Xiao Guijian, Deng Zhongcai, Li Shaochuan, Huang Yun Chongqing University
Abstract: This paper presents an ultrasonic vibration abrasive belt grinding head with flexible contact amplitude compensation. The grinding head includes a driving mechanism, an adapter plate, a tensioning mechanism, an ultrasonic vibration system, an ultrasonic system fixing device, an amplitude compensator, a contact wheel and an abrasive belt. The adapter plate is connected to the moving part of the grinder, and the front panel is composed of a fixed ultrasonic vibrating abrasive belt grinding head. The driving mechanism drives the abrasive belt to rotate, and the tensioning mechanism tensions the abrasive belt; the ultrasonic vibration system is fixed on the adapter plate through a flange, and the horn. The end of the rod is connected to the amplitude compensator; the compensation rod in the amplitude compensator realizes energy-gathering compensation by reducing the end area, and a strong spring is arranged in the middle of the amplitude compensator, the strong spring in the amplitude compensator forms resonance compensation with the ultrasonic vibration of the compensation rod. The structural vibration enhancement of the compensation rod in the amplitude compensator and the resonance vibration enhancement of the strong spring work together to compensate the flexible vibration absorption of the contact wheel. The device can realize the integrated processing of material removal and surface strengthening in abrasive belt grinding.
Ultrasonic vibration assisted machining has been widely used in turning, milling, grinding wheel grinding and other machining fields due to its excellent performance in reducing cutting force, prolonging tool life, improving surface integrity and improving tissue performance. As the final processing process of complex curved surface components such as aero-engine blades, abrasive belt grinding and polishing can eliminate the machining allowance and machining texture of the previous process, and determine the final surface state and surface performance of the components. However, while the abrasive belt grinding and polishing process removes the machining allowance and machining texture, it will also eliminate the surface strengthening layer introduced by the previous process. At present, it is widely used to strengthen the vibration decoration or surface shot peening treatment after the abrasive belt grinding and polishing, the above process combination not only increases the production cycle of the parts, but also increases the production cost. In addition, shot peening, while introducing surface residual stress, usually leads the increase of surface roughness is not conducive to the improvement of the comprehensive surface performance of the workpiece. In order to solve the problems existing in the existing technology, this paper designs an ultrasonic vibration abrasive belt grinding head with flexible contact amplitude compensation.
1. Ultrasonic vibration grinding head with flexible contact amplitude compensation
1.1 Innovative Design of Ultrasonic Vibration Grinding Head with Flexible Contact Amplitude Compensation
An ultrasonic vibration abrasive belt grinding head with flexible contact amplitude compensation has the features including a driving structure 1, an abrasive belt 2, an adapter plate 3, a tensioning mechanism 4, an ultrasonic system fixing device 5, an ultrasonic vibration system 6, an amplitude compensator 7 and a contact wheel 8. The adapter plate is fixed on the abrasive belt grinder, and the upper side of the adapter plate is equipped with a driving structure, a tensioning structure and an ultrasonic vibration system. The driving structure includes driving wheels, couplings and servo motors. The ultrasonic vibration system includes a transducer, an ultrasonic generator and a horn. The amplitude compensator includes a compensation rod, a spring and a limit plate. The contact wheel includes a contact wheel mounting handle and a rubber wheel. The ultrasonic vibration grinding head device is fixed on the adapter plate, which avoids the vibration absorption and vibration reduction of the flexible force control system, realizes the single amplitude controllable propagation of ultrasonic vibration, and increases the vibration amplitude adjustment range of the contact wheel. By adding an amplitude compensator, the device can realize the secondary amplification of the mechanical ultrasonic vibration amplitude at the end of the horn. The primary energy enhancement of the compensation rod and the secondary resonance vibration enhancement of the strong spring work together to compensate the flexible vibration absorption of the contact wheel, increase the adjustable range of ultrasonic vibration amplitude in the belt grinding system. The device realizes the benign application of ultrasonic vibration in abrasive belt grinding. In the process of abrasive belt grinding and removing materials, a small high-frequency impact is carried out on the grinding surface at the same time, which increases the residual compressive stress and refines the microstructure. It improves surface integrity, improves service performance, and realizes precision grinding and surface strengthening fusion processing. It can improve the surface performance, reduce the processing procedures of parts, and improve production efficiency, especially for complex curved surface components that require abrasive belt grinding.
