Porous media heat transfer for injection molding

The cooling of injection molded plastic is targeted. Coolant flows into a porous medium disposed within an injection molding component via a porous medium inlet. The porous medium is thermally coupled to a mold cavity configured to receive injected liquid plastic. The porous medium beneficially allows for an increased rate of heat transfer from the injected liquid plastic to the coolant and provides additional structural support over a hollow cooling well. When the temperature of the injected liquid plastic falls below a solidifying temperature threshold, the molded component is ejected and collected.

FIELD OF THE INVENTION

This application relates to manufacture via injection molding, and more particularly to the use of porous media to enhance heat transfer in an injection molding cooling system.

BACKGROUND OF THE INVENTION

Injection molding utilizes a ram or screw-type plunger to force molten plastic material into a mold cavity, solidifying the plastic into a shape that has conformed to the contour of the mold. Injection molding is most commonly used to process both thermoplastic and thermosetting polymers, with the former being considerably more prolific in terms of annual material volumes processed. Thermoplastics are prevalent due to characteristics which make them highly suitable for injection molding, such as the ease with which they can be recycled, the versatility allowing thermoplastics to be used in a wide variety of applications, and the ability of the thermoplastics to soften and flow upon heating. Examples of components manufactured using injection molding include disposable razors, plastic toys, medical equipment, auto parts, and the like.

To expedite the solidifying of molten plastic within a mold cavity, a variety of cooling systems can be implemented. For example, coolant fluid can be pumped into an empty cavity thermally coupled to the mold walls. However, such an empty cavity does not provide structural support to the mold itself, increasing the likelihood that the shape of the mold deforms or warps during operation, rendering the mold useless. Cooling rods can be thermally coupled to the mold walls, but heat transfer using thermal rods is less efficient than fluid-based cooling solutions. The faster a set of components can be injected, cooled, and ejected from an injection molding machine, the more components can be made in a given time frame, reducing overall manufacturing time.

SUMMARY OF THE INVENTION

A cooling system for an injection molding device is described herein. The injection molding device includes reciprocal mold components that, when coupled, form one or more mold cavities between the coupled mold components. Molten liquid plastic is injected into the mold cavities, and when the temperature of the injected liquid plastic falls below a solidifying threshold, the resulting solidified mold components are ejected and collected.

To expedite the cooling process, one or more porous mediums are disposed within one or more of the mold components. Each porous medium is thermally coupled to at least one mold cavity. Coolant is pumped into the porous mediums, and thermal energy is transferred from the injected liquid plastic to the coolant via the porous mediums. Coolant can be pumped into the porous mediums via one or more porous medium inlets disposed within the porous mediums. The coolant flows from the porous medium inlets, through the porous mediums, and out of the porous mediums via one or more porous medium outlets. The porous medium inlets can be coupled to a cooling system inlet via a first pipe, and the porous medium outlets can be coupled to a cooling system outlet via second pipe.

Coolant can be pumped from a coolant supply tank storing coolant at a pre-determined cooling temperature below the solidifying temperature with a pump coupled to the coolant supply tank. The pump pumps coolant from the coolant supply tank and into the cooling system inlet. As coolant is pumped from the coolant supply tank and into the porous mediums, coolant within the porous mediums is pumped out of the cooling system outlet and back into the coolant supply tank. The timing and pumping of coolant through the cooling system can be controlled by a controller coupled to the pump, and can be based on the injection of liquid plastic into the mold cavities and the temperature of the injected liquid plastic.

The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings and specification. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter.

DETAILED DESCRIPTION

Injection Molding and Cooling System Overview

Injection molding utilizes the high-pressure injection of the liquid or fluid raw material (such as a plastic polymer, or “thermoplastics” hereinafter) into a mold to shape the material into the desired shape. Molds can include a single cavity or multiple cavities. In multiple cavity molds, each cavity can be identical to form uniform molded components or can be unique to form different molded components within a single cycle. Molds are generally made from tool steels, but stainless steels and aluminum molds are also suitable for certain applications.

FIG. 1illustrates an injection molding environment, according to one embodiment. When thermoplastics are molded, typically pelletized plastic granules104are fed through a hopper102into an injection barrel106by a reciprocating screw105. The reciprocating screw105pressurizes and pushes the plastic granules through the injection barrel106, where they are heated by one or more heaters108into a liquid form. The resulting liquid plastic110flows through the injection barrel106and into a mold component for molding.

