U.S. patent application number 11/773336 was filed with the patent office on 2007-10-25 for method and apparatus for controlling a vent gap with active material elements.
This patent application is currently assigned to HUSKY INJECTION MOLDING SYSTEMS LTD.. Invention is credited to Joachim Johannes NIEWELS.
Application Number | 20070246851 11/773336 |
Document ID | / |
Family ID | 35135605 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070246851 |
Kind Code |
A1 |
NIEWELS; Joachim Johannes |
October 25, 2007 |
METHOD AND APPARATUS FOR CONTROLLING A VENT GAP WITH ACTIVE
MATERIAL ELEMENTS
Abstract
Method and apparatus for controlling a vent gap in a mold for an
injection molding machine are provided, and include an active
material insert configured to be regulate the degree of opening of
the vent gap. The active material insert is configured to be
actuated in response to signals from a controller, so as to
selectively block the opening of the vent gap during the molding
process. Wiring structure is coupled to the active material insert,
and is configured to carry the actuation signals. Melt flow sensors
may also be provided to aid in regulating the vent gap, and may be
connected to the controller in order to provide real-time closed
loop control over the operation of the vent gap. Preferably, the
methods and apparatus are used as part of a system for controlling
the flow of melt within a mold cavity.
Inventors: |
NIEWELS; Joachim Johannes;
(Thornton, CA) |
Correspondence
Address: |
PATENT ADMINISTRATOR;KATTEN MUCHIN ROSENMAN LLP
1025 THOMAS JEFFERSON STREET, N.W.
EAST LOBBY: SUITE 700
WASHINGTON
DC
20007-5201
US
|
Assignee: |
HUSKY INJECTION MOLDING SYSTEMS
LTD.
Bolton
CA
|
Family ID: |
35135605 |
Appl. No.: |
11/773336 |
Filed: |
July 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10830438 |
Apr 23, 2004 |
|
|
|
11773336 |
Jul 3, 2007 |
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Current U.S.
Class: |
264/40.7 |
Current CPC
Class: |
B29C 2945/76381
20130101; B29C 2945/76458 20130101; Y10S 425/226 20130101; B29C
45/34 20130101; B29C 2945/76762 20130101; B29C 2945/76859 20130101;
B29C 45/76 20130101; B29C 2945/76257 20130101; B29C 2945/76732
20130101; Y10S 425/812 20130101; B29C 2945/76257 20130101; B29C
2945/76006 20130101; B29C 2945/76732 20130101; B29C 2945/76762
20130101; B29C 2945/76525 20130101 |
Class at
Publication: |
264/040.7 |
International
Class: |
B29C 45/30 20060101
B29C045/30 |
Claims
1. A method of regulating a vent gap in an injection mold,
comprising the steps of: actuating said piezoceramic actuator to
adjust a width of said vent gap, to restrict the flow of melt
through said vent gap.
2. The method of claim 1, wherein the width of said vent gap is
adjusted based upon one or more factors selected from the group
consisting of melt temperature, melt composition, and melt
pressure.
3. A method of controlling a fluid flow path through a mold cavity,
comprising the steps of: injecting melt into said mold cavity;
sensing melt fronts as said melt flows throughout the mold cavity
and transmitting signals corresponding to said melt fronts from
said sensors to said controller; and transmitting signals from said
controller to actuate said active material actuators, wherein said
active material actuators are actuated to control said vents and
control melt flow through said mold cavity.
Description
[0001] The present application is a divisional of U.S. patent
application Ser. No. 10/830,438, filed Apr. 23, 2004, the entire
contents of which are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method and apparatus in
which active material elements are used in injection molding
machine equipment (e.g., hot runner nozzle assemblies) in order to
adjust a vent gap within a mold. "Active materials" are a family of
shape altering materials such as piezoactuators, piezoceramics,
electrostrictors, magnetostrictors, shape memory alloys, and the
like. In the present invention, they are used to adjust the vent
gap within an injection mold, thereby improving the quality of the
molded article. The active material elements may also be used as
sensors.
