Method of forming deep draw twin sheet plastic articles

• US 5,427,732 A
• Filed: 12/28/1993
• Issued: 06/27/1995
• Est. Priority Date: 12/28/1993
• Status: Expired due to Term

• Current Assignee: Lyle H. Shuert
• Original Assignee: Lyle H. Shuert
• Inventors: Shuert, Lyle H.
• Primary Examiner(s): Timm, Catherine
• Application Number:
  US08/174,110
• Time in Patent Office: 546 Days
• Field of Search: 264/545, 425/388
• US Class Current: 264/545
• CPC Class Codes: B29C 51/006 for making articles having hollow walls
• CPC Class Codes: B29C 51/04 Combined thermoforming and prestretching, e.g. biaxial stretching
• CPC Class Codes: B29C 51/10 Forming by pressure difference, e.g. vacuum
• CPC Class Codes: B29C 51/267 Two sheets being thermoformed in separate mould parts and joined together while still in the mould B29C49/0691 takes precedence

Abstract

A method of utilizing a male mold and a complementary female mold to thermoform first and second plastic sheets and thereafter fuse the sheets together to form a twin sheet plastic article. The female mold is moved upwardly into sealing engagement with the underside of the first plastic sheet to form an annular seal with the first plastic sheet; a bubble is formed in the first plastic sheet within the annular seal; the male mold is lowered into the bubble to move the bubble into general conformity with the cavity surface; the male mold is raised; a vacuum is applied to the cavity surface to conform the bubble totally to the cavity surface; a second plastic sheet is positioned between the molds; a pre-draw box is positioned between the second plastic sheet and the female mold and moved upwardly into sealing engagement with the underside of the second plastic sheet to form an annular seal with the second plastic sheet; a bubble is formed in the second plastic sheet within the annular seal; the male mold is moved downwardly into the bubble to generally conform the bubble to the male mold surface; a vacuum is applied to the male mold surface to conform the bubble totally to the male mold surface; the pre-draw box is removed; and the molds are brought together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.

Claims

1. A method of forming a twin sheet plastic article comprising the steps of:

providing a male mold having a protrusion;

providing a female mold having a cavity generally complementary to the male mold protrusion;

positioning the male and female molds in spaced relation;

heating a first plastic sheet to a heated, flowable state;

positioning the first plastic sheet between the molds;

moving the female mold into sealing engagement with a surface of the first plastic sheet to form an annular seal with the first plastic sheet;

forming a first bubble in the first plastic sheet within the annular seal;

moving the male mold into engagement with the first bubble to move the first bubble into general conformity with the cavity surface;

applying vacuum to the cavity surface to conform the first bubble totally to the cavity surface;

heating a second plastic sheet to a heated, flowable state;

positioning the second plastic sheet between the molds;

positioning a pre-draw box between the second plastic sheet and the female mold;

moving the pre-draw box into sealing engagement with a surface of the second plastic sheet to form an annular seal with the second plastic sheet;

forming a second bubble in the second plastic sheet within the annular seal;

moving the male mold into the second bubble to generally conform the second bubble to the protrusion surface;

applying vacuum to the protrusion surface to conform the second bubble totally to the protrusion surface;

removing the pre-draw box; and

with the first and second sheets still in a heated, flowable state, bringing the molds together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.

2. A method according to claim 1 wherein:

the first bubble is formed by supplying pressurized fluid to the female mold cavity to push the sheet upwardly above the female mold cavity.

3. A method according to claim 1 wherein:

the first bubble is formed by creating a vacuum in the cavity of the female mold to suck the sheet downwardly within the female mold cavity.

4. A method according to claim 1 wherein:

the pre-draw box has an open box configuration including an upper peripheral edge surface and a cavity defined within the edge surface; and

the pre-draw box is moved upwardly to move the peripheral edge surface into sealing engagement with the undersurface of the second plastic sheet.

5. A method according to claim 4 wherein:

the second bubble is formed by supplying pressurized fluid to the pre-draw box cavity to push the sheet upwardly above the pre-draw box cavity.

6. A method of utilizing a male mold having a protrusion surface and a female mold having a cavity surface generally complementary to the protrusion surface to thermoform first and second plastic sheets and thereafter fuse the sheets together to form a twin sheet plastic article, characterized in that:

the first and second plastic sheets are heated to a heated, flowable state, the female mold is moved into sealing engagement with a surface of the first plastic sheet to form an annular seal, a first bubble is formed in the first plastic sheet within the annular seal, the male mold is moved into engagement with the first bubble to move the first bubble into general conformity with the cavity surface, vacuum is applied to the cavity surface to totally conform the first bubble to the cavity surface, an auxiliary mold device is moved against a surface of the second plastic sheet to form an annular seal, a second bubble is formed in the second plastic sheet within the annular seal, the male mold is moved into the second bubble to generally conform the second bubble to the protrusion surface, vacuum is applied to the protrusion surface to totally conform the second bubble to the protrusion surface, and, with the sheets still in a heated, flowable state, the molds are brought together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.

7. A method according to claim 6 wherein:

the first bubble is formed by supplying pressurized fluid to the female mold cavity to push the sheet upwardly above the female mold cavity.

8. A method according to claim 6 wherein:

the first bubble is formed by creating a vacuum in the female mold cavity to suck the sheet downwardly within the female mold cavity.

