*Corresponding author. Keywords: Flexible materials, High speed vibration cutting, Eccentric shaft connecting rod, Cutting head modules.

Transcription

1 2016 International Conference on Electrical Engineering and Automation (ICEEA 2016) ISBN: Cyber-physical Modeling of High Speed Machining of Flexible Materials Yao-hua DENG 1,2, Tuo JIN 1, Xia-li LIU 1,*, Jun Ni 2, Hui-qiao Zhou 1 and Hua-zhong GUO 3 1 Guangdong University of Technology, Guangzhou, Guangdong, University of Michigan, Ann Arbor, MI Foshan World Intelligent Technology Co., Ltd. Foshan, Guangdong, *Corresponding author Keywords: Flexible materials, High speed vibration cutting, Eccentric shaft connecting rod, Cutting head modules. Abstract. Due to the structure characteristics of flexible materials, it will easily be deformed in the cutting process and thus the cutting interface be destroyed, resulting in low-quality cutting parts. Based on the cutting process of flexible leather substance, this paper attempts to develop a new high speed vibration cutting mechanism for flexible materials. Research will be on the vibration cutting method for flexible materials, and then a high speed vibration cutting head module will be designed according to motion transformation principle of eccentric shaft and connecting rod structure. Corresponding tests and Experiments are carried out and as the result, the vibration cutting frequency is up to 20,000 times/min, with the angle error within ±1.5. The cutting speed can achieve 120 cm/s, and work noise < 80db. Introduction Vibration processing is to apply one or more different directions of low-frequency or ultrasonic vibrations to cutting tools or tools, turning conventional continuous contact processing into discontinuous, instant and reciprocating intermittent contact processing[1]. Vibration cutting process was proposed by Kumabe J. from Utsunomiya University[2], and has become the research focus in fields like superfinishing, micro processing, new materials and the processing of difficult cutting materials. For instance, the literature [3](2011) researched the high frequency cutting mechanism for flexible materials used in textile fabrics, together with the methods of converting high speed rotary cutting into high frequency linear cutting; For the advanced metal cutting, British Scholar Riaz Muhammad studied the impact of cutting tool geometry and contact conditions on its cutting force and cutting temperature under the condition when low power ultrasonic vibration was added to the cutting tool[4]. N. Suzuki in Japan(2013) improved the processability of elliptical vibration cutting by controlling the amplitude[5]; again in the literature[6](2013), there were studies on characteristics of non-separable elliptical vibration cutting, and analyzed its effectiveness of reducing average radial thrust force, verified successfully the capability of ultrasonic elliptical vibration cutting on reducing cutting force. Flexible materials are different from rigid materials like metal, timber and plastics. They are easy to be deformed, hence its cutting precision and cutting interface can be easily influenced and destroyed, leading to low-quality cut parts[7]. Therefore although the research and application of vibration processing in rigid material processing has made certain progress, few studies were reported for non-rigid and flexible material processing. Based on common flexible leather substance processing in light manufacturing, this paper will explore high speed vibration cutting for flexible materials and its cutting mechanism design. The Principle of High Speed Vibration Cutting Technique for Flexible Material Vibration cutting technique for flexible material is to apply high speed vibrations on regular cutting blades and to replace original continuous cutting with regular pulsing cutting. This will shorten the

2 operating time and to realize instantaneous separation between tools and parts. During this process, only low heat is generated and the spatial condition, as well as time condition between tools and parts will be changed. Thus, the cutting efficiency could be improved, service life of the blades be prolonged, and the smoothness of the cut flexible material be ensured. Figure 1. Schematic diagram of flexible material high frequency vibration cutting movement design. The design principle of high speed vibration cutting movement for flexible material is shown in Figure 1, from which can see the movement of this technique is composed of mainly reciprocating cuttings that are vertical to the worktable and feed movements that move along the cutting track. The main movement shifts high speed rotation into a high frequency up-down cutting. And the feed movements are mainly carried by the headpiece that works along the cutting track in a plane and rotates around the cutting head. The main movement, which turns high speed rotation into high frequency up and down cutting, is the key of the technique. Figure 2 refers to the design principle of connecting rod with eccentric shaft applied in this movement. If we use R to represent the radius of the eccentric shaft, e eccentric distance, ω eccentric angular velocity, t time, angle = t, then the trajectory equation[1] of the eccentric shaft from point A to point B is as below: S S S B 0 e(1 cos t) (1) Figure 2. Eccentric shaft-connecting rod. Figure 3. Installation of eccentric shaft-connecting rod.

