Machining Fixture Datum-Based Reference Surface Generation
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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 traditional assembly tools are cumbersome and costly, necessitating a more efficient method for holding and machining airframe components.
Innovation Solution
A method and apparatus for producing a machining fixture that involves determining a datum based on the relative positions of receiving elements, forming reference surfaces, and using digital models to control machining apparatus, allowing for precise machining of airframe components such as frames and longerons, which can then be used to assemble the aircraft with reduced gaps and increased accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional assembly tools with rigid metal jigs and welded steel frameworks are used, then structural strength and stability are ensured, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The fixture is divided into a base plate and separate support elements (blocks, pins, clamps) that can be independently positioned and adjusted. This segmentation allows the fixture to achieve the required structural strength through strategic placement of load-bearing elements rather than requiring a completely rigid welded framework, thereby reducing overall device complexity while maintaining stability during machining operations
Solution Approach 2:
The fixture employs universal support blocks and adjustable clamping mechanisms that can accommodate multiple workpiece configurations and machining operations. Rather than requiring dedicated rigid jigs for each specific operation, the same base fixture with repositionable support elements can serve multiple functions, reducing the total number of complex specialized tools needed in the workshop
2Manufacturing precision
If traditional dedicated assembly tools are used for each assembly process, then precise positioning of airframe components is achieved, but production time and cost increase due to the need for multiple specialized tools
Solution Approach 1:
The fixture design incorporates adjustable support blocks and repositionable clamping devices that can be configured for different airframe components and machining operations. This universality allows a single fixture to replace multiple dedicated assembly tools, maintaining precise positioning capabilities while reducing the time and cost associated with producing and switching between numerous specialized tools
Solution Approach 2:
The fixture includes pre-positioned support blocks and locating elements that are arranged in advance to accommodate various workpiece configurations. This preliminary arrangement of support elements enables quick setup for different machining operations without requiring time-consuming reconfiguration of dedicated tools, thereby improving production efficiency while maintaining positioning precision
3Productivity
If separate airframe sections are produced independently, then manufacturing flexibility and productivity are improved, but assembly precision deteriorates due to accumulation of tolerance errors and gaps between sections
Solution Approach 1:
The fixture replaces traditional mechanical shimming processes with a precision positioning system based on digital modeling and controlled machining. By using computer-controlled machining operations guided by digital models, the fixture achieves accurate positioning of airframe sections without relying on manual shimming, thereby maintaining assembly precision while preserving the productivity benefits of independent section production
Solution Approach 2:
The fixture employs digital models (CAD/CAM) to create virtual representations of the airframe components and their desired assembled positions. These digital copies guide the machining and positioning operations, ensuring that tolerance accumulations from independent section production are compensated for through precise digital-controlled adjustments, thereby achieving the required assembly precision without sacrificing manufacturing flexibility
Data Source
AI summary
Disclosed is a method of producing a machining fixture for fixedly holding a workpiece during machining of that workpiece. The method comprises: providing an initial machining fixture comprising a plurality of receiving elements for receiving the workpiece to be machined; determining a datum, the datum being dependent upon the relative positions of the receiving elements; determining positions and orientations of one or more reference surfaces with respect to the datum; measuring the surface of the initial machining fixture with respect to the datum; and, thereafter, controlling machining apparatus with respect to the datum to machine the initial machining fixture to form the one or more reference surfaces, thereby producing the machining fixture.