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RESEARCH ON ELECTROCHEMICAL MICROMACHINING AND ITS TECHNIQUES 2006 8 TG662 621.9.047 2006 8 Classified Index: TG662 U.D.C: 621.9.047 Dissertation for the Doctoral Degree in Engineering RESEARCH ON ELECTROCHEMICAL MICROMACHINING SYSTEM AND ITS TECHNIQUES Candidate Li Xiaohai Supervisor Prof. Zhao Wansheng Associate Supervisor Prof. Wang Zhenlong Academic Degree Applied for Doctor of Engineering Speciality Mechanical Manufacturing and Automation Affiliation School of Electro-Mechanical Engineering Date of Defence August, 2006 Degree-Conferring-Institution Harbin Institute of Technology 1m 520m 0.1m 100ns - I - 10m 30m UG CAD/CAM G 50m - II - Abstract Abstract Electrochemical machining (ECM) is a course of the dissolution of anodic metal ion by ion to shape workpieces. Consequently ECM should in theory be able to produce nano-precision parts and be a promising micromachining technique for manufacturing micro parts with dimensions in micrometer order or even in nanometer order. Now, some developed countries have paid close attention to the research on micro-ECM, but the development of micro-ECM of our country stand in a preliminary phase. It is an important problem to make full use of the machining mechanism of metal dissolution ion by ion in the process of ECM, explore the capability of micromachining of ECM and find a new technique to realize the precision machining and micromachining. It will be great signification to thoroughly master the key techniques, develop micro-ECM system and investigate the law of micro-ECM. In this paper, the author first analyzes the machining mechanism of micro- ECM and summarizes the charastrics of micro-ECM, and thus the system of micro-ECM has been designed based on the multifunctional micromachining machine tool which possesses three-axis linkage. The micro-ECM system includes a high-frequency short-pulse micro-energy power supply, a set of mechanism equiptment, circulation system of electrolyte and detection system of machining status. The mechanism equipment consists of the servo mechanism, the worktable, the on-line observation device, the fabrication module of micro tool electrode and so on. In addition, there is a precision rotary spindle. The micro electrode rotates along with spindle at high speed, which possesses the rotary error of 1m. The rotation at high speed of the micro electrode is very helpful to improve the machining status and enhance the machining precision. The design of micro-ECM system is based on the micromachining at scale from several m to several hundred m. The machining gap must be controlled in the range from 5m to 20m to realize micromachining, so the micro-ECM system possesses the micro feed resolution of 0.1m and high feed accuracy. In order to guarantee the machining gap and the stable machining, the corresponding servo strategies are prescribed. Moreover, the micro-ECM system has the sensitive - III - module of detecting machining status and servo control system with high dynamic response for the sake of avoiding the occurrence of micro spark in between electrodes in the process of micro-ECM. The online fabrication of micro electrode by electrical discharge machining (EDM) on the multifunctional machine tool can be performed, which can advance the fabrication and