Pressurized rapid casting process

The present disclosure relates to a pressurized rapid casting process.

Methods for rapid manufacturing are known in the art and have traditionally been employed to produce high quality parts in a reduced amount of time. One example of such a rapid manufacturing process is bridge tooling casting for polymeric materials. The rapid casting process generally begins with obtaining a master pattern, such as through an additive manufacturing technology (e.g., stereo lithography). A silicone material is then poured around the master pattern to create both a first member and a second member of a mold tool. A liquefied polymer can then be poured into the coupled members of the mold tool for casting a part.

The time required to produce a part through rapid manufacturing is significantly shorter than with conventional methods such as sheet metal forming, machining, molding, or other methods known in the art. In this way, rapid manufacturing technology can be used to manufacture high quality parts in relatively small numbers for fit, function, and assembly testing; for product samples; and/or for low volume production runs. The impact on new products is a decrease in overall development time by allowing for problems to be identified and for corrections to be made early in the process.

While parts manufactured through rapid manufacturing technologies can and are used in further assemblies, these parts can suffer from limited performance capabilities such as insufficient mechanical properties. Accordingly, methods and operations for optimizing the rapid casting process and for consistently producing parts are necessary.

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

In one form, the present teachings provide a method for molding a component. The method includes: providing a mold tool having a sprue and a cavity; heating the mold tool to a predetermined mold temperature; placing the heated mold tool into a pressure vessel; pouring a material through the sprue into the cavity of the heated mold tool; prior to complete polymerization of the material in the cavity of the heated mold tool, elevating an internal pressure of the pressure vessel to a predetermined pressure to apply a force to the material in the heated mold tool; completely polymerizing the material in the cavity in heated mold tool to form the molded component; and removing the molded component from the mold tool.

In another form, the present teachings provide a method for molding a component. The method includes: heating a mold tool; preparing a first container having a predetermined mass of a catalyst and a first predetermined mass of a monomer and a second container having a predetermined mass of an activator and a second predetermined mass of the monomer; purging the first and second containers with an inert gas; heating the first and second containers to a temperature above a predetermined temperature to form a first constituent element in the first container and a second constituent element in the second container; combining the first and second constituent elements when the first and second constituent elements have a temperature that is greater than the predetermined temperature to form a mixture; pouring the mixture into the heated mold tool; and densifying the mixture in the mold tool prior to complete polymerization of the mixture.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is an exploded perspective tool of a molded component constructed in accordance with the teachings of the present disclosure, the molded component being shown with a mold tool that is configured to mold the molded component, as well as the molded component as it is removed from the mold tool (with structure corresponding to the sprue and vents in the mold tool);

FIG. 2 is a section view of the mold tool of FIG. 1 ;

FIG. 3 is a schematic illustration in flow-chart form of a method for forming a molded component in accordance with the teachings of the present disclosure; and

FIG. 4 is a perspective view of a pressure vessel into which the mold tool of FIG. 1 is positioned.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

With reference to FIG. 1 of the drawings, a molded component constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral 10 . The molded component 10 can be formed in a polymerization reaction that takes place in a mold tool 12 when the mold tool 12 is exposed to elevated pressure and temperature as will be discussed in more detail below.

With additional reference to FIG. 2 , the mold tool 12 can be any type of bridge tooling or soft tooling, and in the particular example provided, the mold tool 12 is a type of soft tooling that is formed of silicone. Briefly, the mold tool 12 can comprise first and second mold members 14 and 16 that cooperate to define a mold cavity 26 and at least one sprue 70 . If desired, the mold tool 12 can also define one or more risers (not shown) and/or one or more vents 44 . In the particular example provided, an single sprue 70 and a plurality of vents 44 are formed in the first mold member 14 . As will be appreciated by those of skill in the art, the sprue 70 and vents 44 extend from the mold cavity through the second mold member 14 and are configured to fluidly couple the mold cavity 26 to the atmosphere (that surrounds the mold tool 12 ).

With reference to FIGS. 2 and 3 , a method for forming the molded component according to the teachings of the present disclosure is schematically illustrated. The methodology begins at block 100 , where the mold tool 12 can be heated to a predetermined mold temperature. Preferably, the predetermined mold temperature is an elevated temperature which is sufficient to sustain a chemical reaction between reagents that are introduced to the mold cavity 26 as will be discussed in greater detail below.

The methodology can proceed to block 102 , where the reagents used to form the molded component 10 are prepared. In the example provided, a predetermined mass of a catalyst and half of a predetermined mass of a monomer may be weighed and placed in a first container, while a predetermined mass of an activator and another half of the predetermined mass of the monomer may be weighed and placed in a second container. In the particular example provided, the monomer is caprolactam, the catalyst is sodium caprolactamate and the activator is blocked di-isocyanate. If the cast material is required to have a specific color, a predetermined mass of appropriate pigment and/or a heat stabilizer may also be placed in one of the containers (e.g., the second container). The first and second containers can be purged of air with a suitable inert gas (e.g., nitrogen). If desired, thermocouples can be inserted into the first and second containers.

