【摘要】：多點(diǎn)-柔性模成形是一種新型的模具可重構(gòu)技術(shù),結(jié)合了多點(diǎn)成形和軟模成形的優(yōu)點(diǎn),改善了板材成形的表面質(zhì)量并顯著減小了回彈,柔性下模的使用簡化了模具結(jié)構(gòu)和操作流程,降低了生產(chǎn)周期和成本。對其成形過程中板材變形特點(diǎn)和變形規(guī)律的研究可為改善板材成形精度,提高多點(diǎn)成形技術(shù)的經(jīng)濟(jì)性提供有益參考,為模具可重構(gòu)技術(shù)的拓展和應(yīng)用提供一定的理論基礎(chǔ)。本文選用圓柱面為研究對象,采用數(shù)值模擬和實(shí)驗(yàn)研究相結(jié)合的方法,探討了多點(diǎn)-柔性模成形中聚氨酯和板材的變形過程和特點(diǎn),以此為依據(jù)研究了板材彎曲變形規(guī)律,揭示了多點(diǎn)-柔性模成形中回彈減小機(jī)理,獲得了板材回彈及成形輪廓幾何信息的理論計(jì)算方法,并采用1060鋁合金板材的實(shí)驗(yàn)結(jié)果進(jìn)行驗(yàn)證。結(jié)果表明:邊部優(yōu)先成形中壓頭支反力隨著到對稱中心距離的增大而逐漸增大,心部優(yōu)先成形與之相反;板材彎矩隨著附加應(yīng)力的增大和反復(fù)彎曲作用的增強(qiáng)而減小,從而導(dǎo)致回彈減小;反復(fù)彎曲作用下板材成形后的截面輪廓由曲率半徑不等的圓弧相切而成,且優(yōu)先成形區(qū)域的回彈更小。多點(diǎn)-柔性模成形中板材在不同成形方式、不同變形順序下的受力和變形特點(diǎn)不同,采用單一變量法,系統(tǒng)地研究了在無預(yù)加載成形和預(yù)加載成形兩種成形方式下及邊部優(yōu)先成形和心部優(yōu)先成形兩種變形順序下,不同因素對回彈的影響規(guī)律。采用回彈位移和回彈曲率兩種方法表征板材回彈大小,結(jié)合理論分析和數(shù)值模擬結(jié)果,從應(yīng)力應(yīng)變分布、彎矩分布、支反力變化及聚氨酯流動速度變化等方面分析了板材變形特點(diǎn),揭示了多點(diǎn)-柔性模成形抑制回彈的機(jī)理。結(jié)果表明:同無預(yù)加載成形方式相比較,預(yù)加載成形時板材回彈更小,回彈減小了53.25%;無預(yù)加載成形和預(yù)加載成形中不同因素對回彈的影響規(guī)律一致,隨著板材屈服強(qiáng)度和彈性模量比值的減小,目標(biāo)曲率半徑及聚氨酯硬度的減小,板材回彈減小;隨著預(yù)加載量、板材厚度及聚氨酯厚度的增大,板材成形精度提高;采用厚板及流動性較好的聚氨酯柔性模成形時,板材回彈較小;無預(yù)加載成形和預(yù)加載成形時,回彈位移預(yù)修正總量隨著到對稱中心距離的增大分別沿拋物線和四次多項(xiàng)式曲線變化,兩次回彈位移預(yù)修正后,板材回彈位移平均值分別減小了93.40%和97.85%,驗(yàn)證了回彈位移預(yù)修正在提高板材成形精度方面的優(yōu)越性。
[Abstract]:Multi-point flexible die forming is a new kind of reconfigurable die technology, which combines the advantages of multi-point forming and soft die forming, improves the surface quality of sheet metal forming and significantly reduces springback. The use of flexible lower die simplifies die structure and operation flow and reduces production cycle and cost. The study on the deformation characteristics and rules of sheet metal in the forming process can provide a useful reference for improving the forming accuracy and the economy of multi-point forming technology, and provide a certain theoretical basis for the expansion and application of the reconfigurable die technology. In this paper, the deformation process and characteristics of polyurethane and sheet metal in multi-point flexible die forming are discussed by using the method of numerical simulation and experimental study, and the bending deformation law of sheet metal is studied based on the cylindrical surface. The mechanism of springback reduction in multi-point flexible die forming is revealed. The theoretical calculation method of springback and geometric information of forming profile is obtained, and the experimental results of 1060 aluminum alloy sheet are used to verify it. The results show that the reaction force of the head support increases with the distance from the center to the center of the center, but the center of the center is the opposite. The bending moment of the plate decreases with the increase of the additional stress and the reinforcement of the repeated bending action, which leads to the reduction of the springback. The section profile of sheet metal formed after repeated bending is tangent by circular arc with different curvature radius, and the springback of priority forming region is smaller. In multi-point flexible die forming, the stress and deformation characteristics of sheet metal under different forming modes and different deformation sequences are different. The single variable method is used. The effects of different factors on springback are studied systematically under the two kinds of forming modes without preloading and preloading, and the deformation sequence of edge preforming and center preforming. Springback displacement and springback curvature are used to characterize the springback size of the plate. Combined with theoretical analysis and numerical simulation results, the stress-strain distribution and bending moment distribution are analyzed. The deformation characteristics of sheet metal were analyzed in terms of the change of support reaction force and the change of polyurethane flow velocity, and the mechanism of restraining springback by multi-point flexible die forming was revealed. The results show that the springback of the sheet metal is smaller and the springback decreases by 53.2525 when compared with the non-preloading forming method. The effect of different factors on springback is the same as that in non-preloading forming and preloading forming. With the decrease of yield strength and elastic modulus ratio, the radius of curvature and the hardness of polyurethane, the springback of sheet metal decreases. With the increase of preloading, the thickness of sheet and the thickness of polyurethane, the forming precision of sheet is improved, and the springback of sheet is smaller when the thick plate and flexible polyurethane die with good fluidity are used. When there is no preloading and preloading, the total amount of springback displacement precorrection changes along parabola and quartic polynomial curves with the increase of the distance from the center to the symmetric center, and after the pre-correction of the twice springback displacement, The average springback displacement is reduced by 93.40% and 97.85% respectively, which proves the superiority of pre-correction of springback displacement in improving the forming accuracy of sheet metal.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG306

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