[0004] 2. Related Art
[0005] Active materials are characterized as transducers that can
convert one form of energy to another. For example, a piezo
actuator (or motor) converts input electrical energy to mechanical
energy causing a dimensional change in the element, whereas a piezo
sensor (or generator) converts mechanical energy--a change in the
dimensional shape of the element--into electrical energy. One
example of a piezoceramic transducer is shown in U.S. Pat. No.
5,237,238 to Berghaus. One supplier of piezo actuators is Marco
Systemanalyse und Entwicklung GmbH, Hans-Bockler-Str. 2, D-85221
Dachau, Germany, and their advertising literature and website
illustrate such devices. Typically an application of 1,000 volt
potential to a piezoceramic insert will cause it to "grow"
approximately 0.001 5''/inch (0.15%) in thickness. Another
supplier, Mide Technology Corporation of Medford, Me., has a
variety of active materials including magnetostrictors and shape
memory alloys, and their advertising literature and website
illustrate such devices, including material specifications and
other published details.
[0006] FIGS. 1a-5 show a prior art mold to explain the venting
problem. FIGS. 1a-1c show three views of a mold. The left view is
the plan view of the core side, the right view is the plan view of
the cavity side. The center view shows a section through the closed
assembled mold. The mold comprises a cavity block 410 and a core
block 411 and several ejector pins 412, 413 and 414. Both mold
haves contain cooling channels 415 and 416. The cavity block 410
contains a vent 417, vent collector channel 418 and vent exhaust
passage 419. The cavity block 410 also contains a melt sprue
channel 420 for introducing the melt. The core block 411 contains a
melt runner 421, gate 422 and sprue puller 423 machined in the core
block 411. The closed mold encloses the mold cavity 424 which will
form the part to be molded.
[0007] FIG. 2 shows the plastic material being injected into the
closed mold cavity entering via sprue channel 420, runner 421 and
through gate 422. As the resin 425 begins to fill the cavity 424,
it displaces the air 426 that previously occupied that space. The
melt pushes the air ahead of its flow path. Vent 417 has been
positioned in the mold to provide a passageway for the air to
escape and for this passageway to remain open until the resin has
completely filled the mold cavity 424. Thus the vent 417 is usually
positioned at a part of the mold cavity 424 periphery usually the
furthest distance from the gate 422, the point at which the resin
enters the mold cavity. If the vent were to be positioned at some
other point the incoming resin may reach the vent, blocking it off
and prevented any remaining air in the mold cavity from escaping
through it.
[0008] The vent 417 is sized such that when the resin reaches that
location it will not flow into the vent or the vent collector 418
beyond it. The vent gap 430 is typically 0.025 mm-0.075 mm
(0.001''-0.003''), which is a large enough space to allow air to
pass through, but a small enough space to prevent most resins from
being able to flow therethrough. The depth of the vent is called
the land 431 and is typically 0.625 mm-1.250 mm (0.025''-0.050'').
The vent collector 418 is a much larger channel behind the vent 417
to allow unrestricted passage for the air that has passed through
the vent. Vent exhaust passage 419 connects the vent collector 418
to the mold exterior so the air can exhaust to ambient conditions.
The exhausted air exits the mold as indicated by arrow A in FIG. 2.
When the injected melt reaches the vent it is too viscous to enter
the small gap. FIG. 3 shows the filled cavity. FIG. 4 shows the
mold opening and the ejector pins activated to push the solidified
part 441 off the core half of the mold.
[0009] FIG. 5 shows what happens when the injected melt enters the
vent and vent collector. This can happen if the melt injection
pressure is high enough to overcome the clamping force holding the
mold closed and the mold halves are forced apart, consequently
increasing the vent gap and allowing the melt to enter.
Alternatively, the viscosity of the melt being processed may happen
to be much lower than that for which the vent gap has been
designed. Sometimes this molded flash 440 remains attached to the
molded part 441 and is ejected with it as illustrated in FIG. 5. On
other occasions, the flash breaks off and remains in the vent and
vent collector blocking them for the next molding cycle, and
consequently the mold venting functions poorly and may result in a
defective part being molded.
