Abrasive-Waterjet Machining of Composites, Proceedings 2009 Amererican WJTA Conference and Exposition, Houston, TX, August 18-20... Versatility of Waterjet Technology: from Macro and Mi
Trang 1Micro Abrasive-Waterjet Technology 229
4.6 Non-metal samples
Several samples made of non-metal materials were machined with the beta and R&D nozzles to demonstrate the material independence of waterjet technology The materials included various composites and ceramics with machinability indexes ranging from about
700 to 4 (refer to Fig 8) Figure 23 shows miniature samples machined from various composites using the 254-m nozzle (Liu et al., 2010a) The material used for each sample is given in the figure subtitle, along with a number in parentheses that is the thickness of the part in millimeters Details of small features on the order of 100 µm in size remain sharp and crisp There is no delamination or chipping on the edges The thickness of the wheel of the smallest bike is about 200 µm The carbon fiber (dark) and the epoxy (translucent) layers on the wheels are clearly identifiable in Fig 23e
a G-10 (3.2) b Carbon epoxy (4.8) c Fiberglass (2.4)
d G-10 (3.2) e Carbon epoxy (4.8) f Carbon fiber (2.4) Fig 23 AWJ-machined miniature composite parts Numbers in parentheses are thickness of part in mm Scale: 1 mm/div (Liu et al., 2010a)
Figure 24 illustrates features machined with the 254-m nozzle in an alumina plate 0.64 mm thick (M ≈ 4) The sharp and crisp edges of all features are evident
Fig 24 Features machined with the 254-m nozzle in alumina thin plate (Liu, 2009)
Trang 24.7 Multi-nozzle platform
The downsizing of an AWJ nozzle results in a reduction in the flow rate of the waterjet Depending on the size of the orifice, the number of nozzles that can be supported by a pump increases accordingly From Fig 2, a 22.4-kW pump that is capable of supporting one 360-m orifice operating at 380 MPa with a water flow rate of 3.4 l/min is capable of supporting four 254-m nozzles operating at the same pressure A multi-nozzle platform on which four 254-m nozzles could be mounted was designed, assembled, and tested, as illustrated in Fig 25 The platform was subsequently delivered for beta testing at a specialty jewelry manufacturing shop With the nozzles operating in tandem, four identical parts can
be machined simultaneously to boost productivity Among the advantages of using the
254-m nozzle together with 320-mesh garnet are that the amplitude of the striation is small and the finished parts are nearly free of burrs
Fig 25 Four nozzles mounted on a platform for increased productivity (Liu et al., 2011b)
5 Conclusion
Waterjet technology has inherent technological and manufacturing merits that make it suitable for machining most materials from macro to micro scales It has been established as one of the most versatile precision machining tools and has proven amenable to micromachining This technology has emerged as the fastest growing segment of the overall machine tool industry in the last decade.3
The smallest features that can be machined with state-of-the-art commercial AWJ systems are limited to greater than 200 µm Further downsizing of AWJ nozzles for machining features less than 200 µm has met with considerable challenges, as described in Section 3.1 These challenges, which are due to the complexity of the jet flow as the AWJ flow characteristics change into microfluidics, include nozzle clogging by accumulation of wet abrasives, difficulty in the fabrication of mixing tubes with exit orifices less than 200 µm, the degradation in the flowability of fine abrasives, and other relevant issues
Trang 3Micro Abrasive-Waterjet Technology 231 Novel manufacturing and operational processes and ancillary devices have been investigated and developed to meet the above challenges Miniature beta and R&D nozzles, without the need for vacuum assist and water flushing, have been assembled and tested to machine miniature samples made of various materials for a broad range of applications Many of the samples with basic features as small as 100 µm were machined to demonstrate the versatility of waterjet technology for low-cost micromanufacturing of components for medical implants/devices and microelectronics, for green energy production systems, and for the post-processing of various micro-nano products
The advancement and refinement of µAWJ technology continue Efforts are being made to further downsize µAWJ nozzles for machining features around 100 and 50 µm The goal is
