3-d printed molds with variable porosity

Abstract

A mold for the molding of a polymeric material includes a body having a mold contact surface, wherein the mold is formed of a metallic material via 3-D printing, and wherein at least a first region of the body has a porosity of between about 2 and 15 percent.

Description

3-D PRINTED MOLDS WITH VARIABLE POROSITYField of the Invention

[0001] The present invention is directed generally to plastic molding, and more particularly to the construction of molds for plastic molding processes, including injection molding and vacuumforming.Background

[0002] Plastic parts can be formed in a number of different processes. Of these, injection molding is likely the most common. Injection molding involves the injecting of heated molten plastic into the cavity of a mold, allowing the plastic to cool in order to set or freeze, then removing the molded part from the mold. During the injection molding process, air, material-heated gases, and secondary processing fumes should be fully evacuated from the mold cavity for a quality plastic part to be formed without defect. In addition, the removal of such gasses can help to prevent tooling damage and to extend tool life. Consequently, molds will typically include strategically placed vents that enable venting of the aforementioned air and other gasses.

[0003] Thermoforming (also known as vacuumforming) is another plastic manufacturing process. Thermoforming involves forming a heated plastic sheet into a desired shape. Typically a thermoforming mold will include a cavity into which the heated sheet is drawn by suction that is applied to the mold. In some instances the mold will also include a “core” or “plug” that forms the side of the thermoformed part opposite the cavity. In either event, the mold that includes the cavity requires vents that draw the heated plastic sheet toward the surface of thecavity and / or remove air that might otherwise be trapped between the plastic sheet and the mold cavity.

[0004] In view of the foregoing, it may be desirable to provide molding techniques and equipment that simplify molding processes.Summary

[0005] As a first aspect, embodiments of the invention are directed to a method of injection molding a polymeric part. The method comprises the steps of:(a) providing a mold having first and second mold halves, at least the first mold half formed by 3-D printing, a first region of the first mold half having a porosity that enables air to pass therethrough, the first and second mold halves being mounted in an injection molding machine;(b) with the first and second mold halves in a closed condition, injecting molten polymeric material into a cavity defined by the first and second mold halves;(c) with the first and second mold halves in the closed position, allowing gas to escape the cavity through the first regions of the first mold half; then(d) moving the first and second mold halves to an open position to allow the removal of a polymeric part from the cavity.

[0006] As a second aspect, embodiments of the invention are directed to a method of thermoforming a polymeric part. The method comprises the steps of:(a) providing a mold formed by 3-D printing, the mold having a porosity that enables a vacuum to be drawn therethrough;(b) mounting the mold in a thermoforming machine, wherein a first side of the mold is in fluid communication with a vacuum source;(c) positioning a heated polymeric sheet adjacent a second side of the mold, the second side opposing the first side;(d) applying a vacuum to the mold via the vacuum source;(e) engaging the heated polymeric sheet with the second side of the mold so that the heated polymeric sheet takes the shape of the second side of the mold, and(f) cooling the re-shaped heated polymeric sheet to form the polymeric part.

[0007] As a third aspect, embodiments of the invention are directed to a mold for the molding of a polymeric material comprising a body having a mold contact surface, wherein the mold is formed of a metallic material via 3-D printing, and wherein at least a first region of the body has a porosity of between about 2 and 15 percent.Brief Description of the Figures

[0008] FIGS. 1A and IB are schematic side views of an exemplary injection mold, showing the mold both prior to injection of polymeric material (FIG. 1 A) and after the injection of polymeric material (FIG. IB).

[0009] FIGS. 2 A and 2B are a schematic side section view and an enlarged top view of an exemplary vent for an injection mold such as the mold of FIGS. 1A and IB.

[0010] FIG. 3 is a top view of an exemplary mold half that illustrates how primary and secondary vents are routed from the cavity.

[0011] FIGS. 4A and 4B are schematic side views of an injection mold, both prior to injection (FIG. 4A) and after injection (FIG. 4B), in which regions of one of the mold halves (which is 3-D printed) are higher in air permeability to permit the venting of gasses from the cavity.

[0012] FIGS. 5 A and 5B are schematic side views of an exemplary thermoforming process that utilizes a plug opposite the mold in addition to a vacuum source.

[0013] FIGS. 6A-6D are schematic side views of an exemplary thermoforming process that relies on vacuum applied from a vacuum source.

[0014] FIGS. 7A-7D are schematic side views of a thermoforming process according to embodiments of the invention, wherein a 3-D printed convex mold with increased porosity is used to mold a part.

