given point on its path only once in every
revolution.
In an additional preferred embodiment the
robotic arm 26 with affixed, focussed heat sources 70,
74 can be computer controlled and preprogrammed to
trace out any path, thus enabling a variety of
1 3 ~ S
--10--
geometri~lly Ch~F~ bonds to be acoomplich~, as shcwn in FIGS.
13a and 13b. This em}x~l~hent gives a fl~y;h;l;ty of application
to this invention which far ~Yrep~c not only the reci~ w aLing
armature, but also surpasses any bonding machine in the prior
art.
In each embodiment the geometric paths,
ements, velocities, periodicities, t~.~a~res, focal
lengths and duration of heating of the heat sources are
controlled by electr~nic circuitry which can be ~ uy~ammed by
the operation by means of the control panel, not chown.
FIGS. 14-15 shcws a sy_tem more or l~CC as in the
previcu_ c~ci~-c, with certain e~h~r~ L~. It includes press
platens 12 and 14, mounting parts 2 and 4 to be joined, IR
heaters 22 and 24 mounted on a reci~L~aLing arm 26 of a rcbot
machine 36. IR sensing units 122 and 124 are mounted on the IR
heaters and have ~L~ ve temperature control and power contr~l
systems, TC and PC (both per se oonventional) to oontrol platen
positions, reci~L~aLiQn rate and IR heating temperatures and
times. Through this loop oontrol, based on monitoring the
temperature of matrix resin on each of the a~ ls partC 2 and
4, ~LU~e~S paraae*erL are tuned to variable conditions of the
materials to be joined. The sensint units 122 and 124
oontinuously read the rising temperatures of the ~ L;ve
interfa oe bond line zones and send ~;grAlC back to the lamp (22,
24) power oontrols to i~ ase or de~Lease lamp power, U~
varying lamp intensity and projected radiation until both
;,~P;r~ oe temperature r~4~ints match. When the ~a~ ed fusion
temperA~lre of each ma~rial's surfa oe is ~ , the c~ J~
signal the lo~t~ to shut off, the robot arm 26 to withdraw, and
the press (32, 34) to cycle.
Ihe C~ eL~ a of the lines in the temperaturertime
trace of FIG. 16 ~n~c~tes t~hat the upper and lower part
~ temperatures have L.~ ~.~l f~ ol;~Ation temQerature,
which s;~n~lc the rem~val of t'he robotic arm. Thus, the
1~9~5
--11--
temperature of the matrix resin is taken on a oantinucus,
~ La~t basis and is used to precisely c~AlL ~l the overall
welding cycle.
m e heating wavelength of the lamps is approxImately
1.1 microns; the optical s*~o~ have a ~e~al ~ e of 8.0
to 14.0mucrons, which blinds them to v;c;hl~ light. RFC~I1CP the
ambient air may be very hot, the s~ o~ may be providad witn an
air cooling jacket. Alternatively, each s~ can be located
outside the heat area and mounted so that its optical lens faces
~r~ ly positioned right angle mirrors.
High-t~n~c~-~ture thermoplastics and thermoplastic com-
posites tend to cool rapidly. It is eqcPntiA~ ce~, that
the press holding the parts have a rapid dowl,~Loke of at least
one foot per cec~r~. To prevent ~Ple~prious efre~ on the joint
~L~a~e~ by hi~ s~ure impact of the adherends, the press
ut;l;~c a ~lhl P-downstroke function, as s~cwn in FIGS. 17A,
17B, 17C. Ihe press first closes at high s~eed to a ~Plpration
zone, which is about one half inch from material s~rfa oe. Then
final pressure is Ar~ on a ~pcplprated bas~s to a die stop.
FIG. 15 shows that parts 2A and 4A oomprising layered
quasi-isotropic oomposite panels (the cross-s~c~;~ns of which are
P~ praLed) ~ay have faoe layers 22 and 42 which are l~r~lly
reconsolidated. FIG. 15 also indicates the reciprocating
movement (arrow A, dark line and phantom end positions. FIGS.
14-15 also show the parAhnl;c/elliptical focus of the heaL~L~
rP~ e~t;ve portion at points on layers 22, 42.
Adaptable to dem~n~;n~ applications in the
aerospAcP/aircraft, automotive, me~;c~l, and other market
sectors, the process accomodates simple and complex joint
C~f;~lrAt;~nR~ lt~;n~ spot welds, U ~_ limensional welds,
and C~rt;~U~lC welds.
