An experimental study of edge radius effect on cutting single crystal silicon

According to the hypothesis of ductile machining, brittle materials undergo a transition from brittle to ductile mode once a critical undeformed chip thickness is reached. Below this threshold, the energy required to propagate cracks is believed to be larger than the energy required for plastic deformation, so that plastic deformation is the predominant mechanism of material removal in machining these materials in this mode. An experimental study is conducted using diamond cutting for machining single crystal silicon. Analysis of the machined surfaces under a scanning electron microscope (SEM) and an atomic force microscope (AFM) identifies the brittle region and the ductile region. The study shows that the effect of the cutting edge radius possesses a critical importance in the cutting operation. Experimental results of taper cutting show a substantial difference in surface topography with diamond cutting tools of 0° rake angle and an extreme negative rake angle. Cutting with a diamond cutting tool of 0° rake angle could be in a ductile mode if the undeformed chip thickness is less than a critical value, while a ductile mode cutting using the latter tool could not be found in various undeformed chip thicknesses.     

Research into the transition of material removal mechanism for C/SiC in rotary ultrasonic face machining

Ceramic matrix composites of type C/SiC with superior properties have got increasing importance in many fields of industry, especially in the aerospace area. Rotary ultrasonic machining is a high-efficiency processing technology for these advanced materials. However, due to the inhomogeneity and anisotropy of these composites, the machining process is still challenging to achieve desired result due to the lack of understanding and control of material removal mechanism. In this paper, the maximum depth of penetration by diamond abrasives in workpiece material is proposed to quantify the material removal modes. A model of maximum depth of penetration for rotary ultrasonic face machining (RUFM) was developed based on the indentation theory. An experimental RUFM of C/SiC was carried out, and it revealed that the material removal mechanism transited from ductile mode to brittle fracture mode with the decrease of cutting speed. Similar transition was observed with the increase of feed rate and cutting depth. By comparing the measured cutting force with simulation, a critical depth of penetration for the cutting mechanism transition was defined at about 4 μm. The processed surface topography was studied, and the transition of material removal modes was identified by the sudden change of the 3D surface roughness map at the critical penetration depth. Thus, the maximum depth of penetration model developed in this paper can be applied to identify the ductile or brittle fracture removal mode in RUFM of C/SiC using the cutting parameters. This allows controlling the material removal mechanism to achieve desired machining efficiency and quality.     

An experimental study on the machining characteristics in ductile-mode milling of BK-7 glass

Glass is considered as one of the most challenging materials to machine because of its high hardness coupled with high brittleness. The challenge, in machining such a brittle material, lies in achieving the material removal through plastic deformation rather than characteristic brittle fracture. It has already been established that every brittle material, no matter how brittle it is, can be machined in ductile mode under certain critical conditions. The critical conditions are material specific, and hence, every material tends to show unique behavior in terms of critical conditions during machining process. This paper outlines the results of an experimental study to determine the critical chip thickness for ductile–brittle transition, chip morphology, and the effect of cutting speed on the critical conditions in peripheral milling process of BK-7 glass. It is established experimentally that the cutting speed affects the chip morphology, machined surface quality, and critical conditions due to possible thermal effects in such a way that ductile–brittle transition phenomenon is facilitated at high cutting speeds.     

Analysis and monitoring of mode transitions during afm nanomachining of IZO-Coated pyrex glass

The goal of this research is to investigate and monitor machining mode transitions during nanoscale scratching of IZO-coated Pyrex glasses using atomic force microscope (AFM). Among the AFM nanomachining mode features, which include elastic/plastic deformations and crack generation, pile-up (by ploughing) is a key surface phenomenon that can represent plastic deformation characteristics, such as a sign of chip making. Moreover, because the pile-up formation mechanism of coated materials is reported to be distinct from that of bulk materials, the examination of pile-up in coated materials is challenging, along with brittle transition (crack initiation). In this research, the pile-up formation and crack initiation, that occur during nanoscratching, were examined and analyzed near the coating-substrate (glass) boundary. In addition, acoustic emission (AE), a sensing scheme with nanoscale sensitivity, was introduced to detect significant machining state variations and mode transitions. Experimental and analysis results indicate that the proposed scheme is viable for characterizing/monitoring the nanoscale machining of coated materials.     

