【作者】 周楠；

【导师】 崔晓辉；

【作者基本信息】 中南大学 ， 机械（专业学位）， 2025， 硕士

【摘要】 铝合金管件因具有优异的腐蚀性能,在能源输送、海洋工程等领域得到了广泛应用,而管件接头是管路系统的重要组件。压接是一种高效的管件连接工艺,但常规工艺采用分瓣模具易使材料发生不均匀塑形流动,压接接头形貌质量较差,影响管路连接的力学性能。电磁压接工艺具有电磁力分布较均匀、瞬态力场载荷大等优势,在实现管路均匀压接和提高接头质量等方面有较大优势。现有电磁压接工艺主要采用螺线管线圈与集磁器组合的成形系统,但集磁器尺寸大、成本高,主要应用于直径≤30 mm的管件压接变形。因此,本文提出了大尺寸铝/钢接头的(外径160 mm)平面同心线圈电磁压接新工艺,采用有限元仿真手段研究了平面线圈结构对径向变形时材料不均匀塑性变形的影响机制,分析了有模压接成形的径向变形均匀性和连接强度的影响,提出了线圈轴向移动电磁力渐进加载新工艺,实现了管件轴向大面积均匀变形与压接,并采用带矩形槽的钢制内管提高了铝合金管件压接接头的连接强度。主要研究内容和结论如下:(1)为了实现大尺寸铝合金管件的径向变形,将适用于板料成形的平面线圈应用于管件成形,研究了线圈结构、放电位置、管件壁厚和放电电压对径向变形均匀性的影响规律。结果表明:由于同心线圈结构存在局部过渡拐角,导致该处对应管件区域的电磁力较小,进而造成了对应位置材料变形滞后于其他区域;随着线圈放电位置靠近管件端部和采用较小壁厚的管件,管件变形不均匀程度增加,出现起皱现象;随着放电电压从7k V增加至9k V,管件的径向变形量与起皱程度增加。采用半径标准差衡量管件的起皱程度,发现径向变形量为4 mm时半径标准差为0.23,表明管件的变形均匀性较好,为后文压接内管尺寸选择提供了依据。仿真与实验结果基本吻合,证明采用平面同心线圈能够实现大尺寸管件的径向变形。(2)基于平面同心线圈,针对压接成形工艺,研究了外部铝管与内模钢管间隙以及放电电压对压接效果的影响规律。结果表明:压接接头处位移与应变均匀,尽管拐角处材料存在滞后贴模现象,但最终半径标准差接近于0。随着内外管间隙从1 mm增加到4 mm,管件变形最终时刻的厚向压应力在2 mm时达到最大,3 mm以后为拉应力状态;压接区域长度也随间隙增加先增加后降低,在间隙2 mm时达到最大。这是因为内外管间隙影响碰撞的速度与时间,当间隙小于2 mm时,速度越大碰撞产生压应力越大,碰撞后仍有较大的电磁力对压接区域持续保压。当间隙大于2 mm,碰撞速度越大反弹现象越明显,并且碰撞时刻越晚导致后续保压的电磁力越小。随着放电电压的增加,厚向压应力与压接区域长度增加。当放电电压为8 k V,内外管间隙2 mm,压接接头最大压脱力达到8.5 k N。为了进一步增大内外管的连接强度,采用线圈轴向移动的渐进成形工艺实现多区域的连接,在管件两端和中部放电8 k V后,轴向直径标准差为0.024,新工艺具有较好的管件变形均匀性与更优异的连接强度。(3)为了既能进一步提高压接接头的连接强度,又可以减少多次放电的工序步骤,采用带矩形凹槽的内模钢管进行单次放电工艺探索,研究了矩形槽槽宽、内外管间隙和放电电压对接头填充率的影响。结果表明:随着槽宽从10 mm增加至16 mm,填充率先增加后降低,最优槽宽为14 mm,填充率为88.2%。这是因为槽宽过小材料不易填充,线圈导线宽度为10 mm,电磁力作用区域有限,槽宽过大则离线圈较远的矩形槽底部圆角区域电磁力不足。随着内外管间隙的增大,填充率先增加后降低,当内外管间隙为3.5 mm,10 k V电压的填充率为91.3%。这是因为内外管间隙过小,铝管的变形速度过小,难以实现材料向凹槽内填充;间隙过大,铝管与钢管碰撞后发生更大反弹。随着放电电压增加,材料填充率逐渐增大,在14 k V电压下填充率达到97.2%。采用仿真得到的最佳工艺参数,实验结果与仿真基本一致,压脱力达到实验机器最大值(31.18 k N)时接头处依旧没有分离。综上所述,本文提出了平面同心线圈用于大尺寸管件压接成形工艺,为大尺寸管件的塑性变形连接提供了一条可行的新路径。图80幅,表2个,参考文献86篇更多还原

