Rotary ultrasonic vibration assisted electric arc machine design and experiment

Ming-gang XU, Gui-zhen LIU, Ying LIU, Jie-ming ZHAO, Xing GE, Min-xuan LI

(North China University of Technology, Beijing 100144, China)

Abstract: As far as the hard and brittle materials were concerned, the traditional methods of materials processing is usually very difficult to handle.The current density produced by electric arc machining is much greater than that of electrical discharge machining, so the electric arc machining has higher processing efficiency than electrical discharge machining. According to the characteristics of hard brittle materials, a kind of rotary ultrasonic vibration assisted electric arc processing machine tool was designed in this paper. The machine adopt “C” type structure that is composed of machine table and numerical control system. The design of the machine tool is mainly composed of three axes X-Y-Z, ultrasonic rotating spindle, servo motor, marble table, pillar and working liquid trough. The numerical control system is mainly composed of the switch controller, motion control card, servo drive, pulse generator, ultrasonic generator, and industrial control computer. The small hole micro-graphs were studied by this device with different thickness of spring alloy steel. The small hole micro-graphs were analyzed by Mat-lab for small hole edge detection and roundness calculation and compared with each other. The results show that the cavities processed by ultrasonic vibration are better and the edges are smoother.

Key words: Ultrasonic vibration, Electric arc machine, Small experiment

1 Introduction

With the development of industrial production and the progress of science and technology, hard brittle materials are widely used in mechanical industry, and it occupies a large proportion[1]. The electric arc processing can solve the problem of hard brittle materials processing with long cycle and high cost[7]. Electric arc processing is a method to corrosion the metal or nonmetal conductive materials that use of the electric arc discharge between two electrodes groups in case of a gas or liquid medium. A. Blais of Canada presented a three-dimensional numerical model for plasma electric arc. Tokyo university of agriculture, Tokyo, Japan scholars studied the electric arc discharge process of movement Bi-sheng Zhou of Xinjiang university studied short electric arc machining technique and used the electric pulse to remove materials[4]. Hui-Xu and Wan-sheng Zhao of Shanghai Jiaotong University studied porous electrode electric arc discharge machining and got the material removal rate about 14 000 mm3/min[5]. Fu-zhu Han of Tsinghua university proposed Dc motion electric arc milling technology and got a higher material removal rate and better surface roughness. Ultrasonic assisted processing as a kind of effective processing for difficult-to-machine materials composite processing method, has been applied in aerospace, precision instruments, optical and medical and other fields[2]. Numerous studies have found that using ultrasound combined with other special processing technology of compound special processing can achieve high efficiency and high precision processing[3], such as ultrasonic compound electrolytic machining, ultrasonic electrical discharge machining compound machining et al. The ultrasonic vibration technology combines the electric arc processing technology to design the ultrasonic vibration assisted electric arc processing the machine tool. The feasibility of this method has been verified by experiments in this paper.

2 Machine tool design

2.1 Total solution

At present, the electric arc processing technology is applied to rough machining. But the electric spark machining technology has become mature. Spark machining is used between two poles to produce spark discharge to remove the hard brittle material, which will not produce mechanical force in machining process and has relatively high machining efficiency[13]. The electric arc processing is similar to electrical discharge machining. The electric arc processing discharges material by electric arc group. The electric arc machining must have larger relative motion between the tool electrode and work-piece. Relative motion is the purpose of the snap electric arc, and makes the electric arc discharge. Based on the lessons from the existing ultrasonic vibration assisted electrical discharge machining technology, the rotary ultrasonic vibration assisted electric arc processing machine tool was designed[15]. The Rotary ultrasonic vibration assisted electric arc processing machine tool consists of ultrasonic vibration, the synergy of electric arc discharge and rotating electrode. The aim of rotary ultrasonic vibration assisted electric arc processing machine is to improve the high accuracy and the high efficiency. Rotary ultrasonic vibration assisted electric arc machine tools is mainly composed of the X-Y-Z axis, rotary ultrasonic, ultrasonic generator, and a special power supply. The overall design of machine is shown in Fig.1.

