外文资料翻译
NON-CONVETIONAL MACHINING
Non-conventional machining has been well known in ceramics processing due to their high productivity and cost effectiveness. In the past，many researchers have studied machining of advanced ceramics conducted by chemical machining(CM), electrical discharge machining(EDM)，laser beam machining(LBM) and ultrasonic machining(USM)．Non—conventional machining utilizes other forms of energy different from mechanical energy. The energies used in non—conventional machining are thermal energy, chemical energy and electrical energy.
Chemical machining is one of the oldest micromachining technologies．This process applies reactive enchants to remove unwanted part from the work piece surface. It is a corrosive-controlled process. Many studies have been done on CM to investigate its etching rate, surface roughness and dimensional accuracy. CM includes photochemical machining. PCM is a method of fabricating component using reactive etchings to corrosively oxidize selected areas of the component. This process can produce highly complex products with very fine details, at high accuracy and low cost. They present a number of advantages，such as simple set up，quick preparation and no tool required; hence problems such as to
ol wear, machine tool deflections, vibrations and cutting forces are eliminated. In addition, chemical machining minimizes the effect of ceramics brittleness and low fracture. Disadvantages of chemical machining include chemical disposal，the presence of uncontrollable parameters, especially material structure and their rate of chemical reaction with solutions. In addition, high attention is required during processing. ZUBEL studied the silicon anisotropic etching process in water solution of KOH and TMAH with and without both organic and inorganic addition．This study shows that the etching rate is affected by the attendance of organic and inorganic agents．KIM employed the etching process with a
lower oxygen gas flow ratio and found that this action reduces etching damage to the low—k materials.
Abrasive water jet (AWJ) is    a technique that involves forceful impingement of abrasive particles to achieve the removal of surface material. AWJ depends on the water jet pressure ，stand—off distance，abrasive type’s size and flow rate. However, these choices are significantly affected by extreme factors such as the machined material structure and geometry of the jet nozzle. The most common advantage of AWJ is that it yields little heat during machining process therefore no heat affected zone(HAZ) happens，hence the process does not require heat treatment and no damage is reported．Compared with traditional machining technologies. AWJ offers the following advantages：fast speed，able to cut thick material，good accuracy, finishing surface and it cuts virtually anything wi
th no HAZ．Unfortunately, some burr will occur near the cutting area. AWJ is widely used in metal, glass, ceramic，marble and granite cutting machines. GI and GI made a conclusion in their research that AWJ had a great potential as a machining method for brittle and hard materials. Unfortunately, they found a large—scale fracture that easily developed on the backside of the work piece and affected surface finish. Although AWJ has been recognized as the most efficient method to machine ceramics , result showed that the damage in surface always happens in the lower zone of the surface , where a lot of pits were found and lower the surface quality. To overcome this problem，a new cutting head oscillation technique has been introduced. This technique applied to the cutting process produces superior results and shows that the smooth zone depths increase by more than 30％with oscillation as compared with that without oscillation. However, a further study is required to reduce the pits effect that occurs at the lower surface layer.
Electrical discharge machining uses spark erosion to remove small particles from electrically conductive material.
The acceleration of EDM material removal rate increases with the discharge current and working voltage, but decreases with increasing pulse
duration. EDM is especially well—suited for cutting intricate contour that would be difficult to produce with traditional machining. Advantages of EDM include high dimensional accuracy, good surface finish，lack of burr .Ti3SiC2 with excellent electrical conductivity and thermal conductivity is easily machined by EDM but high power is needed. In order to obtain a high material removal rate and better surface roughness，LIU suggested using a suitable chemical additive, dielectric strength，washing capability and viscosity of the machining fluid. They also suggested using a water-based emulsion as the machining fluid as harmful gas is not generated during machining，and the equipment is not corroded. Another suggestion by MUTTAMARA to improve the material removal rate is by employing positive polarity in the case where the conductive layer is sufficient. Study on the EDM of conductive ceramics shows EDM performance is purely dependent on the level of intensity. It has been observed that increasing intensity will tend to increase surface roughness and electrode wear.HU investigated EDM on Ti3SiC2 using water as dialectic and found typical thermal shock cracks and loose grains in subsurface, which result in about 25％of strength degradation. Results of EDM reveal a wide variation in removal rates and surface finishes, as shown in 4 and 5 shows the material removal and tool wear for EDM under roughing condition；and Fig-6 indicates the TIB surface after EDM.
