Simulation of the ductile machining mode of silicon

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.

Simulation of the Ductile Machining Mode of Silicon

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, thesurface is damaged during sawing. The extent of the damage depends primarily on the material removal mode. Undercertain conditions the generally brittle material can be machined in ductile mode, whereby considerably fewer cracksoccur in the surface than with brittle material removal. In the presented paper a numerical model is developed in orderto support the optimization of the machining process regarding the transition between ductile and brittle materialremoval. The simulations are performed with an GPUaccelerated in–house developed code using mesh-free methodswhich easily handle large deformations while classic methods like FEM would require intensive remeshing. Thesimulation results are compared with results obtained from single grain scratch experiments.

Experimental Study of the Impact of a Vibrating Wire on Free Abrasive Machining as Correlated to the Modeling of Vibration Subject to an Oscillating Boundary Condition

In this paper, we study experimentally the impact of a vibrating wire on the free abrasive machining (FAM) process in removing material from the surface of brittle materials, such as silicon. An experimental setup was designed to study the FAM process on silicon substrate surface by using a slurry-fed wire with a periodic excitation. An analytical solution of a wire moving axially, subject to an oscillating boundary condition with damping from abrasive slurry, was derived based on the partial differential equation of motion. Experiments were conducted on the apparatus using a wire with an oscillating boundary. It was found that the amplitudes of vibration were larger at the side of the oscillatory boundary, which caused more FAM interaction near the edge of the oscillatory boundary with larger material removal that was measured and validated. Furthermore, experiments were conducted to elucidate the effectiveness of brittle material removal using FAM with abrasive grits: (i) under dry condition, (ii) with water, and (iii) with abrasive slurry. Experimental results showed that the vibration of wire resulted in plastic deformation on the surface of silicon wafer. The abrasive grits in slurry driven by a vibrating wire generated material removal through observable grooves and fractures on the surface of silicon due to FAM in just a few minutes. The grooves from FAM process is an outcome of brittle machining through fracture formation and concatenation, generated by the indentation of abrasive grits on the silicon surface.

Research on High Volume Fraction SiCp/Al Removal Mechanism under Condition of Ultrasonic Vertical Vibration

High volume fraction SiCp/Al is a new kind of composite materials, with broad application prospect in the aerospace, automobile manufacturing and other fields, and gradually become the key materials in the field of high technology. But with its internal high hardness material (SiC) content increases and the material removal mechanism is not very clear, general machining is more difficult and seriously hinders the development of the material. With the advantages of high material removal rate, effectively processing all kinds of complicated curved surface, especially, in the thin-walled parts processing, milling occupies an absolute advantage. In order to solve the processing problems of high volume fraction SiCp/Al composites, basing on the theory of ultrasonic and brittle material removal. PCD milling experiment of SiCp/Al was carried out with homemade ultrasonic milling system under the condition of ultrasonic vertical vibration, the material removal mechanism was studied, the 2d and 3d model of surface formation was established, finally, microscopic structure on the surface of the workpiece was analyzed by metallographic microscope and electron microscope. Research results show that: SiC particle removal form can be divided into type of cut, pulled, pressed and crack penetration; under the condition of ultrasonic, probability of SiC particles cut type increased, this forms better surface smoothness; due to tool and chip separation characteristics and the ultrasonic impact effect on material, the removal mechanism of SiCp/Al is close to the plastic material, forming better surface quality under condition of ultrasonic. This paper verifies that the ultrasonic vertical vibration cutting is an effective machining method for high volume fraction SiCp/Al.