Papers by Keyword: Surface Integrity

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Authors: Ke Tao Geng, Yu Guo Wang, Xiao Fei Song, Shu Min Wan, Bin Lin
Abstract: With the aesthetics’ enhancement, there is a growing demand for the use of restorative ceramics in dental surgery. However, ceramic materials are hard and brittle, and problems such as surface damage, crack, and fatigue were easily produced in dental abrasive finishing. Consequently, these flaws could cause the strength decrease of the ceramic, which manifest the shortage of the lifespan in dental. Contraposing these problems, a high-speed handpiece with diamond burs was used when finishing the leucite glass ceramic in the dental surgery. In this paper, finishing force, specific energy and surface integrity including the roughness and morphology were observed. the results revealed that both normal and tangential forces increased with the increasing of feed rate and depth of cut, while there is an apparent decrease of the specific energy. These two parameters were bigger in the up finishing than that of down finishing. Finishing parameters have little effect on surface roughness, according to the observation of a scanning electron microscope. It is easily found that the finished surface was consisting of brittle fracture and plastic deformation. For comprehensive, good surface quality could be obtained in the down cutting other than up cutting.
Authors: Alexandre Mondelin, Frédéric Valiorgue, Joël Rech, Michel Coret, Eric Feulvarch
Abstract: This study presents the development of a numerical model for the prediction of residual stresses induced in finish turning of a 15-5PH martensitic stainless steel. This methodology uses a hybrid approach combining experimental results (friction and orthogonal friction tests) with a numerical model. The numerical model simulates the residual stresses generation by applying cyclic equivalent thermo-mechanical loads onto the machined surface without modeling the chip removal process. The three-dimensional approach enables to study the influence of the turning passes interactions. It has been shown numerically that the periodicity of loading leads to a significant heterogeneity of material solicitations. Moreover, overlapping of passes accentuates these effects. So, the model highlights the necessity of a multi-passes simulation to reach a constant evolution of residual stresses along the feed direction. In addition, experimental measurements obtained by X-Ray diffraction have been compared with numerical results to validate the model.
Authors: Stepan Jermolajev, Ekkard Brinksmeier
Abstract: This paper presents a diagram of maximum contact zone temperature Tmax versus contact time Δt, based on the analysis of workpiece surface layer properties after cylindrical grinding experiments. Apart from resulting surface layer properties, process quantities (Tmax, normal and tangential grinding forces Fn, Ft) are investigated with reference to the resulting workpiece surface layer state as well. Ground workpieces are analyzed by performing Barkhausen noise level measurements together with subsequent metallographic and X-ray diffraction investigations. By mapping characteristic values Tmax and the contact time Δt to corresponding surface layer properties, a general analysis of workpiece material response to the thermo-mechanical load during grinding is possible.
Authors: Pierre Mella, René Billardon, Rodrigue Desmorat
Abstract: The high cycle fatigue life of machined parts is affected by the so-called surface integrity induced by the machining process. To model the high cycle fatigue behaviour of turned parts a probabilistic two-scale continuum damage model is developed. While the macroscopic behaviour of the material is assumed to remain elastic during the fatigue loading, the fatigue prediction is based on the incremental evolution of micro-plasticity and damage. The non-standard initial mechanical state of the material in the sub-surface, viz. the plastic strains and residual stresses fields induced by the machining process are taken into account via an initial step prior to the fatigue loading. As far as the micro-geometry of the surface is concerned, an initial micro-crack distribution depending on the depth and shape of the micro-defects observed is introduced.
Authors: Zhong Ning Guo, Jiang Wen Liu, F.Z. Zeng
Abstract: In wire electro-discharge machining with high traveling speed(WEDM-HS), the emulsion is used as working liquid. Because there exists a functional electrolyte, this affects the surface quality of workpiece machined. An investigation has been made into the machining feasibility when the gas or air is employed as processing medium. The first cut on workpiece is done with emulsion, and then air or distilled water is used for the second cut and multi-cuts. After machining, the surface quality and mechanical performance of the specimen under different conditions are compared. The experimental results show that air and distilled water have little influence on the surface roughness, but they can improve the mechanical performance such as the increase of hardness and the decrease of surface cracks. An orthogonal design is adopted to optimize the electric parameters and cutting passes so as to obtain the best integrative result. The experiment with air as medium reveals that it is a feasible and effective way for eliminating the electrolytic layer and improving the surface integrity of workpiece.
