Step Drill Groove Grinding for Step-Edge Rake Angle Control
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Solution Overview
Problem
Conventional step drills with convex blade parts at the cutting edge of the small-diameter portion often result in a larger negative radial rake angle for the step portion's cutting edge, leading to degraded cutting performance due to interference during grinding and subsequent surface roughness failures or tearing during chamfering.
Innovation Solution
A step drill design featuring a small-diameter portion with a first cutting edge having a convex blade part and a tapered step portion with a second cutting edge, where the groove is ground in two passes to form intersecting first and second ground portions, preventing excessive interference and allowing for a more favorable radial rake angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a convex blade part is formed on the cutting edge of the small-diameter portion using a grind stone with a swing angle, then cutting performance of the small-diameter portion is improved, but the radial rake angle of the step portion cutting edge becomes a larger negative angle degrading cutting performance
Solution Approach 1:
The groove grinding process is segmented into two separate passes: first grinding the groove in the small-diameter portion to form the convex blade part, then grinding the groove in the step portion. This segmentation allows each cutting edge to be optimized independently, preventing the radial rake angle degradation that occurs when a single grind stone with swing angle is used for both portions.
Solution Approach 2:
The convex blade part on the small-diameter portion cutting edge is formed first through preliminary grinding. This preliminary action establishes the optimal geometry for the small-diameter portion without subsequently affecting the step portion cutting edge geometry, thereby preventing the radial rake angle from becoming excessively negative.
2Reliability
If a convex blade part is formed on the cutting edge of the small-diameter portion, then cutting quality is enhanced, but surface roughness failures and tearing occur during chamfering
Solution Approach 1:
By segmenting the groove grinding into two separate operations - first for the small-diameter portion and then for the step portion - the invention ensures that the convex blade part geometry does not cause excessive interference during chamfering. This prevents surface roughness failures and tearing while maintaining enhanced cutting quality.
Solution Approach 2:
The invention changes the grinding parameters by using different grind stone configurations for different portions: a grind stone with swing angle for the small-diameter portion to create the convex blade part, and a different grinding approach for the step portion to achieve the appropriate radial rake angle, thereby preventing surface defects during chamfering.
Data Source
AI summary
A step drill and a manufacturing method for a step drill in which cutting performance of a cutting edge of a step portion can be enhanced are provided. A groove includes a first ground portion forming an area embracing a second cutting edge of the step portion and a second ground portion forming an area on the heel side of the step portion relative to the first ground portion. Therefore, a convex blade part can be formed on a first cutting edge by performing grinding with the first ground portion and the second ground portion intersecting with each other. That is, it is possible to form the second cutting edge into a desired shape during grinding of the first ground portion. Therefore, cutting performance of the second cutting edge can be enhanced.