A study of the effect of tool cutting edge radius on ductile cutting of silicon wafers

Ductile mode cutting of silicon wafers can be achieved under certain cutting conditions and tool geometry. An experimental investigation of the critical undeformed chip thickness in relation to the tool cutting edge radius for the brittle-ductile transition of chip formation in cutting of silicon wafers is presented in this paper. Experimental tests for cutting of silicon wafers using diamond tools of different cutting edge radii for a range of undeformed chip thickness are conducted on an ultra-precision lathe. Both ductile and brittle mode of chip formation processes are observed in the cutting tests. The results indicate that ductile cutting of silicon can be achieved at certain values of the undeformed chip thickness, which depends on the tool cutting edge radius. It is found that in cutting of silicon wafers with a certain tool cutting edge radius there is a critical value of undeformed chip thickness beyond which the chip formation changes from ductile mode to brittle mode. The ductile-brittle transition of chip formation varies with the tool cutting edge radius. Within the range of cutting conditions in the present study, it has also been found that the larger the cutting edge radius, the larger the critical undeformed chip thickness for the ductile-brittle transition in the chip formation.     

An edge reversal method for precision measurement of cutting edge radius of single point diamond tools

A method, which is referred to as the edge reversal method, is proposed for precision measurement of the cutting edge radius of single point diamond tools. An indentation mark of the cutting edge which replicates the cutting edge geometry is firstly made on a soft metal substrate surface. The cutting edge of the diamond tool and its indentation mark, which is regarded as the reversal cutting edge, are then measured by utilizing an atomic force microscopy (AFM), respectively. The cutting edge radius can be accurately evaluated through removing the influence of the AFM probe tip radius, which is comparable to the cutting edge radius, based on the two measured data without characterization of the AFM probe tip radius. The results of measurement experiments and uncertainty analysis are presented to demonstrate the feasibility of the proposed method.     

Experimental study on size effect of tool edge and subsurface damage of single crystal silicon in nano-cutting

A method for fabricating a diamond tool with controllable edge radius was proposed. Using diamond tools with different edge radii at a low speed, nano-cutting tests were performed on single crystal silicon using a special instrument with SEM online observation. The chip morphology and deformation coefficient were analyzed to study the size effect of tool edge in the ductile-cut region. Electron back-scattered diffraction and laser micro-Raman spectroscopy were employed to detect subsurface damage in the machined silicon. The results indicated that the cutting-induced amorphous layer thickness is strongly dependent on the depth of cut and tool edge radius. In the beginning, the amorphous damage layer thickness decreases rapidly with the depth of cut, and then it increases gradually with the further increase in the depth of cut. The minimum amorphous damage can be obtained when the depth of cut is comparable to the tool edge radius.     

Tool edge radius effect on cutting temperature in micro-end-milling process

The cutting temperature plays an important role in micro-scale cutting process due to the fact that the dimension of the micro-cutter is small and the value of micro-cutter wear is sensitive to temperature. In this paper, the temperature distribution of the micro-cutter in the micro-end-milling process has been investigated by numerical simulations and experimental approach. Micro-end-milling processes are modeled by the three-dimensional finite element method coupling thermal?Cmechanical effects. The micro-cutter cutting temperature distribution, the effect of various tool edge radii on cutting force, and the effective stress during micro-end-milling of aluminum alloy Al2024-T6 using a tungsten-carbide micro-cutter are investigated on. The simulation results show that with increase of tool edge radius the cutting force increases, while the effective stress and mean cutting temperature decreases slightly. In increasing the tool edge radius, the maximum effective stress and cutting temperature region of the micro-cutter occur from the rake face to the corner on the tool edge and the flank face. The tool edge radius has been found to be the major factor affecting micro-cutter temperature distribution. The experimental verification of the simulation model is carried out on a micro-end-milling process of aluminum alloy 2024-T6 with a high-precision infrared camera. The influence of tool edge radius on cutting temperature distribution was verified in experiments.     