2.2 Machine experimental table

The machine experimental table adopts “C” type structure. The experimental machine tool is composed of the three axesX-Y-Z, ultrasonic rotating spindle, marble slab, column, working liquid trough, and servo motor. The structure is shown in Fig.2. The marble is the base of the machine tool and theXaxis andYaxis show 90 degrees cross stacked butZaxis is arranged vertically. TheX-Y-Zthree axis are achieved by the servo motor driven ball screw motion, which edges through bolts of shaft wall and has a lock nut for the guide screw fixation. Rotary ultrasonic spindle is composed of servo motor, ultrasonic bracket, and tool electrode ultrasonic horns stem, through which the plate bolted on the pillar. In order to prevent over travel movement, the switch is installed on both sides of the shaft. Tool electrode is connected to the rotary ultrasonic spindle tail. The working liquid fixed on theXaxis, and the drainage holes through using insulated nylon. The experimental machine tool is shown in Fig.2.

Fig.1 Machine overall design

Fig.2 Machine mechanical system diagram

2.3 Machine numerical control system

The electric arc processing belongs to the category of special processing, and the machining accuracy could be influenced by many factors. To ensure the stability and reliability of the machine processing, the control system should not only meet the basic requirements of open general NC system but also adopt various hardware modules with each other.

The machine tool numerical control system is mainly composed of industrial PC and motion control card and servo drive module. The machine tool numerical control system function module is shown in Fig.3. Preparation of experiment is adjust to the pulse power supply voltage, pulse width and pulse interval. During the electric arc machining process, wire electrode and work-piece will be kept an accurate position, therefore the experiments will adopt the position control mode. The PC-industrial sends computer processing command signal to IMC-400 control card. The Control card sends the signal to the servo drive. The Servo driver drives motor sports according to the instructions. TheX-Y-Zaxes adjust to the position of the work-piece and tool. The Rotary ultrasonic axis processes the work-piece.

Fig.3 Machine numerical control system function module

3 Electric arc machining experiment

We used the rotary ultrasonic vibration assisted electric arc process machine for experiments. The experimental parameters are shown in Table 1. Tool electrode wire is a dock column with diameter of 0.6 mm. The dock column electrode wire has good electrical conductivity and high strength. Different kinds of alloy sheets are used as the experimental work-piece. The alloy steels with different thickness are processed with or without ultrasonic vibration.

The experimental images are processed under the Matlab software and analyzed by experimental holes of roundness error. These images are extracted the edge character and detected holes edges in Canny algorithm. These holes are processed with the least square method. Image processing is shown in Fig.4 and Fig.5.The images is 0.5 mm, 1.0 mm and 1.5 mm thickness of alloy sheets, respectively. The red line represents the edge of the hole and the green line represents the least squares fitting circle.The experimental results show that these holes have higher machining precision in the case of ultrasonic vibration. With ultrasonic vibration assisted the artifacts wastes is easier to discharge. Ultrasonic vibration changes the original frequency of electric arc machining and forms the electric arc breaking mechanism of ultrasonic vibration assisted.

Table 1 Hole experimental data tables

The expe-riment numberVol-tage/VThe thick-ness of the steel/mm The ultra-sonic fre-quency/kHz PulseWidth/μsPulseInterval/μs1450.507001502450.521.657001503451.007001504451.021.657001505452.007001506452.021.65700150

Fig.4 No ultrasonic auxiliary electric arc holes to fit the image

Fig.5 Ultrasonic auxiliary electric arc holes to fit the image

4 Summary

This paper studied the principle of ultrasonic vibration and electric arc processing mechanism and designed the rotary ultrasonic vibration assisted electric arc machine. The focus of this paper is to design control system and machine mechanical system. The electric arc ultrasonic vibration is verified to help improve the machining precision by experiments. The electric arch of ultrasonic vibration assisted electric arc processing technology could provide a new method for the development of electric technology.

Acknowledgments

The work was accomplished at the North China University of Technology, Beijing, China. This topic is derived from the natural science foundation of Beijing(No.3162011).