9. A method according to claim 6 wherein:

the auxiliary mold device comprises a pre-draw box having an open box configuration including an upper peripheral edge surface and a cavity defined within the edge surface; and

the pre-draw box is moved upwardly to move the peripheral edge surface into sealing engagement with the underside of the second plastic sheet.

10. A method according to claim 9 wherein:

the second bubble is formed by supplying pressurized fluid to the pre-draw box cavity to push the sheet upwardly above the pre-draw box cavity.

11. A method of forming a twin sheet plastic article comprising the steps of:

providing a male mold having a protrusion;

providing a female mold having a cavity generally complementary to the male mold protrusion;

positioning the male and female molds in spaced relation;

positioning a first plastic sheet between the molds;

moving the female mold into sealing engagement with a surface of the first plastic sheet to form an annular seal with the first plastic sheet;

forming a first bubble in the first plastic sheet within the annular seal;

moving the first bubble into general conformity with the cavity surface;

applying vacuum to the cavity surface to conform the first bubble totally to the cavity surface;

positioning a second plastic sheet between the molds;

positioning a pre-draw box, having an open box configuration, including an upper peripheral edge surface and a cavity defined within the edge surface, between the second plastic sheet and the female mold;

moving the pre-draw box upwardly to move the peripheral edge surface into sealing engagement with the undersurface of the second plastic sheet to form an annular seal with the second plastic sheet;

forming a second bubble in the second plastic sheet within the annular seal by creating a vacuum in the pre-draw box cavity to suck the sheet downwardly within the pre-draw box cavity;

moving the male mold into the second bubble to generally conform the second bubble to the protrusion surface;

applying vacuum to the protrusion surface to conform the second bubble totally to the protrusion surface;

removing the pre-draw box; and

bringing the molds together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.

12. A method of forming a twin sheet plastic article comprising the steps of:

providing a male mold having a protrusion;

providing a female mold having a cavity generally complementary to the male mold protrusion;

positioning the male and female molds in spaced relation with the female mold beneath the male mold;

positioning a first plastic sheet between the molds;

moving the female mold upwardly into sealing engagement with the undersurface of the first plastic sheet to form an annular seal with the first plastic sheet;

forming a first bubble in the first plastic sheet within the annular seal;

moving the male mold downwardly into the first bubble to move the first bubble into general conformity with the cavity surface and thereafter raising the male mold;

applying vacuum to the cavity surface to conform the first bubble totally to the cavity surface;

positioning a second plastic sheet between the molds;

positioning a pre-draw box between the second plastic sheet and the female mold;

moving the pre-draw box upwardly into sealing engagement with the undersurface of the second plastic sheet to form an annular seal with the second plastic sheet;

forming a second bubble in the second plastic sheet within the annular seal;

moving the male mold downwardly into the second bubble to generally conform the second bubble to the protrusion surface;

applying vacuum to the protrusion surface to conform the second bubble totally to the protrusion surface;

removing the pre-draw box; and

bringing the molds together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.

13. A method of utilizing a male mold having a protrusion surface and a female mold having a cavity surface generally complementary to the protrusion surface to thermoform first and second plastic sheets and thereafter fuse the sheets together to form a twin sheet plastic article, characterized in that:

the female mold is moved into sealing engagement with a surface of the first plastic sheet to form an annular seal, a first bubble is formed in the first plastic sheet within the annular seal, the male mold is moved into the first bubble to move the first bubble into general conformity with the cavity surface, vacuum is applied to the cavity surface to totally conform the first bubble to the cavity surface, a predraw box, having an open box configuration including an upper peripheral edge surface and a cavity defined within the edge surface, is moved upwardly to move the peripheral edge surface into sealing engagement with the underside of the second plastic sheet to form a annular seal, a second bubble is formed in the second plastic sheet within the annular seal by creating a vacuum in the pre-draw box cavity to suck the sheet downwardly within the pre-draw box cavity, the male mold is moved into the second bubble to generally conform the second bubble to the protrusion surface, vacuum is applied to the protrusion surface to totally conform the second bubble to the protrusion surface, and the molds are brought together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.

14. A method of utilizing a male mold having a protrusion surface and a female mold having a cavity surface generally complementary to the protrusion surface to thermoform first and second plastic sheets and thereafter fuse the sheets together to form a twin sheet plastic article, characterized in that:

the female mold is positioned beneath the male mold and is moved upwardly into sealing engagement with the underside of the first plastic sheet to form an annular seal, a first bubble is formed in the first plastic sheet within the annular seal, the male mold is lowered into the first bubble to move the first bubble into general conformity with the cavity surface, vacuum is applied to the cavity surface to totally conform the first bubble to the cavity surface, a predraw box, having an open box configuration including an upper peripheral surface and a cavity defined within the edge surface, is moved upwardly to move the upper peripheral edge surface into sealing engagement with the underside of the second plastic sheet to form an annular seal, a second bubble is formed in the second plastic sheet within the annular seal, the male mold is moved downwardly into the second bubble to generally conform the second bubble to the protrusion surface, vacuum is applied to the protrusion surface to totally conform the second bubble to the protrusion surface, and the molds are brought together to selectively fuse the first plastic sheet to the second plastic sheet to form the twin sheet plastic article.