Producing nanorelief in machining hard brittle surfaces

Russian Engineering Research -     

Ultraprecision machining of brittle optical materials

Basic design principles for ultraprecision equipment are outlined. The parameters of the basic components are considered, and machining technology for brittle optical materials is described.     

Nano-abrasion machining of brittle materials and its application to corrective figuring

A method of ultraprecision abrasion machining named “Nano-abrasion machining” is proposed for optical finishing of brittle materials. The fundamental characteristics and its applicability for corrective figuring to improve form accuracy of optics of brittle materials are investigated. It is experimentally ascertained that the material removal rate and surface roughness are suitable for optical finishing. However, the cross-sectional profile of the machined spot that is dependent on the collision angle is a combination of V- and W-shape, which is unsuitable for the corrective figuring. Therefore, circular motion machining is introduced and a preferable profile with an axis-symmetric V-shape is realized. The machining method is applied to corrective figuring of optical glass of BK7. The NC program is generated with a computer program developed by modifying the scanning motion and the form accuracy is predicted. According to the simulation results, corrective figuring is performed. The flatness is improved from PV = 151 to 29 nm. From the experimental results, it is clarified that the nano-abrasion machining is applicable to corrective figuring of brittle materials.     

Processing capabilities of micro ultrasonic machining for hard and brittle materials: SPH analysis and experimental verification

Micro ultrasonic machining (micro-USM) is an unconventional micromachining technology that has capability to fabricate high aspect ratio micro-holes, intricate shapes and features on various hard and brittle materials. The material removal in USM is based on brittle fracture of work materials. The mechanical properties and fracture behaviour are different for varied hard and brittle materials, which would make a big difference in the processing capability of micro-USM. To study the processing capability of USM and exploit its potential, the material removal of work materials, wear of abrasive particles and wear of machining tools in USM of three typical hard and brittle materials including float glass, alumina, and silicon carbide were investigated in this work. Both smoothed particle hydrodynamics (SPH) simulations and verification experiments were conducted. The material removal rate is found to decrease in the order of glass, alumina, and silicon carbide, which can be well explained by the simulation results that cracking of glass is faster and larger compared to the other materials. Correspondingly, the tool wear rate also dropped significantly thanks to the faster material removal, and a formation of concavity on the tool tip center due to intensive wear was prevented. The SPH model is proved useful for studying USM of different hard and brittle materials, and capable of predicting the machining performance.     

Design and development of PCD micro straight edge end mills for micro/nano machining of hard and brittle materials

One of the biggest challenges for mechanical micro/nano milling is the design and fabrication of high precision and high efficiency micro milling tools. Commercially available micro milling tools are either too expensive (around several hundred US dollars) or simply made from downsizing of macro milling tools, which is sometimes not appropriate for the specific micro/nano milling requirements. So the design and fabrication of custom micro milling tools are necessary. In this paper, a micro straight edge endmill (SEE) is designed. Static and dynamic FEM analyses have been done for the SEEs with different rake angles trying to identify their stiffness and natural frequencies. By wire electrical discharge machining (WEDM), the SEEs made of polycrystalline diamond (PCD) with three different rake angles have been fabricated. The evaluation milling on tungsten carbide (WC) and silicon wafer have processed on a nano milling center. Experimental results show the SEEs have a good ability to simultaneously micro/nano milling of both the side and bottom surfaces with submicron surface roughness, and the SEE has high accuracy for large aspect ratio thin wall machining. The milling experiments on silicon wafer have successfully demonstrated that ductile mode machining was achieved and the coolant played an important role in silicon wafer milling.     

硬脆材料切削加工负切削力现象的研究

以辉长岩为例,采用聚晶金刚石刀具进行硬脆材料切削加工试验,,在时域和频域内对切削力信号进行数字信号分析处理,提出硬脆材料切削力可分成切削趋势量和切削力随机量两部分;硬脆材料的组成结构特点和切削中刀具的振动是硬脆材料切削力出现负值现象的主要原因。     

Features of wear of brittle inorganic materials during friction and abrasive machining

Laser confocal microscopy reveals fatigue cracking under the surface of silicate glass upon friction and abrasive machining. Surface cracking is also registered and its maximum depth is determined, indicating that its longitudinal cross section has an irregular profile. The stage of fatigue wear of the glass corresponding to debris nucleation shouldbe visualized. It is established that the mass wear rate and the maximum surface cracking depth are correlated: once a definite sliding velocity is reached, the cracking becomes deeper and the wear rate intensifies in both types of tests. The obtained results prove that several wear mechanism can occur simultaneously during abrasive machining of brittle inorganic materials, namely, brittle chipping, low-cycle fatigue, thermomechanical fracture, and local melting (under critical loading conditions).     