to commercialize a µAWJ system by integrating µAWJ nozzles with a low-cost, low-power, high-pressure pump and a precision small-footprint X-Y traverse A host of accessories are already available to be downsized for facilitating 3D meso-micro machining
6 Acknowledgment
This work was supported by an OMAX R&D fund and NSF SBIR Phase I and II Grants
#0944229 and #1058278 A part of the work was supported by U S Pacific Northwest National Laboratory (PNNL) under Technology Assistance Program (TAP) Agreements:
07-29, 08-02, 09-02, and 10-02 Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF and PNNL Contributions from research institutes and industrial partners by furnishing sample materials and part drawings and by evaluating AWJ-machined parts are acknowledged Collaborators include but are not limited to Microproducts Breakthrough Institute (MBI), MIT Precision Engineering Research Group, Ryerson University, and several OMAX’s customers and suppliers The authors would like to thank their colleagues at OMAX for reviewing the article and proving us with constructive feedback
7 References
Bachelor, G K (1967) An Introduction to Fluid Dynamics, Cambridge University Press,
ISBN 0521663962
Begg, N (2011) Blind Transmembrane Puncture Access: Design and Development of a
Novel Laparoscopic Trocar and Blade Retraction Mechanism, Master Thesis,
Mechanical Engineering Department, MIT, pp 103
Chen, W.-L & Geskin, E S (1990) Measurements of the Velocity of Abrasive Waterjet by
the Use of Laser Transit Anemometer, Proceedings of 10th International Symposium on Jet Cutting Technology, BHRG Fluid Engineering, Amsterdam, Netherlands, October
3-November 2, pp 23-36, 1990
Haerle, F.; Champy, M., & Terry, B (Ed) (2009) Atlas of Craniomaxillofacial Osterosynthesis:
Microplates, Miniplates, and Screws, 2nd Ed., Thieme, New York, pp 225
Hashish, M (2008) Abrasive-Waterjet Machining of Composites, Proceedings 2009
Amererican WJTA Conference and Exposition, Houston, TX, August 18-20
Trang 4Henning, A.; Miles, P., Stang, D., (2011a) Efficient Operation of Abrasive Waterjet Cutting
in Industrial Applications, Proceedings of 2011 WJTA-IMCA Conference & , Houston,
Texas, September 19-21
Henning, A.; Liu, H.-T., & Olsen, C (2011b) Economic and Technical Efficiency of High
Performance Abrasive Waterjet Cutting, to appear in ASME Journal of Pressure Vessel & Piping
Jiang, S.; Popescu, R., Mihai, C., & Tan, K., (2005) High Precision and High Power ASJ
Singulations for Semiconductor Manufacturing, Proceedings of 2005 WJTA Conference and exposition., Houston, Texas, August 21–23, Paper 1A-3
Lamb, H (1993) Hydrodynamics (6th Ed.) Cambridge University Press, ISBN 9780521458689 Liu, H.-T (1998) Near-Net Shaping of Optical Surfaces with Abrasive Suspension Jets,
Proceedings of 14 th International Conference on Jetting Technology, Brugge, Belgium,
September 21–23, pp 285-294
Liu, H.-T (2010) Waterjet Technology for Machining Fine Features Pertaining to
MicroMachining, Journal of Manufacturing Processes, Vol.12, No.1, pp 8-18
(doi:10.1016/ j.jmapro.2010.01.002)
Liu, H.-T & McNiel, D (2010) Versatility of Waterjet Technology: from Macro and Micro
Machining for Most Materials, Proceedings of 20 th International Conference on Water Jetting, October 20–22, Graz, Austria
Liu, H.-T & Schubert, E (2010) Piercing and/or Cutting Devices for Abrasive Waterjet
Systems and Associated Systems and Methods, U S Provisional Patent Application
#612348007.US
Liu, H.-T.; Hovanski, Y., & Dahl, M E (2011a) Machining of Aircraft Titanium with
Abrasive-Waterjets for Fatigue Critical Applications, to appear in ASME Journal of Pressure Vessel & Piping
Liu, H.-T.; Schubert E., and McNiel, D (2011b) AWJ Technology for Meso-Micro
Machining, Proceedings of 2011 WJTA-IMCA Conference and Exposition., Houston,
September 19-21
Liu, H.-T.; Miles, P., & Veenhuizen, S D (1998) CFD and Physical Modeling of UHP AWJ
Drilling, Proceedings of 14 th International Conference on Jetting Technology, Brugge,
Belgium, September 21–23, pp 15-24
Liu, H.-T.; Hovanski, Y., Dahl, M E & Zeng, J (2009a) Applications of Abrasive-Waterjets
for Machining Fatigue-Critical Aerospace Aluminum Parts, Proceedings of ASME PVP2009 Conference, Prague, Czech, July 26-30
Liu, H.-T.; Gnäupel-Herold, T., Hovanski, Y., & Dahl, M E (2009b) Fatigue Performance
Enhancement of AWJ-Machined Aircraft Aluminum with Dry-Grit Blasting,
Proceedings 2009 American WJTA Conference, Houston, Texas, August 18-20