installation accuracy of micro electrode. According to the characteristics of micro-ECM, a high-frequency short- pulse micro-energy power supply has been designed. This power supply integrates the detection system of machining status detecting the information of machining voltage and machining current, which can help to realize the machining automatization. Owing to the very little machining current, the frequency of pulse power supply can obtain easily higher frequency, and the minimal pulse width of below 100ns can be realized. Moreover, in according to the characteristics of micro-ECM, a control system can be designed, which can adjust the servo control system and guarantee the stable machining. In the process of micro-ECM, the position finding is a key factor for guaranteeing machining accuracy. A contact perception electrocircuit is designed to find the position relation between design reference and workpiece or tool electrode. The author has carried out the experiment of drilling micro holes by micro- ECM. Low machining voltage, low concentration of passivity electrolyte, high- frequency short-pulse power supply, rapid dynamic response servo system and micro tool electrode rotating at high speed have been synthetically adopted to localize the dissolution area during ECM, so the machining gap can be kept at about 10 m, the micro hole with diameter of 30m can be drilled and the better resolution of machined shape is achieved. In addition, the author put forward a way by adopting the cut-edge electrode to drill deep micro-holes. The cut-edge electrode can greatly improve removal condition of electrolysis product and increase the machining efficiency. The research on how machining parameters during micro-ECM influence the machining accuracy has been carried out, and the machining parameters can be optimized. There are many disadvantages in micro-EC sinking, so a new approach of fabricating microstructures by means of electrochemical milling is proposed as a result of no tool wear during micro-ECM. By utilizing side wall of simple micro - IV - Abstract rotating tool electrode like micro mechanical milling and controlling the movement track and machining parameters, microstructures with high precision can be milled by micro-ECM under lower machining current. Moreover, the fabrication of micro-electrode with complex micro-features can be avoided. The micro-EC milling can improve the machining status in the tiny machining gap and thus make machining stable by simple rotary column electrode. The author also investigates the influence factors on the accuracy of micro-EC milling, such as feed speed, machining voltage and category of electrolyte. At last, the author proposes the technique of the NC generating micro-ECM integrating CAD/CAM technology. The G code for machining complex structure can be generated by the universal CAD/CAM of traditional milling based on UG software, and the machining samples with high precision can be obtained, such as the micro bend beam with width of about 50m. Keywords electrochemical machining, micromachining, high-frequency short- pulse power supply, micro-hole, microstructure - V - . I Abstract.III 1 .1 1.1 .1 1.2 .2 1.3 .5 1.3.1 .6 1.3.2 .6 1.4 .9 1.4.1 .9 1.4.2 .14 1.5 .16 1.5.1 .16 1.5.2 .16 1.6 .17 2 .18 2.1 .18 2.2 .19 2.3 .22 2.3.1 .22 2.3.2 .23 2.4 .24 2.5 .26 2.5.1 .26 2.5.2 .27 2.6 .28 2.6.1 .28 2.6.2 .28 2.7 .30 - - VI 2.8 .32 2.9 .34 2.10 .36 2.11 .37 2.12 .38 3 .39 3.1 .39 3.1.1 .41 3.1.2 .42 3.2 .45 3.3 .46 3.4 .47 3.4.1 .48 3.4.2 .50 3.4.3 .50 3.4.4 .52 3.4.5 .53 3.5 .53 3.5.1 .54 3.5.2 .55 3.5.3 .57 3.6 .57 4 .59 4.1 .59 4.2 .60 4.3 .61 4.4 .63 4.5 .64 4.5.1 .64 4.5.2 .65 4.6 .66 4.6.1 .66 4.6.2 .67 - VII - 4.6.3 .68 4.6.4 .68 4.7 .70 4.7.1 .70 4.7.2 .71 4.8 .74 4.8.1 .74 4.8.2 .75 4.8.3 .76 4.8.4 .77 4.8.5 .78 4.8.6 .79 4.8.7 .79 4.9 .80 5 .81 5.1 .81 5.1.1 .81 5.1.2 .82 5.2 .85 5.2.1 .85 5.2.2 .85 5.2.3 .86 5.3 .87 5.4 .89 5.4.1 .89 5.4.2 .91 5.4.3 .92 5.4.4 .94 5.5 .95 5.6 UG CAD/CAM .96 5.6.1 UG CAD/CAM G .97 5.6.2 .99 5.7 .100 - - VIII .101 .103 .112 .113 .114 114 114 .115 .116 - IX - Content Abstract (In Chinese) . I Abstract (In English).III Chapter 1 Introduction .1 1.1 Background .1 1.2 Recent advance of ECM technology.2 1.3 Research and development on micromachining .5 1.3.1 Traditional cutting micromachining.6 1.3.2 Non-traditional micromachining.6 1.4 Latest research and development on micro-ECM .9 1.4.1 Oversea latest researches and development on micro-ECM .9 1.4.2 Domestic latest researches and development on micro-ECM.14 1.5 Purpose and significance of the present research .16 1.5.1 Source of this project.16 1.5.2 Purpose and significance of this project .16 1.6 Main contents of the research.17 Chapter 2 Study on some basal problems of micro-ECM .18 2.1 Principle of ECM.18 2.2 Characteristics of micro-ECM.19 2.3 Fabrication experiment of micro probes.22 2.3.1 Experimental method and shaping mechanism.22 2.3.2 Experimental results and analysis.23 2.4 Machining mechanism of micro-ECM using ultra short pulses.24 2.5 High-frequency short-pulse micro-ECM .26 2.5.1 Special characteristics of high-frequency short-pulse current .26 2.5.2 Reducing machining gap and homogenizing electrolyte .27 2.6 Electrolyte choice in micro-ECM.28 2.6.1 Influence on micro-ECM by using different electrolytes.28 2.6.2 Special characteristics of passivation electrolyte.28 2.7 Primary factors influencing machining speed.30 - - XContent 2.8 Primary factors influencing machining precision .32 2.9 Primary factors influencing surface quality.34 2.10 Mechanism of micro sparks occurrence .36 2.11 Demands fro micro-ECM system.37 2.12 Summary .38 Chapter 3 Design and realization of micro-ECM system .39 3.1 Design of micro-ECM system .39 3.1.1 Design of structural arrangement of the machine tool .41 3.1.2 Design of main parts of the machine tool .42 3.2 Fabrication of micro electrode for micro-ECM .45 3.3 Electric hardware makeup of micro-ECM system .46 3.4 Design and realization of high-frequency short-pulse power supply.47 3.4.1 Logic producing pulses and power amplitication .48 3.4.2 Regulating machining voltage unit .50 3.4.3 Circuit of machining state detection and interface circuit .50 3.4.4 Protection circuit of micro-energy pulsed power supply .52 3.4.5 Contact sensing circuit .53 3.5 Control system of machine tool for micro-ECM .53 3.5.1 Makeup of control system for micro-ECM.54 3.5.2 Realization of servo system for micro-ECM .55 3.5.3 Servo control strategy for micro-ECM .57 3.6 Summary .57 Chapter 4 Study on drilling micro holes by micro-ECM.59 4.1 Analysis on machining methods of micro holes .59 4.2 Drilling micro holes using