Variable-Helix Step Drill Bit for Chipping-Resistant Cutting
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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, along with a transition portion and flutes, which provides a balanced cutting edge configuration to reduce chipping and enhance drilling efficiency, and optionally coated with wear-resistant materials like TiAIN for extended life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a step drill bit is used with an impact driver, then drilling speed and efficiency are 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. The smaller diameter steps have lower helix angles (5-15 degrees) and lower rake angles (5-20 degrees), while larger diameter steps have higher helix angles (15-30 degrees) and higher rake angles (20-35 degrees). This localized optimization allows each cutting edge to be tailored for its specific diameter, improving both cutting performance and chipping resistance at each step.
Solution Approach 2:
The patent systematically varies the helix angle and rake angle parameters across different steps. The helix angle increases from 5-15 degrees at smaller steps to 15-30 degrees at larger steps, while the rake angle increases from 5-20 degrees to 20-35 degrees. These parameter changes optimize the cutting geometry for each step's specific requirements, balancing productivity and reliability.
2Productivity
If the helix angle is increased to improve chip evacuation, then drilling efficiency is improved, but the cutting edge becomes more susceptible to chipping
Solution Approach 1:
The patent applies different helix angles to different steps based on their diameter. Smaller steps use lower helix angles (5-15 degrees) that provide adequate chip evacuation while maintaining cutting edge strength. Larger steps use higher helix angles (15-30 degrees) that maximize chip evacuation efficiency. This localized approach allows each step to achieve optimal chip evacuation without compromising cutting edge durability.
Data Source
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AI summary
A drill bit (10) includes a shank (12) extending along a bit axis (14) and a body (18) with a proximal end (19A) adjacent the shank and a distal end (19B) opposite the proximal end. The body defines a plurality of axially stacked, progressively sized steps (20A-20M) including a first step (20A) at the distal end and a terminal step (20M) at the proximal end. The drill bit also includes a flute (46) in the body. The flute defines an elongated groove that extends from the distal end to the proximal end. The drill bit further includes a plurality of cutting edges (64A-64M) formed in the body. Each cutting edge is disposed along one of the plurality of steps and defines a helix angle (68C) and a rake angle (66C, 66M). The helix angle of the cutting edge at the terminal step is greater than the helix angle of the cutting edge at the first step. A ratio of the helix angle to the rake angle of the cutting edge at the first step is in a range from 0.5 to 2.4, and a ratio of the helix angle to the rake angle of the cutting edge at the terminal step is in a range of 0.9 to 1.7.