U.S. patent number 11,351,709 [Application Number 17/290,994] was granted by the patent office on 2022-06-07 for injection molding systems and methods.
This patent grant is currently assigned to Google LLC. The grantee listed for this patent is Google LLC. Invention is credited to Jason Evans Goulden, Babak Radi.
United States Patent |
11,351,709 |
Radi , et al. |
June 7, 2022 |
Injection molding systems and methods
Abstract
Techniques are described for injection molding. When material
inside a cavity of a tool is solidified into a molded part, the
tool imparts a finished surface onto the part, including sidewalls
with a zero or low-draft angle. To allow separation from the cavity
without using sleeves or sliders, the cavity is widened, just prior
to the part being ejected. The tool is made from metal with a high
coefficient of thermal expansion, so the size of the cavity can be
manipulated using temperature control. Heat applied to an outer
portion of the metal surrounding the cavity pulls the metal away
from the part creating an air gap within the cavity. Carefully
applied cooling to an inner portion of the metal blocks the heat
and keeps the surface temperature under control, which preserves
the finished surface on the part. When the air gap allows, the part
releases from the cavity with the finished surface intact.
Inventors: |
Radi; Babak (Hsinchu,
TW), Goulden; Jason Evans (Los Gatos, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Google LLC |
Mountain View |
CA |
US |
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Assignee: |
Google LLC (Mountain View,
CA)
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Family
ID: |
70775609 |
Appl.
No.: |
17/290,994 |
Filed: |
May 8, 2020 |
PCT
Filed: |
May 08, 2020 |
PCT No.: |
PCT/US2020/032171 |
371(c)(1),(2),(4) Date: |
May 03, 2021 |
PCT
Pub. No.: |
WO2021/177988 |
PCT
Pub. Date: |
September 10, 2021 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20210362386 A1 |
Nov 25, 2021 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62985559 |
Mar 5, 2020 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C
45/40 (20130101); B29C 45/73 (20130101); B29C
2045/7356 (20130101); B29K 2705/12 (20130101); B29C
2045/7368 (20130101); B29C 2045/7343 (20130101) |
Current International
Class: |
B29C
45/73 (20060101) |
References Cited
[Referenced By]
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Foreign Patent Documents
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Oct 2012 |
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109563337 |
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Apr 2019 |
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CN |
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102013112426 |
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May 2015 |
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DE |
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2170575 |
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Mar 2013 |
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EP |
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S6440313 |
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Feb 1989 |
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JP |
|
02249616 |
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Oct 1990 |
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JP |
|
H0768614 |
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Mar 1995 |
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JP |
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2001260139 |
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Sep 2001 |
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JP |
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2011048365 |
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Apr 2011 |
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WO |
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2012140511 |
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Oct 2012 |
|
WO |
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Other References
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.
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9, 2021, 15 pages. cited by applicant .
"Foreign Office Acton", EP Application No. 20727130.5, dated Jun.
24, 2021, 6 pages. cited by applicant .
"Corrected Notice of Allowance", U.S. Appl. No. 14/247,651, dated
Mar. 9, 2017, 2 pages. cited by applicant .
"International Search Report and Written Opinion", Application No.
PCT/US2020/032171, dated Oct. 20, 2020, 16 pages. cited by
applicant .
"Non-Final Office Action", U.S. Appl. No. 13/964,241, dated Jun.
13, 2016, 8 pages. cited by applicant .
"Non-Final Office Action", U.S. Appl. No. 14/247,651, dated Sep. 7,
2016, 7 pages. cited by applicant .
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2016, 7 pages. cited by applicant .
"Notice of Allowance", U.S. Appl. No. 14/247,651, dated Nov. 23,
2016, 7 pages. cited by applicant .
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2018, 7 pages. cited by applicant .
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2014, 7 pages. cited by applicant .
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11, 2016, 6 pages. cited by applicant .
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30, 2016, 6 pages. cited by applicant .
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http://www.ttmp.com/tooling.html--downloaded from URL on Jun. 12,
2013, 1 page. cited by applicant .
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26, 2021, 5 pages. cited by applicant .
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1993243753, Pub No. JP1995068614 (JPH0768614A), Mar. 14, 1995, 9
pages. cited by applicant.
|
Primary Examiner: Kennedy; Timothy
Assistant Examiner: Esan; Olukorede
Attorney, Agent or Firm: Colby Nipper PLLC
Parent Case Text
RELATED APPLICATIONS
This application is a national stage entry of International
Application No. PCT/US2020/032171, filed May 8, 2020, which claims
the benefit of U.S. Provisional Application No. 62/985,559, filed
Mar. 5, 2020, the disclosures which are incorporated herein by
reference in their entirety.
Claims
What is claimed:
1. A method comprising: injecting a material that solidifies at a
first temperature into a cavity of an injection molding tool with a
zero or low-draft angle wall; expanding the cavity of the injection
molding tool by heating an outer portion of the injection molding
tool above the first temperature to form an air gap between the
material and the cavity while cooling an inner portion of the
injection molding tool that is between the cavity and the outer
portion of the injection molding tool to regulate a surface
temperature of the cavity lower than the first temperature; and
ejecting, from the cavity, a molded part.
