相位角120°锻造曲轴探伤磁痕产生机理及减轻方法
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摘要
曲轴是内燃机中关键传动部件,其性能对内燃机的工作性能具有重要影响。由于锻造改性的优势明显,所以当前曲轴铸改锻工艺比较普遍。对于曲轴热锻成形工艺,材料自由缺陷、锻造工艺不恰当、工人实际操作偏差等均会造成许多产品缺陷,如裂纹、晶粒粗大、错移及折叠等。所以预防以及检测成形过程中的缺陷成为保证曲轴产品质量的关键。磁粉探伤是检测曲轴表面及皮下表层缺陷的一种重要的方式,通过探伤可以无损的检测出附在表层而肉眼无法观察到的细小裂纹,并且能够准确锁定裂纹的位置。通过磁粉探伤检测出来的缺陷或疑似缺陷统称为磁痕。目前曲轴磁痕的发生率比较普遍。
本文以典型的相位角为120°的锻造曲轴为例,基于理化实验与数值模拟,分析了该曲轴磁痕产生的原因。通过理化试验得出:磁痕探伤得到的磁痕是表面微米级细小裂纹的一种显示;这些细小的裂纹是由于沿变形方向分布的化合物成分为MnS和MoS夹杂物暴露在曲轴表面脱落后形成的;曲轴内部组织存在较严重的带状组织,这些带状组织与夹杂物的形成同Mn、Mo及S元素的偏析有关。通过对曲轴锻造工艺的数字模拟,从坯料体内部自由缺陷在坯料变形过程中发生移动的角度来分析探伤磁痕总是集中在1、3、4、6号连杆轴颈分模面内侧及过渡圆角处分布的原因,提出将连续的坯料体分为表层优质层和中心次优质层的包覆结构假设,建立了相应的数值模型,在通过Deform 3D模拟出曲轴成形过程中这两层金属的流动与分布状态,获得了内部自由缺陷在锻件中的堆积趋势及原工艺下的成形速度场对优质层和次优质层流动的影响规律。结果表明:终锻结束后在1、3、4、6号连杆轴颈分模面内侧附近及过渡圆角处主要由中心次优质层金属填充并有厚度较薄的表层优质层金属,这些部位在机加工后中心此优质层金属直接大面积裸露在锻件表面,成为自由缺陷富集的危险区;终锻成形过程中连杆轴颈横截面上金属的单方向流动加大了自由缺陷在危险区的聚集趋势。
最后依据分析结果,从原材料及锻造工艺方面提出了减轻曲轴磁痕的方法,优化了预锻模具连杆轴颈部位的筋板结构,根据模拟结果对比原工艺和优化工艺,发现预锻模具修改后,终锻中后期在连杆轴颈处金属流动的速度场实现了向两侧分流,该处内侧次优质层的宽度减少了28.9mm,优化后的工艺在减轻磁痕方面有更好的表现。
The crankshaft plays a key role in transmission in internal combustion engines and its mechanic heavily influences stability of internal combustion engines. Now it is prevailing that the casting crankshafts are replaced by forgings because the crankshafts forming by forging contains better microstructure than castings. During the hot forging process, the free defects in raw materials, irrational forging process design and operation deviation will result in lots of defections such as crack, coarse grains, mismatch, and fold and so on, so how to prevent and detect defects has become a very important facet in assuring the quality of crankshaft. Magnetic particle inspection technique is extensively applied in detecting defects distributing the surface layer of crankshafts. These defects which cannot be directly observed by eyes will show and are called Magnetic particle marks by Magnetic particle inspection and the location also can be obtained. The Magnetic particle marks are often found at present.
Based on the experimental and numerical simulation, it was analyzed in the paper that the mechanism of Magnetic particle marks of forging crankshaft with a 120°phase angle. The results by physical and chemical Analysis show: the Magnetic particle marks reflect some micron dimension crack on surface of crankshaft; the micron dimension cracks were formed after disarticulation of inclusion which contained MnS and MoS and extended along with the forming direction; the microstructure of crankshaft contained severe banded structure which had something to do with the segregation of Mn, Mo and S. By means of numerical simulation for forging process of crankshaft, it was researched that Magnetic particle marks always appeared in the area of inner parting plan of NO.1, NO.3, NO.4, NO.6 Connecting Rod Journal and transition fillets in the view of the billet inner freedom defects’transition during the forging. The billet was divided into two layer, the outer higher quality layer and inner lower quality layer, and the corresponding finite element model of billet was built. The two layers metal’s flow and distribution during forging were simulated by Deform 3D and the trend of accumulate of inner defects was achieved as well as the influence law of forging velocity on above two layers’flowing. The results show :after final-forging the inner low quality metal was distributed in the area of inner parting plan of NO.1, NO.3, NO.4, NO.6 Rod Journal and transition fillet with thin outer higher quality layer, and at these positions the inner low quality metal would exposed on forging surface after machine working, which are the dangerous areas ; the metal on the cross-section of rod journal flowing only at one direction intensified the trend of free defects accumulating in the dangerous area.
