6120型柴油机发动机活塞结构设计与工艺设计【说明书+CAD】
6120型柴油机发动机活塞结构设计与工艺设计【说明书+CAD】,说明书+CAD,6120型柴油机发动机活塞结构设计与工艺设计【说明书+CAD】,柴油机,发动机,活塞,结构设计,工艺,设计,说明书,仿单,cad
课程设计任务书一、设计题目:活塞结构设计与加工工艺二、设计参数:五十铃6120、排量2.0L、为120135、转速1300rmin顶岸高度F、活塞销直径BO、裙长SL、销座间距A、总长GL、最大爆发压力、活塞销校核 三、设计要求:1用计算机绘制活塞总装配图一张(A1图)、零件图(加工工件)一张(A2图)2设计说明书一份(包括零件图分析、定位方案确定、定位误差计算等内容;最好能写出整个工艺过程)四、进度安排:第一周: 查找课程设计所需要的书籍,资料。第二周: 对活塞进行尺寸设计计算。第三周: 强度校核第四周: 绘图并书写说明书。第五周: 应用制图软件绘制零件图及装配图并完善课程设计说明书。五、总评成绩及评语: 指导教师 签名日期 年 月 课程设计任务书一、设计题目:活塞结构设计与加工工艺二、设计参数:五十铃6120、排量2.0L、为120135、转速1300rmin顶岸高度F、活塞销直径BO、裙长SL、销座间距A、总长GL、最大爆发压力、活塞销校核 三、设计要求:1用计算机绘制活塞总装配图一张(A1图)、零件图(加工工件)一张(A2图)2设计说明书一份(包括零件图分析、定位方案确定、定位误差计算等内容;最好能写出整个工艺过程)四、进度安排:第一周: 查找课程设计所需要的书籍,资料。第二周: 对活塞进行尺寸设计计算。第三周: 强度校核第四周: 绘图并书写说明书。第五周: 应用制图软件绘制零件图及装配图并完善课程设计说明书。五、总评成绩及评语: 指导教师 签名日期 年 月 目 录前 言11活塞的概述21.1活塞的功用及工作条件21.2活塞的材料21.3活塞结构21.3.1活塞顶部21.3.2活塞头部31.3.3活塞裙部32活塞的结构参数43活塞最大爆发压力的计算53.1热力过程计算53.2柴油机的指示参数83.3柴油机有效效率104活塞销的受力分析115活塞的加工工艺13参考文献:14课程设计前 言内燃机的不断发展,是建立在主要零部件性能和寿命不断改进和提高的基础上的,尤其是随着发动机强化程度的提高、功率的增大和转速的增加,零部件尤其是直喷式柴油机活塞的工作环境变得更加恶劣了。活塞的结构直接影响活塞的温度分布和热应力分布,因此就有必要对活塞的结构和性能作出预测和评价。活塞是内燃机上最关键的运动件,它在高温高压下承受反复交变载荷,被称为内燃机的心脏,特别是坦克、舰艇和军用车船用内燃机活塞则要求更高,它已成为制约内燃机发展的一个突出问题。本次课程设计的题目是发动机铝活塞的结构及工艺设计,选择利用合适的机床加工发动机活塞,通过这次课程设计,要求熟练掌握并能在实际问题中进行创新和优化其加工工艺过程。1活塞的概述1.1活塞的功用及工作条件活塞是曲柄连杆机构的重要零件煤气主要功用是承受燃烧气体压力和惯性力,并将燃烧气体压力通过活塞销传给连杆,推动曲轴旋转对外作功。此外,活塞又是燃烧室的组成部分。活塞是内燃机中工作条件最严酷的零件。作用于活塞上的气体压力和惯性力都是周期变化的,燃烧瞬时作用于活塞上的气体压力很高,如增压内燃机的最高燃烧压力可达1416MPa。而且活塞还要承受在连杆倾斜位置时侧压力的周期性冲击作用,在气体压力、往复惯性力和侧压力的共同作用下,可能引起活塞变形,活塞销座开裂,活塞侧部磨损等。由此可见,活塞应有足够的强度和刚度,而且质量要轻。活塞顶部直接与高温燃气接触,活塞顶部的温度很高,各部的温差很大,柴油机活塞顶部常布置有凹坑状燃烧室,使顶部实际受热面积加大,热负荷更加严重。高温必然会引起活塞材料的强度下降,活塞的热膨胀量增加,破坏活塞与气缸壁的正常间隙。另外,由于冷热不均匀所产生的热应力容易使活塞顶部出现疲劳热裂现象。所以要求活塞应有足够的耐热性和良好的导热性,小的线膨胀系数。同时在结构上采取适当的措施,防止过大的热变形。活塞运动速度和工作温度高,润滑条件差,因此摩擦损失大,磨损严重。要求应具良好的减摩性或采取特殊的表面处理。1.2活塞的材料现代内燃机广泛使用铝合金活塞。铝合金导热性好(比铸铁大3-4倍),密度小(约为铸铁的1/3)。因此铝活塞惯性力小,工作温度低,温度分布均匀,对改善工作条件减少热应力延缓机油变质有利。目前铝活塞广泛采用含硅12%左右的共晶铝硅合金制造,外加铜和镍,以提高热稳定性和高温机械性能。铝活塞毛胚可采用金属模铸造,锻造和液压模锻等方法生产。为了提高铝活塞的强度和硬度,并稳定形状尺寸,必须对活塞进行淬火和时效热处理。1.3活塞结构 活塞按部位不同,分为顶部,头部和裙部三部分。 1.3.1活塞顶部活塞顶部是燃烧室的组成部分,其形状与燃烧室形状和压缩比有关,一般有平顶,凸顶和凹顶三种。 1.3.2活塞头部 活塞头部是指由活塞顶部到油环下端面之间的部分。在活塞头部加工有用来安装气环和油环的气环槽和油环槽。在油环槽的低部还加工有回油孔或横向切槽。活塞头部有足够的厚度,从活塞顶部到环槽区的断面要尽可能的圆滑,过度圆角半径应足够大,以减少热流阻力,便于热量从活塞顶部经活塞环传给气缸壁,使活塞环的温度不至于过高。 1.3.3活塞裙部 活塞头以下的部分为活塞裙部,活塞销座位于裙部。裙部起导向作用,并承受侧压力。因此,活塞裙部的形状保证活塞在气缸得到良好的导向,气缸与活塞之间在任何工况下都能保证均匀,合适的间隙,并有一定的承压面积。2活塞的结构参数发动机选取为6120型柴油机,参数设计参照新型铝活塞活塞缸径D=120mm (一)压缩高度KH=80mm(二)顶岸(第一环槽至活塞顶端距离)F=17mm(三)采用三道环(其中两道气环,一道油环)气环高度取5mm,油环高度取7mm第一道环岸高度为6mm 第二道环岸高度略小于第一道环岸高度,为5mm(四)活塞销直径为BO=44mm 顶环槽宽为3mm(五)群长SL=100mm 下裙长为65mm(六)销座间距AA=44mm (七)活塞重量 系数X=0.91.4 取X=1.23,(八)顶部厚度S=15mm 总长=80+65=145mm燃烧室 铝的线性膨胀系数为 活塞头部的最大温度为350摄氏度,所以其变形量为 活塞裙部最大温度为200摄氏度,所以其形变量为3活塞最大爆发压力的计算 最大爆发压力计算参考内燃机原理环境压力 环境温度几何压缩比 有效压缩比燃烧过量空气系数 参与废弃系数参与非其温度 增压空气压力最大燃烧压力 Z点热利用系数B点热利用系数 燃烧室扫其系数燃料质量分数 燃料低3.1热力过程计算充气过程系数 增压器后空气温度: 式中,去增压器内平均多变压缩指数(1) 压缩始点温度 式中,新气预热度,=5K; -比热修正系数,=1.11(2) 压缩始点压力(3) 充气系数(4) 平均多变压缩指数 (1) 式中,a,b常数,对于空气(忽略残余废气),a= 19.26 ,b=0.0025 第一次试算,式(1)等号右端代入=1.37 , 第二次试算,式(1)等号右端代入=1.369, (5) 压缩终点温度(6) 压缩终点压力(7) 燃料燃烧所需理论空气量 (8) 燃烧所需的实际空气量(9) 理论分子变化系数(10) 实际分子变化系数(11) Z点烧去的燃料质量分数(12) Z点处分子变化系数(13) Z点燃烧产物的平均摩尔比定容热容式中,(14) b点燃烧产物的平均摩尔比定容热容式中,(15) z点燃烧产物的平均摩尔比定压热容(16) 燃料发热量压力升高比(17) Cyz段的燃料燃烧公式,就最大燃烧温度简化后得 (2)第一次试算,取式(2)等号右端的= 2000K 得第二次试算,取式(2)等号右端的=2200K 得第三次试算,取式(2)等号右端的= 2196K 得最后取 膨胀过程参数:(18) 初膨胀比(19) 后膨胀比(20) 求多变膨胀指数及膨胀终点温度,zb膨胀线上的后燃公式, (3) (4)将式子(3)与式子(4)联立,得 (5)第一次试计算,取=2000K 得, 第二次试计算,取2189K 得, K最后取 (23) 膨胀终点压力 3.2柴油机的指示参数(21) 理论平均指示压力(以有效行程为准)(22) 实际平均指示压力(以全行程为准)式中, 示功图丰满系数,=0.98(23) 指示油耗(24) 指示效率(25) 增压器中绝热压缩功(26) 增压器中绝热效率式中,k-比热容比,=1.4,;-多变指数,。