2. The method of claim 1, further comprising: regulating, with a
heating system or a cooling system, the surface temperature of the
cavity of the injection molding tool.
3. The method of claim 2, wherein the heating system or the cooling
system is a fluid system and the injection molding tool includes a
fluid channel integrated into the injection molding tool and
surrounding the cavity.
4. The method of claim 2, wherein the heating system is an
induction heating system and the injection molding tool includes an
induction coil integrated into the injection molding tool and
surrounding the cavity.
5. The method of claim 4, wherein the induction coil includes a
plurality of coils stacked within the outer portion and vertically
aligned with a direction of pull from the cavity.
6. The method of claim 2, wherein cooling the inner portion of the
injection molding tool that is between the cavity and the outer
portion of the injection molding tool includes: cooling, with the
cooling system, the inner portion of the injection molding tool to
regulate the surface temperature of the cavity.
7. The method of claim 6, wherein the cooling system is a liquid
cooling system and the inner portion of the injection molding tool
includes a channel surrounding the cavity and configured to
circulate liquid coolant received from the cooling system.
8. The method of claim 1, wherein the inner portion of the
injection molding tool surrounds an opening to the cavity, and the
outer portion of the injection molding tool surrounds the inner
portion.
9. The method of claim 1, further comprising: cooling a portion of
the injection molding tool that is opposite an opening to the
cavity.
10. The method of claim 1, wherein the injection molding tool is
formed of a metal alloy with a coefficient of thermal expansion
sufficient to form the air gap between the material and the
cavity.
11. The method of claim 10, wherein the metal alloy includes
stainless steel.
12. The method of claim 2, wherein the inner portion of the
injection molding tool surrounds an opening to the cavity, and the
outer portion of the injection molding tool surrounds the inner
portion.
13. The method of claim 3, wherein the inner portion of the
injection molding tool surrounds an opening to the cavity, and the
outer portion of the injection molding tool surrounds the inner
portion.
14. The method of claim 4, wherein the inner portion of the
injection molding tool surrounds an opening to the cavity, and the
outer portion of the injection molding tool surrounds the inner
portion.
15. The method of claim 6, wherein the inner portion of the
injection molding tool surrounds an opening to the cavity, and the
outer portion of the injection molding tool surrounds the inner
portion.
16. The method of claim 2, further comprising: cooling a portion of
the injection molding tool that is opposite an opening to the
cavity.
17. The method of claim 3, further comprising: cooling a portion of
the injection molding tool that is opposite an opening to the
cavity.
18. The method of claim 4, further comprising: cooling a portion of
the injection molding tool that is opposite an opening to the
cavity.
19. The method of claim 6, further comprising: cooling a portion of
the injection molding tool that is opposite an opening to the
cavity.
20. The method of claim 2, wherein the injection molding tool is
formed of a metal alloy with a coefficient of thermal expansion
sufficient to form the air gap between the material and the
cavity.
21. The molded part produced by the method of claim 1.
Description
BACKGROUND
Parts manufactured through injection molding often have drafted
sidewalls that are angled inward a few degrees from ninety, which
enables separation from a cavity of an injection molding tool at
the end of the injection molding process. As an alternative to
drafted sidewalls, sleeves or sliders can be used to free the
molded part from the cavity. Either approach typically requires a
finishing step (e.g., sanding, sandblasting, polishing, machining,
painting, etching) to give the part a finished surface with crisp
edges, smooth corners, and sidewalls with a zero or low-draft
angle. Having to finish each part at the end of an injection
molding process may increase manufacturing time, decrease yield,
and increase cost.
SUMMARY
Techniques and systems are described for injection molding, without
performing finishing steps after the part is formed. When material
inside a cavity of an injection molding tool is solidified into a
molded part, the cavity imparts a finished surface or texture onto
the molded part, including crisp edges, smooth corners, and
sidewalls with a zero or low-draft angle. To allow the molded part
to separate from the cavity with the finished surface intact and
without using sleeves, sliders, or other special attachments, the
injection molding tool undergoes thermal expansion to enlarge the
cavity. The injection molding tool is made from metal, such as
stainless steel. Every metal has a particular coefficient of
thermal expansion. A high coefficient of thermal expansion
indicates a greater amount of displacement (e.g., volume, length)
per unit of temperature. By using an injection molding tool made
from a metal alloy with a high coefficient of thermal expansion,
the size and shape of the cavity can be manipulated using
temperature control.