Study of EDM cutting of single crystal silicon carbide

Electrical discharge machining (EDM) is developing as a new alternative method for slicing single crystal silicon carbide (SiC) ingots into thin wafers. Aiming to improve the performance of EDM slicing of SiC wafers, the fundamental characteristics of EDM of SiC single crystal were experimentally investigated in this paper and compared to those of steel. Furthermore, EDM cutting of SiC ingot by utilizing copper foil electrodes was proposed and its performance was investigated. It is found that the EDM characteristics of SiC are very different from those of steel. The EDM machining rate of SiC is higher and the tool wear ratio is lower compared to those of steel, despite SiC having a higher thermal conductivity and melting point. Thermal cracks caused by the thermal shock of electrical discharges and the Joule heating effect due to the higher electrical resistivity are considered to be the main reasons for the higher material removal rate of SiC. It is concluded that the new EDM cutting method utilizing a foil electrode instead of a wire electrode has potential for slicing SiC wafers in the future.     

Critical cutting thickness in ultra-precision machining of single crystal silicon

This paper makes use of a strain gradient theory to obtain excellent consistency between observed experimental phenomena and theoretical calculations in exploring the brittle–ductile transition mechanism of single crystal silicon (SCS). The critical cutting thickness in the ultra-precision machining of SCS is then derived by means of theoretical calculations. SCS was first subjected to nanoindentation, and it was observed that under a particular scale of deformation, the silicon not only underwent plastic deformation, but more importantly also experienced strain gradient effects. This can be attributed to different types of dislocation motion present in the crystal, suggesting that the plastic deformation of SCS is caused by geometrically necessary dislocations, and that a size effect fulfills the necessary conditions for plastic region machining of SCS. Subsequently, the ability of scale gradient theories to link together microscopic mechanisms with observable mechanical properties was utilized to calculate the critical cutting thickness in the ultra-precision machining of SCS as approximately between 110 and 220 nm, a result which was then verified by experimental means.     

The upper bound of tool edge radius for nanoscale ductile mode cutting of silicon wafer

For ductile mode cutting of brittle materials, such as silicon wafers, the undeformed chip thickness has to be smaller than the tool edge radius. In practical application, for high production rate, the undeformed chip thickness is expected to be as large as possible. Therefore, the tool edge radius is expected to be as large as possible. In this study, the upper bound of the tool edge radius is investigated through cutting experiments.     

Modeling of the effect of tool edge radius on surface generation in elliptical vibration cutting

The elliptical vibration cutting (EVC) technique has been found to be a promising technique for ultraprecision machining of various materials. During the EVC process, two-dimension vibration movement of the cutting tool generates consecutively overlapping EVC cycles. In each cycle, the tool position relative to the workpiece gets continuously varied, and meanwhile, cusps are left along the nominal cutting direction. Such vibration marks, which have never been found in conventional cutting process, are considered to be a critical characteristic for the EVC technique. In order to analyze this unique characteristic, an analytical model based on geometrical relationships in the EVC process was developed to calculate the theoretical roughness, where the tool edge is assumed to be perfectly sharp. However, the effect of tool edge radius is probably significant, especially in the situation where the tool edge radius is comparable to the vibration amplitudes. Hence, in the present research, an analytical surface generation model for the EVC process is developed to better understand the surface generation process and predict the surface roughness. The tool edge radius is considered and investigated in detail in this new approach. Mathematical evaluation shows that the surface roughness value along the nominal cutting direction decreases with the increase of the edge radius. In order to validate the proposed model, a series of EVC grooving tests on soft and hard work materials were conducted using a polycrystalline diamond (PCD) tool by applying the ultrasonic EVC technique. The results show that the predicted roughness based on the proposed model correlates well with the experimental results measured by a white light interferometer, and the model considering the tool edge radius performs significantly better than the one without considering the edge radius in predicting the roughness along the nominal cutting direction.     

Study of the upper bound of tool edge radius in nanoscale ductile mode cutting of silicon wafer

In cutting of brittle materials, experimentally it was observed that there is an upper bound of tool cutting edge radius, beyond which, although the undeformed chip thickness is smaller than the tool cutting edge radius, the ductile mode cutting cannot be achieved. However, why there is an upper bound of tool cutting edge radius in nanoscale ductile mode cutting of brittle materials has not been fully understood. In this study, based on the tensile stress distribution and the characteristics of the distribution obtained from molecular dynamics simulation of nanoscale ductile cutting of silicon, an approximation for the tensile stress distribution was obtained. Using this tensile stress distribution with the principles of geometrical similarity and fracture mechanics, the critical conditions for the crack initiation have been determined. The result showed that there is a critical tool cutting edge radius, beyond which crack initiation can occur in the nanoscale cutting of silicon, and the chip formation mode is transferred from ductile to brittle. That is, this critical tool cutting edge radius is the upper bound of the tool cutting edge radius for ductile mode cutting of silicon.     