A new representation with probability distribution for nanometric surface roughness in ultra-precision machining

Ultra-precision machining (UPM) commonly produces nanometric surface roughness (NSR), which is governed by high-frequency components with tool marks sensitive to noise. Its spacing features (SF) majorly affect optical quality by diffraction and interference. However, the ISO SR standard cannot effectively represent SF. In this study, a new representation for SF was developed by evaluating surface derivative, as extra SR parameters. Probability distribution with the 95–99 rule was adopted to reduce noise effects. The results were found that the extra SR parameters well represents SF and are sensitive to spatial frequency. Probability distribution is an efficient means of reducing noise effects. Significantly, the proposed method is simple and efficient to represent SF of NSR in UPM.     

Dicing of hard and brittle materials with on-machine laser-dressed metal-bonded diamond blades

The ultra-precision dicing of hard and brittle materials causes high wear on the abrasive tool which results in the deterioration of blade cross section as well as the decrease of diamond grain exposure. Resin-bonded diamond blades are used due to their in-process self-sharpening capability. Nevertheless, the shape of the blade cross section generated by self-sharpening is random which leads to poor accuracy when precise grooves need to be produced. Metal-bonded diamond blades feature higher tool lifetime and shape accuracy compared to resin-bonded blades, but are not capable of performing self-sharpening. In this study, the laser dressing of metal-bonded diamond blades is investigated to enable their use in the ultra-precision dicing of hard and brittle materials by continuous laser dressing. We investigated laser dressing with and without the presence of cooling water. The sharpness (grain exposure) after dressing is measured by the cutting face surface roughness. The dicing performance is evaluated by observing the dicing results in terms of cutting depth consistency and by monitoring the spindle power during dicing. Dicing blades which have been laser dressed in an environment with coolant feature less grain exposure than dicing blades which have been laser dressed in dry condition. The dicing results show an improvement in the sharpness and durability of laser-dressed dicing blades in comparison with new or conventionally dressed blades. The ability to apply and perform laser dressing on a dicing machine in an environment with coolant shows the feasibility of laser technology for continuous dressing.     

Wear characteristics of various hard materials for machining sic-reinforced aluminum alloy

The results of a machinability study of an Al-40vol.%SiC composite alloy, using a large collection of experimental and commercial cutting tools, are described in this report. It was observed that the wear rate of tools harder than silicon carbide was inversely proportional to their hardness. All cutting tools evaluated, however, wore rather rapidly and only polycrystalline diamond tools provided somewhat useful tool life. The expected production cost of a precision part from this alloy would be high because of the short tool life and relatively high price of the only usable cutting tool for this application.     

Self-tuned ultrasonic elliptical vibration cutting for high-efficient machining of micro-optics arrays on brittle materials

Ultrasonic elliptical vibration cutting is a very promising technique for the machining of brittle materials. However, its machining performance is currently limited by the ductile machining model and the machining strategy with a constant feed rate, leading to low machining efficiency. To overcome this defect, this paper presents a novel self-tuned ultrasonic elliptical vibration cutting (SUEVC) technique to achieve high-efficient ductile-regime machining of the micro-optics array on brittle materials. The proposed SUEVC includes a ductile-regime machining model and a tool path generation method. In SUEVC, the feed rate adaptively changes with respect to the local shape variation of the desired surface along the feeding direction to ensure both crack-free surface and high machining efficiency. Finally, two 1 × 3 spherical micro-optics arrays were successfully fabricated on single-crystal MgF₂ by SUEVC and the traditional machining strategy respectively. Results demonstrated that the SUEVC could enhance the machining efficiency by 30% relative to the traditional machining strategy, while maintaining similar surface roughness and a crack-free surface.     