[0010] Another vent problem that may occur is when the vent gap is
reduced or eliminated by hobbing of the mold. Because the vent is
positioned on the mold's parting line 490 the repeated opening,
closing, and clamping of the mold, as it cycles, can cause the
parting line surface to gradually collapse. The effect of this is
to reduce the vent gap. Periodically as molds wear their vents are
remachined to restore the correct vent gap. When the vent gap is
reduced or eliminated, the resulting poor or no venting of the mold
cavity during the injection process may cause defective parts to be
molded.
[0011] A Plastics Machinery & Equipment article by William J.
Tobin, titled "Venting from the Inside", contains a general
overview of venting in injection molds.
[0012] U.S. Pat. No. 5,238,389 to Brandau et al. discloses a blow
mold clamp mechanism for closing blow mold halves to an adjustable
closed position, leaving a predetermined gap therebetween to act as
a vent. In blow molding, the material in the cavity is a heated
parison or preform that is being expanded in size by a compressed
fluid in order to conform to the cavity shape. While there is a
need to vent the mold to exhaust the air displaced by the expanding
preform, the risk of material entering the vent gap is much lower
than it is in an injection mold in which the material is in a
heated fluid condition.
[0013] U.S. Pat. No. 4,489,771 to Takeshima et al. discloses means
for automatically closing the vent of an injection mold when the
injected material reaches the vent. A complicated, space-consuming
mechanism is used at each vent location to preform this
function.
[0014] EP 0 448 855 to Ryobi discloses a gas vent control valve for
opening and closing a gas vent passage in a mold. The time taken
from when the vent is signaled to close until it is actually closed
is measured and compared to a preset period. If the actual time
taken exceeds the preset period, an alarm is sounded, signaling an
abnormality in operation.
[0015] U.S. Pat. No. 4,995,445 to Shigyo discloses a gas vent valve
in a mold that is operated to close the vent passage in response to
a pressure from the molten material in the mold cavity. A complex,
space-consuming mechanism is mounted in the mold at the periphery
of the mold cavity.
[0016] U.S. Pat. No. 5,397,230 to Brew discloses a vent apparatus
for a mold comprising a reciprocating pin. The vent pin is
responsive to a full resin level in the mold cavity to close the
vent opening. While the vent pin is closed, cleansing fluid is
circulated through the vent passage to clear resin debris prior to
it hardening. The apparatus comprises a comparatively large pin and
operating cylinder arrangement attached to the side of the mold
cavity.
[0017] U.S. Pat. No. 5,683,730 to Katsumata et al. discloses a
mechanically-operated closeable vent arrangement. There is a
detection chamber that reacts to the incoming melt pressure and
moves to operate a pin that closes the vent. A relatively large
apparatus is used that takes up space in the mold structure.
[0018] Thus, what is needed is a new technology capable of closing
a vent passage in a mold when the incoming melt material reaches
the vent means, preferably including adjustable control, and
preferably with embedded sensors and closed loop control of the
closing function.
SUMMARY OF THE INVENTION
[0019] It is an advantage of the present invention to provide
injection molding machine apparatus and method to overcome the
problems noted above, and to provide an effective, efficient means
for adjusting an opening of a vent gap in an injection molding
machine.
[0020] According to a first aspect of the present invention,
structure and/or steps are provided for controlling an injection
mold vent gap, including an active material disposed adjacent the
vent gap and configured to change dimension upon application of an
electrical signal to at least partially close the vent gap, and
transmission structure configured, in use, to supply the electrical
signal to said active material element.
[0021] According to a second aspect of the present invention,
structure and/or steps are provided for an injection mold vent gap
control device including a piezo-electric actuator disposed to at
least partially block a mold vent that is in communication with a
mold cavity.
