Micron Diamond Processing of Advanced Ceramics

Grinding is one of the most complex manufacturing processes in industry and understanding its physics is difficult due to the stochastic nature of the process. In this thesis, the influence of the abrasive grit’s shape and size on the grinding process is considered. A number of parameters are investigated to set a classification of the abrasives based on the grit’s shape and size. These parameters are determined according to image analyses of a large number of abrasive grits. Based on this investigation, the shapes of the abrasive grits could be classified into 21 groups. Typical grit shapes will fall into only few categories dominating the shape population. These dominant shapes are ellipsoid, sphere, quadrilateral frustrum, quadrilateral pyramid and tetrahedron pyramid. After the abrasives are assessed, a test rig for multiple grit scratching and wire saw cutting rig were developped and a series of multiple grit grinding tests are performed. For this purpose, series of scratching tests have been conducted with five different diamond abrasives. The cutting forces and the acoustic emission were used to characterize the grinding mechanism during this experiment. The machining performances of the abrasive grits are evaluated in consideration of the effect of different grit shapes on the grinding process outputs including force and acoustic emission. The experimental results show a high influence of the proportion of different grit shapes on grinding force: abrasive grits with rounded shape imply high cutting forces, while grits with pyramidal shape generate low cutting forces. Furthermore, based on the proportion of the dominant shapes in an abrasive sample a force model of the cutting force and the shape proportion of the abrasives was established. The force model and the experimental results emphasised the importance of taking into consideration the abrasive’s shape as a significant parameter that influences the grinding process. The online grinding surface creation monitoring was carried out by processing the acoustic emission signals. The acoustic emission signals are analysed in both the time and frequency domains. The results show that the signal feature extraction in the frequency domain gives excellent indication in correlation to the surface creation with different abrasive geometrical characteristics

Abrasive Feature Related Acoustic Emission in Grinding

Grinding monitoring enables the online supervision of crucial aspects of the process, such as tool state, surface quality, and dimensional accuracy; and possesses a great advantage over traditional post-process quality control techniques by reducing costs and inspection times. Such an advantage relies on a good interpretation of monitored signals in relation to grinding behaviours. This paper presents an experimental study on acoustic emission (AE) features in abrasive grinding scratch experiments. The acoustic emission signals are analysed in both the time and frequency domains. The results show that the signal feature extraction in the frequency domain gives excellent indication in correlation to the surface creation with different abrasive geometrical characteristics. The AE features in the frequency range between 0 and 200 kHz show good correlation with the characteristics of interaction between abrasive and workpiece in scratching tests and could be an ideal data source for the online monitoring of surface creation in grinding processes

Grinding Acoustic Emission Features in Relation to Abrasive Scratch Characteristics

On-line monitoring of grinding process has substantial advantages over traditional post-process quality control techniques for detecting malfunctions and reducing costs and inspection times. The selection of appropriate sensors and adequate signal processing methods are essential to establish optimum grinding control strategies with good prediction quality within acceptable response times. This paper assessed three signal-processing methods for grinding surface creation monitoring based on acoustic emission (AE) signals in abrasive scratch experiments. The AE signals are analysed in time domain (time direct analysis, TDA), frequency domain (fast Fourier transform, FFT) and in the combined time-frequency domain (singular spectrum analysis, SSA). The result showed that the FFT and SSA signal feature extraction methods gives better indication in correlation to the surface creation with different abrasive geometrical characteristics. For both sapphire and zirconia materials, the results of FFT method showed the best correlation between AE features and surface creation characteristics in scratching tests and the most significative information was in the frequency range between 0 and 200 kHz. This finding allows a great reduction in the sampling frequency of the signal, making this method the most suitable for real time applications. This work reveals that the AE signals processed with the adequate feature extraction method can present good correlation with the characteristics of interaction between abrasive and workpiece in scratching tests and can provide meaningful information for the on-line monitoring of surface creation in grinding processes

Severe childhood autosomal recessive muscular dystrophy with the deficiency of the 50 kDa dystrophin-associated glycoprotein maps to chromosome 13q12

We have recently demonstrated the specific deficiency for the 50 kDa dystrophin-associated glycoprotein (50DAG) in Algerian patients afflicted with severe childhood autosomal recessive muscular dystrophy with DMD-like phenotype (SCARMD). A similar disease affecting Tunisian patients was linked to chromosome 13q but the status of the 50DAG was not investigated. Here we show by linkage analysis of Algerian families that the genetic defect which leads, either directly or indirectly, to the deficiency of the 50DAG in skeletal muscle is localized to the proximal part of chromosome 13q. We have not found any evidence of genetic heterogeneity among the thirteen families studied. It remains to be demonstrated whether the 50DAG gene maps at 13q12, and to determine if it is mutated in this disease