Thermoforming Preform Outer Webs for Friction Control
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Solution Overview
Problem
Three-dimensional preforms with complex shapes often suffer from fiber wrinkling and defects due to friction between the preform and forming tools, leading to non-homogeneous deformation and adhesion issues during thermoforming.
Innovation Solution
The method involves placing nonwoven webs made of a second polymer at the interface between the preform and forming tools, which deform to absorb friction forces, allowing the preform to slide without sticking and ensuring homogeneous deformation by limiting local deformations and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the preform is formed directly between the male and female forming tools without external films, then the forming process is simpler, but fiber wrinkles and defects occur due to friction between the preform and tools
Solution Approach 1:
External films made of a second polymer are introduced as intermediary elements between the initial preform and the forming tools. These films remain in solid state during forming and deform to absorb friction forces, preventing direct contact and adhesion between the preform and tools, thereby eliminating fiber wrinkles and defects.
Solution Approach 2:
The solution changes the physical state parameters of the external films by selecting a second polymer with appropriate thermal properties. The films are chosen to remain solid at the forming temperature of the first polymer, allowing them to deform and absorb friction while maintaining structural integrity and preventing preform adhesion to tools.
2Ease of operation
If the preform slides freely within the press during forming, then adhesion to tools is reduced, but friction forces cause fiber deformation and wrinkles
Solution Approach 1:
The external films serve as intermediary layers that enable the preform to slide freely within the press while protecting it from direct friction contact. The films deform under friction forces, absorbing the stress and preventing fiber deformation and wrinkles in the preform.
3Stability of the object's composition
If external films made of the same polymer as the preform are used, then material compatibility is improved, but adhesion to tooling surfaces occurs
Solution Approach 1:
The solution applies local quality by using a second polymer for the external films that has different properties from the first polymer of the preform. This differentiation in material properties prevents adhesion to tooling surfaces while the films still provide protective functionality. The second polymer is specifically selected to remain solid at the forming temperature and have low adhesion characteristics.
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 reduces or eliminates fiber defects and adhesion issues, enabling the production of complex-shaped composite material parts with improved formability and ease of demolding, particularly in the automotive and aeronautical fields.
Implementation Method 1
The temperature of the preform during forming, called the forming temperature, is defined so that the webs can deform to absorb the friction forces between the webs and the tooling
Implementation Method 2
the outer webs remain in the solid state and deform, said outer webs are non-woven webs formed from filaments of the second polymer
Implementation Method 3
The dry friction forces between the webs and the tooling are less significant than the viscous friction forces between the polymer-coated fibers and the tooling
Data Source
Figure 1~3
Figure 4~6
AI summary
The present invention relates to a method for producing a three-dimensional preform consisting in producing an initial preform (4) comprising a plurality of stacked plies, said plies being formed from unidirectional continuous fibres and a first polymer, and thermoforming the initial preform between the male forming tool (92) and the female forming tool (91) of a press (9) in order to obtain a three-dimensional preform (1). During the forming step, an outer web is positioned at the interface between the initial preform (4) and the male tool (62) and at the interface between the initial preform and the female tool (91), said outer webs being formed from a second polymer such that, during the forming step, the outer webs remain in a solid state and are deformed.