Eduardo Carlos Bianchi

Predicting Surface Roughness in Grinding Using Neural Networks

High rates of manufactured items have been machined by grinding at some stage of their production process, or have been processed by machines whose precision is a direct result of abrasive operations. However, even being the grinding process the most used in industry for obtaining high level of surface quality, it remains as one of the most difficult and least understood processes (Wang et al., 2005). That maybe has origin in the mistaken faith the process is extremely complex to be understood due to the large number of cutting edges and irregular geometry, high cutting speed, and very small depth of cut which varies from grain to grain. In addition, according to (Haussi & Diniz, 2003), grinding is the process indicated when the workpiece demands good surface, dimensional and geometrical quality. Thus, the grinding process is usually one of the last steps in the machining operations chain. When the workpiece reaches this point, it has high aggregated value, which makes a possible rejection very expensive. Monitoring of machining processes is mandatory for their optimization and control. Acoustic emission (AE) has become an increasingly popular monitoring technique. The sensors are inexpensive, easy to mount, and analog signal processing is comparatively simple, but good techniques for extracting reliable process information from the signals are still lacking (Hundt et al., 1997; Aguiar et al., 2002). Electrical power signals have also been largely used in grinding researches. The signal can be monitored either by the electric current of the electric motor or by the product between voltage and current signals, which gives the electrical power consumed by the electric motor. Thus, an estimate of the cutting force can be easily obtained if a model of the electric motor is available (Aguiar et al., 2002). Some researchers have shown the acoustic emission and the cutting power signals combined can provide significant results for monitoring the grinding process phenomena (Aguiar et al., 2002; Dotto et al., 2006; Kwak & Ha, 2004; Aguiar et al., 2006). Neural network has attracted a special interest in grinding research owing to its functions of learning, interpolation, pattern recognition, and pattern classification. Various examples of applications into the production engineering field have been reported (Wang et al., 2005; Dotto et al., 2006; Kwak & Ha, 2004; Aguiar et al., 2006; Wang et al., 2001). According to (Wang et al., 2005), surface roughness is one of the most important factors in assessing and determining the quality of a part. In practical, predicting and controlling the O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m

In-process grinding monitoring by acoustic emission

This work aims to investigate the efficiency of digital signal processing tools of acoustic emission (AE) signals in order to detect thermal damage in grinding processes. To accomplish such a goal, an experimental work was carried out for 15 runs in a surface grinding machine, operating with an aluminum oxide grinding wheel and ABNT 1045. The acoustic emission signals were acquired from a fixed sensor placed on the workpiece holder. A high sampling rate data acquisition system at 2.5 MHz was used to collect the raw acoustic emission instead of root mean square value usually employed. Many statistics have shown effective to detect burn, such as the root mean square (RMS), correlation of the AE, constant false alarm (CFAR), ratio of power (ROP) and mean-value deviance (MVD). However, the CFAR, ROP, kurtosis and correlation of the AE are presented as being more sensitive than the RMS.

MLP and ANFIS Applied to the Prediction of Hole Diameters in the Drilling Process

The control of industrial machining manufacturing processes is of great economic impor‐ tance due to the ongoing search to reduce raw materials and labor wastage. Indirect manufacturing operations such as dimensional quality control generate indirect costs that can be avoided or reduced through the use of control systems [1]. The use of intelligent manufacturing systems (IMS), which is the next step in the monitoring of manufacturing processes, has been researched through the application of artificial neural networks (ANN) since the 1980s [2].

Monitoring of Grinding Burn by Acoustic Emission

The combination of acoustic emission signals and cutting power have been used successfully to determine indicative parameters of burning (Kwak & Ha, 2004). These signals, properly manipulated, allow for the implementation of a burn control system in real time, optimizing thus the grinding process (Dotto et al., 2006). This would be highly beneficial for companies that strictly depend on this process, since the requisite of quality and international competitiveness increases continually with globalization (Brinksmeier et al., 2006).

