WO2002014048A1

WO2002014048A1 - Gas pin assembly, gas assisted injection molding apparatus and method employing same

Info

Publication number: WO2002014048A1
Application number: PCT/US2001/025814
Authority: WO
Inventors: Brentley G. Weeks; Kenneth M. Kincaid
Original assignee: Mack Molding Co., Inc.
Priority date: 2000-08-17
Filing date: 2001-08-17
Publication date: 2002-02-21
Also published as: WO2002014048A9; AU2001285036A1

Abstract

A gas pin assembly for use in a mold having a cavity in gas assisted injection molding includes a sleeve and an insert. The sleeve is extendable through the mold and has an inner surface defining a passageway extending from a first end of the sleeve for receiving pressurized gas and a second end for discharging pressurized gas. The insert has a first portion attachable to the inner surface of the sleeve defining the passageway and a second portion which together with the inner surface of the second end of the sleeve, when the insert is attached to the sleeve, define therebetween an opening for discharging pressurized gas. Advantageously, the insert includes a mid portion having a reduced cross-section disposed between the first and the second portions. Also disclosed are methods and gas assisted injection molding apparatus employing the gas pin assembly.

Description

GAS PIN ASSEMBLY, GAS ASSISTED INJECTION MOLDING APPARATUS AND METHOD EMPLOYING SAME

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/225,908, filed August 17, 2000, and U.S. Application No.

09/687,977, filed October 13, 2000, both entitled "Gas Pin Assembly, Gas Assisted Injection Molding Apparatus and Method Employing Same", the contents of which applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to gas assisted injection molding, and more particularly, to gas pins for gas assisted injection molding.

BACKGROUND OF THE INVENTION

Gas assisted injection molding is a thermoplastic molding process in which an inert gas is injected into a moldable material after it enters the mold. The gas does not mix with the moldable material but remains in the middle of the thicker sections of the molding. By controlling the gas pressure, the quantity of the moldable material injected into the mold, and the rate of gas flow, a hollow channel is formed within the molded part.

The gas pressure compensates for the tendency of the moldable material to shrink at the thicker areas of the molding, preventing warpage and reducing stress. The gas pressure is relieved prior to opening the mold. Introduction of pressurized gas into the mold may be made through the same nozzle that introduces the moldable material into the mold. In the production of some parts, it is desirable to introduce the pressurized gas at a different location than at which the moldable material is introduced, or perhaps at several locations which are all spaced from the nozzle. Typically, a gas pin is used to introduce pressurized gas at a location different than at the nozzle.

Prior art gas pins typically include a constant cross-sectional hollow tubular sleeve and a constant circular cross-sectional interiorly disposed solid pin which extends the length of the sleeve and defines a thin annular passage between the sleeve and the pin along the length of the sleeve. A drawback with such gas pins is that they often become clogged with moldable material during the molding process and must be disassembled and cleaned on a regular basis. In this case, the mold must be removed from a platen assembly and the gas pins cleaned.

Therefore, there is a need for gas pins which are readily fabricated, reduce the likelihood of clogging, are readily assembled and disassembled, and desirably operable with low gas pressures.

SUMMARY OF THE INVENTION

The present invention provides, in a first aspect, a gas pin assembly for use in a mold having a cavity in gas assisted injection molding in which the gas pin assembly includes a sleeve extendable through the mold and having an inner surface defining a passageway extending from a first end of the sleeve for receiving pressurized gas and a second end for discharging pressurized gas, and an insert having a first portion attachable to the inner surface of the sleeve defining the passageway and a second portion which together with the inner surface of the second end of the sleeve, when the insert is attached to the sleeve, define therebetween an opening for discharging pressurized gas.

In a second aspect, a gas pin assembly includes an insert and a sleeve. The sleeve is extendable through the mold and has an inner surface defining a passageway extending from a first end of the sleeve for receiving pressurized gas and a second end for discharging pressurized gas. The insert has a first portion attachable to the inner surface of the sleeve defining the passageway, a second portion which together with the inner surface of the second end of the sleeve, when the insert is attached to the sleeve, define therebetween an opening for discharging pressurized gas, and a mid portion disposed between the first and the second portions. The first portion comprises a first cross-section, the second portion comprises a second cross-section, the mid portion comprises a third cross-section, and the third cross-section is sized less than the first and the second cross-sections. The first portion of the insert includes external threads which matingly engage internal threads disposed on the inner surface defining the passageway of the sleeve for attaching the insert to the sleeve. The first portion of the insert also includes at least one longitudinally-extending slot through the external threads for permitting passage of pressurized gas from the passageway through the first portion of the insert to the second portion.