(27) 增压器实际压缩功式中,-增压器机械效率,=0.96(28) 增压器的相对作功率3.3柴油机有效效率(29) 柴油机总机械效率 式中, ;-增压器相对功率; 。(30) 柴油机平均有效压力(31) 柴油机有效油耗(32) 有效功率(33) 活塞形成容积比例尺 代表 ;压力比例尺代表0.1Mpa。压缩容积: =18.4 代表 压缩终点压力: 代表压缩始点容积 代表 压缩始点压力 代表最大压力的容积 代表 ,计算压缩曲线ac上各点压力,即 式中,在1至之间选定。计算膨胀曲线zb上各点压力,即 式中,x在1至之间选定。根据以上两式,计算出压缩曲线和膨胀曲线各点坐标参数兵列表如下:表3-1序号压缩线上的膨胀线上的1234567891011123456789101118994.563.047.337.831.527.023.621.018.917.212.574.476.618.9511.4813.217.019.923.026.23.368.615.022.230.138.644.457.112.003.014.025.036.047.048.059.0628.4638.763.590.18118.6171.9200.4229.1257.8根据上表画出示功图图3-1 6120型柴油机计算示功图Fig.3-1 Table of 6120 diesel engine calculate exploit show4活塞销的受力分析活塞受力分析:曲轴在10度转角时产生最大爆发压力,如图所示:60sin10=200sin 所以sin=600.1736/200=0.0521所以=3度图4-1Fig.4-1 其中:D活塞直径 R曲轴半径 mj往复运动质量 连杆比=R/l=60/200=0.3 n=1300r/min 曲轴转速 对活塞销的校核:1、画出活塞销的Q、M图 图4-2 Fig. 4-2活塞销外径44mm,内径do=0.25d=11mm=选活塞销材料为45号钢,调质处理,得所以该活塞销符合强度。5活塞的加工工艺表5-1活塞加工工艺过程Tablet.5-4 piston machining technics process工序号工序名称定位基准及技术条件设备工装0毛坯锻造按活塞锻造工艺进行1粗车底面B止口110粗基准是毛坯外圆,金属模液压锻造,壁厚均匀有的用内腔做为基准车床三角卡盘自动定心2粗镗活塞销孔44下端面B,内止口及毛坯销孔,活塞顶部压紧镗床镗刀3粗车顶面C,圆120及环槽下端面B内止口销孔处半自动车床,液压、仿型、多刀专用刀具4钻销座油空顶面C定位下断面销孔定位方向台钻钻模5精车下端面B,内止口110精基准:外圆面环槽端平面车床专用夹头6精车:环槽外圆面顶面精基准:下端面B内止口销孔拉紧仿型、多刀车床专用刀具7精车燃烧室基准“统一原则”同工序6车床成形刀8铣裙部圆弧外圆面活塞销孔专用铣床铣刀9精细镗活塞销孔顶面圆柱销孔专用镗床精镗销孔夹具10车锁环槽销孔定位车锁环车床镗刀11液压销孔销孔定位液压销孔车床液压器12精磨裙部外圆外圆面定位仿型磨床参考文献:1刘达利,齐丕骧编著.新型铝活塞.北京:国防工业出版社,1999.8(专著)2刘永长主编.内燃机原理.武汉:华中科技大学出版社,2001.6 (专著) 3吴建华,常绿主编.汽车发动机原理.北京:机械工业出版社,2005.7(专著)4甘永立主编.几何量与课程设计.上海:上海科学技术出版社,2005.7(专著)5陆耀祖主编.内燃机构造与原理.北京:中国建材工业出版社,2004.1(专著)6李凤平等主编.机械图学.沈阳:东北大学出版社,2003.9(专著)7唐大放等主编.机械设计工程学. 徐州:中国矿业大学出版社,2001.9(专著)8单辉祖编.材料力学. 北京:高等教育出版社,2004.4(专著)9刘希恭主编.微型汽车零部件及代换手册.天津:天津科学技术出版社,2000.2(专著)10曾东建主编.汽车制造工艺学.北京:机械工业出版社,2005.9(专著)15 防止活塞销冷挤压工艺中出现流动缺陷的新方法D.J.Lee ,D.J.Kim, B.M.Kim精密机械工程系,研究生院,釜山国家大学,釜山,韩国机械设计工程部门,研究生院,釜山国家大学,釜山,韩国机械工程系,工程研究中心,釜山国家大学,釜山,韩国编号3Janjeon-董,Kumjeong-顾,釜山609-735,韩国摘要:这份报告主要研究的是作为汽车零部件之一的活塞销的流动缺陷。在联合冷挤压制活塞销的工艺中,起皱就是一种流动缺陷,它是由死金属区引起的。具有这种缺陷的部件带有很明显的外部特征,特征是被一微小而且厚的块状物嵌入材料中,这种缺陷对保证尺寸精度和降低材料损失是不利的,活塞销的这种缺陷对于其强度和疲劳寿命也有不利的影响。因此,在工艺设计的早期预测并防止这种缺陷是非常重要的。防止其产生的最好方法就是通过控制材料流动来限制或减少死金属区。有限元模拟分析方法被应用于流动缺陷研究分析当中,这份研究报告提出了通过去除死金属区防止产生流动缺陷的新工艺方法有限元分析法。将有限元分析的结果与实验结果做比较,结果表明有限元分析的结果与实验结果相符合。关键词:流动缺陷;活塞销钉;材料流动控制;前后双向冷挤压;死金属区;有限元分析1、序言冷加工是一种及其重要而且经济的加工方法,尤其对于大批量制件的加工,其优点更为突出。由于冷加工具有高的成品率、精确的尺寸精度、良好的表面光洁度,优良的机械加工性和冶金工艺性等优点,因此冷加工是工业生产当中应用最为广泛的零件加工工艺。冷锻制件广泛应用于飞机制造、摩托车、螺母和螺栓等生产制造。但是,冷锻制件也有可能产生缺陷,这主要取决于金属材料的变形过程、成形加工的外部条件和材料的流动方式等。可延伸的裂纹缺陷是由材料的引应力状态和变形过程引起的;流动缺陷是由不稳定的材料流动引起的;低的尺寸精度是由低的模具尺寸精度和摩擦情况引起的,总之,锻压制件的缺陷主要包括两类,分别是内部缺陷和外部缺陷。这些缺陷危害到产品的质量和制造成本,因此,在工艺设计中的早期预防是非常重要的。利用有限元分析法中的不同可用标准来研究大型锻件的可延伸裂纹缺陷。KIM和KIM对两道加强筋进行冷挤压件的内部和外部缺陷研究,并还在进行一种防止产生这些缺陷的加工工艺设计。这份报告是一份关于汽车活塞销产生的缺陷的测试报告,而这种活塞销是采用前后双向联合挤压的方式支撑的。这份报告中也提出了新的工艺方法可在工艺设计的早期防止产生流动缺陷,而这些新工艺方案是通过有限元分析研究得出的,实验证明,这些新工艺方案是可行的。2、成形工艺与缺陷形成分析2.1、成形工艺活塞销是汽车零部件当中用来连接活塞与曲轴的并传递动力的部件,当采用冷冲压制活塞销时,设计要求必须保证前后双向冲压时具有相同的高度并且不能出现锻压缺陷,因为活塞销在周期性大载荷作用下工作。制作活塞销的材料是AISI-4135H合金钢,它具有如下材料流动性 768.06*0.139 ,润滑措施是采用润滑油类的磷镀在活塞销表面进行润滑,经试验测试摩擦系数M为0.1。加工活塞销钉以前用的是多步骤加工法(如图3所示),前两步通过导圆角和冲出非圆形的基准孔等预处理工序来减少缺陷的产生,从而可以提高尺寸精度和模具寿命,第三步和第四步相同,分别是从前后双向冲出圆形的腹板,最后一步是修整工序,从而得到活塞销的形状,然而,用普通加工方法加工的结果显示:第三步的早期会在腹板部位形成缺陷,更严重的是在缺陷产生的部位出现了一种不一致的流动形式,这种形式是一种非常坏的流动形式的延伸 图1 活塞销钉的形状和尺寸 图2 活塞销钉的流动缺陷 图3活塞销钉传统的形成过程2.2用有限元分析预测缺陷的产生塑性变形组织分布和有效应力对比图的应用,暗示着有限元精密塑造程序在成形与缺陷分析领域中的商业价值。最初的坯料直径为30mm,深度为61mm,最终成品的体积为43.118,这种成形工艺看上去类似于普通加工结果。最大的裂缝值可以结算出断裂缺陷产生的可能性,在这个冲压过程中,其大小只有0.08mm,而且分布在坯料和冲床活塞冲头接触的端部。因此,可以避免流动缺陷的产生,因此这种缺陷并不能产生可延展的裂纹。金属流动的流线图是由Altan和Knoerr提出的,他们正在从事这种缺陷的分析研究,随着冲头冲压深度的增加,剧烈变动的流线出现了不同的流动速度,从而导致实验中缺陷的产生(如图5所示)。