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When fixed abrasive wire saw is used to cut polysilicon, free SiC abrasives are added into the cutting coolant to form the fixed and free abrasive combined wire sawing process, so as to impact and roll the as-sawn wafer surface to remove the ductile amorphous silicon layer. Then, the as-sawn wafer can be textured by acid etching technology. The movement characteristics of free abrasives in sawing area directly affect their lapping behavior and the morphology generation of as-sawn wafer surface. In this paper, the flow field characteristics of cutting coolant and the movement characteristics of free SiC abrasives in the sawing area were studied, when using an abrasive groups interval distribution diamond wire for sawing. A three-dimensional model of cutting coolant in sawing area was established. Based on FLUENT, the influences of wire speed, feed speed, wire pretensioning force, viscosity of cutting coolant and wire surface structure parameters on the concentration peak position of free SiC abrasives in the cutting coolant along the wire axial direction were analyzed. The results show that the concentration peak of free abrasives will gradually shift to both sides along the circumferential direction of the wire in the sawing area. The deflection angle and width angle of free abrasives concentration peak are only related to the length of the bare wire area, and decrease with the increase of its length. Comprehensively considering the hydrodynamic pressure effect in the bare wire area, reducing the wire speed and tension, and increasing the feed speed and cutting coolant viscosity are conducive to enhance the lapping effect of free SiC abrasives on the as-sawn wafer surface. The change of wire structure parameters has no regular effect on the lapping behavior of free SiC abrasives in the bare wire area. [ABSTRACT FROM AUTHOR]

This paper presents a novel fixed and free abrasive combined wire sawing which uses the diamond wire with surface abrasive-groups interval distribution and combines with free SiC abrasives slurry to obtain sliced surface that can be textured by acid etching. During the sawing process, the ability that the free abrasives lapping the sawn surface has a positive correlation with the elasto-hydrodynamic (EHD) pressure, and the appropriate size of the free abrasives is related to the minimum film thickness of the cutting coolant. In this paper, the EHD action during the FFACWS is analyzed, and the film thickness equation and Reynolds equation of the sawing area are deduced. The influences of feed speed, wire speed, wire tensioning force, cutting coolant viscosity, core wire diameter, and surface structure parameters on EHD pressure and film thickness are analyzed, which provides theoretical reference for selection of the free abrasives diameter and analysis of their lapping effect on the slice surface. The research results show that the EHD pressure changes periodically in the direction of the wire axis in the entire sawing area. The change period is the same as a structural change period of the abrasive area (AA) and the bare wire area (BWA) on the wire surface. In one period, there are two EHD pressure peaks. The size range of free abrasives should be greater than the protruding height of the fixed abrasives on the diamond wire and less than the minimum film thickness in BWA, so that the free abrasives can be constrained in BWA to lap the slice surface. [ABSTRACT FROM AUTHOR]

In the slicing process of KDP crystal, due to the characteristics of long sawing kerf length, low hardness, and easy cracking, etc., there is a high requirement for the lubrication and chip discharge performance of the sawing area during slicing. So there are higher requirements on the structure and cutting performance of the saw wire to improve the sawn surface accuracy and the stress distribution in the processing area to avoid crystal cracking. In this paper, based on the technical idea of orderly arrangement of abrasives on the surface of superhard abrasive tool, the fabrication process, surface structure parameters, and sawing performance of a new type of abrasives-helix-distribution electroplated saw wire for slicing KDP crystal are carried out. The manufacturing process of the abrasives-helix-distribution saw wire was established, and the electroplating process parameters were determined. The relationship between the surface structure parameters of the new type wire was analyzed, and the influences of different structural parameters on the cutting performance of the new type wire were studied; then, the reasonable combination of the surface structure parameters of the new type wire was determined. The results are helpful to further understand the influences of surface structure parameters on the sawing performance of the new type wire, and provide experimental basis and reference for the development of the abrasives-helix-distribution saw wire for slicing KDP crystal. [ABSTRACT FROM AUTHOR]

There are large brittle fracture pits on the surface of photovoltaic polysilicon wafer cut by diamond wire saw, because of the problems such as poor flow of cutting fluid and difficulty in chip discharge. At the same time, the anti-corrosion amorphous layer on the wafer surface can obviously block the subsequent acid etching and texturing reaction. In order to solve these problems, a new type of diamond abrasives-helix-distribution saw wire is used as the sawing tool to obtain the surface characteristics of photovoltaic polysilicon wafer suitable for acid texturing, then research on wire sawing photovoltaic polysilicon based on controlling subsurface microcrack damage depth control is carried out. The concept of high-quality cutting abrasives (HQCA) is defined, and the cutting process of polycrystalline silicon is numerically calculated based on the established new type diamond wire model, the influence of the process parameters and the structural parameters of the saw wire on the cutting characteristics is analyzed, and the reasonable matching between the process parameters and the saw wire parameters is discussed. The study results show that the number and proportion of HQCA in all abrasive grains involved in sawing can be increased by increasing the workpiece feed speed or reducing the moving speed of saw wire, properly reducing the abrasive concentration on the saw wire surface or increasing the abrasives size, or setting the ratio of axial distance between the abrasive area on wire surface and the bare wire area as 1:1. In this case, the formation of the wafer surface tends to be removed in the way of material microbrittleness, and the subsurface crack depths are in the optimal etching depth range. The number and proportion of HQCA remain basically unchanged when the workpiece feed speed changes in constant proportion to the wire speed, and the screw pitch of the abrasive groups on the surface of the saw wire has little effect on it. [ABSTRACT FROM AUTHOR]

At present, the fixed abrasive wire sawing (FAWS) technology is gradually used in the photovoltaic industry to cut polycrystalline silicon slices. However, there are obvious directional wire marks, parallel grooves, and amorphous silicon layer on the surface of the slices formed by the FAWS, which leads to a high optic reflectivity of the textured surface obtained after the mature acid etching texturization technology. So the slices cannot meet the requirements of the photovoltaic cell. In the paper, a novel fixed-free abrasive combined wire sawing (FFACWS) technology for cutting PV polycrystalline silicon is presented to solve this problem, by adding loose SiC abrasives to cooling lubricant during the fixed abrasive wire sawing. A single-factor and orthogonal experimental study on sawing characteristics was carried out. The effect of size and mass fraction of SiC abrasives in the slurry, workpiece feed speed and wire speed on the surface morphology, roughness, and kerf loss were studied. The results show that within the range of the processing parameters in the paper studied, the obvious wire marks, parallel grooves, and ductile layers on the surface of the slices can be removed by the FFACWS. The surface roughness of the slices along the wire movement direction and the workpiece feed direction increases with the increase of the mass fraction of SiC abrasives in the slurry and workpiece feed speed and it decreases with the increase of wire speed. But the effect of the size of SiC abrasives is related to the matching of the protruding height of the fixed abrasives on the wire surface along the workpiece feed direction. In the wire movement direction, it increases with the size of SiC abrasives. The kerf loss increases with the increase of size and mass fraction of SiC abrasives in the slurry and the wire speed but has little effect with the change of workpiece feed speed. [ABSTRACT FROM AUTHOR]