Preliminary Research On Cemented Carbide And Thin Bronze Plate Laser Processing

This paper is mainly about preliminary investigation on cemented carbide and thin bronze plate laser processingLaser milling is a new technology of removing materials with high energy laser beam according to appointed patterns, which works as same as that of mechanical milling on manufacturing workpieces. In fact, the course of laser milling is removing materials by a series of densely overlapped laser pulses.It is very difficult to process the hard and brittle materials although their good application prospect in industry. Moreover, the present processing methods exist different disadvantages, which are the main obstacle for the hard and brittle materials to be used more widely. In this paper, systemic experiments of laser milling on cemented carbide had been carried out with plused YAG laser. At the same time, the mechanisms and arts of laser milling were studied comparatively. Moreover, different patterns on the materials were milled by the use of the optimized process of laser milling. Following is the major results of this dissertation:The experimental results demonstrated that cemented carbide could be milled with a higher efeciency pulsed lasers. The laser parameters affected the speed and quality of laser milling greatly and had shown different rules for the materials. Generally, the milling speed increased with the single pulse energy, but the quality of the milled surface decreased. The influences of laser repetition rate and scanning velocity on the milling speed and quality were different for different materials. In order to assure the miling speed and quality, the process of proper single pulse energy, repetition rate and scanning velocity for different materials should be chosen during laser milling. Moreover, in order to improve the milling speed and quality, compound milling process were necessary, which included two steps: firstly, the process with higher single pulse energy, lower repetition rate, wider laser pulse and higher scanning velocity were used to mill the workpieces roughly. And then, the arts with lower single pulse energy, narrow pulse width and lower scanning velocity were used to mill the workpiece finely. For different materials, the accuracies of the milled patterns were as follows: size precision IT7-IT8, roughness of the milled surface Ra4-Ra8.There existed three mechanisms of laser milling the hard and brittle materials, which included laser ablation, laser induced ejection of molten matter and laser induced ablation of pieces. Generally, the three mechanisms may be existed at the same time during the process of laser milling, but which one is the main mechanism will be decided by the laser parameters and the materials. For example, when laser milling single-crystal silicon with narrow pulse width (nonosecond or narrower)and lower laser output(mJ level),the milling mechanism is mainly due to the laser ablaion that behaves as the rapid evaporation of materials. But for laser milling the high molten point and high brittleness materials (such as WC-Co cemented carbide)with high repetition frequencies laser, the milling mechanism is mainly the peel of brittle matter. Especially, when laser pulse becomes wider and the single pulse energy becomes higher, the milling mechanism is the ejection of liquid mater induced by the reverse punch of the assistant gas.The model of the ideal milling speed was established and the following formula was given.According to the formulas above mentioned, the effects of single pulse energy, repetition rate and scanning velocity on the milling speed and roughness of the milled surface were analysed, which was very important in theory for further applications.In a word, the research on laser milling have given a new technique to process the hard and brittle materials effectively, which shows that this technique has valuable utility and a good prospect in applications.