Prepreg Slitting Using Polymeric Sheet Backing
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Solution Overview
Problem
In the production of prepreg strips for composite materials, the use of backing paper during slitting leads to debris and width variations, necessitating intentional gaps between strips to avoid overlaps, which is problematic for high-quality applications like aerospace components.
Innovation Solution
Using a flexible polymeric sheet as the outer backing instead of paper during slitting, which remains in place and reduces width variations, allowing for tighter tolerances and minimizing gaps between strips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If backing paper is used during slitting, then the prepreg can be handled and rolled without sticking, but paper debris is produced and width variations occur
Solution Approach 1:
The invention removes the backing paper from the slitting process entirely. Instead of using paper that creates debris and width variations, the patent uses a polymeric sheet that is either omitted or used in a modified form that does not interfere with the slitting operation, thereby eliminating the source of paper debris and width variations while maintaining handling capabilities through alternative means.
Solution Approach 2:
The invention changes the material parameter from paper to polymeric sheet. This material substitution fundamentally alters the interaction with the slitting blades, eliminating debris generation and width variations. The polymeric sheet either passes through the slitting unit without creating debris or is designed to be removed separately, thereby resolving the contradiction between ease of handling and manufacturing precision.
2Reliability
If intentional gaps are imposed between strips, then overlaps are avoided, but the gap width increases
Solution Approach 1:
The invention employs a pneumatic system with air knives positioned above and below the slitting blades. This pneumatic mechanism controls the width of the polymeric sheet as it passes through the slitting unit, enabling precise gap control between strips. The air flow dynamically adjusts the sheet width to maintain consistent, minimal gaps while preventing overlaps, thereby resolving the contradiction between reliability and precision.
Solution Approach 2:
The invention incorporates a feedback control system that monitors the width of the polymeric sheet and adjusts the air knife positioning or slitting blade positioning accordingly. This closed-loop control ensures that gaps between strips remain within specified tolerances, preventing overlaps while minimizing gap width. The system continuously adjusts based on measured deviations, resolving the contradiction between avoiding overlaps and controlling gap dimensions.
3Productivity
If wider strips of prepreg are used, then productivity increases, but wrinkling occurs during lay-up
Solution Approach 1:
The invention segments the wider prepreg strip into multiple narrower strips through the slitting process. By dividing the wide strip into multiple narrower parallel strips, the system maintains the productivity benefits of working with wider material while preventing wrinkling that would occur with single wide strips during automated lay-up. The segmented narrower strips are then laid down parallel to each other, resolving the contradiction between productivity and shape integrity.
Data Source
AI summary
A strip of curable prepreg comprising unidirectional fibers aligned with the length of the strip, the fibers being at least partially impregnated with curable thermosetting resin and comprising a flexible polymeric sheet on an outer face of the strip, wherein the strip has a substantially rectangular cross-section defining a width and a thickness of the strip.