Asymmetric End Mill Geometry for Accurate Pilot Bore Roundness
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Solution Overview
Problem
Existing end milling cutters struggle to maintain the required dimensional accuracy and roundness of pilot bores, especially when made at large angles to the workpiece surface, with permissible roundness deviations often exceeding 3 to 6 μm.
Innovation Solution
The end mill features point asymmetry of the front cutting edges combined with a 90° pitch angle offset between them, along with unequal cutting edge pitches and slightly positive rake angles, which suppress natural vibrations and improve roundness accuracy by distributing cutting loads effectively, using hard materials like solid carbide for stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional end milling cutters with point symmetry and equal pitch angles are used, then the tool structure is simple and easy to manufacture, but the roundness accuracy of pilot bores deteriorates with deviations exceeding 3 to 6 μm
Solution Approach 1:
The patent applies asymmetry by deliberately designing unequal pitch angles between adjacent cutting edges (e.g., 90°, 120°, 150° instead of equal 120° spacing). This asymmetric arrangement suppresses tool vibrations during oblique machining, thereby improving pilot bore roundness accuracy to within 3-6 μm deviations while accepting increased geometric complexity in the cutting edge configuration.
Solution Approach 2:
The patent changes the pitch angle parameters from equal to unequal values, and introduces inclination angles for cutting edges. By optimizing specific parameter combinations (pitch angles, inclination angles, rake angles), the tool achieves superior roundness accuracy despite the increased complexity of the cutting edge geometry.
2Manufacturing precision
If face cutting edges are offset by equal pitch angles for simplicity, then the tool is easy to manufacture, but natural vibrations cannot be suppressed effectively, deteriorating bore roundness
Solution Approach 1:
The patent replaces symmetric equal-pitch angle arrangements with asymmetric unequal-pitch angle configurations. This asymmetry disrupts the vibration patterns that cause poor roundness, while the manufacturing complexity is managed through precise geometric definition rather than complex physical structures.
Solution Approach 2:
Different cutting edges are given different pitch angles and inclination angles tailored to their specific positions and functions. This local optimization allows each cutting edge to contribute optimally to vibration suppression and roundness accuracy, rather than using a uniform design for all edges.
3Stability of the object's composition
If peripheral cutting edges have negative rake angles for stability in tough materials, then cutting edge stability improves, but deflection during initial bore introduction increases
Solution Approach 1:
The patent applies different rake angle characteristics to different cutting edges or cutting edge sections. While maintaining overall stability through appropriate rake angles, the design optimizes local conditions at the initial contact point to minimize axis deflection during the critical first phase of bore introduction.
Solution Approach 2:
The cutting edge geometry is designed to optimize performance in advance for the initial contact phase. By pre-configuring the rake angles and inclination angles, the tool is prepared to minimize deflection before the full cutting load is engaged, ensuring better initial bore accuracy.
Data Source
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AI summary
An end milling cutter (10) is described with four straight face cutting edges (24-1 to 24-4) arranged on one face side and a corresponding number of peripheral cutting edges (28-1 to 28-4), which are separated from each other by chip flutes (30). One of the front cutting edges merges into a second front cutting edge via a flank intersection line (32). The other end cutting edges lying in between in the cutting direction (RS), which can be offset from one another by a first pitch angle (TW1) of 180°, end in front of the center (36). In order to be able to use the end milling cutter in a particularly advantageous manner for the introduction of pilot bores that are accurate in terms of shape and position or for mirroring curved workpiece surfaces, all the pitch angles of the end cutting edges are different from one another