所以金属流动只出现在第四步的反向冲压而不出现在正向冲压,并且在靠近腹板处的金属被拔起形成一条筋,很像是重叠缺陷,因此,活塞销的流动缺陷产生并发展的原因是:正反冲压时由于死金属区域产生而造成的金属流动速度的不同,这种现象在像活塞销这种薄壁件冲出尺寸精度高,材料损耗少的孔的制件中是非常明显的。对于活塞销这类工作温度高,载荷大而且为交变载荷的零件来说,这种流动缺陷的产生会对其强度和疲劳寿命产生有害的影响。因此,有必要研究一种新工艺来防止产生流动缺陷。 图4有效的负荷和裂缝价值的关系图5金属流动和速度的关系3.防止缺陷的工艺分析与设计流动缺陷产生的原因是金属限制死金属区域的流动。为了在传统工艺中早期的冲压部位(第三步)消除死金属区,正冲压或反冲压工艺被改为联合正反冲压工艺,这种工艺在两个完全相反的方向上同时进行同样地动作。由于正反两向不同的冲压率和冲压长度,要使两个方向上同时完成材料流动是很困难的,因此在提前完成材料流动就会出现传统工艺一样出现的死金属区。因此,在活塞销成形这种情况下,两个方向的冲压率和冲压长度都是1.89和51mm。目前,一项关于活塞销的冲压长度的调查研究正在进行开模正反冲压工艺的分析,两个方向上的冲压长度是不同的,正向冲压长度长为24.9mm,反向冲压长度如图6所示要比正向的短。反向金属流动必须强制性的被限制才能满足设计要求,而这就意为着死金属区会产生。因此,要想在两个方向上得到相同的冲压长度,提出了三种控制金属流动的方法,这三种方法都不同程度的强制限制金属流动。图6反向冲压长度3.1 改变初加工的形状在正反双向冲压之前,为了保证从腹板中心处起正反两个方向的冲压长度相等,就得要求初加工要将反向冲压筋的长度设计与双向冲压长度24.9mm有所不同。图7展示了这种改进的工艺的结果,图8展示了在这种情况下采用正反双向冲压工艺时最后一步中金属的流动。从模拟实验的结果可以得出,两个方向的冲压筋的长度都是51mm,这恰好满足设计要求和活塞销的尺寸要求。另外,死金属区的金属流动形式相同,而不像采用普通加工时会产生流动缺陷,而且在两个方向上的流动速度也是连续变化的,这就意为着金属流动在整个过程中是一致的,不会出现限制其流动的死金属区。 图七 多级样板的修改过程 图八金属网的流动 3.2 驱动冲压模膛驱动模膛工艺被用来控制金属流动从而满足设计要求,这种设备采用向相反方向运动的模膛先与已经冲压成形的一侧接触(如图9所示),这样就有助于加快后冲压方向上的金属流动而减慢先冲压方向上的金属流动速度,采用这种工艺制作的活塞销,由于反方向冲压提前完成,而此时活塞正沿着这个方向移动从而增加了金属沿着这个方向的流动,这个工艺的首要变化因素是冲头与活塞的相对速率和金属材料与活塞之间的摩擦条件。在这个研究中,由于摩擦系数m0.1(在毛胚材料和模膛之间),模拟实验只与相对速率这一变量有关。如果相对速率小于满足同时成型最合适的速率,则在反向方向上的冲压过程就会比正向冲压提前完成,这样的话就会像采用普通加工一样在相同部位产生流动缺陷,相反,如果相对速率大于最适宜的速率,则正向冲压过程就会比反向冲压过程提前完成,这样就会在相反地部位产生缺陷。因此,为了满足设计要求,采用半分法可以找出最佳的相对速率,从结果来看,最佳的相对速率是0.48,图10和11显示了相对速率分别为0.1 、0.48、1.0时采用一次冲压变形过程和金属流动情况。图11(c)显示了当采用最佳相对速率0.48时的金属流动形式,它记录了一个可以防止缺陷产生的流动形式。图9轴向移动的箱体示意图图10根据相对速度比率变化的活塞销钉形态图11根据相对速度比率比较的金属3.3 修改模具结构这种被提出的修改模具结构的工艺可以限制金属在反方向上的流动,而在这个方向上容易提前完成变形,从而可以实现在两个方向上同时完成变形,采用这种工艺时,为了能在两个方向上同时完成变形过程而得到相同的变形长度,卸料器又被设计者重新采用,它是一种使冲头从制件中抽出的装置。如果采用普通加工工艺中的固定式卸料器,则由于材料流动受到限制,会出现死金属区,而此时产生的部位与采用双向冲压时产生在中间位置不同。因此,一种利用弹簧弹力的结构可以推迟金属材料沿反方向的流动。图12显示了这种模具结构,采用这种方法,选用合适的弹簧弹力对于满足变形同时完成的要求来讲是很重要的,因而有限元模拟可以计算出这种必要地弹力。从模拟结果来看,需要给卸料器施加5吨的弹力。图13展示了这种工艺下金属流动形式,与其它改进的工艺方法相比,这种工艺在死金属区没有出现不连续的流动速度,此处的金属流动形式是相同的。 图12使用冲压模板的凹模模子结构示意图 图13使用冲压模板的金属流动4.结果和实验通过有限元分析法分析出的三种方法中是适合防止金属的流动缺陷。每个方法的情况如下。第一种方法是初步加工的产品需要三级过程(预制, 正反压挤,穿孔)并且有一个简单的模具结构;第二方法是使用沿轴方向移动的冲孔模板;第三种方法是轴向移动的箱体需要二级过程(前后压挤,穿孔)并且有一个复杂的模具结构。关于在里面形成的负荷,这三个方法都非常相似。特别是在沿轴方向移动的大约10吨的箱体情况下形成最大的负荷比其他方法小,因为在穿孔过程中沿轴方向移动的箱体会增加材料的流动。通过表1分析出的方法为形成做出了比较。在这项研究过程中,一个用在初步加工产品的实验被进行,并且为了证实模拟结果所以使用一个250吨能力的多级样板。在穿孔之前,为了金属的观察蚀刻流动能够正常被进行,所以必须为活塞销做一个流动缺陷检查。图14就是表示这个实验结果,这种方法改变了初步加工的产品。实验结果证明了在缺陷区域内金属流动的缺陷是相同的,并且满足形成同时完成和在两个挤压方向长度相同。这种过程和模拟的结果相符。传统方法初步加工的产品的使用冲压模板的使用移动箱体的用途 最大负荷(吨)97.296.396.184.0挤压的过程2个阶段2个阶段1个阶段1个阶段缺陷存在不存在不存在不存在表1 各个方法的比较 图14 对流动缺陷的消除5.结论在这项研究过程中,流动缺陷过程和预防缺陷的过程都已经被有限元分析重新设计。,缺陷的原因已经被分析,并且通过分析已经模拟出了结果。从模拟结果中可以看出,有限元分析方法是可以防止流动缺陷并且满足生产过程中控制材料的流动状态。通过有限元分析的结果和实验的结果做比较,可以得出以下几个结论:(1)活塞销里存在流动缺陷的原因是材料限制死金属区域的流动。消除这个区域最重要的是控制材料的流动。(2)初步加工的产品设计和改变模具结构是使用轴向运动的挤压箱来消除挤压过程中出现的流动缺陷。(3)被提出的方法满足了工艺的要求,向前挤压的长度部分和落后的部分都是相同的,这些已经由实验所证实。参考文献:1 T.Altan,S.I.Oh,L.Gegel,Metal forming,ASM(1983).2 T. Okamoto,T. Fukuda,H. Hagita,Source Book on Cold Forming,ASTM,1997,pp. 216226.3 S.W.Oh,T.H.Kim,B.M.Kim,J.C.Choi,KSME 19 (12) (1995) 31213129.4 R.C.Batra,N.V.Nechitailo,Int.J.Plast. 13 (4) (1997) 291306.5 A.S. Wifi,A.Abdel-Hamid,N. El-Abbasi, J. Mater. Process. Technol.77 (1998) 285293.6 D.J. Kim,B.M. Kim,J. KSTP 8 (6) (1999) 612619.7 D.C. Ko,Pusan National University Dissertation,1998.8 T. Altan,M. Knoerr,J. Mater. Process. Technol. 35 (1992) 275302.9 K. Osakata,X. Wang,S. Hanami,J. Mater. Process. Technol. 