The hottest micro cutting technology

Micro machining technology

1 Introduction

with the development of science and technology, higher and higher requirements are put forward for machining. First, higher and higher machining efficiency, machining accuracy and surface quality should be met; Secondly, it requires economy and Ecology (that is, green production requirements). In order to meet these requirements, researchers have done a lot of research work and developed a variety of advanced cutting technologies, such as high-speed cutting, dry cutting, hard cutting and so on

MEMS is a new field derived from the research on integrated circuit (IC) manufacturing and materials in the 1960s. Therefore, the manufacturing technology used at the beginning of development must comply with the manufacturing requirements of integrated circuits, and the materials used must also meet the manufacturing standards of integrated circuits, such as polysilicon, monocrystalline silicon, silicon oxide, silicon dioxide and other silicon-based materials, or aluminum, copper and other metals. However, with the diversified development of MEMS and MEMS, materials that traditionally meet the requirements of integrated circuit manufacturing have their limitations, and the demand for micro components with different mechanical and electronic properties is becoming more and more urgent. MEMS technology has become one of the fastest-growing industries in the world. Industries that need to manufacture extremely small high-precision parts, such as biology, medical equipment, optics and Microelectronics (including mobile communications and computer components), have a large demand. However, not every micro component applied in MEMS or micromachine can be produced by integrated circuit technology. Therefore, new materials, new micro manufacturing technology and micro cutting technology have been studied and developed in succession

2 scale division

researchers from different research institutions and different research fields have different opinions on the division of scale. Experts in materials science believe that the scale between 10-12th Power M and 10-9th Power M belongs to the research field of quantum mechanics; The scale between the - 9th power of 10 m and the - 6th power of 10 m belongs to the research field of Nano Mechanics; The scale between the - 6th power of 10 m and the - 3rd power of 10 m belongs to the research field of mesoscopic mechanics; The scale between the - 3rd power of 10 m and the 0th power of 10 m belongs to the field of micromechanics; The scale greater than 10 to the power of 0 m belongs to the research field of macro mechanics. Mechanical processing disciplines often take the power of 10-6 m (1 μ m) For the machining error scale, the error scale of traditional machining is mostly measured by wire (1 wire =10 μ m) The error scale of precision machining can reach micron level. It can be seen that material science takes the characteristic length of the research object as the basis for scale division, and the machining accuracy of the research object is taken as the basis for scale division in the field of machining, so the machining is divided into ordinary machining, precision machining and ultra precision machining, etc., which does not involve the size of workpiece machining characteristic scale

as shown in Figure 1, precision machining can be divided into macro scale machining, meso scale machining and micro scale machining according to the scale of workpiece machining characteristics. Generally, machining mostly refers to macro scale machining. The technical performance requirements of parts are reflected in the macro scale or surface structure. The size of machining features is relatively large and the scope of machining is wide; Micro scale machining refers to micro nano machining, which mainly uses precision and ultra precision machining technology, micro machining technology and nano machining technology to process, emphasizing "extremely thin cutting" and microstructure. The size of machining features is relatively small. In the micron, submicron and nano levels, the focus of research is the microstructure of materials; Those in between are called mesoscale machining or mesoscale machining

Figure 1 Division of precision machining scale

at present, some electromechanical products are neither as small as micro electromechanical systems (micro machines) in nanotechnology, nor as large as ordinary electromechanical products. For the convenience of differentiation, they can be called "micro machines". The processing characteristics of micro machinery span many different scale levels (see Figure 2), including both the micro scale between the - 3rd power m of 10 and the 0 Power M of 10, the mesoscopic scale between the - 6th Power M of 10 and the - 3rd power m of 10, and the nano scale between the - 9th Power M of 10 and the - 6th Power M of 10. It should be pointed out here that at present, the machining accuracy that most micro manufacturing technologies can achieve is still in the range of submicron to micron, and there is still a large gap from the commonly known nano scale (10-10th Power M ~ 10-7th Power M)

Figure 2 scale grade of micro machining features

micro machinery has a large market in national defense, aviation, aerospace and civil, such as micro satellites, aircraft, machine tools, steam turbine generator sets, vehicles, firearms, etc. From the perspective of product development, miniaturization is one of its directions, such as cameras, video cameras, projectors, etc. are becoming smaller and smaller, but the functions are constantly improving and improving. Therefore, the research of micro machining theory and technology has broad application prospects

3 micro manufacturing technology

at present, micromanufacturing technology commonly used in MEMS can be divided into micromachining of silicon-based materials and non silicon-based materials, which can be basically divided into four categories:

(1) etching technology

this technology uses dry etching, wet etching or photolithography to carry out isotropic or non isotropic etching and removal processing of processed materials, Generally, bulk micromachining or surface micromachining can be performed on the processed materials. The advantages of etching technology are high machining accuracy, large batch production capacity, compatibility with IC manufacturing, and the technology is relatively mature; The disadvantages are that the processed materials are fixed, the processing speed is slow, the risk of etchant is high, the investment of equipment is large, and the requirements for processing environment are high

