Composite Multi-Spar Box Curing with External Forming Tools
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Solution Overview
Problem
Conventional methods for manufacturing multi-spar boxes from composite materials result in imprecise dimensions and positions of outer spars, leading to bowed, inclined, or displaced cores, which necessitate the use of expensive shims for precise mechanical connections.
Innovation Solution
The method involves forming outer spars with a C-shaped cross-section on rigid, lateral forming tools during curing, using impermeable nylon tubular bags lined with ventilation layers and a tubular release film to achieve precise outer profiles and positions, eliminating the need for inner tools and reducing variability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional inner tools and tubular bags are used to form spars during curing, then the manufacturing process can be completed, but the outer spars exhibit imprecise dimensions and positions with variations up to 3 mm
Solution Approach 1:
The invention removes the inner tools (plugs) from the tooling system entirely. Instead of using rigid inner tools that limit deformation and cause imprecision, the patent extracts this element and replaces it with a direct forming approach where the C-shaped spar cores are formed externally on lateral forming tools, eliminating the source of dimensional variability.
Solution Approach 2:
The invention inverts the conventional approach by forming the outer surface of the C-shaped spar cores on external lateral forming tools rather than using internal plugs to define the shape. This external forming method allows precise control of the outer profiles and positions, achieving tolerance ranges of ±0.1 mm.
2Reliability
If inner tools are used to support tubular bags during curing, then the spars can be formed, but the cores of outer spars bow, tilt, or displace uncontrollably
Solution Approach 1:
The invention applies preliminary action by pre-forming the C-shaped cross-section of the outer spars on rigid lateral forming tools before the curing process. This pre-forming step ensures that the outer profiles and positions are established with high precision (±0.1 mm tolerance) before the resin is applied and cured, preventing subsequent deformation.
3Ease of manufacture
If conventional manufacturing methods are used, then spars can be produced, but expensive shims are required to achieve precise mechanical connections
Solution Approach 1:
The invention implements self-service by making the lateral forming tools an integral part of the final structure. The external surfaces of these tools become the precise reference surfaces for mechanical connections, eliminating the need for separate shims. The process self-corrects by directly forming the required precision surfaces during the curing process itself.
4Ease of manufacture
If rigid inner tools are used to define spar shape, then the tubular bags can be positioned, but the extraction of inner tools becomes difficult after polymerization
Solution Approach 1:
The invention extracts the inner tools from the system entirely, eliminating the extraction problem. By forming the spars externally on lateral forming tools without using internal plugs, the patent removes the element that causes both extraction difficulty and dimensional inaccuracy.
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 ensures high geometric precision of outer spar surfaces, achieving tolerance ranges of ±0.1 mm, eliminating the requirement for shims and enhancing the manufacturing efficiency by maintaining precise reference surfaces for mechanical connections.
Implementation Method 1
The entire assembly is enclosed inside a vacuum bag. The vacuum is applied to the system thus formed.
Implementation Method 2
During the autoclave polymerization step, pressure is applied by the bag to the outer surfaces of the (top and bottom) panels and to the bases of the spars
Implementation Method 3
multi-spar box made of fibre-reinforced, polymerizable, thermosetting material
Data Source
Figure 1~5
Figure 6~9
Figure 10~12
AI summary
Two panels (1 1, 12) of composite material are placed on a first plate (17) and a second panel (18). One or more intermediate spars (14a, 14b) of composite material are suspended above the first panel (12), said spars being arranged between elongated inner tools (15a, 15b, 15c) which are each enclosed inside a respective pressurisable impermeable tubular bag (16). Two outer lateral spars (13a, 13b) of composite material with a C-shaped cross-section are inserted inside two respective C-shaped seats (28a, 28b) directed towards each other and formed in two respective, rigid, lateral, outer tools (27a, 27b). The lateral outer tools (27a, 27b) are moved towards each other such that the inner tools (15) wrapped in pressurisable bags (16) are partially inserted inside the C-shaped outer spars (13a, 13b). The spars (13a, 13b, 14a, 14b) are brought into contact with the panels (11, 12) so that the multi-spar box to be polymerized is closed between the first plate (17), the second plate (18) and the two lateral outer tools (27a, 27b). Open opposite ends of the tubular bags (16) are sealed so that the pressure applied in an autoclave during a following curing step causes expansion of the tubular bags, compressing them against the bases and the cores of the spars. The box is cured in an autoclave by applying heat and pressure.