71 (1997) 105112.10Journal of Materials Processing Technology 139 (2003) 422427 New processes to prevent a flow defect in the combined forwardbackward cold extrusion of a piston-pin D.J. Lee a , D.J. Kim b , B.M. Kim c, a Department of Precision Mechanical Engineering, Graduate School, Pusan National University, Pusan, South Korea b Department of Mechanical Design Engineering, Graduate School, Pusan National University, Pusan, South Korea c Department of Mechanical Engineering, Engineering Research Center for Net Shape and Die Manufacturing, Pusan National University, No. 3, Janjeon-Dong, Kumjeong-Ku, Pusan 609-735, South Korea Abstract A flow defect of a piston-pin for automobile parts are investigated in this study. In the combined cold extrusion of a piston-pin, a lapping defect, which is a kind of flow defect, appears by the dead metal zone. This defect is evident in products with a small thickness to be pierced and is detrimental to dimensional accuracy and decrease of material loss. The flow defect that occurs in the piston-pin has bad effects on the strength and the fatigue life of the piston-pin. Therefore, it is important to predict and prevent the defect in the early stage of process design. The best method that can prevent the flow defect is removing or reducing dead metal zone through the control of material flow. Finite element simulations are applied to analyze the flow defect. This study proposes new processes which can prevent the flow defect by removing the dead metal zone. Then the results are compared with the results of experiments for verification. These FE simulation results are in good agreement with the experimental results. 2003 Elsevier Science B.V. All rights reserved. Keywords: Flow defect; Piston-pin; Material flow control; Forwardbackward extrusion; Dead metal zone; FE simulation 1. Introduction Cold forming is extremely important and economical pro- cesses, especially for producing parts in large quantities. Because of advantages of cold forming such as high pro- duction rates, excellent dimensional tolerances and surface finish, mechanical and metallurgical properties, cold form- ing is by far the largest application of industry for producing parts. However, cold forged parts are also used in manufactur- ing aircraft, motorcycles, nuts and bolts 1, but it is possible for defects to occur in forged parts, depending on the de- formation history, forming conditions and material flow pat- tern, etc. The kind of defects are ductile fracture caused by the state of stress and the deformation history, flow defects caused by unstable material flow, and poor dimensional tol- erances caused by inferiority of the die and friction condi- tion. Further, defects in forged parts are classified as internal defects and external defects 24. These defects have harmful effects on the quality of the product and an increase in the cost of production. Therefore, Corresponding author. Tel.: +82-51-510-3074; fax: +82-51-514-7640. E-mail address: bmkimpusan.ac.kr (B.M. Kim). it is important to predict and prevent defects in the early stage of process design. Wifietal.5 studied ductile fracture in bulk formed parts, using different workability criteria by the finite ele- ment method. Kim and Kim 6 studied internal and exter- nal defects of cold extruded products with double ribs and performed process design to prevent these defects. In this study is examined a defect which occurs in produc- ing a forwardbackward extrusion product, a piston-pin for an automobile part, and new processes are designed to pre- vent the defect by finite element method in the early stage of process design. Then the results are compared with the results of experiments for verification. 