An outer portion of the injection molding tool is quickly heated
while an inner portion between the outer portion and the cavity is
simultaneously cooled. The heat applied to the outer portion of the
metal surrounding the cavity just prior to ejection causes thermal
expansion in the tool. The thermal expansion enlarges the cavity,
pulling it away from the sidewalls of the molded part, thereby
producing an air gap between the cavity and the sidewalls, which
are of a zero or low-draft angle. Controlled cooling of the inner
portion while heating the outer portion regulates the temperature
of the inner portion and the molded part. Keeping the solidified
sidewalls of the molded part cool by cooling the inner portion of
the tool, preserves the finished surface applied by the cavity
earlier during the molding process. The molded part is ejected from
the cavity when the air gap is of sufficient size to allow the
molded part to release from the cavity. In this way, the molded
part can release with a finished surface and sides with a zero or
low-draft angle, without requiring any additional finishing steps.
Manufacturing injection molded parts without a need for finishing
steps shortens manufacturing time, increases yield, or reduces
cost.
In some aspects a method is described including injecting a cavity
of an injection molding tool with material while the injection
molding tool is at a first temperature effective to solidify the
material into a molded part with a wall having a finished surface
and a zero or low-draft angle. The method further includes heating
an outer portion of the injection molding tool to a second
temperature while cooling an inner portion of the injection molding
tool that is between the cavity and the outer portion of the
injection molding tool to keep the finished surface of the molded
part at or below the second temperature when the air gap is formed.
The method further includes ejecting, from the cavity, the molded
part.
This document also describes computer-readable media having
instructions for performing the above-summarized method. Other
methods are set forth herein, as well as systems and means for
performing the above-summarized and other methods.
This summary is provided to introduce simplified concepts about
achieving a finished surface through injection molding, which is
further described below in the Detailed Description and Drawings.
This summary is not intended to identify essential features of the
claimed subject matter, nor is it intended for use in determining
the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
The details of one or more aspects of achieving a finished surface
through injection molding are described in this document with
reference to the following drawings. The same numbers are used
throughout the drawings to reference like features and
components:
FIG. 1 illustrates an example system configured to create a part
through injection molding, including an isometric view and a bottom
view of a tool.
FIG. 2 illustrates multiple three-dimensional views of the tool
shown in FIG. 1.
FIG. 3 illustrates thermal zones of the tool shown in FIG. 2.
FIG. 4 illustrates an example method performed by a system
configured to create a part through injection molding.
FIG. 5-1 illustrates an exterior side view of the tool shown in
FIG. 2.
FIG. 5-2 illustrates a bottom view of the tool shown in FIG. 2.
FIG. 5-3 illustrates a cross-sectional side view of the tool shown
in FIG. 2.
FIG. 5-4 illustrates a cross-sectional bottom view of the tool
shown in FIG. 2.
FIG. 6-1 illustrates a cross-sectional side-view of another tool
configured to create a part through injection molding.
FIG. 6-2 illustrates a bottom view of the other tool shown in FIG.
6-1.
FIG. 7-1 illustrates a cross-sectional side view of an additional
tool configured to create a part through injection molding.
FIG. 7-2 illustrates a bottom view of the additional tool shown in
FIG. 7-1.
FIG. 8 illustrates a temperature graph of an example system
configured to create a part through injection molding.
DETAILED DESCRIPTION
The techniques and systems described herein relate to one or more
aspects of creating parts through injection molding. When material
inside a cavity of a tool is solidified into a molded part, the
tool imparts a finished surface onto the part, including undrafted
sidewalls, which by definition have a zero or low-draft angle that
is close to zero degrees from ninety. To allow separation from the
cavity without using sleeves or sliders, the cavity is widened,
just prior to the part being ejected. The tool is made from metal
with a high coefficient of thermal expansion, so the size of the
cavity can be manipulated using temperature control. Heat applied
to an outer portion of the metal surrounding the cavity pulls the
metal away from the part, creating an air gap within the cavity.
Carefully applied cooling to an inner portion of the metal
regulates the temperature of the cavity, which preserves the
finished surface on the molded part. When the air gap allows, the
part releases from the cavity with the finished surface intact. In
this way, the molded part has a finished surface including sides
with a zero or low-draft angle upon ejection from the tool, without
requiring any additional finishing steps. Manufacturing injection
molded parts without a need for a finishing step may, alone or in
combination, decrease manufacturing time, increase yield, or
decrease cost.
FIG. 1 illustrates an example system 100 configured to create a
part with a finished surface through injection molding, including
an isometric view and a bottom view of the tool 102. The system 100
includes an injection molding tool 102, a heating system 104, a
cooling system 106, and a control unit 140.
The heating system 104 is operatively coupled to the injection
molding tool via links 118-1 and 118-2 (collectively "links 118").
The heating system 104 may be a hot liquid heating system or some
other heating system configured to heat the outer portion of the
tool 102. In other examples, as shown in FIG. 1, the heating system
104 is an induction heating system. The links 118 distribute
electrical current or hot liquid that is output from the heating
system 104. The output form the heating system 104 produces heat at
the injection molding tool 102 in areas closes to the heating coil
108.
The heating system 104 is operatively coupled to the control unit
140 via link 122-1, for example, to receive control inputs output
by the control unit 140. The heating system 104 adjusts the
electrical current or hot liquid being output via link 118-1. For
an induction system. the heating system 104 increases the
electrical current or amount of time in which the electrical
current is applied to heat the injection molding tool 102 to a
particular temperature that the heating system 104 derives from the
control inputs. The amount of electrical current or hot liquid
required to heat the injection molding tool 102 is proportional to
the mass of the tool 102.
