东北大学学报:自然科学版   2015, Vol. 36 Issue (3): 368-371   PDF (513 KB)    
锥形方管无模拉伸断面形状变化的实验
夏鸿雁1, 卞清2, 吴迪1    
1. 东北大学 轧制技术及连轧自动化国家重点实验室, 辽宁 沈阳 110819;
2. 沈阳大学 机械工程学院, 辽宁 沈阳 110044
摘要:对锥形方管进行无模拉伸基础实验研究.探讨各种工艺参数对锥形方管外形、断面形状和锥度变化的影响,分析方管无模拉伸时断面圆化程度的影响因素及影响规律,并提出减轻断面圆化程度的具体方法.研究结果表明,采用无模拉伸的方法可以加工带有一定锥度的锥形方管,锥管角精度在1.0 % 以内,加工后锥形方管的轮廓与控制曲线的计算结果一致性很好;方管拉伸断面形状膨胀率随着拉伸变形区宽度增大而减小;壁厚较大,断面形状膨胀率较小,当壁厚和变形区宽度都比较大时,几乎不产生膨胀现象.
关键词无模拉伸     锥形方管     锥管角精度     断面形状膨胀率     变形区宽度    
Experiment Study on Section Shape Variations During Tapered Square Pipe Dieless Drawing
XIA Hong-yan1 , BIAN Qing2, WU Di1    
1. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China;
2. School of Mechanical Engineering, Shenyang University, Shenyang 110044, China.
Corresponding author: XIA Hong-yan, E-mail: xia__hongyan@yeah.net
Abstract: Dieless drawing of tapered square pipe was carried out. The influences of process parameters on the variation of pipe profile, section shape and conical degree were studied. The influence factors and law on the section rounding of square pipe were analyzed and the methods of alleviating rounding factor were given out. In the experiments, square section steel pipes were mainly used, and tapered pipes with large angles were obtained. The drawing precise can be conducted within an error of 1.0 % in taper angle. The tapered pipe profile drawn by dieless drawing is in good agrees with the calculated ones. The expansion rate of section shape decreases with the increase of deformation width. The thicker the wall, the larger the expansion rate. When the wall thickness and width are all relatively large, the expansion is relatively little.
Key words: dieless drawing     tapered square pipe     cone angle precision     section shape expansion rate     deformation width    

锥形方管是由板料冲压成形后焊接而成的,其生产效率低,成品尺寸精度差[1, 2].在本实验中,讨论用无模拉伸方法加工锥形方管,主要研究变形区域宽度等工艺参数对方管断面形状、表面质量和锥形方管锥度等影响规律.

1 实验方法

锥形方管无模拉伸方法如图 1所示.无模拉伸时拉伸速度v1与冷热源移动速度v2的比值决定断面减缩率Rs的大小,拉伸中v1(或v2)一定,使v2(或v1)发生变化,都可以加工锥形方管[3, 4, 5, 6].

图1 锥形方管无模拉伸图 Fig. 1 Schematic of tapered square pipe dieless drawing

在实验中使用的是20mm×20mm,壁厚1.2~2.3mm的普通碳素方形钢管.拉伸速度v1为5.0~2.5mm/min,加热线圈移动速度v2为40~75mm/min,加工温度为800℃,实验在无模拉伸试验机上进行.

加热线圈形状和尺寸如图 2所示,实验中采用的加热线圈有3种,线圈宽度分别为10,22,36mm,加热线圈上的空气冷却装置有6个直径为1mm的喷嘴,实验时压缩空气为0.5kg/cm2.图 3为空气冷却器的形状和尺寸.

图2 加热线圈形状尺寸 Fig. 2 Shapes and dimensions of heating coils (a)—单圈线圈; (b)—双圈线圈; (c)—三圈线圈.

图3 空气冷却器形状尺寸 Fig. 3 Shapes and dimensions of compressed-air cooler

本研究作为简化加工锥度的方法,采用v2值一定,拉伸速度v1 阶段变化的方法.这时,断面减缩率与拉伸速度和冷热源移动速度的关系[7, 8, 9]

2 实验结果与讨论 2.1 方管断面变形情况

方管无模拉伸时,即使断面减缩率一定,随着变形区宽度(加热宽度)不同,方管边长、壁厚也会不同.方管拉伸时,方管的断面形状畸变问题也会发生,因此,需要了解变形区宽度对拉伸后方管的断面尺寸及形状缺陷的影响.

