Variable-Angle Step Drill Bit for Chip-Resistant Impact Drilling
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Solution Overview
Problem
Step drill bits used with impact drivers are prone to chipping due to the cutting edge's susceptibility when drilling through thin-walled workpieces, limiting their effectiveness and lifespan.
Innovation Solution
A step drill bit design featuring axially stacked, progressively sized steps with varying helix and rake angles, where the helix angle at the terminal step increases by at least 70% and the rake angle by at least 40% relative to the first step, along with a protective coating like titanium aluminum nitride, to enhance cutting efficiency and prevent chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a step drill bit is used with an impact driver, then drilling capability is improved, but the cutting edge becomes more prone to chipping
Solution Approach 1:
The patent applies different helix angles and rake angles to cutting edges at different steps of the drill bit. Specifically, the helix angle increases from the first step to the terminal step, and the rake angle is optimized at each step to prevent chipping while maintaining drilling efficiency. This local differentiation of geometric parameters allows each cutting edge to be optimized for its specific function.
Solution Approach 2:
The patent changes the geometric parameters (helix angle and rake angle) of the cutting edges across different steps. The helix angle at the terminal step is greater than at the first step, and the rake angle ratio between helix and rake angles is controlled within specific ranges (0.5-2.4 for first step, 0.9-1.7 for terminal step). These parameter variations optimize both drilling performance and chip resistance.
2Speed
If the helix angle and rake angle are increased to improve cutting efficiency, then drilling speed is improved, but the cutting edge becomes more susceptible to chipping
Solution Approach 1:
Different steps of the drill bit have different helix and rake angles optimized for their specific functions. The terminal step has a greater helix angle for efficient material removal, while intermediate and first steps have smaller helix angles that provide better chip evacuation and reduced chipping risk. Each cutting edge's geometry is locally optimized rather than uniform throughout.
Solution Approach 2:
The patent systematically varies the helix angle and rake angle parameters across different steps. The helix angle increases progressively from the first step to the terminal step, while the ratio of helix angle to rake angle is maintained within specific ranges. This controlled parameter variation allows the drill bit to achieve high drilling speed at the terminal step while maintaining cutting edge durability at other steps.
Data Source
AI summary
A step drill bit includes a shank and a body having a proximal end adjacent the shank and a distal end opposite the proximal end. The body defines a plurality of axially stacked, progressively sized steps including a first step at the distal end, a terminal step at the proximal end, and a plurality of intermediate steps having incrementally increasing diameters disposed between the first and terminal steps. The step drill bit also includes a plurality of cutting edges each disposed along one of the plurality of steps. Each edge defines a helix angle and a radial rake angle. The radial rake angle and the helix angle of the cutting edge at the terminal step is greater than the radial rake angle and the helix angle of the cutting edge at the first step.