The tool 102 includes a metal 110, such as stainless steel, which
is of an alloy that is selected based on its coefficient of thermal
expansion. The tool 102 is formed of materials that are suitable to
support injection molding of a particular type of material (e.g.,
resin). Some materials have lower hardening points or require more
or less time to solidify. The tool 102 is formed of a metal alloy
which can not only withstand the temperature fluctuations that
occur during the injection molding process, but which can also
realize a large amount of displacement due to thermal expansion, in
a short amount of time.
The cooling system 106 is a liquid (e.g., water, oil, glycol)
cooling system and is operatively coupled to the injection molding
tool via links 120-1 and 120-2 (collectively "links 120"). For
example, the links 120 distributes a temperature-regulated coolant,
such as water, that circulates between the injection molding tool
102 and the cooling system 106. The cooling system 106 maintains
the coolant at a particular temperature. The coolant dissipates
heat from the injection molding tool 102 as the coolant circulates
in and out of the cooling system 106 and the injection molding tool
102. The cooling system 106 prevents the inner surface temperature
of the cavity 114 from becoming out of control due to rapid heating
(e.g., which can increase the bulk temperature of the injection
molding tool within a few seconds). The cooling system 106
regulates the cavity surface temperature. The cooling system 106 is
controlled to keep the inner surface temperature of the cavity 114
to low, which prevents the material (e.g., plastic) from thermally
expanding and keeps the molded part hard and solid.
The cooling system 106 is operatively coupled to the control unit
140 via link 122-2. For example, the cooling system 106 determines
the desired temperature from control inputs received from the
control unit 140. The cooling system 106 adjusts the coolant
temperature and/or rate of circulation through the channels 120
based on the control inputs to bring the temperature of the
injection molding tool 102 to the desired temperature.
The control unit 140 directs the heating system 104 and the cooling
system 106 to control an injection molding process involving the
injection molding tool 102. The control unit 140, or other control
units or processors (not shown) may control other parts of the
injection molding process. To eject a part having been shaped with
the injection molding tool 102, the control unit 140 directs the
heating system 104 to quickly heat an outer portion of the
injection molding tool 102 above a hardening point of injection
material to cause thermal expansion in the tool 102.
Optional telemetry (not shown) of the injection molding tool 102 is
operatively coupled to the control unit 140 via link 122-3. The
control unit 140 receives telemetry information, including
information about the temperature of the injection molding tool 102
at various places within the metal 110. Other examples of telemetry
information include position data about an orientation or another
operating condition of the injection molding tool 102. Through
control over the heating and cooling systems 104 and 106, the
control unit 140 regulates the temperature of the metal 110 based
on the telemetry information received via link 122-3.
The injection molding tool 102 forms a cavity 114 in which material
is solidified into a molded part. An injector (not shown) injects
the cavity 114 with the material while the temperature of the tool
102 is at the hardening point of the material. The material
solidifies into a molded part with a wall having a finished surface
and a zero or low-draft angle imparted onto the molded part by the
cavity 114.
In some cases, the injection molding tool 102 interfaces with a
core tool. Where the injection molding tool 102 shapes an exterior
portion of the molded part, the core tool shapes an interior
portion of the molded part. FIG. 1 shows the direction of draw for
such a core tool. The direction of draw is perpendicular to an
opening of the cavity 114, which is also congruent with a
longitudinal axis Z of the injection molding tool.
The cavity 114 has sidewalls with a zero or low-draft angle, about
the longitudinal axis Z. The sidewalls are perpendicular to the
cavity opening and separated by a width Wt1 when the metal 110
surrounding the cavity 114 is not undergoing thermal expansion. The
zero or low-draft angle of the sidewalls of the cavity 114 cause a
force that prevents the molded part from releasing from the cavity
114 in the direction of draw.
The injection molding tool 102 includes a heating coil 108
integrated into the metal 110 of the injection molding tool 102 and
surrounding the cavity 114. The heating coil 108 produces heat
(e.g., from the electrical current or hot liquid output by the
heating system 104 over link 118-1 and returned to the heating
system 104 over link 118-2).
Channel 112 is integrated into the injection molding tool 102. The
channel 112 is formed within an inner portion 132 of the metal 110
surrounding the cavity 114, and the heating coil 108 lies within an
outer portion 130 of the metal 110. The channel 112 is operatively
coupled to the cooling system 106 by links 120-1 and 120-2. The
cooling system 106 circulates a liquid coolant through the channel
112 and the links 120-1 and 120-2. The channel 112 is closer to the
walls of the cavity 114 than the heating coil 108, which enables
greater temperature control of the walls of the cavity 114. The
exact locations of the channel 112 and the heating coil 108 depend
on the geometry and design of the tool 102 and the molded part and
can be determined through heat transfer and thermal expansion
simulations.
