Analysis And Experimental Research Oil Cooler Weld Defects FEM

Oil cooler is a device used to cool engine lubricating oil. Its quality,stability and reliability has a direct effect on the performance of the engine. At present, the key process in quality detection of oil cooler goes to tightness detection. Factories now use aerated immersion method to detect tightness, which is inefficient and costly. In this paper, a bar-shaped oil cooler of certain type, produced by Yangzhou Puxin Cooler Co., Ltd., was used as an example to study the influences of welding defects on system parameters to find a simple detection way of judging the quality of the cooler.Analyzing the structural features of the oil cooler on the basis of vibration theory verifies that the existence of defects can affect the natural frequency of the oil cooler. As for the relationship between existence and change of defects and natural frequency, this paper mainly studied the following aspects. First, the oil cooler was simplified, based on the mechanical vibration theory, into a multiple-DOF and continuous system, and, the first three order natural frequencies of the cooler model have been figured out based on theoretical calculation. Second, by using the finite element software of ABAQUS and by taking the approach of Lanczos, the cooler model was established and its modal parameters were calculated. On the model some man-made welding defects were simulated to analyze the effects of defects’position, size and quantity on the natural frequencies of the model, with finding that these defects had a complex, integrative impact on natural frequencies. But in general, defects tend to lower the natural frequencies Finally, on the basis of finite element calculations, the oil cooler has been conducted with an experimental research, in which the signal of the specimen was collected by using a sound level meter, and then the nature frequencies of the specimen were analyzed by using the CRAS vibration and dynamic signal process system. The electrical discharge machining was then adopted to form on the specimen some defects of different sizes and at different positions. And then the natural frequencies of the oil cooler with the man-made defects were actually measured. A comparison indicates that the results of actual measurement essentially agree with that of FEM modal analysis.In the process of research, we found that the existence of defects makes an influence on stiffness of the oil cooler, while variation in natural frequency of the structure is in relation to its own stiffness changes. And decreasing in natural frequency is connected to the positions and sizes of defects. With certain positions and dimensions, the defects will have relatively larger impacts on the higher-order natural frequencies of the model. Given the defects’sizes, the positions of the defects will make complex influence on the frequency changes. Seen through the whole experimental study, the defects of the oil cooler have a significant effect on the bar-shaped cooler’s frequencies above the range of2000Hz.An approach of identifying out the suspicious products has been put forward according to the research results. Firstly pick out a number of samples from a batch of qualified oil coolers of a certain type, to actually measure natural frequencies within sensitive frequency range, calculate the corresponding mean value and variance, and determine the alarm-limitation of suspicious products on the ground of3a theorem. Next, knock the products on the production line, to measure the audio signals, and make analysis to their natural frequencies. If one natural frequency goes beyond the limitation, then corresponding sample can be regard as a suspicious product, which needs to be further detected manually.