System and method for twin sheet forming

• US 6,372,176 B1
• Filed: 03/01/1999
• Issued: 04/16/2002
• Est. Priority Date: 03/01/1999
• Status: Expired due to Fees

• Current Assignee: Kiefel Technologies, Inc.
• Original Assignee: Kiefel Technologies, Inc.
• Inventors: Ekendahl, Lars O., Landsteiner, Rudolf, Posch, Georg
• Primary Examiner(s): Silbaugh, Jan H.
• Assistant Examiner(s): Lee, Edmund H.
• Application Number:
  US09/260,851
• Time in Patent Office: 1,142 Days
• Field of Search: 264/545, 264/551, 264/248, 264/250, 425/388, 425/116, 156/285, 156/292
• US Class Current: 264/545
• CPC Class Codes: B29C 2049/4881 having a mandrel or core e.g. two mould halves with a core in-between
• CPC Class Codes: B29C 2949/3006 having tangentially different components within one layer, e.g. longitudinal stripes
• CPC Class Codes: B29C 49/06914 using parallel sheets as a preform
• 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 51/12 of articles having inserts or reinforcements
• CPC Class Codes: B29C 51/20 having movable moulds or mould parts
• CPC Class Codes: B29C 51/261 Handling means, e.g. transfer means, feeding means B29C51/44 takes precedence
• CPC Class Codes: B29C 51/262 Clamping means for the sheets, e.g. clamping frames
• 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
• CPC Class Codes: B29C 65/02 by heating, with or without pressure
• CPC Class Codes: B29C 66/137 Beaded-edge joints or bead seals for sealing or securing package folds or closures B65B51/24
• CPC Class Codes: B29L 2031/7172 Fuel tanks, jerry cans

Abstract

A twin sheet forming system and method is used to form a hollow article, such as an automotive fuel tank, from first and second sheets of thermoplastic material. The system includes first and second loading stations, first and second heating stations, and first and second thermoforming stations in an in-line arrangement. The in-line arrangement allows the sheets to be transferred independently between the stations and the separate thermoforming stations allows the sheets to be thermoformed independently. Each of the thermoforming stations includes an upper and lower platen generally in a side by side arrangement for supporting thermoforming tools and plug assists. After heating, the sheets are independently transferred to the thermoforming stations and formed using the thermoforming tools and plug assists. The thermoforming tool and thermoformed piece in one of the thermoforming stations is then transferred to the other station, and the thermoformed pieces are fused together. The press platen in this station thus has a two stage capability for both plug assisting and fusing. In one example, the plug assist can be an insert to be secured and left within the article during the thermoforming process.

Claims

1. A method of twin sheet thermoforming comprising:

loading first and second sheets of thermoplastic material into respective separate first and second loading stations;

transferring the loaded first and second sheets of thermoplastic material to respective separate first and second heating stations;

heating said first and second sheets of thermoplastic material within said respective separate first and second heating stations;

independently transferring the heated first and second sheets of thermoplastic material from said first and second heating stations to separate first and second thermoforming stations respectively, wherein the heated first and second sheets of thermoplastic material are positioned between respective first and second thermoforming tools and first and second plug assists;

moving said first and second thermoforming tools and said first and second plug assists together for thermoforming said first and second sheets independently into respective first and second thermoformed pieces, wherein said first thermoformed piece remains in said first thermoforming tool and said second thermoformed piece remains in said second thermoforming tool;

transferring said first thermoforming tool to said second thermoforming station, for positioning said first thermoformed piece opposite said second thermoformed piece; and

moving said first thermoforming tool and said second thermoforming tool together in said second thermoforming station, for fusing said first and second thermoformed pieces together.

2. The method of claim 1 wherein the step of loading includes loading said first and second sheets of thermoplastic material from roll stock.

3. The method of claim 1 wherein the step of loading includes loading said first and second sheets of thermoplastic material from sheet stock.

4. The method of claim 1 wherein said first and second sheets of thermoplastic material are transferred in-line from said first and second loading stations to said first and second heating stations and to said first and second thermoforming stations.

5. The method of claim 1 wherein said second thermoforming station applies a force to fuse said first and second thermoformed pieces that is greater than a force applied by said first and second thermoforming stations to thermoform said first and second sheets of thermoplastic material.

6. The method of claim 1 wherein one of said first and second sheets of thermoplastic material is transferred to a respective one of said first and second thermoforming stations prior to transferring the other of said first and second sheets of thermoplastic material to the other one of said first and second thermoforming stations.

7. The method of claim 1 wherein said first and second sheets of thermoplastic material are transferred simultaneously to said first and second thermoforming stations.

8. The method of claim 1 wherein at least one of said first and second plug assists is an insert, and wherein said insert is left within a respective one of said first and second thermoformed pieces after thermoforming.

9. The method of claim 8 wherein said insert is fused to an inner surface of both said first and second thermoformed pieces.

10. The method of claim 1 further including thermal clamping edges of said first and second sheets of thermoplastic material at said first and second heating stations, wherein said edges are thermally clamped as said first and second thermoplastic material are moved from said heating stations to said thermoforming stations.

11. The method of claim 1 wherein said plug assists manipulate said first and second sheets of thermoplastic material while a vacuum force is applied by first and second thermoforming tools.