Twist Drill Variable Helix for Composite Drilling
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Solution Overview
Problem
Hand drilling of composite materials like carbon fibre reinforced plastic (CFRP) and glass fibre reinforced plastic (GFRP) is challenging due to variable thrust force and hole quality, which is operator-dependent and prone to 'pushing' or 'pull through' effects, leading to inconsistent results.
Innovation Solution
A twist drill with a variable helix and specific relief angles, including primary and secondary facets, is designed to minimize thrust force and enhance hole quality, featuring a helix angle that decreases from 25° to 60° at the drill tip to 0° to 35° in the drill body, along with primary and secondary relief angles, and a secondary chisel edge for improved cutting performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hand drilling is used for composite materials, then operator flexibility and accessibility are improved, but hole quality consistency and thrust force control deteriorate
Solution Approach 1:
The drill geometry parameters are specifically optimized for composite materials: helix angle varies from 10° at the tip to 30° at the body, relief angles are set to 10°-20° for primary facet and 5°-15° for secondary facet, and point angle is 90°. These parameter changes enable the drill to maintain consistent performance regardless of operator variability.
Solution Approach 2:
The drill is segmented into distinct functional zones: drill tip for initial penetration, drill body for main cutting action, and flutes for chip evacuation. Each segment has optimized geometry to handle specific aspects of composite material drilling, reducing overall system variability.
2Device complexity
If conventional drill geometry is used, then simplicity of design is maintained, but thrust force and delamination increase
Solution Approach 1:
Different portions of the drill have different geometric properties optimized for their specific function. The drill tip has a smaller helix angle (10°) for controlled entry, while the drill body has a larger helix angle (30°) for efficient chip evacuation. The primary and secondary facets have different relief angles to separately address cutting edge strength and chip flow.
Solution Approach 2:
The helix angle is designed to vary dynamically along the length of the drill rather than being constant. This dynamic geometry allows the drill to adapt to different cutting conditions at different depths, reducing thrust force variability and preventing delamination throughout the drilling process.
3Productivity
If high helix angle is used throughout the drill, then chip evacuation is improved, but thrust force at the drill tip increases causing delamination
Solution Approach 1:
The helix angle is segmented into two distinct zones: a low helix angle (10°) zone at the drill tip for controlled entry and reduced thrust force, and a high helix angle (30°) zone in the drill body for efficient chip evacuation. This segmentation allows both contradictory requirements to be satisfied in different locations.
Solution Approach 2:
The helix angle parameter is changed along the length of the drill rather than remaining constant. This parameter variation enables the drill to optimize for thrust force reduction at the tip while maintaining chip evacuation efficiency in the body, resolving the contradiction between these two functions.
Data Source
AI summary
The present invention is concerned with twist drills for drilling of composite materials such as carbon fibre reinforced plastic (CFRP) and glass fibre reinforced plastic (GFRP). The present invention proposes that a twist drill (2) is provided with a variable helix having a defined start and finish helix angle, in combination with primary and secondary relief angles such that the drill (2) is adapted to minimise thrust force, particularly when used for drilling fibre-containing composite materials and especially for hand drilling. Start and finish helix angles of 50° and 10°; 50° and 30°; and 30° and 10° have been shown to provide excellent cutting performance and exit hole quality. A large secondary chisel edge angle (24) has also been found to contribute to excellent performance with composite materials, including stack machining.