Machinery's Handbook, 31st Edition
1194 MICROFABRICATION PROCESSES AND PARAMETERS
100
FEA, axial depth 17% cutter Ø FEA, axial depth 34% cutter Ø Experiment
80
A B
60
Tool-failure Zone
40
Tool-safe Zone
20
0 5 1015202530 Chipload/Cutter Ø (%) 0 C
Fig. 38. Catastrophic Failure Threshold of Micro-Milling Tools as Percentage of Tool Diameter. Dry milling 316L stainless steel, Ø1 mm tool diameter, 2 flutes, 0.348 mm axial depth of cut.
1010 steel, 138 m/min 316 SS, 68 m/min 6061 aluminum, 296 m/min PVC plastics, 190 m/min
0 250 200 150 100 50 300
300 250 200 150 100 50
Drill speed = 0.54 millspeed
0
0.5 1.0
2.5 3.0 1.5 2.0 3.5
0 100 200 300 400 500 Micromilling Speed (m/min)
Milling Cutter Diamter (mm) Fig. 39. Recommended Chip Load as a Function of Carbide Cutter Size for Various Materials.
Fig. 40. Relationship of Drilling versus Milling Speed Using Carbide Tools on Different Engineering Materials.
Table 13a and Table 13b tabulate starting speeds and feeds for uncoated micrograin carbide micromilling and microdrilling tools, in US customary and metric units respectively. Drilling speed is normally reduced to approximately 50 percent of the milling speed of the same material, due to the high aspect ratio and difficulty of chip evacuation in microdrilling (Fig. 40). Example 17, Micromill and Microdrill Selection: Select parameters to micromill and microdrill 316L stainless steel using an uncoated carbide Ø1 mm, 2 flute microtool. Micromilling: Speed selection depends on tool life and cutting fluid. Table 13b suggests 68 m/min for micromilling. Both radial and axial depth of cut affect selection of feed. Select 35% axial depth (0.35 3 tool diameter = 0.35 mm), and 60% radial depth (0.60 3 tool diameter = 0.6 mm). From point A (60%) on the vertical axis of Fig. 38, draw a horizontal line that intersects the threshold line at point B, then find point C on the horizontal axis. The chip load that causes immediate tool fracture would be slightly more than 5% of tool diameter (50 m m/tooth). A conservative chip load would be 13 m m/tooth as indicated in Table 13b. Microdrilling: Table 13b suggests 28 m/min speed and 13 m m/tooth feed for drilling. Reduction of drilling speed to only 50–60% (59% in this example) of milling speed is necessary to facilitate chip removal in microdrilling.
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