Experimental Study On Drilling Of Engineering Ceramics Using Abrasive Water Jet

Engineering ceramics is one kind of inorganic non-metallic materials formed afterhigh-temperature sintering. It has high strength, high hardness, high corrosion-resistance, lowdensity and low electromagnetic induction. Therefore it is widely used in optics, aero-space,machinery, electrinc, bio-engineering and chemical industry. There is great theoreticalsignificance and actual value in studying of machining process for engineering ceramics.Abrasive water jet （AWJ） is a newly special machining technology developed on basis ofmachining process of pure water jet and high speed grinding technology. AWJ features for itsstrong cold erosion grinding effect with low heat effect, minimum counteraction, no spark,high cutting speed and good incision quality. It can be applied in many cutting conditionssuch as heat-sensitive materials, pressure-sensitive materials, high hardness, high brittlenessmaterials, difficult to cut materials and space navigation composite materials. Nowdays, it hasbeen widely used in cutting metal, ceramics, stone, laminated glass, coated composites andtitanium alloy plate.In this thesis, theoretical formula of speed of water jet, flow and other basic water jetparameters are derived from hydrodynamics equations, law of conservation of energy andbasic theory of the momentum theorem, which provides us theoretical foundation of abrasivewater jet and builds theoretical mode of machining engineering ceramics by abrasive waterjet.In this thesis, effects of structure of inner outline of nozzle on abrasive track and speed aresimulated based on DPM of software Fluent. A nozzle with optimal structure is selected toperform this experiment based on the current lab equipment. The effect of machiningparameter of Al2O3engineering ceramics processing on material processing capacity andquality are analyzed.The study is focused on effect of jet pressure, target distance, jet speed and abrasive flow onhole depth and its wall roughness in Al2O3processing. According to the studying result, jetspeed, impact and abrasive kinetic energy are increasing in proportion to jet pressure. Then itis converted failure energy to objectives, i.e. the destory degree for the material, and drillingdepth. On the other hand, hole wall surface roughness value is decreased with increasing jetpressure. Within optimum target distance range, along with increasing of jet target distance,energy of the abrasive water jet spreads, abrasive particles uniformly washout the creamics material driven by water jet along the jet axis, which makes the roughness of hole surfacedecreases. When beyond optimum target distance range, as target distance increases, drillingdepth decreases rapidly but roughness increases gradually. Under condition that jet speed islow, impact time of water jet on objective will be longer and drilling depth will also be greater.With increasing of jet speed, impact frequency is smaller, and there is obviously decreasing indrilling depth. When jet speed is beyond a certain value, there is little decreasing of drillingdepth and it will finally be stable at a certain drilling depth. But roughness of hole surface isincreasing with jet speed increasing. When abrasive flow increases, there is almost a linearrelationship between hole depth and abrasive flow obtained. But with increase of abrasiveflow, the hole depth is increasing mildly. Compared with increase of hole depth, decrease ofroughness for hole surface is not obvious.Orthogonal experiment method and range analysis method are used in experiment ofengineering ceramic machining using abrasive water jet and data analysis. Result of rangeanalysis of drilling depth shows that jet pressure strongly affects result of the experiment.Secondly, target distance also has a stong effect on depth. A primum combination isdetermined according to expereiment parameters and results, i.e. water jet speed230MPa, jettarget distance3mm, jet speed5mm/min, abrasive flow95.8g/min. Range analysis of holesurface roughness shows that water jet pressure has the strongest effect on roughness of holesurface. Then comes the abrasive flow and water jet speed. Finally a better combination isdetermned according to experiment parameter level and range analysis results, i.e. water jetpressure230MPa, target distance7mm, jet speed10mm/min, abrasive flow95.8g/min.Multiple regression analysis method and Matlab language are used to establish a predictionmodel of drilling detph （H） and hole surface roughness （Ra） for machining engineeringcreamics by abrasive wate jet.Prediction model of drilling detph H is specified as follows,H=4.609×10^-4P^1.8814S^-0.1684V^-0.2015Q_m^0.1759;Prediction model of hole surface roughness Ra is specified as follows,Ra=2.008×10⁸P^-3.1430S^-0.011V^0.016Q_m^0.1438.