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Machining of hardened steel with cBN end millEndurance data

Machining of hardened steel with cBN end mill
Endurance data – Cutting test using cBN radius end mill

Purpose of test
A cBN radius end mill was tested for slot machining in hard materials, which is a difficult process with conventional carbide end mills due to their machining inefficiency and limited tool life.

Test environment
Machine YBM-640V
Work material SLD(HRC60)
Cutting fluid Oil mist
Tool used cBN radius end mill (φ1 × R 0.1 × 6 (effective length)), manufactured by Kyowa

Test description
Cut slots 1 mm wide by 6 mm deep in a block measuring 80×60×30 mm, followed by visual evaluation at 200× magnification.

Machining conditions
Spindle rotational frequency :18,000rpm(56.5m/min)
Feed speed :500mm/min(0.013mm/tooth)
Cutting :10 μm × 600 strokes per slot
Cutting length :80 mm × 600 strokes = 48000 mm (48 m) per slot
Machining time :1 h 42 min per slot

Test results
A cBN radius end mill was able to cut ten slots 1 mm wide by 6 mm deep by 80 mm long in a hard material. However, beginning with the fifth slot, traces of wear or chipping can be seen at the corners. The total cutting length attempted in this test was 48 mm × 10 slots = 480 mm, but a practical length is 48 mm × 4 slots = 192 mm. (Only one slot can be cut with a carbide end mill.) However, increasing the cutting speed (1.5 to 2 times faster) would provide more favorable conditions.

Data on fine machining of glass with ball end mill
Table 1 Cutting conditions
Workpiece Pyrex
Tool cBN, R0.2mm
Feed rate 0.24mm/min
Axial depth of cut 20μm
Rotation rate 20000rpm, 40000rpm, 60000rpm
Effects of rotational frequency and cutting oil on machined surfaces
Rotational frequency Machined edge Machined surface

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