【作者】 王建珑；

【导师】 王刚；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2011， 硕士

【摘要】 快速气压胀形工艺可一次成形各种形状复杂、质轻、强度高且近无加工余量的板类零件,近年来开始逐渐应用于汽车工业。摩擦和润滑在成形过程中起着非常重要的作用,采用合适的润滑剂和润滑部位,对于提高板材成形性能和胀形件质量具有重要意义。基于此目的,本文通过在不同润滑条件下分别采用不同模具进行快速气压胀形试验,研究了摩擦对胀形件壁厚分布、成形能力、微观组织及表面质量的影响规律。采用Marc有限元软件对盒形件不同摩擦系数下的快速气压胀形过程进行了分析,发现摩擦系数越小,盒形件壁厚分布越均匀,盒形件最后成形部位的等效应力及等效应变也越小。减小板料与模具之间的摩擦系数可改善壁厚分布,提高成形性能,避免最后成形部位破裂的发生。通过圆环镦粗试验测得无润滑、氮化硼润滑、石墨润滑、二硫化钼润滑四种条件下的摩擦系数分别为0.56、0.21、0.26、0.5,使用润滑剂后可减小摩擦系数,其中氮化硼效果最明显,石墨次之,二硫化钼最差。润滑条件对锥形件胀形高度及壁厚分布影响不明显,无润滑、氮化硼润滑、石墨润滑、二硫化钼润滑四种条件下所成形出的锥形件高度分别为38.40mm、38.84mm、38.64mm、38.62mm,壁厚不均匀度分别为0.67、0.66、0.68、0.69。润滑条件对盒形件壁厚分布影响很大,无润滑、氮化硼润滑、石墨润滑、二硫化钼润滑四种条件下底部壁厚不均匀度分别为0.35、0.06、0.13、0.26,侧壁壁厚不均匀度依次为0.27、0.44、0.39、0.23。将氮化硼分别喷涂在盒形凹模底部、侧壁及入口圆角时,底部润滑条件下拐角底部成形最充分,成形效果最好;但在入口圆角部位喷涂氮化硼或石墨润滑剂之后,板料会发生大量局部减薄,容易导致破裂的产生。盒形件快速气压胀形过程中,有些部位涂抹润滑剂对成形有利,而有些部位涂抹润滑剂对成形产生不利影响。使用润滑剂后可提高杯形件成形能力。在氮化硼润滑条件下,可在300s成功成形出直径80mm、高30mm的杯形件,而无润滑条件下成形过程中底部圆角附近会发生破裂。使用润滑剂后,能够避免表面微小刮痕及波浪状流痕的产生,从而提高金属表面质量。氮化硼对金属表面的保护性最好;石墨铺展性较氮化硼差,高温下容易氧化,粘附在金属表面不容易清理;二硫化钼耐高温性差,会与金属表面发生化学反应而牢牢结合在一起,不容易清理,铺展性最差。氮化硼润滑条件下,盒形件底部中心部位晶粒尺寸比无润滑条件下要均匀,且晶粒仍保持等轴状态,没有呈现出拉长状态;但底部圆角部位晶粒尺寸不如无润滑条件下均匀。在凹模底部喷涂氮化硼润滑剂,并采用阶梯式加载方式,在300s成功成形出了带凸槽盒形件,且盒形件底部壁厚较为均匀,壁厚不均匀度仅为0.06。更多还原

【Abstract】 The quick plastic forming (QPF) offers significant opportunity for forming complex, lightweight, highstrength sheet metal parts with almost no allowances, and it is increasingly used in automotive industry in recent years. Friction and lubrication play an important role during the forming process, so appropriate lubricant and lubricating area is of great significance to the improving of the performance and forming quality. For this purpose, this paper investigated the effect of tribological issues on the wall thickness distribution, forming ability, microstructure and surface quality by deforming the sheet into different molds under different lubricating conditions.The QPF of rectangle part with different friction coefficients were analyzed by using MSC.MARC. It was found that the smaller the friction coefficient was, the more uniform the thickness distribution was and the smaller the equivalent stress and strain for final forming area of the part. Reducing the friction coefficient between the sheet metal and mold can improve the wall thickness distribution, increase the forming ability, and prevent the premature rupture.The friction coefficients of no lubrication, boron nitride, graphite, and molybdenum disulfide were 0.56, 0.21, 0.26, 0.5 as measured under the ring upsetting process. The lubricants can reduce friction coefficients. Boron nitride had the most obvious effect, followed by graphite, and molybdenum disulfide was the worst.Lubricating conditions had little influence on the bulging height and wall thickness distribution of conical parts. The heights of the conical parts were 38.40mm, 38.84mm, 38.64mm, 38.62mm, respectively and the wall thickness inhomogeneities were 0.67, 0.66, 0.68, 0.69, respectively under four lubricated conditions (no lubrication, boron nitride, graphite, molybdenum disulfide).Lubricating conditions had great influence on the wall thickness distribution of rectangle pieces. The thickness inhomogeneities of bottom area were 0.35, 0.06, 0.13, 0.26 and the inhomogeneities of wall thickness were 0.27, 0.44, 0.39, 0.23 under four lubricating conditions (no lubrication, boron nitride, graphite, molybdenum disulfide).When the boron nitride was sprayed on the bottom, side wall and entrance filleting of the rectangle die respectively, the bottom of corner formed best under the lubricated condition of bottom. Spraying boron nitride or graphite on the entrance filleting led to a large number of local thinning and premature rupture. During the QPF process of rectangle parts, lubrication on some areas of the mold was good for forming, but lubrication on other areas of the mold was bad for forming.Lubricants could increase the forming ability of cylindrical parts. By using boron nitride, the cylindrical part with the diameter of 80mm and height of 30mm could be formed successfully in 300s, and rupture occurred near the bottom corner during forming process under no lubrication condition.The surface scratches and small gallings were avoided as well as the surface quality was improved by using lubricants. Boron nitride offered the best protection to the metal surface. Graphite had poor spreadability than boron nitride and was easily oxidized at high temperature. Molybdenum disulfide reacted with the metal surface and its spreadability was worst. Both graphite and molybdenum disulfide were not easy to be cleaned up from the surface.The grain size at the bottom center of rectangle piece under boron nitride lubrication was more uniform than that under no lubrication, but the situation was opposite at the bottom filleting.Spraying boron nitride on the bottom of the mold and taking multi-stage loading could form rectangle part with convex slot successfully in 300s. The thickness inhomogeneity of bottom was only 0.06.更多还原