1.2 Multi-dimensional ultrasonic vibration auxiliary grinding device
Ultrasonic vibration assisted machining is widely used in the machining of high service performance components due to its excellent advantages in reducing grinding force, reducing grinding temperature, improving surface quality and functional texture surface machining. However, the application research of ultrasonic-assisted machining in the field of abrasive belt grinding is relatively limited, especially the research of three-dimensional ultrasonic-assisted machining in the field of abrasive belt grinding has not been carried out. In order to explore the surface quality and service performance under the new grinding process, the team designed and developed a three-dimensional ultrasonic-assisted abrasive belt grinding platform (Figure 5). The designed normal ultrasonic-assisted abrasive belt grinding head drives the abrasive belt through the contact wheel. The coordinated processing of ultrasonic drive and abrasive belt material removal can meet the processing requirements of complex curved surfaces. The two-dimensional vibration platform can realize the adjustment of vibration angle and vibration phase difference, and the plane two-dimensional vibration of the workpiece can be realized by fixing the workpiece on the two-dimensional vibration platform. The successful development of the three-dimensional ultrasonic vibration platform is a new breakthrough in the team’s multi-energy field auxiliary processing, laying a hardware foundation for ultrasonic-assisted abrasive belt research. At present, the team has carried out ultrasonic-assisted abrasive belt grinding surface quality and service performance research.
2. Experimental study of ultrasonic vibration abrasive belt grinding head with flexible contact amplitude compensation
2.1 Experimental equipment
The ultrasonic vibration abrasive belt grinding head experimental platform with flexible contact amplitude compensation is the first auxiliary platform of laser abrasive belt collaborative processing equipment developed in China, the research and development of this equipment is based on the characterization of the laser abrasive belt multi-energy field collaborative processing model and the material removal mechanism, the microstructure fitting creation based on the “melting and rubbing” model and its strengthening mechanism, and the enhanced microstructure laser abrasive belt collaborative creation parameter control And precision compensation and typical strengthened microstructure laser abrasive belt collaborative processing experiment and performance test and other key technology research and development, it belongs to the first set of high-service surface laser abrasive belt collaborative processing equipment at home and abroad (Figure 6), forming a systematic processing technology system for difficult-to-process materials such as high-temperature alloys and brittle and hard materials, which can achieve bionic or functional micro-nano structure High efficiency, high precision and enhanced processing. The equipment can precisely process computer-designed micro-nano structures such as pits and reticulate patterns on the surface of the material, and can process hydrophobic functional microstructures with a scale of 1μm, and the contact angle can reach 156 °. Compared with the existing ultra-fast laser processing, the efficiency can be increased by 180 times, and the processability of difficult-to-process materials is improved, and the wear of abrasive belts and material damage are reduced. Relevant research results have published 35 SCI/EI papers, 7 Chinese T-level papers and 12 invention patents. The equipment has been applied in Sichuan University, Sichuan Institute of Light Industry, Shanghai Institute of Optics and Precision Machinery, Chinese Academy of Sciences, Nanjing Cuizhi Laser Application Technology Research Institute Co., Ltd., etc., for super-hydrophobic, drag reduction and other bionic functional surfaces. Large-area processing provides an innovative method, which helps to improve the processing level of high-service rotating components such as blades and propellers.
