Experimental and numerical analysis of wear flat generation and growth in alumina grinding wheels.

183 p.El proceso de rectificado supone entre un 20-25% del coste total de fabricación, suponiendo el consumo de muela un porcentaje muy elevado del coste total. De entre los diferentes tipos de desgaste, el wear flat es el más perjudicial para el proceso. Asimismo, nuevos generaciones de materiales abrasivos, como la alúmina microcristalina sinterizada, se van haciendo hueco en aplicaciones industriales. Sin embargo, su comportamiento ante el desgaste no está caracterizado. Es por ello, que este trabajo de investigación aborda la caracterización de la generación y evolución del wear flat en muelas de alúmina, analizando la influencia de la estructura cristalina de los granos abrasivos en el wear flat, desgaste de naturaleza triboquímica. Para ello, se realiza un análisis tanto experimental como numérico.Desde el punto de vista experimental, se realizan ensayos de rectificado en los que se aísla el desgaste de wear flat de los demás tipos de desgaste. Tras estos y debido a la importancia del contacto en el desgaste, se diseña un tribómetro pin-on-disk en el cual se controlan exhaustivamente las condiciones de contacto y se reproduce el ciclo térmico de los granos abrasivos para la cuantificación del desgaste triboquímico. Por último, desde un punto de vista numérico, se realiza un modelo térmico en FEM, para determinar la influencia de la temperatura en las propiedades de la alúmina y un modelo de desgaste en DEM, con el objetivo de simular el desgaste de un grano abrasivo, teniendo en cuenta su estructura cristalina. Como resultado se observan mayores valores de %A para la alúmina microcristalina durante el proceso de rectificado, ya que las altas temperaturas modifican la apariencia de la superficie desgastada de la muela. Sin embargo, las reacciones triboquímicas son más importantes en la alúmina WFA, como muestran los resultados tribológicos y numéricos

Modeling and simulation of grinding processes based on a virtual wheel model and microscopic interaction analysis

Grinding is a complex material removal process with a large number of parameters influencing each other. In the process, the grinding wheel surface contacts the workpiece at high speed and under high pressure. The complexity of the process lies in the multiple microscopic interaction modes in the wheel-workpiece contact zone, including cutting, plowing, sliding, chip/workpiece friction, chip/bond friction, and bond/workpiece friction. Any subtle changes of the microscopic modes could result in a dramatic variation in the process. To capture the minute microscopic changes in the process and acquire better understanding of the mechanism, a physics-based model is necessary to quantify the microscopic interactions, through which the process output can be correlated with the input parameters. In the dissertation, the grinding process is regarded as an integration of all microscopic interactions, and a methodology is established for the physics based modeling. To determine the engagement condition for all micro-modes quantitatively, a virtual grinding wheel model is developed based on wheel fabrication procedure analysis and a kinematics simulation is conducted according to the operational parameters of the grinding process. A Finite Element Analysis (FEA) is carried out to study the single grain cutting under different conditions to characterize and quantify the grain-workpiece interface. Given the engagement condition on each individual grain with the workpiece from the physics-based simulation, the force, chip generation, and material plastic flow can be determined through the simulation results. Therefore, the microscopic output on each discrete point in the wheel-workpiece contact zone can be derived, and the grinding process technical output is the integrated product of all microscopic interaction output. From the perspective of process prediction and optimization, the simulation can provide the output value including the tangential force and surface texture. In terms of the microscopic analysis for mechanism study, the simulation is able to estimate the number of cutting and plowing grains, cutting and plowing force, probability of loading occurrence, which can be used as evidence for process diagnosis and improvement. A series of experiments are carried out to verify the simulation results. The simulation results are consistent with the experimental results in terms of the tangential force and surface roughness Ra for dry grinding of hardened D2 steel. The methodology enables the description of the \u27inside story\u27 in grinding processes from a microscopic point of view, which also helps explain and predict the time dependent behavior in grinding. Furthermore, the process model can be used for grinding force (or power) estimation for multiple-stage grinding cycles which includes rough, semi-finish, finish, and spark out. Therefore, the grinding process design can be carried out proactively while eliminating \u27trial and error\u27. In addition, the grinding wheel model itself can be used to guide the recipe development and optimization of grinding wheels. While the single grain micro-cutting model can be used to study the mechanism of single grit cutting under various complex conditions, it can also be used to derive the optimal parameters for specific grains or process conditions

Expectations and limitations of Cyber-Physical Systems (CPS) for Advanced Manufacturing: A View from the Grinding Industry

