The ability to machine microstructures is desirable for many applications ranging from miniaturization to functionalization of large surfaces. This includes the microstructuring of electrodes for die-sinking EDM applications, the micromachining of hierarchal structures for self-cleaning surfaces, and the use in the watch- and jewelry industry. In order to machine microstructures, high demands are placed on machine accuracy, spindle speed, the inverter, tools, and so on.
Micromilling experiments are conducted with a Mikron HSM 400 U 5-axis-machining center from GFMS in Switzerland. A Mach Serie 200 spindle from MachSwiss provides a rotation speed as high as nmax = 200.000 rpm and is controlled by a ACO5000A inverter from Ornika SA.
As extreme spindle speeds and high spindle efficiency are required, the ACO5000A is equipped with a Pulse Amplitude Modulation (PAM). Furthermore, PAM has low switching losses compared to Pulse Width Modulation (PWM). The PWM is usually employed if low spindle speeds are desired. The ACO5000A provides an output frequency of 5000 Hz, thus covering the necessary frequency up to ~3330 Hz, and a voltage of 200 V. Both are required for a spindle speed of nmax = 200.000 rpm.
Micromilling is carried out using a 200 µm diameter tungsten carbide micro-end milling tool from Dixi Polytools in Switzerland. In tungsten reinforced copper (WCu), defined structures with a height of 200 µm and width of 60 µm are feasible to machine. To avoid burr formation and to guarantee low surface roughness, the cutting speed – and respectively the spindle speed – must be set as high as possible for such small tools.
An ACO5000A inverter with a control panel for spindle speed regulation
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Doctoral Student in Mechanical Engineering