Title: Device for welding thermoplastic plastic parts forming a hollow body by means of laser radiation
Abstract: A device for welding a plurality of thermoplastic plastic parts (parts to be joined) forming a hollow body with an opening by a laser, comprising a vacuum holder having a vacuum chamber which communicates with a vacuum pump, is open on one side and, together with the hollow body, forms a closed chamber that can be evacuated. When a vacuum is applied, the vacuum holder holds the hollow body stationary, holds the joined parts together and enables testing of the tightness of the weld.
Patent Number: 6,841,034 Issued on 01/11/2005 to Zuehlke, et al.
| Inventors:
|
Zuehlke; Hans-Ulrich (Jena, DE);
Eberhardt; Gabriele (Jena, DE);
Preuss; Norbert (Jena, DE);
Griebel; Martin (Jena, DE);
Weisser; Juergen (Jena, DE)
|
| Assignee:
|
JENOPTIK Automatisierungstechnik GmbH (Jena, DE)
|
| Appl. No.:
|
125206 |
| Filed:
|
April 17, 2002 |
Foreign Application Priority Data
| Apr 23, 2001[DE] | 101 20 351 |
| Current U.S. Class: |
156/379.8; 29/743; 156/272.8; 156/273.7; 156/304.2; 156/304.6; 156/380.9; 156/499; 219/121.63; 269/21 |
| Intern'l Class: |
B32B 031/28 |
| Field of Search: |
156/272.2,272.8,273.7,304.1-304.2,304.6,380.9,378,379.8,499,285-287
65/36
228/212,44.3,49.1,221,218
269/21
219/121.6-121.66
29/559,743,760
|
References Cited [Referenced By]
U.S. Patent Documents
| 3876409 | Apr., 1975 | Sangermano et al.
| |
| 4414460 | Nov., 1983 | Sudo et al. | 219/121.
|
| 4857811 | Aug., 1989 | Barrett et al. | 318/3.
|
| 4982555 | Jan., 1991 | Ingemann.
| |
| 6000600 | Dec., 1999 | Erikson et al. | 228/212.
|
| Foreign Patent Documents |
| 3704792 | Sep., 1988 | DE | .
|
| 54 080338 | Jun., 1979 | JP.
| |
| 59 184 750 | Oct., 1984 | JP.
| |
| 11 348132 | Dec., 1999 | JP.
| |
Other References
English Abstract of JP 54 080338.
English Abstract of JP 11 348132.
English Abstract of JP 59 184 750.
|
Primary Examiner: Copenheaver; Blaine
Assistant Examiner: Rossi; Jessica
Attorney, Agent or Firm: Reed Smith LLP
Claims
What is claimed is:
1. A device for welding a plurality of thermoplastic plastic parts forming
a hollow body with an opening, comprising:
a device for holding stationary the hollow body composed of the
thermoplastic plastic parts;
a device for generating a force which presses together surfaces of the
thermoplastic plastic parts forming a joint zone; and
a tool head which is guided along the joint zone and which introduces laser
radiation resulting in a weld into the joint zone;
said device for holding and said device for generating a force being
comprised of an individual vacuum holder which has a vacuum chamber that
communicate with a vacuum pump, is open on one side and, together with the
hollow body, forms a closed chamber which can be evacuated,
wherein the open side of the vacuum chamber is smaller in cross section
than the opening of the hollow body, and the hollow body rests on a
sealing disk surrounding the open side of the vacuum chamber by a
terminating surface forming the opening.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority of German Application Serial No. 101 20
351.9, filed Apr. 23, 2001, the complete disclosure of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a device for welding thermoplastic plastic
parts forming a hollow body by means of laser radiation as is known
generically from JP 11348132.
b) Description of the Related Art
Thermoplastic plastic parts (parts to be joined) can be connected to one
another by different welding methods in which different kinds of energy,
such as laser radiation, are used to fuse the parts to be joined.
