Wear behavior of the abrasive grains used in optical glass polishing

In this work the wear behavior of cerium oxide abrasive grains during the glass polishing was studied. Polishing tests have been done by different types of cerium oxide abrasive grains. The grains have been recovered and examined during the operation. The morphology, the granulometric distribution, the chemical composition and the agglomeration phenomenon of recovered grains have been studied.     

Simulation of erosive smoothing in the abrasive jet micro-machining of glass

Abrasive jet micro-machining (AJM) is a promising technique to machine micro-features in brittle and ductile materials. However, the roughness of micro-channels machined using AJM is generally greater than that from other methods of micro-machining such as wet etching. Previous investigators have suggested that the surface roughness resulting from AJM can be reduced by post-blasting with abrasive particles at a relatively low kinetic energy. This approach was investigated in the present work by measuring the roughness reduction of a reference unmasked channel in borosilicate glass as a function of post-blasting particle size, velocity, dose, and impact angle. Post-blasting the reference channels reduced the roughness by up to 60%. It was observed that post-blasting at shallower angles was more efficient, probably due to the increased amount of edge chipping as opposed to cratering, which contributed to the enhanced removal of profile peaks, leaving a smoother surface. Moreover, post-blasting with smaller particles ultimately resulted in smoother surfaces, but at the penalty of requiring a relatively large particle dose, and consequently a significantly increased channel depth, before reaching the steady-state roughness. Hence, finishing with smaller particles until reaching the steady-state roughness may not be practical when a shallow channel is desired. A previously developed numerical model was modified and used to simulate the post-blasting process leading to the creation of smooth channels as a function of particle size, velocity, dose, impact angle, and target material properties. The model simulated both crater formation (due to growth of lateral cracks) and the chipping of facet edges. Comparisons with centerline roughness measurements for channels in borosilicate glass showed that the model can predict the transient roughness reduction with post-blasting particle dose with a 7% average error.     

Fixed abrasive machining of non-metallic materials

This paper summaries advancements in fixed abrasive machining of non-metallic materials, which include reinforced concretes, stones, rocks, carbon fiber reinforced plastic, metal and ceramic matrix composites, wood, wood-fiber plastic composite, biomaterials (bone, plaque, and enamel), and structural and electronic ceramics. The broad impacts, diverse applications, and innovations of fixed abrasive machining processes are presented. Benefits of the engineered deterministic distribution of abrasive grain grinding tools are demonstrated. Industrial perspectives and future research on innovative fixed abrasive machining technologies that enable new processes and improve the productivity are highlighted.     

Abrasive jet micro-machining of planar areas and transitional slopes in glass using target oscillation

Analytical models are presented which allow the prediction of the shape, sidewall slope, and depth of abrasive jet micro-machined planar areas and transitional slopes in glass using a novel technique in which the target is oscillated transversely to the overall scan direction. A criterion was developed to establish the minimum oscillation velocity to ensure negligible surface profile waviness in the scanning direction. If the oscillation velocity is sufficiently greater than the scanning velocity, the target receives an approximately uniform energy flux, resulting in a high degree of flatness for both masked and unmasked planar areas micro-machined in glass. It was also found that particle scattering from the mask edge caused the sidewalls of a planar area to be very shallow, on the order of a few degrees. Two methods were investigated to machine planar areas with increased sidewall slope using target oscillation: (i) machining micro-channels adjacent to the planned planar area, and (ii) target oscillation with an obliquely oriented nozzle. Among these two methods, target oscillation with an obliquely oriented nozzle created steeper sidewalls and was easier to implement, but it also caused appreciable mask under-etching. A major distinction between the target oscillation approach and a previously published method that was based on the superposition of the erosion profiles of adjacent nozzle scans, is that the latter is capable of machining an arbitrary surface profile over a large area, whereas the present target oscillation technique is intended only for the machining of flat planar areas at a single elevation. For such applications it is the preferred approach.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.     

On the analysis of the electrochemical spark machining process

The electrochemical spark machining (ECSM) process has been proved as a potential process for machining of low machinability high-strength electrically non-conducting materials, but the mechanism of material removal during the process, by and large, is not yet understood. In the present work, the electrochemical discharge is modelled as a phenomenon similar to that which occurs in arc discharge valves. This phenomenon is used to explain various experimental results, on the basis of circuit and arc discharge valve characteristics. The spark energy and the approximate order of hydrogen gas bubble diameter are computed by the proposed valve theory. Material removal rate is evaluated by modelling the problem as a 3-D unsteady state heat conduction problem. The problem is solved by the finite element method to compute the temperature distribution which is post-processed for estimating material removal per spark, overcut obtained in the machined cavity, and attainable maximum penetration depth. The conclusion drawn is that the application of valve theory to the ECSM process seems to be realistic. Estimated material removal rate, overcut and maximum penetration depth show a good agreement with experimental findings.     

