Thermoplastic Prepreg Slit Design for Complex Shape Molding
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Solution Overview
Problem
Existing fiber-reinforced thermoplastic prepregs face challenges in forming complicated shapes due to draw-down issues during preheating for stamping molding, which affects shape stability and mechanical properties.
Innovation Solution
A prepreg design with unidirectionally aligned reinforcement fibers, featuring slits that cut reinforcement fibers to specific lengths and orientations, ensuring at least one end is positioned at an edge, and alternating band sections to suppress draw-down and enhance moldability into complex shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If continuous reinforcement fibers are used to achieve excellent mechanical properties, then the mechanical properties are improved, but it becomes difficult to form complicated three-dimensional shapes
Solution Approach 1:
The continuous reinforcement fibers are segmented into chopped fibers with specific length ratios (first chopped fibers: 1/10 to 1/5 of sheet length, second chopped fibers: 1/20 to 1/10 of sheet length). This segmentation enables the fibers to conform to complicated three-dimensional shapes while maintaining adequate mechanical properties through the distributed fiber network.
2Adaptability or versatility
If chopped prepregs are used to improve shapeability, then shapeability is improved, but draw-down occurs during preheating causing shape change
Solution Approach 1:
Different regions of the prepreg contain different types and lengths of chopped fibers. The first chopped fibers (longer) provide dimensional stability to suppress draw-down during preheating, while the second chopped fibers (shorter) provide shapeability for complicated forms. This local differentiation of fiber properties resolves the contradiction between stability and shapeability.
Solution Approach 2:
The invention uses a composite structure combining two types of chopped fibers with different length characteristics within the same prepreg. This composite fiber arrangement allows the material to simultaneously exhibit both dimensional stability (from longer fibers) and shapeability (from shorter fibers), resolving the contradiction between these opposing requirements.
3Adaptability or versatility
If incisions are inserted into prepreg to improve shapeability, then shapeability is improved, but heat sagging occurs during preheating causing shape change
Solution Approach 1:
Instead of inserting incisions that compromise structural integrity, the invention uses locally differentiated chopped fiber lengths to achieve shapeability. The shorter second chopped fibers enable conformability to complex shapes while the longer first chopped fibers maintain dimensional stability during preheating, avoiding the heat sagging problem associated with incisions.
4Stability of the object's composition
If skin material with high softening temperature is provided to suppress draw-down, then dimensional stability is improved, but flow of reinforcement fibers and resin is inhibited deteriorating molding of three-dimensional shapes
Solution Approach 1:
The invention uses a composite fiber system within a single resin matrix instead of adding a separate skin material layer. The different length ratios of chopped fibers (first: 1/10 to 1/5, second: 1/20 to 1/10 of sheet length) create internal structural differentiation that provides both dimensional stability and flow capability, avoiding the fiber flow inhibition caused by high-softening-temperature skin materials.
Solution Approach 2:
The invention changes the fiber length parameter distribution within the prepreg rather than changing the resin softening temperature. By controlling the length ratios of different chopped fiber populations, the material achieves dimensional stability during preheating while maintaining adequate flow characteristics for three-dimensional molding, without requiring high-softening-temperature skin materials that would inhibit fiber and resin flow.
Data Source
AI summary
A prepreg formed from a resin and unidirectionally aligned reinforcement fibers, characterized in that: the prepreg is sheet-shaped; the prepreg has cutouts of a depth for cutting the reinforcement fibers, and includes reinforcement fibers (A) cut by the cutouts to a length of 10 to 50 mm and reinforcement fibers (B) having a length of equal to or more than 50% of the sheet length of the prepreg in the alignment direction of the reinforcement fibers; the surface area of a band section including the reinforcement fibers (B) in a plan view is 1.4% to 35.0% of the entire surface area of the prepreg in a plan view; and at least one end of the reinforcement fibers (B) is positioned at an end portion of the prepreg in the alignment direction of the reinforcement fibers.