Liu, H.-T.; Hovanski, Y., Caldwell, D D., & Williford, R E (2008a) Low-Cost
Manufacturing of Flow Channels with Multi-Nozzle Abrasive-Waterjets: A
Feasibility Investigation, Proceedings of 19 th International Conference on Water Jetting,
Nottingham, UK: October, 15-17
Trang 5Micro Abrasive-Waterjet Technology 233 Liu, H.-T.; Schubert, E., McNiel, D., & Soo K (2010a) Applications of Abrasive-Waterjets for
Precision Machining of Composites, Proceedings of SAMPE 2010 Conference and Exhibition, May 17-20, Seattle, Washington, USA
Liu, H.-T., Schubert E., and McNiel, D (2010b) “Development of Micro Abrasive-Waterjet
Technology,” SciTopics, October, pp 4 (http://www.scitopics.com/Development_ of_Mirco_Abrasive_Waterjet_Technology.html) (8 August 2011)
Liu, L X.; Marziano, I., Bentham, A C., Litster, J D., White, E T., & Howes, T (2008b)
Effect of Particle Properties on the Flowability of Ibuprofen Powders, International Journal of Pharmerceutical Oct 1; 362(1-2): pp 109-17 Epub 2008 Jul 4
Miller, D S (2005) New Abrasive Waterjet Systems to Complete with Lasers, Proceedings of
2005 WJTA Conference and exposition, Houston, Texas, August 21-23, Paper 1A-1
Miller, D.; Claffey, S., & Grove, T (1996) Technology Package for Abrasive Waterjets, BHR
Croup Limited
Momber, A W & Kovacevic, R (1998) Principles of Abrasive Water Jet Machining,
Springer-Verlag, Berlin
Olsen, J H (2009) Limits to the Precision of Abrasive Jet Cutting, Proceedings of the 9th
Pacific Rim International Conference on Water Jetting Technology, Koriyama, Japan,
November 20-23, Invited Paper
Olsen, J H (1996) Motion Control with Precomputation, U.S Patent No 5,508,596, April
Olsen, J H (2005) Automated Fluid-Jet Tilt Compensation of Lag and Taper, U S Patent
No 6,922,605, July
Roth, P.; Looser, H., Heiniger, K C., & Buhler, S (2005) Determination of Abrasive Particle
Velocity Using Laser-Induced Fluorescence and Particle Tracking Methods in
Abrasive Waterjets, Proceedings of 2005 WJTA Conference and exposition., Houston,
Texas, August 21–23, Paper 3A-2
Smith, R W.; Hirshberg, M H., & Manson, S S (1967) Fatigue Behavior of Materials under
Strain Cycling in Low and Intermediate Life Range, NASA Technical Note D-1574, NASA Lewis Research Center, pp 25
Stevenson, A N J & Hutchings, I M (1995) Scaling Laws for Particle Velocity in the
Gas-Blast Erosion Test, Wear, 181-183, pp 56-62
Swanson, R K.; Kilman, M., Cerwin, S., & Tarver, W (1987) Study of Particle Velocities in
Water Driven Abrasive Jet Cutting, Proceedings of 4th U.S Water Jet Conference,
ASME, Berkeley, CA, August 26-28, pp 103-107
Trieb, F H (2010) Waterjet Cutting in Austria - History and Actual Status, Keynote Speech,
Proceedings of 20th International Conference on Water Jetting, Graz, Austria, October
20-22, pp 3-17
Trimble, A Z (2011) Vibration Energy Harvesting of Wide-Band Stochastic Inputs with
Application to an Electro-Magnetic Rotational Energy Harvester, Ph.D Dissertation, Mechanical Engineering Department, MIT, June, pp 207
Yu, W.; Muteki, K., Zhang, L & Kim, G (2011) Prediction of Bulk Power Flow Performance
Using Comprehensive Particle Size and Particle Shape Distribution, Journal of Pharmaceutical Sciences., Vol.100, No.1, January (also DOI 10.1002/jps.22254)
Trang 6Webers, N.; Olsen, C., Miles, P & Henning, A (2010) Etching 3D Patterns with Abrasive
Waterjets, Proceedings of 20th International Conference on Water Jetting, Graz, Austria,
October 20–22, pp 51-63
Zeng, J & Kim, T J (1995), Machinability of Engineering Materials in Abrasive Water Jet
Machining, International Journal of Water Jetting Technology, Vol.2, No.2, pp 103-110
Trang 711
Electrochemical Spark Micromachining Process
Anjali Vishwas Kulkarni
Centre for Mechatronics, Indian Institute of Technology Kanpur,
India
1 Introduction
Electrochemical spark micromachining process (ECSMM) is a process suitable for micromachining of electrically non-conducting materials Besides the classic semiconductor technology, there are various methods and processes for micromachining such as Reactive Ion Etching (RIE) (Rodriguez et al., 2003), femto-second pulse laser radiation (Hantovsky et al., 2006), chemical etching and plasma-enhanced chemical vapor deposition (Claire, 2004)], spark assisted chemical engraving (Fasico and Wuthrich, 2004) and micro-stereo-lithography (Rajaraman, 2006) in practice Use of photoresist as sacrificial layer to realize micro-channels in micro fluidic systems is discussed in (Coraci, 2005) All these methods are expensive as they need the vacuum, clean environment and mostly involve in between multi processing steps to arrive at the final microchannel machining results There is a need
