Demands on process and process energy sources for the electro-erosive erosive and electrochemical micromachining

Transkript

1 11th ESAFORM Conference on material forming INSA-Lyon, France, April 2008 MS20: Non-conventional processes Demands on process and process energy sources for the electro-erosive erosive and electrochemical micromachining by Dipl.-Ing. Dirk Borkenhagen Dipl.-Ing. Stephan Burkert Otto-von-Guericke-University Magdeburg, IGET

2 Outlines 1. Motivation for the Investigation 2. Definition of the 3. Selected for Micromachining 4. 1/30

3 Micromachining with non-conventional machining processes, no processing with the same equipment and only changed parameters is! 500 ms/cm 1 ms/cm 1 µs/cm ECM ECM ECM PECM PECM µ-pecm Combined Machining EDM (H 2 O) EDM Combined Machining 1 ps/cm EDM EDM (HC) (HC) Influence of electrical conductivity of the Micromachining on non-conventional processing Use of the efficient non-conventional machining for the micromachining! Use of the high machining accuracy Machining of very complex structures (filigree structures) Machining of hard materials High surface levels 2/30

4 Micromachining with non-conventional machining processes, no processing with the same equipment and only changed parameters is! Applications Microdetails (µm) at macroelements Feeder loop L Feed motion unit Completely microelements (µm) Nanodetails (nm) at microelements Contact elements? Process energy source Completely nanoelements (nm) Gap parameters Technological Parameters 3/30

5 Advantages Process energy source ECM & High quality of surface & No thermal affected zone & High processing rate Feeder system EDM & High processing accuracy & Different local removal & No chemical etching Optimisation L, C, R Process in the Gap Working fluid Electrode arrangement 4/30

6 Schematic block diagram of non-conventional machining including the gap Power Supply Measurement Measurement Technology Technology Control Control Systems Systems Safety Safety Control Control Process Energy Source Feeder System Working gap features 5/30

7 Conditions of the Working gap - Micromachining (electrical conductivity) Process Energy Source Feeder System Working gap Gap width < 10 µm EDM normal conditions ECM critical conditions Surface < 100 mm² EDM no limitation of current ECM critical current densities State of working medium EDM critical condition (Basis medium is liquid) ECM critical condition 6/30

8 Conditions of the Working gap - Micromachining (electrical conductivity) Process Energy Source Feeder System Working gap Gap contaminations EDM critical conditions ECM critical conditions Gap regeneration EDM slow (local) ECM fast (plane) Particle/Gap-Ratio EDM critical condition ECM critical condition 7/30

9 Conditions of the Working gap - Micromachining (Contamination) Process Energy Source Feeder System Critical Phases Working gap Tool Flow Gap < 1 µm Bridge Layer Workpiece Type S (solid) Particles Layer Propagation Type G (gas) Bubbles Type L (liquid) Additives Pyrolysis Additive Working Fluid 8/30

10 Conditions of the Working gap - Micromachining (Contamination) Type S (solid) Particles Flow Bridge Layer Critical Phases Workpiece Slime Gap < 1 µm Influence of the Double Layer Effects on EDM and ECM?? Type S is the result in series of the removal process (pulse energy) and washed-out effects of the working medium. EDM varying ignition conditions discharge channel splitting!? ECM varying current density distribution problem: discharge or short circuit? Additional flow through fast gap alternation. Oscillation, rotation or/and vibration 9/30

11 Conditions of the Working gap - Micromachining (Contamination) Type G (gas) Bubbles Flow Propagation Layer Critical Phases Gap < 1 µm Passivation?? Type S is the result in series of the evaporation processes (pulse energy) of working medium and electrode surfaces EDM evaporation of solid materials (low) and evaporation of working fluid (high) ECM Joule heating and cathodic hydrogen reduction Additional pressure conditions within the gap. Oscillation, rotation or/and vibration 10/30

