مطالعه شبیه سازی در اندازه حفره سرامیک Si3N4 در فرایند قابل توجه میکرو انفجار ماشینکاری قوس

In order to study the effect of machining parameters on machining efficiency, the size of ablation cavity for Si3N4 ceramics during process of micro-detonation of striking arc machining (MDSAM) is simulated. By means of simulation method and machining test, the cavity size can be achieved. Influences of machining parameters on cavity depth and diameter are computed and analyzed by single factor experiment. The results show that the experimental results are consistent with the simulation results as taking into account the loose deteriorative layer. Big working current, pulse width and small working distance can cause big machining efficiency. The nozzle radius should range from 1 mm to 1.4 mm. The research can present a method for precisely controlling the process of MDSAM. The simulation method can precisely calculate the cavity size and the process of MDSAM can be controlled more accurately.

Engineering ceramics have excellent mechanical properties such as, high hardness, high thermal resistance and chemical stability, and could be applied to many areas [1]. Due to inherent hardness and brittle behaviors of ceramic materials, diamond wheel grinding was the most widely used machining method for ceramics. Moreover, grinding usually results in low material removal rates and high machining costs which may account for 60-90 % cost of product [2]. Researchers developed many nontraditional machining technologies to improve machining efficiency of ceramics, such as laser machining[3], EDM [4], plasma arc cutting [5] and high pressure abrasive water jet machining [6]. Some noticeable results are obtained, too. However, above technologies have their own limitations. The wide engineering application of above technologies can not be realized now. The authors have proposed a novel machining technology for engineering ceramics, named as microdetonation of striking arc machining (MDSAM) [7]. Machining experiments showed that this method could be used to machine different shapes stably and reliably, such as hole, plane surface, groove, cylinder, complex shaped surface, and so on. During the machining process, the plasma jet with high temperature and high pressure is sprayed out from the nozzle of micro-detonation generator. In single pulse width duration, as the plasma jet is applied on the material surface, the surface temperature exceeds the boiling point of the material causing rapid melting or vaporization and an ablation cavity is generated. For MDSAM is a rough machining technology, high machining efficiency is the most important target.The machining efficiency can be represented by the volume of ablation cavity in single pulse. In this paper, the cavity size of Si3N4 in process of MDSAM is studied by means of simulation and experiment.The influence laws of parameters on cavity shape are given to analyze the material removal ability of parameters.

(1) The simulation dimension of cavity is 1.12 mm in radial direction and 0.508 mm in thickness direction. The machining test shows that the cavity is in shape of a spherical cap and its cross section is approximately circle and the cavity size is measured as diameter of 2 mm and depth of 0.18 mm. The difference in thickness direction is owing to the generation of loose deteriorative layer on the machined surface, the thickness of which ranges from 0.15mm to 0.2 mm. (2) The depth and dimension of cavity increase by increasing the working current and pulse width and decrease with the increase working distance. For nozzle radius, over big or small is not suitable for ceramics machining. The nozzle radius which ranges from 1 mm to 1.4 mm can machine the ceramics safely and efficiently.