冷敲花键相邻齿槽之间成形影响的分析.pdf

第42卷第11期Vol． 42 No． 11FORGING 2.金属材料成形理论与技术山西重点实验室,山西太原030024;3.山东省青岛生建机械厂,山东青岛266106; 4.太原科技大学机械工程学院,山西太原030024)摘要:在分析花键冷敲成形原理的基础上,采用ABAQUS/ Explicit算法对花键冷敲相邻齿槽成形过程进行了有限元模拟仿真,研究了工件经过不同敲打次数后两个相邻齿槽的应力、应变分布规律。在自行研制的LQ200型冷敲设备上加工花键轴,利用光学显微镜研究冷敲花键不同成形区的显微组织形貌,以及不同成形区的影响层深度。结果表明:冷敲成形属于局部表层成形,敲打齿槽在敲击时应力波扩散到了相邻齿槽,应力波对相邻齿槽齿顶、齿侧、齿根的影响依次减小,敲打齿槽在敲击时对相邻齿槽的应变影响很小;齿顶成形区分度圆以上均为影响区,相比齿侧、齿根成形区,齿顶影响区范围最大;齿侧成形区的影响区深度大约为1 mm;齿根成形区的影响区深度大约为600 μm。关键词:冷敲成形;花键;相邻齿槽; ABAQUS;微观组织;局部表层成形DOI: 10． 13330/j． issn． 1000-3940． 2017． 11． 013中图分类号: TG315． 79 文献标识码: A 文章编号: 1000-3940 (2017) 11-0066-07Analysis on forming effect between adjacent cogging of cold strike splineNiu Ting1, Li Yongtang1,2, Wang Limin3, Lu Hongyu4(1. School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China;2. Shanxi Key Laboratory of Metal Forming Theory and Technology, Taiyuan 030024, China;3. Qingdao Production and Construction Machinery Factory, Qingdao 266106, China;4. School of Mechanical Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China)Abstract: Based on the principle of cold strike forming for spline, the cold strike forming of adjacent cogging was simulated by ABAQUS/Explicit, and the stress and strain distributions of adjacent cogging by different striking times were analyzed. Then, a spline shaft was pro-cessed by the self-designed LQ200 spline cold striking equipment, and the microstructure and the influence depths of different formingzones were obtained by the optical microscope. The results show that the cold strike forming belongs to the local surface forming, and thestress wave of the striking cogging can spread to the adjacent cogging. Then, the influences of stress wave on tooth top, tooth flank andtooth root weaken gradually, and the influence on the strain of adjacent cogging is small when the striking cogging is struck. The experi-mental results show that the influence area of tooth top is above the pitch crack, and the influence area is larger than that of tooth flank andtooth roof. Therefore, the influence area is about 1 mm in the depth of tooth flank, and the influence area is about 600 μm in the depthof tooth