Optimization of Ceramics Grinding

Grinding is the most common designation used to define the machining process which uses a tool consisting of abrasive particles to promote material removal. It is traditionally considered as a finishing operation, capable of providing reduced surface roughness values along with narrow ranges of dimensional and geometrical tolerances (Lee & Kim, 2001; Malkin, 1989). The interactions between abrasive grains and workpiece are highly intense, causing the required energy per unit of volume of removed material to be almost consummately transformed in heat, which is restricted to the cutting zone. The temperatures generated can be deleterious to the machined part, causing damages such as surface and subsurface heating, allowing also for surface tempering and re-tempering. Formation of non-softened martensite may also occur, generating undesirable residual tensile stresses and reducing thus the ultimate fatigue strength of the component. Moreover, uncontrolled thermal expansion and contraction during grinding contribute to dimensional and shape errors, leading mainly to roundness errors. The grinding severity used is limited by the maximum permissible temperatures during the process. When these are exceeded, they may lead to deterioration of the final quality (Liao et al., 2000; Silva et al., 2007). In order to optimize the process, aiming for the control of thermal conditions, an increasing focus on proper tool selection emerges, for each material to be ground. Also, the lubrirefrigeration method and types of cutting fluid applied have the main roles of reducing friction and heat, being responsible, as well, for expelling the removed material (chips) from the cutting zone. Adopting those procedures, it can be possible to machine with high material removal rates, as well as to obtain products with high dimensional and shape quality, and also ensuring the abrasive tool a greater life (Webster, 1995). Cutting fluids in machining have the specific function of providing lubrication and cooling, thus minimizing the heat produced due to friction during cutting. Its drastic reduction or even complete elimination can undoubtedly lead to higher temperatures, causing reduced cutting tool life, loss of dimensional and shape precision and even variations in the machine thermal behavior. An important and often forgotten function, which plays a decisive role in practice, is the ability to expel chips. When abrasive tools are used, a reduction in cutting fluid may render it difficult to keep the grinding wheel pores clean, favoring the tendency for clogging and thus contributing further to the aforementioned negative factors. However,

Analysis of the performance of superabrasive and alumina grinding wheels with different bonds and machining conditions

This paper presents a review of researches on CBN (cubic boron nitride) grinding wheels with the purpose of identifying the state of art in abrasive machining and serving as the basis for future researches and laboratory tests. The scientific studies investigated here report on interesting results involving grinding, published by Brazilian and foreign authors. The methods and the results are presented and discussed. In addition, a grinding setup is presented which provides more reliable experimental results about the surface integrity of fragile materials. This setup was obtained for grinding tests in several grinding conditions during the wheel service life, using alumina and vitrified and resin bond CBN grinding wheels. Results of cutting force, surface roughness and G ratio are also presented and discussed. They confirm the excellent machining capacity of the CBN wheel, with stable behavior in cutting force and roughness results during the tests. The G ratio values are in agreement with the results found by other researchers.

Application viability evaluation of the Minimum Quantity Lubrication coolant technique under different flow rates in Plunge Cylindrical Grinding of the ABNT 4340 steel with aluminum oxide wheel

The coolant delivery technique known as Minimal Quantity Lubrication (MQL) has been employed in machining since the end of the 20th Century and has gained considerable evidence in the last years as a viable alternative to the use of the conventional coolant technique (flood). Due to the low oil flow rate delivered by the MQL technique in grinding operations, that generally varies from 20 to 240 ml / h in relation to near 600,000 ml / h flow rate of the conventional coolant technique, the MQL technique provides a reduced risk for human health and environmental damage associated with the use, maintenance and disposal of cutting fluids. In this context, this study was carried out to evaluate the application viability of the minimum quantity lubrication coolant technique under different flow rates in the plunge cylindrical grinding of ABNT 4340 steel with an aluminum oxide wheel. Three flow rates were tested: 30, 60 and 120 ml/h. Grinding trials with the conventional coolant delivery method were also tested for comparative purposes. The output variables used to assess the efficiency of the MQL technique in this work are: roughness, roundness and hardness of the workpiece. Grinding wheel wear and power consumption were also monitored. The results showed that, despite the higher values of roughness and roundness of the workpiece, as well as the grinding wheel wear, the values of these same parameters obtained after machining with the MQL technique were close to those obtained after machining with the conventional technique. No thermal damages and cracks on the machined surface, or even below the machined surface, were observed after grinding ABNT 4340 steel irrespective of the coolant-lubrication condition investigated. The results showed that the MQL with 120 ml/h can be an alternative coolant technique due to cleaner environment and lower consumption of fluid in grinding under the conditions investigated in this work.