rotary micro electrode with micro-ECM.60 4.3 Principle of drilling micro holes with micro-ECM.61 4.4 Servo control strategy for drilling micro holes.63 4.5 Machining experiments of drilling micro holes.64 4.5.1 Electrochemical reaction of cathode and anode.64 4.5.2 Example of drilling micro holes .65 4.6 Main factors influencing machining efficiency .66 4.6.1 Influence of machining voltage on machining efficiency .66 4.6.2 Influence of electrode rotating speed on machining efficiency .67 - XI - 4.6.3 Influence of frequency and duty ratio on machining efficiency .68 4.6.4 Influence of electrolyte additive on machining efficiency.68 4.7 Influence of fashion of micro electrode on drilling micro holes.70 4.7.1 Drilling micro holes using no rotating electrode .70 4.7.2 Drilling deep micro holes using rotating edge-cut electrode .71 4.8 Influence of main machining parameters on machining precision.74 4.8.1 Influence of machining voltage on machining gap .74 4.8.2 Influence of electrolyte concentration on machining gap .75 4.8.3 Influence of feed speed on machining gap .76 4.8.4 Influence of machining frequency on machining gap.77 4.8.5 Influence of duty ratio on machining gap.78 4.8.6 Influence of electrode diameter on machining gap .79 4.8.7 Some samples of drilling micro holes with micro-ECM.79 4.9 Summary .80 Chapter 5 Study on micro-EC milling.81 5.1 Machining methods of machining microstructures with micro-ECM.81 5.1.1 Micro-EC sinking by micro contoured electrode.81 5.1.2 Micro-EC milling by simple column electrode.82 5.2 Machining experiments of micro-EC milling .85 5.2.1 Preparation of micro electrode for micro-ECM.85 5.2.2 Fashion of servo feed control for micro-EC milling.85 5.2.3 Feasibility experiment of micro-EC milling .86 5.3 Improve surface quality by reducing the machining gap .87 5.4 Process experiments of micro-EC milling .89 5.4.1 Influence of feed speed on side machining gap .89 5.4.2 Influence of different electrolytes on side machining gap.91 5.4.3 Other factors influencing micro-EC milling .92 5.4.4 Some samples machined by micro-EC milling .94 5.5 Process modeling for predicting the shape in micro-EC milling .95 5.6 Study on technology for micro-EC milling based on CAD/CAM of UG .96 5.6.1 Generation of G codes by using CAD/CAM system of UG.97 5.6.2 Sample of machining experiment .99 5.7 Summary .100 - - XIIContent Conclusions .101 References .103 Appendix .112 Publications in the period of Ph.D. study .113 Statement of copyright .114 Letter of authorization 114 Management of secret 114 Acknowlegement.115 Resume .116 - XIII - 1 1 1.1 1834 20 20 1921 Gusseff ECM (Electrochemical Machining) 1, 2 3 20 60 70 80 (PECM ) (DECM ) f ( ) t on (ms ) 20 90 MOSFET IGBT (kHz ) (s ) (HPECM) - 1 - 4-6 7-12 1.2 (s ns ) MOSFET, IGBT (kHz ) (s ) ( ) 0.05 mm 0.05 mm Ra0.40m 13,14 MOSFET 1000A 2000A 15 - 2 - 1 1-1 a) 16-20 GE 1-1 b) 19 a) b) 1-1 19 Fig.1-1 Schematic diagram of NC ECM and ingetral wheel machined by NC ECM 19 21-26 1-2 a) - 3 - 1-2 b) K. Katahira ELID AlN 25 a) b) 1-2 ELID AlN 25 Fig.1-2 The setup of ELID and AlN ceramics workpiece ground by ELID 25 27-29 A.K.M. Desilva 2m Ra0.01 1-3 a) 85m 29 Wiba 1-3 b) 28 27,28 Fig.1-3 Cover of electric shaver and miniature part machined by precision ECM 27, 28 - 4 - 1 30-39 600m 100m 1-4 a) 35 1-4 b) 36 a) b) 1-4 35, 36 Fig.1-4 