2. Forming and defect-occurrence analysis 2.1. Forming process The piston-pin is an automobile components used in the transmission of power between the connecting rod and the crankshaft. In the cold extrusion of a piston-pin, the design requirements are to keep the same height of the forward extruded part and the backward part (Fig. 1) without any defect in the forged product, for use under high and repeated 0924-0136/03/$ see front matter 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0924-0136(03)00515-6 D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 423 Fig. 1. Shape and dimension of the piston-pin. Fig. 2. Photograph of a flow defect of a piston-pin. load. The material used for the piston-pin is AISI-4135H (Fig. 2) alloy steel, with the following flow stress behavior: = 768.06 0.139 (MPa) Fig. 4. Distribution of effective strain and fracture value. Fig. 3. Conventional forming process for a piston-pin. The lubricant used is phosphate coating and bond lube. The friction factor, m, is assumed to be 0.1, which is confirmed by the ring compression test. The sequence of the conventional process for the piston-pin is performed using a multi-stage former (Fig. 3). The first and second stages are pre-upsetting to eliminate defects by the cropping process such as ovality and ec- centricity of the billet for improvement of dimensional tolerances and die life whilst the third and forth stages are forward or backward extrusion for the forming of one di- rection from the web, and final stage is the piercing process for the pin shape. However, the results of experiment for the conventional process displayed a defect in the web part formed early in the third process (Fig. 3). Especially, a nonuniform flow pattern is observed in part of the defect occurrence, which looks like a flow defect similar to lapping with an undesirable flow pattern. 2.2. Prediction of defects by FE analysis DEFORM is used, which is commercial code of a rigid-plastic FE program for forming and defect analy- sis. The diameter of the initial billet is 30 mm and the height is 61 mm, the whole volume of final product being 424 D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 Fig. 5. Metal flow and velocity distribution, where a defect occurs according to stroke. 43,118 mm 3 . The forming is simulated with a conventional process sequence. The maximum fracture value that can estimate the occur- rence of a crack 7 is small at 0.08 and is distributed in a position within the head part of the punch, so that a de- fect does not occur. Thus this defect is not one due to duc- tile fracture (Fig. 4). Then flow line-tracking scheme that was proposed by Altan and Knoerr 8 is performed for de- fect analysis. According to the progress of the punch stroke, severe variation of flow lines appears and discontinuity of velocity occurs in the part that a defect occurred in the ex- periment (Fig. 5). Consequently, the metal flows only in the backward di- rection without flow to the forward direction in the fourth process and metal near the web part is pulled up in the rib part like a lapping defect. Therefore, the cause of the ini- tiation and development of the flow defect that occurred in piston-pin is the velocity discontinuity between backward and forward direction by the formation of a dead metal zone. This appearance evidently occurs in products like a piston-pin with a low thickness to be pierced for the dimen- sional accuracy and the decrease of material loss. A flow defect occurring in a piston-pin has harmful effects on the strength and the fatigue life of a piston-pin that has high and repeated load at high temperature. Therefore, it is necessary for a new process to prevent the flow defect. 