Micro/nano Indentation and Single Grit Diamond Grinding Mechanism on Ultra Pure Fused Silica

The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very smoothed surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage.The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass.In this paper,the critical brittle/ductile depth,the inf...     

石英玻璃的单颗磨粒划擦应力场解析模型及损伤可控磨削机理研究

构建了单颗磨粒划擦各向同性硬脆材料的弹性应力场解析模型,并以此为基础提出单颗磨粒划擦各向同性硬脆材料表面的裂纹失稳扩展临界函数,临界函数包含原始表面应变速率、磨削液等因素对裂纹扩展造成的影响。将石英玻璃作为研究对象,深入分析了表面微裂纹损伤的可控磨削机理。在进行石英玻璃的磨削试验中,材料的磨削机理随单颗磨粒磨削深度的增加而变化,依次是塑性域去除、低载半脆性域去除、全脆性域去除和高载半脆性域去除。在1 mm/min的工件进给速度下,可以对石英玻璃进行塑性域磨削,从而获得无裂纹损伤的光滑磨削表面,然而其磨削效率较低,在实际生产中不能发挥理想的作用。对石英玻璃开展全脆性域磨削时,材料去除率较高、加工表面表面质量好、微裂纹损伤深度较小,砂轮自锐性良好,是一种优良的精密磨削工艺。     

Specific grinding energy as an in-process control variable for ductile-regime grinding

This article addresses the problem of monitoring the material removal regime (ductile versus brittle) that occurs during the grinding of brittle materials. Often a ductile grinding regime is desired, but currently there is no way to measure the grinding ductility “in process.” A model is developed to describe the dependence of the specific grinding energy on the material removal regime. It is found that the specific grinding energy will remain relatively constant for ductile-regime grinding but will decrease in a power-law relationship with an increasing material removal rate for brittle-regime grinding. Experimental confirmation of the proposed model is presented. The potential for using measurements of specific grinding energy to control the grinding ductility is established, and the benefits of such a closed-loop feedback system in ductile-regime grinding are explained.     

单晶硅片磨削表面相变研究

为了揭示硅片自旋转磨削加工过程中材料的去除机理,采用显微拉曼光谱仪研究了硅片磨削表面的相变。结果表明：半精磨和精磨硅片表面存在-Si相、Si-III相、Si-IV相和Si-XII相,这表明磨削过程中Si-I相发生了高压金属相变（Si-II相）,Si-II相容易以塑性方式去除。粗磨硅片表面没有明显的多晶硅,只有少量的非晶硅出现,材料以脆性断裂方式去除。从粗磨到精磨,材料去除方式由脆性断裂去除向塑性去除过渡。粗磨向半精磨过渡时,相变强度越大,材料的塑性去除程度越大;半精磨向精磨过渡时,相变强度越小,材料的塑性去除程度越大。     

A study on the effect of tool-edge radius on critical machining characteristics in ultra-precision milling of tungsten carbide

A crack-free surface can be finished on brittle materials by a specialized but traditional machining technique known as ductile-mode machining. In ductile-mode machining of brittle material, crack propagation is suppressed by selecting a suitable combination of tool and machining parameters leading to the removal of material through plastic deformation enabled by dislocation motion. In ductile-mode machining, the tool–workpiece interaction is of critical significance for the capability of the cutting process to finish a crack-free surface on a brittle material. This interaction is largely dictated by the cutting-edge radius of the tool when the undeformed chip thickness is comparable to the edge radius as is the case of ductile-mode machining. This paper presents the experimental results of ductile-mode milling of tungsten carbide to investigate the effect of cutting-edge radius on certain critical machining characteristics associated with the ductile–brittle transition specific to milling process of brittle material. The experimental results have established that an increase in the cutting-edge radius within a certain range increases the critical feed per edge leading to the improvement of material removal rate in ductile-mode milling. An increasingly negative effective rake angle is desired during milling with larger edge-radiused tool to suppress the crack propagation in the cutting zone to achieve ductile-mode machining. The results also identify the effect of the edge radius on certain other parameters such as critical specific cutting energy, plowing effect and subsurface damage depth to comprehend the ductile–brittle transition phenomenon in ductile-mode milling.     