[0022] According to a third aspect of the present invention,
structure and/or steps are provided for an injection mold,
including a first mold half, a second mold half, a vent for venting
gas from at least one of the first mold half and the second mold
half, and a piezoelectric element configured to change dimension
upon application and removal of an actuation signal thereto, said
dimension change at least partially closing or opening said vent to
control the venting of gas therethrough.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Exemplary embodiments of the presently preferred features of
the present invention will now be described with reference to the
accompanying drawings in which:
[0024] FIGS. 1a, 1b, and 1c show three schematic views of a prior
art mold with a conventional vent;
[0025] FIG. 2 is a sectional view of the mold in FIG. 1b with the
incoming material partially filling the mold cavity;
[0026] FIG. 3 is a sectional view of the mold in FIG. 1b with the
material filling the mold cavity;
[0027] FIG. 4 is a sectional view of the mold in FIG. 1b with the
mold in a partially open position and the molded part being
ejected;
[0028] FIG. 5 is a sectional view of the mold in FIG. 1b with the
mold in a partially open position and the molded part having a
flashed vent portion being ejected;
[0029] FIG. 6 is a sectional view of a mold showing one embodiment
of the invention in which a vent gap is regulated using an active
material insert;
[0030] FIG. 7 is a sectional view of a mold in FIG. 6 with the
incoming material partially filling the mold cavity; and
[0031] FIG. 8 is a sectional view of a mold showing a second
alternate embodiment of the invention in which a vent is regulated
using an active material insert.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY
EMBODIMENTS
1. Introduction
[0032] The present invention will now be described with respect to
several embodiments in which a plastic injection-molding machine is
supplied with one or more active material elements which serve to
regulate vent gaps in injection molds. However, the active material
sensors and/or actuators may be placed in any location in the
injection molding apparatus in which venting may be desirable.
Other applications for such active material elements are discussed
in the following related applications: (1) U.S. patent application
Ser. No. 10/830,434, filed concurrently on Apr. 23, 2004, entitled
"Method and Apparatus for Countering Mold Deflection and
Misalignment Using Active Material Elements", (2) U.S. patent
application Ser. No. 10/830,403, filed concurrently on Apr. 23,
2004, entitled "Method and Apparatus for Adjustable Hot Runner
Assembly Seals and Tip Height Using Active Material Elements", (3)
U.S. patent application Ser. No, 10/830,435, filed concurrently on
Apr. 23, 2004, entitled "Method and Apparatus for Assisting
Ejection from an Injection Molding Machine using Active Material
Elements", (4) U.S. patent application Ser. No. 10/830,485, filed
concurrently on Apr. 23, 2004, entitled "Method and Apparatus for
Mold Component Locking Using Active Material Elements", (5) U.S.
patent application Ser. No. 10/830,488, filed concurrently on Apr.
23, 2004, entitled "Methods and Apparatus for Vibrating Melt in an
Injection Molding Machine Using Active Material Elements", (6) U.S.
patent application Ser. No. 10/830,436, filed concurrently on Apr.
23, 2004, entitled "Method and Apparatus for Injection Compression
Molding Using Active Material Elements", and (7) U.S. patent
application Ser. No. 10/830,437, filed concurrently on Apr. 23,
2004, entitled "Control System for Utilizing Active Material
Elements in a Molding System".
[0033] As discussed above, there is a need in the art for a method
and apparatus for adjusting one or more vent gaps in an injection
molding machine mold in a proactive manner by providing active
material means and methods for adjusting vent gaps. In the
following description, piezoceramic inserts are described as the
preferred active material. However, other materials from the active
material family, such as magnetostrictors and shape memory alloys
could also be used in accordance with the present invention. A list
of possible alternate active materials and their characteristics is
set forth below in Table 1, and any of these active materials could
be used in accordance with the present invention: TABLE-US-00001
TABLE 1 Comparison of Active Materials Temperature Nonlinearity
Structural Cost/Vol. Technical Material Range (.degree. C.)
