活塞销冷镦挤成形微折叠缺陷分析及改进措施
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摘要
针对活塞销采用原冷镦挤工艺方案成形后转角处出现的微折叠缺陷,通过微观组织观察和数值模拟确定微折叠产生于第2次反挤压,产生原因为:反挤压成形过程中,连皮厚度降低至一定值后,金属在转角处径向流动,导致一少部分连皮处金属在杯底转角处出现异常褶皱流动,形成微折叠缺陷。为提高活塞销成形质量和避免成形缺陷,提出采用"反挤压预成形+复合挤压终成形"的改进工艺方案取代两步反挤压成形的原工艺方案。数值模拟结果显示,采用改进工艺方案成形的活塞销锻造流线连续,未出现折叠缺陷。生产实践表明,改进方案可避免活塞销转角处微折叠缺陷的产生,能够满足实际生产要求。
When the piston-pin was formed by the original cold upsetting-extruding process,the folding defect was found at the corner.Through microstructure observation and numerical simulation,it was determined that the folding defect occurred during the second backward extrusion. The reason showed in the process of backward extrusion,when the web thickness was reduced to a certain value,the metal flowed in the corner in radial direction,which leaded to abnormal fold flow of a small part of metal at the corner of the bottom of the cup,and formed micro-folding defect. In order to improve the forming quality of piston-pin and avoid forming defects,an improved process scheme of ‘backward extrusion preforming + compound extrusion final forming'was proposed to replace the original process scheme of two-step backward extrusion forming. The numerical simulation results show that the piston-pin forging line formed by the improved process scheme is continuous,and without any folding defect. The production practice shows that the improved scheme can avoid the micro-folding defects at the corner of piston-pin and meet the actual production requirements.
When the piston-pin was formed by the original cold upsetting-extruding process,the folding defect was found at the corner.Through microstructure observation and numerical simulation,it was determined that the folding defect occurred during the second backward extrusion. The reason showed in the process of backward extrusion,when the web thickness was reduced to a certain value,the metal flowed in the corner in radial direction,which leaded to abnormal fold flow of a small part of metal at the corner of the bottom of the cup,and formed micro-folding defect. In order to improve the forming quality of piston-pin and avoid forming defects,an improved process scheme of ‘backward extrusion preforming + compound extrusion final forming'was proposed to replace the original process scheme of two-step backward extrusion forming. The numerical simulation results show that the piston-pin forging line formed by the improved process scheme is continuous,and without any folding defect. The production practice shows that the improved scheme can avoid the micro-folding defects at the corner of piston-pin and meet the actual production requirements.
引文
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[2]郭文芳,冯继军,陶长城,等.活塞销失效分析及工艺改进[J].理化检验(物理分册),2005,41(6):307-310.GUO Wenfang,FENG Jijun,TAO Changcheng,et al. Failure analysis and process improvement of piston pin[J]. Physical Testing and Chemical Analysis(Part A:Physical Testing),2005,41(6):307-310.
[3]王贤鹏,王雷刚,申剑,等.薄壁深筒形件活塞温冷复合挤压成形工艺研究[J].热加工工艺,2016,45(5):104-107.WANG Xianpeng,WANG Leigang,SHEN Jian,et al. Study on warm and cold combined extrusion forming process of thin-walled deep cylindrical pieces of piston[J]. Hot Working Technology,2016,45(5):104-107.
[4]李炳,陈伟,李名尧,等.汽车活塞销温-冷复合挤压成形工艺研究[J].铸造技术,2016,37(10):2204-2207.LI Bing,CHEN Wei,LI Mingyao,et al. Study on warm and cold composite extrusion forming process for automobile piston pins[J]. Foundry Technology,2016,37(10):2204-2207.
[5] LEE D J,KIM D J,KIM B M. New processes to prevent a flow defect in the combined forward-backward cold extrusion of a piston-pin[J]. Journal of Materials Processing Technology,2003,139(1):422-427.
[6] GIULIANO G. Process design of the cold extrusion of a billet using finite element method[J]. Materials&Design,2007,28(2):726-729.
[7]王德俊,姚志英,李艳红,等.活塞销冷挤压成形工艺研究[J].热加工工艺,2011,40(17):86-88.WANG Dejun,YAO Zhiying,LI Yanhong,et al. Study of cold extrusion forming process for piston pin[J]. Hot Working Technology,2011,40(17):86-88.
[8]梁强.载重汽车用直齿圆柱齿轮连续冷挤压冷整形复合成形关键技术研究[D].重庆:重庆大学,2016.LIANG Qiang. The key technology on precision forming process by continuous cold extrusion and cold finishing of spur gears on camion[D]. Chongqing:Chongqing University,2016.
[9]张莉,李升军. DEFORM在金属塑性成形中的应用[M].北京:机械工业出版社,2009.ZHANG Li,LI Shengjun. DEFORM in the application of metal plastic forming[M]. Beijing:China Machine Press,2009.
[10]肖志玲,刘百宣,刘华,等.螺旋道钉多工位冷镦成形工艺优化及数值模拟[J].锻压技术,2014,39(2):79-83.XIAO Zhiling,LIU Baixuan,LIU Hua,et al. Process optimization and numerical simulation of multi-stage cold heading for railway screw spike[J]. Forging&Stamping Technology,2014,39(2):79-83.
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