The cavity 114 is shown having a circular shape, although many
other shapes and sizes are possible. The control unit 140 is
configured to direct the heating system 104 to quickly and briefly
(e.g., in less than a few seconds) heat the outer portion 130 of
the injection molding tool 102 to cause thermal expansion of the
metal 110 surrounding the cavity 114 effective to form an air gap
116 between the wall of a molded part and the cavity 114. The
heating system 104 outputs electrical current or hot liquid to the
heating coil 108 until the air gap 116 has a width Wt2, which is
greater than the original width of the cavity 114 Wt1. To keep a
finished surface applied to the molded part while in the cavity 114
when the air gap 116 is formed, the control unit 140 directs the
cooling system 106 to keep the inner portion 132 of the injection
molding tool 102 (between the cavity 114 and the outer portion 130)
below the melting point of material inside the cavity 114. The air
gap 116 creates an amount of separation Wt2-Wt1 between the cavity
114 and the molded part. The amount of separation required to allow
the molded part to separate from the cavity 114 can depend on the
texture on the surface of the cavity 114. For a smooth cavity
surface, less expansion of the cavity 114, and therefore less
separation may be required. A rough cavity surface exerts more grip
on the molded part than a smooth cavity surface. For a rough cavity
surface, more expansion of the cavity 114 may be needed before a
molded part can release from the tool 102.
As the metal 110 undergoes thermal expansion, and while the air gap
116 is between the cavity 114 and the molded part, the control unit
140 controls the system 100 to eject the molded part from the
cavity 114. The air gap 116 allows the molded part to break the
force keeping the molded part in the cavity 114, and eject from the
injection molding tool 102 with sides that have a zero or low-draft
angle and a finished surface intact. Exterior walls of an injected
part include a surface imparted on them from the cavity 114 during
solidification; the walls solidify with a zero or low-draft angle.
In this way, the molded part has a finished surface and sides with
a zero or low-draft angle upon ejection from the tool, without
requiring any additional finishing steps. Manufacturing injection
molded parts without a need for finishing steps may decrease
manufacturing time, increase yield, or decrease cost, alone or in
any combination.
FIG. 2 illustrates multiple three-dimensional views of the tool 102
shown in FIG. 1. The heating coil 108 is shown integrated into the
injection molding tool 102, contacting or nearly contacting an
outer portion 130 (e.g., exterior surface) of the metal 110 that
surrounds the cavity 114. Inlets to the cooling channel(s) 112
within the tool 102 are also shown. Terminal ends of the heating
coil 108 are visible in the view shown in the upper left corner of
FIG. 2.
The heating coil 108 includes two coils stacked within the outer
portion 130 of the metal 110. The heating coil 108 can include more
than two coils, for instance, to provide better control over the
temperature of the outer portion 130 of the metal 110 or to provide
temperature control over a larger area of the metal 110. In cases
where the heating coil 108 is an inductive heating coil, the
heating coil 108 can have an insulation layer between the metal 110
and the heating coil 108 to prevent the metal 110 from conducting
the electrical current circulating through the coil 108.
The individual coils of the heating coil 108 are centered around
the cavity 114 and vertically aligned with the perpendicular
direction of pull (Z) from the cavity. By evenly heating the outer
portion 130 of the metal 110, the cavity 114 expands from width Wt1
to width Wt2, due to thermal expansion. The thermal expansion forms
the air gap 116, which enables a molded part with a finished
surface, including sidewalls with zero or low-draft angles, to
eject from the cavity 114 of the tool 102. Expansion times and
displacement amounts vary depending on the metal 110, the injecting
material (resin) and capacity for heating.
FIG. 3 illustrates different thermal zones of the tool shown in
FIG. 2. A quarter-sectional view 300-2 of the tool 102 is shown in
dashed line to indicate relative positioning of the different
thermal zones 302 and 304. The cooling channel 112 surrounds an
inner portion of the walls of the cavity 114. Additional cooling
channels may be used, for example, integrated near the top of the
cavity 114, at an end opposite the opening to the cavity 114. The
thermal zones 302 and 304 are located within portions of the metal
110, where the temperature of the metal 110 is regulated. The
control unit 140 of the system 100 can direct the heating and
cooling systems 104, 106 to heat the tool 102 and regulate the
temperature of the cavity 114 for ejecting.
The thermal zones 302 are stacked vertically, surrounding the walls
of the cavity 114. Each of the thermal zones 302 encompasses an
outer portion of the metal 110, including the parts of the metal
110 that are nearest to the heating coil 108. The thermal zones 302
may include more than two zones, for example, to provide a more
uniform heating and eventual thermal expansion of the outer portion
of the metal 110. Left unregulated, the heat from the thermal zones
302 increases the temperature of the cavity 114.
The thermal zone 304 represents a temperature regulated, inner
portion of the metal 110 between the cavity 114 and the outer
portions of the metal 110 that is receiving the heat from the
heating coil 108. The thermal zone 304 surrounds the walls of the
cavity 114 to regulate the temperature of the cavity 114. Just
prior to ejection, heat is applied around the tool 102 in the
thermal zones 302 to cause thermal expansion.