(Hysteresis) Integrity ($/cm3) Maturity Piezoceramic -50-250 10%
Brittle 200 Commercial PZT-5A Ceramic Piezo-single -- <10%
Brittle 32000 Research crystal TRS-A Ceramic Electrostrictor 0-40
Quadratic <1% Brittle 800 Commercial PMN Ceramic Magnetostrictor
-20-100 2% Brittle 400 Research Terfenol-D Shape Memory Temp. High
OK 2 Commercial Alloy Nitinol Controlled Magn. Activated <40
High OK 200 Preliminary SMA NiMnGa Research Piezopolymer -70-135
>10% Good 15* Commercial PVDF (information derived from
www.mide.com)
2. The Structure of the First Embodiment
[0034] The first preferred embodiment of the present invention is
shown in FIGS. 6 and 7, which depict a piezoceramic insert 450
mounted in a mold cavity block 460 in a vent location. The insert
is electrically connected via conduit 451 to a controller 452. A
melt sensor 453 is mounted in the cavity block 460 close to the
insert 450 and in a position to detect the incoming melt before it
reaches the insert 450. The sensor 453 is also connected via
conduit 454 to controller 452.
[0035] According to an alternate embodiment of the present
invention, a mold cavity may include multiple piezoceramic insert
controlled vents at several locations. These inserts are all
connected to the same controller, and their operation is
synchronized and coordinated by the controller to adjust the
individual vent gaps to vary the amount of venting available at
each location. This in turn will influence to some degree how the
melt front progresses in the filling of the mold cavity. Thus, it
is possible to control the melt front causing it to accelerate in
some areas and decelerate in others by a coordinated actuation of
the various vent gaps.
[0036] According to the presently preferred embodiment according to
the present invention, a piezoceramic insert 450 is connected by
wiring 451 to a controller 452, although wireless methods of
control are also possible. Optionally, one or more separate
piezoceramic sensors (not shown) may be provided to detect changes
in the vent gap opening, and when provided are also connected by
wiring 451 to the controller 452. The piezoelectric elements used
in accordance with the present invention (i.e., the piezo-electric
sensors and/or piezo-electric actuators) may comprise any of the
devices manufactured by Marco Systemanalyse und Entwicklung GmbH. A
piezo-electric sensor may detect the state of the vent gap, and
transmit a corresponding sense signal through the wiring
connections 451, thereby effecting closed loop feedback control.
The piezo-electric actuator receives an actuation signal through
the wiring connections 451 and applies a corresponding force to
adjust the opening of the vent gap. Note that piezo-electric
sensors may also be provided to sense pressure from any desired
position. Likewise, more than one piezo-electric actuator may be
provided, mounted serially or in tandem, in order to effect
extended movement, angular movement, etc.
[0037] Piezoceramic actuator 450 is preferably a single actuator.
According to a presently preferred embodiment, the actuator
increases in size by approximately 0.015% when a voltage of 1000 V
is applied via wiring 451. However, use of multiple actuators
and/or actuators having other shapes are contemplated as being
within the scope of the invention, and the invention is therefore
not to be limited to any particular configuration of the
piezoceramic insert 450.
[0038] Note that piezoceramic sensors may be provided to sense
pressure at any desired position. Likewise, more than one
piezoceramic insert 450 may be provided, mounted serially or in
tandem, in order to effect extended movement, angular movement,
etc. Further, each piezoceramic element may be segmented into one
or more arcuate, trapezoidal, rectangular, etc., shapes which may
be separately controlled to provide varying vent closing forces at
various locations between the vent gap. Additionally,
piezo-electric actuators and/or actuator segments may be stacked in
two or more layers to effect fine sealing force control, as may be
desired.
[0039] The wiring 451 is coupled to any desirable form of
controller or processing circuitry 452 for reading the
piezo-electric sensor signals and/or providing the actuating
signals to the piezo-electric actuators. For example, one or more
general-purpose computers, Application Specific Integrated Circuits
(ASICs), Digital Signal Processors (DSPs), gate arrays, analog
circuits, dedicated digital and/or analog processors, hard-wired
circuits, etc., may control or sense the piezo-electric element 450
described herein. Instructions for controlling the one or more
processors may be stored in any desirable computer-readable medium
and/or data structure, such floppy diskettes, hard drives, CD-ROMs,
RAMs, EEPROMs, magnetic media, optical media, magneto-optical
media, etc.
