Airframe Section Machining Using a Reference Structure
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Solution Overview
Problem
The production of aircraft airframes faces challenges in achieving precise assembly due to difficulties in producing separate sections with tight tolerance bounds, often requiring lengthy and expensive shimming processes and dedicated assembly tools.
Innovation Solution
The use of a frame machining fixture with precision-ground blocks and locator pins, along with a CNC milling machine, to accurately manufacture longeron landings and attach components, and an assembly jig with fewer pickups to ensure accurate positioning and reduced gaps between airframe sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate airframe sections are produced using traditional dedicated assembly tools, then assembly operations can be carried out, but the production precision and tolerance bounds are insufficient, requiring lengthy shimming processes
Solution Approach 1:
The patent uses a reference frame that is a precise copy or replica of the actual airframe structure. This reference frame serves as a master template during machining operations, allowing the CNC milling machine to reproduce the exact geometry and tolerances of the intended airframe configuration. By copying the reference frame's precision onto the airframe components, the system achieves tight tolerance bounds without requiring post-assembly shimming processes
Solution Approach 2:
The patent implements preliminary action by pre-machining the airframe components to their final dimensions and tolerances before assembly. The CNC milling machine, guided by the reference frame, performs all necessary machining operations while components are still individually manufacturable, ensuring they arrive at assembly already within the required tolerance bounds. This eliminates the need for corrective shimming operations after assembly
2Manufacturing precision
If separate airframe sections are produced with tight tolerance bounds, then assembly becomes easier, but the manufacturing complexity and cost increase
Solution Approach 1:
The patent creates a universal reference frame that can serve multiple functions: it acts as a machining guide for the CNC milling machine, a verification tool for quality control, and a template for reproducing different airframe configurations. This single multi-functional device replaces what would traditionally require multiple dedicated assembly tools, each designed for specific operations, thereby reducing overall device complexity while maintaining high precision
Solution Approach 2:
The patent replaces complex mechanical assembly tools with a computer-controlled system. The CNC milling machine, guided by the reference frame through coordinate measurement and control systems, achieves precise machining without requiring complex mechanical fixtures, jigs, and adjustment mechanisms. This substitution of mechanical systems with automated control reduces device complexity while maintaining or improving precision
3Ease of manufacture
If traditional assembly tools are used, then components can be assembled, but the tools are expensive and require exacting manufacturing standards
Solution Approach 1:
The patent inverts the traditional approach by making the reference frame the primary precision element rather than the assembly tools themselves. Instead of manufacturing expensive precision tools to achieve accuracy, the system uses a precisely manufactured reference frame as the source of truth, and all other components are measured and machined relative to this reference. This inversion shifts the precision requirement from multiple tools to a single reference artifact, simplifying manufacturing
Data Source
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AI summary
Disclosed is a method of producing part of an airframe (4) for attachment to a system (5). The method comprises: providing an initial structure;providing a reference structure (64); positioning the initial structure with respect to the reference structure (64) such that its position/orientation relative to the reference structure (64) is the same as the position/orientation relative to the system (5) that it would have if the part of the airframe (4) was attached to the system (5); specifying an inner mould line;applying, to an outer surface of the initial structure, material (90); and machining the material (90) such that the position/orientation of the outer surface of the material (90) with respect to the reference structure (64) is the same as the position/orientation with respect to the system (5) that the inner mould line would have if the part of the airframe (4) was attached to the system (5).