Two-Step Injection Molding for Plastic Components
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Solution Overview
Problem
Current methods for producing mechanically high-strength plastic components, such as those using RTM, face challenges like burr formation, complex post-processing, and high production costs due to the need for precise parameter control and additional sealing steps, which hinder the achievement of true-to-net-shape production and efficient recycling.
Innovation Solution
A method involving a two-step injection molding process where a high-viscosity thermoplastic compound is used to seal the mold in the first step, followed by injection of a low-viscosity reactive compound, ensuring adequate sealing and fixation of a textile preform within the mold, thereby preventing burr formation and reducing post-processing needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-viscosity reactive materials are used in injection molding, then the material can flow easily and impregnate the textile preform, but burrs form on the mold parting plane
Solution Approach 1:
A thermoplastic sealing component is injected into the mold cavity before the reactive material, creating a sealed environment that prevents burr formation during subsequent low-viscosity material injection. The sealing component is placed in advance to establish the containment boundary before the main impregnation process occurs.
Solution Approach 2:
The mold cavity contains a composite structure consisting of a thermoplastic sealing component and a textile preform. The thermoplastic material forms a sealed framework that holds the textile structure in place while allowing the reactive material to impregnate the textile without causing burrs on the parting plane.
2Strength
If RTM method is used to produce fiber-reinforced plastic components, then mechanically high strength is achieved, but complex post-processing including trimming and sealing is required
Solution Approach 1:
The sealing function and the structural component function are merged into a single integrated part. The thermoplastic sealing component is injected directly into the mold cavity and forms both the sealing boundary and a functional part of the final component, eliminating the need for separate sealing operations and reducing post-processing requirements.
Solution Approach 2:
The sealing operation is extracted from the post-processing stage and integrated into the injection molding process itself. By injecting the thermoplastic sealing component during the molding process, the separate sealing step is eliminated, reducing production complexity and post-processing requirements.
3Ease of operation
If preform is placed with large tolerance to tool edge, then insertion is easier, but low-viscosity reactive component advances on tool wall and traps air in preform
Solution Approach 1:
The thermoplastic sealing component acts as an intermediary between the preform and the mold wall. It fills the gap between the preform and the tool edge, preventing the reactive material from advancing on the tool wall and trapping air, while still allowing easy preform insertion with larger tolerances.
4Manufacturing precision
If thermoplastic material with high viscosity is used for sealing, then adequate sealing of mold parting plane is achieved, but material flow is restricted
Solution Approach 1:
The injection process is segmented into two sequential steps: first injecting the high-viscosity thermoplastic sealing material to establish the seal, then injecting the low-viscosity reactive material for impregnation. This segmentation allows each material to perform its specific function optimally without compromising the other.
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 allows for the production of components with improved contour accuracy and mechanical properties, reducing post-processing requirements and costs, while ensuring complete encapsulation and impregnation of the textile preform, thus enhancing the resilience and reproducibility of the final product.
Implementation Method 1
a thermoplastic molding compound with high viscosity is used to ensure adequate sealing of the tool or the cavity in the mold parting plane
Implementation Method 2
a very low-viscosity molding compound is injected into the mold in a second step
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method for producing plastic components, which have a high mechanical load-bearing capacity, with a correct final contour. The aim of the invention is to mitigate disadvantages known from the prior art. This is achieved by a method of the aforementioned type for producing plastic components, which have a high mechanical load-bearing capacity, with a correct final contour, wherein an injection casting process is carried out in a first step using a thermoplastic molding compound (K1) in a closed tool consisting of a female die (1, 1') and a male die (2), a thermoplastic molding compound (K1) with a high viscosity being used in order to provide a sufficient seal of the tool or the cavity (4) at the tool parting plane between the female die (1, 1') and the male die (2) in comparison to a molding compound (K2) with an extremely low viscosity used in a second step. The cavity (4) is increased prior to the second step such that the seal formed by the molding compound (K1) is fixed on or in the molding compound (K2) with the extremely low viscosity after said molding compound (K2) is injected and cured to such an extent that the molding compounds forms a composite component.