The mold component can include a male mold component112and a female mold component114. The injection barrel106is coupled to the mold component, for instance via a check valve (not illustrated in the embodiment ofFIG. 1). The mold component includes a mold cavity coupled to the injection barrel, and the liquid plastic110forcibly flows into the mold cavity, filling the mold cavity. The injection time required to fill the mold cavity can be less than 1 second.

After the mold cavity is filled with the liquid plastic110, the check valve can close, separating the filled mold cavity from the injection barrel106. The liquid plastic110within the mold cavity then cools and solidifies, forming a molded component. To expedite the cooling process, a coolant supply118can provide a coolant to the mold via a coolant inlet120. Coolant flows from the coolant supply118into the mold via the coolant inlet, cooling the liquid plastic within the mold cavity, and out of the mold via one or more coolant outlets122(such as coolant outlet122aand coolant outlet122b.

Once the temperature of the plastic within the mold cavity has fallen before a temperature threshold associated with the solidifying temperature of the plastic, the male mold component and the female mold component can decouple, and the molded component can be ejected (for instance, using one or more injection pins) from the mold cavity and down into a receiving container124for collection. One or more of the mold components can be coupled to a mold track116, allowing the mold components to move and decouple. One or more temperature sensors (not illustrated in the embodiment ofFIG. 1) can be used to determine if the temperature of the plastic within the mold cavity has fallen below a solidifying temperature threshold. For example, the mold components can decouple and eject the molded component into the receiving container in response to a determination by each of a plurality of temperature sensors that the temperature of the plastic within the mold cavity has fallen below the solidifying temperature threshold.

The male mold component112and the female mold component114can securely couple using one or more securing pins, locks, valves, latches, or any other suitable securing components. In some embodiments, when the mold components are securely coupled, the mold cavity is air tight. In other embodiments, the mold cavity can include an air valve allowing air to escape when liquid plastic flows into the mold cavity from the injection barrel106.

FIG. 2aillustrates decoupled injection molding mold components, according to one embodiment. The embodiment ofFIG. 2aincludes a male mold component112uncoupled from a female mold component114. The male mold component includes one or more mold protrusions204, and the female mold component includes one or more corresponding mold recesses206configured to align with the mold protrusions when the mold components are securely coupled. The male mold component includes a mold inlet202configured to allow for the flow of liquid plastic from a source external to and through the male mold component112.

FIG. 2billustrates securely coupled injection molding mold components, according to one embodiment. In the embodiment ofFIG. 2b, the male mold component112is securely coupled to the female mold component114, forming a mold cavity208between the corresponding mold protrusions of the male mold component and the mold recesses of the female mold component. The mold cavity208is configured in dimensions selected by (for instance) a manufacturer to produce a molded component of a desired shape. In some embodiments, the mold cavity is configured to produce a plurality of molded components. It should be noted that although an “M”-shaped mold cavity is illustrated in the embodiment ofFIG. 2b, the mold cavity208can be of any shape or shapes as desired by a user of the injection molding environment.

FIG. 3illustrates an injection molding cooling system, according to one embodiment. In the embodiment ofFIG. 3, a male mold component112includes a plurality of mold protrusions, mold protrusions302aand302b, each including a cooling well, cooling well306aand306b, respectively. The outer surface of the mold protrusions302are separated from the cooling wells306by a mold wall304. The mold wall304can be made of a thermally conductive material, such as steel or any other suitable material.

The male mold component ofFIG. 3includes a coolant inlet120configured to receive a coolant (such as water), and a coolant outlet122. The coolant flows from the coolant inlet120, through the cooling wells306, and out of the coolant outlet122. The coolant can be pumped into the male mold component112, for instance in response to a determination that the liquid plastic within the mold cavity requires cooling. Upon entering the coolant inlet120, the coolant can be configured to reduce the temperature of the mold wall304by absorbing heat from the mold wall (and accordingly, from the liquid plastic). Accordingly, the temperature of the coolant flowing out of the coolant outlet122is higher than the temperature of the coolant flowing into the coolant inlet120after absorbing heat from the mold wall304.

