Formation and control of burrs in precision machining
The existence of the metal cutting burr not only reduces the dimension and shape accuracy of the workpiece, but also increases the manufacturing cost. Currently, the burr has been the most troublesome obstruction to high productivity and automation of machining processes. In this paper, the hazard of the burrs is systematically discussed in the precision or ultra-precision machining firstly and then, the formation principle and morphology of burrs in precision turning, planing, drilling and milling are studied. Finally many new technologies and methods of restraining or decreasing burrs have been developed by the cutting experiments.
The Burrs Formation Prediction and Minimization Based on the Optimal Cutting Parameters Design Method
Researches have shown the cutting parameters and the burrs formation are close related, but these relationships cannot be formed in a simple formula. The mechanism of burrs formation and its appearance occurred to the cutting material quite depends on the method of machining and cutting condition. Although the relationships are nonlinear, the residual burrs can be reduced significantly by selecting appropriate cutting parameters during machining. In this research, a series of cutting experiments that based on Taguchi experimental method has been conducted to explore the formation of burrs size and types under different cutting conditions. The relationship of cutting parameters and the burrs formation data are collected for further study. With the burr size as the evaluation index, cutting speed, feed-rate, and depth of cut are chosen to cut the medium carbon steel (S50C). The Taguchi Method and Artificial Neural Network are adapted to establish the burrs formation model, and then the neural network based on optimal design method as a tool in cutting parameters optimization is employed. The result shows the goal of reduce burrs size into a reasonable region can be accomplished by adjusting cutting parameters. The experiments proved the burrs size with the optimal design method can be reduced as much as 67 to 78% that comparing with experienced cutting condition. As this point of view, the parameters optimization operations by optimal parameters design method offer an effective tool to reduce the burrs size in machining.
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.