In third and fourth aspects, mold assemblies for use in gas assisted injection molding of a part, and gas assisted injection molding apparatus, include the above noted gas pin assemblies.

In a fifth aspect, a method for forming a part includes providing a mold having a cavity, introducing a moldable material into the cavity, introducing pressurized gas through a gas pin assemblies as noted above into the cavity to displace the moldable material in the cavity to form the part, venting the pressurized gas from the cavity, and removing the part from the mold.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, together with further objects and advantages thereof, may best be understood by reference to the following detailed description of the preferred embodiments and the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a gas assisted injection molding apparatus according to one embodiment of the present invention;

FIG. 2 is an enlarged, exploded cross-sectional view of the gas pin assembly of FIG. 1;

FIG. 3 is a cross-sectional view of the assembled gas pin assembly of FIG. 2;

FIG. 4 is a view taken along line 4-4 of FIG. 2; and

FIG. 5 is an enlarged view taken along line 5-5 of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates one embodiment of a gas assisted injection molding apparatus 10 according to the present invention. Gas assisted injection molding apparatus 10 generally includes a mold 20 having a first mold half 22 and a second mold half 24 positioned between a fixed support plate (not shown) and movable platen 12, an injection assembly 30 for introducing a moldable material into mold 20, a gas injecting/gas venting assembly 40 for introducing pressurized gas such as nitrogen gas or carbon dioxide gas or a similarly suitable relatively non-viscous fluid into mold 20 and venting thereof, and a controller 50. Gas assisted injection molding apparatus 10 also includes gas pin assemblies 100 as explained in greater detail below.

First mold half 22 and second mold half 24 define a cavity 26 having a profile of a part 70 to be formed. In addition, first mold half 22 and second mold half 24 define a sprue 28 therebetween having a first end which connects to injection assembly 30 and a second end which opens into cavity 26. Injection assembly 30 includes a nozzle which mates with sprue 28 and allows moldable viscous material to flow through sprue 28 and into cavity 26.

As described in greater detail below, controller 50 such as a microprocessor or computer, is operably connected to injection assembly 30, and gas injecting/gas venting assembly 40 to operatively control the forming of part 70.

FIGS. 2-5 illustrate gas pin assembly 100 in greater detail. In this illustrated embodiment, gas pin assembly 100 includes a sleeve 110 and an insert 140. Sleeve 110 is extendable through mold 20 (FIG. 1) and includes an inner surface 112 defining a passageway 120 extending from a first end 114 of sleeve 110 for receiving a supply of pressurized gas and a second end 116 for discharging the supply of pressurized gas.

Insert 140 includes a first portion 144 which is attachable to inner surface 112 defining passageway 120 of sleeve 110 (as best shown in FIG. 3). A second portion 146 which together with inner surface 112 of second end 116 of sleeve 110 define therebetween an opening 160 (best shown in FIG. 5) for discharging the supply of pressurized gas.

Insert 140 also includes a mid portion 148 disposed between first and second portions 144 and 146, respectively, to define a chamber 147 (FIG. 3) between mid portion 148 and sleeve 110. First portion 144 comprises a first cross-section, second portion 146 comprising a second cross-section, mid portion 148 comprises a third cross-section, and the third cross-section is sized less than the first and the second cross- sections. Desirably, chamber 147 provides a greater cross-sectional passage compared to the cross-sectional passage of opening 160.

Chamber 147 may also be configured to have a cross-sectional passage greater than the cross-section of passageway 120.

While first portion 144, mid portion 148, and second portion 146 have circular cross-sections so that opening 160 is annular, it will be appreciated that other cross-sectional configurations may be suitable, such as, for example, a square cross-section.

Advantageously, first portion 144 of insert 140 includes external threads which matingly engage internal threads disposed on inner surface 112 defining passageway 120 of sleeve 110 for attaching insert 140 to sleeve 110. To allow for transfer of pressurized gas from first end 114 of sleeve 110 to opening 160, first portion 144 of insert 140 includes a pair of longitudinally-extending slots 150 (FIG. 4) disposed along and through the external threads. Desirably, longitudinally-extending slots 150 extend along first portion 144, mid portion 148, and second portion 146.

Second portion 146 of insert 140 desirably has a fustoconical portion 145 which extends upwardly and outwardly away from second end FIG. 3. Fustoconical portion 145 desirably reduces the likelihood of damage to the molded part when ejecting the molded part from the mold cavity. Fustoconical portion 145 includes a taper of about 10 degrees. Advantageously, the uppermost portion of upper fustoconical portion comprises means, e.g., a slot for a screwdriver or cross slots for a Phillips screwdriver, for readily enabling attachment and removal of insert 140 from sleeve 110. Removal of insert 140 from sleeve 110 may be readily performed when mold 20 is in an open position.