[0015] FIGS. 8A-8D are schematic side views of a thermoforming process according to alternative embodiments of the invention, wherein a 3-D printed concave mold with increased porosity is used to mold a part.

[0016] FIG. 9 is a schematic side view of a thermoforming mold as might be used in the process shown in FIGS. 7A-7D.

[0017] FIG. 10 is a chart illustrating testing results using a 3-D printed mold in a vacuumforming process.

[0018] FIG. 11 is a chart that illustrates the results of porosity testing on a 3- D printed vacuumforming mold.Detailed Description

[0019] The present invention will now be described more fully hereinafter, in which embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.

[0020] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be furtherunderstood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. As used herein the expression “and / or” includes any and all combinations of one or more of the associated listed items.

[0022] In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0023] Well-known functions or constructions may not be described in detail for brevity and / or clarity.

[0024] Referring now to the drawings, FIG. 1A schematically illustrates an exemplary injection mold, designated broadly at 10. The mold 10 includes mold halves 12, 14, that come together (as shown in FIG. IB) to define a mold cavity 16in the shape of a plastic part to be molded. Molten plastic 18 is injected into the mold cavity 16 via a nozzle 20, a sprue 22, and runners 24. After injection (FIG. IB), the molten plastic is allowed to cool / harden, at which point the mold halves 12, 14 separate and the plastic part is removed via ejector pins 26.

[0025] As discussed above, a typical injection mold includes vents that enable air and other gasses to be removed from the mold cavity 16 to allow the molten plastic to fully fill the mold cavity 16. As shown in FIGS. 2A and 2B, a vent 28 may be included at the “parting line” 30 between the mold halves 12, 14 (the “parting line” is the interface at which the surfaces of the mold halves 12, 14 meet during molding and separate after molding). Often the vent 28 is divided into a primary vent segment 32, which leads directly from the mold cavity and is relatively short and shallow, and a secondary vent segment 34, which is routed from the primary vent 32 to the atmosphere or to a different portion of the mold 10. FIG. 3 illustrates a mold half 14’ in which short, shallow primary vent segments 32’ and longer, deeper secondary vent segments 34’ serve as a pathway for air and / or other gasses that might otherwise be trapped in the mold during injection and cooling.

[0026] As can be envisioned by the foregoing discussion and FIGS. 1A-3, the inclusion of vents in an injection mold can be a complicated design matter: it involves an understanding of where air and other gasses might tend to be trapped (which may vary, depending on the geometry of the part being molded), the type of plastic being molded, and the presence of other components of the mold (e.g., cooling lines, ejector pins, side action mechanisms, etc.). As such, a technique for simplifying the venting of a mold may be desirable.

[0027] One such approach may be constructing either or both mold halves so that the mold half has some porosity and / or has some permeability to air. Three- dimensional (3-D) printed components can be so constructed. More specifically,Metal Powder Bed Fusion 3-D Printing (3DP) / Additive Manufacturing (AM) technologies (which are commonly referred to under the following alternative naming conventions: Direct Metal Laser Sintering (DMLS), Metal Laser Sintering (MLS), Direct Metal Printing (DMP), and Direct Metal Laser Melting (DMLM)) can produce three-dimensional (3D) components by melting, fusing, or sintering fine metal powders at the sub-100-micron level (< 0.1mm particle size) with a laser to fix them into solid metal components. As used herein, the term “3-D printing” is intended to encompass all of these techniques. As is conventional with 3-D printing, these techniques utilize a layered process where each printed cross- sectional layer is applied or “stacked” on top of the preceding layer until a physical 3-D component is fully formed.

[0028] While components formed by 3-D printing with these materials are typically essentially impermeable to air, it has been discovered that, by modifying the fixing process (e.g., by reducing the power of the laser used to fix the powder), the percentage of grains of powder that become fused can be reduced. When this occurs, pores can form in the fixed layer. By repeating this step with each subsequent layer, a somewhat porous / air permeable solid is produced. Moreover, because of the control the 3-D printing process affords, a solid material can be produced in which certain regions are porous and other regions are not, or in which regions vary in permeability.

