Unit 16 Unconventional Machining Processes (),Laser Beam Machining Electron-beam Machining Water-jet Machining Abrasive Water-jet Machining Photochemical 光化学 Machining (PCM),Laser beam machining (LBM) utilises the energy from the coherent light beams called laser (light amplification by stimulated emission 放射 of radiation 辐射 ).,1. Laser Beam Machining,The basic principle utilised in LBM is that,under proper conditions light energy of a particular frequency is used to stimulate the electrons in an atom to emit additional light with exactly the same characteristics of the original light source.,One of the important properties of laser is,Typical power densities used for cutting are of order of,At the higher end of this power scale, the material changes directly from solid state to vapour 汽化 state without going through the molten state and is used in some laser markers.,the coherency.,1.5103 to 1.5105 kw/cm2,Fig.1 Schematic set up of a laser drilling operation,Laser beams are also used for the following:,(1) Welding (2) Small-scale and localized heat treating of metals and ceramics to modify their surface mechanical and tribological 摩擦学的 properties (3) The marking of parts, such as letters, numbers, codes, ect,2. Electron-beam Machining,Fig.2 Schematic illustration of the electron-beam machining process,3. Water-jet Machining,A pressure level of about 400 MPa (60 ksi) is generally used for efficient operation, although pressures as high as 1,400 MPa (200 ksi) can be generated.,A variety of materials can be cut, including,Jet-nozzle 喷嘴 diameters range between 0.05 mm and 1 mm (0.002 in. and 0.04 in.).,plastics, fabrics, rubber, wood products, paper, leather, insulating 绝缘的 materials, brick, and composite materials.,A water-jet cutting machine and its operation are shown in Fig.3.,Fig.3 Schematic illustration of water-jet machining,4. Abrasive Water-jet Machining,In abrasive water-jet machining (AWJM), the water jet contains abrasive particles (such as silicon carbide or aluminum oxide), which increase the material-removal rate above that of water-jet machining.,silicon carbide,aluminum oxide,5. Photochemical Machining (PCM),Fig.4 Processing of substrates coated with negative- and positive-working photoresists,A machining process in which heat is produced by a focused electron beam at a sufficiently high temperature to volatilize 挥发 and thereby remove metal in a desired manner; takes place in a vacuum. Abbreviated EBM.,Electron-beam Machining,A water jet cutter is a tool capable of slicing into metal or other materials using a jet of water at high velocity 高速 and pressure, or a mixture of water and an abrasive substance. The process is essentially the same as water erosion found in nature but accelerated and concentrated by orders of magnitude.,Water-jet Cutter,The process of using photochemical machining is ideal for thin metal parts fabrication, fine line etching 蚀刻 , and engineering of micro machined parts. Many of these thin metal parts are then precisely formed into complex shapes.,Photochemical Machining,The advantages of photochemical machining are quite diverse in what it can do for metal parts manufacturing. Large format panels, tight tolerances, and low cost of tooling are but a few of the advantages with PCM for producing burr free intricate metal parts. Additionally the time from concept design engineering, to prototype 标准件 , to manufacturing the parts, is substantially reduced.,Notes,The basic principle utilised in LBM is that under proper conditions light energy of a particular frequency is used to stimulate the electrons in an atom to emit additional light with exactly the same characteristics of the original light source. 句意：激光加工的基本原理是在一定条件下采用特定频率的光激发原子中的电子，使其发射特征与原光源完全相同的光。,