Compression-Molded Composite with Cellulose Core and Vacuum Air Removal
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Solution Overview
Problem
Compression molding of sandwich-type composite components with a cellulose-based core often results in poor surface finish due to air trapped between the core and skins, leading to debossing and uneven shapes, limiting the production of complex parts with undercuts and curved geometries.
Innovation Solution
A method involving a compression mold with vacuum assistance to seal and cool the sandwich stack of thermoplastic skins and a cellulose-based core, where the air in cavities pushes softened materials inward, preventing debossing and enhancing surface appearance by applying vacuum at the outer surfaces during cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If compression molding is used to manufacture sandwich-type composite components with cellulose-based core, then light weight and high strength are achieved, but poor surface finish and debossing occur due to trapped air
Solution Approach 1:
The patent extracts and removes trapped air from the molding cavity through vacuum application. The vacuum system creates negative pressure that draws air out from between the core and skins during compression molding, preventing air pockets that cause debossing and poor surface finish while maintaining the structural integrity of the sandwich composite component.
Solution Approach 2:
The patent employs vacuum (a pneumatic principle) to control air removal during the molding process. By applying vacuum pressure differential, the system manages the air evacuation from the molding cavity, ensuring complete contact between the softened skins and the core surface, thereby eliminating debossing defects and achieving smooth surface finish.
2Manufacturing precision
If vacuum is applied during compression molding, then surface defects are minimized, but device complexity increases
Solution Approach 1:
The mold cavity is designed to serve multiple functions: it provides the shaping geometry for the composite component and simultaneously acts as a vacuum chamber for air removal. The vacuum ports are integrated into the mold structure, allowing the same mold to perform both forming and air evacuation functions, thereby minimizing additional device complexity while achieving improved surface finish.
3Reliability
If air is trapped between molding compound and mold cavity surface, then porosity occurs, but complete evacuation is difficult with complex geometries
Solution Approach 1:
The patent applies vacuum before and during the compression phase to proactively remove air from the molding cavity. By establishing negative pressure early in the process, air is drawn out from complex geometries and undercuts before the material fully sets, preventing porosity formation and ensuring complete evacuation even from difficult-to-reach areas of the component geometry.
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
The method effectively inhibits debossing and improves the surface finish of compression-molded composite components, allowing for the production of parts with enhanced aesthetic appeal and structural integrity, suitable for automotive applications.
Implementation Method 1
Vacuum during compression molding of thermoset parts has been used to minimize surface defects of the type known as porosity. Porosity is caused by air that is trapped between the molding compound (i.e. raw materials) and the surface of the mold cavity. The mold chamber or cavity is sealed from the surrounding atmosphere and then the chamber is evacuated before pressure is applied to the raw materials.
Implementation Method 2
The heated blank or stack is allowed to cool in the mold cavity in the closed position until inner surfaces of the skins are bonded to top and bottom surfaces of the core by the sheets to seal the core cavities.
Implementation Method 3
Air in the sealed cavities urges softened portions of the sheets and portions of the core inwardly towards the cavities of the core as the air in the cavities cools to inhibit debossing and improve surface appearance of a first outer surface of the blank or stack during the step of allowing.
Data Source
AI summary
A method of making a sandwich-type, compression-molded, composite component having improved surface appearance is provided. Reinforced thermoplastic skins, first and second sheets of thermoplastic adhesive and a cellulose-based core of a blank or stack of sandwich materials are heated to a softening temperature of the thermoplastics. The heated blank or stack is allowed to cool in the mold cavity until inner surfaces of the skins are bonded to top and bottom surfaces of the core by the sheets to seal core cavities. Air in the sealed cavities urges softened portions of the sheets and portions of the core inwardly towards the cavities of the core as the air in the cavities cools to inhibit debossing and improve surface appearance of a first outer surface of the blank or stack.