FIG. 4 illustrates an example method 400 performed by a system
configured to create a part through injection molding. The method
400 is described in the context of the system 100. The operations
performed in the example method 400 may be performed in a different
order or with additional or fewer steps than what is shown in FIG.
4.
At 402, the system 100 inject a material that solidifies at a first
temperature into a cavity of an injection molding tool having a
zero or low-draft angle.
At 404, the system 100 lets the material solidify into a molded
part with a wall having a finished surface and a zero or low-draft
angle. As the material hardens, the walls of the cavity 114 impart
a finished surface onto an exterior surface of the molded part. The
exterior surface of the molded part is solidified to include a
texture imprinted on the part that matches the texture on the walls
of the cavity 114. The texture may be smooth, coarse, or a
combination thereof.
At 406 and 408, after the molded part solidifies, the system 100
simultaneously heats and cools different portions of the tool 102
(e.g., outer and inner portions 130 and 132), which results in an
air gap being created. The air gap allows the part to release from
the cavity 114.
At 406, the system 100 quickly and briefly heats outer portion 130
of the injection molding tool to a temperature that causes thermal
expansion of the tool 102, effective to form an air gap between the
molded part and the cavity. For example, the control unit 140
directs the heating system 104 to output electrical current or hot
liquid to the heating coil 108 to rapidly heat the outer portion of
the injection molding tool 102 sufficient to cause thermal
expansion in the tool 102. Quickly heating the injection molding
tool 102 at step 406 occurs briefly, for example, in under a few
seconds. The brief, intense heating induces thermal expansion of
the metal 110 surrounding the cavity 114, which is effective to
form an air gap 116 between the wall of the molded part and the
cavity 114, for enough time to eject the molded part without
damaging the tool 102 or the molded part.
During this brief moment when the injection molding tool 102
undergoes thermal expansion, at 408 the system 100 regulates a
surface temperature of the cavity, e.g., by simultaneously cooling
an inner portion of the injection molding tool 102 between the
cavity and the outer portion. The cooling keeps the molded part at
or below the hardening temperature when the air gap is formed. For
example, the control unit 140 directs the cooling system 106 to
circulate coolant within the channel 112 to cool the thermal zone
304 and regulate the surface temperature of the cavity 114. The
cooling system 104 cools the thermal zone 304 located in the inner
portion of the metal 110, to or below the hardening temperature of
the material to keep the molded part solidified within the cavity
114.
At 410, while the air gap is formed between the wall of the molded
part and the cavity, the system 100 ejects the molded part from the
cavity with at least one exterior wall having a finished surface
and a zero or low-draft angle. As explained, the air gap 116 allows
the molded part to overcome the force caused by zero or low-draft
angle sides in the tool 102, which might prevent the molded part
from releasing from the cavity 114. This way, the air gap 116
allows separation from the cavity 114 without melting or softening
the finished surface of the solidified part.
FIG. 5-1 illustrates an exterior side view 500-1 of the tool shown
in FIG. 2. The tool 102 includes the heating coil 108 integrated
within the tool 102. The heating coil 108 wraps around the exterior
surface of the tool 102 or is integrated within the metal of the
tool 102. The heating coil 108 may be surrounded by the metal of
the tool 102. As shown, the heating coil 108 is partially
surrounded by the metal of the tool 102, within a cutout that
surrounds the cavity 114 of the tool 102.
FIG. 5-2 illustrates a bottom view 500-2 of the tool shown in FIG.
2. An opening to the cavity 114 is circular. Other cavity shapes
are possible, including rectangular openings.
FIG. 5-3 illustrates a cross-sectional side view 500-3 of the tool
102 shown in FIG. 2. In the view 500-3, the tool 102 includes the
heating coil 108 wrapped around the tool a further distance from
the cavity 114 than the cooling channel 112.
FIG. 5-4 illustrates a cross-sectional bottom view 500-4 of the
tool 120 shown in FIG. 2. The channel 112 is shown as a dashed
lines because the channel is contained within the metal 110
surrounding the cavity 114 and therefore not visible from the
cross-sectional bottom view 500-4. The exact positioning of the
channel 112 depends on size of the cavity 114 and the mass and
geometry of the tool 102. FIG. 5-4 illustrates positioning of the
heating coil 108 relative to the channel 112, within the metal 110
of the injection molding tool 102. The channel 112 is contained
within an inner portion of the injection molding tool 102 and
surrounds an opening to the cavity 114. The heating coil 108 is
positioned adjacent to or within an outer portion of the injection
molding tool 102. Therefore, the heating coil 108 is further from
the cavity 114 than the inner portion which contains the channel
112. By heating the outer portion of the injection molding tool
102, the metal 110 expands the cavity 114 by pulling the walls of
the cavity 114 apart. Simultaneously cooling the inner portion of
the injection molding tool 102, which is located between the outer
portion of the tool 102 and the cavity 114, protects material that
has solidified within the cavity 114 from the heat causing the
thermal expansion of the tool 102.
