Dissertation > Transportation > Road transport > Automotive Engineering > Automotive structural components > Electrical equipment and accessories

Analysis and Improvement for the Crack of Mounting Hole of BEC

Author LiHongSheng
Tutor WangJianWen; ZhangYiDing
School East China University of Science and Technology
Course Mechanical Engineering
Keywords Interference Fit Weld Line Finite element MoldFlow
CLC U463.6
Type Master's thesis
Year 2012
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The issue that occurs in the production is very complex. So it’s necessary to find a good way to deal with it. For this paper, FTA(Fault Tree Analysis) is introduced first. It’s a simple way to deal with problem during production. After analyzed by this way, it got that the possible cause of the crack of mounting hole of BEC maybe lie on two sides:Design Problem of Mounting Hole and Weld line Problem of Mounting Hole.For the weld line problem, this paper expounds the cause of formation, classification, formation mechanism and basic improvement way of weld line fist. From those theories, it shows that it’s necessary the mounting hole has weld line. And on the other hand, it shows the weld line on the mounting hole is later period weld line, so it’s certain to impact the strong of the mounting line. Second, this paper uses the MoldFlow as tool to analyze the BEC. By the analysis, the existence and location of weld line is confirmed. And it’s close meet to the theory analysis before. It shows that the analysis of MoldFlow is reliable. And confirm that there’s weld line on the mounting hole. Third, this paper is doing some improvement analysis by MoldFlow. And got the best solution for weld line improvement is to add gate location.For design problem of mounting hole, this paper starts from the theory of interference fit. And calculate the design of mounting hole by traditional theory. After calculating by many different amount of interference fit, gets the relative curve of the pressure ratio of material and the mounting hole. From this study, it shows that it’s possible the mounting hole has crack. Besides, base on finite element, this paper does simulation analysis for the mounting hole by Hyperworks software. The simulation analysis basis on the different amount of interference fit0.04mm,0.06mm,0.1mm,0.2mm,0.3mm,0.7mm. Get below conclusions after analysis:first, the analysis of finite element is to closely meet the traditional analysis. Second, the present design,0.7mm amount interference fit is too big. So it happen plastic deformation on the most of the element of the hole. The hole doesn’t crack because of the good plasticity of the material. But if there are some defects on the hole, such as weld line, it will crack.After study on the crack problems, the root cause of the crack is found. And this paper gives the solutions. For the weld line, adding gate location is the best way. For design issue, this paper gives some good structure of hole for plastic material.

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