3. Process redesign and analysis for the prevention of defect The cause of the initiation and development of the flow defect is the restriction of metal flow by the dead metal zone. For the elimination of the dead metal zone in the early extruded part (3rd process) in the conventional process, the forward or backward extrusion process is modified to combined forwardbackward extrusion, which is performed simultaneously in the two directions. Because of the variety of extrusion ratios and lengths in the forward and backward directions, the simultaneous completion of the material flow in the both directions is very difficult. Consequently, one of the directions is completed early, then material flow stopped and dead metal zone appears in this part just like that in the conventional process. Therefore, in the case of piston-pin forming, the extrusion ratio and the length of both directions are the same at 1.89 and 51 mm. First, analysis of open die forwardbackward ex- trusion is performed for an investigation of extrusion lengths of the piston-pin. The difference of two extruded ribs is 24.9 mm and the backward extruded rib is shorter than the forward extruded rib as shown in Fig. 6. The metal flow of backward direction must be restricted compulsorily for the satisfaction of the design conditions and this means the occurrence of a dead metal zone. There- fore, for the same extrusion length in both directions, three Fig. 6. Extrusion length in forwardbackward extrusion. D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 425 Fig. 7. Modified process sequence for a multi-stage former. methods are proposed to control the metal flow without the compulsory restriction of metal flow 3.1. Change of preform shape To secure the same length of both directions from the center of web, it is required that the backward extruded rib is performed by preform design as the difference of both-direction lengths at 24.9 mm from the above results, before forwardbackward extrusion. Fig. 7 shows the mod- ified process sequence, and Fig. 8 shows the metal flow of the final stage of forwardbackward extrusion in this case. From the results of simulation, the lengths of two extruded ribs are 51 mm, which is the dimension of the piston-pin and satisfied the design condition. In addition, the metal flow is uniform in the defect zone where the flow defect occurred in the conventional process, and there is not a discontinu- ity of velocity in both extrusion directions. This means that metal flows uniformly in the whole process without a dead metal zone by restriction of metal flow. Fig. 8. Metal flow of web in case of using preform. Fig. 9. Schematic diagram of the axially moving container die structure. 3.2. Driving of extrusion container The driving extrusion container method 9 is used for metal flow control for the satisfying of the design condi- tion. This structure is that the extrusion container is moved in the counter direction to the early extruded one (Fig. 9). This has the effect of increasing the metal flow in the late extruded direction and restricting metal flow in the early ex- truded direction. In the case of the piston-pin, because of the early completion of backward extrusion, the extrusion container is moved in the forward direction for the increase of metal flow to