METHOD OF VACUUM FORMING AN OBJECT USING A FLEXIBLE MOLD AND AN APPARATUS FOR VACUUM FORMING AN OBJECT
A method of vacuum forming an object includes heating a plastic sheet. After heating the plastic sheet, a vacuum is applied to pull the sheet against an outer surface of a flexible mold so that the plastic sheet has a formed shape that conforms to a contoured shape of the outer surface of the flexible mold. A rigid core is withdrawn from a cavity in the flexible mold. The flexible mold is then withdrawn from the plastic sheet by applying force to the flexible mold in a single direction, thereby causing flexing of the flexible mold past the undercut. An apparatus for vacuum forming a plastic sheet includes the flexible mold.
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This application is a divisional of and claims the benefit of priority to U.S. patent application Ser. No. 14/557,516 filed on Dec. 2, 2014, which is hereby incorporated by reference in its entirety.
TECHNICAL FIELDThe present teachings generally include a method of vacuum forming an object and an apparatus for vacuum forming an object.
BACKGROUNDVacuum forming is a process by which a plastic sheet is heated and then formed to the shape of a die by applying a vacuum to draw the sheet against the surface of the object. The die must then be withdrawn. Objects suitable for vacuum forming on a unitary rigid die have heretofore been limited to those that do not have undercuts, as an undercut prevents withdrawal of the die from the formed sheet without damage to the formed sheet. Alternatively, a complex, costly die with sliding die portions would be required to allow removal of the sheet.
SUMMARYA method of vacuum forming an object includes heating a plastic sheet. After heating the plastic sheet, a vacuum is applied to conform pull the plastic sheet to a contoured shape of an outer surface of a flexible mold so that the plastic sheet has a formed shape that includes an undercut. Typically, such an undercut would cause a die lock condition. Vacuum forming of an object to achieve such a formed shape was therefore not an option. However, under the method disclosed herein, a rigid core is withdrawn from a cavity in the flexible mold. The flexible mold is then withdrawn from the plastic sheet by applying force to the flexible mold in a single direction, thereby causing flexing of the flexible mold past the undercut. Because the mold is flexible, the plastic sheet is formed to replicate the object, including the undercut. Thus, objects with undercuts that previously required more costly processes, such as a complex die assembly with slides, or injection molding, can instead be vacuum formed.
An apparatus for forming an object from a plastic sheet includes a mold having an inner surface defining a cavity and having an outer surface that has a contoured shape. A rigid core is configured to fit within the cavity. A vacuum source is positioned to vacuum form the plastic sheet to the outer surface of the mold to form the object having a formed shape, including an undercut, that conforms to the contoured shape of the mold. The formed shape includes an undercut. The mold is flexible, allowing the mold to be withdrawn from the plastic sheet past the undercut by applying force in a single direction after the rigid core is withdrawn from the cavity.
The above features and advantages and other features and advantages of the present teachings are readily apparent from the following detailed description of the best modes for carrying out the present teachings when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numbers refer to like components throughout the views,
As shown in
The method 100 enables the use of the flexible mold 20 that is of a flexible material such as silicone. As best shown in
Next, the method 100 proceeds to suspending the rigid core 36 above the female mold 50 in the container 52 in step 110 so that a gap 58 exists between the female mold 50 and the rigid core 36.
Next, in step 114, the flexible mold 20 is separated from the female mold 50 by withdrawing the base 24 and rigid core 36 from the container 52 and flexing the mold 20 out of the female mold 50. Next, in step 116, the flexible mold 20 is again placed on the rigid core 36 which is supported on the base 24, as best shown in
The plastic sheet 18 is then prepared for vacuum forming. The plastic sheet may be polyethylene terephthalate (PTEG), Acrylonitrile butadiene styrene (ABS), Polypropylene (PP), thermoplastic, or another polymeric material suitable for vacuum forming. In step 118, the plastic sheet 18 is clamped to an oven tray 60.
With the plastic sheet 18 sufficiently heated, the flexible mold 20 is then raised into contact with the plastic sheet 18 in step 126 by moving the base 24 with the rigid core 36 and flexible mold 20 mounted thereon upward toward the sheet 18 as indicated by directional arrow D in
Next, in step 132, the rigid core 36 is withdrawn from the cavity 32 in the flexible mold 20 as shown by the directional arrow E in
Excess material of the plastic sheet 18 can then be trimmed from a perimeter P of the formed shape of the plastic sheet 18 in step 136. The perimeter P is shown in
While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.
