Comparative study of three different types of dental diamond burs

Abstract

Wear mechanisms of three different types of dental burs were studied by means of cutting experiments performed on machinable glass ceramic using a laboratory system designed for this purpose. The dental handpiece used for this research was subjected to a constant feed rate in order to better simulate the actual working conditions of a dental bur. The new and the worn-out burs were studied by optical and scanning electron microscopy. Diamond particle wear-out was found to be the dominant wear mechanism in all cases; a quantitative analysis was performed on the optical micrographs of the new and worn burs. In situ force measurements showed that the forces exerted by the bur increase with the blunting process in order to keep the required feed rates; each bur type seems to have a different characteristic curve of force versus the number of cuts.     

Wear mechanisms in coated carbide tools

Micrographic evidence is presented which shows the retention of thin, 5μm carbide coating even when the ‘crater’ depth far exceeds the original coating thickness. Whereas earlier authors have attributed this retention to chip smearing, the present authors have shown that cratering can occur by plastic deformation with the coating remaining almost intact. X-ray images from the electron microprobe analyser and from the energy dispersive X-ray analyser support the micrographic findings. Plastic deformation results in flank bulging which causes the coating to wear rapidly by abrasion: the substrate, however, is able to withstand further deterioration. Chip notching on the rake face and grooving wear on the clearance faces also cause removal locally. Severe grooving wear on the end cutting edge as a possible result of oxidation and catalytic action is highlighted     

Performance studies of deep cryogenic treated tungsten carbide cutting tool inserts on machining steel

Abstract

Machining studies were conducted on a carbon steel workpiece using both untreated and deep cryogenic treated P-20 tungsten carbide cutting tool inserts. The flank wear of deep cryogenic treated carbide tools is lower than that of untreated carbide tools on machining of C45 steel. The cutting force during machining of C45 steel is lower with the deep cryogenic treated carbide tools when compared with the untreated carbide tools. The surface finish produced on machining the C45 steel workpiece is better with the deep cryogenic treated carbide tools when compared with the untreated carbide tools.     

Wear of water lubricated silicon nitride in ball on disc test

Abstract

The ball on disc test configuration is preferred to the flat ended pin on disc because the ball is self-aligned and measurement of wear on the ball is of higher accuracy, compared to the pin. Silicon nitride, sliding on itself in water, was tested with the ball on disc tribometer. Misalignment of the test ball from its proper position behind the disc axis of rotation leads to friction measurement errors, which were analysed. The disc wears non-uniformly, the wear track depth and width vary in longitudinal direction by a factor of 2–3. The uneven wear of the disc is explained by the combined effects of sliding surface anisotropy and disc material non-homogeneity on the one hand and by the friction force and the normal load periodic variation on the other hand. During the running-in process at particular sliding velocity amplitude modulated friction force was observed and an explanation by the mechanical vibration 'beating' phenomenon was suggested. Predictive model of the running-in process is presented, which describes the evolution of the ball wear scar area, the contact pressure and the wear rate. The model predictions are consistent with the experimental data.     

Tribological properties of lubricated nanocrystalline diamond surfaces for various loads and geometries

Abstract

Diamond and diamond-like carbon films are well known for their outstanding properties such as high hardness, low coefficient of friction, good thermal conductivity, excellent biocompatibility and electrical insulation. Diamond films with nanocrystalline grains offer added advantages of higher hardness, improved surface finish (less roughness), very high sp³ content, etc. In view of the above, the present investigation is undertaken to explore the possibility of using nanocrystalline diamond films in advanced tribological applications. In this work, a nanocrystalline diamond film is deposited using a unique chemical vapour deposition (CVD) technique. The microstructural features are characterised using atomic force microscopy (AFM). Tribological behaviour of these films is evaluated by means of a reciprocating model tribometer with various lubricants. The worn surfaces are examined using three-dimensional confocal microscopy. The results show that these films have comparable friction coefficient with and without lubricants. Furthermore, they exhibited negligible wear for the tested range of loads.     

Wear residues of aramid fibre formation in friction materials

Abstract

Friction and wear characteristics of aramid fibres in the automotive friction material are investigated using a pad on disc type friction tester. By means of SEM and X-ray analysis, the melting aramid fibre and its residues are detected and observed on the rubbing surfaces and lateral surfaces. The aramid fibres suffer the chemical and physical changes due to severe heating induced during braking. When the temperature of the rubbing surfaces of aramid fibres reaches or exceeds the melting point, the fibres on the surface move in the melting state. The melting particles of aramid fibres act as an interface lubricant. So it does not only lead to good wear resistance of the frictional materials, but also causes the coefficient of friction to reduce. The friction and wear mechanism of aramid fibre is discussed and analysed.     