this direction. In this process, the princi- pal process variables are the relative velocity ratio of the punch and the moving extrusion container, and the friction condition between the material and the moving extrusion container. In this study, because the friction factor, m, is 0.1 be- tween the material and container, simulation is performed only according to the variation of the relative velocity ratio (V C /V P = 0.1, 0.25, 0.5, 0.75, 1.0). If the relative velocity ratio is smaller than the optimum which can complete form- ing simultaneously, extrusion in the backward direction is completed earlier than in the forward direction and a flow defect occur in the same part as in the conventional process. Otherwise, if the relative velocity ratio is larger than the op- timum one, extrusion in the forward direction is complete earlier than backward direction and a flow defect occurs in the opposite part to where a defect occurs in the conven- tional process. Therefore, for satisfaction of the design conditions, the optimum relative velocity ratio is searched for by an opti- mization technique, the bisection method. From the result, the optimum relative velocity ratio is 0.48. Figs. 10 and 11 show the deformation modality and metal flow according to the relative velocity ratio (0.1, 0.48, 1.0) for a punch stroke of 42.7 mm, respectively. Fig. 11(c) shows the metal flow 426 D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 Fig. 10. Deformation modality of the piston-pin according to the relative velocity ratio. Fig. 11. Comparisons of metal flow according to the relative velocity ratio. at the optimum relative velocity (0.48) where an improved flow pattern without a flow defect can be noted. 3.3. Modification of die structure A modification of the die structure is proposed which can restrict the metal flow of backward direction, which is deformed early, for simultaneous completion of extrusion in both directions. In this case, for simultaneous completion and the same length in both directions, the stripper, which is Fig. 12. Schematic diagram of die structure using stripper. equipment for punch extraction from products, is redesigned. If a fixed stripper of conventional type is used, a dead metal zone appears from the middle stage of backwardforward extrusion by the restriction of material flow. Therefore, a structure is used that can delay the metal flow in the backward direction by spring force. Fig. 12 shows the die structure. For this method, it is very important to decide the proper spring force for simultaneous completion of forming. Therefore, the necessary spring force for this is calculated by FE simulation. From the simulation result, it was 5 t to be applied load to stripper. Fig. 13 shows metal flow in this case. The metal flow is similarly uniform at the defect zone without discontinuity of velocity in comparison with other modification methods. Fig. 13. Metal flow of web in case of using stripper. D.J. Lee et al. / Journal of Materials Processing Technology 139 (2003) 422427 427 Table 1 Comparison process for each of the proposed method Conventional method Use of preform Use of stripper Use of moving container Maximum load (t) 97.2 96.3 96.1 84.0 Process of extrusion 2 stage 2 stage 1 stage 1 stage Defect Exist None None None 4. Results and experiment From the FE simulation, the three proposed methods are proper to prevent a flow defect by metal flow control. The characteristics of each process are as follows. The first method that uses a preform needs