The methodology can proceed to block 104 , where the contents of the first and second containers can be heated to a predetermined temperature. In the particular example provided, the predetermined temperature exceeds the melting point of the materials that make up the contents of the first and second containers such that the contents of the first and second containers are liquefied. Thereafter, the methodology can proceed to block 106 , where the contents of the first and second containers can be combined and mixed thoroughly to form a homogeneous liquefied mixture.

The methodology can proceed to block 108 where the liquefied [polymeric] material can be introduced through the sprue(s) 70 into the mold cavity 26 in the heated mold tool 12 to form a liquid-filled mold tool. Typically, the mold tool 12 is filled with the liquefied mixture to the point where the mold cavity 26 is completely filled and the vents 44 and sprue(s) 70 are at least partly filled.

The methodology can proceed to block 110 where the liquid-filled mold tool can be introduced into a pressure vessel 72 ( FIG. 4 ), the pressure vessel can be closed and a pressurized gas, such as air, may be introduced into the pressure vessel to elevate the gauge pressure within the pressure vessel to a predetermined gauge pressure. It will be appreciated that the pressurized gas within the pressure vessel will act directly on the liquefied mixture through the sprue(s) 70 and vents 44 . In the case where a form of soft tooling is used for the mold tool 12 , the pressurized gas can also exert a force over the exterior surface of the mold tool 12 that will apply a compressive force to the liquefied mixture that resides in the mold tool 12 .

In some instances, it can be beneficial to elevate the pressure in the pressure vessel 72 ( FIG. 4 ) to the predetermined gauge pressure within a predetermined time span after the first and second components have been mixed (in block 106 ). For example, a time span that is less than or equal to 60 seconds may be employed to ensure that polymerization of the liquefied mixture starts to take place only after the liquefied mixture is introduced to the mold cavity 26 and has been exposed to the predetermined gauge pressure in the pressure vessel 72 ( FIG. 4 ). Stated another way, the predetermined time span can be shorter than a reaction time needed to initiate polymerization of the liquefied mixture, and/or can be shorter than a time at which the material (i.e., the liquefied mixture) ceases to behave as a fluid when exposed to the predetermined (gauge) pressure. Performance of the methodology in this manner permits the molded component 10 ( FIG. 1 ) to achieve a uniform density. It may be satisfactory, however, to use a different (e.g., longer) time span in situations where it would be permissible to expose the liquefied mixture to the predetermined gauge pressure in the pressure vessel 72 ( FIG. 4 ) after polymerization of the liquefied mixture has started to take place.

Pressure within the pressure vessel 72 ( FIG. 4 ) can be maintained for a predetermined dwell time at the predetermined gauge pressure to permit the liquefied mixture to completely polymerize. As will be appreciated by those of skill in the art, suitable pressures and dwell times can vary depending on the desired structural properties and/or the surface area and/or volume of the molded component. We believe that suitable predetermined gauge pressures can range from 40 p.s.i.g. to 120 p.s.i.g., and suitable predetermined dwell times can range between 10 to 20 minutes. In the particular example provided, the liquefied mixture polymerizes to form AP Nylon 6, the predetermined gauge pressure is 80 p.s.i.g. and the predetermined gauge pressure is maintained on the mold tool 12 (in the pressure vessel) for 20 minutes.

The elevated pressure that acts on the liquefied mixture in the mold tool 12 helps to compact the resulting polymer so that the density of the molded component 10 ( FIG. 1 ) is relatively denser than would otherwise occur if the molded component was to be formed at ambient air pressure (i.e., 0 p.s.i.g.).

After elapse of the predetermined dwell time, the methodology can proceed to block 112 , where the pressure vessel 72 ( FIG. 4 ) is vented and the mold tool 12 is cooled to a desired temperature. It will be appreciated that the elevated pressure may be maintained on the mold tool 12 while the mold tool 12 is cooled (after which the pressure vessel is vented), or that the pressure vessel could be vented prior to the (desired) cooling of the mold tool 12 .

In block 114 , the molded component 10 ( FIG. 1 ) is removed from the mold tool 12 and finished in a desired manner. For example, material corresponding to the vents 44 and the sprue 70 (i.e., materials 44 a and 70 a in FIG. 1 ) may be removed from the molded component 10 .

While the above methodology has been described as including the placement of a heated, liquid mixture-filled mold tool into a pressure vessel, those of skill in the art will appreciate that in the alternative the heated mold tool may be placed within the pressure vessel and thereafter filled with the liquid mixture.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.