Thermoplastic-Epoxy Connecting Element for Weldable Composite Joints
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Solution Overview
Problem
Existing methods for connecting composite components, such as carbon fiber reinforced plastics (CFRP), often rely on adhesion or thermoplastic layers that may not provide sufficient mechanical strength or durability, especially at elevated temperatures and in humid conditions.
Innovation Solution
A method involving the partial dissolution of a high-temperature thermoplastic polymer in an uncured epoxy resin, followed by curing at temperatures above 150°C, creating an intermediate layer that enhances mechanical stability and allows for friction welding without damaging the epoxy resin, thereby forming a strong and weldable connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thermoplastic layer is applied to an uncured epoxy resin and the epoxy resin is cured at temperatures above the melting temperature of the thermoplastic polymer, then the thermoplastic polymer and epoxy resin mix and form a bond, but the thermoplastic polymer completely dissolves in the epoxy resin, preventing subsequent welding operations
Solution Approach 1:
The patent applies parameter changes by carefully controlling the curing temperature profile to remain below the melting temperature of the thermoplastic polymer. This temperature parameter control allows the epoxy resin to cure and bond to the thermoplastic layer without causing complete dissolution, thereby maintaining both bond strength and subsequent weldability
Solution Approach 2:
The patent employs partial action by allowing some dissolution of the thermoplastic polymer in the uncured epoxy resin to create a strong bond, but deliberately limiting the extent of dissolution by controlling temperature parameters. This partial dissolution achieves adequate adhesion while preserving enough thermoplastic material for welding operations
2Productivity
If the curing temperature is increased to accelerate epoxy resin curing, then the curing speed increases, but the thermoplastic polymer melts and completely dissolves, destroying the weldable surface
Solution Approach 1:
The patent changes the temperature parameter from high-temperature curing to low-temperature curing below the melting point of the thermoplastic polymer. This parameter change slows the curing speed but preserves the thermoplastic layer's integrity and weldability, resolving the contradiction between productivity and compositional stability
Solution Approach 2:
The patent applies preliminary action by first applying the thermoplastic layer to the uncured epoxy resin before curing, ensuring the layer is in place and will not be damaged by subsequent high-temperature processing. This sequence allows controlled curing at lower temperatures that preserve the thermoplastic layer
3Ease of manufacture
If conventional adhesive bonding is used to connect composite components, then the connection can be made, but the mechanical strength and durability are insufficient, especially at elevated temperatures and in humid conditions
Solution Approach 1:
The patent uses composite materials by combining thermoplastic polymer and thermosetting epoxy resin in a layered structure. The thermoplastic layer provides weldability and temperature resistance, while the epoxy resin provides strong adhesion and structural integrity, creating a composite connection system that outperforms conventional adhesive bonding in durability and reliability
Solution Approach 2:
The patent exploits phase transitions of the thermoplastic polymer (solid at room temperature, melt during welding, then resolidifies) to enable friction stir welding. This phase transition mechanism allows for strong mechanical interlocking and diffusion bonding that superior to conventional adhesives, especially under elevated temperature and humid conditions
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 produces a structurally stable composite with improved mechanical resilience and resistance to temperature and humidity, enabling continuous welding without weakening the epoxy resin, thus maintaining the strength properties of the composite over its entire operating temperature range.
Implementation Method 1
the first thermoplastic polymer is soluble in the epoxy resin used to produce the composite component at a temperature of at least 150°C
Implementation Method 2
the thermoplastic polymer has a glass transition temperature higher than 185°C, in particular higher than 200°C, wherein the uncured epoxy resin has a curing temperature of at most 180°C
Implementation Method 3
curing the raw composite component at a temperature of at least 150°C, wherein the first thermoplastic polymer dissolves in the at least one uncured epoxy resin at the temperature of at least 150°C
Implementation Method 4
the epoxy resin extends from the composite component in the direction of the first layer in the form of a plurality of adjacent and/or at least partially interconnected volume sections, in particular bubbles, into the intermediate layer
Implementation Method 5
a component connected to the connecting element, wherein the component is welded to the first and/or a second layer of the connecting element by welding, in particular by friction welding, preferably by circular vibration friction welding
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3C
AI summary
The present invention provides a connecting element comprising: a composite component comprising a cured epoxy resin; a first layer comprising a first thermoplastic polymer; an intermediate layer arranged between the composite component and the first layer, containing both the cured epoxy resin of the composite component and the first thermoplastic polymer of the first layer; wherein the first thermoplastic polymer has a melting temperature, in particular a glass transition temperature, which is above a curing temperature of the epoxy resin; and wherein the first thermoplastic polymer is soluble in the epoxy resin used to manufacture the composite component at a temperature of at least 150 °C. The present invention further provides a connecting arrangement with such a connecting element, a method for manufacturing such a connecting element, and a method for manufacturing the connecting arrangement.