Ball End Mill Gash Geometry for Fracture Prevention
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Solution Overview
Problem
In ball end mills, the formation of protrusion ends with a convex V-shaped cross-section is challenging due to shear drop and wear, leading to machining accuracy issues and potential fracturing of end cutting edges, as the edges often overlap or form pointed projections near the axis, affecting chip dischargeability and surface quality.
Innovation Solution
The design features two gashes extending beyond the axis, with one gash's tip flank face extended to intersect with the second flank face at an obtuse angle, forming a concavely curved surface to prevent projection formation and enhance chip dischargeability, while ensuring the second end cutting edge intersects the concavely curved surface at an obtuse angle to secure strength and prevent fracturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the gash is formed by a gash grinding wheel with a convex V-shaped cross-section, then the end cutting edge should be formed at the apex central portion, but the protrusion end is rounded due to shear drop and wear, making it difficult to form a strict acute angle intersection
Solution Approach 1:
The patent changes the geometric parameters of the gash, specifically making the inner peripheral end of the gash extend beyond the axis in the tip direction. This parameter change compensates for the rounding effect of shear drop and wear, ensuring the end cutting edge is properly formed even with a rounded protrusion end.
2Reliability
If the gash is formed to a position slightly separated from the axis to avoid overlapping, then the end cutting edge is formed at the intersection ridgeline portion, but a pointed projection portion is formed that deteriorates machining accuracy and may cause fracturing
Solution Approach 1:
Instead of separating the gash from the axis to avoid overlapping, the patent inverts the approach by extending the gash beyond the axis. This creates an obtuse angle intersection that eliminates the pointed projection portion while maintaining proper end cutting edge formation, thus preventing both machining accuracy deterioration and fracturing.
3Manufacturing precision
If the first tip flank face is extended to intersect with the second tip flank face at an obtuse angle, then a concavely curved surface is formed to eliminate projection, but the structure becomes more complex
Solution Approach 1:
The patent segments the tip flank face into distinct portions: the first tip flank face, the extended portion, and the concavely curved surface. This segmentation allows each portion to serve a specific function in eliminating the projection portion while maintaining manufacturability through standardized grinding operations.
Data Source
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AI summary
In the ball end mill, at least two end cutting edges (9) are extended to the vicinity of an axis (O) at a tip portion of an end mill main body (1) which rotates around the axis (O). In two gashes (7) in which two end cutting edges (9) adjacent to each other in a circumferential direction are formed, a first gash (7A) on the end mill rotation direction (T) side extends beyond the axis (O) on the tip of the end mill main body (1) and a second gash (7B) on the rear side in the end mill rotation direction (T) does not exceed the axis (O). A first tip flank face (8A) which intersects with the first gash (7A) through a first end cutting edge (9A) is extended toward a second tip flank face (8B) which intersects with the second gash (7B) through a second end cutting edge (9B). A concavely curved surface (10) which is concavely curved and connected to an extended portion (8c) of the first tip flank face (8A) and extends toward the outer periphery side is formed between the extended portion (8c) of the first tip flank face (8A) and the second tip flank face (8B). The second end cutting edge (9B) intersects with the concavely curved surface (10) at an obtuse angle.