DE 19510493 describes a thermoplastic housing and a method for welding
thermoplastic housing parts by means of a laser. The basic idea consists
in that the two housing parts to be welded, at least in the region of the
joint zone (entire area in which a melt is formed), are made on the one
hand from a material which is extensively transparent to the laser
radiation and, on the other hand, from a material which extensively
absorbs the laser radiation, and the laser radiation is directed to the
housing in such a way that it initially penetrates the material that is
transparent to the laser radiation and subsequently impinges on the
material which absorbs the laser radiation.
The fact that the energy needed for producing the weld connection can reach
the joint zone via one of the parts to be joined allows the possibility of
a free arrangement of the weld seam in the housing, i.e., the weld seam
need not extend in a plane, but may also extend three-dimensionally or in
the interior of the housing. In principle, this allows a much more
flexible possibility for shaping the housing parts and joint zone compared
with other methods known from the prior art. Moreover, even housings with
very thick walls can be welded. The parts to be joined can be butt-joined
or lap-joined.
The quality of a weld formed in this way, which is intended in particular
to ensure a tight connection between the joined parts, but also should be
formed without melt flashing so as to avoiding finishing work, is
influenced by various steps in the prior art. This may involve special
arrangements of the housing parts in the area of the joint zone which
influence the shape of the melt and/or producing an engagement (frictional
or positive connection) between the housing parts to be joined during the
welding process in order to achieve a defined joining gap.
It is stated in DE 195 10 493 that the quality of the weld can be enhanced
by applying pressure to the joining zone until cooled. In so doing, the
pressure should preferably be applied adjacent to the focus of the laser
beam, so that the laser radiation can penetrate into the workpiece without
hindrance. Also expressed is the idea of using transparent clamping means
in the area of the laser beam in order to be able to carry out the
application of pressure directly in the area in which the laser radiation
acts. The pressure action should preferably follow the movement of the
laser beam along the joint zone.
A disadvantage in generating applied force, as suggested herein, is that
the parts to be joined must be shaped in such a way that clamping means
can make contact in the area of the joint zone. Readjustment of the
clamping means requires constant tightening and loosening which, in
particular, requires additional expenditure on apparatus. Moreover, the
time in which force is applied in each instance is very limited when
readjusting the clamping means unless the duration over which the process
is carried out is increased.
In DE 4432081, devices for fixing the parts to be joined for welding by
radiation energy are criticized as disadvantageous because of their
wastefulness. The stated object is to find a solution in which plastic
parts can be welded together by means of radiation energy without devices
for fixing the parts to be connected. The solution consists in that the
parts to be joined are fixed with respect to one another by a positive
engagement, particularly in the effective direction of force, starting
with the formation of the melt (melt pressure), e.g., by means of a
snap-in connection or a thread. It is also suggested that the parts to be
joined be fixed relative to one another by an "inner frictional engagement
such as screws or magnets". Fixing must then be dimensioned only in such a
way that the local welding pressure moving along the contour of the seam
as the beam is guided is absorbed.
However, this means that special steps must be taken in every case with
respect to the construction of the two parts to be joined. Even if this
did not contradict the function and desired arrangement, it necessarily
means increased preliminary fabrication costs and additional material
costs, e.g., for the above-mentioned magnets or screw connections. In the
case of large-series manufacture and mass production, the increased
expenditure may far exceed the expenditure on apparatus for fixing, which
can be reused over and over.
DE 4225679 is directed to a method and a device for welding the upper part
and lower part of a housing, wherein a filter disk is introduced between
the housing parts to be welded. In this case, particularly strict
requirements are imposed on the dimensional tolerance of the joint gap and
on the strength of the joint seam. Continuous quality control must be
carried out. In the described device, the individual parts to be welded
must be arranged one on top of the other and pressed together by a
pressing device, while a laser beam is guided along the joint seam to be
welded. No mention is made in the description regarding the pressing
device or the contact pressing force generated by it.