[0029] Applying this concept to an injection mold, those of skill in this art will understand that a mold half may be formed via 3-D printing that has one or more regions that are sufficiently porous that air and other gasses that might otherwise be trapped by a non-porous mold can escape from the mold cavity. An example of such a mold is illustrated schematically in FIGS. 4 A and 4B. Therein is shown a mold 110 formed of mold halves 112, 114. Together, the mold halves 112, 114 form a mold cavity 116. A sprue 122 and runners 124 are present as inthe mold 10 shown in FIGS. 1A and IB and described above. However, instead of including vents of the sort shown at 28 in FIG. 2 and at 32734’ in FIG. 3, instead the mold half 114 includes two regions 140, 142 that are porous (these are shown in FIGS. 4A and 4B as stippled regions), whereas the remainder of the mold half 114 is non-porous (i.e., solid). Thus, when the mold halves 112, 114 are brought together and molten plastic material 118 is injected through the sprue 118 and runners 120 into the mold cavity 116, air and other gasses that might become trapped in the mold cavity can exit the mold cavity through the porous regions 140, 142. The presence of the porous regions 140, 142 can enable the mold 110 to function smoothly without the need for discrete vents such as the vents 28 of the mold 10 or the vents 32734’ of the mold half 14’.

[0030] The extent to which a mold half has regions that are porous may very; in some embodiments, the porous regions 140, 142 may occupy between about 5 to 100 percent of the total volume of a mold half. Also, the extent of porosity of the porous regions 140, 142 may vary between molds. In some embodiments, the porous regions 140, 142 may have an open volume of between about 2 and 25 percent (e.g., between about 2 and 15 percent).

[0031] In some embodiments, the porous regions 140, 142 may define an elongate path that extends from the mold volume. In some embodiments, the porous regions 140, 142 may be generally cylindrical. In other embodiments, the porous regions 140, 142 may expand in cross-sectional area with increasing distance from the mold volume (e.g., a cone). In further embodiments, the porous regions 140, 142 may define a non-rectilinear path for air to follow; e.g., a porous region may be angled, arced, serpentine, or the like. When so shaped, a porous region may be able to avoid interfering with other components of the mold (such as cooling lines).

[0032] It is also contemplated that the porous regions 140, 142 may be located on certain areas of the mold that would be anticipated to trap air or other gasses if a vent were not present. Examples include corners, edges, “dead ends,” areas where a weld line is formed, undercuts, and the like.

[0033] By employing 3-D printing of the type described above, injection molds can be created that have sufficient strength and structural integrity that they can withstand typical injection molding pressures. However, such molds may also have the requisite porosity in one or more porous regions where needed to eliminate the need for conventional vents.

[0034] Those skilled in this art will appreciate that other types of molds may benefit from selectively porous materials formed by 3-D printing. FIGS. 5 A and 5B schematically illustrate one typical thermoforming process. A preheated sheet 200 is mounted on clamps 202 or other holders and positioned between upper and lower mold halves 212, 214 of a mold 210. The upper mold half 212 is lowered into the lower mold half 214, trapping the plastic sheet 200 therebetween within a mold cavity 216 (FIG. 5B). The upper and lower mold halves 212, 214 form the plastic sheet 200 into a desired shape. Once the plastic cools, the mold halves 212, 214 separate, and the thermoformed plastic part is removed.

[0035] Notably, the lower mold half 214 includes a series of vents 220 that are routed away from the mold cavity 216 to the atmosphere. The vents 220 typically receive suction from a suction source 222 that both draws the heated plastic sheet into the lower mold 214 and removes any air present in the lower mold 214 that might have been otherwise trapped between the plastic sheet and the lower mold 214.

[0036] An alternative thermoforming arrangement is shown in FIGS. 6A-6D, in which no upper mold half is employed. Instead, suction applied to the lower mold half 214’ through the vents 220’ draw the heated plastic sheet 200’ into thecavity 216’ of the mold half 214’. The plastic is allowed to cool, then removed from the mold half 214’.

[0037] In the arrangements of both FIGS. 5A-B and FIGS. 6A-D, the vents 220, 220’ in the molds 214, 214’ comprise discrete holes, channels, manifolds and the like through which suction is applied. However, in somewhat the same manner as described above, forming either of the molds 214, 214’ of a porous / air permeable material via 3-D printing may provide a mold to which suction can be applied without the need to form discrete vents. Thus, a thermoforming process can be completed with a mold that has no (or fewer) discrete vents.

[0038] Because thermoforming operations are typically performed at much lower pressures than injection molding, the molds employed in thermoforming do not require the same degree of structural integrity. Thus, in addition to being formed of a metallic material, thermoforming molds may alternatively be formed of other materials (such as high temperature polymers) that are lighter, more easily formed into a desired shape, and less expensive. Thus, thermoforming molds formed by 3-D printed may employ polymeric 3-D printable materials. One exemplary 3-D printable polymeric material is a polyamide PA- 12 powder, which is a nylon-based material. Other potentially suitable technologies for 3-D printing polymeric molds include Selective Laser Sintering (SLS) and Multi Jet Fusion (MJF). All of the aforementioned techniques for 3-D printing of polymeric materials are intended to be encompassed in the definition of 3-D printing set forth earlier.