of an innovative process which is cost effective and straight forward without employing intermediate processing steps One such process thought of and being researched is electrochemical spark micromachining (ECSMM) process The ECSMM process is a stand alone process unlike others and it does not demand on intermediate processing steps such as: masking, pattern transfer, passivation, sample preparation etc The use of separate coolants is also not required in performing the micromachining by ECSMM
Micromachining needs are forcing reconsideration of electrochemical techniques as a viable solution (Marc Madau, 1997) Another similar process termed as spark assisted chemical engraving (SACE) (Wuthrich et al., 1999) has been employed for the micromachining of glass ECSMM is a strong candidate for microfabrication utilizing the best of electrochemical machining (ECM) and electro discharge machining (EDM) together Applications of ECS for microfabrication can be in the field of aeronautics, mechanical, electrical engineering and similar others It can successfully process silicon (Kulkarni et al., 2010a), molybdenum (Kulkarni et al., 2011c), tantalum (Kulkarni et al., 2011a), quartz (Deepshikha, 2007; Kulkarni et al., 2011a), glass ((Kulkarni et al., 2011a, 2011b); Wuthrich et al 1999)), alumina (Jain et al., 1999), advanced ceramics (Sorkhel et al., 1996) and many other materials
The chapter discusses the details of the experimental set-up developed in the next section The procedure for micromachining using the developed set-up is outlined next The experimental scheme to perform machining on glass pellets (cover slips used in biological applications) is presented Discussion of the micro machined samples is presented This discussion is based on various on line and post process measurements performed The qualitative material removal mechanism is presented based on the results and discussions
Trang 82 Experimental set-up
A functional set-up of the ECSMM process is designed, developed and fabricated as shown
in Figure 1 (Kulkarni et al., 2011b) The main components of the ECS set-up are as follows and are described in the following sub sections:
1 Machining Chamber
2 Power Supply System
3 Exhaust System
4 Control PC
2.1 Machining chamber
The machining chamber houses X-Y table, Z axis assembly, tool feed and tool holder assembly and ECS cell X, Y, Z and tool feed stages are motorized
Fig 1 Photograph of experimental set-up (Kulkarni et al., 2011b)
2.1.1 X-Y table
X-Y table has resolution of 2 μm in X and Y directions and traverse of 100 mm in X as well as
Y directions The guide ways use non-recirculating balls as rolling elements The mechanical drive is a ground lead screw of 400 μm pitch made of aluminium alloy Rotation to the X and Y screws is provided by separate stepper motors The table is mounted on a chrome plated MS plate Chrome plating protects the plate from corrosion The MS plate has mounting tapped holes on a 25 mm grid to mount the ECS cell Bellows are provided to protect the motors and lead screws from the electrolyte splashes and fumes produced
2.1.2 Z axis assembly
The Z axis is automated to move up or down to maintain a constant work piece-tool gap The worm and worm wheel with a gear ratio of 1:38 transmit the power to a lead screw of
200 μm pitch All the parts are fabricated with stainless steel and brass to resist corrosion due to acidic environment It has positioning accuracy of 50 μm and maximum vertical travel of 80 mm
Control PC
Machining Chamber
Power Supplies Exhaust System
Trang 9Electrochemical Spark Micromachining Process 237
2.1.3 Tool feed and tool holder assembly
Tool feed assembly is mounted on Z axis assembly A glass tool holder is designed and developed This tool holder provided the tool insulation and hence reduction in the stray currents This glass tool holder is used to hold the tool wire in place A fixture made of Perspex material is designed and fabricated to hold the tool holder on Z assembly Cu wire
of 200 μm diameter is used as a cathode (tool)
2.1.4 ECS cell
It is a rectangular box of 10 cm x 8 cm x 6 cm dimensions made up of Perspex material It is mounted on X-Y table It houses separate fixture arrangement for graphite anode and work piece holder It is filled with the electrolyte The electrolyte level is maintained at 1mm above the flat surface of the work piece Electrolyte used is NaOH in varied concentration in the range of 14-20 %
