Applied Mechanics and Materials Vol. 660 (2014) pp 65-69 Submitted: 14.07.2014 (2014) Trans Tech Publications, Switzerland Revised: 22.07.2014 doi:10.4028/www.scientific.net/amm.660.65 Accepted: 14.08.2014 The effect on the application of coolant and Ultrasonic Vibration Assisted Micro Milling on machining performance RASIDI Ibrahim 1, E. A. RAHIM 2, A. A. IBRAHIM, N. A. MASKAM, S.C.GHANI Advanced Machining Research Group, Faculty of Mechanical Engineering and Manufacturing, Universiti Tun Hussein Onn Malaysia 86400 BatuPahat, Johor E-mail: 1 rasidi@uthm.edu.my, 2 erween@siswa.uthm.edu.my Keywords:Ultrasonic vibration assisted micro-milling (UVAM), surface roughness, dimension tolerance, material removal rate (MRR) ABSTRACT Advancing of micro-milling process via ultrasonic vibration assist has been proven able to improve machining characteristics such as surface roughness quality and dimension accuracy. The improvement is due to the cutting motion of Vibration Assisted Machining (VAM) process. Thus, for every vibration motion manner, the cutting characteristic of the VAM system will be difference from one to another. This paper presents the development approach of ultrasonic vibration assisted micro-milling (UVAM) using tilted 45 XY stage. It covers theoretical perspective and the influence of Minimum Quantity Lubrication (MQL) system as cutting fluid. It will emphasize on the theory of surface roughness, dimension tolerance and cutting tool life. Piezo-actuator is used as fast servo vibration mechanism in specific axis input with controlled signal. The input signal is sine wave with controllable frequency and amplitude to allow mechanism control algorithms to be develop during the process. In addition, the effect of cutting fluid was be analyzed to understand the potential capabilities of this aid on UVAM process. Introduction Ultrasonic vibration assisted micro-milling (UVAM) is an advanced machining process by imposing vibration into the machining process. It is a part of vibration assisted machining process. UVAM can be divided into several class depend on the vibration axis, either in single axis or compound axis and vibration input. The vibration can be imposed on the cutting tool or on the work piece using UVAM worktable. UVAM is consider as an effective method for machining hard and brittle material but had huge downfall in machining temperature. Ultrasonic milling will produce higher machining temperature compare to conventional milling process due to the increase on rubbing motion during the vibration[1].however, the vibration assist reduce the cutting force because stress release during gaping period. In cutting performance, ultrasonic vibration able to improve the quality of surface roughness by reduce surface roughness value. The surface roughness reduce linearly by increases of vibration amplitude[2]. The improvement is cause by the unique cutting motion of the system. Therefore, in order to develop a new design of UVAM worktable, a scientific theoretical support is important to predict the process output with high accuracy. It help to improve the understanding the nature of the UVAM mechanism.
66 Advances in Mechanical, Materials and Manufacturing Engineering 2. Theoretical modeling This part content detail on the modelling of UVAM process outcomes, i.e. the surface roughness generated and tool wear. The first steps in developing the models taking account of the vibration as shown in Fig. 1. The vibration amplitude, W will determine the dispalcement of the cutting tolerance dispalcement and the vibration wave length, will determine the frequency of the vibration. Value of W Value of0.25 (i) Cutting tolerance displacement, Figure 1: Values of displacement, in vibration t d From Fig. 2, we understand that cutting tolerance displacement is a vector of amplitude vibration motion in tilted X-axis, X ' and tilted Y-axis, Y '. So we can deduce the cutting tolerance displacement equation as shown in Equation 1. While the UVAM feed rate, Fv at specific time will depend on motion of cutting tolerance displacement rate of times and machining feed rate, fr as shown in Figure 3. Thus the equation of UVAM feed rate can be deduce as shown in Equation 2. t d Fv 2 2 X ' + Y ' d fr + (( td dt ) / 60) (1) (2) Figure 2: Vibration amplitude when tilted in X-axis and Y-axis Figure 3: Effect of vibration amplitude on cutting slot
Applied Mechanics and Materials Vol. 660 67 (ii) Surface finish By assuming the process in ideal condition. The cutting pattern will fully obey the motion of the cutting tool. Thus, the surface roughness, R a will be directly corresponding to cutting pattern: 2 fr R a (3) 32( R ± fr n) π In this equation, the sign + is for up milling and sign for down milling. By combining the vibrations as shown in Figure 3. R a 2 ( Fv) 32( R ± ( Fv ) n) n t π (4) Where n is the number of points each position of vibration signal. (iii) Tool wear Tool wear occur when the cutting tool lose it original shape during cutting process. Feed rate and cutting speed in 2D vibration machining obviously influenced tool wear. As shown in equation below [3]. n m n m vt fr KTref frref (5) Where v is cutting speed, T is cutting tool life and K is cutting tool constant. The present of vibration during cutting process lead to the release cutting stress during the negative amplitude of displacement, thus it will reduce the cutting force. However, due to ultrasonic motion of the cutting tool with the work piece, cutting temperature will become higher compare to conventional cutting process due to the friction[8]. This may lead to two possibility. First, if the cutting temperature lower than melting point, it will improve the surface roughness quality. Second, if the temperature near to melting point, it will reduce the surface roughness quality and increase the cutting force due to excessive plastic deformation occur during cutting process. 3. Experiment Setup The experiment has been setup with following parameter below. Figure 4: Instrumentation setup From Figure 4, signal generator is used to produce input signal to piezo-actuator. This signal is monitor by using oscilloscope. The input wave then will be transform into vibration by the piezoactuator and transmit it to the work piece by UVAM worktable. For lubrication system, Minimum Quantity Lubrication (MQL) system had used with synthetic ester as the lubrication oil. MQL