roof.Key words: cold strike forming; spline; adjacent cogging; ABAQUS; microstructure; local surface forming收稿日期: 2017 -05 -27;修订日期: 2017 -08 -10基金项目:国家自然科学基金资助项目(51475316);山西省重点学科建设经费资助作者简介:牛 婷(1986 - ),女,博士研究生E-mail: niuting861010@163． com通讯作者:李永堂(1957 - ),男,博士,教授E-mail: liyongtang@ tyust． edu． cn冷敲成形属于一种精密锻造技术,是一种零件锻造成形后不再加工即符合零件要求的少无切削的近/净锻造成形技术,是先进制造技术的重要组成部分。该技术较传统成形技术,一方面减少了切削加工量、材料与能源消耗,缩短了加工工序,提高了生产效率;另一方面,由于冷敲成形工艺不切断组织纤维以及冷作硬化等冷成形特点,该工艺提高了产品的强度、硬度及耐磨性。同时,相比同类生产花键、齿形轴类零件的冷滚压、冷搓等冷成形加工技术,冷敲成形克服了加工花键模数较小的缺点。冷敲成形工艺在保证产品质量的同时降低了生产成本,所以,该制造工艺广泛应用于汽车、矿山、航空、航天、兵器、能源、建筑等重要领域[1 -2]。万方数据Zella L等采用有限元法研究了冷敲渐开线花键成形过程中轴对称加载和非轴对称加载情况下的接触情况,并提出了花键成形过程中应力、应变求解方法[3]。 Kurz N通过有限元数值仿真方法,得出了成形过程中工件应力、应变值的大小,并结合试验数据验证了花键冷敲技术的可行性[4]。崔凤奎等考虑了冲击成形条件下变形温度、变形速率对流动应力的影响,基于Zener - Hollomon本构模型,结合试验数据对冷敲过程材料本构关系进行了研究,并通过有限元软件进行了冷敲成形过程热力耦合模拟,得到了工件的应力场和温度场分布,初步研究了一组节点在冷敲成形过程中的流动轨迹[5 -7]。张丰收等研究了冷敲成形过程中残余应力的分布情况与工艺参数的关系[8]。谢亚飞对冷敲成形过程表面加工硬化机理进行了研究,分析了流动应力、位错密度与加工硬化的关系[9]。太原科技大学近年来在冷敲成形设备及工艺方面做了一系列相关研究,主要包括冷敲成形工艺本构关系模型研究[10],成形工艺参数[11]研究及成形质量试验研究[12]。本文针对冷敲成形这一高速冷体积成形过程中,成形机理不明确、变形区金属流动行为复杂、局部表层变形剧烈这一特点及难点,重点研究了花键冷敲成形过程中相邻齿槽成形之间的影响以及变形层分布特点。1 花键冷敲成形原理与有限元建模花键冷敲成形原理[1]如图1所示,模型中两个滚打轮关于工件等距对称分布于两侧,滚打轮绕主轴B高速旋转,旋转速度大小相同,方向相反。滚打轮绕主轴B每旋转1周,击打工件1次,在每次打击过程中,工件沿Z向连续轴向进给但不旋转,当滚打轮与工件不接触(即工件不受打击)时,工件旋转一个齿对应的角度,再接受下一次打击,即工件每转过一个齿对应的角度会受到滚打轮的一次打击。如此连续击打,最终在工件全长上形成齿槽。成形过程中,一方面滚打轮由高速旋转的主轴带动进行高速旋转,另一方面工件做轴向进给和间歇旋转。在有限元建模过程中,兼顾模拟效率和精度,选取一个滚打轮对工件进行敲击,研究两个齿槽的敲击成形过程。采用ABAQUS软件建立三维模型并完成模型装配,设定速度边界条件和本构方程等[13 -14],具体数值见表1。本构模型中, σy为流变应力; A为初始屈服应力; B为材料应变硬化模量;图1 花键冷敲成形原理Fig． 1 Principle of cold strike forming for splineεP为应变; n为材料硬化指数; C为材料应变率强化参数; l为材料热软化指数; ε· ∗为无纲量应变率;T∗为同系温度。滚打轮采用离散刚体,约束滚打轮除绕主轴旋转外的其他5个自由度,对工件施加轴向进给和周向旋转的边界条件。图2为滚打轮对工件的冷敲成形有限元模型。表1 花键冷敲成形模拟基本参数Table 1 Basic parameters of cold strike formingsimulation for spline参数数值滚打轮直径/ mm Φ30滚打轮模数m 2． 5滚打轮压力角α/ (°) 20毛坯直径/ mm Ф90毛坯长度/ mm 40毛坯密度/ (kg· m -3) 7890主轴转速/ (r· min -1) 1400工件进给速度/ (mm· s -1) 60摩擦系数μ 0． 1泊松比0． 269杨氏模量/ MPa 20900本构模型σy =(A +BεnP)· (1 +Cln ε· ∗ )· (1 -T∗ l)2 结果与分析2． 1 敲打齿槽对相邻齿槽的应力分布影响图3为相邻齿槽沿路径方向(图2)的应力分布曲线。可以看出:敲打齿槽在进行第2次敲击时,对相邻齿槽的应力分布产生了影响,相邻齿槽沿路径方向的应力值都有所增大,应力曲线最低点右移,这表明敲打过程产生的应力波影响了相邻齿槽沿路76第11期牛 婷等:冷敲花键相邻齿槽之间成形影响的分析 万方数据图2 花键冷敲成形有限元模型Fig． 