Papers by Keyword: Machinable Ceramics

Abstract: In this paper, the compact SiO₂-B₂O₃-Al₂O₃-MgO-F machinable ceramics were prepared through melt-cast and sintering method. The phase composition and microstructure of the ceramics were analyzed and observed using XRD and SEM, and the relationship between processing and microstructure were discussed. The results showed that, after the heat treatment, the main phase of the ceramics changed from fluorophlogopite (mica like) to fluoramphibole (rod like). When the crystallization temperature at 950°C, the nuclei growth rate of the mica glass-ceramics was higher. Meanwhile, a small quantity of forsterite (Mg₂SiO₄) was also crystallized out in the process. The best heat treatment process was nucleated at 630°C for 2h and crystallized at 950°C for 2h.

Abstract: The performance of three different micro-drills in drilling a machinable ceramic material has been evaluated in terms of the critical feed speed (mm/min) at a given rotation rate (rpm). The critical speed is the feed speed from and above which the chipping on the rear side of the machinable ceramic material takes place. The determined critical speed turns out to increase with rotation rate in the tested range of 2k-8k rpm, forming the critical boundary line. The drilling performance of the micro-drills can be evaluated quantitatively by using the position of the critical boundary lines in the space of feed speed vs. rotation rate: the upper the critical boundary line, the higher the drilling performance of the micro-drill.

Abstract: Machinable SiC/graphite composites were fabricated by Plasma Activated Sintering (PAS), which characterized by high heating rate, short time sintering and high efficiency process. The staring powder mixture included SiC, graphite power and a few sintering aids. They were sintered by PAS under 30 MPa Pressure in vacuum at 1500°C and 1550°C, respectively. The density, bending strength and hardness were measured. The phase and the microstructure of the composites were also investigated. The results indicated that the relative density of SiC/C(graphite) composite sintered at 1550°C was more than 99.5%, the bending strength was 336.6MPa, but surface Vickers hardness was 5.8GPa far lower than SiC ceramics. The machinability of SiC/Graphite sintered by PAS in 1500°C was good because the continuous weak microstructure played a crucial role in the machining process, including a lot of weak interface between the grains of SiC and graphite partials and nearly 20vol% pores in the composite ceramics.

Abstract: The characteristic of tools wear is analyzed through turning fluorophlogopite glass-ceramics. And the process of tools wear can be divided into three periods. Through single factor test, the influence of tools wear was discussed such as tool material, cooling conditions, cutting depth and feed speed. The study indicates, the tools material and cooling condition are major factors to affect tools wear. The high-speed steel tool is not suitable for turning fluorophlogopite. Because sustaining time of cutting is short and efficiency is low in machining, the tungsten-cobalt carbide tool is not perfect tool. And ceramics tool is better than the both. The tools wear rate can be decreased under cooling conditions. Influential curve of tools wear rate versus cutting depth is a part of parabola curve.

Abstract: In this study, the machining characteristics of developed AlN-hBN composites were investigated in the end-milling and precision lapping processes. To achieve the objectives, material properties of the developed AlN-hBN composites were evaluated according to the variation of hBN contents. And, required experimental works were performed to investigate the machining characteristics of the composites. First, the machiniability of the composite was evaluated in the end-milling process under various cutting conditions, such as spindle speed, feederate, and depth of cut variations. Also, generated micro cracks caused by the cutting process were investigated via SEM photographs. Next, precision lapping experiments were performed under various conditions, and the results were estimated.

Abstract: In this study, micro patterns were formed on the developed AlN-hBN composites using powder blasting techniques, which have been considered as one of the most appropriate micro machining methods for hard and brittle materials such as ceramics. To achieve the objective, first, material properties of the developed AlN-hBN composites were evaluated according to the variation of h-BN contents. And, a series of required experiments were performed, and the results were analyzed. As the results, it was investigated that the machiniability of the developed AlN-hBN composites increased with the increase of the h-BN contents in the composites. From the experimental results, it was possible to determine optimum blasting conditions for micro pattern making on the developed AlN-hBN composites.

Abstract: Quartzite microcrystallite glass ceramics is one of the most promising machinable ceramic materials due to its many outstanding properties. The density of quartzite microcrystallite glass ceramics is smaller than the aluminum alloy and its thermal conductivity approaches to the zirconia and its elastic module is also very small; All these advantages meet the requirements for structural components to work at higher temperature; Compressive properties of quartzite microcrystallite glass ceramics had been studied at room temperature and 500°C in this paper; The specimens had been aged at 1000°C for 5, 10, 20, 30 hours, respectively. Through SEM observations of the fracture surface of the specimens, the microstructural changes had been determined; The tests showed: the compressive property of the machinable glass ceramic declined as the ageing time increasing; but the compressive property of the specimen aged for 10 hours was inferior to that aged for 20 hours; Then compressive property declined as the ageing time increasing. The SEM observation indicated that with the extend of ageing time, the grains grew bigger and microporous and microcracks increased in the specimens; Comparing the compressive property at room temperature with that at 500°C, one found that the change of compressive property was very small when the ageing time was the same; With the extend of ageing time, the curve of the compressive property changed from smooth curves to broken lines.

Abstract: Fluorophlogopite ceramics, which possesses very good machinability, high electrical resistance and high dielectric strength, is very difficult to be sintered to fully dense state. It is usually made through glass-ceramics processing. In this paper the effects of particle size distribution and sintering agents on sintering of fluorophlogopite ceramics are investigated. The study concludes that dense fluorophlogopite ceramics can be produced through ceramic processing, including careful synthesis of fluorophlogopite powder as raw material, grinding with attrition mill, and pressureless sintering with the help of plumbum contained boron silicate glass as sintering agent in the temperature range of 1100 to 1200°C.

Abstract: The machinable fluorophlogopite was drilled with tungsten-cobalt carbide and high-speed steel drill bits, respectively. The wear widths of major flank were measured, and the wear characteristic of twist was analyzed during drilling fluorophlogopite ceramics.Drilling experiments were carried to consider influence factors of drill bit wear, such as tool materials, cooling condition, spindle speed and tool angles. Tool materials and cooling conditions are the major factors to affect wear of drill bits. High-speed steel drill bits are not suitable for drilling fluorophlogopite ceramics. Cooling condition affects wear remarkably. With the rising of spindle speed, the wear widths of major flank grows. But apex angle has little affects on the tool wear rate. Research results indicate that low tool wear can be obtain through optimizing tool material and machining parameters in drilling fluorophlogopite ceramics.