Ball End Mill with Convex Cutting Edge and Negative Rake Angle
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Solution Overview
Problem
Existing ball end mills face challenges with chip clogging and vibration during deep milling and plunging, leading to poor chip removal performance and increased cutting resistance, especially when producing thick chips.
Innovation Solution
The ball end mill features a rake angle range of -10° to 0° for the cutting edge, maximized at the middle point, with a convex shape in the tool rotation direction, and includes a chisel edge and gashes to guide chips smoothly, reducing cutting resistance and enhancing edge strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inner end of each ball end cutting edge is extended to the other ball end cutting edge side beyond the rotation center, then plunging is allowed and chip removal performance at the rotation center is improved, but under deep milling conditions, thick chips do not flow smoothly along the narrow gash, resulting in chip clogging
Solution Approach 1:
The invention divides the single narrow gash into multiple gashes (first gash and second gash) in the rotation center. The first gash is formed by the extended ball end cutting edges, and the second gash is additionally provided to create multiple chip ejection paths. This segmentation allows thick chips to flow smoothly through multiple channels, preventing chip clogging during deep milling while maintaining plunging capability.
2Adaptability or versatility
If the ball end cutting edges are arranged over the center core, then the structure is simplified and plunging is enabled, but the cutting force is strong and vibration is likely to occur, making it difficult to ensure stable processing
Solution Approach 1:
The invention positions the ball end cutting edges asymmetrically relative to the center core, with each edge extended to the other edge side beyond the rotation center. This asymmetric arrangement creates multiple gashes that distribute cutting forces more evenly, reducing vibration while maintaining plunging capability. The chisel edge in the rotation center further balances the cutting forces.
3Reliability
If a chisel edge is provided in the rotation center, then chip removal performance is improved, but the cutting edge is more likely to be chipped, reducing tool life
Solution Approach 1:
The invention applies different geometric characteristics to different parts of the cutting edge. The ball end cutting edges have specific radius and extension characteristics, while the chisel edge in the rotation center has optimized geometry. This local differentiation allows the chisel edge to effectively remove chips from the rotation center while maintaining sufficient strength through its specific geometric design.
Data Source
AI summary
A ball end mill in which a ball end cutting edge (3) has a convex shape in a tool rotation direction with respect to a line connecting a rotation center (O) and a radially outer end (3o) of the ball end cutting edge (3), in a front view of the tool. In the ball end mill, a rake angle (γ) of each portion of the ball end cutting edge (3) is set in a range from −10° to 0°, and the negative value of the rake angle (γ) is increased from a tip of the ball end cutting edge (3) and a radially outer end (3o) of the ball end cutting edge (3) toward a middle point in the radial direction, and is maximized at approximately the middle point in the radial direction.