According the analysis results of Magnetic particle marks above, the methods to mitigate Magnetic particle marks of forging crankshaft were brought up from the aspects of raw material and forging process. The structure of rib plate of pre-forging die was optimized. Comparing the original process and optimized process, the new pre-forging die realized the metal flow state along with the left side and right side at the same time at late final-forging process. The width of inner low quality metal was reduced by 28.9mm, which means better performance in mitigating Magnetic particle marks.
本文以典型的相位角为120°的锻造曲轴为例,基于理化实验与数值模拟,分析了该曲轴磁痕产生的原因。通过理化试验得出:磁痕探伤得到的磁痕是表面微米级细小裂纹的一种显示;这些细小的裂纹是由于沿变形方向分布的化合物成分为MnS和MoS夹杂物暴露在曲轴表面脱落后形成的;曲轴内部组织存在较严重的带状组织,这些带状组织与夹杂物的形成同Mn、Mo及S元素的偏析有关。通过对曲轴锻造工艺的数字模拟,从坯料体内部自由缺陷在坯料变形过程中发生移动的角度来分析探伤磁痕总是集中在1、3、4、6号连杆轴颈分模面内侧及过渡圆角处分布的原因,提出将连续的坯料体分为表层优质层和中心次优质层的包覆结构假设,建立了相应的数值模型,在通过Deform 3D模拟出曲轴成形过程中这两层金属的流动与分布状态,获得了内部自由缺陷在锻件中的堆积趋势及原工艺下的成形速度场对优质层和次优质层流动的影响规律。结果表明:终锻结束后在1、3、4、6号连杆轴颈分模面内侧附近及过渡圆角处主要由中心次优质层金属填充并有厚度较薄的表层优质层金属,这些部位在机加工后中心此优质层金属直接大面积裸露在锻件表面,成为自由缺陷富集的危险区;终锻成形过程中连杆轴颈横截面上金属的单方向流动加大了自由缺陷在危险区的聚集趋势。
最后依据分析结果,从原材料及锻造工艺方面提出了减轻曲轴磁痕的方法,优化了预锻模具连杆轴颈部位的筋板结构,根据模拟结果对比原工艺和优化工艺,发现预锻模具修改后,终锻中后期在连杆轴颈处金属流动的速度场实现了向两侧分流,该处内侧次优质层的宽度减少了28.9mm,优化后的工艺在减轻磁痕方面有更好的表现。
The crankshaft plays a key role in transmission in internal combustion engines and its mechanic heavily influences stability of internal combustion engines. Now it is prevailing that the casting crankshafts are replaced by forgings because the crankshafts forming by forging contains better microstructure than castings. During the hot forging process, the free defects in raw materials, irrational forging process design and operation deviation will result in lots of defections such as crack, coarse grains, mismatch, and fold and so on, so how to prevent and detect defects has become a very important facet in assuring the quality of crankshaft. Magnetic particle inspection technique is extensively applied in detecting defects distributing the surface layer of crankshafts. These defects which cannot be directly observed by eyes will show and are called Magnetic particle marks by Magnetic particle inspection and the location also can be obtained. The Magnetic particle marks are often found at present.
Based on the experimental and numerical simulation, it was analyzed in the paper that the mechanism of Magnetic particle marks of forging crankshaft with a 120°phase angle. The results by physical and chemical Analysis show: the Magnetic particle marks reflect some micron dimension crack on surface of crankshaft; the micron dimension cracks were formed after disarticulation of inclusion which contained MnS and MoS and extended along with the forming direction; the microstructure of crankshaft contained severe banded structure which had something to do with the segregation of Mn, Mo and S. By means of numerical simulation for forging process of crankshaft, it was researched that Magnetic particle marks always appeared in the area of inner parting plan of NO.1, NO.3, NO.4, NO.6 Connecting Rod Journal and transition fillets in the view of the billet inner freedom defects’transition during the forging. The billet was divided into two layer, the outer higher quality layer and inner lower quality layer, and the corresponding finite element model of billet was built. The two layers metal’s flow and distribution during forging were simulated by Deform 3D and the trend of accumulate of inner defects was achieved as well as the influence law of forging velocity on above two layers’flowing. The results show :after final-forging the inner low quality metal was distributed in the area of inner parting plan of NO.1, NO.3, NO.4, NO.6 Rod Journal and transition fillet with thin outer higher quality layer, and at these positions the inner low quality metal would exposed on forging surface after machine working, which are the dangerous areas ; the metal on the cross-section of rod journal flowing only at one direction intensified the trend of free defects accumulating in the dangerous area.