~ h;s inNP~ has been prA~;rF~ to achieve cu~ ~ing
weld ~LL~ ~ U ~ with 1~ a~ PPring thermoplastic
mater;~l~ of ~;g~f;~At~t military and commerc;al utility uses.
39~5
These materials include glass-, carbon-, and aramid-fiber
reir~ d poly~U~U~erketone (PE~, polyphenylene ~11 f;~
(PPS), polya~ P (PAI), polyetherimide (~ 1), polyarylate,
polysulfones, thermoplastic polymldes, and 1;~ crystal polymer
(LCP ' s) .
ll~r~ ctic c~rncites (TPC's) for hi~l ~e~Lo~
applications generally consist of a high-performance
theremoplastic matrix resin rei~o~e~ with fibers of ~d~Lul~,
graphite, fiberglass, or aramld. Some matrix resins used in
TPC's-are c~p~hle of oontinuous servi oe at 350' F to 700'F. m ey
include ~K, PPS, PEI, PES, PAI, and cth~h~s. m e reinLo~tments
are usually continucus and parallel or lamina~ed in different
directions to provide a stress-free, lightweight sheet of unNsual
L~Ll~.
m e potential performance and economic benefits of
thermoplastics vis-a-vis thermosets in advanced composite
~pli~Ations has been well documented and ; n~ e lower-cost
manllfA~lring, ir~f;n;te ~ Y~y stability, ~ f~ h;l;ty of
flat sheet stock r~e~ocessing to correct flaws and effect
repalrC~ ra~Le~ ~LU~ g cycles, high to~ s, and easier
quality oontrol. Most of these a~ L5y~ are due to the fact
that unlike thermosets, which are infusible and cannot be
soL~ ~ by heating once cured into shape, thermoplastics become
more viscous and flow when subjected to heat. m is
characteristic makes thermoplastics ~ hle and facilitates the
elimination of A~hP~q;ves and ~r~ ;c~l fasteners, koth of which
are less than desirable for high-performance structural
~rl;~A~ C. See, ~ ~2~, et al., ~ c For fusion R~n~;n~
ThermoplAct~F Co~po6ites", SAMPE Qyarterly Vol. 18, No. 1 (Oct.
1986).
m ere are many problems applying these tradit~O~Al
thermqplastic welding nk~l~ils to hi~. ~t~u~nance TPC~8 Such as
APC-2 rArh~n fiber re~L~oL~d ~kK or Ryton PFS oomposites, which
are LoLy~ie~ for ~rrl~cAticns that may require ~oints that are as
4 ~ 5
~LL~1~ as the composite itself. TPc laminates oomprise up to
seventy wt.% of reinforcement. While the introduction of
reinforcing fibers into a matrix dramatically upgrades the
physical ~,uL~ies of the c~Y~C;te, it often makes welding more
~;ff;~1lt since there is less resin avA;lAhle to melt and
LeC~ nl ;~te into a fused joint. Reducing the amount of
reil~oL~ment may i~Y~e wel~Ah;l;ty, but only at the ~'~L~ CP
of cr~s;te ~L~ ~ Ul. Also, the a~cu~31 1~ LIlA~tiss us~d as
matrix resins in T~c's m~st be ~Lu~ se~l at higher temperatNres
and have rui~n~er Il~L~ c;~ win~ s" than ccmmLdity and general
purpose en~;nPering resins. Ihis denands extremely precise
control of welding variables - par~ Arly the amcunt and time
of heat to achieve optimum joints. Welding m~U~s such as
induction, resistance, ultrasonics, and others that involve
preclamping of parts before the intr~ ~t;~ of hect do not
readily facilitate the direct sensing and mea~urement of joint
melt temperatures without the embedment of thermao~ ~ or
sensors in the joint area, a possible negative in many
Arrl;cAtions- ~he ~h~ invention avoids these ~;ff; ~11 ties.
m e basic ~LW~S steps used to join high ~e~LuLmance
TPC's using focused i~Lo~d melt fusion are as follows:
Surfaoe preparation: good wetting of a clean, rple~c~
agent-free, bond line is essential. ~l~An;~g ~oll~;~ns or plasma
treat~ t is preferable to sanding or abrading the surfaoe, which
may remove resin in the two facing a~ ~ plies and loosen the
fibers. Ihe high temperatures of the fo~lce~ IR reci~,u~aLing
beams (up to 1,200'F) tend to burn off surfa oe contaminants that
may be LL~ in asperites of the interfaoe layers.
