27-11-2012, 03:41 PM
MICRO MACHINE TOOLS
MICRO MACHINE.ppt (Size: 3.01 MB / Downloads: 176)
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
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
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
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