[0039] Referring now to FIGS. 7A-7D, a thermoforming process utilizing a 3-D printed mold is illustrated therein. As shown in FIG. 7A, a mold 314 is formed via 3-D printing in a manner that provides air permeability to the mold 314. The mold 314 is positioned within a thermoforming machine 330 so that the vents 320 thereof can apply vacuum to the mold 314. The heated polymeric sheet 300 islowered onto the mold 314. Suction is applied to the mold 314 via the vents 320; because of the porosity of the mold 314, that suction reaches the heated polymeric sheet 300 and draws it onto the upper surface 316 of the mold 314. The plastic is allowed to cool, then removed from the mold 316 (FIG. 7D).

[0040] Notably, and as can be seen in FIGS. 7A-7C, the mold 314 has a convex surface that contacts the heated sheet (i.e. , a “convex mold”). This is in contrast to the molds shown in FIGS. 5A-B and 6A-D, in which the molds 214, 214’ have a contact surface with the heated sheet that is convex. One advantage of the 3-D printed mold 314 is the capacity to easily apply a vacuum to a mold 314 having a convex contact surface. As such, the mold 314 produces a part having a concave surface that is / was in contact with the mold surface 316, and which therefore can include detailed aspects (gloss, texture, intricate structures) on its concave surface that may otherwise be difficult to consistent produce without intricate venting or other surface contact (e.g., plug assist).

[0041] FIGS. 8A-8D illustrate a 3-D printed mold 414 that has a concave contact surface, thereby demonstrating that a similar type of mold can be used to form a part having a convex surface that contacts the mold surface 416. The other advantages mentioned above (e.g., detail replication) may also be provided.

[0042] The extent to which a thermoforming mold has regions that are porous may very; in some embodiments, the porous regions may occupy between about 5 to 100 percent of the total volume of a mold. The extent of porosity may be varied by, for example, material type, sintering conditions, orientation relative to deposition and laser, etc. Particularly when the porosity of the material is relied upon as the vehicle by which suction is applied to the mold cavity, a porosity of the mold of between about 2 and 25 percent (and in particular between about 2 and 15 percent) may be desirable. Porosity may also be varied in post-processing.

[0043] Moreover, the thickness of the molds 314, 414 themselves may vary. As an example, although the molds 314, 414 are illustrated as solid block-type structures, it is also contemplated that 3-D thermoforming molds may be formed of substantially constant thickness (see mold 314’ in FIG. 9). As the degree of vacuum that can be applied to the heated sheet may vary with the thickness of the mold, molds of substantially constant thickness in maintaining a relatively uniform vacuum on the heated sheet during molding. Although any thickness may be suitable, generally speaking a mold having a thickness of between about 1 and 2.5 mm may be desirable, and in particular a thickness of between about 1.5 and 2 mm.

[0044] It is also contemplated that the extent of porosity of the porous regions may vary between molds.

[0045] Those of skill in this art will recognize that the concepts discussed herein may be applicable to molds used for other molding techniques. For example, molds employed in single-wall and double-wall blow-molding are typically vented to prevent the trapping of air when the parison being molded is inflated. Molds for blow-molding may be constructed by either of the techniques discussed above, with the porosity of the molds being controlled to permit the escape of air during molding as needed. Twin-sheet thermoforming processes may also benefit from the use of molds as described above.

[0046] Further details regarding embodiments of the invention are provided in the following non-limiting examples.Example 1 Vacuumforming Trials

[0047] In order to prove the viability of thermoforming / vacuumforming with 3-D printed molds, tests were conducted with molds with certain process andmaterial parameters being varied. More specifically, molds were 3-D printed material into the shape shown in FIG. 9. The 3-D printing technique used was Powder Bee Fusion and was performed on a Hewlett-Packard Multi-Jet Fusions 3- D printer. The molds were formed of either polyamide- 12 or high temperature amber (which were used as controls), and the thickness was varied for different molds. The molds were installed in a Vaquform DT2 vacuumforming apparatus. Parts were then thermoformed of either High Impact Polystyrene (HIPS) or polyethylene terephthalate glycol (PETG). The finished parts were then assessed visually for various attributes and scored on a 1-4 scale.