Grinding is a critical technology in the manufacturing of high added-value precision parts, accounting for approximately 20–25% of all machining costs in the industrialized world. It is a commonly used process in the finishing of parts in numerous key industrial sectors such as transport (including the aeronautical, automotive and railway industries), and energy or biomedical industries. As in the case of many other manufacturing technologies, grinding relies heavily on the experience and knowledge of the operatives. For this reason, considerable efforts have been devoted to generating a systematic and sustainable approach that reduces and eventually eliminates costly trial-and-error strategies. The main contribution of this work is that, for the first time, a complete digital twin (DT) for the grinding industry is presented. The required flow of information between numerical simulations, advanced mechanical testing and industrial practice has been defined, thus producing a virtual mirror of the real process. The structure of the DT comprises four layers, which integrate: (1) scientific knowledge of the process (advanced process modeling and numerical simulation); (2) characterization of materials through specialized mechanical testing; (3) advanced sensing techniques, to provide feedback for process models; and (4) knowledge integration in a configurable open-source industrial tool. To this end, intensive collaboration between all the involved agents (from university to industry) is essential. One of the most remarkable results is the development of new and more realistic models for predicting wheel wear, which currently can only be known in industry through costly trial-and-error strategies. Also, current work is focused on the development of an intelligent grinding wheel, which will provide on-line information about process variables such as temperature and forces. This is a critical issue in the advance towards a zero-defect grinding process.The authors gratefully acknowledge the funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program for funding the project “Scientific models and machine-tool advanced sensing techniques for efficient machining of precision components of Low-Pressure Turbines” (DPI2017-82239-P)

Manufacturing glass-fiber reinforcement for grinding wheels

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.Includes bibliographical references (leaves 104-105).By analyzing the manufacturing process for organic grinding wheels, some characteristics of the reinforcing glass fiber disc added during the fabrication of these wheels are determined. The toughening mechanisms at work in a fiber glass reinforced grinding wheel are analyzed. The stresses inside a grinding wheel in use are determined. Different designs for a reinforcing glass fiber disc are then presented and discussed. One design is chosen and the plans for a prototype machine that will manufacture a reinforcement disc with the chosen design are presented. The different tasks and the issues associated with the manufacturing process are discussed. Finally, an economic and material feasibility analysis is made to determine the possibility of eliminating the current reinforcement supplier.by Nicolas Joseph Avril.S.M

Micro-grinding of titanium

Titanium and its alloys are difficult-to-cut materials, commonly used in several application fields, such as: medicine, aerospace, automotive and turbine manufacturing due to their biocompatibility, corrosion resistance, excellent mechanical and thermal properties, and light weight. However, its machining is associated with several difficulties, such as high tool wear, low surface quality, high cutting forces and high costs. To overcome these problems, using a proper and efficient manufacturing process seems essential. Micro-grinding provides a competitive edge in the fabrication of small-sized features and parts with superior surface quality compared with other processes. The quality aspects such as surface integrity of the parts produced by micro-grinding is influenced by various factors related to the induced mechanical and thermal loads during the process. Therefore, the machining parameters must be carefully chosen and controlled. Hence, developing an advanced, highly effective and efficient method, which can produce high quality micro-parts without inducing sub-surface damage, seems essential.In this study, experimental and analytical investigations on 2D micro-grinding of titanium are presented. The run-out of micro-tools can be affected by the relatively high forces induces by mechanical dressing, meaning that the dressing and tool-conditioning possibilities are limited. Therefore, a proper set of dressing parameters is obtained for dressing of micro-grinding tools. An analytical model, which considers grits interaction, heat transfer and actual micro-grinding tool topography is developed which is able to predict the surface roughness and cutting forces for a given set of dressing and grinding parameters. It is shown that the topography of the tool varies with changing the dressing parameter which affects the grinding forces and surface roughness. In the analytical model the actual topography of the tool is considered in the simulation for the first time.\ua0 Additionally, the model is able to determine grinding parameters that generate minimum surface roughness with minimizing the grinding forces. To determine the correct chip thickness with the maximum material removal rate, an appropriate grinding tool and optimum process parameters to generate highly accurate contours in a micron scale will be further analyzed. Using the analytical model, the effects of process parameters and tool surface topography are mapped to the process outputs, i.e. surface roughness and grinding forces. The results show that the analytical model enables the prediction of micro-grinding forces with a total error of 13.5% and surface roughness with the total error of 16%. The simulation results match with the experimental results to a greater degree in the low cutting speed range, rather than at higher cutting speeds. The results also indicate that the dressing parameters, such as the dressing overlap ratio and the speed ratio are influential factors, affecting surface roughness and grinding forces. Using higher values of dressing overlap ratio (Ud up to 1830) reduced the surface roughness, however, leads to approximately 70% higher cutting forces. The observed 40% reduction in the grinding forces is achieved by increasing the cutting speed from 6 to 14 m/s, but this increases the surface roughness. Higher values of the dressing overlap ratio reduce the chip cold-welding on the abrasive grains and causes less loading of the tool in form of chip nests. Welded clogging of the grinding pin at lower Ud values deteriorates the surface quality resulting in increased surface roughness. Using the up-dressing method leads to lower chip loading over the surface of the grinding tool, which improves the ground surface. Moreover, the down-dressing of micro-grinding pins results in higher value of surface roughness and lower grinding forces compared with up-dressing

Dry grinding technology for automotive gears manufacturing: process modeling and optimization