JP 11348132 also discloses a method and a device for laser welding. In this
case, also, two housing parts forming a hollow body are to be welded
together by means of a laser. Specifically, the hollow body mentioned
herein is a lamp with a reflector as lower part of the housing and a light
disk as upper part of the housing. The reflector is arranged horizontally
in a stationary manner so as to be supported by its edge on the cylinder
wall of a holding device. A pressing device supported on the light disk
presses the light disk firmly on the edge of the reflector. On the one
hand, the holding device and the pressing device in cooperation perform
the function of the pressing or clamping devices known in the art in that
they press together the two parts to be joined at their joining surfaces
forming the joint zone; on the other hand, it serves to hold and
accordingly position the housing relative to the laser which is guided
along the joint zone for carrying out the welding process. Compared with
the solutions known in the art for pressing together the joint surfaces,
this solution is characterized in that the housing is held and positioned
by it in addition.
However, the disclosed device is narrowly limited in its application with
respect to the shape of the housing and the position of the joint zone in
the housing. Further, the shape of the pressing device must be adapted to
the surface shape of the light disk.
It is not known from the prior art whether a device of this kind performs
additional functions beyond those of pressing together the joint surfaces
and holding the housing.
OBJECT AND SUMMARY OF THE INVENTION
It is the primary object of the invention to provide a device by which a
hollow body which comprises a plurality of parts to be joined and which is
provided with an opening can be held stationary for purposes of welding by
laser radiation, held together and tested for tightness of the weld. The
device must generate a uniform joining pressure in the joint zone and be
usable for a variety of differently shaped hollow bodies.
The object of the invention is met for a device for welding a plurality of
thermoplastic plastic parts forming a hollow body with an opening in that
the device for holding and the device for generating a force are comprised
in an individual vacuum holder (1) which has a vacuum chamber (2) that
communicates with a vacuum pump (4), is open on one side and, together
with the hollow body, forms a closed chamber which can be evacuated.
An idea essential to the invention consists in that, due to the fact that a
vacuum chamber which is open on one side is closed by the part of the
hollow body having the opening, all joint zones between the parts to be
joined which form the hollow body are acted upon, regardless of their
position and geometric shape, by a joining pressure when the vacuum
chamber is evacuated.
The invention will be described more fully in the following with reference
to embodiment examples and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 shows a schematic view of a device according to the invention with a
first construction of the vacuum holder with a first housing; and
FIG. 2 shows a schematic view of a second construction of the vacuum holder
with a second housing.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The device shown in FIG. 1 essentially comprises a vacuum holder 1 with a
vacuum chamber 2 and a sealing disk 3 and a vacuum pump 4 connected to the
vacuum chamber 2, a pressure sensor 5, a signal-transmitting unit 6 and a
control unit 7. The device serves to hold a hollow body comprising a
plurality of parts to be joined, to press together the parts to be joined
and to test the tightness of the weld produced between the joint surfaces.
The specific construction of the vacuum holder 1 may vary depending on the
shape of the hollow body to be held. In the construction shown in FIG. 1,
a lamp housing is to be held, this lamp housing comprising a reflector 8
constituting the lower part to be joined and a light disk 9 constituting
the upper part to be joined. The reflector 8 is constructed so as to be
rotationally symmetric at the end remote of the light disk 9 with an
opening about its axis of symmetry. The terminating surface surrounding
the opening is a radial plane surface. The reflector 8 is placed by this
plane surface on the sealing disk 3 resting on the vacuum chamber 2. In
every case, the vacuum chamber 2 is a chamber which is open on one side
and which, only after insertion of the entire hollow body into the vacuum
holder 1, forms together with the latter a closed chamber which can be
evacuated. When the reflector 8 is placed on the sealing disk 3, it is
guided along its circumferential surface into an O-ring 10 in such a way
that the opening of the reflector completely encloses the open side of the
vacuum chamber. In the lamp housing shown in FIG. 1, the two parts to be
joined are connected with one another in a positive engagement to the
extent that there is still a free translatory movement direction. The
positive engagement serves merely as an aid for assembly in this case and
conceals the joint zone from the outside. This positive engagement no
longer has a holding function after the vacuum is applied in the vacuum
chamber 2. When a vacuum is generated, the light disk 9 is pressed by its
joint surface against the joint surface of the reflector 8 with a force
proportional to the vacuum and accordingly also presses the reflector 8
itself around the opening on the sealing disk 3 by its plane surface. It
is not possible with any of the clamping means known from the description
of the prior art to generate such a uniform and easily controllable
joining force without obstructing free access to the joint zone for the
welding tool. A tool head (not shown) for directing the laser beam to the
joint zone can be directed axially to radially on the joint zone from many
different directions. The joint zone can accordingly occupy virtually any
position on the hollow body. Hollow bodies comprising more than two parts
to be joined can also be held for laser welding with this vacuum holder 1.