光学玻璃塑性模式超精密磨削加工的研究

利用超精密磨床磨削加工6种典型的光学玻璃,先从理论上研究了脆性材料脆塑转变的临界值,然后对脆性材料作了大量磨削实验,实验结果表明,超精密磨削脆性材料时存在着断裂模式,断裂与塑性模式、塑性模式,这些模式主要由砂轮磨粒的切削深度进行控制,该磨削表面粗糙度与磨粒尺寸的大小,砂轮的进给量及玻璃的材料有关,当光学玻璃在塑性模式磨削时,其表面层不会产生任何裂纹缺陷,利用超精密磨床进行磨削加工,获得的表面粗糙度Ra低于5nm。     

光纤端面研磨加工机理研究

给出了研磨光纤时的材料去除机理,选用粒度为微米及亚微米级的金刚石磨料砂纸,在研磨压力为0.48Mpa时,在KE-OFP-12型光纤连接器研磨机上对光纤端面进行了研磨实验.结果表明:光纤研磨加工的材料去除存在脆性断裂、半脆性半延性、延性等3种模式.材料去除模式主要取决于磨料的平均粒度,磨料粒度为3μm时,为脆性断裂到延性研磨的临界转换点.并从理论上对结果进行了分析,光纤以延性模式研磨加工时,光纤表面粗糙度Ra可达到纳米级,其表面看不到任何划痕,而光纤以脆性断裂模式研磨加工时,其表面粗糙度只能达到亚微米级,证明材料以延性模式去除是提高光纤表面质量的有效方法.     

A review on ductile mode cutting of brittle materials

Brittle materials have been widely employed for industrial applications due to their excellent mechanical, optical, physical and chemical properties. But obtaining smooth and damage-free surface on brittle materials by traditional machining methods like grinding, lapping and polishing is very costly and extremely time consuming. Ductile mode cutting is a very promising way to achieve high quality and crack-free surfaces of brittle materials. Thus the study of ductile mode cutting of brittle materials has been attracting more and more efforts. This paper provides an overview of ductile mode cutting of brittle materials including ductile nature and plasticity of brittle materials, cutting mechanism, cutting characteristics, molecular dynamic simulation, critical undeformed chip thickness, brittle-ductile transition, subsurface damage, as well as a detailed discussion of ductile mode cutting enhancement. It is believed that ductile mode cutting of brittle materials could be achieved when both crack-free and no subsurface damage are obtained simultaneously.     

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.     

A review on the current research trends in ductile regime machining

Ductile regime machining is an alternative method for polishing of brittle materials to obtain a high quality surface finish by a ductile or plastic material removal process. Hence, there is a growing interest to study ductile regime machining over several decades. This paper reviews current state of research and development in ductile regime machining. The research and development associated with mechanism of brittle–ductile transition, surface integrity, and the factors influencing ductile regime machining are discussed in details in this paper.     

超声波振动金刚石刀具对脆性材料临界切削深度的影响

通过脆性材料沟槽切削试验,研究了超声波直线振动金刚石刀具和超声波椭圆振动金刚石刀具对脆性材料临界切削深度的影响,与没加超声波振动的金刚石刀具相比,超声波振动金刚石刀具能增大对脆性材料塑性切削的临界切削深度。提出了超声波振动金刚石刀具切削脆性材料临界切削深度计算公式,分析了导致超声波振动金刚石刀具增大脆性材料塑性切削的临界切削深度的原因。     