According the analysis results of Magnetic particle marks above, the methods to mitigate Magnetic particle marks of forging crankshaft were brought up from the aspects of raw material and forging process. The structure of rib plate of pre-forging die was optimized. Comparing the original process and optimized process, the new pre-forging die realized the metal flow state along with the left side and right side at the same time at late final-forging process. The width of inner low quality metal was reduced by 28.9mm, which means better performance in mitigating Magnetic particle marks.
引文
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[3]尹长城,孙玮琪.含裂纹曲轴的有限元模态析[J].现代制造工程, 2009, 24(1):12-14.
[4]李海国.国内外内燃机曲轴制造技术现状及发展趋势.制造技术与机床,2003,(5):12-15.
[5] Silva,F.S. Analysise of a vehicle crankshaft failure. Elseriver Science, 2003, (10): 605-616.
[6]王一治.国内外曲轴制造工艺综述.山东农机, 2001, (5):22-23.
[7]孙小孟.微车曲轴精密锻造成形工艺及模具的研究[D].重庆大学, 2006.
[8]冯亚玲.曲轴模锻工艺数值模拟研究[D].燕山大学, 2004.
[9]董湘怀.材料加工理论与数值模拟[M].北京:高等教育出版社,2005,89~99.
[10]代风悦等.磁粉探伤的磁痕分析[J].无损探伤, 1996, (6):31-33.
[11]徐高太. A型曲轴磁痕分析[J].无损探伤, 2008, 32(2):41-43.
[12]吕炎.锻件缺陷分析与对策[M].北京:机械工业出版社, 2009.
[13]罗晴岚,曹红亮.汽车内燃机曲轴锻件生产论述[J].锻压装备与制造技术, 2004, (2):24-27.
[14]彭运钧.大型运输车辆发动机构造与维修[M].北京:人民交通出版社, 2006.
[15] J Haats, S Wambach. Lightweight crankshaft drives by forging. Steel times.1999; sept: 346-347.
[16] Shinichirio Fujikawa. Application of CAE for hot-forging of automotive components. Journal of Materials Processing Technology. 2000, (98):176-181.
[17] Peiran Ding, Tatsuo Inoue, Shoji Irnatani, Dong-ying Ju and Wwin de vries. Simulation of the forging precess incorporating strain induced phase transformation using the finite volume method. Materials science research international, 2001, 7(1):19-26.
[18] Quanlin Jin, Jie Qu , Bingye Xu. The parameter identification of thermal visco-plastic model considering dynamic recrystallization. Materials processing and design: modeling, simulation and application[M]. Numiform 2004: 369-374.
[19]王纪武,刘庄,王本一. 280曲轴RR法成形的三维有限变形弹塑性有限元模拟[J].塑性工程学报, 1999, 6(2): 73-77.
[20]王颖翔.锤锻曲轴弯曲型槽设计要点[J].锻压机械, 1997, (5)26-27.
[21]刘建生,王仲仁,卢志永.曲轴RR法镦锻成形的数值模拟与缺陷预测[J].中国机械工程, 2001, 12 (4):429-432.
[22]徐戊矫,王凯庆等.大型全纤维曲轴TR镦锻装置失效分析[J].重庆大学学报, 2009, 32(4):396~401.
[23] Chun H L, A C W, YI S C, et al. The coupled thermo-mechanical analysis in the upsetting process by the dynamic FEM[J]. Journal of Material Processing Technology, 2008, 20(1): 37~42.
[24] Ghasem D, Sayed M M V, Mostfaf L, et al.Computational and experimental failure analysis of continuous-annealing furnace radiant tubes exposed toexcessive temperature[J]. Engineering Failure Analysis, 2008, 15: 445~457.
[25]韩松涛,郝志勇.6102B型柴油机曲轴三维有限元模态分析与试验研究[J].农业机械学报,2001,32(4):74~77.
[26]尹玲,佟莹.曲轴锻造过程中的温度场仿真预测[J].加工工艺,2009,38(11):99-102.
[27] Malu fo,Milan Mt,Spinel Lid. Effects of surface rolling on fatigue behavior of a pearlitic ductile castiron. JMaterEngPerform2004,13:195-199.
[28] Lee YL,Morrissey W. Uncertainties of experimental crankshaft fatigue strength assessment.IntJ Mater Prod Tech2001,16:390–392.
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