2 Finite element model of cold strike forming for spline径方向的应力分布;在应力曲线最低点之前,实线和虚线的应力差值逐渐减小,表明沿路径方向的敲击应力波逐步衰减;在应力曲线最低点之后,实线和虚线的应力差值逐渐增大,这主要是因为相邻齿槽的另一侧为边界面,应力波传播至该边界面后反图3 相邻齿槽沿路径方向的应力分布曲线Fig．3 Stress distribution curves of adjacent cogging along the striking path射,导致该区域内的应力叠加,因此,实线和虚线的应力差值增大[15]。图4为敲打齿槽和相邻齿槽经过不同敲打次数后的应力云图。可以看出,随着敲打次数增加,应力波的传播影响范围变大。图4 敲打齿槽和相邻齿槽经过不同敲打次数后的应力云图(a)敲打齿槽经过2次敲打、相邻齿槽经过1次敲打 (b)敲打齿槽经过3次敲打、相邻齿槽经过2次敲打(c)敲打齿槽经过4次敲打、相邻齿槽经过3次敲打 (d)敲打齿槽经过5次敲打、相邻齿槽经过4次敲打Fig． 4 Stress distributions of striking cogging and adjacent cogging after different striking times(a) Striking cogging after two beats and adjacent cogging after one beat (b) Striking cogging after three beats and adjacent cogging after two beats(c) Striking cogging after four beats and adjacent cogging after three beats (d) Striking cogging after five beats and adjacent cogging after four beats86锻 压 技 术 第42卷万方数据图5为敲打齿槽和相邻齿槽经过不同敲打次数后,齿顶、齿侧、齿根(位置如图4a所示)的应力分布云图。可以看出,受到敲打齿槽敲击力的影响,相邻齿槽的齿顶、齿侧、齿根处的应力急剧增大,其中在齿顶处的应力增幅最大,齿侧相对齿根处的应力增幅稍大些,表明敲打齿槽对相邻齿槽齿顶处的应力影响最大,其次为齿侧,最小为齿根。从图5a看出,在初始阶段最终齿侧的应力值最大,其次为齿根,最小为齿顶。这是由于初始阶段相邻齿槽成形时,工件主要沿其周向变形,所以,齿侧受到的挤压力最大,其次为齿根,齿顶处为自由面,应力会得到释放,应力值最小;敲打齿槽经过3次和相邻齿槽经过2次敲打后,齿侧最终应力值相对减小,随着敲打次数的增加,齿根应力值成为最大值,其次为齿侧,最小为齿顶。这可能是因为,随着工件的轴向进给,主要的变形受力形式发生了改变,周向变形不再是主要的变形方式,所以,齿侧所受的挤压力相对减小,最终齿根处的应力为最大值,其次为齿侧,最小为齿根。图5 不同敲打次数后的齿顶、齿侧、齿根处应力分布曲线(a)敲打齿槽经过2次敲打、相邻齿槽经过1次敲打 (b)敲打齿槽经过3次敲打、相邻齿槽经过2次敲打(c)敲打齿槽经过4次敲打、相邻齿槽经过3次敲打 (d)敲打齿槽经过5次敲打、相邻齿槽经过4次敲打Fig． 5 Stress distributions at top, flank and root of tooth after different striking times(a) Striking cogging after two beats and adjacent cogging after one beat (b) Striking cogging after three beats and adjacent cogging after two beats(c) Striking cogging after four beats and adjacent cogging after three beats (d) Striking cogging after five beats and adjacent cogging after four beats2． 2 敲打齿槽对相邻齿槽的应变分布影响图6为相邻齿槽沿路径方向的应变分布曲线。可以看出:敲打齿槽在进行第2次敲击时对相邻齿槽的应变分布产生了影响;在应变曲线最低点之前,相邻齿槽沿路径方向的应变值略有偏差;在应变曲线最低点之后,实线和虚线的应变差值几乎为零,表明敲打齿槽在敲击时对相邻齿槽的应变影响很小。图7为敲打齿槽和相邻齿槽经过不同敲打次数后的应变云图。可以看出,经过不同敲击次数后,敲打齿槽变形区内塑性变形仅发生在离表层较小深度内,随着敲打次数增加,接触面积逐步增大,等效塑性应变范围逐渐扩大,但始终未扩大至相邻齿槽,表明花键冷敲成形仅对工件表层敲打处局部材料的塑性应变影响较大。