Wear mechanisms of WC coated and uncoated tools in finish turning of Inconel 718

This paper presents the results of an experimental investigation on the wear mechanisms of uncoated tungsten carbide (WC) and coated tools (single-layer (TiAlN) PVD, and triple-layer (TiCN/Al₂O₃/TiN) CVD) in oblique finish turning of Inconel 718. Tool wear rate and wear mechanisms were evaluated for cutting speeds, 50<V<100 m/min, and feed rates, 0.075<f<0.125 mm/rev, at a constant depth of cut of 0.25 mm. It was concluded that abrasive and adhesive wear were the most dominant wear mechanisms, controlling the deterioration and final failure of the WC tools. While the triple layer CVD coated tools exhibited the highest wear resistance at high cutting speeds and low feeds, uncoated tools outperformed the single and multi-layer coated tools in the low range of cutting speeds and intermediate feeds. The cutting tool with single-layer PVD coating outperformed the other tools at the medium cutting speed.     

Wear of dental enamel

Teeth wear for a number of reasons. One of the causes for wear is the use of abrasive tooth pastes. A study is reported in which enamel was damaged by single pass sliding of a diamond indenter. In single crystals of fluorapatite, wear occurs by flaking out of chips of material and severely fractured substrate is left behind. On the other hand teeth are made of small rods of polycrystalline hydroxyapatite of the order of 5 μm in diameter oriented perpendicular to the tooth surface. This rod structure of human teeth prevents large scale flaking out of material. Apparently the subsurface cracks do not extend from one rod to the other so that subsequent passes do not result in severe wear. Small abrasive particles may do considerable damage to rods, but the overall effect is small. Large abrasive particles with high loads cause separation of rods, and cracks appear to propagate but without severe permanent damage.     

Wear mechanisms and tool performance of TiAlN PVD coated inserts during machining of AISI 4140 steel

The tribological influences of PVD-applied TiAlN coatings on the wear of cemented carbide inserts and the microstructure wear behaviors of the coated tools under dry and wet machining are investigated. The turning test was conducted with variable high cutting speeds ranging from 210 to 410 m/min. The analyses based on the experimental results lead to strong evidences that conventional coolant has a retarded effect on TiAlN coatings under high-speed machining. Micro-wear mechanisms identified in the tests through SEM micrographs include edge chipping, micro-abrasion, micro-fatigue, micro-thermal, and micro-attrition. These micro-structural variations of coatings provide structure-physical alterations as the measures for wear alert of TiAlN coated tool inserts under high speed machining of steels.     

CVD金刚石薄膜涂层刀具的技术进展

简要介绍了化学气相沉积金刚石刀具的涂层材料及制备技术的研究开发现状,总结了当前可以有效提高金刚石涂层刀具膜/基结合强度的措施和方法,分析了化学气相沉积金刚石涂层刀具各种表面抛光工艺的优缺点,最后展望了化学气相沉积金刚石薄膜涂层刀具技术的发展趋势.     

Wear processes in the diamond grinding of zirconia ceramics

he wear features on a number of test blocks of partially stabilized zirconia used in creep feed grinding tests have been examined using scanning electron microscopy. The morphology of the as-ground surfaces suggests that in addition to the expected abrasive wear component a delamination wear mechanism is also operating.     

Wear and performance of coated carbide and ceramic tools

The essential properties of modern high production cutting tools include high wear resistance, toughness, chemical stability at high temperature and under high sliding forces and a sufficiently high flow strength. It is difficult to achieve all these properties in a single tool material and techniques have been developed for coating a thin layer of a highly wear-resistant and friction-reducing material such as TiC, TiN, Ti(C,N), Al₂O₃ and Ti(C,N,O) onto a tough and strong substrate such as cemented carbides.The performance of such coated tools and their wear mechanisms were investigated.     

多颗粒金刚石小砂轮的耗损规律研究

多颗粒金刚石小砂轮轴向进给磨削能实现工程陶瓷等硬脆材料的高效加工,横向裂纹和中位裂纹的扩展均产生材料的去除.通过对多颗粒金刚石小砂轮结构和实验方案设计,能更好地研究端面边缘金刚石对陶瓷加工过程的影响及金刚石的磨损规律.还利用边缘检测和轮廓曲线拟合的方法来实时追踪检测金刚石顶尖曲率半径变化来研究金刚石颗粒的耗损规律,实验结果证明:磨粒顶锥角越大,金刚石磨粒磨削行程越长;材料磨削深度与进给速度两加工参数越大,磨削力和磨削温度越高,金刚石颗粒磨削行程越短.     