An experimental study on formation mechanisms of edge defects in orthogonal cutting of SiCp/Al composites

In this study, orthogonal cutting of SiCp/Al composites with a polycrystal diamond tool has been carried out. The influences of cutting velocity, cutting depth, and tool rake angle on the cutting force and edge defects near the exit of orthogonal cutting were analyzed in detail. The research results show that the influence of the cutting depth on cutting force is most obvious, and there is a close relationship between the cutting force and the size of edge defects. At the same time, the fractographs indicated that the brittle fracture mode corresponds to the dominant failure mode during machining of SiCp/Al composites with higher volume fraction and larger SiC particle. Therefore, in the precision and super-precision manufacturing of SiCp/Al composites, with a proper tool rake angle, adopting higher cutting velocity and lower cutting depth not only can reduce the cutting force effectively but also can ensure cutting edge quality.     

Investigation of the effect of cutting tool edge radius on material separation due to ductile fracture in machining

This paper investigates the interaction between cutting tool edge radius and material separation due to ductile fracture based on Atkins’ model of machining. Atkins’ machining model considers the energy needed for material separation in addition to energies required for shearing at the primary shear zone and friction at the secondary shear zone. However, the effect of cutting tool edge radius, which becomes significant at microcutting conditions, was omitted. In this study, the effect of cutting tool edge radius is included in the model and its influence on material separation is investigated. A modification to the solution methodology of Atkins’ machining model is proposed and it is shown that the shear yield stress and the fracture toughness of the work material can be calculated as a function of uncut chip thickness.     

Sustainability analyses of cutting edge radius on specific cutting energy and surface finish in side milling processes

The aim of this work is to determine the influence of cutting edge radius on the specific cutting energy and surface finish in a mechanical machining process. This was achieved by assessing the direct electrical energy demand during side milling of aluminium AW6082-T6 alloy and AISI 1018 steel in a dry cutting environment using three different cutting tool inserts. The specific energy coefficient was evaluated as an index of the sustainable milling process. The surface finish of the machined parts was also investigated after machining. It was observed that machining with the 48.50-μm cutting edge radius insert resulted in lower specific cutting energy requirements when compared with the 68.50 and 98.72-μm cutting edge radii inserts, respectively. However, as the ratio of the undeformed chip thickness to cutting edge radius is less than 1, the surface roughness increases. The surface roughness values gradually decrease as the ratio of undeformed chip thickness to cutting edge radius (h/r _e) tends to be 1 and at minimum surface roughness values when the ratio of h/r _e equalled to 1. However, the surface roughness values increased as h/r _e becomes higher than 1. This machining strategy further elucidates the black box and trade-offs of ploughing and rubbing characteristics of micro machining and optimization strategy for minimum energy and sustainable manufacture.     

An experimental study on machining techniques of cutting composite armors

The machining of laminated composite components or armors consisting of engineering ceramics, fiber-reinforced plastic, and even aluminum or titanium alloy is a great challenge to manufacturing engineers. So far, quite limited literatures can be found concerning the machining of laminated composite components, and the quite limited studies are mainly focused on the stacks consisting of metal plates and composite materials. Also, there is hardly any report concerning the cutting techniques of laminated composite components or armors. In this work, the cutting techniques of three types of composite armors such as the Kevlar fiber-reinforced plastic (KFRP) protection inner lineplate, the ceramic composite armor (ceramics/glass fiber-reinforced plastics/aluminum alloy laminate), and the double-plate composite armor (ceramics/KFRP laminate) were studied experimentally on a desktop cutting machine, using a sintering diamond saw. Two types of machining processes such as cocurrent cutting and reverse cutting were discussed, and finally, reverse cutting is recommended for better cutting quality. Cutting tests indicated that under proper processing conditions, high-quality cutting of composite armors can be carried out by using a sintering diamond saw.     