Thick tool steel coatings using HVOF spraying for wear resistance applications

This paper deals with the processing of thick cold work tool steel coating using high velocity oxy-fuel (HVOF) spraying process. A full factorial experimental design was established to identify the influencing process parameters on the formation of dense coating with low oxidation. Microstructural analysis of the coating was carried out using optical, SEM and XRD techniques. Cold work tool steel coatings with a thickness up to 2 mm were developed on bond coated low carbon steel substrates for wear resistance evaluation. A pin on disc test was performed to examine the wear resistance of thick cold work tool steel coatings on different types and sizes of abrasive papers. The wear results were compared with the wear resistance of a standard high speed steel pin. The abrasive wear resistance of cold work tool steel coated pins was found to be superior against soft and fine abrasive papers than the standard high speed steel. Besides, the performance of the coated pins against hard and coarser abrasive papers was found to be similar to standard high speed steel. The study showed the potential of HVOF spraying on the development of thick cold work tool steel coatings for wear resistance applications.     

磨料水射流抛光技术及其发展

磨料水射流抛光技术是应用于表面抛光加工的新技术.利用含有细小磨料粒子的抛光液在高压作用下,与工件表面发生冲击、冲蚀而微去除材料,以达到抛光目的.论述了磨料水射流抛光技术的基本原理和特点,以及影响抛光效果的主要工艺参数,并对其发展趋势进行了展望.     

Magnetic field assisted abrasive based micro-/nano-finishing

Micro-/nano-machining (abbreviated as MNM) processes are classified mainly in two classes: traditional and advanced. Majority of the traditional MNM processes are embedded abrasive or fixed geometry cutting tool type processes. Conversely, majority of the advanced MNM processes are loose flowing abrasive based processes in which abrasive orientation and its geometry at the time of interaction with the workpiece is not fixed. There are some MNM processes which do not come under the abrasive based MNM category, for example, laser beam machining, electron beam machining, ion beam machining, and proton beam machining. This paper gives a comprehensive overview of various flowing abrasive based MNM processes only. It also proposes a generalized mechanism of material removal for these processes. The MNM processes discussed in this paper include: Abrasive Flow Finishing (AFF), Magnetic Abrasive Finishing (MAF), Magnetorheological Finishing, Magnetorheological Abrasive Flow Finishing, Elastic Emission Machining (EEM) and Magnetic Float Polishing. EEM results in surface finish of the order of sub-nanometer level by using the nanometer size abrasive particles with the precisely controlled forces. Except two (AFF and EEM), all other processes mentioned above use a medium whose properties can be controlled externally with the help of magnetic field. This permits to control the forces acting on an abrasive particle hence the amount of material removed is also controlled. This class of processes is capable to produce surface roughness value of 8 nm or lower. Using better force control and still finer abrasive particles, some of these processes may result in the sub-nanometer surface roughness value on the finished part. Understanding the mechanism of material removal and rotation of the abrasives in these processes will help in rationalization of some of the experimental observations which otherwise seem to be contradicting with the established theories. It also explains why a magnet used in MAF should have a slot in it even though the area under the slot has “non-machining” zone. It elaborates based on the experimental observations why to use pulse D.C. power supply in MAF in place of smooth D.C. power supply.     

磨料水射流喷嘴收缩段锥角对磨料粒子混合程度的影响

介绍了磨料水射流的起源、用途、特点及抛光原理,针对混合腔内磨料粒子与高压水束混合不均匀而影响抛光表面质量及磨料砂管使用寿命的缺陷,通过对磨料水射流切割喷嘴结构的研究,建立了对称双管供料喷嘴几何模型,并运用CFD软件对喷嘴内部流场进行仿真研究,分析了喷嘴收缩段锥角对磨料粒子和高压水束混合均匀程度的影响。研究结果表明:选择30°和45°的收缩段锥角有利于延长砂管使用寿命及提高磨料粒子与水射流的均匀混合,从而在抛光加工中提高工件表面质量。     

Modelling of Abrasive Waterjet Machining: A New Approach

Abrasive waterjet (AWJ) machining is one of the recent non-traditional methods starting to be used widely in industry for material removal of different materials. The cutting performance of AWJ is achieved by a very high speed, small-scale erosion process. In this paper, a modified form of Finnie's model for erosion is developed for application to AWJ. This modified form is able to deal with curved surfaces rather than flat surfaces only. Furthermore, the new modelling approach is capable of simulating multiple particle erosion. This approach uses standard material properties and requires no calibration constants. The modelled results agreed well with both experimental and analytical data.     

