Investigations on the wire sawing process

Abstract

The wire sawing technology plays an important role on the manufacturing of thin discs out of brittle materials and is used for example in the solar-and microelectronic industry. The surface of a wire sawn disc shows a characteristic geometry, which suggests the influence of oscillations during the slicing process. In order to examine the process a distinct-elementmodel is used to simulate the motion and the interaction of the abrasive particles with the moving wire and the workpiece. The simulation shows interesting phenomena like clustering of particles and reacting forces to the wire, which could be one reason for the observed oscillations in the process. Wire sawingThe wire sawing process is used for example in the photovoltaic industry to cut silicon into thin wafers. A moving wire, wounded for several times around some wire pulleys is used in addition with a slurry, which contains abrasive particles, to slice through the silicon ( The main material removal mechanism is represented by Moeller et al. [1]. He shows that the removal process can be understood as the sum of single indentations, which may be caused by a rolling particle motion. This motion can not be easily observed, so in this paper the Distinct-Element-Method (DEM) is used to investigate the motion of the particles and the influence of the interaction between particles in more detail. Distinct-element-model Particle interactionEssential for the simulation of the wire sawing process are the forces which act onto the surface of the sliced material. To calculate these forces, the interaction between the wire and the abrasive particles have to be considered under the influence of the slurry, which contains these abrasive particles. Therefore the used DEM-Code, which is originated from the Institute of Computational Physics in Stuttgart [2], was extended by a simple fluid model. It contains the influence of a shear flow between the wire and the ingot surface, leading to shear forces onto the particles and to a lift force in direction towards the wire (Fig. 2).The lapping particles are modeled as viscoelastic bodies. Therefor two-dimensional polygons are assigned with physical properties like mass, Young's modulus and shear modulus. The later two are used to calculate stiffness constants in order to model the viscoelastic material behavior (Fig. 3 and 4, Equations 1 and 2). The direction of the contact force is determined by the edges of the overlapping area and the center is used as the point of application of the forces.With n -normal direction, t -tangential direction A o -"overlap"-area, k (n,t) -stiffness constant, b (n,t) damping constant and v rel -relative velocity between colliding particles. The stiffness constant of such a contact depends on the Young's modulus

Evolution and present status of silicon carbide slurry recovery in silicon wire sawing

“…Moller (2004) has reviewed this mechanism. Liedke et al (2007) report simulation studies conducted on particle movement in the cutting groove of the wire saw. According to the rolling-indenting model, since the silicon surface is chipped by the indenting action of sharp abrasive particles, depth of crack and chip size should be comparable to the size of the abrasive particles.…”

Discrete element simulation of micromechanical removal processes during wire sawing

“…First attempts thereto can be found e.g. in Liedke et al [24] (see also Fig. 2) or in Hejazialhosseini et al [17].…”

“…However, the complex behavior of multiple abrasive particles in the kerf is still less investigated. Originally developed for rock-mechanics [13], the discrete element method (DEM) offers the possibility to capture a large number of discrete particles and is therefore suitable to model the motion and interaction of abrasive particles during the wire lapping procedure [24,5,38].…”