3 According to equation 1, we can further deduct that the connecting rod s speed v e sin t 2 and its acceleration a e cos t, so as to change high speed rotation of the eccentric shaft into connecting rod s high frequency up and down reciprocating harmonic motion. Based on the mentioned principles, we would go further on the topic of structure design of high speed vibration cutting module for flexible materials in the next Section. The Design of High Speed Vibration Cutting Module Structure for Flexible Materials Cutting Head Structure Design As stated in Section 2 The Principle of High Speed Vibration Cutting Technique for Flexible Material, the cutting head is used for the main movement, which converts the high speed rotations of the motor into up and down reciprocating vibrations of the cutting tool. Figure 3 below illustrates the eccentric shaft-connecting rod structure. Figure 4 shows the overall structure of the cutting head which consists of four parts-base, transmission gear, drive control and cutting tool. The base is made up of direct current stand, fixation jacket, copper shaft sleeves and other components, functioned as the support and protection. The transmission gear is composed of coupling, eccentric shaft, bearing and connecting rod. One end of the horizontal coupling joints the intermediate shaft of the eccentric shaft, while the other end of the eccentric shaft connects into the I-shaped neck through additional bearing. Figure 4. The overall structure of the cutting head. The middle of the connecting rod is installed into the copper shaft sleeve and is allowed to slide up and down, and blades are attached to the lower part. The drive control then contains two parts-horizontally arranged direct current motor and controller (which is placed inside the controller shell). The bearing on eccentric shaft is the deep-groove ball bearing, mainly for taking the radial force. It rotates in a high frequency together with the eccentric shaft, in the meantime sets the connecting rod in up-down high frequency vibration. In order to ensure the service life of the bearing, grease with large lubrication temperature range and high viscosity should be applied based on the working conditions of the part used. When adopting this kind of structure for high speed vibration cutting, the mechanism is not fully balanced. This is because of the mass unbalance of eccentric shaft-the difference between center of gravity and center of shaft produces an eccentricity. Hence when the spindle rotates, it generates bending deformation due to the centrifugal inertia force from mass unbalance[9]. In the design, the dynamic balance requirements of the eccentric shaft should be fully considered, so as to eliminate any factors that will cause the unbalance. The design of the eccentric shaft is as shown in Figure 5.

4 Figure 5. Section view and side view of eccentric shaft. Figure 6. Structure diagram of connecting rod. Connecting rod is formed by upper part, middle part and lower part connecting together using screw threads(shown in Figure6). The I-shaped neck on the upper part can place additional bearing on it. The middle part plays the role as a connection, and the bottom of the lower part can attach cutting blades. As a transmission gear, the connecting rod s structural performance has a direct impact on the life of the cutting module. It vibrates continuously when it is in operation, so the blades will experience a complex squeeze from materials, resulting in a certain degree of deformation of the connecting rod. And the bigger the horizontal stress the more severe the bending deformation. This also increases the stress of the copper shaft sleeve and creates a dynamic unbalance, which may affect the cutting precision[10]. Therefore, the length of the connecting rod should be shortened if possible according to actual needs, and shear marks should be avoided in the processing of connecting rod in order to improve its stiffness. Handpiece Structure Design The handpiece is used to implement trajectories in cutting planes, as well as for lifting and rotations of the cutting head. Figure 7 is the diagram for handpiece structure. The rotating structure is mainly composed of rotating servomotor, synchronous pulley and belt. In the cutting process, rotating servo driver accepts signals from the controller and put the servomotor in rotation, making the synchronous pulley, which is fixed onto the servo motor shaft, rotate simultaneously. Then through the synchronous belt, the synchronous pulley installed in the cutting head module will rotate accordingly to carry out the rotation of the cutting head, eventually achieve the tangential cutting between cutting part and outline trajectory[11]. The transmission of the synchronous belt is accurate and has a constant transmission ratio, it works smoothly, has a high cushioning and shock-absorption ability and generates little noise, thereby assure the accuracy of the rotating blades. The cut-in and return of blades are completed by the lifting structure. As shown in the diagram, the servo motor drive will go up and down along the elevator guide rail. Figure 7. Structure diagram of the head. Figure 8. Figure of cutting module. Figure 9. Cutting machine of RZCUT-2510.

