Cemented Carbide Cutting Tap with Variable Chamfer Angles
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Solution Overview
Problem
Cutting taps made from cemented carbide are prone to chipping, especially the narrow cutting edges, due to their lower strength compared to high-speed steel, limiting their use in applications where high-speed steel taps can be used.
Innovation Solution
A cutting tap design with a chamfered fluted section where the thickness of material removed by the second cutting thread is smaller than the first, and a non-linear or angled chamfer to reduce the forces on the cutting edges, enhancing their strength and resistance to chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cemented carbide material is used for cutting taps, then hardness and high temperature stability are improved, but strength decreases making cutting edges prone to chipping
Solution Approach 1:
The patent applies different chamfer angles to different sections of the cutting tap. The first chamfer section has a larger angle (15-30 degrees) to strengthen the cutting edges, while the second chamfer section has a smaller angle (5-15 degrees) for proper thread formation. This local variation in geometry addresses the strength weakness of cemented carbide at critical locations without compromising the material's overall hardness and heat resistance.
Solution Approach 2:
The patent incorporates a chamfered fluted section at the leading end of the tap before the full threading section. This preliminary chamfered section pre-strengthens the cutting edges by removing material that would create stress concentrations, allowing the cemented carbide tap to approach the hole wall at an optimized angle that reduces impact forces on the cutting edges during engagement.
2Strength
If a straight cutting face with constant chamfer angle is used, then manufacturing is simplified, but cutting force increases and edge strength decreases
Solution Approach 1:
The patent divides the chamfered fluted section into multiple segments with different chamfer angles. The first chamfer section has a larger angle (15-30 degrees) for strength, while the second chamfer section has a smaller angle (5-15 degrees) for thread formation. This segmentation allows optimization of cutting edge strength without requiring complex curved surfaces, as each segment can be manufactured with standard grinding techniques.
Solution Approach 2:
The patent alternatively provides for a curved chamfer surface that transitions smoothly between different angles. This curved geometry continuously varies the cutting angle along the chamfer length, optimizing edge strength at the leading end while maintaining proper thread formation capability toward the rear, eliminating the need for sharp transitions between discrete chamfer sections.
Data Source
AI summary
A cutting tap includes a body having an axial forward end and an axial rearward end and a central longitudinal axis. The body has a fluted section at the axial forward end. The fluted section includes a chamfered fluted section extending from the axial forward end of the body and terminating at a first full cutting thread. The chamfered fluted section includes a first cutting thread located a first distance from the axial forward end of the body, and a second cutting thread located a second distance from the axial forward end of the body. The second distance is greater than the first distance. The chamfered fluted section is shaped such that a thickness of a section of material removed by the second cutting thread is smaller than a thickness of a section of material removed by the first cutting thread. A method of making the cutting tap is also disclosed.