Rotary Drill Bit Cutting Insert with T-Land and Negative Rake
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Solution Overview
Problem
Existing roof drilling bits experience high stress on the cutting edge, leading to frequent failure through breaking or chipping, which increases the time and hazards associated with the roof bolting process in underground mining, necessitating a solution for improved durability and efficiency.
Innovation Solution
A rotary drill bit with a cutting insert featuring symmetrical halves, a T-land surface, and a negative axial rake angle, which reduces stress on the cutting edge and minimizes the risk of chipping, combined with materials like cemented tungsten carbide and coatings for enhanced durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cutting insert with a positive or neutral axial rake angle is used, then the cutting edge can be formed with a simple geometry, but the cutting edge experiences high stress and fails frequently through breaking or chipping
Solution Approach 1:
The patent changes the rake angle parameter from positive or neutral to negative axial rake angle. This parameter modification fundamentally alters the stress distribution on the cutting edge, reducing the stress concentration that causes breaking and chipping, thereby improving reliability while maintaining manufacturability through the T-land surface design
Solution Approach 2:
The patent incorporates a T-land surface that is formed before the cutting edge during the manufacturing process. This preliminary structural feature pre-prepares the cutting insert to distribute stress more evenly during operation, preventing stress concentration at the cutting edge and reducing failure modes such as breaking and chipping
2Reliability
If the drilling process takes longer to complete, then more time can be spent on safety checks and quality control, but the overall roof bolting process becomes less efficient and safer
Solution Approach 1:
The patent employs a disposable cutting insert design with a T-land surface and negative rake angle that maintains sharpness and cutting efficiency throughout its service life. This allows for faster drilling operations with reliable cutting performance, improving productivity while the insert itself is designed to be replaced rather than repaired, maintaining safety standards
Solution Approach 2:
By changing the rake angle to negative and incorporating the T-land surface, the cutting insert achieves optimal stress distribution that maintains cutting edge integrity during high-speed drilling operations. This parameter optimization enables faster drilling speeds without compromising cutting reliability, thus improving overall productivity while maintaining safety
3Productivity
If the cutting edge is made sharper to increase penetration rate, then drilling speed improves, but the cutting edge becomes more susceptible to chipping and breaking
Solution Approach 1:
The T-land surface is formed as a preliminary structural feature during manufacturing, creating a stress-distributing geometry before the cutting edge is used. This pre-formed feature prevents stress concentration at the cutting edge during high-speed drilling, allowing sharper cutting edges to maintain both high penetration rates and resistance to chipping and breaking
Solution Approach 2:
The negative rake angle parameter change fundamentally alters how stress is distributed across the cutting edge during penetration operations. This parameter modification allows the cutting edge to be sharper for improved penetration rate while the negative rake angle and T-land surface combination prevents the sharp edge from being prone to chipping and breaking, thus maintaining reliability
Data Source
AI summary
A rotary drill bit for engaging an earth strata material includes an elongate drill bit body having an axial forward end and an axial rearward end, and a cutting insert attached to the axial forward end of the elongate drill bit body. The cutting insert has an elongate insert body rotatable about a central axis and includes a pair of symmetrical halves symmetrical about the central axis, each symmetrical half including a leading face, a top surface having a relief surface, a T-land surface extending between the leading face and the relief surface and a cutting edge formed at the intersection of the T-land surface and the relief surface. The cutting edge can have a negative axial rake angle. The relief surface can include a primary relief surface and a secondary relief surface.