[0040] Use of the piezoceramic insert 450 according to the present
embodiment allows the various components of the injection mold
assembly described above to be manufactured to lower tolerance,
thereby decreasing the cost of manufacturing the injection mold
components and associated machinery. Previously, tolerances of 5-30
microns were used in order to achieve a functional vent gap.
Further benefits include the ability to control the size of the
vent gap more efficiently, thereby preventing leakage of melt from
the vent gap, or clogging of the vent gap, thereby reducing the
length of any equipment down time.
3. The process of the First Embodiment
[0041] In operation, the piezoceramic insert 450 is sized and
positioned in the mold cavity block 460 to provide an optimum vent
gap, which can be larger than the nominal 0.025 mm-0.075 mm
(0.001''-0.003'') range, a size that would allow the melt to enter
the vent gap. At this optimum vent gap the air being exhausted from
the mold cavity experiences no resistance to flow as it passes
through the vent gap and vent collector 455. FIG. 7 shows the
injected plastic melt 491 advancing towards the vent area. As the
melt approaches and eventually touches the sensor 453, which may
detect a rapid rise in temperature or pressure, sensor 453
transmits a signal via conduit 451 to controller 452.
[0042] When the piezo-electric sensor is used with the actuator in
a closed loop control configuration, the sensor element generates a
signal in response to contact with the injected plastic melt 491
(which may be based on changes in temperature, pressure, etc.), and
transmits the signal via conduit 451 to the controller 452. Based
on the signals received from the sensor, the controller then
generates appropriate actuation signals that are transmitted via
conduit 451 to the actuator element, energizing it in accordance
with the data received from the sensor to accomplish proper vent
gap control. For example, the controller 452 may be programmed to
cause the sealing force at the vent gap or to increase and/or
decrease according to the detected temperature, pressure, etc.
[0043] Controller 452 may include a computer or PLC or similar
device for receiving the sensor's signal, evaluating its magnitude
and consequently sending a command signal to the piezoceramic
insert 450 via conduit 451. The command signal may energize the
insert sufficiently to partially reduce the vent gap or to
completely close the vent gap depending upon the resin being
injected into the mold and/or a variety of other parameters that
may have been input to the controller. For example, the injection
rate, melt temperature, mold temperature and injection pressure are
parameters that may be sensed and input to the controller since
they all have an effect on the way the melt will fill the mold
cavity and consequently affect the timing and gap setting
parameters of the vent. Some or all of these parameters may be
included in the controller's computation of the command signal it
eventually dispatches to the insert 450. The command signal to the
insert 450 will activate the insert to either prevent plastic from
entering the vent and collector, or it may be activated earlier in
the filling process based other sensed parameters, such as those
listed above, so that an alteration in the vent gap will alter the
speed at which air is exhausted from the mold, which in turn may
cause the melt front to alter direction or speed thereby effecting
a control on how the melt fills the cavity.
4. The Structure of the Second Embodiment
[0044] A second preferred embodiment according to the present
invention is shown in FIG. 8, which shows a mold cavity 474 with
two gates 470 and 471 such that melt enters the cavity from two
places. The respective melt fronts 472 and 473 eventually meet at
some point near the middle of the mold cavity 474. Clearly air in
the mold cavity is pushed by both melt fronts and can become
trapped in the middle of the cavity absent a vent. To exhaust the
air a vent 475 is provided at the location where the melt fronts
472 and 473 are expected to meet. A piezoceramic insert 476 is
positioned at the vent 475 to control the vent gap. The insert is
connected via conduit 477 to a controller 483 for controlling the
vent gap as previously described. Vent collector channel 478
provides an enlarged passageway for the air to exit the vent. Arrow
B indicates the air exhausting from the mold cavity as the melt
fronts approach each other.
[0045] Sensors 479 and 480 are positioned either side of the vent
475 and are connected via conduits 481 and 482 to the controller
483 to signal the approach of each of the melt fronts respectively.