Porous Medium-Based Injection Molding Cooling System

To aid in the cooling of molten plastic injected into a mold cavity, a porous medium can be used within a cooling well thermally coupled to a mold wall. As used herein, a porous medium refers to any solid material with cavities or pathways within the material to allow fluid to flow through the medium. One example of a porous medium is a hardened foam. A porous medium may be of uniform porosity and permeability. Alternatively, a porous medium may be of a gradient porosity. In one embodiment, the permeability and the porosity of a porous medium are approximately 3.74×10−10m2and 0.45, respectively. In one embodiment, the porosity of the porous medium is between 0.2 to 0.7. The relative density of the porous medium may be between 10% and 30%. As used herein, “relative density” refers to the volume of a solid material within a porous media relative to the total volume of the porous media.

In order to maximize heat exchange, the porous medium may be composed of a highly thermally conductive material. For example, the porous medium may be composed of copper foam, gold or gold-deposited foam, any metallic or otherwise thermally-conductive foam, metallic composites with isotropic or anisotropic properties, micro-machined or photolithographically-produced microchannel inserts, and doped ceramics. The structure of the porous medium may also include pillars extending from the top, bottom and sides of the porous medium, in either a structured order or randomly. The properties (such as the conduction rates and gradients) of the porous medium can be selected for homogenous heat transfer across the heat exchanger. In one embodiment, the porous medium may be produced by 3-dimensional printing technologies.

The varying cross sectional shape of the structure of a porous medium causes the turbulent flow of fluid pumped into the porous medium, increasing the rate of heat transfer between the fluid and the porous medium (and relatedly, any mediums coupled to the porous medium). Heat transfer (and accordingly, cooling times) can be improved by as much as 300% or more between fluid within the porous medium and the porous medium itself as compared to the heat transfer between a fluid flushed through an empty cavity and walls of the cavity. In addition to the benefit of increased heat transfer, the structure of a porous medium can provide increased structural support within a cooling cavity (a cavity thermally coupled to a medium to be cooled) compared to an empty cavity.

FIG. 4illustrates a porous medium within an injection molding coolant system, according to one embodiment. The embodiment ofFIG. 4illustrates a cooling system within a male mold component112, though it should be noted that such a cooling system can be implemented within a female mold component or any other injection molding component according to the principles described herein.

The male mold component112includes a porous medium404awithin a first cooling well, and includes a porous medium404bwithin a second cooling well. It should be noted that although the male mold component112ofFIG. 4includes two cooling wells, each filled with a porous medium404, in other embodiments, mold components can include any number of cooling wells within any number of porous mediums. In addition, in the embodiment ofFIG. 4, the cooling wells are separated from a mold cavity (formed when the male mold component112is coupled to a reciprocal female mold component) by a mold wall304(which thermally couples the mold cavity to the porous mediums within the cooling wells).

The male mold component112includes a mold inlet202, a coolant inlet120and a coolant outlet122. The coolant inlet120is coupled to a pump410, which is coupled to a coolant supply tank408, which in turn is coupled to the coolant outlet122. Coolant is pumped from the coolant supply tank408by and through the pump410and into the male mold component112via the coolant inlet120. Coolant in turn flows out of the male mold component112via the coolant outlet122and into the coolant supply tank408. It should be noted that in some embodiments, a pump (not illustrated in the embodiment ofFIG. 4) can pump coolant from the male mold component112through the coolant outlet122and into the coolant supply tank408.

Coolant pumped into the male mold component112via the coolant inlet120flows into the porous mediums404aand404bvia porous medium inlets402aand402b. The porous medium inlets402are coupled to the coolant inlet120such that coolant flowing through the coolant inlet120into the male mold component112flows out of the porous medium inlets402and into the porous mediums404. In some embodiments, the porous medium inlets402are located within the porous mediums404such that the porous mediums404partially or completely surround the porous medium inlets402. In other words, each porous medium inlet402is located within the porous medium404such that the porous medium inlet is not in direct contact with the mold wall304. In some embodiments (such as the embodiment ofFIG. 4), the porous medium inlets402include a length of pipe and extend into the porous medium404such that the pipe walls of at least a portion of the length of pipe is surrounded by the porous medium.

Coolant pumped into each porous medium404via a corresponding porous medium inlet402flows from the porous medium inlet, through and out of the porous medium via one or more porous medium outlets (such as the porous medium outlets406aand406b), and out of the male mold component112via the coolant outlet122. The coolant flows through the porous mediums404, allowing for the transfer of thermal energy from liquid plastic pumped into a mold cavity, through the mold wall304, and to the coolant within the porous mediums404. As described above, the porous mediums404allow for the cooling of molded components due to the transfer of thermal energy from the molded component to coolant within the porous mediums at a faster rate than hollow cooling wells.