96第11期牛 婷等:冷敲花键相邻齿槽之间成形影响的分析 万方数据图6 相邻齿槽沿路径方向的应变分布曲线Fig． 6 Strain distribution curves of adjacent cogging along striking path3 试验试验原料为经过调制处理的45钢,工件加工参数为:花键齿数z = 36,滚打轮模数m = 2． 5,分度圆直径d1 = Ф90 mm,大径d2 = Ф92． 05 mm,小径d3 = Ф85． 5 mm。在自行研制的LQ200型花键冷敲设备上进行冷敲花键试验。工艺参数为:轧辊主轴转速1400 r· min-1,工件轴向进给速度60 mm· min-1。冷敲完成后的试件如图8所示。从该试验件上切取部分试件,磨削后利用4%硝酸酒精进行腐蚀,随后利用光学显微镜观察齿形成形区组织形貌特征。图7 敲打齿槽和相邻齿槽经过不同敲打次数后的应变云图(a)敲打齿槽经过2次敲打、相邻齿槽经过1次敲打 (b)敲打齿槽经过3次敲打、相邻齿槽经过2次敲打(c)敲打齿槽经过4次敲打、相邻齿槽经过3次敲打 (d)敲打齿槽经过5次敲打、相邻齿槽经过4次敲打Fig． 7 Strain distributions of striking cogging and adjacent cogging after different striking times(a) Striking cogging after two beats and adjacent cogging after one beat (b) Striking cogging after three beats and adjacent cogging after two beats(c) Striking cogging after four beats and adjacent cogging after three beats (d) Striking cogging after five beats and adjacent cogging after four beats图8a为该冷敲设备生产的花键轴,从图8b和图8c可以看出,花键齿形轮廓清晰完整,说明冷敲成形过程中,相邻齿槽成形没有受到敲打齿槽成形的影响,这与上述仿真结果一致,说明冷敲成形属于表层局部成形。图9a、图9b、图9c分别为齿根、齿侧、齿顶的光学显微镜组织形貌图。可以看出,齿顶、齿侧、齿根的变形影响层依次减小。齿顶变形影响区域最大,这是由冷敲成形金属流动特点决定的[16]。根据冷敲成形过程金属流动规律可知,分度圆以上的齿顶区域是冷敲过程中滚打轮敲击齿槽的位置,使金属产生挤压流动,形成齿顶区域,所以,齿顶处参与变形的区域最大。齿侧分度圆位置处,变形影响层深度为1 mm左右;齿根处影响层深度为600 μm07锻 压 技 术 第42卷万方数据图8 冷敲成形花键轴(a)冷敲花键轴整体 (b)轴端图 (c)齿形局部放大图Fig． 8 Spline shaft of cold strike forming(a) Unitary of cold strike spline shaft (b) Picture of shaft end (c) Local enlarged picture of tooth shape图9 组织形貌图(a)齿根 (b)齿侧 (c)齿顶Fig． 9 Structure morphology(a) Tooth root (b) Tooth frank (c) Tooth top17第11期牛 婷等:冷敲花键相邻齿槽之间成形影响的分析 万方数据左右。说明了冷敲成形仅对工件表层敲打处局部材料的塑性应变影响较大。冷敲成形属于局部表层成形,这一结论与有限元模拟结果一致。4 结论(1)敲打齿槽敲击时的应力波扩散到了相邻齿槽的整个区域,应力波在传播过程中逐步衰减,相邻齿槽的齿顶、齿侧、齿根所受应力波影响程度依次减小;在变形过程中,初始阶段主要为工件周向变形,齿侧的应力值最大,随后发生改变,齿根的应力值最大。(2)敲打齿槽在敲击时对相邻齿槽的应变影响很小,表明花键冷敲成形仅对工件表层敲打处材料的塑性应变影响较大。(3)试验得到了冷敲花键轴,轴端轮廓清晰完整,敲打齿槽成形对相邻齿槽的成形没有产生影响;冷敲花键在不同成形区域的变形影响层深度不同,齿根处最小,其次为齿侧,最大为齿顶处。齿根影响层深度为600 μm左右,分度圆齿侧处为1 mm左右,分度圆以上齿顶成形区都为变形影响区。参考文献:[1] 牛婷,李永堂,刘志奇,等.花键冷敲执行机构运动参数与运动学仿真[J].机械设计, 2014, 31 (4): 41 -45.Niu T, Li Y T, Liu Z Q, el al. 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Taiyuan: Taiyuan University of Science and Technol-ogy, 2010.27锻 压 技 术 第42卷万方数据