Application example of micro-ECM 35, 36 1.3 39-43 MEMS 44 MEMS MEMS LIGA 1m - 5 - m MEMS LIGA X X LIGA 45-53 (MEMS) 1.3.1 54-64 10000150000 r/min (1m) 54 1.3.2 ( - 6 - 1 ) 65 10m 65-68 ( ) 1m Ra 0.030.10m 10m 1020 69 70,71 10 8 10 10 W/cm 2 - 7 - 1m 50 20 50 3m 0.1m( 0.01m 3nm) 10 6 10 9 W/cm 2 2.5mm 50 0.4mm 72 73-75 - 8 - 1 1.4 1.4.1 1.4.1.1 IBM 1-5 a) 55m 20m Na SO NaCl NaNO 2 4 3 - 9 - 76-78 79 1-5 b) 200m 5M NaNO 3 50m IBM 76 a) b) 1-5 a) b) IBM 76 Fig1-5 a) Micro-hole and microstructures machined by through-mask micro-ECM b) Letters machined by electrolyte jet 76 1.4.1.2 Chikamori 0.0156m/step 1-6 a) 200m 170m 3.8V - 10 - 1 200ms 160ms 14g/l NaClO 10m 1-6 b) 500m 10 90 2 4 3 80 B. Bhattacharyya 1-7 a) 1.5%NaNO 3 10V 50Hz 15ms 1-7 b) a b) 1-6 80 Fig.1-6 The micro-hole and square micro-electrode machined by micro-ECM 80 a) b) 1-7 33 Fig.1-7 Experimental setup of micro-ECM and micro hole machined by micro-ECM 33 - 11 - 33 1.4.1.3 R. Frster 1-8 a) 50Hz 200m 87.8 50m 1-8 b) 81 a) b) 1-8 81 Fg.1-8 Micro electrode and micro-ECM machined cavity with vibrating electrode 81 1.4.1.4 82-88 Young- Mo Lim Soo Hyn Kim - 12 - 1 1-9 a) 4mm 50m 1m 88 1-9 b) 30m 29 a) b) 1-9 29, 88 Fig.1-9 Micro-pin machined by micro-ECM 29, 88 1.4.1.5 2000 Fritz-Haber Rolf Schuster ( ) 1m 9, 89, 90 1-10 a) Rolf Schuster Ni 90 1-10 b) 0.01M HClO 4 +0.1M CuSO 4 10m 10m15m15m 5m10m12m 9 1-10 c) 0.2M HCl 2m 3ns a) b) c) 9, 89, 90 Fig1-10 Micro parts machined by ultra-short pulse micro-ECM 9, 89, 90 - 13 - 5m 89 Rolf Schuster 20nm 90 LIGA 0.1M H 2 SO 4 1-11 60m 304 60ns 1s 20m40m85m 91 Rolf Schuster STM Au 5nm 0.31nm 92-93 1-11 91 Fig.1-11 Micro structures machined by micro-ECM with micro-dish electrode 91 1.4.2 - 14 - 1 1.4.2.1 (CVD) 10% NaClO 3 0.5ms 180m 300m 220m 1-12 a) 1-12 b) 300m 150m (CVD) 95 a) b) 1-12 a) b) 95 Fig.1-12 The micro-hole and microstructure machined by micro-ECM 95 1.4.2.2 1-13 a) “ECM” 30m 1-13 b) 30m 40m 96 a) b) 1-13 96 Fig. 1-13Micro-letters and micro cross groove by micro-ECM 96 - 15 - 1.4.2.3 (CELT: Confined Etchant Layer Technique) CELT IC LIGA 97, 98 1.5 1.5.1 1.5.2 LIGA MEMS - 16 - 1 10m MEMS MEMS 1.6 (1) (2) (3) (4) (5) - 17 - 2 (micro Electrochemical Machining micro-ECM) (1m1mm) m-0.1mm 10,11 2.1 (10 -1 nm ) ( ) 9 2-1 H 2 M +n i e i e 2-1 Fig.2-1 The principle of electrochemicalmachining - 18 - 2 10 -10 m M M +n M V It Q M = = (2-1) It It V = = (2-2) M V Q I t 2-1 2-2 2.2 - 19 - 102,103 1999m 1 - 20 - 2 PVD CVD SiC Si 3 N 4 95 2 2 410V 0.11mm 1020m m - 21 - 2.3 2m 99 NaOH 2.3.1 2-2 2-2 Flg.2-2 Sketch map of Experimental setup NaOH 30 2V 20kHz 25s NaOH 35g/L 0.5mm NaOH - 22 - 2 100 + + + 6e O 4H WO 8OH W 2 2 4 + + 2OH H 2e O 2H 2 2 87 WO 4 2- OH - 2.3.2 R 0.01m 2-3 60m 2-3 CCD Fig.2-3 micro electrode and nano-scale probe machined by micro-ECM - 23 - 2-4 2-4 a) STM AFM a) b) 2-4 Fig.2-4 Surface contrast between two probes machined by micro-ECM and micro- EDM respectively 2.4 / RC 2-5 = cd c d - 24 - 2 R n R w 9 2-5 101 Fig2-5 Principle of ultra-short pulsed micro-ECM 101 0 c t t t c 0 0 ) exp( 1 ( ) ( = 2-3 ButlerVolmer ) exp( ) exp( 0 0 0 cd t f i f i i c = 2-4 i 0 f f=F/(RT) F R T 2-4 91 Rolf Schuster 1m 20s 5m 9,101 - 25 - 2.5 2.5.1 2-6 2-7 i i di d di d 2, 105, 106 2-6 2-7 2 Fig.2-6 Pulsed power supply Fig.2-7 Current efficiency vs current density 2 - 26 - 2 1020m 2.5.2 2-8 J. Kozak 