three stage processes (pre- forming, forwardbackward extrusion, piercing) and has a simple die structure; however, the second method that uses a stripper and the third method that uses an axially mov- ing container need two-stage processes (forwardbackward extrusion, piercing) and have a complex die structure. In respect of the forming load, the processes are similar to each other. Especially, the maximum forming load is smaller than that of other processes by about 10 t in the case of the axially moving container, because the axially moving container in- creases material flow in the direction punch movement. It is compared with the proposed method for forming by a press in Table 1. In this study, an experiment using a preform is performed and uses a multi-stage former having 250 t ca- pacity for the verification of simulation. Etching for obser- vation of metal flow is performed to examine for a flow defect for the piston-pin before piercing. Fig. 14 shows the experiment result, based on the first proposed method, changing the preform. The experiment result shows that metal flow is uniform in the defect zone where the flow de- fect had occurred, and satisfied the simultaneous completion of forming and the same length in both extrusion directions. This tendency is in good agreement with the simulation result. Fig. 14. The elimination of the flow defect by the first proposed method. 5. Conclusions In this study, the flow defect that occurs in the manu- facturing process of the piston-pin is examined and a new process to prevent the defect is redesigned by FE analysis. First, the cause of the defect is investigated, and the analyti- cal approach is verified by comparison of experimental and simulation results. From these results, it is possible to de- sign processes that can prevent the flow defect and satisfy the design condition to control the material flow. Comparing the experiment and FE analysis for the pro- posed new processes, several conclusions can be drawn: (1) The cause of the flow defect that occurs in the piston-pin forming is a dead metal zone by restriction of material flow, and it is very important to control the material flow for eliminating this zone. (2) Design of the preform and change of the die structure and the use of an axially moving extrusion container are proposed to secure simultaneous filling for elimination of the flow defect in the combined forwardbackward extrusion process. (3) The proposed methods satisfy the requirements of pro- cess design, i.e. the same length of the forward extru- sion part and the backward one, and these are verified by experiment. Acknowledgements The authors wish to thank the Engineering Research Cen- ter for Net Shape and Die Manufacturing, located in Pusan National University, Pusan, South Korea, for the support of this research. References 1 T. Altan, S.I. Oh, L. Gegel, Metal forming, ASM (1983). 2 T. Okamoto, T. Fukuda, H. Hagita, Source Book on Cold Forming, ASTM, 1997, pp. 216226. 3 S.W. Oh, T.H. Kim, B.M. Kim, J.C. Choi, KSME 19 (12) (1995) 31213129. 4 R.C. Batra, N.V. Nechitailo, Int. J. Plast. 13 (4) (1997) 291306. 5 A.S. Wifi, A. Abdel-Hamid, N. El-Abbasi, J. Mater. Process. Technol. 77 (1998) 285293. 6 D.J. Kim, B.M. Kim, J. KSTP 8 (6) (1999) 612619. 7 D.C. Ko, Pusan National University Dissertation, 1998. 8 T. Altan, M. Knoerr, J. Mater. Process. Technol. 35 (1992) 275302. 9 K. Osakata, X. Wang, S. Hanami, J. Mater. Process. Technol. 71 (1997) 105112.
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