图 4给出了加工前后方管的断面形状,方断面形状拉伸后趋向圆形.设ξ为无模拉伸后方管边长减少率、ν为壁厚减少率、η为断面形状缺陷膨胀率,则:

其中:L0为加工前方管边长;L1,L2分别为加工后方管实际边长和理论边长;t0,t分别为加工前后方管壁厚.

图4 加工前后方管断面形状 Fig. 4 Cross-section shape of square pipe before and after drawing

方管拉伸时,ξ,ν,η受变形区宽度W的影响.变形区宽度W对方管边长减少率ξ的影响情况如图 5所示.实验中,使断面减缩率值为20 % ,边长减少率随着变形区宽度的增加而增加,变形区宽度越大,边长减少率也越大.断面减缩率为20 % ,变形区宽度W对方管壁厚减少率ν的影响如图 6所示,随着变形区宽度W减小,壁厚减少率ν增大.

图5 边长减少率与变形区宽度间的关系 Fig. 5 Relationships between reduction rate of side length and deformation width

图6 壁厚减少率与变形区宽度的关系 Fig. 6 Relationships between reduction rate of wall thickness and deformation width

由实验结果可知,变形区宽度W较小时,壁厚减少率ν增大,主要是管的壁厚减小.变形区宽度W较大时,边长减少率增大,主要是管的边长减小.

当断面减缩率为20 % 时,变形区宽度W对方管断面形状缺陷膨胀率η的影响如图 7所示.对于各种不同的壁厚t0,变形区宽度增大,断面形状缺陷膨胀率减小.壁厚增大,也会使断面形状缺陷膨胀率减小.例如,当t0=2.3mm,W=33mm,即壁厚和变形区宽度都比较大时,则几乎不产生膨胀现象.

图7 断面形状膨胀率与变形区宽度的关系 Fig. 7 Relationships between section shape expansion rate and deformation width

锥形方管拉伸断面膨胀率随断面减缩率的变化规律如图 8所示.3圈线圈加热时断面膨胀率最小.同时,断面减缩率增大时,断面膨胀率相应增大,断面减缩率减小时,断面膨胀率也减小.

图8 断面膨胀率随断面减缩率的变化 Fig. 8 Relationships between expansion rate and reduction rate

如上所述,要得到较高的锥角加工精度,需要采用较小的变形区宽度;考虑抑制膨胀现象,则应采用较大的变形区宽度.提高锥角加工精度与抑制断面形状膨胀对变形区宽度要求不同.

2.2 锥形方管锥度

锥形方管加工后边长与轴向尺寸的关系如图 9所示.实验中采用的加热线圈为2圈,v1按5—10—15—20—25mm/min阶梯变化,时间间隔40s,v2保持定值40mm/mim,最终的工件加工轮廓与计算结果一致性很好.

图9 拉伸后边长相对轴向尺寸变化 Fig. 9 Variation of side length along longitudinal direction of pipe after drawing

工件加工后锥角Ф′与设计锥角Ф的关系如 图 10所示.采用1圈或2圈加热线圈时,加工件的锥角与设计锥角相对一致,加工件的锥角与设计锥角的误差在±1.0 % 以内.采用3圈加热线圈时加工件锥角较设计值偏大.

图10 成品锥角与设计锥角的关系 Fig. 10 Relationship between experimental taper angle of products and calculated ones
3 结 论

1) 在断面减缩率一定的条件下,方管边长的变化由无模拉伸变形区宽度(加热宽度)决定,变形区宽度W越大,边长减少率ξ也越大;同样,方管壁厚变化也由无模拉伸变形区宽度决定,方管变形区宽度W越大,则壁厚减少率ν越小.

2) 无模拉伸方管断面形状膨胀率η随着拉伸变形区宽度W增大而减小,壁厚对断面形状膨胀率也有影响,壁厚较大,断面形状膨胀率较小;当壁厚和变形宽度都比较大时,几乎不产生膨胀现象.

3) 锥型方管拉伸采用1圈或2圈加热线圈时,加工件的锥角与设计锥角相对一致,采用3圈线圈锥角较设计值偏大,锥型方管拉伸如果需要得到较高的锥角加工精度,应采用较小的变形区宽度.

4) 采用无模拉伸的方法可以加工带有一定锥度的锥形方管,锥管角精度在1.0 % 以内,加工后锥形方管的轮廓与控制曲线的计算结果一致性很好.

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