*Research Scientist Gi-dae Kim, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea. Tel: +82-2-880-1678 Fax: +82-2-880-7259

**Assistant Professor Won-tae Kwon, Department of Mechanical Engineering, University of Seoul, Seoul 130-743, Korea. Tel: +82-2-2210-240 Fax: +82-2-2248-5110

***Associate Professor Chong-nam Chu, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Korea. Tel: +82-2-880-7136 Fax: +82-2-875-2674

Quasi-static cutting force variation in milling process was measured indirectly using spindle motor current. Quasi-static sensitivity of the spindle motor current is higher at higher spindle speed range. The spindle motor current is independent of feed direction. The linear relationship between the cutting force and the spindle motor RMS current at various spindle rotational speeds was obtained. Frequency to voltage (F/V) converter voltage was measured to identify the spindle speed and to determine the cutting force at various spindle speeds. Based on these measurements, cutting force was regulated at a constant level by feedrate control. Practicability of the cutting force regulation system using spindle motor current was shown by

implementation to an FMS.

Fig. 2: Bode plot of current hall effect sensor.

Fig. 3: Quasi-static sensitivities of the feed and spindle drive systems.

(a) Feed drive system

(b) Spindle drive system

Fig. 4: Relationship between the spindle rotational speed and the voltage measured from F/V converter

Fig. 5: Cutting force and spindle motor current vs. feedrate.

(Machine: MCH-10, DOC: 3 mm, Spindle speed: 1,000 rpm,

Tool: carbide flat endmill, 2 teeth, Diameter = 20 mm, Workpiece: SM45C)

(a) Cutting force vs. feedrate

(b) Spindle motor current vs. feedrate

Fig. 6: Spindle motor current vs. cutting force.

(Machine: MCH-10, DOC: 3 mm, Spindle speed: 1,000 rpm,

Tool: carbide flat endmill, 2 teeth, Diameter = 20 mm, Workpiece: SM45C)

(a) In high gear ratio

(b) In low gear ratio

Fig. 7: Experiments at various cutting speeds in TCH-80 machining center.

(Machine: TCH-80, Gear change: 1400 rpm, DOC: 0 mm ~ 5 mm,

Feedrate: 200 mm/min, Tool: HSS flat endmill, 4 teeth, Diameter = 25 mm,

Workpiece: GC30)

Fig. 8: Experimental set-up for feedrate control.

Fig. 9: Flowchart of feedrate control.

Fig. 10: Cutting force regulation pattern according to the proportional gain (K_p).

Fig. 11: Taper machining of composite material (DOC: 1 mm ~ 4 mm, 600 rpm).

1. Feedrate fixed (160 mm/min)
2. Feedrate controlled

Fig. 12: Workpiece shape and tool path for circular machining.

Fig. 13: Circular taper machining (DOC: 2 mm ~ 5 mm, 3000 rpm).

1. Feedrate fixed (170 mm/min)
2. Feedrate controlled

F_T : Tangential force acting on the tool.