Perforated Sheet Retainer for Thermoforming Thickness Control

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Solution Overview

Problem

Existing single sheet thermoforming methods involve multiple steps, lack control over thermoplastic sheet thickness on contoured mold surfaces, leading to variable physical and aesthetic issues in molded articles.

Innovation Solution

A method using a mold apparatus with a contoured and perforated interior mold surface and a sheet retainer with a perforated upper surface, allowing controlled positioning and rotation to draw a heated thermoplastic sheet into contact with the mold surface via reduced pressure, ensuring uniform thickness and contour matching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a preformed thermoplastic sheet is used in single sheet thermoforming, then the manufacturing process can be simplified, but the thickness control over contoured mold surfaces becomes insufficient

Engineering Contradiction:

Improvemanufacturing process simplicityVSAvoidthickness control

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The sheet retainer is made dynamically adjustable, allowing it to move along the perimeter edge and rotate around its longitudinal axis. This dynamic positioning enables the retainer to adapt to different mold contours while maintaining controlled contact with the thermoplastic sheet, thereby achieving both process simplicity and precise thickness control over contoured surfaces.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system incorporates controlled interaction between the sheet retainer and the thermoplastic sheet through reduced pressure application. The retainer's position and rotation are adjusted based on the sheet's response to vacuum pressure, creating a feedback mechanism that ensures uniform thickness distribution across the molded article while maintaining manufacturing simplicity.

Inventive Principle:

Principle #23Feedback

2Manufacturing precision

If multiple steps are used in prior art thermoforming methods, then thickness control may be improved, but the manufacturing time and process complexity increase

Engineering Contradiction:

Improvethickness controlVSAvoidmanufacturing cycle time

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The invention merges multiple functions into a single integrated operation. The sheet retainer simultaneously performs positioning, thickness control, and contour matching functions that were previously separate steps. By combining these functions into one coordinated action using reduced pressure and dynamic positioning, the process achieves precise thickness control without increasing manufacturing time.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The sheet retainer is pre-positioned and configured before the thermoforming operation begins. The retainer's location and orientation are established in advance, allowing the thermoplastic sheet to be drawn into contact with the mold surface in a single continuous operation rather than requiring multiple sequential steps, thereby reducing cycle time while maintaining precision.

Inventive Principle:

Principle #10Preliminary action

3Manufacturing precision

If the sheet retainer is made reversibly and controllably positionable and rotatable, then the contact and contouring of the thermoplastic sheet is improved, but the device complexity increases

Engineering Contradiction:

Improvecontour matching accuracyVSAvoidsheet retainer mechanism complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The sheet retainer mechanism is segmented into independent positioning and rotation functions. The retainer can be positioned along the perimeter edge and rotated around its longitudinal axis as separate controllable actions. This segmentation allows each function to be optimized independently, achieving precise contour matching while keeping the overall mechanism manageable and not excessively complex.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This approach minimizes steps, provides precise control over thermoplastic sheet thickness, and enhances the uniformity of molded articles' physical and aesthetic properties.

Implementation Method 1

drawing reduced pressure through the perforations of the upper surface of the sheet retainer, so as to retain a first portion of a second surface of the heated thermoplastic sheet thereon

Methodology Applied

Scientific EffectReduced pressure: Vacuum

Implementation Method 2

drawing reduced pressure through the perforations of the interior mold surface, so as to draw the heated thermoplastic sheet into contact therewith, so as to match the contour thereof

Methodology Applied

Scientific EffectReduced pressure: Vacuum

Implementation Method 3

cooling the heated thermoplastic sheet so as to form a shaped thermoplastic sheet that retains the contour of the interior mold surface

Methodology Applied

Scientific EffectCooling: Cooling

Data Source

PatentUS8371837B2Apparatus of preparing a molded article

Publication Date: 2013.02.12 D & D MANUFACTURING LLC

AI summary

A sheet molding apparatus including at least one molding surface with a plurality of perforations, at least one sheet retainer with a plurality of vacuum perforations, and an accompanying vacuum mechanism for controllably drawing reduced pressure through the perforations. The sheet molding apparatus can be used for rapidly and accurately positioning thermoformable thermoplastic sheets to match the molding surfaces in producing molded articles.