【Abstract】 Aluminum Aluminum alloy tube fittings are widely used in fields such as energy transportation and marine engineering due to their excellent corrosion resistance,and tube joints are important components of piping systems.Crimping is an efficient tube connection process.However,the conventional process using split molds is prone to non-uniform plastic deformation flow of the material,resulting in poor crimping joint appearance quality and affecting the mechanical properties of the piping connection.Electromagnetic crimping has the advantages of uniform distribution of electromagnetic force and large transient load,which is beneficial for achieving uniform crimping of piping and improving joint quality.The existing electromagnetic crimping process mainly uses a forming system composed of a solenoid coil and a magnetic flux concentrator.However,the magnetic flux concentrator is large in size and expensive,and is mainly used for crimping deformation of tubes with a diameter of≤30 mm.Therefore,this thesis proposes a new process of planar concentric coil electromagnetic crimping for large-diameter Al/steel joints(with an outer diameter of 160 mm).The finite element simulation method was used to study the influence mechanism of planar coil structure on the non-uniform plastic deformation of the material during radial deformation.The influence of die crimping on the radial deformation uniformity and connection strength was analyzed,and a new process of axial coil movement for electromagnetic force progressive loading was proposed to achieve axial large-area uniform deformation and crimping of the tube.The connection strength of the aluminum alloy tube crimping joint was improved by using a steel inner tube with a rectangular groove.The main research contents and conclusions are as follows:(1)In order to achieve radial deformation of large-diameter aluminum alloy tubes,the planar coil suitable for sheet forming was applied to tube forming.The influence laws of coil structure,discharge position,tube wall thickness,and discharge voltage on radial deformation uniformity were studied.The results show that due to the local transition corner of the concentric coil structure,the electromagnetic force at the corresponding tube area is small,which causes the material deformation at the corresponding position to lag behind other areas.As the coil discharge position approaches the tube end and the tube with a smaller wall thickness is used,the degree of non-uniform deformation of the tube increases,and wrinkling occurs.As the discharge voltage increases from 7k V to 9 k V,the radial deformation and wrinkling of the tube increase.The radius standard deviation was used to measure the wrinkling degree of the tube.When the radial deformation was 4 mm,the radius standard deviation was 0.23,indicating good deformation uniformity of the tube,which provided a basis for the selection of the inner tube size for subsequent crimping.The simulation and experimental results are in good agreement,proving that the planar concentric coil can be used to achieve radial deformation of large-diameter tubes.(2)Based on the planar concentric coil,the influence laws of the gap between the outer aluminum tube and the inner die steel tube and the discharge voltage on the crimping effect were studied.The results show that the displacement and strain at the crimped joint are uniform.Although there is a lag in material filling at the corner,the radius standard deviation is close to 0 in the end.As the gap between the inner and outer tubes increases from 1 mm to 4 mm,the maximum through-thickness compressive stress at the end of tube deformation is reached at a gap of 2 mm,and it becomes tensile stress after a gap of 3mm.The length of the crimped area also increases first and then decreases with the increase of the gap,reaching the maximum at a gap of 2 mm.This is because the gap between the inner and outer tubes affects the collision speed and time.When the gap is less than 2 mm,the higher the speed,the greater the compressive stress generated by the collision,and there is still a large electromagnetic force to maintain the pressure on the crimped area after the collision.When the gap is greater than 2 mm,the higher the collision speed,the more obvious the rebound phenomenon,and the later the collision time,the smaller the subsequent electromagnetic force for maintaining pressure.As the discharge voltage increases,the through-thickness compressive stress and the length of the crimped area increase.When the discharge voltage is 8 k V and the gap between the inner and outer tubes is 2 mm,the maximum pull-off force of the crimped joint reaches 8.5 k N.In order to further increase the connection strength between the inner and outer tubes,the new process of axial coil movement for progressive forming was used to achieve multi-zone connection.After discharging 8 k V at both ends and the middle of the tube,the axial diameter standard deviation is 0.024.The new process has better tube deformation uniformity and more excellent connection strength.(3)In order to reduce the steps of multiple discharges while further improving the connection strength of the crimped joint,a single discharge process using an inner die steel tube with a rectangular groove was explored.The influence of groove width,inner and outer tube gap,and discharge voltage on the joint filling rate was studied.The results show that as the groove width increases from 10 mm to 16 mm,the filling rate first increases and then decreases,with the optimal groove width being 14mm and the filling rate being 88.2%.This is because when the groove width is too small,the material is not easy to fill.The coil wire width is 10mm,and the electromagnetic force acting area is limited.When the groove width is too large,the electromagnetic force at the bottom corner of the rectangular groove far from the coil is insufficient.As the gap between the inner and outer tubes increases,the filling rate first increases and then decreases.When the gap between the inner and outer tubes is 3.5 mm and the voltage is 10 k V,the filling rate is 91.3%.This is because when the gap between the inner and outer tubes is too small,the deformation speed of the aluminum tube is too small to achieve material filling into the groove.When the gap is too large,the aluminum tube rebounds more after colliding with the steel tube.As the discharge voltage increases,the material filling rate gradually increases,reaching 97.2%at a voltage of 14k V.Usingthe optimal process parameters obtained by simulation,the experimental results are in good agreement with the simulation.The joint still did not separate when the pull-off force reached the maximum value of the experimental machine(31.18 k N).In summary,this thesis proposes the use of planar concentric coils for the crimping forming process of large-diameter tubes,providing a feasible new path for the plastic deformation connection of large-diameter tubes.更多还原