12 Conditions of the Working gap - Micromachining (Contamination) Type L (liquid) Additives Flow DL-Double Layer Gap < 1 µm Type L is the result in series of additives and pyrolysis effects EDM Working fluid (hydrocarbon or deionised water)- Joule heating ECM Joule heating and cathodic hydrogen reduction (chemical reactions) lower effects. Effects of the Double layer! Pyrolysis Undefined Additives Additive most shorter and faster or/and Charge-defined. 11/30

13 Schematic feeder system Process Energy Source Feeder System Working gap Contact / Source Parallel Feeder Contact / Gap Loop / Source Pulse units Loop / Gap 12/30

14 Schematic feeder system Influences of the rise time and fall time of current and voltage Minimisation of the feeder inductivity! Optimization of the ratio inductivity/capacitance! Feeder parameter in concurrence to Gap parameter Additional the parasitic parameter???? 13/30

15 Process energy sources - EDM Process Energy Source Feeder System Working gap Reduction of the pulse energy: Fixed burning voltage and minimum current amplitude (~ 800 ma) Glow discharge is undesirably (evaporation of the dielectric fluid) Reduction of the pulse duration is limited by the electronic components Reduction of the pulse duration is limited by the feeder parameter (L, C) All parameters are depended of the materials! Discrepancy between process stability (high ignition voltage) and small gap (small average gap voltage) 14/30

16 Process energy sources - EDM Process Energy Source Feeder System Working gap Process control (Signal analysis) Magnitude process signal to noise signal Small current and voltage, rise and fall times (EMC problems) Coupling of the external noises Short time for signal processing Strong dependency of the ignition process on the micro geometry and the surface topology 15/30

17 External ECM-Sources Process Energy Source Feeder System Working gap DC-Sources Pulsed-ECM Bipolar-ECM Simple construction High parts of process safety Inflexible process control Complex construction Different parts of process safety High flexible process control More complex construction Higher quality of surface Limited using for micromachining with special electrolyte t i > 1 ms 1 ms < t i < 50 µs 50 µs < t i < 20 µs Micromachining t i < 20 µs Development area 16/30

18 Process energy sources - PECM Process Energy Source Feeder System Working gap : Working gaps smaller than 50 µm Application on higher current densities (trans-passivation) Regeneration of the working gap conditions Realisation of high current pulse rate of rise Strong dependency of the processing accuracy on the gap width (In normal case not constant gap width e.g. oscillation) 17/30

19 Internal ECM-Sources Process Energy Source Feeder System Working gap µ-pulsed-ecm Double Layer Reload Simple construction (Nanostructures) Different parts of process safety Inflexible process control Complex construction Problem of the transient current t i < 1 ns 1 ns < t i < 500 ns 500 ns < t i < 2 µs t i >2 µs Micromachining Nanomachining Development area 18/30

20 Process energy sources Combined processes Process Energy Source Feeder System Working gap Static Pulse Energy Source Current source Current source Voltage source Voltage source EDM Output ECM 19/30

21 Micro Electrical Discharge Machining (µedm) Source-Concept for µedm Needle Pulse Process Energy Source Pulse duration Minimum Current magnitude Constant Burning voltage Control of the Plasma channel bases 20/30

22 Micro Electrical Discharge Machining (µedm) Tool - Cathodic Gap ~ 1,5 µm Gap ~ 5 µm Gap variation for Micromachining Phase 1: Pre-ignition to ~20 ns Workpiece - Anodic Phase 2: Pre-ignition to ~80 ns Phase 3: Pre-ignition to ~120 ns Base of the Plasma channel Pure liquid discharge! 21/30

