【作者】 郑晖；

【导师】 王国栋；

【作者基本信息】 东北大学 ， 材料加工工程， 2012， 博士

【摘要】 随着国家对可持续发展的迫切需要,再制造技术日益受到重视。再制造技术是消除环境污染,减少资源浪费的有力武器。轴类零件和轴系部件是机械装置中的重要组成部分,我国年产轴类零件的总量约在10亿件左右,需要经过校直工艺的约占70%。如何将再制造技术和校直技术有机的组合在一起成为人们关注的焦点。20世纪80年代以来,激光熔覆及淬火技术在国内外的诸多工业领域里得到广泛应用,尤其对于机械零件的再制造修复。本文在此基础上将激光再制造技术应用于轴类零件的校直。本文通过激光校轴可行性试验的探索研究,证实激光再制造校轴切实可行；通过激光熔覆工艺参数试验的系统研究,确定工艺参数对校轴量的影响规律；通过熔覆过程中熔覆区附近点的温度采集与分析,初步验证激光熔覆校轴过程的温度梯度机理；通过ANSYS有限元数值模拟得到激光熔覆校轴过程的瞬态温度场、应力分布以及所对应的变形情况,进一步深层次探索了激光熔覆校轴的机理；通过工程实例有力的证实了激光熔覆校轴有着广泛的应用前景；最后通过激光再制造技术校轴的展示界面将这一技术简洁直观向有需求的企业做介绍和推广。论文主要研究成果如下：(1)可行性试验证明,阶梯轴在激光淬火和激光熔覆后均发生了朝向激光束的弯曲变形,因此采用激光淬火和激光熔覆的工艺方法可以对弯曲轴进行校直,证实了最初的立项以及分析的正确性。激光淬火方法可以使轴的跳动值改变0.09mm,激光熔覆可以使轴的跳动值改变0.71mm。可见激光淬火校直能力有限,可校回量(轴跳动值校回)最大为0.1mm,轴跳动值超过0.1mm的弯曲轴基本不必考虑激光淬火校直,转而考虑用激光熔覆的方法进行校轴。(2)在激光熔覆校轴时,确定了衡量轴弯曲量的β角,即轴弯曲带所对中心角的一半。显著影响校轴效果的工艺参数有熔覆区所对应的中心角α和熔覆层数n。当中心角α小于900时,熔覆面积与轴弯曲量tanβ成正比关系,中心角α大于90°时,弯曲量tanβ减小,因此轴类零件激光熔覆校轴时,理论上讲熔覆中心角α最大可取90°,实际操作要根据客户要求和轴上允许熔覆面积做具体调整。熔覆层数n与轴弯曲量tanβ成正比关系,可以根据弯曲量适当改变熔覆层数。(3)利用ANSYS有限元软件,对轴类零件激光熔覆过程温度场进行了模拟,可知激光熔覆过程中熔覆区的温度分布最高,过渡区其次,轴基体的温度最低,变化很小。而且距离熔覆区越远,温度基本不变。温度梯度沿轴长方向和轴半径方向的分布。任意时刻温度场分布状况相似,即光斑中心处温度最高,并以光斑为中心向外逐层降低,等温线近似椭圆形,椭圆中心位于光斑中心。光斑经过处的温度和温度变化率随时间变化急剧,升温变化率很高,降温变化率也很高,表现出典型的急冷急热的特性。(4)利用ANSYS有限元软件,对轴类零件激光熔覆过程应力分布进行了模拟,可知熔覆区是高热应力区,熔覆区的热应力在熔覆过程中呈现动态变化,时而受拉应力时而受压应力,光斑中心点的总应力以压应力为主,不能笼统的认为熔覆过程熔覆区材料受压应力。在冷却过程中熔覆层的热应力在X,Y,Z三个方向上均为拉应力,由于熔覆区材料冷却收缩引起。(5)通过对熔覆区所在横截面圆周方向各点的温度分析可知,不论在激光熔覆过程中还是在轴冷却过程中,轴圆周方向上所测点的温度都是不同的,这样就产生了温度梯度,温度梯度使得各处的变形不均匀,由此产生了轴的弯曲和热应力。从一方面证实了激光熔覆校轴的温度梯度机理。通过ANSYS有限元对温度场和应力场的分析得出激光熔覆过程中沿轴长方向和轴径方向存在的巨大温度梯度导致热应力从而导致变形,进一步证实了温度梯度机理。(6)工程实例的成功实施确定了采用激光熔覆技术进行校轴的合理工艺路线,良好的校轴效果充分证明,只要确定弯曲量大小和弯曲类型,经具体分析,合理安排激光淬火或激光熔覆工艺,激光校轴是切实可行的,且有巨大的经济效益和广阔的应用前景。更多还原

