GURAV TUSHAR TUKARAM JITHISH K S ME11M113 ME11M116 MICRO MACHINE TOOLS GURAV TUSHAR TUKARAM JITHISH K S ME11M113 ME11M116

Micromachining Basics • Refers to techniques for fabrication of 3D structures on the micrometer scale • Applications include MEMS devices e.g. airbag sensor, medical devices, micro-dies and molds, etc. • Most methods use silicon as substrate material

Micromachining Micromachining is the basic technology for fabrication of micro-components of size in the range of 1 to 500 micrometers

Mechanical Micromachining • Lithography and/or etching methods not capable of making true 3D structures e.g. free form surfaces • Also, limited in range of materials • Mechanical machining is capable of making free form surfaces in wide range of Materials Two approaches used to machine micron and sub-micron scale features – Design ultra precision (nanometer positioning resolution) machine tools and cutting tools • Ultra precision diamond turning machines – Design miniature but precise machine tools • Micro-lathe, micro-mill, micro-EDM, etc

Ultra Precision Machine Tools

Miniature Machine Tools Micro Lathe Micro Mill Micro Drill

Micro Cutting Tools Cutting tools made by Focused Ion Beam (FIB) machining

Basic Components of Micro machine Tools

Actuation and Control Unit Spindle supported by appropriate bearings and coupled to a drive of variable speed Consists of actuation mechanism and drives for machine tool slides Miniaturization of Tools Requires cutting tools of smaller size and they must be stronger than work material. Metal removal rate is very small, the breakage strength of work material approaches its theoretical value G/2π unpredictable tool-life and premature tool failure

Setting and Resetting of Work At micro level, loading and unloading of work cannot be done by hand. Hence dedicated manipulators to handle workpieces are required along with the micro- machine Machine Surveillance Microscope or computer controlled cameras are required along with the micro-machine system to monitor or to grasp the working situation directly. This is usually achieved by an optical microscope connected to display unit

Micro lathe

Design of a proposed micro-lathe After a careful study and analysis of various micro- machines or micro-mechanisms developed earlier. It is therefore proposed to develop a micro-lathe with following preliminary specifications

Micro Lathe System 1. Human handling of machine: The cutting equipment is assembled and operated by human hand. The cutting machine is a kind of interface that connects the work piece and the human operator. Even though the work is very small, a suitable size of working machine is necessary for human operating. 2. Observation: In order to grasp the working situation and the shape directly, it is necessary to observe with an optical microscope or an electron microscope while working. Using an optical microscope is preferable provided that the cutting status is visible because handling of the work is easier in an open space.

3. Setting or resetting of the work piece: Assembling and disassembling of the work piece must be convenient and the connection with the next working processes should be conveniently arranged. 4. Working accuracy: When the dimension of the work piece becomes small, the dimensional tolerance becomes very strict. For example, the dimension tolerance of a fitting shaft 10 mm in diameter is about 15 mm. The ratio of the tolerance to the total size is 0.0015 5. Miniaturization of tool point: Without suitable micro machine tools, micro machining cannot

Structure of a micro lathe turning system Spindle unit Main shaft is supported by two micro bearings preloaded by a spring to reduce the amount of whirling in rotation. A DC motor, approx. 0.5 W, is directly connected to the spindle by a coupling. The rotation speed of the spindle is variable from approx. 3000 to 15,000 rpm by adjusting the input voltage on the micro motor. A four-jaw collet chuck mounted on the end of the spindle. The chuck grips a work piece at the shank of 0.3 mm in diameter

Cutting tool unit As a micro point tool matching to the micro work piece, a diamond probe used in a scanning tunneling microscope is applied for the cutting tool The trigonal pyramid of the single diamond, mounted in a rod 0.25 mm in diameter, is employed with the rake and the included angles 0°and 60° respectively. The tool shaft is fixed on the tool rest which can be rotate by a micro handle.

Advantages As the name implies, micro lathes are smaller than full sized lathes More affordable Easily fit in a small store, basement, or garage Reduced motor and internal gear noise - quieter operation Better overall finish and quality

DISADVANTAGES Less precise in cutting than a standard lathe Limited in the type of objects that they can shape

Application Engineering parts Micro-filters Micro-needles Micro-probes Locksmithing Jewels

Case study: Development of a CNC micro-lathe for bone micro implants Cortical bone samples with controlled features had to be adequate to the correct size to be micro machined in the micro-lathe; these samples are human cortical bone cylinders and were turned controlling the operating conditions to remain with the same chemical composition. Cortical bone porosity is shown in at levels below 100 μm is evident that the size of the porous is close to the size of the entire implant and this could affect its machinability, the architecture and the behavior of the implant interacting with the receptor

Interpolation mode

Contour cutting

Deflection of work piece under cutting force

Conclusion Mechanical machining is capable of making free form surfaces in wide range of materials. Smaller tool edge radius induces lower stresses in the chip separation zone which will lead to lower cutting forces but it induces higher stresses in the machined surface. An optimum value for tool edge radius can be found. Micro turning with the CNC micro-lathe has been proved as a method for the fabrication of bone microimplants with controlled geometries

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