Claims
1. An apparatus for forming an object from a plastic sheet comprising:
- a mold having an inner surface defining a cavity and having an outer surface; wherein the outer surface has a contoured shape;
- a rigid core configured to fit within the cavity;
- a vacuum source positioned to vacuum form the plastic sheet to the outer surface of the mold to form the object having a formed shape that conforms to the contoured shape of the mold, the formed shape including an undercut; and
- wherein the mold is flexible, allowing the mold to be withdrawn from the plastic sheet past the undercut by applying force in a single direction after the rigid core is withdrawn from the cavity.
2. The apparatus of claim 1, further comprising:
- a base on which the rigid core is secured;
- wherein the base has a series of openings extending around the rigid core; and wherein the vacuum source is in fluid communication with the series of openings.
3. The apparatus of claim 2, wherein the base has a surface on which the rigid core is secured; and wherein each opening of the series of openings extends through the base from the surface on which the rigid core is secured to an opposite surface of the base.
4. The apparatus of claim 2, wherein the series of openings completely surround the rigid core.
5. The apparatus of claim 2, wherein the base has a surface on which the rigid core is secured; wherein the undercut forms a first angle relative to the surface of the base; wherein the force is applied to the mold to withdraw the mold from the plastic sheet past the undercut at a second angle relative to the base; and wherein the second angle is different than the first angle.
6. The apparatus of claim 5, wherein the second angle is a 90 degree angle such that the force is applied perpendicular to the base.
7. The apparatus of claim 1, further comprising:
- a base having a base surface on which the rigid core is secured; and
- wherein the force is applied perpendicular to the base surface.
8. The apparatus of claim 7, wherein the undercut is parallel to the base surface.
9. The apparatus of claim 1, wherein a protruding portion of the mold forms the undercut.
10. The apparatus of claim 9, wherein the object is a scale model of a vehicle having a wheel and a bumper, and the undercut is at the wheel or at the bumper.
11. The apparatus of claim 1, wherein the mold is silicone.
12. The apparatus of claim 1, wherein the outer surface of the flexible mold is configured to be coextensive with an inner surface of the object.
13. The apparatus of claim 1, wherein an outer surface of the object is substantially identical to the contoured shape of the outer surface of the flexible mold.
14. An apparatus for forming an object from a plastic sheet comprising:
- a mold having an inner surface defining a cavity and having an outer surface; wherein the outer surface has a contoured shape;
- a rigid core configured to fit within the cavity;
- a vacuum source positioned to vacuum form the plastic sheet to the outer surface of the mold to form the object having a formed shape that conforms to the contoured shape of the mold, the formed shape including an undercut;
- a base having a surface on which the rigid core is secured;
- wherein the base has a series of openings completely surrounding the rigid core; wherein each opening of the series of openings extends through the base from the surface on which the core is secured to an opposite surface of the base; wherein the vacuum source is in fluid communication with the series of openings; and
- wherein the mold is flexible, allowing the mold to be withdrawn from the plastic sheet past the undercut by applying force in a single direction after the rigid core is withdrawn from the cavity.
15. The apparatus of claim 14, wherein the force is applied perpendicular to the base surface.
16. The apparatus of claim 15, wherein the undercut is parallel to the base surface.
17. The apparatus of claim 14, wherein a protruding portion of the mold forms the undercut.
18. The apparatus of claim 17, wherein the object is a scale model of a vehicle having a wheel and a bumper, and the undercut is at the wheel or at the bumper.
19. The apparatus of claim 14, wherein the outer surface of the flexible mold is configured to be coextensive with an inner surface of the object.
20. The apparatus of claim 14, wherein an outer surface of the object is substantially identical to the contoured shape of the outer surface of the flexible mold.
Type: Application
Filed: Jul 19, 2018
Publication Date: Nov 8, 2018
Applicant: GM Global Technology Operations LLC (Detroit, MI)
Inventor: Thomas E. Houck (Bloomfield Hills, MI)
Application Number: 16/039,882