Study On Erosion Rate And Cutting Quality Of Monocrystalline Silicon Cut By Micro Abrasive Air Jet

In this paper,a set of erosion experiments by micro abrasive air jet (MAAJ) under large jet incidence angle are performed to research the microscopic erosion mechanisms of monocrysalline silicon associated with micro abrasive air jet cutting.Furthermore,a detailed experimental investigation is carried out to study the effect of process parameters on the cutting ability and cutting quality in MAAJ cutting of monocrystalline silicon.A new concept of 'effective abrasive particle flux effect' is proposed firstly,and the erosion rate model based on the so-called effective abrasive particle flux effect is developed.In addition,predictive mathematical models for cutting width,cutting depth,cutting aspect ratio and the cutting profile of the kerf are also developed.The research results can provide some further insight into the erosion mechanisms of hard and brittle monocrystalline materials and increase the industry application of MAAJ cutting.Especially,the research results can offer some useful guides for the effective use of this technology in cutting and slicing the thin-sheet of hard and brittle materials with negligible heat affected zone and small cutting forceThe erosion experiment of MAAJ under large jet incidence angle is carried out and the characteristics of eroded dimples are investigated.The impressions produced on monocrysalline silicon are classified into different erosion types depending on their scale and shape.Moreover,the respective percentages of the number of the impressions under different erosion types with respect to the total number of large-scale impressions in each dimple have been calculated.The critical particle velocities for the nucleation of radial/median,lateral and hertzian cracks are compared and the effect of stress field and workpiece crystallographic orientation on the nucleation and propagation of the crack are analyzed.It is found that the impressions can be classified into three categories,namely craters,scratches and micro-dents.The large craters have been further classified into the CC,CCR,CCC and CCCR types.Likewise,four types of scratches have been identified,i.e.,SC,SCR,SCC and SCCR. Furthermore,it has been found that the CC,CCR,SC and SCR types of impressions do not play an important role in material removal.By contrast,the CCC,CCCR,SCC and SCCR types of impressions can lead to large-scale fracture on the target surface.It is interesting to note that no discernible evidence of ring cracks is observed on all erosion dimples. It is proven that the percentage of the impressions involving cleavage fracture increases with an increase in the air pressure and the percentage of the created craters increases with an increase in the jet incidence angle. As most particles bounce away from the target surface without sliding or rolling during an impact,most impressions are formed in crater-type erosions.Craters with cleavage fracture surface have been found to dominate the material removal process.It is found that the nucleation and propogation of crack are affected by the anisotropic mechanical properties of monocrystalline silicon such as hardness,elastic modulus and fracture toughness,as well as the abrasive particle shape,the stress field plays a more important role than workpiece crystallographic orientation in governing the nucleation and propagation of the crack.The effect of process parameters on the erosion rate in MAAJ cutting of monocrystalline silicon is investigated.A new concept of 'effective abrasive particle flux effect' is proposed firstly and the effective abrasive particle flux effect model is developed,and then erosion rate model as a function of the effective abrasive particle flux effect is developed and verified with respect to corresponding experiment data.It is shown that the erosion rate increases with an increase in the air pressure,jet incidence angle and nozzle traverse speed,while decreases with an increase in the abrasive flow rate.Moreover,it is found that the collision probability between the particles rebounding from the target surface and the incident particles increases with an increase in the abrasive flow rate and a decrease in nozzle traverse speed,which accounts for the reduction in erosion rate.The prediction of the erosion rate model is in good agreement with the experimental data.The characteristics of the top kerf edge and the cross section of the kerf is investigated.The effect of process parameters on the major cutting performance,such as the smoothness of the top kerf edge,cutting width, cutting depth,aspect ratio and the cross section of the kerf have been discussed.Generally,the kerf edge is flat and there is some surface damge nearby the kerf.It is found that the top kerf edge becomes smoother with a decrease in air pressure and the jet incidence angle. While the effects of the nozzle traverse speed and abrasive flow rate on the smoothness of the top kerf edge are negligible.The cutting width increases with an increase in air pressure,abrasive flow rate,while decreases with an increase in nozzle traverse speed.With all other factors held constant,the cutting width is the smallest when the jet incidence angle is 60°,while the largest cutting width can be obtained when the jet incidence angle is 30°.Consequently,the lower air pressure and abrasive flow rate,as well as the larger nozzle traverse speed should be used to gain the smaller cutting width.The cutting depth increases with an increase in air pressure,abrasive flow rate and jet incidence angle, while decreases with an increase in nozzle traverse speed.Therefore,the larger air pressure,abrasive flow rate and jet incidence angle,as well as the lower nozzle traverse speed should be used to gain the larger cutting depth.The bottom of the kerf becomes more flat and the slope of the kerf wall becomes steeper with a decrease in air pressure,abrasive flow rate and nozzle traverse speed,while the bottom of the kerf becomes less flat and the slope of the kerf wall becomes smaller with a decrease in jet incidence angle.The cutting apsect ratio increases with an increase in air pressure,abrasive flow rate and jet incidence angle,while decreases with an increase in nozzle traverse speed.Mathematical models for cutting width,cutting depth,cutting aspect ratio and the cutting profile of the kerf are developed.Based on the theory of quasi-static indentation theory and the mass distribution of abrasive particles,the cutting width model is developed.Based on the relationship among erosion rate,the mass of employed abrasive particles and the weight of material removed,the cutting depth model is developed. A dimensional analysis technique has been used to develop the cutting aspect ratio model considering the major process parameters and workpiece mechanical properties.Based on the cross section profile of the kerf,a new function of profile is constructed,and then the dependence of profile on process parameters is determined by the dimensional analysis technique.Some experimental investigations verify these models which can effectively predict the cutting quality in MAAJ cutting process.