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.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.