FIG. 6-1 illustrates a cross-sectional side view 600-1 of another
tool configured to create a part through injection molding. An
injection molding tool 602 is an example of the injection molding
tool 102, but with a cavity 604 that is of a different shape than
the cavity 114. Rather than rounded corners, the cavity 604
includes sidewalls with zero or low-draft angles and sharp,
perpendicular corners where the sidewalls meet the bottom of the
cavity 604, at an end of the cavity 604 opposite an opening of the
cavity 604.
FIG. 6-2 illustrates a bottom view 600-2 of the other tool shown in
FIG. 6-1. An opening to the cavity 604 is rectangular. The cavity
604 can take many other shapes and forms.
FIG. 7-1 illustrates a cross-sectional side view 700-1 of an
additional tool configured to create a part with a finished surface
through injection molding. FIG. 7-2 illustrates a bottom view 700-2
of the additional tool shown in FIG. 7-1.
An injection molding tool 702 is an example of the injection
molding tool 102, but with additional cooling channels and heating
coils. The injection molding tool 702 includes a cavity 704
surrounded by a plurality of heating coils 706-1 through 706-n
(collectively "heating coils 706"). An opening to the cavity 704 is
square. However, the cavity 704 can take many other shapes and
forms including a circular or elliptical form. The heating coils
706 are an example of the heating coil 108. The heating coils 706
are stacked vertically with the direction of draw from the cavity
704 to provide even heating to the sidewalls of the cavity 704. The
cavity 704 is further surrounded by a plurality of cooling channels
708-1 through 708-m (collectively "cooling channels 708"). The
cooling channels 708 are examples of the cooling channel 112 and
configured to circulate liquid coolant around the cavity 704.
Having more than one cooling channel 708 and/or more than two
heating coils 706 allows greater control over the temperature of
the injection molding tool 702, which may further aid in molding
complex parts with finished sides, which have a zero or low-draft
angle.
FIG. 8 illustrates a temperature graph 800 of an example system
configured to create a part with a finished surface through
injection molding. The temperature graph 800 is described in the
context of system 100 and is meant as an example process.
Temperatures and timings associated with the described techniques
vary depending on the type of material and the coefficient of
thermal expansion associated with the metal tool being used. For
this example, the injection material is a polycarbonate but other
injection materials may be used in other implementations.
The temperature graph 800 includes a temperature reading 802 of an
outer portion of the tool 102 throughout the injection molding
process. For example, the temperature reading 802 corresponds to a
temperature taken within one of the thermal zones 302 from FIG. 3.
The temperature graph 800 further includes a temperature reading
804 of a surface on the inside of the cavity 114 of the tool 102
(also referred to as the surface temperature of the cavity 114).
The temperature reading 804 approximates the temperature of the
molded part.
The hardening point (H.P. in FIG. 8) depends on the molded
material, this is the temperature that the material changes to a
solid body. The surface temperature of the cavity (the temperature
reading 804) cannot exceed the hardening point without liquifying
or softening the material. Therefore, the surface temperature 804
of the cavity 114 cannot exceed the hardening point and kept within
a range of eighty to one hundred thirty-five degrees Celsius, plus
or minus ten degrees depending on different types of polycarbonate
materials used.
Both 804 and 802 start from the same temperature at time 1, and the
system injects material into the cavity 114. The material
solidifies at the hardening point, which, for polycarbonate may be
100 degrees Celsius or a range between ninety to one hundred twenty
degrees Celsius. The injecting material can rise above and fall
below the hardening point upon injection. At time 2, the
temperature 804 in cavity surface rapidly goes high with the
increase in the temperature 802 of the tool.
However, almost immediately when the induction heater goes on, both
802 and 804 temperatures increase, but the temperature in 804 does
not go higher than the hardening point because the cooling system
that is located between the induction heater and the cavity surface
is regulating the surface temperature of the cavity 114.
Thermocouple(s) that reads the temperature and sends the feedback
to the controller can be installed near the cavity surface (right
underneath of the cavity surface). This point is critical and
important to be measured. The controller changes the current and
time the induction heater is on based on the surface temperature
804 of the cavity 114.
Once the molded part is solid, at time 2, the system 100 quickly
and briefly (e.g., in less than one or in under a few seconds)
heats the outer portion of the tool 102 to a temperature that
causes sufficient thermal expansion, referred herein as an
expansion point (E.P.) of the cavity 114. The thermal expansion
produces an air gap 116 that allows the molded part to release from
the cavity 114. During this expansion, however, the surface
temperature of the cavity 804 could be just below the hardening
point of the material during ejection at time 3. Between times 2
and 3, the temperature reading 802 increases greatly from the
hardening point and reaches the temperature for thermal expansion.
Between times three and four, the outer portion of the tool 102
cools.
Even though the temperature reading 802 increased, the temperature
reading 804 of the surface of the cavity 114 remains below the
hardening temperature because of the cooling simultaneously being
applied between the heat source and the cavity 114. For
polycarbonate, the cooling may be around seventy degrees Celsius if
the outer portion of the tool is heated between ninety to one
hundred twenty degrees Celsius. In this way, the molded part within
the cavity 114 has a finished surface and sides with a zero or
low-draft angle that remain intact after being ejected.