Electrochemical discharge machining(ECDM)is a modification of EDM. Materials are removed or depo
sited with the transferring of ions based on the anodic dissolution mechanism, so that high precision is achievable and it has the feasibility of micromachining. In order to obtain better machining accuracy and smaller machining size，many research works have been done on electrolyte, electrode’s insulation and systematic control of machining process. BHATTAC HARYYA found that the machining rate and accuracy could be enhanced through effective and precise control of the spark generation. Taper side wall and flat front tool tip are the most effective parameters for controlled machining. The advantages of ECDM include higher material removal rate , use of nontoxic electrolyte components with
reactive翻译very little changes in their composition during operation ，minimal waste disposal ，monitoring and control of electrolyte .
Laser assisted machining is a thermal process. The laser is used as a heat source with the beam focused on the un—machined section of the work piece .The addition of heat softens the surface layer of the material, so ductile deformation happens rather than brittle deformation during cutting. LAM power requirements depend largely on the material and the nature of the machining process. In LAM ，cutting force is obviously significantly reduced and the ease of cutting is increased accordingly ，resulting in evident improvement in surface roughness. The possibility of vaporizing material during LA
M may cause surface problems due to its severity in much the same way as in discharge machining. The advantages of laser are that it provides high speed and precise cut when cutting thin material ；Laser yields no burr and a little HAZ. LAM has demonstrated its ability to reduce cutting force and lower dynamic forces，less sharp segmented chip and smooth surface finish is produced .It is suitable to cut non—reflection mild steel．LAM disadvantages include it requires high energy, high cost and must be conducted in a specify condition .The power of laser must be controlled properly to obtain a satisfactory result and    a lot of power is needed to conduct this machining .CHANG and KUO showed that LBM clearly appropriate for predicting the temperature distribution of difficult—to—machine materials during the LAM process．Tool wear is a major factor affecting the surface roughness of the work piece．Data shows the comparison of tool wear in LAM with conventional machining. They found that cutting resistance of processing aluminum oxide ceramics is extremely large, thus increasing the tool wear and affecting surface quality. BLACK showed that surface glaze usually possesses a different linear expansion rate to the underlying substrate．The large thermal gradient due to laser beam causes the lower substrate to expand at a different rate，resulting in cracking of the glaze．Ultrasonic machining (USM) is a process where material is removed primarily by repeated impact of the abrasive particles .the main parameters, which are static
force, vibration amplitude, and grit size, have significant effects on the material removal rate .Material removal occurs when the abrasive particles, suspended in the slurry between the tool and work piece, impact the work piece due to the down stroke of the vibrating tool. It is mentioned in many reports that, for deeper cut, a vacuum-assist to ensure adequate flow of the suspension is strongly recommended. Another type of USM is rotary ultrasonic machining .The difference between USM and RUM is the tool used. USM uses a soft tool and slurry loaded with hard abrasive particles, while in RUM the hard abrasive particles are handed on the tools .The major advantage of USM is that it is a non-thermal, non-chemical, and non—electrical process．Therefore，metallurgical，chemical or physical properties of work piece remain unchanged．However, in USM．The material removal rate is considerably slow and even stops as penetration depth increases；the slurry may wear away the wall of the machined hole as it passes back towards the surface，which limits the accuracy; and considerable tool wear happens，which in turn makes the process very difficult to hold close tolerances. Efforts have also been made to develop models to predict the material removal rate in RUM from control variables. ZENG concluded that RUM tools could be designed in a way so that the lateral face is shorter. Tools with shorter latter face use less diamond grains and hence lower manufacturing cost.

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