【Abstract】 With the urgently needed of the sustainable development of a country, re-manufacturing technology has been given increasing attention. Re-manufacturing technology is a useful weapon in eliminating its environmental pollution and reducing the resource waste. Shaft parts are very important components in mechanical assembly. The annual output of the shaft parts in our country is about ten hundred million. Roughly70%shafts among them need to be straightened. How to combinate the re-manufacturing technology and shaft straightening together is the focus of attention. Since the1980’s, laser cladding and laser hardening technology have been widely used both at home and abroad.It has been applied in many industrial fields especially for re-manufacturing of mechanical parts. On this basis, laser re-manufacturing technology has been used for shaft straightening in this paper. The feasibility of laser technology for shaft straightening is proven by means of feasibility test. The effects of technological parameters on the shaft straightening degree is analyzed by means of technological parameter trail of laser cladding. Temperature gradient mechanism is preliminary verified by means of the collection and analysis of temperature data adjacent to cladding area. Transient temperature field and stress distribution and corresponding deform are obtained by use of the finite element numerical simulation method, which utilize the ANSYS software. Temperature gradient mechanism is further discussed. Successful completions of the engineering projects effectively prove that laser re-manufacturing straightening have extensively applied foreground. And finally this technology is introduced and extended intuitively and simply to the enterprise which in need. The main works involved as follows:(1) Laser hardening and laser cladding both can be used for shaft straightening. Stepped shaft is bent towards the laser beam. It confirm the feasibility of the project approval and the correctness of the analysis The eccentricity which is straightened by laser hardening is below0.09mm. The eccentricity which is straightened by laser cladding is larger than0.1mm. So if the shaft’s eccentricity is below0.1mm, laser hardening technology can be chosen. Or else laser cladding can be chosen.(2) In laser cladding straightening technology, center angle corresponding to the bending zone β has been chosen as the parameter to measure the bending degree. The technological parameters which have great effect on the bending degree are laser axial angles a and number of cladding layer n. When the axis angle a is smaller than90°, the shaft bending degree tanβ is directly proportional to the cladding area and when the angle a is greater than90°, the shaft bending degree tanβ is decreased. So theoretically the maximum of axial angles a is90°. The shaft bending degree tanβ is directly proportional to the number of cladding layer n. In practice the technological parameters is chosen according to the bending degree and the request of the client.(3) Temperature field simulation of the laser cladding straightening is obtained by use of the ANSYS finite element software. The temperature in cladding area is highest. The temperature in transition region is middle and the temperature in shaft is lowest. Temperature gradient is appeared along the length of the shaft and along the cross section of the shaft. Temperature field at any time are similar. That is the temperature in laser spot is highest and decreased outward centered on the laser spot. The isothermals are approximate ellipse. The center is the laser spot. The temperature of the location where the laser spot pass through has rapid variation, quick temperature rising and quick drop. Put up the typical sharp quenching and snap heating characteristic.(4) Thermal stress distribution simulation of the laser cladding straightening is obtained by use of the ANSYS finite element software. The thermal stress in cladding area is highest. The thermal stress distribution present dynamical change. Sometimes tensile stress and sometimes compressive stress. But there is always compressive stress in the center of the laser spot. So it can’t be considered that cladding area present compressive stress during laser cladding. Cladding area present tensile stress in X, Y and Z direction during cooling process. It is caused by cooling shrinkage of cladding area.(5) According to the trail data, either in laser cladding process or in cooling process, temperature in different points in circumference is different. There is temperature gradient along the cross section of the shaft. Temperature gradient makes the deformation at different location unevenness and then causes the thermal stress. Temperature gradient mechanism is preliminary verification. In temperature field simulation and thermal stress distribution simulation, temperature gradients appear along the length direction and along the cross section clearly which cause the thermal stress and shaft deformation. Temperature gradient mechanism is further verified.(6) The reasonable process route has been set during the engineering projects. Successful completions of the engineering projects effectively prove that laser cladding straightening is feasible. After the bending degree is measured and the bending direction is ensured and the specific analysis is done, the reasonable laser technology is arranged to straighten the shaft. It brings enormous economic benefit and has extensively applied foreground.更多还原