2.2 Power supply system
DC regulated power supplies of different ratings are used for driving stepper motors, machining supply and control circuitry Use of separate power supply ensures the noise free operation
2.3 Exhaust system
Proper exhaust system is designed and provided to take away the electrolyte fumes generated during the spark process inside the machining chamber A small DC operated fan
is placed in the machining chamber where the fumes are generated These are carried away
by a hose pipe and thrown away from the room with an exhaust fan
2.4 Control PC
Stepper motors used for driving X, Y, Z and tool feed are all interfaced to motion controller card installed in PC Precise control and drive of the machine is achieved with NI 7834 PCI card and NI 7604 drive board interfaced to a computer Contouring functions in LabVIEW platform are used to carve different shapes of the micro channels [Kulkarni et al., 2008]
3 Experimental procedures
The supply voltage, electrolyte concentration and table speed are the control parameters Pilot experiments are performed to determine the optimum window of these operating parameters
It is observed that sparking occurs at supply voltage of 30 V and above Glass samples break above 50 V supply voltage Hence the working supply voltage range chosen is 40 V – 50 V Use of base solution is preferred over the acidic electrolyte It was observed that in the acidic environment the surface roughness increases The fumes formed of acidic solutions during the electrochemical sparking process are harmful During the pilot experiments it was observed that machining takes place in diluted sodium hydroxide (NaOH) solution as electrolyte The concentration window was decided upon by performing many experiments
to arrive at a permissible concentration range It was observed that machining does not take place below 14% concentration of NaOH Above 20 % concentration of NaOH, the machined surface roughness is notable Hence 14% -20% concentration range for NaOH electrolyte is
Trang 10arrived at Moreover use of low concentration of NaOH as electrolyte makes the ECSMM process as a ‘green process’ Level of electrolyte is maintained at 1 mm above the work piece surface in the ECS cell
The table speed is chosen ranging between 12.5 μm/s – 25 μm/s It is such that the traverse
is not too slow to dig the micro channel and not too fast to miss the micro machining in that region
Micro channels are formed using the ECSMM process on microscopic glass pellets using platinum wire as a tool of 500 μm diameter Pellets are of 180 μm thickness, 18 mm diameter circles in size Length of the tool protruding out of the tool holder is 4 mm The gap between the cathode tool electrode tip and the work piece surface is maintained at around 20 μm using the tool feed device mounted on Z-axis The distance between the tool and the anode
is 40 mm Figure 2 shows the photograph of the electrolytic cell with the spark visible at tool tip and electrolyte interface Graphite anode is seen in the cell It is a non consuming electrode
Fig 2 Photograph of the ECSMM cell with graphite anode, tool and work piece The spark
is visible near the tool tip (Kulkarni et al., 2011b)
Experiments are conducted with Voltage, Electrolyte Concentration and Table Speed as the control variables The experiments are conducted in accordance with the central composite design scheme developed by the software ‘Design Expert 07’ to study the response surface The range of the control variables chosen is as shown below:
- Factor 1 (Vs): Supply voltage ranging between 40 V - 50 V
- Factor 2 (EC): Electrolyte Concentration (NaOH) ranging between 14% - 20%
- Factor 3 (TS): Work piece Table Speed ranging between 12.5 µm/s – 25 µm/s
The design resulted in total of twenty one experiments, out of these twenty one experiments, six central experiments were performed at 45 V supply voltage, 17 % electrolyte concentration and 18.75 µm/s table speed as the values for the control variables
The responses measured are: average process current (I), width of microchannel (W) and depth of microchannel (D) formed using ECSMM The scheme of the experiments is as shown
in Table 1 Columns 2-4 list Vs, EC, and TS respectively Columns 5-7 give average current, width, and depth of the microchannels respectively as the responses measured post process