(2) thin film technology

this technology mainly uses thin film growth technology and etching technology to process the microstructure required. It can generally be used for 2D surface micromachining, and is mainly used in the manufacturing of micro components in VLSI. In addition to the mature technology, excellent IC compatibility and mass production of micro components without special assembly technology, the disadvantages of thin film technology are the same as those of etching technology

(3) LIGA technology

this technology combines the technologies of deep X-ray lithography, micro electroforming and micro molding. The weight of Li is only 250 kg. In addition to the advantages of high accuracy, good surface roughness, good IC circuit compatibility and mass production of impact testing machine in this energy range, Compared with IC manufacturing technology, LIGA technology can process more kinds of materials and has better 3D microstructure manufacturing ability with high aspect ratio. However, the biggest disadvantage of LIGA technology is that the cost of synchrotron radiation X-ray required for manufacturing is extremely expensive. In addition, the manufacturing cost and time consumption of X-ray mask are also very high. Therefore, in submicron scale microstructures, relatively inexpensive Liga like technology has been used to replace X-ray etching, such as ultraviolet lithography using alternative light sources Excimer laser processing, reactive ion etching (RIE) and other technologies. Although the processing accuracy of these alternative technologies is not as high as LIGA technology, the light source equipment is small and the price is relatively cheap

(4) micromachining technology

in addition to the above (1) ～ (3) types of micromachining technology, most of them can be classified as such processing technology. Micromachining technology can be divided into three categories: micro cutting technology, non cutting technology and special processing (see Figure 3). This paper mainly introduces micro cutting technology

Fig. 3 Classification of micro machining technology

4 micro machining technology

micro machining is a fast and low-cost machining method of small parts, and it is not limited by materials. Using CNC machining center can realize the micro machining of 2D, 2.5D simple features to complex 3D curved parts (see Fig. 4). The micro mold processed by this method can achieve the purpose of mass production. The following mainly introduces micro cutting equipment, cutting tools and cutting mechanism

Figure 4 micro cutting parts

4.1 micro cutting equipment

the size and machining quality (machining accuracy, surface roughness, repetition accuracy) of parts are closely related to the performance of their machining machine tools (such as accuracy, dynamic characteristics, etc.). The performance of the machine tool is mainly related to the spindle, workbench and control system. The diameter of the tool used in micro cutting is very small. In order to improve the machining efficiency, the spindle speed of the micro cutting machine tool is very fast. In order to meet the torque requirements, motorized spindles and hybrid angular contact bearings are usually used. This kind of bearing causes thermal expansion due to friction heat, and the maximum speed is generally not more than 60000 R/min. When the speed is higher, the air bearing should be used, but the torque provided by the air bearing is small. At present, the maximum speed of the air bearing spindle can reach 200000 R/min. In order to obtain higher cutting speed, the taper of the spindle is consistent with that of the high-speed cutting tool shank. The worktable of micro cutting precision machine tools is generally driven by linear motors. Compared with ordinary drives such as ball screws, the linear motor drive system has no cumulative error caused by friction and electromagnetic coupling, nor precision loss caused by wear. There is no gap, and it can provide large acceleration. The accuracy of the linear motor drive system can reach ± 1 μ m。 Micro cutting precision machine tools have good rigidity and low vibration, and most of them are equipped with various sensors and actuators. However, due to its large size and strict control requirements for the surrounding environment, the cost of processing small parts is high. The machining centers and CNC lathes available in the market for micro cutting are shown in Figure 5

Figure 5 machining center and CNC lathe for micro cutting

because the machining feature size of micro mechanical products is very small, researchers are trying to develop micro machine tools to process micro parts. The volume and size of micro machine tools are very small, which can save a lot of raw materials. Therefore, materials with better performance can be used for manufacturing. In addition, due to its small mass, the natural frequency of the micro machine tool is higher than that of the ordinary machine tool, which makes the micro machine tool can be used stably in a wide range of spindle speed without chattering. Even if vibration occurs, the amplitude of the micro machine tool is small under the same load. The positioning accuracy of micro machine tools can reach the nanometer scale, and the machining accuracy is sub micron

Figure 6 micro machine tool

the development of micro machine tool introduces a new concept, namely "micro chemical plant". The micro chemical plant covers a very small area and can be placed anywhere in any building, even in the battlefield or space station, which is almost impossible for ordinary machine tools. Micro chemical plants consume very little energy, which greatly saves the use of energy. There are different production units in the micro chemical plant, such as micro lathes, micro milling machines and other equipment

the development of micro machine tools is currently facing a series of challenges, such as the need to develop sensors and actuators small enough to be installed in micro machine tools. Micro machine tools are less rigid than micro cutting precision machine tools. In addition, in order to prevent external interference, micro machine tools need to add vibration isolation devices to meet the requirements of machining accuracy. Reducing the processing cost of micro chemical plants and developing multi-functional composite micro machine tools are the development trend of micro cutting equipment in the future

Figure 7 micro chemical plant

4.2 micro cutting tools

in the field of micro cutting technology, how to refine the grain of tool material and miniaturize the tool in order to process micro workpieces has always been the focus of research