Simulation of the ductile machining mode of silicon

Hagen Klippel,Konrad Wegener,Mohamadreza Afrasiabi,Uygar Pala,Matthias Röthlin,Stefan Süssmaier

doi:10.1007/s00170-021-07167-3

Abstract

Diamond wire sawing has been developed to reduce the cutting loss when cutting silicon wafers from ingots. The surface of silicon solar cells must be flawless in order to achieve the highest possible efficiency. However, the surface is damaged during sawing. The extent of the damage depends primarily on the material removal mode. Under certain conditions, the generally brittle material can be machined in ductile mode, whereby considerably fewer cracks occur in the surface than with brittle material removal. In the presented paper, a numerical model is developed in order to support the optimisation of the machining process regarding the transition between ductile and brittle material removal. The simulations are performed with an GPU-accelerated in-house developed code using mesh-free methods which easily handle large deformations while classic methods like FEM would require intensive remeshing. The Johnson-Cook flow stress model is implemented and used to evaluate the applicability of a model for ductile material behaviour in the transition zone between ductile and brittle removal mode. The simulation results are compared with results obtained from single grain scratch experiments using a real, non-idealised grain geometry as present in the diamond wire sawing process.

Highlights

Hard and brittle materials, such as silicon, are difficult to machine as they exhibit high hardness and withstand high temperatures but show low resistance in shear and tension
Brittle cutting allows for higher material removal rates but leads to surface damage which is unwanted in the manufacturing process of silicon wafers and has to be removed by subsequent etching processes
This paper presents a simulation of silicon cutting with a single diamond grain

Summary

Introduction

Hard and brittle materials, such as silicon, are difficult to machine as they exhibit high hardness and withstand high temperatures but show low resistance in shear and tension. The material removal can change from ductile to brittle when increasing the depth of cut. Brittle cutting allows for higher material removal rates but leads to surface damage which is unwanted in the manufacturing process of silicon wafers and has to be removed by subsequent etching processes. It is desired to generate the wafer surface in the ductile. This paper presents a simulation of silicon cutting with a single diamond grain. Its geometry was determined before cutting using optical microscopy. The resulting grain geometry was 3D meshed and used to drive a process simulation with numerical methods.

Objectives

Methods

Results

Discussion

Conclusion