[0048] FIG. 10 sets forth the results of the testing. It can be seen in FIG. 10 that the although the part could be vacuumformed under all conditions, best results were seen when the mold was 1.5 or 2 mm in thickness. This was true for both HIPS and PETG parts. Other observations included:- Molds began to cave at a mold thickness <1 ,5mm- Pre-print parameters (e.g., heat / powder refresh rate / build density) can increase porosity but may decrease mold strength and finish- Embossed features benefitted from thinner molds more than debossed features- Mold texture was more apparent with thinner molds- Vacuum may be non-uniform with some mold shapesExample 2Porosity assessment for Vacuumforming Molds

[0049] Tests were conducted on a Zeiss Metrotom 800 Industrial CT scanning machine to determine the porosity of 3-D printed samples of Powder Bed Fusion samples as discussed above. Both vertical and horizontal samples wereassessed (i.e., in both the direction of added material during printing (vertical) and the direction normal thereto (horizontal). Samples measuring 1, 1.5 and 2 mm in thickness were assessed.

[0050] The results of the testing are shown in FIG. 11. It was determined that, generally speaking:- The thinner the samples were, the higher the relative porosity is within the samples- The vertical samples were more porous than the horizontal samples- The vertical samples showed a higher variation in % Volume Porosity as the thickness of the material changes

[0051] The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

That Which is Claimed is1. A method of injection molding a polymeric part, comprising the steps of:(a) providing a mold having first and second mold halves, at least the first mold half formed by 3-D printing, a first region of the first mold half having a porosity that enables air to pass therethrough, the first and second mold halves being mounted in an injection molding machine;(b) with the first and second mold halves in a closed condition, injecting molten polymeric material into a cavity defined by the first and second mold halves;(c) with the first and second mold halves in the closed position, allowing gas to escape the cavity through the first region of the first mold half; then(d) moving the first and second mold halves to an open position to allow the removal of a polymeric part from the cavity.

2. The method defined in Claim 1 , wherein the porosity of the first region of the first mold half is between about 2 and 25 percent.

3. The method defined in Claim 1 , wherein the 3-D printed mold is formed of a metallic material.

4. The method defined in Claim 1 , wherein the first mold half is devoid of vents leading from the cavity to a location external of the first mold half.

5. The method defined in Claim 1, wherein the first region of the first mold have has a different porosity than a second region of the first mold half.

6. A method of thermoforming a polymeric part, comprising the steps of:(a) providing a mold formed by 3-D printing, the mold having a porosity that enables a vacuum to be drawn therethrough;(b) mounting the mold in a thermoforming machine, wherein a first side of the mold is in fluid communication with a vacuum source;(c) positioning a heated polymeric sheet adjacent a second side of the mold, the second side opposing the first side;(d) applying a vacuum to the mold via the vacuum source;(e) engaging the heated polymeric sheet with the second side of the mold so that the heated polymeric sheet takes the shape of the second side of the mold, and(f) cooling the re-shaped heated polymeric sheet to form the polymeric part.

7. The method defined in Claim 6, wherein the porosity of the mold is between about 2 and 15 percent.

8. The method defined in Claim 6, wherein the 3-D printed mold is formed of a polymeric material.

9. The method defined in Claim 6, wherein the second surface of the mold is convex.

10. The method defined in Claim 6, wherein the second surface of the mold is concave.

11. The method defined in Claim 6, wherein step (c) comprises positioning the heated polymeric sheet above the mold.

12. The method defined in Claim 11 , wherein a heating unit is located above the heated polymeric sheet.

13. The method defined in Claim 6, wherein a wall thickness of the mold is between about 1 and 2 mm.

14. A mold for the molding of a polymeric material, comprising: a body having a mold contact surface; wherein the mold is formed of a metallic material via 3-D printing; and wherein at least a first region of the body has a porosity of between about 2 and 15 percent.

15. The mold defined in Claim 14, wherein the porosity of the first region is a first porosity, and wherein the body includes a second region having a second porosity, and wherein the second air porosity is less than the first air permeability.

16. The mold defined in Claim 15, wherein the first region is in fluid communication with the mold contact surface.

17. The mold defined in Claim 15, wherein the first region is adjacent to a feature of a cavity in the mold, the feature being selected from the group consisting of: a corner; an edge; a dead end; an undercut; and a weld line.

18. The mold defined in Claim 14, wherein the mold is a first mold half that is configured to mate with a second mold half in an injection molding process.

19. The mold defined in Claim 18, mounted in an injection molding machine.

20. The mold defined in Claim 14, mounted in a thermoforming machine.

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