Wear of monocrystalline diamond tools during ultraprecision machining of nonferrous metals

In studying the wear behavior of diamond cutting tools, a pragmatic appraoch has been chosen in which the tool wear and the change in cutting forces have been specifically determined as a function of tool life. Several nonferrous metals, such as copper, aluminium, and electroless nickel, have been machined. The influence of microstructural characteristics, crystallographic orientation, and mechanical surface state of diamonds on tool-wear behavior is investigated in considerable detail. It has been found that wear behavior of diamond tools depends strongly on workpiece material, so that when machining aluminium, all types of diamond show considerable and almost the same degree of wear. However, machining copper and electroless nickel entails much subtler wear characteristics; in fact, great differences in wear resistance between different types of diamonds were discerned. Type all diamonds in particular, both synthetic and natural, appear to be highly resistant to wear. The best crystallographic orientation for wear-resistant diamonds depends on the way the cutting tools are used.     

Wear of dimethacrylate resins used in dental composites

Wear of dimethacrylate resins used as the matrix phase in dental restorative composites was characterized by two-body abrasion and singlepass sliding. Ranking of the resins was obtained by both tests. Two resins that had low values of tangential force and track width also showed relatively ductile modes of surface failure for the normal loads tested. A monomethacrylate fluorine-containing resin did not show improved wear properties by these methods of testing.     

Wear and frictional mechanisms of copper-based bearing alloys

The present study investigated the role of alloy microstructure and surface roughness on wear and friction behavior of leaded and unleaded tin bronzes. Ball-on-disk experiments were carried out under dry conditions with steel balls sliding against bronze disks. Scanning electron microscopy (SEM), energy dispersive electron microscopy (EDX), x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy were performed to analyze the sliding tracks and the ball scars. The wear reducing effect of lead was associated to the formation of an oxidized lead rich layer. When no such film formed on the leaded bronze wear was more severe than in case of unleaded bronze. Nevertheless, the presence of lead in the alloy was a necessary but not sufficient condition to obtain a smeared layer and thus a lubricating effect of the leaded alloy. Two mechanistic hypotheses were formulated to explain the formation of the smeared layer.     

Wear of diamond grinding wheel in ultrasonic vibration-assisted grinding of silicon carbide

It is recognized that grinding efficiency and ground surface quality are determined by grinding wheel performance. Additionally, the investigation on wear behavior is essential for evaluating the grinding wheel performance. There is a lack of research on the tool wear behavior during ultrasonic vibration-assisted grinding (UAG), whose grain motion trajectory differs from that in conventional grinding (CG). In the present work, CG and UAG tests of silicon carbide (SiC) were conducted in order to investigate the effects of ultrasonic vibration on the tool wear through tracking observation of grains. Meanwhile, the grinding forces and ground surface roughness correlated to the tool wear stages were studied. The results demonstrated that the main wear types during UAG were micro-fracture and macro-fracture which caused the wheel sharpening, while during CG, the main wear type was attritious wear that made the wheel blunt. As a result, UAG obtained lower and more stable grinding forces while slightly rougher ground surface in comparison with CG.     

Wear behavior of coated tools in laser assisted micro-milling of hardened steel

This paper presents a comparison of the performance of different cutting tool coatings for Laser Assisted Micro-Milling (LAMM). A thermal model is used to predict the temperature rise in the material removal surface which helps in analyzing the severity of the thermal conditions experienced by the cutting tool in LAMM. Machining experiments are then carried out to evaluate the wear behavior of different commercially available (TiCN, TiAlN) and customized coated tools (TiSiN, Al₂O₃, Al₂O₃+ZrN). These coatings were selected since they have the capability to withstand the temperatures experienced in LAMM. The results of micro-milling experiments indicate that commercially available coatings like TiCN perform poorly due to their inferior adhesion characteristics with the base material. Delamination is found to be the principal wear mechanism of TiCN, TiSiN, and Alumina (Al₂O₃) coated tools for the conditions investigated in this study. In addition, the results indicate that the wear performance of TiAlN and Al₂O₃+ZrN coated tools is superior.     

Wear mechanisms of the C/SiC brake materials

The C/SiC brake materials were fabricated by chemical vapor infiltration combined with liquid melt infiltration. The wear mechanisms of C/SiC brake materials were investigated. The main wear mechanisms were grain-abrasion, oxidation-abrasion, fatigue wear, and adhesive wear. These wear mechanisms always occurred simultaneously , and showed mutual enhancing effects between them. Grain-abrasion mainly was the result of hard SiC grain action. Adhesive wear could cause high wear rates and a large unstable friction coefficient. Si was the significant factor on the adhesive wear, so Si in the C/SiC brake materials must be removed.