107 107 Fig.2-8 Relation between feed rate and machining gap at different pulse width 107 d /d - 27 - 107-110 2.6 2.6.1 1020m ( HCl H 2 SO 4 ) 104 NaCl ( NaNO 3 NaClO 3 ) NaHSO 4 Na 4 P 2 O 7 2.6.2 (NaNO 3 ) (NaClO 3 ) (NaCl) - 28 - 2 NaClO 3 Fe E-i 2-9 Fe NaCl 2-9 Fig.2-9 Polarization curve Fe NaClO 3 NaCl 2-10 Fe NaClO 3 Fe NaCl 100% 2-9 NaClO 3 cd 2-10 i B i B Fig.2-10 Current density vs current efficiency Fig.2-11 Current density vs speed - 29 - NaClO 3 NaClO 3 NaNO 3 NaClO 3 NaCl 100% NaClO 3 2-10 NaClO 3 i i B 2- 11 NaCl NaClO 3 NaNO 3 ( NaNO 3 NaClO 3 ) 2.7 F A I i = = 2-5 = = E U U i R 2-6 It wF = 2-7 - 30 - 2 i A F U R U E I w t (2-5) (2-7) ( ) (2-5) NaCl 100% -i NaNO 3 NaClO 3 -i i i i B (2-5) i ( ) - 31 - 2.8 1020 m 10m f b ) ( E U D = 2-8 + + = f f b b ) ( ) ( d E U E U d d d d b U - E D i f - 32 - 2 ( ) 32 (2-6) (2-8) ( HCl H 2 SO 4 ) (MHz) 2-12 a) R.Schuster Ni 0.2M HCl R.Schuster 200 MHz 500ps 0.1M HCl 40nm 2-12 b) 89 - 33 - a) b) 2-12 89 Fig.2-12 The grooves and microstructure machined by ultra-short current 89 2.9 PH PH PH PH - 34 - 2 111 (4) i di iA iA d I dI tI tdI w dw = = = = ) ( 2-10 i di I dI tI tdI V dV = = = 2-11 A i i di i - 35 - 2.10 112 - 36 - 2 2.11 (1) (2) 1020 m 0.1 m (3) 1 m (4) - 37 - 2.12 - 38 - 3 3 1 3.1 0.10.7mm - 39 - 1 2 3 1m 3 4 5 3-1 CCD 3-1 Fig.3-1 The structure of overall design of micro-ECM system 3-2 - 40 - 3 3-2 Fig.3-2 The principle map of micro-ECM experimental setup 3.1.1 3-3 X Y Z O X Y Z 3-3 Fig.3-3 The solid figure of designed result of the multifunction machine and coordinate - 41 - Z Z Y Y X X Z Z Z 0.002mm/100mm 3.1.2 3.1.2.1 X Y Z - PI M-511.DD 3-1 3-1 Table 3-1 Performance index of servo mechanics (mm) m (m) m/mm m/mm (mm/s) M- 511.DD 102 0.1 0.1 1/100 1/100 50 0.05m - 42 - 3 0.1m / ( 1m/100mm) ActiveDrive TM PWM PWM 125mm/s 3.1.2.2 113, 114 3-4 T 3-4 Fig.3-4 The worktable of the setup for micro-ECM - 43 - 3.1.2.3 NSK 1m 3-5 1 00025 000rpm 3-5 Fig.3-5 The spindle kit of the setup for micro-ECM - 44 - 3 3.1.2.4 NaClO 3 Cl Cl PH 3-6 PH 3-6 Fig.3-6 The circulation system of electrolyte 260 CCD 3.2 - 45 - (WEDG) 3-7 a) b) 3-7 Fig.3-7 On-line fabrication of micro-electrrode on multifunction tool 3-8 10m m 1m 3-8 Fig.3-8 Micro electrode machined by micro-EDM for micro-ECM 3.3 3-9 - 46 - 3 Fig.3-9 The buildup of electric control hardware for micro-ECM PI C- 842 PIC A/D CHB-25NP/SP5 C-842 3.4 - 47 - 3-10 A/D 3-10 Fig.3-10 The principle and the structure of pulse power supply for micro-ECM 3.4.1 ( ) Scenix 50M Scenix 74F07 - 48 - 3 1 1MHz 2 3 12V MOSFET TPS2812 MOSFET TPS2812 TPS2812 MOSFET MOSFET MOSFET IR MOSFET IRF730 t r t f 15ns 14ns IRF730 TPS2812 +12V 74F07 Scenix +5V 220V 7812 +12V 7805 +5V PIC PIC 8 SX28AC 50MB 5000 /s - 49 - 3.4.2 220V 010V MOSFET IRF730 Tektronix 200M 100ns 010V 01A 3.4.3 A/D 3-11 3-11 Fig.3-11 The detection circuit of machining state of pulse power supply ( - 50 - 3 ) ( ) A/D A/D PC CHB-25NP/SP5 CHB-25NP/SP5 3-2 3-2 CHB-25NP/SP5 Table 3-2 Performance index of CHB-25NP/SP5 1A 200 25mA 100kHz 0.1% 0+70 1215V DC 0.1% ms A/D 12Bit A/D A/D 9s PIC - 51 - PIC PIC A/D 3.4.4 3-12 3-12 Fig.3-12 The protection circuit of pulse power supply R1 R2 V R R R V 2 1 2 Samp + = V Samp R 1 R 2 V Scenix V Samp ( ) V ref V Samp V ref Scenix - 52 - 3 s 3.4.5 x y z 3-13 012V 12V D R 3-13 Fig. 3-13 Contact sensing circuit 3.5 - 53