Transition temperature and fracture mode of as‐castand austempered ductile iron

The ductile to brittle transition temperature is a very important criterion that is used for selection of materials in some applications, especially in low‐temperature conditions. For that reason, in this paper transition temperature of as‐cast and austempered copper and copper–nickel alloyed ductile iron (DI) in the temperature interval from ?196 to +150°C have been investigated. The microstructures of DIs and ADIs were examined by light microscope, whereas the fractured surfaces were observed by scanning electron microscope. The ADI materials have higher impact energies compared with DIs in an as?cast condition. In addition, the transition curves for ADIs are shifted towards lower temperatures. The fracture mode of Dls is influenced by a dominantly pearlitic matrix, exhibiting mostly brittle fracture through all temperatures of testing. By contrast, with decrease of temperature, the fracture mode for ADI materials changes gradually from fully ductile to fully brittle.     

Characteristics of ultrasonic vibration-assisted ductile mode cutting of tungsten carbide

In this study, investigations were carried out to evaluate the characteristics of ultrasonic vibration-assisted cutting of tungsten carbide material using a CNC lathe with CBN tool inserts. The cutting forces were measured using a three-component dynamometer, and the machined workpiece surfaces and chip formation were examined using a SEM. The experimental results showed that the radial force F _x was much larger than the tangential force F _z and axial force F _y . The SEM observations on the machined workpiece surfaces and chip formation indicated that the critical condition for ductile mode cutting of tungsten carbide was mainly the maximum undeformed chip thickness when the tool cutting edge radius was fixed, that is, the ductile mode cutting can be achieved when the maximum undeformed chip thickness was smaller than a critical value. Corresponding to the chip formation mode (ductile or brittle), three types of the machined workpiece surfaces were obtained: fracture free surface, semi-fractured surface and fractured surface. It was also found that the cutting speed has no significant effect on the ductile chip formation mode.     

Effect of speed on material removal behavior in scribing of monocrystalline silicon

This paper investigates the effect of scribing speed on the surface morphology and material removal behavior in diamond wire sawing of monocrystalline silicon through specially designed high-speed diamond scribing experiments. High-speed scribing tests are performed on a (100) monocrystalline silicon wafer over a wide range of speeds. The results show that a higher scribing speed is prone to inducing more surface defects such as burrs and tearing in the ductile scribing region, and more radial cracks in the brittle scribing region. The critical scribing depth of ductile-to-brittle transition is found to decrease with increasing scribing speed. A strain rate hardening effect is evident in the experimental data, which explains the underlying mechanism for promotion of brittle fracture at higher scribing speeds.     

NANOSCALE CUTTING OF MONOCRYSTALLINE SILICON USING MOLECULAR DYNAMICS SIMULATION

It has been found that the brittle material, monocrystalline silicon, can be machined in ductile mode in nanoscale cutting when the tool cutting edge radius is reduced to nanoscale and the undeformed chip thickness is smaller than the tool edge radius. In order to better understand the mechanism of ductile mode cutting of silicon, the molecular dynamics (MD) method is employed to simulate the nanoscale cutting of monocrystalline silicon. The simulated variation of the cutting forces with the tool cutting edge radius is compared with the cutting force results from experimental cutting tests and they show a good agreement. The results also indicate that there is silicon phase transformation from monocrystalline to amorphous in the chip formation zone that can be used to explain the cause of ductile mode cutting. Moreover, from the simulated stress results, the two necessary conditions of ductile mode cutting, the tool cutting edge radius are reduced to nanoscale and the undeformed chip thickness should be smaller than the tool cutting edge radius, have been explained.     

岩石切削过程中破坏机制的离散元分析

利用离散单元方法(DEM)对两种不同属性的花岗石样本模型进行了切割模拟,通过调整不同的切削参数计算并分析了岩石切削过程中的切削力、切削深度、切削比能及切削力倾角的变化规律,从细观上探讨了临界切深对岩石脆性破坏模式和塑性破坏模式及其转变的影响,指出了当切削深度逐渐增大时,破坏模式依次从塑性破坏模式到过渡破坏模式最后转变为脆性破坏模式,同时切削力倾角并不随切削深度变化。将离散单元法分析的结果与实际实验进行了比较,表明该方法是合理的。