68 Advances in Mechanical, Materials and Manufacturing Engineering system is a lubrication system that minimize the usage of lubrication. The lubricant is spray into mist with high pressure air toward cutting tool tip during the cutting process. It help to improve surface roughness quality and cutting tool life by reduce the friction between the cutting tool and workpiece and reduce the cutting temperature. This happened due to cutting fluid slip between work piece surface and cutting tool surface. The MQL set to 0.2 MPa spray pressure and 4 times nozzle turns. All cutting parameter is shown in Table 1. Experiment Parameter Amplitude (µm) 0.5, 1.0 Frequency (khz) 1.0,4.0,20.0,40.0 Spindle Speed (rpm) 30000 Feed Rate (mm/min) 30.0 Depth of Cut (mm) 0.05 Cutting tool 2 flute flat endmill 0.5 mm diameter 4. Surface roughness comparison Figure 5 Surface roughness versus frequency From Figure 5, under low frequency region, as frequency increase the surface roughness quality of the work piece will increase. This happen due to the frequency of gapping motion increase. However as the vibration enter ultrasonic region, the surface roughness will reduce. At this region, the friction due to the motion of cutting tool will increase the cutting temperature up to entering the melting zone. It will reduce the cutting effectiveness. By increasing the vibration amplitude, the surface roughness of the work piece will slightly increase because it will increase the releasing gap between cutting tool and work piece. By reducing the stress build up during the cutting process, it will improve the cutting deformation like reducing the build-up edge (BUE) problem on the cutting tool surface. The result also shown that MQL helps to slightly improve the surface roughness. Cutting fluid will reduce the cutting temperature and friction by slipping between the cutting tool and work piece surface. 5. Cutting Tool Wear Figure 6 Flank wear versus cutting time
Applied Mechanics and Materials Vol. 660 69 Dry Flank Wear 8.0 µm MQL Flank Wear 1.6 µm Figure 6: Flank wear at 2400 s cutting time Significant improvement can be observe after using cutting fluid on UVAM process. The flank wear rate in dry cutting is 0.003 µm/s while semi-wet cutting is 0.0007 µm/s. It help to reduce the flank wear rate up to 4.28 times. This improvement is cause by the MQL system help to reduce the cutting temperature as well as reduce the friction between cutting tool surface with work piece surface. Thus, it help to prolong cutting tool life during UVAM process. From the tool wear equation, it only relate the cutting speed and feed rate. However from the result, MQL help to reduce the tool wear without changing the cutting speed and feed rate. Thus it prove that other factors like cutting temperature and cutting force should be consider in predicting the cutting tool life. Summary From the experiment result we understand that vibration contribute difference result in difference frequency region. Machining performance is increase at low frequency vibration assist and reduce as the vibration enter the ultrasonic region. MQL slightly improve the machining performance and greatly improve the cutting tool life. It is recommended for future research been conduct to understand the relation between cutting temperature, cutting force on UVAM performance. It will helps to formulate an accurate cutting tool wear formula. References [1] L. Demas, F. Sthal, E. Bigler, J.J. Boy, S. Galliou, R. Bourquin, Experimental study of temperature effect in vibrating beam and thickness-shear resonators of GaPO4 ultrasonic milling, FEMTO-ST Institute, UMRCNRS 6174, DeptLCEPENSMM. [2] J. Graževičiūtė, I. Skiedraitė, V. Jūrėnas, A. Bubulis, V. Ostaševičius, Application of highfrequency vibrations for surface milling, ISSN 1392-1207. MECHANIKA, Nr. 1(69) (2008), 46-49. [3] M. R. Ibrahim, Vibration Assisted Machining: Modelling, Simulation, Optimization, Control and Application, School of Engineering and Design, Brunel University (2010), 2-176. [4] J. Pujana, A.Rivero, A.Celaya, L.N.Lo pezdelacalle, Analysis of ultrasonic-assisted drilling ofti6al4v, International Journal ofmachine Tools & Manufacture, 49th Ed. (2009),500 508. [5] Gwo-LianqChern, Yvuan-Chin Chang, Using two-dimensional vibration cutting for micromilling International Journal of Machine Tools & Manufacture 46th Ed. (2006),659 666. [6] H. Lian, Z. Guo, Z. Huang, Experimental research of Al6061 on ultrasonic vibration assistedmicro-milling, Procedia CIRP, 6th Ed. (2013), 561 564. [7] M. P. Groover, Fundamental of Modern Manufacturing: Materials Processes and Systems, Third edition (2007), John Wiley & Sons, Inc [8] D. Xing, J. Zhang, X. Shen, Y. Zhao, T. Wang, Tribological Properties of Ultrasonic Vibration Assisted Milling Aluminium Alloy Surfaces, Procedia CIRP, 6 th Ed. (2013), 539-544