Method and apparatus for differentially heating and thermoforming a polymer sheet
AssigneeGeneral Electric Company
InventorsHerman F. Nied, Alexander T. Chen
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Abstract
A method and apparatus for thermoforming 3-dimensional articles of chosen wall thickness dimensions from a polar polymer sheet. The polymer sheet is dielectrically heated, the heating being controlled to impress a predetermined thermal pattern on the sheet. The thermal pattern is selected in accordance with the amount of stretching to which each area of the sheet is subjected during the subsequent work-forming step, the areas subjected to greater stretching being heated to a lower temperature and vice versa. Thus, the stretching action is balanced and results in accurate control of the wall thickness of the final article.
Claims21
A method for dielectrically heating a sheet of polar polymer material, comprising the steps of:
- placing said sheet between first and second spaced electrodes, wherein at least said first electrode comprises a plurality of discrete electrode segments proximately positioned to each other, and
- dielectrically heating said sheet by applying RF energy to said first and second electrodes;
- varying the RF energy applied to respective ones of said plurality of discrete electrode segments so that different segments can have different applications of RF energy to impress a selected thermal pattern on said sheet.
A method for thermoforming a sheet of polar polymer material into articles having chosen cross-sectional thickness dimensions, said method comprising the steps of:
- positioning said sheet between a first electrode having a plurality of discrete electrode segments and a second electrode such that said electrodes face opposite sheet surfaces;
- dielectrically heating said sheet by energizing said electrodes with a high frequency power source;
- varying the high frequency power applied to respective ones of said plurality of discrete electrode segments so that different segments can have different applications of high frequency power to impress a selected thermal pattern on said sheet;
- and
- die-forming said articles from said thermally patterned sheet such that each of said thickness dimensions is determined by the temperature of the originating sheet area and the physical working performed thereon during the die-forming step.
Apparatus for dielectrically heating an article, said apparatus comprising:
- a first electrode, said first electrode comprising a plurality of discrete electrode segments;
- a second electrode spaced from said first electrode to receive an article to be heated therebetween;
- a source of RF energy connected to said first and second electrodes;
- and
- control means for varying the RF energy applied to respective ones of said plurality of discrete electrode segments so that different segments can have different applications of RF energy to impress a selected thermal pattern on said article.
Apparatus for forming a polar polymer sheet into articles having chosen cross-sectional dimensions, said apparatus comprising:
- a first electrode, said first electrode comprising a plurality of discrete electrode segments;
- a second electrode spaced from said first electrode;
- means for positioning a polar polymer sheet between said first and second electrodes;
- a source of RF energy connected to said first and second electrodes;
- control means for varying the RF energy applied to respective ones of said plurality of discrete electrode segments so that different segments can have different applications of RF energy to impress a selected thermal pattern on said sheet;
- and
- means for die-forming articles from said thermally patterned sheet such that each of said thickness dimensions is determined by the temperature of the originating sheet area and the physical working performed thereon by said die-forming means.
Dependencies are inferred from the claim text.