With the advancement of nanotechnology, products continue to develop toward miniaturization, and micro-electromechanical systems with feature sizes of micrometers are receiving more and more attention.
MEMS (Micro-Electro-Machanical Systems) includes micro-mechanisms, micro-sensors, micro-actuators and corresponding processing circuits. MEMS has been applied to precision machinery, optoelectronic communication, image transmission, biochemical medical and information. Storage and other fields, such as micro-gear, plug-in fiber optic connectors, medical micro-pumps, light guides, microlenses, endoscopic parts, microfluidic chips, micro-containers for cell culture, and diffraction gratings in rotation sensors A micro mold is needed. The international MEMS market has developed rapidly in recent years, and the growth rate of China's MEMS market will also accelerate. According to relevant data, the growth rate of MEMS in China is expected to reach 29.2% by 2011.
The so-called micro-mold, if defined in terms of size and manufacturing precision, the micro-mold has the following characteristics: the molded part has a small size, generally a volume of about 1 mm 3 ; the formed microscopic size ranges from a few micrometers to several hundred micrometers, and the surface of the mold is rough. The degree of Ra ≤ 0.1 μm, and the manufacturing precision of the mold is ≤ 1.0 μm.
A micro-die does not necessarily mean a small-sized mold, and a part of a large-volume mold having a microstructure characteristic. This part can also be called a micro-mold. The micro-cavity part of the mold structure can be on a small-volume module. Processing, and then inserting the small module as a module into the large mold, which not only facilitates the micro-machining of the micro-die, but also allows the insert to be replaced to improve the life of the overall mold.
The difficulty in manufacturing micro-die is the processing of micro-cavity or micro-concave structure. Generally, the machining method cannot process parts with too small size, that is, it is difficult to process micro-die of microstructure size, and the dimensional accuracy and surface roughness are up to Less than the requirements of micro-tools, especially the stress of machining, has a great influence on the processing of micro-die. Although micro-turning machines, micro-milling machines, and micro-grinding machines have been developed, they have their limitations and are difficult to fit into micro-cavity processing of micro-die. The main processing technology for micro-mold processing is special processing technology, including light production technology and micro-EDM technology. The new light-making technology developed in recent years, LIGA technology, is a combination of deep X-ray etching, electroforming and plastic molding. It is a high-precision microstructured part processing technology, but LIGA can only process columnar Microstructures, as a means of processing micro-tools, also have certain limitations.
Micro-EDM is widely used in the field of micro-machining, and has become an important development direction in micro-mold processing. Micro EDM micro-die has a number of advantages:
Low stress. This is especially important for the processing of micro-mold and micro-structure parts. Since micro-EDM is processed by micro-pulse energy, it is less stress than general EDM, and is more suitable for micro-mold processing.
Can process high hardness materials. This has a special advantage, which may be unmatched by other processing methods. It is of great significance for improving the life of micro-die.
Can process complex micro cavity molds. The processing of complex microcavities depends on the shape of the electrodes. Unlike LIGA, which can only process cylindrical microstructures, micro-turning is only suitable for processing rotary micro-parts, and micro-grinding is only suitable for processing groove-like microstructures.
No burrs. The microcavity of the micro mold does not allow burrs, and it is very difficult to deburr with burrs.
Micro-EDM processing has a relatively high level of technology, and micro-energy pulse power supply, micro-feed system, servo control system, numerical control system, etc. have been developed and applied in the electric spark micro-hole machining. The surface roughness Ra of micro-EDM can reach 0.05μm. In the processing of micro-cavities or micro-structural parts, the processing precision can reach ≤1μm, which can meet the processing requirements of micro-die.
But a key issue in micro EDM is the fabrication of microelectrodes. So far, the wire electrode electric spark grinding method (WEDG) developed by Professor Zeng Zelong of the University of Tokyo in Japan has been an effective method for making fine electrodes. It is a miniature electrode developed on the basis of EDM reverse copy processing. Production Method. The main features of WEDG:
The 1-line electrode is in point contact with the workpiece (micro-electrode), so the machining shape of the workpiece is only related to the forming motion. Therefore, the cylindrical workpiece only needs single-axis numerical control, and the 2-axis or 3-axis numerical control can process a variety of complicated shapes.
2 Since the wire electrode is rotated (moving), the machining amount is small, so the wire electrode loss is extremely small, which is beneficial to improve the machining accuracy; and the machining accuracy mainly depends on the forming motion accuracy.
3 The discharge part is a point area, which has little influence on the vibration or bending of the workpiece during the discharge process, and is suitable for processing micro-electrodes (workpieces) and can achieve high precision.
4 Because discharge is a point in contact with relative anti-copy is less efficient. Taking the processing of fine cylindrical workpieces as an example, the WEDG method can process 70 μm of copper, 20 μm and 13 μm of tungsten, and even smaller diameters can be processed.
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