With reference again to FIG. 1 , the operation of gas assisted injection molding apparatus 10 initially includes heating mold 20. For example, mold 20 may include tubes 25 through which a heated fluid such as a heated oil is passed to regulate the temperature of the mold. Once mold 20 is at a desired temperature, a calibrated (less than 100 percent of the volume of cavity 26) short shot of moldable material is introduced into cavity 26.

The flow of pressurized gas takes place through lines 42 and 44 which communicate with the two gas pin assemblies 100 located adjacent to sprue 28. The pressurized gas from gas injecting/gas venting assembly 40 is suitably provided by a prepressurized chamber or storage chamber or pump assembly (not shown) and regulated by selective actuation of, for example, one or more valves (not shown), controlled by controller 50. The pressurized gas displaces the moldable material in cavity 26 and forces the moldable material along the profiled surfaces of mold 20 forming cavity 26. The pressurized gas is desirably maintained in the cavity during the cooling phase of the cycle. Gas pins 100 connected to lines 42 and 44 may also sequentially aid in venting the cavity as controlled by controller 50 and gas injecting/gas venting assembly 40. Thereafter, for venting the pressurized gas from the cavity, a third gas pin assembly 100 located at an opposite end of part 70 is connected to a line 46 which is connected to gas injecting/gas venting assembly 40. Upon activation of gas injecting/gas venting assembly 40, e.g., controlled by controller 50, valves therein (not shown) are opened to allow the venting of the pressurized gas from cavity 26. Gas pins 100 connected to lines 42 and 44 may also sequentially aid in venting the cavity as controlled by controller 50 and gas injecting/gas venting assembly 40. Desirably, prior to venting, a pressurized shot of gas (having a pressure greater than the pressure in the cavity) is first introduced into gas pin assembly 100 to insure the cleaning of opening 160. The pressurized gas in the cavity is then vented. Desirably, chamber 147 of gas pin assembly 110 allows the rapid evacuation of pressurized gas from cavity 26. At the end of the cooling cycle, ejection pins (not shown) are suitably used to eject the formed part from the mold.

An additional step in the operation may include using the third gas pin assembly to introduce a pressurized gas which acts as a counter pressure to the introduction of the moldable material.

In still another embodiment, the gas assisted injection molding apparatus need not include the third gas pin assembly described above.

In this embodiment, the two gas assemblies 100 disposed adjacent to sprue 28 can provide gas introduction and evacuation according to the following process. Initially, moldable material is introduced into cavity 26. Pressurized gas is then introduced through a first gas pin assembly 100 (connected to line 42) disposed closest to the sprue or gate to completely displace the moldable material before activating a second gas pin assembly 100 (connected to line 44). Thereafter, the pressurized gas through first gas pin assembly 100 (connected to line 42) is reduced and the second gas pin assembly 100 (connected to line 44) is opened to allow gas to vent from the mold. Sequencing of the two gas pin assemblies can be done using various timing of pressures and venting for forming a part.

The present invention is suitable for low-pressure gas assisted injection molding of parts and particularly for forming a moldable material containing a reinforcing material such as reinforcing fibers. For example, pressurized gas in the range of, e.g., about 10 psi to less than 1,000 psi, and desirably in the range of about 50 psi to about 400 psi, and preferably about 250 psi, are suitable for use in gas assisted injection molding apparatus 10 of forming materials such as, for example, polyesters such as polyethylene terephthalate (PET), and polybutylene terephthalate (PBT), with about 15 percent fiberglass, or other fiber material, or other solid material. For such low pressure operation with fiber reinforced moldable plastics, opening 160 of gas pin assembly 100 may have an inside diameter of about 0.188 inch and a radial thickness of about 0.001 inch.

Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.

Claims

CLAIMS:

1. A gas pin assembly for use in a mold having a cavity for forming a part in gas assisted injection molding, said gas pin assembly comprising: a sleeve extendable through the mold and having an inner surface defining a passageway extending from a first end of said sleeve for receiving pressurized gas and a second end for discharging pressurized gas; and an insert having a first portion attachable to said inner surface of said sleeve defining said passageway and a second portion which together with said inner surface of said second end of said sleeve, when said insert is attached to said sleeve, define therebetween an opening for discharging pressurized gas.

2. The gas pin assembly of claim 1 wherein said insert comprises a mid portion disposed between said first and said second portions, said first portion comprising a first cross-section, said second portion comprising a second cross-section, said mid portion comprising a third cross-section, and wherein said third cross-section is sized less than said first and said second cross-sections.

