No description available.

No description available.

This study examines the lapping machining process used during the manufacturing of polycrystalline diamond compacts (PDCs). More specifically, it is aimed at improving the productivity of the process by developing a better understanding of the parameters that affect the material removal rate (MRR) and MRR uniformity of lapped PDC samples. Experiments that focused on several controllable lapping parameters were performed to determine to what extent they affected the process. It was determined that the MRR can be modeled with the Preston equation under certain ranges of pressure and speed. It was also found that using a hard and rigid sample holder produces higher MRRs than soft and flexible sample holders. The results have also shown that MRRs in excess of 300 micrometers per hour can be achieved while using 10 grams of diamond abrasive per PDC per hour of lapping. The productivity of the lapping process can also be improved by placing the maximum allowed PDC samples in a concentric circle on the edge of the sample holder. The MRR uniformity between samples lapped on the same sample holder was found to be dependent on the sample holder material. This thesis is composed of six chapters. The first chapter introduces the need for PDC's as extreme cutting tools, the manufacturing process of PDC's, and the lapping process. The second chapter discusses the motivation behind this research and the primary objectives that were established. The third chapter details the materials and the experimental procedure, and the fourth chapter presents the results. The fifth chapter discusses the results, and the sixth chapter presents conclusions and information on possible future work.

A general closed-form analytical solution is derived for the lapping tracks with its kinematics for the concentric V-groove lapping system. The lapping tracks on the ball surface for the three contact points are fixed circles, and their lengths of the lapping tracks are linearly proportional to , , and , respectively. In practice, if the orientation is randomized as the ball enters the lap again, then the distribution of the lapping tracks are dense after many cycles, and the larger the lapping length in each cycle, the smaller is the number of cycles required achieving the maximum lapped area ratio. In the geometry design of ball lapping, the V-groove half-angle should be larger than 45¢X, but to prevent the splash of abrasives, it should be less than 75¢X. Since the spin angular speed with its angle continuously varies with time for the eccentric lapping system, lapping tracks are not fixed circles. In practice, the lapped areas are complementary at the contact points of A and B. The total lapped area ratio is higher than 87% for a slip ratio less than 0.5. Hence, it is possible to lap all the surface of a ball by changing the slip ratio during the lapping process. Moreover, the larger the V-groove half-angle, the less is the eccentricity to achieve the optimum lapped area ratio. In order to understand the ball motion and ball lapping mechanism in the magnetic fluid lapping system, the forces and moments equilibrium equations are derived and numerical methods are analyzed. As the balls traveling in a train are assumed to be the same size, only one ball is considered in the dynamic analysis. Results show that as the ball separates from the shaft and the float, the spin angle increases quickly and approaches to 90¢X. Hence, the ball changes its attitude and thereby generates a new lapping tracks on the ball surface. Consequently, after repeating many cycles, lapping tracks would be scoping out more space and this is one of the spherical surface generation mechanisms. Surface waviness of ball causes a variation in the lapping load. When , it is possible to cause the ball separated from float and the lapping load is zero during the separation period. No matter how the ball separates from float, the spin angle always varies in a small range. Hence, only a very small region can be grounded due to the effect of the surface waviness. Therefore, it is not the main lapping mechanism of the spherical surface generation. In fact, during the lapping process, many balls with different diameters are lapped. To understand the ball¡¦s lapping mechanism of the spherical surface generation, it is necessary to consider a batch of balls. For a batch of balls with different diameters, the applied load on each should be different from each other. Generally, the larger the diameter of a ball, the larger is the friction force between the ball and shaft and the ball circulation speed. Therefore, it is possible to cause the collision between the larger and the smaller balls. To understand the interaction between balls traveling in a train, the dynamic analysis of multiple balls is developed. As the ball interacts with each other, it is possible to change the spin angle, and thereby to achieve the larger variation range of the lapping tracks. During the lapping process of a batch of balls, it is also possible to cause the separation between the shaft and the ball, and it causes the ball to change its attitude and to achieve more uniform lapping tracks.

Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02-17Bitstream added on 2014-06-13T19:06:29Z : No. of bitstreams: 1 zhu_nxj_me_bauru.pdf: 4158261 bytes, checksum: bafc2c29b13e8c6fb309c4a1b184788a (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Atualmente tem-se verificado crescente demanda por processos de fabricação capazes de produzir peças sob estreitas faixas de tolerâncias dimensionais e geométricas. Dentre os processos utilizados para conferir acabamento superficial e correção de forma destacam-se a retificação e a lapidação. Porém, muitas peças mostram-se suscetíveis ao calor gerado pela retificação, como no caso da deformação de peças delgadas ou então naquelas peças passíveis de mudanças microestruturais, recorrendo-se nestes casos à lapidação que, por sua vez, é um processo de difícil seleção de parâmetros. Neste trabalho é iniciado o desenvolvimento de um processo híbrido capaz de aliar algumas importantes características da retificação e da lapidação, no qual do primeiro é usado a operação de dressagem e do segundo o movimento cinemático. Dessa forma dotou-se uma... / Lately, one can verify that there has been a growing demand for manufacturing processes capable of producing workpieces under tight dimensional and geometric tolerance rangers. Among the processes used to assure surface finish and shape correction to the part, grinding and lapping arise as the most used. However, many parts show themselves sensitive to the heat generated during the grinding process, as in the case of thin ones, or those susceptible to micro-structural changes. On these cases, one can use lapping, even though being a more difficult parameter selection process. In these studies, the development of a hybrid process capable of binding some important grinding and lapping features is initiated; the dressing operation, for the case of grinding and, for the case of lapping, the cinematic movement... (Complete abstract click electronic access below)

No description available.

No description available.

