CENTRE FOR TOOL BASED MICRO MACHINING RESEARCH (CTBMMR)

ABOUT MICRO MACHINING 

Micro systems find wide applications in bio-medical electronics, optics, micro-mechanics, micro fluidics, dies, moulds etc. Component parts used in these systems have feature dimensions in micrometers and part volumes less than 1 mm3. Manufacture of these components with high accuracy is a challenge.

THRUST AREAS 

  1. Micro-Electro-Discharge

    Machining (micro-EDM)

 Micro EDM is a thermo-electric process for machining electrically conducting materials regardless of their mechanical properties. Being a noncontact process, micro-EDM is one of the best alternative methods that can be used for machining high aspect ratio 3D micro structures.

 2. Tool based Mechanical micromachining

Tool based mechanical micromachining technology is gaining importance in Micro-Electro Mechanical System device fabrication because of its ability to machine 3D micro features on different engineering materials.


DISCRIPTION

In micro-EDM, the pulse energy  supplied is of the order of few tens of micro Joules (μJ) and the discharge duration is a few micro seconds (μs). During machining, tool and work wears out and the spark gap increases. To maintain an optimum spark gap for stable machining condition, tool should be fed at a rate equal to the sum of Material Removal Rate (MRR) and Tool Wear Rate (TWR). Since the optimum spark gap is few micrometers, a precise control over the tool feed is essential in micro- EDM.

                                                                                                     Photograph of micro-EDM Set up

In this research work a prototype micro Electrical Discharge Machine (micro-EDM) is developed with FET based pulse generator and an amplified Piezoactuator (APA 400M, Cedrat Technologies, France) for tool feed has been developed in the centre. An in-situ measurement system based on electrical contact sensing is incorporated in the setup. During tool wear and blind hole depth measurement, tool positioning is  achieved by contact sensing and tool displacement is obtained by a Laser- Optical Displacement Measuring System (ILD 1402-10, Measuring range 10mm, 1 micrometer resolution, from Micro-Epsilon, Germany).  

The tool based mechanical micromachining center with piezoactuated workpiece feeding system has been developed. A high speed spindle (HSS) is used to rotate the micromilling/drilling tool at a speed of 12,000 to 60,000 rpm. A thermoelectric based liquid cooling system is developed to control the temperature of the high speed spindle at a set value. Along with the X-Y positioning system, the workpiece is also mounted on a piezoactuator to provide Z-axis motion during machining operation. An electrical continuity based tool-workpiece contact detection system is developed to overcome premature tool failure during initial tool registration with the workpiece. Based on the developed tool- workpiece contact sensor, an in-situ measurement system is developed to measure the micromachining depth. Experiments have been conducted to measure the performance of spindle cooling system and in-situ measurement system.

                                                             

Tool based Mechanical  Micromachining set-up

High Speed Spindle Cooling system


    ACHIEVEMENTS

The research work entitled “Development of Micro-Electro- Discharge machine (Micro-EDM) with Piezoactuated Tool Feed System presented by N. M. A. M. Institute of Technology, Nitte has been judged as the fifth best research work among the 100 research works presented  in Academia-Industry Pavilion at IMTEX-2014 exhibition held in Bangalore. This research work was jointly funded by Visvesvaraya Technological University Belgaum and Nitte Education Trust, Mangalore.


A jury committee formed by Indian  Machine Tool Manufacturer's  Association (IMTMA) is reviewing the research

work presented by NMAMIT, Nitte at IMTEX-2014 held at Bangalore, in January 2014

PUBLICATIONS

1.  ‘Investigations on a directly coupled Piezoactuated tool feed system for Micro-Electro-Discharge Machine, International Journal of Machine Tools and Manufacture, 49,  1197-1203

 2. Wear ratio based tool wear compensation for micro electro discharge machining of silicon through process simulation, Journal of Micro/Nanolithography MEMS and MOEMS, 9, 013040-46, 2010  

3. ‘Estimation    of    tool    wear compensation during micro-electro- discharge machining of silicon using process simulation”, Proceedings of SPIE, Symposium on MOEMS- MEMS 2010, Micromachining and Microfabrication Process Technology XV, San Francisco, California, USA, January, 2010, Vol. 7590

  4. “Development of micro-EDM Incorporating In-situ Measurement System Proceedings of International Conference on Advances i Manufacturing and Materials Engineering,    (AMME 2014) organized by NITK, Surathkal during   27th to 29th March 2014.

    
RESEARCH FACILITIES

1. 200W DC Motor with ER8 collet and speed controller  Micro-EDM spindle drive with ER8 collet is used to hold and rotate the   micro   tools   at   a   speed   of  0-12000rpm.


Micro-EDM Spindle drive with  speed controller

2. Computer controlled XY stage Motorized, Computer controlled XY stage is used for positioning the workpiece with respect to tool.


                                                                                                                   Motorized XY stage
3. Laser Displacement Sensor  ILD 1402-10 with measuring range of 10 mm and 1 micrometer resolution, is used to measure the tool feed, tool wear and the depth of machining.


ILD 1402-10 Laser Displacement Sensor

4. Current Probe with Amplifier The current probe is used to measure the gap current during micro-electro discharge machining process.


TCP 305 Current Probe with TCPA  300 Amplifier

5. Data Acquisition System  The DAQ system is used for in-situ measurement of tool feed, tool wear and machining depth  during micro- EDM.


NI USB 6251 Data Acquisition System

6. Metallurgical Microscope with High-Definition Camera: Optical Microscope (LEICA DM750M, magnification 500X, Leica Mikrosysteme-Germany) is used for obtaining the image of the micro-features machined using micro-EDM process and the feature dimensions are measured using Leica Application Suit software.


DM750M Metallurgical Microscope with ICC50 HD Camera

7. Piezoactuator with driver   APA400M piezoactuator from CEDRAT Technologies, France, is used to feed the tool during machining and in-situ measurements.

APA400M Piezoactuator with driver

8. High Speed Spindle  The high speed spindle (GDZ-48-300, 75V 4.5A, AC 3-Phase 1000Hz) is used to rotate the micromilling/drilling tool  in  the  range  of  12,000  to   60,000rpm. The spindle speed is controlled by a variable frequency drive (CGK2D00150, 1.5kW, 0-240V,  0-1500Hz, 7.0A).

High Speed Spind le with Variable Frequency Drive

9. Piezoactuator and driver APA230L piezoactuator (Dis place- ment 236mm, -20 to 150V, 2-4nm resolution, from Cedrat Technologies, France) is used to feed the work piece   in Z-direction towards the tool.


APA230L Piezoactuator and drive

10. Spindle cooling system    A thermoelectric based liquid cooling system is developed to control the temperature of the high speed spindle at a set value.


Thermoelectric based High Speed Spindle Cooling System

11. NI PCI 6221 Data Acquisition System  NI PCI6221 DAQ card has 32 analog inputs of 16 bits resolution, 250 kS/s, 48 digital I/O lines, and four analog outputs. It is used to acquire the tool feed data, spindle temperature, spindle speed data during micromachining experiments.

NI PCI 6221 DAQ with SCB68 Connector Block

Dr. Omid Ansary, Senior Associate  Dean for Academic Affairs, Penn State

Harrisburg visiting Micromachining Research Laboratory in the MEchanical Engineering Department.