Annual 4M Conference on Multi-Material Micro Manufacture 3 – 5 October 2007, Boroverts, Bulgaria Process Capabilities of Micro-EDM and Its Applications K. Liu, E. Ferraris, J. Peirs, B. Lauwers, D. Reynaerts Division PMA, Department of Mechanical Engineering Katholieke Universiteit Leuven Leuven, Belgium kun.liu@mech.kuleuven.be
Outline • Introduction • Characteristics of micro-EDM • Pulse generation • Application examples • Conclusions Process Capabilities of Micro-EDM and Its Applications 2
Introduction • E lectrical D ischarge M achining ( EDM ) – Pulsed Thermo-Electrical material removal process – Characteristics • Conductive materials • No physical contact between workpiece and tool • Rz ~ 0.4 µm • Different machining configurations Wire EDM – Application Die sinking EDM • Accuracy to a few micrometers • Die and mould manufacturing EDM milling • Burr-free hole drilling Process Capabilities of Micro-EDM and Its Applications 3
Introduction Chinese Pagoda* • Micro EDM – Geometry Scaling down – Machining products or features in sub-mm range – Applications Contact lens moulds** • Difficult-to-make structures: Micro moulds, Injection nozzles, micro gas turbine Micro beam (Si) and impellers… the tool • Wide range of materials Mould for optical fiber aligner (Si) – Metal – Hard metal Stainless steel – Silicon propeller 20 mm – Ceramic composites Micro gas turbine 1 mm impeller (Si 3 N 4 -TiN) *:Y.-S, Liao, et al , 2005 **: B. Rooks, 2004 Process Capabilities of Micro-EDM and Its Applications 4
Characterization of Micro-EDM • Requirements for Micro-EDM Overview of the micro-EDM capabilities – Small material U nit R emoval Machining Geometric Min. Feature Max. Surface ( UR ) Complexity size ASP quality Ra Variation • Low energy input Drilling 2D 5 µm ~40 0.05 – 0.3 • Small craters Sinking 3D ~20 µm ~15 0.05 – 0.3 – High precision equipment Milling 3D ~20 µm ~10 0.1 – 0.5 • Accurate motion drive WEDM 2 ½ D ~30 µm ~100 0.1 – 0.2 – Small sparking gap WEDG Axi. 3 µm 30 0.8 – Precision movement • Fast reaction servo control • Variable configurations and its capabilities – Drilling, die-sinking, Wire EDM, Milling – WEDG: Shaping electrodes specially for micro application Wire Electric Discharge Grinding (WEDG) Source: T. Masuzawa, 1985 Process Capabilities of Micro-EDM and Its Applications 5
Pulse Generation • For Micro scale EDM – Resistance Capacitance (RC) based generator • High peak current • Short pulse duration • Small energy input (~ nJ ) – Available micro-EDM machine • Sarix SX-100-HPM – Precision of positioning: ± 2 µm – Resolution: 0.1 µm • Electric parameters R S 2 Parameters Symbol Unit i Polarity -/+ C V cc Tool Energy E (index) electrode Voltage U V i Current I (index) Frequency F kHz workpiece S 1 Width W µs Process Capabilities of Micro-EDM and Its Applications 6
Pulse Generation • Pulse characterization – Experimental set-up • Oscilloscope TEKTRONIX TDS 754A – 500 MHz bandwidth, 2 GS/s sample rates – 1 mV/div -10 V/div sensitivity • Tektronix A6303 current probe • Tektronix P5205 floating high voltage differential probe • AM503 Current amplifier Generator ��� ��� � ���� Oscilloscope � i ��������� Process Capabilities of Micro-EDM and Its Applications 7
Pulse Generation • Pulse characterization – Waveforms of voltage and current in pulse measurement of normal discharges • Multiple-step charging • Correspondent input value to open gap voltage • Frequency of each charge step • Very short pulses ≈ 300 – 400 ns � �� �������� ����������� ��� � � �� � �!�"��#�!������� � ��� � ��� Input parameters � � � ��� P = - � �� � �� E = 110 ���������� � �� U = 100 V I = 80 � �� � �� F = 120 kHz ����������� � � � W = 3 µs � � �!�"��#��������� � �� � Process Capabilities of Micro-EDM and Its Applications 8
Pulse Generation • Pulse characterization – Varying parameter energy • Charging pattern varied • Discharge current is highly related • No dramatic differences in discharge duration • Possibility to obtain low energy input pulses � � � � � � $���� ������ �� �� � � � � � � '��� �(���� ���� �� �� ���� %&��'� %&��� Process Capabilities of Micro-EDM and Its Applications 9
Pulse Generation • Pulse characterization • Nominal discharge current ↑ – Increasing parameter voltage • Discharge energy ↑ � �� • Charging steps ↑ � )� • Effective pulse frequency ↓ � �� ��� � � � �� � � � �� ��� � � �� � � �� � � � �� '(*� � � ��� �� � � � � � � � � � �� � Input U = 200 V Input U = 100 V Nominal current i e = 6.4 A Nominal current i e = 2 A Process Capabilities of Micro-EDM and Its Applications 10
Pulse Generation • Pulse characterization • Nominal discharge current same – Increasing parameter current Charge steps ↓ • Effective pulse-off time ↓ • � �� • More abnormal discharges observed ��� � � � �� � � ��� � � �� � � � � �� � � � � �� � � � � � � � �� �� � � �� � Input I = 80 Input I = 100 Nominal current i e = 2 A Nominal current i e = 2 A Process Capabilities of Micro-EDM and Its Applications 11
Application • Micro air compressor manufactured on SARIX • Tool electrode – Material: Tungsten carbide – Geometry: • Ø 0.3 mm for the center hole • Ø 0.04 mm for finishing blades • Workpiece: – Material: stainless steel – Ø 1.0 mm cylindrical rod – Smallest feature size 30 µm Process Capabilities of Micro-EDM and Its Applications 12
Application • Milling configuration Side wall – Layer-by-layer machining with µm- range incremental depth – Automatic tool feeding: wear compensation Overcut – Integrated WEDG unit for tool shaping zero run-out • Results evaluation Eccentricity error – Good consistence with all the blades: Tolerance < 1 µm – No taper angle and obvious scallop at side walls – Eccentricity error ~ 20 µm Process Capabilities of Micro-EDM and Its Applications 13
Application • Result evaluation – For surface quality • Roughing craters diameter ~ 21 µm • Finishing craters diameter ~ 6.5 µm • Estimated R max for finishing ~ 0.85 µm 6.36 � m 20.8 � m 22.2 � m 6.53 � m 6.70 � m 20.2 � m roughing finishing Process Capabilities of Micro-EDM and Its Applications 14
Conclusion – Advanced RC-based generator • Fine pulse generation • Low energy input • Better control of the EDM process • Assures good surface quality – Limited understanding of the machining parameters • Physical meaning • “Sarix User-club” Process Capabilities of Micro-EDM and Its Applications 15
Thank you for your attention! Process Capabilities of Micro-EDM and Its Applications 16
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