Automobiles have become an integral part of our daily life as more and more mopeds, motor cycles, cars, trucks, busses and trains are being used for transport. The main parts of an automotive engine are cylinder, piston assembly, connecting rod and crank shaft. The piston assembly consists of Piston, Piston rings and Piston Pin. Piston rings are important parts of a piston assembly. Any non-conformance in any quality characteristic of the piston ring leads to deterioration of engine performance. M/S Goetze (India) Limited a medium scale industry and a sister concern of engineering giant M/S Escorts Limited is manufacturing "GOETZE PISTON RINGS" and is producing about 800 varieties of piston rings ranging from 35.00 mm to 228.5 mm nominal diameter. The management was facing serious problem due to high scrap rate in certain types of their manufactured piston rings. Hence instead of trying to handle all of them at the same time, it seemed reasonable to tackle and find a suitable approach to solve the quality problem by taking the most notorious ring first, so that once the methodology is understood, documented and applied to the quality problem of this ring, the same can also be invoked for other rings to improve upon their quality, and thus reducing the scrap rate. One particular ring of 83.0 mm diameter which is delicate and costly, having an average scrap rate of 36.2% in past three years is selected for the study. No systematic effort was made in the past to identify the quality characteristics and the processes which were responsible for this high scrap rate and thus no immediate measure could be recommended. As a matter of fact at the beginning of the study it was not even clear which quality characteristics were mainly responsible for such high rejection. So in July' 1999 a pareto analysis was done for the first time to identify the culpability of each quality characteristic for the rejection of the ring. From the Pareto analysis it was observed that maximum proportion of rejection was due to nonconformity in axial thickness. The scrap rate due to nonconformity in axial thickness were collected for each month from Jul’ 999 to Jan'2000 which averaged at 8.7%. Since in every month the major malefactor for rejection was the nonconformity of axial thickness it was decided to first try to improve the quality of axial thickness, before trying to tackle other quality issues associated with this particular piston ring under study. Once the most problematic quality characteristic namely the axial thickness was identified, as a first step towards the goal of improving the quality of axial thickness, it was necessary to pay attention and isolate the manufacturing processes or operations affecting the axial thickness and study them in detail. So first, the entire manufacturing process flow diagram of the piston ring was studied. From the process flow diagram it appeared that there are 4 operations affecting axial thickness viz. Rough Grinding ,Medium Grinding, First Lapping and Finish Lapping. So each of these processes was critically observed to assess whether they were under statistical control or not. Studies were conducted at each of these 4 operations by collecting samples using the rational subgroup method and control charts were plotted. From the control charts, it was observed that the Rough Grinding and Medium Grinding operations were in statistical control with acceptable Cp, Cpk values. But First Lapping and Finish Lapping operations were not in statistical control. Thus we finally identified the two critical processes namely the First Lapping and Finish Lapping operations which were not in statistical control but were crucially affecting the quality of axial thickness. Since the First and Finish Lapping operations were identified as the major source of the quality problem, an in-depth study was undertaken to analyze these two processes. A brain storming session was conducted with all concerned personnel from production, maintenance, design, quality assurance and tool room to get all possible causes which might be affecting the axial thickness variation at these two processes. During the brain storming session the team suggested that the First Lapping process can be processed in medium grinding machine (DFS machine) instead of Lapping machine. The reasons behind this were two fold. First since the aim of the First Lapping is just to remove excess material which was deposited during chrome plating, the same operation can be performed in DFS machine. Since the required surface finish on axial surface was any way being aimed at the Finish Lapping operation, a similar precursory First Lapping'operation in a Lapping machine was really felt not necessary. Secondly since the performance of the DFS machine was found to be under control, albeit for the grinding operation, it was hoped that the Lapping operation in the same machine would also exhibit a similar performance. For this purpose a study was conducted on the First Lapping operation with the DFS machine. It was found that the process was well within the control limit with decent Cp and Cpk values. Thus this procedure of performing the First Lapping operation in a DFS machine took care of the first one of the two problematic processes affecting the quality of axial thickness. Next for tackling the problem with the other critical process, viz. the Finish Lapping operation, various causes were suggested by the team for axial thickness variation in the Finish Lapping operation. Based on these causes, an Ishikawa diagram (cause and effect diagram) was prepared. This Ishikawa diagram had thrown light into number of possible deficiencies in Man, Machine, Method and Material which were responsible for axial thickness variation at finish Lapping. The Ishikawa diagram was carefully analyzed. The causes were narrowed down to 6 factors. These are Grinding wheel rotating speed, Grinding Time, Grinding pressure, Holding plate, Holes (fixtures) within the holding plate and Positions within a ring. The 3 factors namely grinding wheel speed, time and pressure were identified as the control factors. Holding plate, Hole position within a plate and Checking position within a ring on the other hand were the noise factors whose different levels might exhibit a variability of axial thickness. Since there were only 3 control factors, it was decided to conduct a full factorial experiment with each control factor at 3 levels. Hence altogether there were 27 experiments at a fixed given combination of speed, time and pressure. There were 4 holding plates with each plate having 6 slotted holes leading to machining 24 rings at a time during the finish lapping operation. Next 3 measurements were taken for each one of these 24 rings. Thus altogether there were 72 observations for one of these experiments. Each experiment was replicated twice by taking measurements for 2 consecutive batches of rings. From the analysis of variance of the results of these experiments for both S/N ratio and mean it was observed that all the three main factors and their interactions were significant. The Normality assumption of standardized residuals for the S/N ratio and mean was validated by normal probability plot and Kolmonogorov-Smirnoff test. The homoscedasticity assumption was validated through Bartlett’s test and residual plots. It was found that the experiment no. 23 (Speed 84 RPM, Time 10 sees and Pressure 300 daN) yielded highest S/N ratio (η) with mean within the specification limit. That the mean and S/N ratio for the experiment no.23 were significantly different from others was established by means of Tukey's multiple comparison test. Next control charts for experiment no. 23 were plotted and was found to be well within control with acceptable Cp and Cpk values. Hence we concluded that the non-conformance in axial thickness can be substantially reduced by using the following optimal setting of factors i.e. grinding speed with 84 RPM, grinding pressure with 300 daN and grinding time with 10 seconds. Using this optimal setting the earlier average rejection rate of 8.7% due to non-conformance in axial thickness was reduced to 0.05%. Under this optimal setting, the process capability index (Cpk) of finish Lapping operation was estimated to be 2.5, which is well above acceptable standard. Due to this reduction in rejection rate in one quality characteristics of one particular ring out of 800 types, the net savings to the organization is approximately Rs. 10,44,000 per year.

Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-13Bitstream added on 2014-06-13T19:31:49Z : No. of bitstreams: 1 cruz_jhd_me_bauru.pdf: 3641948 bytes, checksum: b4c0a20ae031697c0e2cd3d13e4151ae (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os clientes dos fabricantes de equipamentos exigem cada vez mais eficiência com melhor desempenho e maior economia de energia. Prova disso são produtos que vem diminuindo no tamanho e no peso. Um componente mais eficiente necessita de melhor qualidade de acabamento superficial e tolerâncias mais apertadas. Na fabricação de componentes precisos destaca-se a usinagem, os processos convencionais mais precisos são a retificação, a lapidação e o brunimento. Entretanto desenvolvimentos recentes nas áreas de eletrônicos e computadores geraram a necessidade de tolerâncias nanométricas, métodos ultra-precisos, que usam abrasivos livres, trabalham com tolerâncias de milésimos de micrometros. A retificação é o processo abrasivo mais utilizado para promover acabamento e formas finais em componentes de precisão. Utiliza como ferramenta um rebolo abrasivo, e conta com a operação de dressagem para controle da capacidade de corte. As elevadas temperaturas geradas podem provocar danos térmicos e deformações dimensionais e de forma na peça de trabalho. Na lapidação são utilizados grãos abrasivos livres e o perfil é transferido a peça através de movimentos aleatórios. O grande número de variáveis envolvidas na lapidação a tornam complexa e dispendiosa. Nos anos 90, difundiu-se um processo abrasivo de grãos fixos, no qual as peças e o rebolo abrasivo composto de pastilhas de CBN ou diamante, produzem movimento análogo ao da lapidação. Esse processo, muitas vezes denominado por brunimento plano, traz vantagens em relação à lapidação, como: peça limpa, reduzido desperdício de abrasivo e maior taxa de remoção. Neste trabalho é descrito um equipamento denominado de lápidoretificadora que usina peças pelo processo de lápidoretificação. Diferente de qualquer outro processo a lápidoretificação une uma cinemática que gera riscos aleatórios com uma ferramenta... / Customer's equipment manufacturers demand more efficiency with better performance and greater energy saving. In parallel is development of products with less size and weight. The most efficient components need quality of surface finish and increased manufacturing accuracy. Precise component manufacturer is normally produced by cutting process. Grinding, lapping and honing are the most commons manufacturing precision processes in practice today. Recent developments in electronics and computers created the need for nanometer tolerances, ultra precision cutting machines, which use free abrasive process, working tolerances in thousandths of microns. Grinding is the most common abrasive process used to promote final form in precision components. Using an abrasive wheel as a tool, it is possible to control the cutting conditions with the dressing operation. The high temperatures generated can cause thermal damage and dimensional deformation. Lapping use free abrasive grains with random movements. The immense numbers of variables involved in the lapping make the process to complex and expensive. In the '90s, it spread a fixed abrasive grains process using CBN or diamond wheels, with movements similar to lapping. This process, often called flat honing, product clean surfaces, reduced abrasive waste and increased removal rate. This paper described a device named lappingriding machine. Different of any other process, the lappingriding kinematics generates random risks with an abrasive tool prepared by dressing operation. The surface fining quality is similar to lapping or flat honing and the operational versatility is similar to grinding processes. The lappingring machine has specific functions such as the kinematics of workpiece fixing device and automatic dressing device. Its main features are rigidity and effectiveness of control, providing precision and cutting capacity stabile.

Orientador: Luiz Eduardo de Angelo Sanchez / Banca: Carlos Alberto Fortulan / Banca: Carlos Elias da Silva Junior / Resumo: Atualmente tem-se verificado crescente demanda por processos de fabricação capazes de produzir peças sob estreitas faixas de tolerâncias dimensionais e geométricas. Dentre os processos utilizados para conferir acabamento superficial e correção de forma destacam-se a retificação e a lapidação. Porém, muitas peças mostram-se suscetíveis ao calor gerado pela retificação, como no caso da deformação de peças delgadas ou então naquelas peças passíveis de mudanças microestruturais, recorrendo-se nestes casos à lapidação que, por sua vez, é um processo de difícil seleção de parâmetros. Neste trabalho é iniciado o desenvolvimento de um processo híbrido capaz de aliar algumas importantes características da retificação e da lapidação, no qual do primeiro é usado a operação de dressagem e do segundo o movimento cinemático. Dessa forma dotou-se uma... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Lately, one can verify that there has been a growing demand for manufacturing processes capable of producing workpieces under tight dimensional and geometric tolerance rangers. Among the processes used to assure surface finish and shape correction to the part, grinding and lapping arise as the most used. However, many parts show themselves sensitive to the heat generated during the grinding process, as in the case of thin ones, or those susceptible to micro-structural changes. On these cases, one can use lapping, even though being a more difficult parameter selection process. In these studies, the development of a hybrid process capable of binding some important grinding and lapping features is initiated; the dressing operation, for the case of grinding and, for the case of lapping, the cinematic movement... (Complete abstract click electronic access below) / Mestre