Machinery's Handbook, 31st Edition
Microcutting Tools
1159
Effect of Depth of Cut (Chip Load) in Micromachining
Negative rake angle
Positive rake angle
Microtool
Microtool
Deep depth
Shallow depth
Spring back
Chip
r
r
Workpiece
Workpiece
Fig. 2a. Microfacing, Depth of Cut < 0.5 r .
Fig. 2b. Microfacing, Depth of Cut > 0.5 r .
Negative rake angle
Positive rake angle
Microtool
Microtool
High chip load
Spring back
Low chip load
r
r
Workpiece
Workpiece
Fig. 2c. Micromilling, Chip Load < 0.5 r Fig. 2d. Micromilling, Chip Load > 0.5 r . Fig. 2a and Fig. 2c illustrate rubbing and plowing of material with negative effective rake angle at a shallow depth of cut. Fig. 2b and Fig. 2d illustrate chip removal from material with positive effective rake angle at a deep depth of cut. It is crucial to verify the tool edge radius before deciding on cutting parameters. Measur ing of tool edge radius, however, is not trivial. A tool edge radius can be estimated from a scanning electron microscopic picture when the cutting edge is parallel to the electron beam (Fig. 6), or from a scanned image at the neighborhood of a cutting edge on an atomic force microscope (Fig. 3a and Fig. 3b), or by scanning an edge on an optical microscope profiler in different views to reconstruct a 3D image of the tool edge before finding its radius. Tool Edge Measurement by Atomic Force Microscopy Note the different vertical and horizontal scales.
nm
40 nm
500
20
nm
nm
800
200
600
150
100
400
50
200
Fig. 3b. New Single Crystalline Diamond Tool with a 10 nm Edge Radius.
Fig. 3a. New Polycrystalline Diamond Tool with a 750 nm Edge Radius.
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