With respect to the chosen example of a lamp housing, it may be useful,
e.g., to form the light disk from a plurality of segments and connect it
to the reflector. In principle, the shape of the individual parts to be
joined is unimportant; it is only necessary that, together, they form a
hollow body with an opening.
The manner of operation of the device shown in FIG. 1 will now be
described.
After the reflector 8 is placed on the vacuum chamber 2 and the light disk
9 has been joined to the reflector (naturally, the parts can also be
assembled beforehand) and a vacuum of suitable intensity has been
produced, the laser welding process begins. As in conventional methods and
devices, the laser beam is guided along the joint zone. After the welding
process has been concluded, the vacuum is still maintained for a while in
order to test the tightness of the weld. In so doing, the device according
to the invention fulfills its third function. The vacuum is monitored via
a pressure sensor 5. In the embodiment example described with reference to
FIG. 1, the pressure sensor 5 is connected with a signal-transmitting unit
6 and a control unit 7. The signal-transmitting unit 6 can be, for
example, a unit transmitting a video signal, namely, a monitor, on which
the pressure increase and pressure drop are illustrated graphically. It
can also deliver an acoustic signal, e.g., in case of a too rapid increase
in pressure resulting from a leaky weld. However, it can also be a printer
which documents the test results as proof of 100% quality control. By
forwarding the measurement results of the pressure sensor 5 to the control
unit 7 connected with the vacuum pump 4, it is possible to regulate the
vacuum generation as a function of the pressure increase, particularly
during the welding process, in order to ensure a constant joining
pressure. Of course, a determined pressure curve can also be realized by
means of the control unit instead of a constant joining pressure during
the welding process. FIG. 2 shows a second construction of a vacuum
holder. It likewise serves to receive a lamp housing comprising a
reflector 8 and a light disk 9. The reflector 8 is also substantially a
rotationally symmetric part with an opening around the axis of symmetry in
this case. However, the surface bordering the opening is not located in a
radial plane in this case, but rather in a plane which is inclined
relative to the axis of symmetry. This surface is therefore not
particularly well suited to act as a sealing surface directly or
indirectly via a sealing disk 3. Therefore, another circumferential
surface of the hollow body must be found for sealing. A collar on the
reflector 8 placed on the sealing disk 3 is available for this purpose. At
the same time, the collar also offers the joint surface necessary for
producing the weld connection with the light disk 9.
The signal-transmitting unit 6 mentioned in the first embodiment example is
not necessary when there is no testing of tightness carried out with the
device. In principle, the use of the device is not limited to application
in laser welding. However, it can be used in a particularly advantageous
manner for this purpose, since the possibilities of guiding the tool head
relative to the housing remain entirely unaffected and the advantages of
laser welding can accordingly be exploited to the fullest.
While the foregoing description and drawings represent the present
invention, it will be obvious to those skilled in the art that various
changes may be made therein without departing from the true spirit and
scope of the present invention.
List of Reference Numbers
1 vacuum holder
2 vacuum chamber
3 sealing disk
4 vacuum pump
5 pressure sensor
6 signal-transmitting unit
7 control unit
8 reflector
9 light disk
10 O-ring
*