Authors: Rosemar Batista da Silva, Márcio Bacci da Silva, Wisley Falco Sales, Emanuel Okechukwu Ezugwu, Álisson Rocha Machado
Abstract: Machining efficiency of titanium alloys is crucial to the aerospace industry especially in the manufacture of bladed discs (blisks) where over 80% of titanium alloy material is roughed out to generate the complex shapes and contours of components. The choice of the right tool materials for machining titanium alloys contributes enormously to reducing the overall machining time by significantly lowering the cycle time and indexing of the cutting edges. These improvements lead to a reduction of the manufacturing cost by up to 30%. Uncoated and coated carbide tools have demonstrated encouraging performances when turning Ti-6Al-4V alloy, especially under roughing operations complemented by high pressure cooling technology, at high cutting speed and depth of cut conditions that increase the metal removal rate. Under such cutting conditions there is no significant difference in performance between coated or uncoated carbide tools when turning Ti-6Al-4V alloy. Super abrasives like ceramics and cubic boron nitride (CBN) tools are not suitable for machining titanium alloys as low tool life with no economic benefit is achieved because of severe chipping and fracture of the cutting edge. Machined surfaces produced with ceramic tools have very low surface integrity status because of loss of form as a result of accelerated tool wear and the consequent chipping and fracture encountered during machining. Polycrystalline diamond (PCD) tools are suitable for finish turning Ti-6Al-4V alloy at cutting speeds up to 250 m/min.
Authors: R. Ashofteh, A. Rastkerdar, S. Kolahdouz, A. Daneshi
Abstract: Creep-Feed Grinding(CFG) is one of the none-traditional machining in which form grinding to full depth is performed in limited number of passes. One of the most significant criteria which is taken into account to display valid machining parameters, is surface integrity. Surface integrity in CFG process is influenced by four main factors including surface roughness, superficial micro-crack, burning and changes in micro-hardness. According to prior investigations in CFG process, depth of cut plays an important role in surface integrity. In this study, the influence of cutting depth on workpiece surface integrity of cast nickel-based superalloy with alummina wheels, was investigated. During this study, a sample part was machined with variable depth of cut while the other parameters were Constant. After machining, surface roughness of each specimen was measured and in order to investigate existence and dimensional situation of surface micro-cracks, Chemical Etch + FPI and Thermal shock + FPI were performed. For determining micro-structural changes in ground specimens as a clarifier criteria in measuring the level of residual stress, a set of recrystallization processes were carried out on them and average grain size were measured. The results show, however, changing in depth of cut hasn't influenced on micro-cracks, quality of surface roughness has descended in terms of increasing the cutting depth.
Authors: Bernhard Karpuschewski, Florian Welzel, Konstantin Risse
Abstract: A variety of current scientific work shows the importance and possibilities of an effective conditioning of tribological contacts to minimize friction and wear, respectively an increase in performance of tribological highly stressed components. By slight modifications of the finishing process positive effects like the increase of lifetime or increase of power can therefore be generated. Based on this approach the tribological system piston ring/cylinder running surface of internal combustion engines is an example with high potential for optimization of production. This paper introduces alternative production and conditioning processes. The evaluation of chemical modifications of boundary layers, which are used in addition to the topography as a representative indicator for the description of the functionalities of produced surfaces is considered to be a special aspect. The present paper combines considerations of manufacturing technology with tribological tests showing the relationships and dependencies between the process characteristics of finishing and the operational behavior of the examined components.
Authors: Sven Kuschel, Jens Sölter, Ekkard Brinksmeier
Abstract: In order to generate desired functional properties in the surface layer of machined parts, today several iterative attempts are needed to achieve the specified surface and subsurface properties. Despite progress in simulation and modelling, which is limited to individual processes and investigations, a predictive adjustment of a manufacturing process in terms of a specific state of surface integrity is not possible. In this work, an alternative view regarding manufacturing processes, based on occurring internal physical mechanisms, is presented. It is shown for several processes, that the surface integrity due to material modifications can be correlated with internal material loads occurring during the process. To utilise this method in practical applications, approaches are presented which should enable a reduction in the complexity of the mathematical description of the internal material loading states.
Authors: Yuan Gao, Xin Huang, Ming Jie Lin, Zheng Guo Wang, Rong Lei Sun
Abstract: Surface integrity is widely used for evaluating the quality of machined components. It has a set of various parameters which can be grouped as: (a) topography parameters such as surface roughness, textures and waviness (b) mechanical parameters such as residual stresses and hardness, and (c) metallurgical state such as microstructure, phase transformation, grain size and shape, inclusions etc. Surface roughness and residual stresses are among the most significant parameters of surface integrity, so that it is worth investigating them particularly. Many factors affect the surface integrity of machined components, including cutting parameters, tool parameters, material properties and vibrations. We can make prediction and optimization for surface integrity by taking advantage of these factors. This paper reviews previous studies and gives a comprehensive summary of surface integrity in the following order: introduction of surface integrity, main parameters of surface integrity, factors affecting surface integrity, prediction and optimization for surface integrity.
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