K. P. Rajurkar Distinguished Professor of Engineering,

1. Complex Shapes by Micro-EDM, Micro-ECM & Micro-USM K. P. Rajurkar Distinguished Professor of Engineering, Center for Nontraditional Manufacturing Research, University of Nebraska-Lincoln. US-Korea Workshop on Miniaturization Technologies September 9, 2004

2. Presentation Outline • Introduction • Micromachining Technology • Micro EDM • 1. 3D Micro Cavity Machining • 2. Application Planetary Movement • Micro ECM • 1. Gap Modeling • 2. Experimental Results • Micro USM • Summary

3. Micromachining Applications • IC Packages with Micro Devices • Fuel Injection Nozzle for Automobiles • Biotechnology • Medical Applications • Multifunctional Compact Devices (CD/DVD players)

4. Micro-EDM

5. Basics of Micro EDM Material Removal Mechanism of EDM electrode -cathode workpiece +anode (b) A spark is generated between tool and workpiece. (a) Tool and workpiece immersed in dielectric liquid. (d) At the end of the pulse, the molten material is ejected from surface, leaving a shallow crater. (c) The high temperature causes the melting and vaporization of electrodes.

6. Macro Vs. Micro EDM

7. Micro EDM Equipment

8. Machining Parameters • Discharge Voltage (60V to 110V) • Capacitance (usually up to 3300pF) • Tool Material (Tungsten, other conductive materials) • Tool Size (4μm to 1mm) • Dielectric (Mineral oil or deionized water)

9. Capabilities of Micro EDM • Machine any conductive materials. • Single or medium size production. • Holes (Aspect ratio, 5:1 in oil, 10:1 in deionized water, • 18:1 using special method, 100μm in diameter, stainless steel). • 4. Slots and Arbitrary 3D micro molds.

10. 3D Micro Cavities Machining ● The electrode wear ratio in micro EDM is larger than that of conventional EDM. ● The fabrication of complex shaped electrodes itself is a kind of micromachining. ● No CAD/CAM system is available to generate tool paths when simple shaped electrodes are used to generate complex cavities because the electrode wear cannot be easily taken into account.

11. Simple Shaped Electrode Wear (a) Conventional Wear. (b) Uniform Wear.

12. Concept of Uniform Wear Method The uniform wear concept is based on the fact that under certain conditions, the shape of the electrode is regained due to the electrode wear after machining one layer. Rules of the tool path design: (a) Layer-by-layer machining. (b) To-and-from Scanning. (c) Tool paths overlapping. (d) Machining the central part and the boundary of the machined surface alternately.

13. CAD ModuleCAM Module Generating tool paths for machined features Slicing the machined features and calculating area of each sliced surface Part Modeling Tool paths data Re-generating tool paths and compensating electrode wear length based on the uniform wear method Tool paths data generation by the new approach Area of sliced surfaces Feature Data Post processor Transferring NC codes to micro-EDM NC codes Integration of Uniform Wear Method with CAD/CAM

14. Open circuit voltage 80V Capacitor 100pF Workpiece material SUS304 Electrode material Tungsten Machining Conditions

15. CAD Drawing using Pro-Engineer CAD design of a complex cavity (Dimension: µm).

16. Geometry Machined (a) Top View. (b) Oblique View.

17. Design CAD design of a complex cavity (Dimension: µm).

18. Machining Results (a) Top View. (b) Oblique View.

19. Tool Electrode Electrodes after machining.

20. Planetary Movement in Micro EDM ● Planetary movement of electrode provides an extra space for easier removal of debris from the discharge gap. ● Reduces the debris concentration. ● Reduces the occurrence of abnormal discharges. ● Reduces the electrode wear. ● Improves the machining efficiency.

