Structural parameter optimization of combine harvester cutting bench

Abstract: With the rapid development of agricultural mechanization in China, the combine harvester has been applied widely in the past decade. As the critical component of the combine harvester, the Cutting table frame bears some parts, such as the blade and reel, and is subjected to the unbalanced inertial force of blade mechanism, the impact load of cutting the crop, the incentives from the engine, and other dynamic loads of road excitation. If its natural frequency is close to the frequency of the dynamic load, resonance would be produced; it will even happen to the whole header and machine. The dynamic stress produced by resonance will seriously affect the performance of the combine harvester, the service life, reliability, and human body comfort. Therefore, it is particularly important to study the vibration of the header frame. In the paper, the parametric modeling of the combine harvester Ruilong-4LZ-2.5B Cutting table frame was developed using the three-dimensional modeling software UG. After meshing, the modal parameters as well as the modal vibration shapes were calculated utilizing the NX Nastran, and the first 4 modal frequencies were 12.1, 28.96, 46.35 and 76.17 Hz respectively. In order to verify the accuracy of the modal analysis results, the laboratory modal testing the combine harvester Ruilong-4LZ-2.5B Cutting table frame was implemented by exciting vibration methods with the DH5902 dynamic analysis system. Then, experimental modal parameters were obtained, and the first 4 modal frequencies were 12.21, 29.54, 46.88 and 72.27 Hz respectively. By comparing the above results, it could be seen that the theoretical modal frequencies were close to the experimental modal frequencies (the maximum error is 5.39%) and their mode shapes were also basically the same, which verifies the correctness of the calculated results and the accuracy of the Cutting table frame finite element model. Then, the excitation frequencies of the exciting vibrations from the pavement as well as the engine, cutter bar, vibrating screen, and threshing cylinder of the combine harvester were analyzed, and the result demonstrated that the first natural frequencies of the combine harvester Cutting table frame were close to or overlapped with the above excitation frequencies, which implies the combine harvester was vulnerable to resonance in operation. Therefore, in order to improve the modal frequencies to avoid the resonance, a reasonable optimization proposal was conducted by the Global sensitivity method. The optimization results indicated that when the thickness of the every beam of the frame is reduced from 3 mm to 2.8 mm and the thickness of the floor and the side of the frame is reduced from 1.2 mm to 0.8 mm, the first 4 order modal frequencies separately are 8.85, 24.31, 40.92, and 72.96 Hz, and each of them is beyond the range of the excitation of the combine harvester, which effectively avoids the resonance. The weight of the clump weight for the transmission shaft of the header is increased by 254.90 g, the vibration amplitude of the bearing block of the transmission shaft along the advancing direction of the combine harvester is reduced 0.691 mm, and the up-and down vibration amplitude is reduced 0.216 mm. This research provides references for the design and improvement of the header structure of the combine harvester.