切削用量和钝圆半径对铣削45号钢的温度研究

在铣削加工过程中,刀具温度的变化情况对刀具的性能和寿命有重要的影响。本论文运用有限元分析软件Advant Edge FEM分析了切削用量和钝圆半径对铣削45号钢材料时刀具的温度变化情况。得到切削用量和钝圆半径对切削温度的影响规律,为铣削加工45号钢材料时铣刀刃口钝圆半径的设计提供依据。     

Influence of cutting edge radius on surface integrity and burr formation in milling titanium

The influence of the cutting edge micro geometry on cutting process and on tool performance is subject to several research projects. Recently, published papers mainly focus on the cutting edge rounding and its influence on tool life and cutting forces. For applications even more important, however, is the influence of the cutting edge radius on the integrity of the machined part. Especially for titanium, which is used in environments requiring high mechanical integrity, the information about the dependency of surface integrity on cutting edge geometry is important. This paper therefore studies the influence of the cutting edge radius on surface integrity in terms of residual stress, micro hardness, surface roughness and optical characterisation of the surface and near surface area in up and down milling of the titanium alloy Ti–6Al–4V. Moreover, the influence of the cutting edge radius on burr formation is analysed. The experiments show that residual stresses increase with the cutting edge radius especially in up milling, whereas the influence in down milling is less pronounced. The influence of the cutting edge radius on surface roughness is non-uniform. The formation of burr increases with increasing cutting edge radius, and is thus in agreement with the residual stress tests.     

Study of micro ball end mill geometry and measurement of cutting edge radius

Cutting edge radius plays an important role in conventional micro machining process, as it is of the same order as uncut chip thickness. Therefore it is important to measure the edge radius accurately. There is no recommended methodology, as of now, to measure edge radius of a ball end mill. An attempt is made in this paper to study edge radius of ball end mill at normal and transverse planes on a virtual ball end mill generated using kinematic relations in CAD environment. In the present study, non-destructive methods using confocal microscope and stereo microscope are used to measure edge radius. These measurements capture the edge radius on the transverse plane. For confirmation, the tool sectioned in the transverse plane by a low speed diamond saw is examined under scanning electron microscope and the radius is assessed using suitable software. Among the non-contact approaches proposed in this work, confocal method appeared to be more reliable considering the reproducibility aspect.     

A simple approach to fabricate amorphous silicon pattern on single crystal silicon

Scratch tests on single crystal silicon under dry sliding and pentadecane lubrication are performed on a commercially available nano-scratch tester. Loads range of elastic, elasto-plastic deformation and fracture are classified according to depth-load curves. A fully plastic removal of single crystal silicon below critical load for fracture is observed under pentadecane lubrication, which is quite different from that under dry sliding. Raman micro-spectra indicate that the phase compositions of the scratched track under dry sliding consist of a number of phases, including Si-I, Si-III, Si-XII and a-Si, while the phase composition of the track under pentadecane lubrication consists of single a-Si. Based on the results obtained, a simple approach to fabricate amorphous silicon pattern on single crystal silicon is introduced and discussed.     

An experimental study of cutting performance on monocrystalline germanium after ion implantation

Monocrystalline materials, such as silicon and germanium, are widely used in the semiconductor industry and optical engineering due to their excellent electrical and optical characteristics. However, it is difficult to achieve an ultraprecise mirrored surface with the turning process due to the hard and brittle nature of those materials. It has been proved that the machinability of silicon and silicon carbide can be enhanced in nanometric or ultra-precise diamond cutting by ion implantation. In this paper, we present diamond cutting of monocrystalline germanium implanted with copper ions and study the brittle–ductile transition phenomenon. Raman spectra and transmission electron microscopy are used to investigate details of the modified layer. The results show that a uniform amorphous layer is produced after implantation. The brittle–ductile transition depth of the modified germanium is up to 730 nm, which is an obvious increase from unmodified c-Ge.     

An experimental study on microcutting of silicon using a micromilling machine

Micro-end-milling can potentially create desired 3D free-form surface features on silicon using ductile machining technology. A number of technological barriers must be overcome for micro-end-milling to be applied in the cutting of single crystal silicon. To produce smooth surfaces on brittle materials, such as silicon, it is important that the material be machined in the ductile mode. A major limitation of machining brittle materials is that the process of removing the material can generate subsurface damage. We have carried out an experimental study to find the optimum cutting conditions for obtaining ductile regime machining using a micromilling machine. The ductile and brittle regimes in the machining of silicon using diamond-coated end mills were demonstrated by machining grooves. The force ratio, F_t/F_c, was used to determine the milling performance on silicon. The experimental data show that the dominant ductile cutting mode was achieved when F_t/F_c?>?1.0.