Small-Diameter Ball End Mill Geometry for Coating Peel Resistance
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Solution Overview
Problem
Ball end mills with small diameters (2 mm or less) face issues with hard coating film peeling, leading to premature wear and reduced service life due to high cutting loads and low rotation speeds, making stable cutting challenging, especially when intersecting the chisel portion.
Innovation Solution
The design incorporates two chip discharge grooves on the outer circumference of the end mill main body, with a convex hemispherical bottom blade, optimized ratios of chisel portion width and length, and a specific rake angle to prevent peeling and chipping, ensuring a sufficient coating film extension and chip discharge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hard coating film is applied to the distal end portion of the end mill main body to improve wear resistance, then the service life is extended, but the coating film peels off due to high cutting loads and low rotation speeds in small diameter ball end mills
Solution Approach 1:
The patent applies different geometric characteristics to different parts of the end mill. The chisel portion is designed with specific width and length ratios (W/D and L/D) to optimize its mechanical properties locally, while the outer circumferential blades have different characteristics suited for their cutting function. This local optimization ensures the chisel portion can support the hard coating film under high loading conditions without peeling.
Solution Approach 2:
The patent changes geometric parameters of the chisel portion, specifically setting the width-to-diameter ratio (W/D) to 0.01 to 0.06 and the length-to-diameter ratio (L/D) to 0.05 to 0.15. These parameter changes optimize the structural integrity and stress distribution in the chisel portion, preventing coating film peeling while maintaining cutting effectiveness.
2Adaptability or versatility
If the diameter of the bottom blade is reduced to 2 mm or less to achieve small diameter ball end mill functionality, then the versatility for fine work is improved, but the rotation speed becomes small and cutting load increases causing coating film peeling
Solution Approach 1:
The patent optimizes the chisel portion geometry locally to compensate for the high cutting loads inherent in small diameter ball end mills. By setting specific W/D and L/D ratios, the chisel portion is designed to distribute stresses more effectively, enabling small diameter tools to handle fine work while maintaining sufficient structural strength to support hard coating films under increased loading conditions.
3Ease of manufacture
If the chisel portion width and length are not optimized, then manufacturing is simpler, but the hard coating film peels off and chipping occurs
Solution Approach 1:
The patent establishes specific parameter ranges for the chisel portion geometry (W/D: 0.01 to 0.06, L/D: 0.05 to 0.15) that balance manufacturing feasibility with coating film stability. These parameter changes provide clear design guidelines that maintain manufacturing simplicity while ensuring reliable coating adhesion and preventing chipping during operation.
Data Source
AI summary
Provided is an end mill which includes an end mill main body having a bottom blade having a convex hemispherical shape, and a hard coating film coated on at least a surface of a distal end portion of the end mill main body. A diameter D (mm) of the bottom blade is 2 mm or less. A ratio W/D of a width W (mm) of a chisel portion to the diameter D (mm) is within a range of 0.020 to 0.060. A ratio L/D of a facing length L (mm) of chip discharge grooves to the diameter D (mm) is within a range of 0.014 to 0.090. A rake angle of the bottom blade in a range in which a chisel edge is formed in the chisel portion is within a range of −15° to −30°.