LI Xiaogao, GONG Tao, LIU Yong, SHEN Guolang, PAN Haipeng

(Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended abstract:[Background and purposes] Fiber ceramics are brittle and hard, with excellent high-temperature resistance, chemical stability and insulating properties, mainly consisting of alumina, zirconia, silicon nitride, silicon carbide and silicon dioxide, which are often used as refractory materials, heat insulation materials, and filtration materials, in aerospace, automotive, construction, circuitry and electronics. Common fiber ceramic processing methods include grinding, milling, drilling, turning and cutting. During the machining process, defects, such as cracks, spalling, cuts and burrs, often occur, resulting in low surface accuracy and high machining difficulty. In view these problems, kinematic analysis of rotary ultrasonic vibratory grinding processing, important process parameters in the machining process as the experimental factors and axial drilling force as the judging indexes were evaluated, for fiber ceramics, aiming to provide a theoretical basis for the high-efficiency and high-quality processing of ceramic materials.[Methods] Single-factor and orthogonal experiments were conducted under conditions of normal machining and rotary ultrasound-assisted machining, with the experimental factors A-D being the presence or absence of ultrasound, material type, spindle speed, and feed rate, respectively, while the axial drilling force was selected as the judging index. Fiber ceramic machining properties were studied using a four-factor, five-level, equal-level orthogonal experimental scheme. Since the number of levels of each factor is different, the proposed level method is used to fill in the remaining three levels in ultrasonic machining randomly, with ordinary machining and ultrasonic machining, which is also adopted for the fiber ceramic material factor. Orthogonal experiments were carried out according to the level values to analyze the influence law of factors such as with or without ultrasonic machining, spindle speed, feed rate and different fiber ceramic materials on the axial drilling force, and to derive the degree of influence of each factor on the axial drilling force.[Results] With the rotary ultrasound-assisted machining device, systematic analysis of processing quality was carried out, revealing the effects of feed rate, spindle speed, the nature of fiber ceramic materials and so on, on the law of the drilling force, in order to optimize the machining process of fiber ceramic materials and provide theoretical basis and practical guidance. Rotary ultrasound-assisted machining method showed great reduction in the axial drilling force of the spindle when processing fiber ceramics, for the single-crystal type and polycrystalline type structures, as well as standard type one. Compared with non-ultrasound-assisted machining methods, ultrasound-assisted machining method has a significant reduction in the axial drilling force, with the minimum value of 32%, the maximum value of 54% and the average level of 45%. The structure and composition of the material have a greater impact on the drilling force during machining. The drilling force for processing single-crystalline fiber ceramics is larger than that for processing polycrystalline ones, while the axial drilling force for processing standard, high alumina and zirconium-containing fiber ceramics increased gradually. Among the machining parameters, feed rate had the greatest effect on drilling force, followed by the presence or absence of ultrasonic assistance, spindle speed and material type.[Conclusions] In view of the characteristics of fiber ceramic materials, which are brittle and difficult to machine, the feasibility of applying rotary ultrasonic-assisted machining method was studied, to improve the machining quality and the influence of machining parameters on the axial drilling force of the tool. The size of axial drilling force of fiber ceramic materials with different structures and compositions was measured, with and without rotary ultrasonic assisted machining, while the variation of axial drilling force with the spindle speed and feed rate was analyzed under various conditions. The rotary ultrasound-assisted machining method exhibited great reduction in the axial drilling force when machining ceramic fiber materials, with minimum, maximum and average reduction rates of 32%, 54% and 45%, respectively. Among the machining parameters, feed rate had the greatest effect on drilling force, followed by the presence or absence of ultrasonic assistance, spindle speed and material type.

Key words: fiber ceramics; rotary ultrasonic assisted machining; drilling processing; spindle drilling force