Posit;~n;n~ of parts into press: two parts are rl~e~
into upper and lower h~ fixtures in a suitable press. m e
facing parts are held in oQen position durLng the heating stage.
Pn~ Ation of matrix tape t~p~;or~l): A fiber-free
tape of film or resin may be ~r~ to one part surfa oe (the
tape is chemically and thermally compatible with the matrix resin
1 3 ~
-14-
of the composite; a resin-rich surfa oe on the cr~pocite S~a~S
may elimlnate the need for this step). Au~U~r variable that may
enhance weld ~L~-yLh is to have the graphite fibers in
u m directional orientation in the first interface layers of each
adherend.
Setting of welding parameters: Surface melt
temperature gfals for each a~ ~ are set on two temperature
controllers; the press cycle time, robotic stroke distan oe, and
speed are set.
When the start button is ~#~3~, the robot will move
the fo~lcP~ ir~cL~ heating lamps into the cpen press area and
cxl:l3~ce horizontal reci~L~a~ion over the bond lines. during
the reci~ aLion stage, the l~o illuminate ;mme~;ately on the
first stroke and remain on while the np~r~l S~SUL~ read the
rising surfa oe temppr~lre of each interfa oe . The Sk~e~u~ sign21
the lamps' power controls to i~ ase or U~Lle down each
lamp's ;nt~C;ty until both ifiterfa oe temperature ~L~rints
match. At this point, the s~ ~ signal the robot to remove the
lamp fixtures fm m the press and start the dowl~LL~ ~ of the
press for completing the aperation. the press remains olq~e~
until the part ccols ~lff;~.;P~tly for removal and h~n~
The focal ~e~L of the upper heat sour oe is pointed
u~h~nd; the focal ~e~u~ of the lower heat scur oe is pointed
dkqnb~lnd. To limit peroolation in the la~ m ates (which can cause
interlam~inar slippAge, separation of fibers, and matrix
~;C~rt;n~)~ the parts to be joined are held as close to the
focal Vt~ of the lamp fixtures as ~Y~R;hl~.
During the reci~ aLion stage the surfa oe temperature
of hoth akn~ int~L~ac~B il~L~aSeB with each aLL~~e of the
robotic arm. Rec~llRe the plastic has a relatively low
coPff;~;Pnt of heat a~-7~;vity, during each brief cool;~ pbase
heat r~ t~R away fram the surface to the air LaU~ than to
interior layers of the composite. Thus, the ;r~rl~l temper~lre
remains virtually unaffected while the surface ten4~eLaL~re
1339~05
--15--
i~L~2SeS to the melt n~ point.
If the fo~lc4~ illrLar~ heat lam.~s were stationary over
the a~ ~~s at these high temperatures the matrix resin would
burn im~ediately. However, the bean is m~ving and not in any one
place long enough to cause b~u~l~ng. During the reci~o~ion of
the lam~s the material of each adherend ~ ~e~es an Ar~el~rated
exothermic reaction, that is, a chemir~l change in which there is
a liberation of heat, and an endothermic r~A~tin~ that is, a
rh~m;cAl change in ~hich there is an absorption of heat. It is
the periodicy of the intensely fo~lcP~ moving beams that creates
a faster growth of temperature at just the i~ Lrace~ of each
a~ ~ his alternate "~ ~k~P~mic/eYx*~l3rmic" ~LU~S iS a
unique aspect of fo~l-ce~ infrared melt fusion.
Bond lines up to s;Yte~n inches long and four inches
wide have been prQ~lcP~ and it is EYy~c;hle to prcduce much larger
bond line areas. Bond line length is controlled by the length of
the fo~lRP~ infrared lamp6, which are commercially available up
to one l~w~a~ inches long. The reci~lu~aLion zone controls bond
line width. Very wide bcnd lines are E~Y~c;hle by using multiple
lamp fixtures that are ~ side-by-side on the rnhot;c arms.
For example, four sets of back ~o ~0~ forty eight inch foQlcP~
infrared lamps ~F~re~ four inches apart can be used to heat a
bond line area twenty inches wide by forty eight inches long.