COMPARAÇÃO DE DESGASTE PARA DOIS TIPOS DIFERENTES DE DIAMANTES SINTÉTICOS CVD EM SUA UTILIZAÇÃO PARA A DRESSAGEM DE PONTA ÚNICA DE REBOLOS DE ÓXIDO DE ALUMÍNIO

RESUMO: A dressagem pode ser definida como a operacao de afiacao da ferramenta da retificacao, do rebolo. Uma das formas de dressagem mais utilizadas e com utilizacao do dressador de ponta unica, cuja ponta e formada por um pequeno diamante. Com o passar dos anos e a crescente preocupacao com o meio ambiente buscou-se utilizar do diamante sintetico como substituto para os diamantes naturais utilizados em dressadores. O diamante sintetico e ainda muito pouco utilizado para dressagem, devido principalmente as poucas pesquisas existentes na area. Neste trabalho, buscou-se observar a atuacao de dois tipos de diamantes sinteticos, para determinar qual deles apresenta menor desgaste em relacao ao outro. A metodologia empregada foi o de dressar um rebolo de oxido de aluminio ate 160 passadas e, a cada 20 passadas com um avanco da profundidade de dressagem de 40 um, tirar uma imagem da ponta deste diamante. Essas imagens foram analisadas atraves de um software e calculados os volumes gastos. Foram realizados tres ensaios para cada tipo de diamante CVD – o CDM e o TRUST – com mesmas dimensoes e volume total de 0,63 mm 3 . O diamante tipo CDM foi o que apresentou menor volume desgastado com relacao ao seu volume total, apresentando desgaste maximo de 0,36 mm 3 e o TRUST apresentou 0,62 mm 3 . Portanto, o diamante CDM foi o que apresentou melhores resultados nas condicoes utilizadas neste trabalho. Palavras-chave: Meio ambiente. Dressadores. Retificacao.

Grinding Wheel Surface Cleaning Using A Compressed Air System, In External Plunge Grinding Of Ceramics Using The Minimum Quantity Lubricant (mql) Technique [limpeza Da Superfície De Corte De Rebolos Por Um Sistema De Ar Comprimido Na Retificação Cilíndrica Externa De Mergulho De Materiais Cerâmicos Refrigerados Com A Técnica Da Mínima Quantidade De Lubrificante (mql)]

In grinding, the use of cutting fluids aims to improve the final quality of the process, because their purpose is to lubricate the contact area between workpiece and tool and the surface cooling, thus avoiding damages on the machined part. Therefore, this subject has been constantly studied, in order to diminish the amounts applied, due to some problems it may cause. The cost of the final product enhances considerably with the application of cutting fluids; they are environmentally hazardous substances, and the cause of many illnesses to the people involved. In this case, industries, universities and research centers are prompted to research alternative methods which are less harmful to the environment. Between these arises the minimum quantity lubricant (MQL) technique, however having also its disadvantages, like the formation of a grout on wheel surface, which generates higher surface roughness on the workpiece. Aiming to minimize the problems concerning this grout, compressed air jets can be applied in order to clean the abrasive tool, which is the subject of the present work. This study aims to analyze some output variables of the external plunge grinding as surface roughness and roundness errors. Using the obtained results, it is intended to study MQL technique, aiming its improvement through the surface cleaning of the grinding wheel by compressed air jets.

AVALIAÇÃO DO DESGASTE DE DIAMANTES SINTÉTICOS NA DRESSAGEM (AFIAÇÃO) DE REBOLOS

Rebolos sao ferramentas abrasivas utilizadas na fabricacao de pecas de precisao na industria mecânica. Periodicamente os rebolos devem ser dressados (afiados) por ferramentas denominadas por dressadores. Estes sao, normalmente, fabricados com diamantes naturais que estao cada vez mais escasso e oneroso. Pelo que foi constatado em contato com fabricantes de dressadores, o volume de dressadores e outras ferramentas abrasivas e substancialmente elevado, o que inviabiliza a utilizacao destes. A proposta deste trabalho foi de se estudar um diamante sintetico que possa substituir, com vantagens tecnicas e economicas os tradicionais diamantes naturais. O diamante em questao foi avaliado ao longo da sua vida util e mostrou-se ser resistente e com plenas potencialidades de ser utilizados na fabricacao de dressadores.