3. The gas pin assembly of claim 1 wherein said first portion of said insert comprises external threads which matingly engage internal threads disposed on said inner surface defining said passageway of said sleeve for attaching said insert to said sleeve.

4. The gas pin assembly of claim 3 wherein said first portion of said insert comprises at least one longitudinally-extending slot through said external threads for permitting passage of pressurized gas from said passageway to said opening.

5. The gas pin assembly of claim 1 wherein said second portion of said insert comprises a fustoconical portion which extends outwardly from said second end of said sleeve when said insert is attached to said sleeve.

6. The gas pin assembly of claim 1 wherein said second portion of said insert comprises means for enabling removal of said insert from said sleeve.

7. A gas pin assembly for use in a mold having a cavity for forming a part in gas assisted injection molding, said gas pin assembly comprising: a sleeve extendable through the mold and having an inner surface defining a passageway extending from a first end of said sleeve for receiving pressurized gas and a second end for discharging pressurized gas; and an insert having a first portion attachable to said inner surface of said sleeve defining said passageway, a second portion which together with said inner surface of said second end of said sleeve, when said insert is attached to said sleeve, define therebetween an opening for discharging pressurized gas, and a mid portion disposed between said first and said second portions, said first portion comprising a first cross- section, said second portion comprising a second cross-section, said mid portion comprising a third cross-section, and wherein said third cross- section is sized less than said first and said second cross-sections; said first portion of said insert comprising external threads which matingly engage internal threads disposed on said inner surface defining said passageway of said sleeve for attaching said insert to said sleeve; and said first portion of said insert comprising at least one longitudinally-extending slot through said external threads for permitting passage of pressurized gas from said passageway through said first portion of said insert to said second portion.

8. The gas pin assembly of claim 7 wherein said second portion of said insert comprises a fustoconical portion which extends outwardly away from said second end of said sleeve when said insert is attached to said sleeve.

9. The gas pin assembly of claim 8 wherein said second portion of said insert comprises means for enabling removal of said insert from said sleeve.

10. A mold assembly for use in gas assisted injection molding of a part, said mold assembly comprising: a first mold portion and a second mold portion defining a cavity for molding the part; at least one of said first and second mold portions having an opening therein for allowing injection of a moldable material into said cavity; and a gas pin assembly of claim 1 for allowing at least one of injection of and venting of pressurized gas into and from said cavity.

11. A mold assembly for use in gas assisted injection molding of a part, said mold assembly comprising: a first mold portion and a second mold portion defining a cavity for molding the part; at least one of said first and second mold portions having an opening therein for allowing injection of a moldable material into said cavity; and a gas pin assembly of claim 7 for allowing at least one of injection of and venting of a pressurized gas into and from said cavity.

12. A gas assisted injection molding apparatus for molding a part, said apparatus comprising: a first mold portion and a second mold portion defining a cavity for molding the part; an injection assembly for injection moldable material into said cavity; and a gas pin assembly of claim 1 for allowing at least one of injection of and venting of pressurized gas into and from said cavity.

13. The apparatus of claim 12 further comprising a controller for controlling injection of moldable material into said cavity and a supply of pressurized gas into and from said cavity.

14. A gas assisted injection molding apparatus for molding a part, said apparatus comprising: a first mold portion and a second mold portion defining a cavity for molding the part; an injection assembly for injection moldable plastic material into said cavity; and a gas pin assembly of claim 7 for injection of and venting of pressurized gas into and from said cavity.

15. The apparatus of claim 14 further comprising a controller for controlling injection of moldable material into said cavity and a supply of pressurized gas into and from said cavity.

16. A method for forming a part, the method comprising: providing a mold having a cavity; introducing a moldable material into the cavity; introducing pressurized gas through a gas pin of claim 1 into the cavity to displace the moldable material in the cavity to form the part; venting the pressurized gas from the cavity; and removing the part from the mold.

17. The method of claim 16 wherein the moldable material comprises a solid reinforcing material.

18. The method of claim 17 wherein the pressurized gas comprises between about 10 psi to less than 1000 psi.

19. The method of claim 18 wherein the pressurized gas is between about 50 psi and about 400 psi.

20. A method for forming a part, the method comprising: providing a mold having a cavity; introducing a moldable material into the cavity; introducing pressurized gas through a gas pin of claim 7 into the cavity to displace the moldable material in the cavity to form the part; venting the pressurized gas from the cavity; and removing the part from the mold.

21. The method of claim 20 wherein the moldable material comprises a solid reinforcing material.

22. The method of claim 21 wherein the pressurized gas comprises between about 10 psi to less than 1000 psi.

23. The method of claim 22 wherein the pressurized gas is between about 50 psi and 400 psi.