Sawtooth Drill Structure for Low-Damage CFRP Drilling
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Solution Overview
Problem
Drilling carbon fiber reinforced polymer composites often results in defects such as delamination, burrs, and cracks at the hole entrance and exit due to the anisotropic nature of the material and rapid tool wear, which complicates the drilling process and reduces the quality of the drilled holes.
Innovation Solution
A sawtooth structure with specific helical arrangements of sawteeth and grooves on the cutting edges of drills, featuring different helix angles for right-hand and left-hand sawteeth, which provides a reverse cutting function to re-cut materials at the entrance and exit, reducing burrs and delamination by allowing uncut materials to rebound and be cut off effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional drill structures are used for drilling CFRP, then drilling operation can be performed, but delamination and burrs are generated at hole entrance and exit due to large thrust force
Solution Approach 1:
The drill bit is divided into multiple functional zones along its length: a first cutting edge zone for initial material removal, a second cutting edge zone for finishing, and an intermediate non-cutting zone. This segmentation allows different parts of the drill to perform different functions, reducing the concentration of thrust force at any single location and preventing delamination at the hole entrance and exit.
Solution Approach 2:
The invention inverts the conventional drill structure by placing the active cutting edges at both the top and bottom of the intermediate zone, rather than having a single continuous cutting edge. This inverted arrangement allows the drill to cut material at both the entrance and exit surfaces, reversing the usual sequence where material is only removed at the entrance.
2Reliability
If diamond coating is applied on drill bits to overcome tool wear, then cutting ability is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention changes the geometric parameters of the drill bit, specifically the distribution and arrangement of cutting edges along the drill length. By creating multiple cutting zones with specific geometry rather than relying on surface coatings, the drill achieves improved tool life and cutting ability through structural design alone, avoiding the need for diamond coating.
3Manufacturing precision
If multiple drilling processes such as drilling-rough reaming-finish reaming are used, then drilling quality is improved, but manufacturing time and process complexity increase
Solution Approach 1:
The invention merges multiple drilling operations (rough drilling, reaming, and finishing) into a single unified drill bit structure. The first cutting edge performs rough drilling, while the second cutting edge performs finishing operations, all in one pass. This eliminates the need for separate rough reaming and finish reaming steps, reducing manufacturing cycle time while maintaining high drilling quality.
Solution Approach 2:
The drill bit is designed with multi-functionality, where a single tool performs multiple functions: initial material removal by the first cutting edge, intermediate material removal and guidance by the intermediate zone, and final surface finishing by the second cutting edge. This universal design replaces the need for multiple specialized tools and processes.
Data Source
AI summary
A kind of sawtooth structure with reversed cutting function and its drill series are presented in this invention. This invention is suitable for drilling low-damage holes on carbon fiber reinforced polymers (CFRP). The sawtooth structure is comprised of sawteeth and grooves located on the cutting edges of drill. And the sawtooth structure is helically arranged with a specific helix angle around the axis of the drill. It can be classified as the left-hand helix sawtooth structure and the right-hand helix sawtooth structure based on the helix angle value. The bottom edges of the left-hand helix sawtooth structure are the cutting edges, and the rake angles are positive; while the top edges of the right-hand helix sawtooth are the cutting edge with the positive rake angles. The sawtooth structure can be applied to various drilling tools, which proves to be universal. And it can effectively reduce delamination at both hole entrance and hole exit as well as burrs defects. The series of drilling tools include the double point angle drill, the twist drill and the stepped drill all of which have the sawtooth structure on the cutting edges. These series of drilling tools can achieve the CFRP holes with minimum drilling defects. The drilling performance of the tools is improved to a great extent, the tool life is extended and the costs are reduced.