The following thesis focused on the dry grinding process modelling and optimization for automotive gears production. A FEM model was implemented with the aim at predicting process temperatures and preventing grinding thermal defects on the material surface. In particular, the model was conceived to facilitate the choice of the grinding parameters during the design and the execution of the dry-hard finishing process developed and patented by the company Samputensili Machine Tools (EMAG Group) on automotive gears. The proposed model allows to analyse the influence of the technological parameters, comprising the grinding wheel specifications. Automotive gears finished by dry-hard finishing process are supposed to reach the same quality target of the gears finished through the conventional wet grinding process with the advantage of reducing production costs and environmental pollution. But, the grinding process allows very high values of specific pressure and heat absorbed by the material, therefore, removing the lubricant increases the risk of thermal defects occurrence. An incorrect design of the process parameters set could cause grinding burns, which affect the mechanical performance of the ground component inevitably. Therefore, a modelling phase of the process could allow to enhance the mechanical characteristics of the components and avoid waste during production. A hierarchical FEM model was implemented to predict dry grinding temperatures and was represented by the interconnection of a microscopic and a macroscopic approach. A microscopic single grain grinding model was linked to a macroscopic thermal model to predict the dry grinding process temperatures and so to forecast the thermal cycle effect caused by the process parameters and the grinding wheel specification choice. Good agreement between the model and the experiments was achieved making the dry-hard finishing an efficient and reliable technology to implement in the gears automotive industry

Remanufacturing and Advanced Machining Processes for New Materials and Components

"Remanufacturing and Advanced Machining Processes for Materials and Components presents current and emerging techniques for machining of new materials and restoration of components, as well as surface engineering methods aimed at prolonging the life of industrial systems. It examines contemporary machining processes for new materials, methods of protection and restoration of components, and smart machining processes. • Details a variety of advanced machining processes, new materials joining techniques, and methods to increase machining accuracy • Presents innovative methods for protection and restoration of components primarily from the perspective of remanufacturing and protective surface engineering • Discusses smart machining processes, including computer-integrated manufacturing and rapid prototyping, and smart materials • Provides a comprehensive summary of state-of-the-art in every section and a description of manufacturing methods • Describes the applications in recovery and enhancing purposes and identifies contemporary trends in industrial practice, emphasizing resource savings and performance prolongation for components and engineering systems The book is aimed at a range of readers, including graduate-level students, researchers, and engineers in mechanical, materials, and manufacturing engineering, especially those focused on resource savings, renovation, and failure prevention of components in engineering systems.

Laser Machining of Structural Ceramics: Computational and Experimental Analysis

Outstanding mechanical and physical properties like high thermal resistance, high hardness and chemical stability have encouraged use of structural ceramics in several applications. The brittle and hard nature of these ceramics makes them difficult to machine using conventional techniques and damage caused to the surface while machining affects efficiency of components. Laser machining has recently emerged as a potential technique for attaining high material removal rates. Major focus of this work is to understand the material removal mechanisms during laser machining of structural ceramics such as alumina (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC) and magnesia (MgO). A 1.06 μm wavelength pulsed Nd:YAG laser was used for machining cavities of variable dimensions in these ceramics and an ab-initio computational model was developed to correlate attributes of machined cavities with laser processing conditions. Material removal in Al2O3, Si3N4 and SiC takes place by a combination of melting, dissociation and evaporation while dissociation followed by evaporation is responsible for material removal in MgO. Temperature measurement at high temperatures being difficult, thermocouples were used to measure temperatures in the low temperature regime (700- 1150K). A thermal model was then iterated to obtain trends in absorptivity variation below phase transition temperature for these ceramics. Following this, measured machined depths were used as a benchmark to predict absorptivity transitions at higher temperatures (\u3e 1150K) using the developed thermal model. For temperatures below phase transition, due to intraband absorption, the absorptivity decreases with increase in temperature until the surface temperature reaches the melting point in case of Al2O3, Si3N4 and SiC and the vaporization temperature in case of MgO. The absorptivity then continues to follow increasing trend with increasing temperature due to physical entrapment of laser beam in the cavity evolved during machining of certain depth in the ceramic. Rate of machining was predicted in terms of material removed per unit time and it increased with increase in heating rate. Such a composite study based on comput ational and experimental analysis would enable advance predictions of laser processing conditions required to machine cavities of desired dimensions and thus assist in controlling the laser machining process more proficiently

NASA SBIR abstracts of 1990 phase 1 projects

The research objectives of the 280 projects placed under contract in the National Aeronautics and Space Administration (NASA) 1990 Small Business Innovation Research (SBIR) Phase 1 program are described. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses in response to NASA's 1990 SBIR Phase 1 Program Solicitation. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 280, in order of its appearance in the body of the report. The document also includes Appendixes to provide additional information about the SBIR program and permit cross-reference in the 1990 Phase 1 projects by company name, location by state, principal investigator, NASA field center responsible for management of each project, and NASA contract number