磨料水射流切割面粗糙度研究

对在磨料水射流切割过程中进给速度和磨料流量两点进行了讨论。磨料颗粒采用直径为80目的石榴石。测量了切割不同深度的粗糙度。实验结果表明:对切割表面影响最大的是切割速度。同时也研究了切割面粗糙度和磨料水射流其他参数之间的关系。     

Truing of diamond wheels – Geometry,kinematics and removal mechanisms

An investigation is made into traverse truing of diamond grinding wheels using various truing grit types, grit sizes and truing parameters. Geometry and kinematics of the truing contact are modeled. Specific energies are found to depend on truing-grit size but not on truing parameters, indicating little to no size effect. Removal mechanisms are analyzed via SEM examination of diamond- and truing-wheel swarf. A fundamental relationship is established relating the truing compliance number to the truing efficiency, which encompasses truing parameters and truing- and diamond-grit sizes. Recommendations are made for optimum conditions to minimize force-constrained truing time.     

Capability Profile of Hard Cutting and Grinding Processes

This keynote paper aims at matching the supply of research results with the industrial demands in hard cutting and grinding. The capability profiles of the processes are characterised and several manufacturing solutions are discussed. The comparison of hard cutting and grinding operations is carried out with regard to certain evaluation criteria based on the functionality of the machined workpiece itself, discussed at different levels, and the process economical efficiency. The basis for a roadmap of future development of hard machining technology is provided, e. g. the main technological developments associated with multi-processing hard machining concepts are given detailed consideration.     

Characteristics of abrasive slurry jet micro-machining: A comparison with abrasive air jet micro-machining

Abrasive slurry jet micro-machining (ASJM) uses a well-defined jet of abrasive slurry to erode features in a solid target. Compared with abrasive water jet machining (AWJM), the present ASJM system operates at pressures that are roughly two orders of magnitude lower and uses a premixed slurry of relatively low concentration. The objective of the present study was to gain a better understanding of the mechanics of erosion in ASJM by comparing its performance in the micro-machining of holes and channels in borosilicate glass with that of abrasive air jet micro-machining (AJM), a process that is simpler and relatively well understood. A new ASJM system was developed and used to machine blind holes and smooth channels of relatively uniform depth that did not suffer from the significant waviness previously reported in the literature. The effect of particle velocity, particle concentration, jet traverse speed and jet impact angle were examined. A direct comparison of ASJM and AJM results was possible since novel measurements of the crushing strength of the aluminum oxide abrasive particles used in both experiments proved to be unaffected by water. Brittle erosion was shown to be the dominant material removal mechanism in both ASJM and AJM in spite of the significant flow-induced decrease in the local impact angles of many of the particles in ASJM. A new model of the rapid particle deceleration near the target surface helped explain the much smaller erosion rates of ASJM compared with those in AJM. The modeling of the erosion process during the micro-machining of channels showed that the effect of the local impact angle at the leading edge of the advancing jet was much more significant in ASJM than in AJM, primarily due to the narrower focus of the jet impact zone in ASJM. The differences in the water and air flow fields and associated particle trajectories were used to explain the steeper side walls and flatter bottoms of the holes and channels machined with unmasked ASJM compared to those with masked AJM. The respective structures of the water and air jets also explained the much sharper definition of the edges of these features using ASJM compared with maskless AJM. The results of the study show that ASJM can be used to accurately micro-machine channels and holes with a width of 350–500 μm and an aspect ratio of 0.5–1.3 without the use of masks.     

强力快速送进打磨——国外精铸技术进展述评（10）

介绍一种新型磨料——氧化铝纳米陶瓷,其硬度接近金刚石,打磨时,能承受大压力施压,打磨速度快、磨具使用寿命长。微细转印砂带的问世,改变了磨粒粘附在衬带上的方式,并将磨削助剂添加在砂带上,使砂带的打磨效率提高,使用寿命延长。     

砂带磨削及其机床设计

本文从国内外发展和应用的现状出发,阐述了砂带磨削的原理、特点及砂带机床的主要机构,并介绍了一个砂带磨床设计的实例