The piezo-electric elements used in accordance with the present
invention (i.e., the piezo-electric sensors and/or piezo-electric
actuators) may comprise any of the devices manufactured by Marco
Systemanalyse und Entwicklung GmbH. The piezo-electric sensors can
detect the pressure at various interfaces within the nozzle
assembly and transmit a corresponding sense signal through the
conduits 481 and 482, thereby effecting closed loop feedback
control. The piezo-electric actuators then receive actuation
signals through the conduits 481 and 482, and apply corresponding
forces. Note that piezo-electric sensors may be provided to sense
pressure or temperature from any desired position. Likewise, more
than one piezo-electric actuator may be provided in place of any
single actuator described herein, and the actuators may be mounted
serially or in tandem, in order to effect extended movement,
angular movement, etc.
[0046] As mentioned above, one of the significant advantages of
using the above-described active element inserts is to allow the
manufacturing tolerances used for the vent gap to be widened,
thereby significantly reducing the cost of machining those features
in the mold.
5. The process of the Second Embodiment
[0047] Similar to the process of the first embodiment, in
operation, the controller receives sensor signals indicating the
proximity of the melt fronts to the vent 475, and based on these
signals, sends commands to the piezoceramic actuator 476 to alter
the size of the vent gap, thereby ensuring that melt does not enter
the vent gap. According to the present embodiment, the energizing
piezoceramic element 476 preferably will generate an increase in
length of about 0.15% when approximately 1000 V is applied
thereto.
[0048] The piezoceramic actuator 476 is sized and positioned in the
mold cavity block 460 to provide an optimum vent gap. When the vent
gap is properly sized, the air being exhausted from the mold cavity
(arrow B) experiences no resistance to flow as it passes through
the vent 475. FIG. 8 shows the injected plastic melt fronts 472,
473 advancing towards the vent area. As the melt approaches and
eventually touches sensors 479, 480, the sensors detect a rapid
rise in temperature or pressure, and transmit signals via conduits
481, 482 to controller 483.
[0049] Controller 483 may include a computer or Programmable Logic
Controller (PLC) or similar device for receiving the sensor's
signal, evaluating its magnitude and consequently sending a command
signal to the piezoceramic actuator 476 via a conduit. The command
signal may energize the insert sufficiently to partially reduce the
vent gap or to completely close the vent gap depending upon the
resin being injected into the mold and/or a variety of other
parameters that may have been input to the controller.
6. Conclusion
[0050] Thus, what has been described is a method and apparatus for
using active material elements in an injecting molding machine,
separately and in combination, to effect useful improvements in
injection molding apparatus, including provision of adjustable
venting in an injection mold.
[0051] Advantageous features according the present invention
include: 1. A piezo ceramic element used singly or in combination
to control a vent gap anywhere in an injection mold; 2. The use of
one or more vent gaps to direct the movement of a melt front of
injected plastic in a mold cavity; 3. An injection mold including a
vent gap regulated by active material elements; 4. Dynamic
adjustment of vent gaps using local force generating unit.
[0052] While the present invention provides distinct advantages for
injection-molded PET plastic preforms generally having circular
cross-sectional shapes perpendicular to the preform axis, those
skilled in the art will realize the invention is equally applicable
to other molded products, possibly with non-circular
cross-sectional shapes, such as, pails, paint cans, tote boxes, and
other similar products. All such molded products come within the
scope of the appended claims.
[0053] The individual components shown in outline or designated by
blocks in the attached Drawings are all well-known in the injection
molding arts, and their specific construction and operation are not
critical to the operation or best mode for carrying out the
invention.
[0054] While the present invention has been described with respect
to what is presently considered to be the preferred embodiments, it
is to be understood that the invention is not limited to the
disclosed embodiments. To the contrary, the invention is intended
to cover various modifications and equivalent arrangements included
within the spirit and scope of the appended claims. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
[0055] All U.S. and foreign patent documents discussed above (and
particularly the ions discussed above in paragraph [0030]) are
hereby incorporated by reference into the Detailed Description of
the Preferred Embodiments.
* * * * *
References