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.

An Iterative Size Effect Model of Surface Generation in Finish Machining

In this work, a geometric model for surface generation of finish machining was developed in MATLAB, and subsequently verified by experimental surface roughness data gathered from turning tests in Ti-6Al4V. The present model predicts the behavior of surface roughness at multiple length scales, depending on feed, nose radius, tool edge radius, machine tool error, and material-dependent parameters—in particular, the minimum effective rake angle. Experimental tests were conducted on a commercial lathe with slightly modified conventional tooling to provide relevant results. Additionally, the model-predicted roughness was compared against pedigreed surface roughness data from previous efforts that included materials 51CrV4 and AL 1075. Previously obscure machine tool error effects have been identified and can be modeled within the proposed framework. Preliminary findings of the model’s relevance to subsurface properties have also been presented. The proposed model has been shown to accurately predict roughness values for both long and short surface roughness evaluation lengths, which implies its utility not only as a surface roughness prediction tool, but as a basis for understanding three-dimensional surface generation in ductile-machining materials, and the properties derived therefrom.

The importance of wavelength for tight temperature control during μ-laser-assisted machining

The area of single point diamond turning of brittle materials like semiconductors and ceramics is significantly benefitted by incorporation of laser assistance. In a new developmental technology that is now recognized as micro-laser-assisted machining (μ-LAM), a laser is shone through a diamond tool to soften the high-pressure phase transformed ductile machining phases that in turn allows thermal softening and thereby enables a higher material removal rate during ductile mode machining. One of the lasers currently used in μ-LAM is the neodymium-doped yttrium aluminum garnet (Nd:YAG) laser operating at 100 W (continuous wave) at the wavelength of 1064 nm. Although this configuration has worked to the benefit of the technology, here we report futuristic developments that will significantly enhance temperature control by selecting a laser wavelength according to the material being machined, allowing tunable machining properties. The concept is illustrated with sample calculations for μ-LAM of silicon, and it appears to offer better target temperatures, thus enhancing the performance of the μ-LAM process.

MD simulation of stress-assisted nanometric cutting mechanism of 3C silicon carbide

Purpose This paper aims to reveal the mechanism for improving ductile machinability of 3C-silicon carbide (SiC) and associated cutting mechanism in stress-assisted nanometric cutting. Design/methodology/approach Molecular dynamics simulation of nano-cutting 3C-SiC is carried out in this paper. The following two scenarios are considered: normal nanometric cutting of 3C-SiC; and stress-assisted nanometric cutting of 3C-SiC for comparison. Chip formation, phase transformation, dislocation activities and shear strain during nanometric cutting are analyzed. Findings Negative rake angle can produce necessary hydrostatic stress to achieve ductile removal by the extrusion in ductile regime machining. In ductile-brittle transition, deformation mechanism of 3C-SiC is combination of plastic deformation dominated by dislocation activities and localization of shear deformation. When cutting depth is greater than 10 nm, material removal is mainly achieved by shear. Stress-assisted machining can lead to better quality of machined surface. However, there is a threshold for the applied stress to fully gain advantages offered by stress-assisted machining. Stress-assisted machining further enhances plastic deformation ability through the active dislocations’ movements. Originality/value This work describes a stress-assisted machining method for improving the surface quality, which could improve 3C-SiC ductile machining ability.

Ultrasonic vibration-assisted microgrinding of glassy carbon

Glassy carbon is an amorphous material which, due to its unique material properties, has recently been introduced to micro/nanoimprinting as mold substrates. However, since glassy carbon is a hard, brittle, and highly elastic material, the precision machining of micro/nanostructures on it remains a challenging task. In this research, ultrasonic vibration-assisted microgrinding was proposed for ductile machining of glassy carbon. To find suitable conditions, the effects of ultrasonic vibration assistance and tool inclination were investigated. The results showed that by utilizing ultrasonic vibration assistance and tool inclination, a ductile response was achieved with improved surface roughness. In addition, the periodical waviness of the groove edge due to material elastic recovery was successfully prevented. This study provided an insight into the kinematics in ultrasonic vibration-assisted grinding of a highly elastic, hard, and brittle material.