MACHINING ECONOMETRICS Machinery's Handbook, 31st Edition
1227
Face Milling
End Milling
AE
ar
hmax
hmax
ar
hm
AE
hm
f z
f z
2
ar D -----
ar D -----
cos AE = 1 – 2 ×
cos AE = 1 – 2 ×
Fig. 24. Comparison of face milling and end milling geometry: High-speed end milling refers to values of ar / D that are less than 0.5, in particular to ar / D ratios which are considerably smaller. When ar / D = 0.5 ( AE = 90 degrees) and diminishing in end milling, the chip thick ness gets so small that poor cutting action develops, including plowing or scratching. This situation is remedied by increasing the feed/tooth, as shown in Table 2a as an increasing f z / f z 0 ratio with decreasing ar / D . For end milling, the f z / f z 0 feed ratio is 1.0 for ar / D = 1 and also for ar / D = 0.5. In order to maintain the same hm as at ar / D = 1, the feed/tooth should be increased, by a factor of 6.38 when ar / D is 0.01 and by more than 10 when ar / D is less than 0.01. Hence high-speed end milling could be said to begin when ar / D is less than 0.5 In end milling, the ratio f z / f z 0 = 1 is set at ar / D = 1.0 (full slot), a common value in vendor catalogs and handbooks, for hm = 0.108 mm. The face milling chip making process is exactly the same as end milling the side of a workpiece and ar / D = 0.5 or less. However, when face milling close to and along the work centerline (eccentricity is close to zero) chip making is quite different, as shown in Fig. 24. When ar / D = 0.74 ( AE = 95 degrees) in face milling, the f z / f z 0 ratio = 1 and increases up to 1.4 when the work width is equal to the cutter diameter ( ar / D = 1). The face milling f z / f z 0 ratio continues to diminish when the ar / D ratio decreases below ar / D = 0.74, but very insignificantly, only about 11 percent when ar / D = 0.01. In face milling, f z / f z 0 = 1 is set at ar / D = 0.74, a common value recommended in vendor catalogs and handbooks, for hm = 0.151 mm. Fig. 25 shows the variation of the feed/tooth-ratio in a graph for end and face milling.
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5
fz/fz 0 , Face Milling fz/fz 0 , End Milling
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
ar/D
Fig. 25. Feed/Tooth versus ar / D for Face and End Milling
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