| In traditional free abrasive wire sawing process,the abrasive particles are often difficult to be transported into the long and narrow slot zone,thus leading to the wire sawing performance deteriorated,such as poor surface quality,high kerf loss,and low cutting efficiency,et.al.These problems are more prominent when slicing large size of the silicon crystal.In order to transport more abrasive particles into the cutting zone,a novel method named as magnetic induction-free abrasive wire sawing is proposed.It is a hybrid process that introduces a uniform magnetic field into traditional free abrasive wire sawing technology.A ferromagnetic saw wire is magnetized by the external uniform magnetic field,and it then generates a high gradient magnetic field around itself.Magnetic abrasive particles are attracted to the surface of the wire by the magnetic force,which leads to more abrasive particles carried into the sawing channel.This novel method effectively improves the utilizing rate of abrasive particles and is helpful to improve the wire sawing performance.To better understand the mechanism of this novel method,combining theoretical modeling and experimental verification,this paper mainly focuses on studying the dynamic behavior of magnetic abrasive particles in the being about to go into the cutting area,the formation mechanism of magnetic abrasive particle layer adsorbed on the wire surface,the mechanical behavior of magnetic abrasive particle in the magnetic induction cutting area,magnetic induction-free abrasive wire sawing test and other aspects(1)Firstly,force analysis of magnetic abrasive particles motioned around the wire saw was conducted,and a dynamic model of magnetic abrasive particle was established near the entry to the sawing channel.Secondly,the effects of different magnetic orientations on the dynamic characteristic of magnetic abrasive particle were investigated by using the finite element(FEM)software COMSOL Multiphysics.Finally,an experimental platform for observing the adsorption of magnetic abrasive particle was built,and the experimental studies on observing the motion behavior of magnetic abrasive particles around the saw wire surface were carried out.The results showed that magnetic abrasive particles of traditional free abrasive wire sawing process motioned with the fluid flow,and a very small amount of magnetic abrasive particles was detained on the wire surface because of the fluid viscosity.However,there was no adsorption of magnetic abrasive particles.This indicated a small number of abrasive particles were carried into the sawing channel.While in magnetic induction-free abrasive wire sawing process,a large amount of magnetic abrasive particles were adsorbed on the surface of wire saw due to the magnetic force.Moreover,the magnetic abrasive particles were acted on attractive force,and they were only adsorbed to both sides of the wire where align parallel to the background magnetic field orientation,the so-called paramagnetic(PM)region.While in the both sides of the saw wire where orients perpendicular to the background magnetic field orientation,the so-called diamagnetic(DM)region,magnetic abrasive particles were acted on repulsive force.Hence,there is no adsorption of magnetic abrasive particles.(2)According to the force analysis of magnetic abrasive particles in the high gradient magnetic field formed around the saw wire surface,a mathematical model of magnetic abrasive particle layer formed on the saw wire was established.The theoretical analysis results revealed that the tangential range of the nickel-plated silicon carbide(SiC)particle layer on the wire was determined by the magnetic force dividing line,which was the location of the magnetic force acting on paramagnetic abrasive particles converted from attraction to repulsion.And its critical radial range was determined by the equilibrium of the magnetic force,fluid drag force and gravitational force acting on the magnetic abrasive particle.Then the formation mechanism of magnetic abrasive particle layer under different process parameters was investigated in the numerical analysis software MATLAB.The wire adsorptions of the magnetic abrasive particle layer were observed at an experimental setup utilizing a high-speed camera and the designed magnetic system.The results show that magnetic induction-free abrasive wire sawing magnetized the steel wire and attracted the magnetic abrasive particles in the wire PM region,where they could readily enter the sawing channel.A large number of magnetic abrasive particles were adsorbed by the wire,causing the magnetic abrasive particle layer to be formed.And the shape of the magnetic abrasive particle layer was approximated as an annular sector.In the direct observations of the magnetic abrasive particle layer on the surface of the saw wire it could be seen that the magnetic abrasive particle layer was mainly formed at the upstream PM region of the saw wire.The thickness of the magnetic abrasive particle layer formed on the wire surface,which is the distance from the wire surface to the last layer,was measured using the post processing software of the high speed camera.And the comparison between the theoretical calculation results and experimental results were analyzed.Both the results showed that the thickness of the magnetic abrasive particle layer increased as the magnetic field strength and particle size increased,while decreased as the fluid viscosity and the slurry flow increased.The experimental results were in good agreement with the theoretical results,which further verified the correctness of the mathematical model and calculation results.(3)Based on the removal mechanism of brittle material and the movement contact state of the magnetic abrasive particle in the magnetic induction-cutting zone,the magnetic abrasive particles were divided into effective machining magnetic abrasive particles and instantaneously effective machining magnetic abrasive particles.Then the mathematical relationship between the average force on the single magnetic abrasive particle and the process parameters was established.The influences of different process parameters on the average force on single magnetic abrasive particle and instantaneously effective machining magnetic abrasive particles were calculated using numerical analysis software MATLAB.The results showed that the number of instantaneously effective machining magnetic abrasive particles was inversely proportional to the average force of single magnetic abrasive particle,and the numerical calculation results showed that the number of instantaneously effective machining magnetic abrasive was obviously larger than that of traditional free abrasive wire sawing process,and the average force of single magnetic abrasive particle becomes smaller.In magnetic induction-free abrasive wire sawing process,the number of instantaneously effective machining magnetic abrasive particles increased as the magnetic field intensity increased,while the normal force and shear force acting on the single magnetic abrasive particle decreased.With the increase of cutting fluid viscosity,slurry feed flow and magnetic abrasive particle size,the number of instantaneously effective machining magnetic abrasive particles decreased,while the normal force and shear force acting on the single magnetic abrasive particle increased.(4)The experimental platform of magnetic induction-free abrasive wire sawing was built on a WXD170 reciprocating wire sawing machine consisting of the uniform magnetic field generating device.Single factor test method was used to study different process parameters on the magnetic induction-free abrasive wire sawing performance.The experimental results showed that the magnetic field is beneficial for improving the wire sawing performance,both the kerf loss and edge collapse width were minimum when the background magnetic field orientation is parallel to the feed direction of the work-piece.The suitable background magnetic field intensity for improving magnetic induction-free abrasive wire sawing process was not the bigger the better,and the range was 9.6×10~4~1.2×10~5 A/m.In the magnetic induction-free abrasive wire sawing process,the required magnetic abrasive particle size should be chosen according to the actual cutting condition,and it can reduce the usage of the cutting fluid and magnetic abrasive particles without changing the wire sawing performance by adding an appropriate amount of water in the cutting fluid,thereby reducing the slicing cost and the contamination to the environment.Based on the surface morphologies of the work-piece and saw wire after sawing test,it was concluded that the increase of magnetic abrasive particles in the magnetic induction-cutting area would reduce its normal force and improve the surface quality of the work-piece.This result verified the correctness of the force behavior mathematical model of the magnetic abrasive particles in the magnetic induction cutting area. |
PDF Full Text Request