Study On The Principle And Relevant Technology Of Ultrasonic Milling

Ultrasonic machining (USM) is suitable for machining hard, brittle materials, and the complex three-dimensional contours can be easily machined. However, ultrasonic machining needs a complex tool. The machining processes of three-dimensional shaped tools are time consuming and expensive. And other problems such as serious tools wear, low-efficiency and poor surface integrity still exist in the machining process when machining complex and deep cavity. They all affect the machining precision and efficiency severely.Based on the layered machining in rapid prototyping technology, this dissertation put forward a new machine method-ultrasonic milling, which is a CNC machining process using simple tools to machine three-dimensional workpiece, and the unwanted material is removed layer by layer. It has the following advantages, the machining processes and wear compensation of tools are simple, complex three-dimensional contours can be manufactured, and without macroscopical force between tools and workpiece. Ultrasonic milling is a new ultrasonic machining technology, and at present it is becoming one of the investigation hotspot in ultrasonic machining domain. The mechanism and processing performances of ultrasonic milling are studied by means of theoretical analysis combined with experimental research presented in this dissertation to improve the technology.On the basis of processing experiment of traditional USM, the material removal mechanism of ultrasonic milling is studied by analyzing the combined effect of tool's ultrasonic oscillation, rotary and feed movement of machine. There are three actions of impact, abrasion and cavitation in ultrasonic milling. Tool's rotary and feed movement of machine afford advantageous condition for generation and extension of indentation cracks. At the same time they can enhance the possibility of cracks generation and extension greatly and make the material removal increase. A theory model of the material removal rate for ultrasonic milling is proposed by using the theory of indention fracture. The model shows that influencing factor of the material removal rate are static load, abrasive dimension and concentration, tool dimension and workpiece material performances, etc. in ultrasonic milling.Frequency equations of horn are the main theory ground for designing and choosing the dimension of ultrasonic horn. However, the existing theory formulae of complex horn can only denote relation of two adjoining segment and cannot executing more comprehensive analysis. Aim at this question, and based on the wave equation of non-uniform shaft, the formulas of Ladder-type horn with tapered and exponential transition are deduced using method of four-node network. The formulae denote relation of three segment of horn. They are convenient for designing and analyzing the performance of ultrasonic horn. At the same time, the complex horn with tapered transition is machined and tested. The test experimentsshow that the small diameter segment length has significant affects on the frequency of horn. The frequency increases as the length of L₃ decreases. It can be used for modifying the ultrasonic horn.The formulas of Ladder-type horn with hyperbolic transition are deduced. And according to the frequency equations, the influence of ultrasonic tools on the performance of complex horn is discussed. It is found that the frequency decreases as the length and diameter of tools increase. In order to keep frequency of horn constant after tool assembled, we can decrease the length of horn's small segment properly and then fix the tools. The formulae of frequency equation and magnification time of horn with tools afford the theory ground for designing and machining the horn and simple tools.Finally, a series of experiments of ultrasonic NC drilling are conducted using ultrasonic numerical control drilling machine that is reconstructive. Some questions such as crack phenomenon on the border of hole, tools wear seriously and machining efficiency comparatively lower was detected in ultrasonic NC drilling experiment and corresponding improvement measure to these question are brought forward. The phenomena of tools wear and its generant reason and mechanism in ultrasonic milling are discussed. Then, the effects of various process parameters on tools wear are researched. It is educed through analysis and compare that compensation methods of tools wear according to the path length of tools is more suitability for ultrasonic milling. Subsequently, some experiments are carry accomplished to study the technology law of material removal in ultrasonic milling. The experiments show that the mode of ultrasonic milling is completely feasible, and the compensation of tools longitudinal wear can be realized.Compared with traditional ultrasonic machining, ultrasonic milling makes control of machining process simple. And it does not need machine complex tools. So, flexible performance of all machine system is increased greatly and the machining cost of workpieces is decreased. However, the disadvantage of this machining mode is lower efficiency. The machining mode is more suitable for machining middle and small contour, thin molding surface, complex curve and combination molding surface.