Process Capabilities of Micro-EDM and Its Applications K. Liu, E. - - PowerPoint PPT Presentation

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

Annual 4M Conference on Multi-Material Micro Manufacture 3 – 5 October 2007, Boroverts, Bulgaria

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Process Capabilities of Micro-EDM and Its Applications

Outline

• Introduction
• Characteristics of micro-EDM
• Pulse generation
• Application examples
• Conclusions

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Process Capabilities of Micro-EDM and Its Applications

Introduction

• Electrical Discharge Machining

(EDM)

– Pulsed Thermo-Electrical material removal process – Characteristics

• Conductive materials
• No physical contact between

workpiece and tool

• Rz ~ 0.4 µm
• Different machining configurations

– Application

• Accuracy to a few micrometers
• Die and mould manufacturing
• Burr-free hole drilling

Wire EDM Die sinking EDM EDM milling

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Process Capabilities of Micro-EDM and Its Applications

Introduction

• Micro EDM

– Geometry Scaling down – Machining products or features in sub-mm range – Applications

• Difficult-to-make structures:

Micro moulds, Injection nozzles, micro gas turbine impellers…

• Wide range of materials

– Metal – Hard metal – Silicon – Ceramic composites

20 mm Chinese Pagoda* Contact lens moulds** Micro beam (Si) and the tool Mould for optical fiber aligner (Si) Micro gas turbine impeller (Si3N4-TiN) Stainless steel propeller 1 mm

*:Y.-S, Liao, et al, 2005 **: B. Rooks, 2004

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Process Capabilities of Micro-EDM and Its Applications

Characterization of Micro-EDM

• Requirements for Micro-EDM

– Small material Unit Removal (UR)

• Low energy input
• Small craters

– High precision equipment

• Accurate motion drive

– Small sparking gap – Precision movement

• Fast reaction servo control

0.8 30 3 µm Axi. WEDG 0.1 – 0.2 ~100 ~30 µm 2 ½ D WEDM 0.1 – 0.5 ~10 ~20 µm 3D Milling 0.05 – 0.3 ~15 ~20 µm 3D Sinking 0.05 – 0.3 ~40 5 µm 2D Drilling Surface quality Ra Max. ASP

• Min. Feature

size Geometric Complexity Machining Variation

Overview of the micro-EDM capabilities Wire Electric Discharge Grinding (WEDG)

Source: T. Masuzawa, 1985

• Variable configurations and its capabilities

– Drilling, die-sinking, Wire EDM, Milling – WEDG: Shaping electrodes specially for micro application

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Process Capabilities of Micro-EDM and Its Applications

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

Tool electrode workpiece R C Vcc i i S1 S2

W F I U E Symbol Unit Parameters µs Width kHz Frequency (index) Current V Voltage (index) Energy

• /+

Polarity

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Process Capabilities of Micro-EDM and Its Applications

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

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Process Capabilities of Micro-EDM and Its Applications

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
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Input parameters P = - E = 110 U = 100 V I = 80 F = 120 kHz W = 3 µs

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Process Capabilities of Micro-EDM and Its Applications

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

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Process Capabilities of Micro-EDM and Its Applications

Pulse Generation

• Pulse characterization

– Increasing parameter voltage

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• '(*
• Input U = 200 V

Nominal current ie = 6.4 A

• Nominal discharge current ↑
• Discharge energy ↑
• Charging steps ↑
• Effective pulse frequency ↓
• Input U = 100 V

Nominal current ie = 2 A

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Process Capabilities of Micro-EDM and Its Applications

Pulse Generation

• Pulse characterization

– Increasing parameter current

• Input I = 100

Nominal current ie = 2 A

• Nominal discharge current same
• Charge steps ↓
• Effective pulse-off time ↓
• More abnormal discharges observed
• Input I = 80

Nominal current ie = 2 A

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Process Capabilities of Micro-EDM and Its Applications

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

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Process Capabilities of Micro-EDM and Its Applications

Application

• Milling configuration

– Layer-by-layer machining with µm- range incremental depth – Automatic tool feeding: wear compensation – Integrated WEDG unit for tool shaping zero run-out

• Results evaluation

– Good consistence with all the blades:

Tolerance < 1 µm

– No taper angle and obvious scallop at side walls – Eccentricity error ~ 20 µm

Eccentricity error Side wall Overcut

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Process Capabilities of Micro-EDM and Its Applications

Application

• Result evaluation

– For surface quality

• Roughing craters diameter ~ 21 µm
• Finishing craters diameter ~ 6.5 µm
• Estimated Rmax for finishing ~ 0.85 µm

20.8 m 22.2 m 20.2 m 6.36 m 6.53 m 6.70 m roughing finishing

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Process Capabilities of Micro-EDM and Its Applications

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”

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Process Capabilities of Micro-EDM and Its Applications

Thank you for your attention!