Structural Foam Molding with Continuous Fiber Preforms
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Solution Overview
Problem
Current composite injection molding (CIM) and structural foam molding (SFM) processes are limited by the use of short, randomly oriented fibers, which restrict the production of high-strength structural components and geometrically complex parts due to high shear forces and turbulent fluid dynamics during the injection process, leading to inadequate stress distribution and fiber orientation control.
Innovation Solution
Incorporating assemblages of aligned and continuous fiber-bundle-based preforms into the mold cavity before injecting the foam/composite mix, allowing for controlled fiber alignment and longer fiber lengths, and utilizing co-melting of resins to create a coherent matrix for enhanced strength and stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If short, randomly oriented fibers are used in CIM and SFM processes, then the injection process can be performed with high pressure and turbulent fluid dynamics, but the resulting parts have inadequate stress distribution and poor fiber orientation control
Solution Approach 1:
The patent applies preliminary action by pre-aligning continuous fibers in a preform structure before injection. The fibers are arranged in desired orientations and patterns in advance, then the preform is placed in the mold cavity before injection. This eliminates the need to rely on turbulent flow to randomize short fibers, while maintaining the efficiency of the injection process.
2Speed
If high pressure injection is used in CIM and SFM processes, then the material can be injected quickly into the mold cavity, but the shear forces cause fibers to become short and randomly oriented
Solution Approach 1:
The patent segments the fiber reinforcement function into two parts: (1) continuous fibers pre-aligned in a preform structure that provides the desired strength and orientation, and (2) the injection process that fills the remaining volume. This segmentation allows the preform to maintain fiber integrity while the injection process maintains speed, resolving the contradiction between injection speed and fiber quality.
3Strength
If continuous fiber-bundle-based preforms are incorporated into the mold cavity, then parts with aligned fibers and improved structural integrity can be produced, but the process complexity increases
Solution Approach 1:
The patent merges the preform placement step with the existing injection molding process. The preform is placed in the mold cavity, and then the injection process follows the conventional steps of injecting material, foaming, and curing. This merging approach integrates the continuous fiber reinforcement into the existing workflow without requiring entirely new equipment or processes.
4Ease of manufacture
If short fibers are used in CIM and SFM, then the material can be easily processed through injection, but the parts cannot withstand high stress and are limited in structural applications
Solution Approach 1:
The patent uses composite materials by combining continuous fibers with the polymer matrix in a preform structure. This composite approach maintains the ease of injection processing for the matrix material while the continuous fibers provide the necessary stress resistance. The preform acts as a composite reinforcement that enhances the overall mechanical properties without compromising processability.
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 enables the production of stronger and stiffer parts with aligned fibers, overcoming the limitations of previous processes by allowing for specific fiber placement and orientation, resulting in parts with improved structural integrity and geometric complexity.
Implementation Method 1
If the foaming agent is initially in a liquid state, this expansion involves a phase change to a gaseous state.
Implementation Method 2
Flow exiting the nozzle and entering the mold cavity undergoes rapid expansion due to a significant pressure drop across the nozzle outlet.
Implementation Method 3
Any bubbles that reach the mold surface 'pop' as surface tension breaks due to contact, leaving a 'skin' on the surface of the final part
Implementation Method 4
co-melting of resins to bond the foam core to the preform fibers
Data Source
AI summary
A method for making structural foam parts having continuous aligned fibers includes placing an assemblage of fiber-bundle-based preforms in an injection mold, creating a melt flow of resin and, optionally, short, loose fiber, and adding foaming agent to the melt flow. When the foaming agent/melt flow mixture is introduced into the injection mold, the foaming agent foams. The assemblage is structured and positioned so that fibers therefrom adopt a desired alignment and position in the final part. Structural foam fills the remainder of the volume of the part.