23 Phase degree in MC2 10µm MC2 2500µm n-dodecane measuring cell (6x6)- MC2 polished surface arrangement MC1 (Cylinder-Cylinder) MC2 15µm MC2 20µm MC1 2500µm MC1 7000µm 100 1k 10k 100k 1M 10M Admiitance in S 10m 1m 100µ MC2 20µm 10µ MC2 15µm MC2 10µm 1µ 100n MC1 7000µm 10n MC1 2500µm MC2 2500µm 1n 100p k 10k 100k 1M 10M Frequency in Hz Frequency in Hz Phase degree in MC µm MC2 10 µm MC2 15 µm MC2 20 µm Admittance in S 100m 10m 1m 100µ De-ionized water 1,4 µs/cm measuring cell MC2 polished surface Plate-Plate (6) MC2 10 µm MC2 15 µm MC2 20 µm MC µm k 10k 100k 1M 10M Frequency in Hz 30/30 10µ k 10k 100k 1M 10M Frequency in Hz

24 Micro Electrical Discharge Machining (µedm) Bode-Plot for n-dodecane with different gap widths (1) Phase degree in MC2 10µm MC2 2500µm n-dodecane measuring cell (6x6)- MC2 polished surface arrangement MC1 (Cylinder-Cylinder) MC2 15µm MC2 20µm MC1 2500µm MC1 7000µm 100 1k 10k 100k 1M 10M Admiitance in S 10m 1m 100µ 10µ 1µ 100n 10n 1n MC2 10µm MC2 15µm MC2 2500µm MC2 20µm MC1 2500µm MC1 7000µm 100p k 10k 100k 1M 10M Frequency in Hz Frequency in Hz MC1 Wire- Wire-Electrode-Arrangement (Macromachining) MC2 Peak-Peak-Electrode-Arrangement (Micromachining) 22/30

25 Micro Electrical Discharge Machining (µedm) Bode-Plot for de-ionised water with different gap widths (2) Phase degree in MC µm MC2 10 µm MC2 15 µm MC2 20 µm Admittance in S 100m 10m 1m 100µ De-ionized water 1,4 µs/cm measuring cell MC2 polished surface Plate-Plate (6) MC2 10 µm MC2 15 µm MC2 20 µm MC µm k 10k 100k 1M 10M Frequency in Hz 10µ k 10k 100k 1M 10M Frequency in Hz MC2 Peak-Peak-Electrode-Arrangement (Micromachining) 23/30

26 Micro Electrical Discharge Machining (µedm) Influence of the gap variation The Bode-Plots show better gap conditions for n-dodecane De-ionised water leads to electrochemical effects De-ionised water show big changes in the capacitive feature The pure capacitive gap characteristic of the n-dodecane give the possibility to calculate with a simple equivalent circuit. Changed between capacitive and ohms-capacitive conditions 24/30

27 Current i Micromachining for EDM, ECM and hybrid machining Adjustable current magnitude Source-Gap-Characteristic OP EDM Source characteristic i total Breakdown i edm i EC i ecm 0 u lim u bv Adjustable Gap characteristic voltage Voltage u OP ECM Micro hole sinking i ecm in lateral gap 25/30

28 Micromachining for EDM, ECM and hybrid machining Source-Gap-Characteristic Transition time Fall time Rise time Break duration 26/30

29 Current i Micromachining for EDM, ECM and hybrid machining Burning phase Source-Gap-Characteristic OP EDM Source characteristic i total de-ionised water i EC n-dodecane 0 Gap characteristic u bv u lim u lim u ig Voltage u 27/30

30 Current i Micromachining for EDM, ECM and hybrid machining Current constant Source-Gap-Characteristic i total OP ECM Gap constant i EC OP ECM 0 u lim 28/30

31 Micromachining for EDM, ECM and hybrid machining Source-Gap-Characteristic I max, a I max, p J max R a I trans-p 29/30

32 Exact defined micromachining conditions are possible! Selection of use cases Micromachining conditions are result of technological parameters, processing size and removal rate process Micromachining make demands on equipment new solutions and a greater parameter ranges Quality of the Micromachining is a result of the quality of the Process Energy Source Otto-von-Guericke-University Magdeburg Institute for Fundamental Electrical Engineering and EMC Werner-von-Siemens-Building Tel.: , Fax: hans-peter.schulze@ovgu.de 30/30

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