Milling Head Free Length Optimization for Lens Vibration Control
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Solution Overview
Problem
Existing milling heads for spectacle lenses face limitations in achieving high-precision processing due to vibration issues, particularly when producing lenses with small radii of curvature, as the number and arrangement of cutting edges are constrained by the available space, leading to suboptimal excitation frequencies.
Innovation Solution
The milling head design is optimized by ensuring the free length (L) in relation to the outer diameter (D) and radius (R) satisfies the condition |L| = 0.18 (|D|-2|R|) + 54 ± a, with a shank diameter between 10 mm and 32 mm, and incorporating a blade ring with 12 cutting tips, which helps in suppressing negative influences on excitation frequency and enhancing vibration behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of cutting edges is increased to improve productivity, then the manufacturing precision deteriorates due to limited space on the milling head circumference
Solution Approach 1:
The patent transitions from a two-dimensional arrangement of cutting edges on the circumference to a three-dimensional configuration by adding cutting edges on the end face of the milling head. This dimensional expansion allows increasing the total number of cutting edges without compromising the circumferential spacing, thereby maintaining manufacturing precision while improving productivity.
Solution Approach 2:
The cutting edges are segmented into two distinct groups: one group arranged on the circumference and another group on the end face. This segmentation allows independent optimization of each group's positioning and spacing, enabling the system to achieve both high productivity through increased cutting edge count and high precision through optimized spatial distribution.
2Object-affected harmful factors
If the free length L is reduced to improve vibration behavior, then the adaptability of lens shapes deteriorates
Solution Approach 1:
The patent optimizes the free length L to a specific value range (0.18(|D|-2|R|) + 54 ± a) rather than simply minimizing it. This parameter optimization achieves the dual goal of suppressing vibrations through appropriate length selection while maintaining sufficient length to accommodate various lens shape requirements, thus preserving adaptability.
Solution Approach 2:
The milling head design incorporates dynamic considerations by optimizing the free length based on operational parameters such as rotation speed and cutting edge configuration. This dynamic optimization allows the system to achieve stable vibration characteristics across different operating conditions while maintaining versatility for various lens production requirements.
3Productivity
If the rotation speed is increased to improve productivity, then the manufacturing precision deteriorates due to excitation frequency issues
Solution Approach 1:
The patent utilizes periodic action by arranging cutting edges at specific angular intervals and optimizing the rotation speed to create favorable excitation frequencies. The 12 cutting edges distributed around the circumference generate periodic cutting forces that, at optimized speeds, avoid resonant frequencies and minimize vibrations, thereby maintaining precision at high productivity.
Solution Approach 2:
The patent optimizes the rotation speed parameter within a specific range (15,000-30,000 rpm) and correlates it with the number of cutting edges and free length to achieve favorable excitation frequencies. This parameter optimization allows high-speed operation while suppressing vibrations that would otherwise degrade manufacturing precision.
Data Source
Figure 1~2a
Figure 2b~3
AI summary
The invention relates to a milling head 1 for a milling machine for manufacturing spectacle lenses from plastic, comprising a rotational axis 1.1, a coupling part 1.2 for clamping in a milling spindle chuck 2, a shoulder 1.5 adjoining the coupling part 1.2 with a stop surface 1.5a for the milling spindle chuck 2, a shank 1.3 adjoining the shoulder 1.5, and a cutting ring 1.4 adjoining the shank 1.3, comprising several cutting inserts 14a, 14b, 14c with a radius R and having an outer diameter D, wherein a free length L is provided between the cutting ring 1.4 at the level of the outer diameter D and the stop surface 1.5a. The magnitude of the free length L in relation to the magnitude of the outer diameter D and the magnitude of the radius R satisfies the following condition: |L| = 0.18 (|D|-2|R|) + 54 ± a, with a maximum deviation a of 3.