2.2 Ultrasonic Vibration Assisted Grinding Experiment
2.2.1 Purpose of the experiment
Abrasive belt grinding is widely used in surface processing due to its flexibility and flexible structure, which can avoid surface damage, microcracks and other defects in processing. However, the traditional grinding method has certain restrictions on the quality of the workpiece, and it is difficult to adapt to the surface processing of complex parts. In order to meet the high-performance processing of complex parts, an ultrasonic vibration abrasive belt grinding head with flexible contact amplitude compensation is designed for experimental research, and the influence of grinding parameters on surface integrity is explored, and the influence of linear speed and feed speed on surface integrity is discussed.
2.2.2 Experimental Materials
The material used in the ultrasonic vibration assisted grinding experiment is nickel-based superalloy GH4169 plate with a geometric dimension of 120mm * 80mm * 10mm. GH4169 has excellent comprehensive properties, such as high temperature strength, oxidation resistance, heat corrosion resistance and fatigue resistance. However, its high strength makes it easy to produce surface defects such as surface burns and microcracks during processing. The stress concentration sensitivity of GH4169 makes it prone to fatigue failure, thus having higher fatigue strength processing requirements. The sample of the test material is shown in Figure 7. The specific chemical composition and mechanical properties are shown in Table 1 and Table 2 respectively.
2.2.3 Experimental parameters
In order to explore the influence of different grinding parameters on surface integrity, two sets of comparative experiments were set up in the experiment, and one group used ultrasonic vibration-assisted grinding.
In the experiment, the frequency is set to 23.25kHz; Another group of experiments adopts common grinding method, and its grinding parameters are consistent with those of ultrasonic vibration assisted grinding. The specific grinding parameters are shown in Table 3.
3. Experimental tests and results
3.1 surface topography
The surface texture and morphology after grinding are shown in Figure 8. Figure A is the surface texture of conventional grinding; Figure B is the three-dimensional morphology of conventional grinding; Figure c is the surface texture of ultrasonic vibration assisted grinding; Figure d is the three-position morphology of ultrasonic vibration assisted grinding. It can be seen from the figure that the surface texture fluctuation during conventional grinding is larger than that of ultrasonic vibration-assisted grinding, but due to the flexibility of the abrasive belt, its surface quality is relatively high, which can meet the processing requirements to a certain extent. Figs. c and d can be seen that the grinding surface texture fluctuates less, the surface quality is better, and the roughness is slightly lower when grinding is not assisted by ultrasonic vibration.
3.2 surface roughness
The surface topography detection of ultrasonic-assisted grinding and conventional grinding is shown in Figure 9, Figure A shows ultrasonic-assisted grinding topography, and Figure B shows conventional grinding. As can be seen in the figure, the surface of ultrasonic-assisted grinding is more delicate, and the roughness value is lower than that of conventional grinding. Its surface roughness Ra = 1.25 μm ,Rz = 13.1 μm, texture peak 4.2 μm, and grinding depth 6.2 μm. In the figure, the roughness Ra = 1.71 μm ,Rz = 10.55 μm, the texture peak is 4.6 μm, and the grinding depth is 7.8 μm. This is consistent with the front surface texture.
In this paper, an ultrasonic vibration abrasive belt grinding head with flexible contact amplitude compensation is designed. During the removal of abrasive belt grinding materials, the device applies ultrasonic vibration perpendicular to the contact surface on the processing surface to make a small high-frequency impact. The device realizes the organic fusion of surface precision grinding and polishing processing and surface strengthening, introduces larger surface residual compressive stress and refined microstructure in the process of abrasive belt polishing processing, improves surface quality, and enhances the material The integrity and comprehensive mechanical properties of the surface are of great significance for reducing parts processing procedures, improving production efficiency and improving surface comprehensive properties. The comparative study of conventional grinding experiments and ultrasonic-assisted grinding experiments shows that ultrasonic-assisted machining is beneficial to improving the surface quality of materials. At the same time, the ultrasonic vibration abrasive belt grinding head with contact amplitude compensation plays an important role in ultrasonic assisted grinding.