The following are additional examples of systems and techniques for
achieving a finished surface through injection molding:
Example 1. A method comprising: injecting a material that
solidifies at a first temperature into a cavity of an injection
molding tool with a zero or low-draft angle wall; expanding the
cavity of the injection molding tool by heating an outer portion of
the injection molding tool above the first temperature while
cooling an inner portion of the injection molding tool that is
between the cavity and the outer portion of the injection molding
tool to regulate a surface temperature of the cavity; and ejecting,
from the cavity, the molded part.
Example 2. The method of example 1, further comprising: regulating,
with a heating system or a cooling system, the surface temperature
of the cavity of the injection molding tool.
Example 3. The method of example 2, wherein the heating system or
the cooling system is a fluid system and the injection molding tool
includes a fluid channel integrated into the injection molding tool
and surrounding the cavity.
Example 4. The method of example 2, wherein the heating system is
an induction heating system and the injection molding tool includes
an induction coil integrated into the injection molding tool and
surrounding the cavity.
Example 5. The method of example 4, wherein the induction coil
includes a plurality of coils stacked within the outer portion and
vertically aligned with a direction of pull from the cavity.
Example 6. The method of any of examples 2 through 5, wherein
cooling an inner portion of the injection molding tool that is
between the cavity and the outer portion of the injection molding
tool includes: cooling, with the cooling system, the inner portion
of the injection molding tool to regulate the surface temperature
of the cavity.
Example 7. The method of example 6, wherein the cooling system is a
liquid cooling system and the inner portion of the injection
molding tool includes a channel surrounding the cavity and
configured to circulate liquid coolant received from the cooling
system.
Example 8. The method of any of examples 1 through 7, wherein the
inner portion of the injection molding tool surrounds an opening to
the cavity, and the outer portion of the injection molding tool
surrounds the inner portion.
Example 9. The method of any of examples 1 through 8, further
comprising cooling a portion of the injection molding tool that is
opposite an opening to the cavity.
Example 10. The method of any of examples 1 through 9, wherein the
injection molding tool is formed of a metal alloy with a
coefficient of thermal expansion sufficient to form an air gap
between the material and the cavity.
Example 11. The method of example 10, wherein the metal alloy
includes stainless steel.
Example 12. A system comprising means to perform any one of the
methods of examples 1 through 11.
Example 13. A computer-readable storage medium comprising
instructions that, when executed, cause at least one processor of a
control unit to direct a system to perform any one of the methods
of examples 1 through 11.
Example 14. An injection molding tool comprising: a cavity having a
zero or low-draft angle wall and configured to contain an injection
of a material that solidifies at a first temperature; an outer
portion comprising one or more heating channels surrounding the
zero or low-draft angle wall of the cavity, the one or more heating
channels being arranged in the outer portion to allow for uniform
expansion in size of the cavity when the outer portion is heated
above the first temperature either from a heating fluid circulating
through the one or more heating channels or from one or more
electrical heating coils at least partially contained in the one or
more heating channels; and an inner portion comprising one or more
cooling channels surrounding the zero or low-draft angle wall of
the cavity and positioned between the zero or low-draft angle wall
of the cavity and the outer portion, the one or more cooling
channels being configured to circulate a cooling fluid and arranged
in the outer portion to allow for uniform cooling of the zero or
low-draft angle wall of the cavity to regulate a surface
temperature of the zero or low-draft angle wall of the cavity when
the outer portion is heated to expand the size of cavity.
Example 15. The injection molding tool of the example 14, wherein
the one or more heating channels are stacked within the outer
portion, the one or more cooling channels are stacked within the
inner portion, and the one or more heating channels and the one or
more cooling channels are vertically aligned with a direction of
pull from the cavity.
Example 16. The injection molding tool of the example 14, wherein
the inner portion surrounds an opening to the cavity and the outer
portion of the injection molding tool surrounds the inner
portion.
Example 17. The injection molding tool of the example 16, further
comprising: one or more additional cooling channels positioned
beneath the cavity opposite the opening and configured to circulate
additional cooling fluid before injection of the material, during
the injection of the material into the cavity, or after the
material is ejected from the cavity.
Example 18. The injection molding tool of the example 14, wherein
the injection molding tool is formed of a metal alloy with a
coefficient of thermal expansion sufficient to form an air gap
between the material and the cavity.
Example 19. A system comprising means configured to perform any one
of the methods of examples 1 through 11, wherein the means include
the injection molding tool of any of the examples 14 through
18.
While various embodiments of the disclosure are described in the
foregoing description and shown in the drawings, it is to be
understood that this disclosure is not limited thereto but may be
variously embodied to practice within the scope of the following
claims. From the foregoing description, it will be apparent that
various changes may be made without departing from the spirit and
scope of the disclosure as defined by the following claims.
* * * * *
References