21. Machining Conditions

22. Influence on Edge and Corner Square holes without planetary movement Square holes with planetary movement

23. Electrode feed Vs. Machining time

24. Material Removal Rate

25. Electrode Wear Ratio

26. Water Pump Water Reservoir Valve Computer Workpiece Y-Z Stage Probe Electrode Planetary Movement Controller Horizontal Electrode Feed Mechanism Conductivity Meter Micro EDM Controller Water Deionizing Resin Horizontal Machining Setup for Micro Holes of High Aspect Ratio

27. Machining Conditions for Deep Hole Drilling

28. A Micro Hole with Aspect Ratio of 18 Micro hole through 2.5mm plate. Hole exit (D=120µm). Hole entrance (D=145µm). When the plate is drilled through, besides the normal tool wear, the reduction of subsequent discharges (because the debris is ejected out from the hole exit easily) result in a small exit diameter.

29. Electrode After Machining Electrode before cleaning after hole drilling. Electrode after cleaning after hole drilling.

30. Effect of Dielectric on Machining time

31. Surface Roughness Measurement • Atomic Force Microscope • Stylus based Profilometer • Optical Interferometer 

32. Surface Roughness Calculation Raw Data Waviness (Freq = 100mm-1) Roughness

33. Experiment Results

34. Discharge Energy Vs Crater Size 220pF 100pF 3300pF 1000pF 80V, 5mm deep

35. Micro-ECM

36. Electro Chemical Machining (ECM) • Anodic dissolution process in an electrolyte cell “The amount of material dissolved is directly proportional to the amount of charge passing through the electrodes” Tool electrode Workpiece ECM Cell

37. Side Gap along Width Sx Side Gap along Length Sy Frontal Gap from the Face of the tool Sf ECMM PROCESS Duty Cycle Initial Inter electrode Gap Electrolyte Concentration Tool electrode Feed Rate Voltage Frequency ECMM Factors

38. ECMM Process Modeling • Cylindrical electrode with flat face • Linear potential distribution • No changes in electrolyte properties • Gas generation effect is negligible • Homogeneous work piece material • Surface of anode is uniformly covered by the electrolyte

39. Designed Setup 1.2 Vertical Slide 6. Light Source regulator 2. Microscope 5. Oscilloscope 1. Drive System 3. Electrolyte jet nozzle 4. Power supply

40. Statistical Analysis Results • Coefficient of multiple determination = 95%. • Voltage, feed rate, and duty factors have been found significant on all performance measures. • Frequency does not affect the frontal gap. • The interaction of voltage with duty factor in case of side gap along width has been found significant. • Duty factor gives better results at lower level (0.3). • Frequency gives better results at 1000 KHz.

41. Experimental Investigation: Effect of Voltage Feed rate (Vf) = 42 mm/min Pulse frequency = 1MHz, Duty Factor = 0.3

42. Experimental Investigation: Effect of Feed Rate • Voltage (U) = 5 V, • Duty factor = 0.3 • Pulse Frequency = 1MHz,

43. Theoretical Experimental Linear Theoretical Linear experimental Verification of Theoretical Model Feed rate (Vf) = 42 mm/min Pulse frequency = 1MHz, Duty Factor = 0.3

44. Theoretical Experimental Linear Theoretical Linear experimental Verification of Theoretical Model Cont… Feed rate (Vf) = 42 mm/min Pulse frequency = 1MHz, Duty Factor = 0.3

45. 160 m 2.18 mm 0.6 mm ECMM Generated Micro Cavities Workpiece material SS 440 Tool electrode material Tungsten Tool electrode diameter 100 m Voltage 6 volt Pulse frequency 1MHz Duty cycle 0.3 Initial interelectrode gap 20 m Feed rate 42 mm/min Electrolyte concentration 10%

46. Micro-USM

47. Micro Ultrasonic Machining (USM) Mandrel Abrasive Slurry Micro Tool Workpiece Ultrasonic Generator Transducer

48. Equipment Setup

49. Setup - Pictures V-Shaped Bearing Mandrel Carriage Stages Ultrasonic generator Weighing Balance Transducer Micro Tool

50. Machining Conditions for 3D Cavity Generation