| Automobile pannels have many characteristics,such as complicated shape,large structure dimensions,high accuracy and strict demand for surface quality.Compared with other parts of the automobile,the automobile panels,especially outer panels change most frequently and their market time are shortest.Its surface quality is one of the most factors affecting the whole automobile and it affects not only service performance but also car load extrinsic feature directlly. Shallow shell is acted as thr representative of automobile pannels,such as trunk-cover, engine-cover board and car's door are all the characters of shallow.The tailor welded blank become more and more important to the automobile industry for the technology of tailor welded blank has many advantages, such as reduce cost, lighten weight and protect environment. So it will bring great progress if TWBis used to make automobile pannels.Despite of these advantages of TWBs, there are also some technical problems in welding and punching, and there are great difference of stress and strain in the each side of blank for the difference in the thickness between the two side of TWBs which makes the formability more complex compared with the blank, such as cracking, wrinkling, weld-line movement and springback. Researchers have done a great deal of works on cracking, wrinkling and weld-line movement, but little work has done on springback, especially trimming springback,and only a few references are available.In order to ravel springback's mechanism of TWBs and the affection of panel,weld line,mould and technologic parameter for TWBs' springback. The following is the main content of this thesis:1) Theoretical analysis on springback of TWBs:Based on the theoretical analysis about springback of drawing parts and trimming parts for the rectangle cylinder shallow shell, the formula about TWBs'trimming springback is deduced through some necessary hypothesis and using TWB owning different thickness but the same geometrical center At the same time the elastic-plastic harden model is adopted during formula is deduced. Material parameters radius of curvature of punch die,thickness and difference of thickness of blank for springback is analysed during the rectangle cylinder shallow shell is drawed and trimmed. The neutrosp-here ,neutrosphere's move and its influence for springback are studied,and the paper tries to dicuss mechanism of trimming springback about TWBs'single-curvature shell.2) The study on springback of drawing parts and trimming parts for the TWBs cylinder shallow shell: The finite element model of springback of drawing parts and trimming parts for the TWBs cylinder shallow shell can be built up. The springback law of cylinder direction(X-direction), (Y-direction) of TWBs cylinder shallow shell and the TWBs' springback impact from weld line are researched and the stress-strain relation is also discussed in the conditions of different blank parameters (blank thickness, the difference of thickness), different mould parameters (the die profile radius), different technology parameters (blank holder force). Compared to the theoretical value accounted by the formula of springback based on the plane stress assumption, the results show that the simulation value and the theoretical value are similar.3. The research on springback of drawing parts and trimming parts for the TWBs hyperboloid shallow shell: The finite element model of springback of drawing parts and trimming parts for the TWBs hyperboloid shallow shell can be built up. The springback law of hyperboloid direction(X-direction), (Y-direction) of TWBs cylinder shallow shell and the weld line movement affected by blank holder force , die string height, blank thickness, the difference of blank thickness are researched and the stress-strain relation is also discussed. The results indicated that the springback in the long hyperboloid shallow shell direction is bigger than the short, and the short hyperboloid direction points to the die, with the long keeping away from the die after unloading. |
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