Material removal model of ultrasonic elliptical vibration-assisted chemical mechanical polishing for hard and brittle materials

Friction stir welding (FSW) has emerged as an attractive process for fabricating aerospace vehicles. Current FSW state-of-the-art uses large machines that are not portable. However, there is a growing need for fabrication and repair operations associated with in-space manufacturing. This need stems from a desire for prolonged missions and travel beyond low-earth orbit. To address this need, research and development is presented regarding two enabling technologies. The first is a self-adjusting and aligning (SAA) FSW tool that drastically reduces the axial force that has historically been quite large. The SAA-FSW tool is a bobbin style tool that floats freely, without any external actuators, along its vertical axis to adjust and align with the workpiece’s position and orientation. Successful butt welding of 1/8 in. (3.175 mm) thick aluminum 1100 was achieved in conjunction with a drastic reduction and near elimination of the axial process force. Along with the SAA-FSW, an innovative in-process monitor technique is presented in which a magnetoelastic force rate-of-change sensor is employed. The sensor consists of a magnetized FSW tool that is used to induce a voltage in a coil surrounding the tool when changes to the process forces occur. The sensor was able to detect 1/16 in. (1.5875 mm) diameter voids. It is concluded that these technologies could be applied toward the development of a portable FSW machine for use in space.     

基于噪声信号的难加工表面损伤在线监测

提高难加工材料的加工效率在机械加工中有着巨大的经济价值,但是由于一些加工表面损伤的存在如白层,难加工材料的加工效率仍处于一个很低的状态.加工材料表面的白层只能在加工之后才能被发现.这对刀具磨损,加工质量等有着巨大的危害.因此在线监测难加工表面损伤具有巨大的经济意义.建立一个基于实时切削噪声信号的在线监测系统对白层,表面质量和刀具磨损进行监测分析.实验表明噪声信号均方根值,频率与白层有着极大的相关性.     

Precision grinding device for radioactive tracer diffusion studies in very hard ceramic materials

Precision grinding equipment for the removal of very thin layers of hard materials containing slowly diffusing isotope tracers is described. The system is unique in the use of vacuum techniques to hold the sample in place and in the procedures used to insure maintenance of an optically flat sample with essentially parallel faces throughout the removal process.     

A study on combined vibration drilling by ultrasonic and low-frequency vibrations for hard and brittle materials

This research aims to improve machining accuracy concerning the method of drilling ceramics and other hard and brittle materials as well as to establish a drilling technology that would ensure high efficiency and longer life of tools. Specifically, the authors contrived a new drilling method that combines ultrasonic vibrations of a diamond core drill and low-frequency vibrations of the workpiece and produced a combined vibration drilling apparatus experimentally. In this paper, the combined vibration drilling apparatus is used for a series of experiments under different vibration conditions to examine the behavior of drilling force, drilled hole accuracy, and edge chipping on the drilled hole surface. In addition, the behavior of tools during combined vibration drilling are theoretically examined. As a result of these considerations, the authors found that combining ultrasonic and low-frequency vibrations is one of the most effective methods for drilling hard and brittle materials.     

弹性薄片零件精密加工技术

分析了弹性薄片零件难以加工的原因 ,并对其精密加工的技术途径进行了研究。     

Influence of material microstructure changes on surface integrity in hard machining of AISI 52100 steel

Residual stresses are a consequence of thermo-mechanical and microstructural phenomena generated during the machining operation. Therefore, for improving product performance in machined hardened steels, material microstructure changes (commonly referred to as white and dark layers) must be taken into account. This paper presents a finite element model for white and dark layers formation in orthogonal machining of hardened AISI 52100 steel. In particular, a hardness-based flow stress and empirical models for describing the white and dark layers formation were developed and implemented in the finite element code. A series of experiments was carried out in order to validate the proposed simulation strategy and to investigate the influence of material microstructure changes on residual stresses. As main results, it was firstly demonstrated by surface topography analysis as both the white and dark layer are the result of microstructural alterations mainly due to rapid heating and quenching. Furthermore, it was found as both the presence of white and dark layers influence the residual stress profile. Particularly, the former significant impacts on the magnitude of maximum residual stress and on the location of the peak compressive residual stress; the latter reduces the compressive area.