5 Performance Test & Cutting Experiment To evaluate the practical application of the cutting module, cutting speed, cutting precision and work noise were selected as the three indicators of the processing performance test. The cutting module is as shown in Figure 8, with working principle introduced in Figure 1. Three flexible materials with different thicknesses (1-mm thick cape skin, 1.5-mm thick PU skin, 2-mm thick cattle hide) were tested in the cutting experiment. The experiment employed numerical-control leather cutting machine, model: RZCUT-2510, cutting speed: cm/s, cutting thickness: 0.5~6mm, effective cutting size: 2500mm*1000m, material fixation mode: vacuum partition absorption, main engine working voltage: alternating current 220V, main engine working frequency: 50Hz, Figure 9 shows the cutting machine. The cutting shape is demonstrated in Figure 10. It is a square with 50mm-long side. The cutting started from point A, in the counterclockwise direction. Before cutting, a software of open and class system was used to draw the square cutting track and saved as cgm format file. Then imported the cutting system and set the installation distance as 1mm. Packing was carried out manually. Twelve square patterns were placed on the working platform, then the materials were arranged and fixed on the platform through vacuum partition absorption and were cut and processed (Figure 11 is the diagram for cutting process, Figure 12 is the completed sample of flexible materials). Figure 10. Graphics of cutting. Figure 11. Process of cutting. Few samples were not evenly placed on the worktable, so they were not fully absorbed. They in consequence slide locally during cutting, making the starting point unmatched with the ending point. Not taking these samples into consideration. 10 sets of samples were chosen from each material to measure the angle error. Figure 13 shows the pre-processed sample data. We evaluated the processing results using equations absolute error = measured value-true value and relative error = (measured value-true value)/true value. From the analysis of above 30 sets of data, it can be seen that the angle error for all samples was within ±1.5 if the cutting module designed herein is adopted. Among all, the fifth cutting sample-cape skin had the largest angle error as you can see from Figure 13(a), in which the absolute error was 1.2 and the relative error 1.316%. This was due to the material s characteristics and because it was not fully absorbed during cutting. It can be further observed that 2mm-thick cattle hide had the best effect of cutting, then were the 1.5mm-thick PU skin and 1mm-thick cape skin successively. When the vibration frequency is 16,000 times/min, the cutting speed can achieve 120 cm/s, with the work noise < 80db. (a) 1-mm thick cape skin (b)1.5-mm thick PU skin (c)2-mm thick cattle hide (d)three flexible materials Figure 12. Cutting renderings of 1-2mm thickness of flexible materials.

6 (a) Sample data of cape skin (b) Sample data of PU skin (c) Sample data of cattle hide Figure 13. Sample data of flexible materials cutting. Conclusion This paper studied the high speed vibration cutting method for flexible materials. Worked out a high speed vibration cutting module for the high speed cutting of flexible materials based on the motion transformation technology of eccentric shaft and connecting rod structure. From the analysis of experiment data, the cutting mechanism has the following advantages: (1) the cutting thickness of the cutting mechanism module for flexible materials ranged is from 0.5mm to 6.0mm, with the angle error within ±1.5. (2) Within this range, when the vibration frequency is times/min, the cutting speed can achieve 120 cm/s, and work noise < 80db. (3) the cutting module can cut and process real and artificial leather and other common flexible materials, and is also applicable to flexible materials like paperboard, slab rubber, grey board, thin pieces, etc. Acknowledgements This work is partially supported by National Natural Science Foundation of China (Grant no ); Foshan Science and Technology Innovation Team project in2015(no.2015it100102);

7 Science and Technology Planning Project of Guangdong Province, China (no.2014a , no.2015b and no.2015a ); Thanks for the helps. References [1] Nie L.X., Li B.D. Analysis of vibration cutting characteristics & forming mechanism [J]. Mechanical Research & Application, 2006, 19(4): (in Chinese) [2] Zhang D.Y. Light alloy difficult to machine vibration cutting technology [J]. New Technology & New Process, 2009(2): (in Chinese) [3] Jiang J.W., Gu Y.Q. The design and balance check of the blade cutting mechanism in CNC clothes cutter machines [J]. Advanced Textile Technology, 2011, 19(2): (in Chinese) [4] Riaz M. Turning of advanced alloys with vibrating cutting tool [J]. Solid State Phenomena, 2012, 1719 (188): [5] Suzuki N., Zhang J., Shamoto E. Investigation on Machining Performance of Amplitude Control Sculpturing Method in Elliptical Vibration Cutting. Procedia CIPP 2013(8): [6] Li W., Yin Q. Study on the unseparated ultrasonic elliptical vibration cutting force [J]. Acta aeronautics et astronautics sinica, 2013, 34(9): (in Chinese) [7] Yaohua Deng, Qiwen Lu, Jiayuan Chen, Sicheng Chen, Liming Wu, Luxin Tang.Study on the Extraction Method of Deformation Influence Factors of Flexible Material Processing Based on Information Entropy[J]. Advances in Mechanical Engineering, 2014, 2014(1): 1-8. [8] Ge H.W., Wan Z.K., Zhou T.H. Dynamics analysis and design of leather cutting mechanism [J]. Journal of Mechanical & Electrical Engineering, 2013,30(10): (in Chinese) [9] Zou Y. Discussion on movement of centre-to-centre driven off-centered wheel cam mechanism [J]. Journal of Northwest Institute of Light Industry,1998, 16(4): (in Chinese) [10] Yaohua Deng, Sicheng Chen, Qiwen Lu, Jiayuan Chen, Qiaofen Zhang, Liming Wu, Jiandong Shi, Xiali Liu. Study and Simulation of Deformation Mechanics Modeling of Flexible Workpiece Processing by Rayleigh-Ritz Method [J]. Mathematical Problems in Engineering, 2015, 2015: 1-7. [11] Wang T.P., Zhang Z.S., Zhao X.D. Research on cutter knife tangent following and compensating algorithm [J]. Ordnance Industry Automation, 2013, 32(2): (in Chinese)