In some embodiments, coolant is pumped from the coolant supply tank408, into the male mold component112, through the male mold component, and out of the male mold component to the coolant supply tank via piping, tubing, or any other coupling medium configured to allow for the transfer of coolant (“pipe” or “piping” hereainafter). In some embodiments, each porous medium inlet402within the male mold component112is coupled to the coolant inlet120via a first pipe. Likewise, in some embodiments, each porous medium outlet406is coupled to the coolant outlet122via a second pipe.

In some embodiments, the pump410can include or be coupled to a coolant system controller (not illustrated in the embodiment ofFIG. 4) configured to control the pumping of coolant from the coolant supply tank408and into the male mold component112. For instance, the coolant system controller can determine when liquid plastic is injected within a mold cavity, can pump coolant through the male mold component112in response to such a determination, can detect when the temperature of the injected liquid plastic falls below a solidifying threshold, and can stop pumping coolant into the male mold component in response to such a determination. In some embodiments, the coolant system controller can control the injection of liquid plastic into the mold cavity, the coupling and decoupling of mold components, and any other functionality associated with the operation of an injection molding system. In alternative embodiments, an external injection molding system controller controls such functionalities, and is communicatively coupled to the coolant system controller, for instance communicating to the coolant system controller when liquid plastic is injected into the mold cavity. The coolant system controller can be communicatively coupled to one or more thermal sensors coupled to the mold cavity or mold wall304and configured to provide the temperature of injected liquid plastic to the coolant system controller.

The coolant supply thank408is configured to maintain the temperature of coolant within the tank, for instance by reducing the temperature of coolant flowing out of the coolant outlet122and into the coolant supply tank408to a pre-determined temperature threshold. It should be noted that although the coolant supply tank408and the pump410are coupled to one mold component in the embodiment ofFIG. 4, in practice, the coolant supply tank408can provide coolant to any number of mold components using one or more pumps. For example, the coolant supply tank408can provide coolant to a first mold component (such as a male mold component) and a second mold component (such as a female mold component) when the first and second mold components are coupled to form a mold cavity and liquid plastic is injected within the mold cavity.

FIG. 5illustrates a porous medium within a mold component, according to one embodiment. Coolant flows from a coolant inlet120and into a porous medium504via a porous medium inlet506. Likewise, coolant flows out of the porous medium504and through a coolant outlet122via a porous medium outlet508. Although only one mold protrusion is illustrated in the embodiment ofFIG. 5, in practice, any number of mold protrusions can be implemented within a mold component.

In the embodiment ofFIG. 5, a mold protrusion502within a mold component includes an impermeable outer surface and an internal porous medium504filling the mold protrusion from a porous medium inlet to the impermeable outer surface. As the porous medium provides structural support within the mold protrusion502, the mold protrusion does not need a separate and additional mold wall (such as the mold wall304ofFIG. 4) to provide structural support (though it should be appreciated that the impermeable outer surface of the mold protrusion502has some necessary thickness). In addition to providing structural support within the mold protrusion502, the absence of a mold wall can beneficially increase the transfer of thermal energy from a liquid plastic injected within a mold cavity to the coolant within the porous medium504.

It should be noted that the mold protrusion502ofFIG. 5can be implemented within any mold component, such as the male mold component112of the embodiment ofFIG. 4. Further, it should be noted that the shape of any mold protrusion and mold component illustrated herein is for the purposes of illustration only. The porous medium-based coolant system described herein can be implemented within mold protrusions and mold components of any shape or size accordingly to the principles described herein.

FIG. 6is a flow chart illustrating a process for cooling molded plastic in an injection molding environment, according to one embodiment. Mold components are securely coupled600, forming a mold cavity between the mold components. Liquid plastic is injected610into the mold cavity. Coolant is pumped620into a porous medium thermally coupled to the mold cavity, such as a porous medium within a mold component protrusion. Thermal energy is transferred from the injected plastic to the coolant within the porous medium. Responsive to the temperature of the injected plastic falling below a solidifying threshold, the mold components are decoupled630.

Additional Considerations

While particular embodiments and applications have been illustrated and described herein, it is to be understood that the embodiment is not limited to the precise construction and components disclosed herein and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatuses without departing from the spirit and scope.