厚壁管件有芯棒开式冷挤压成形极限分析

Analysis on the Forming Limit of Cold Open-die Extrusion with Mandrel for the Thick-walled Tube

采用有芯棒开式冷挤压成形厚壁管件比传统切削方法耗材低、效率高。通过对厚壁管件有芯棒开式冷挤压成形特点进行分析确定成形极限的主要影响参数。采用流函数方法建立变形区连续速度场,利用上限原理得到成形极限的理论模型。通过编程计算、分析,得到诸参数(坯料原始厚径比、摩擦因数、模具锥角)对成形极限的影响规律:随着模具锥角的增大,极限变形程度(成形极限)先增大后减小,即极限变形程度有一个极大值,得到了最佳模具锥角,最佳模具锥角范围为15°～20°;随着摩擦因数增大,极限变形程度减小。对比理论计算结果与试验结果,误差小于8%,满足工程要求。研究内容与结果对制订厚壁管件有芯棒开式冷挤压成形工艺具有重要的指导作用。

The forming of open-die extrusion with mandrel for the thick walled tube is of low material consumption and high efficiency compared with the traditional cutting.An analysis on the forming characteristics of the mandrel open-die cold extrusion is performed and the main influence parameters of the forming limit are defined.Continuous velocity field of the deformation zone is established by using stream function method,the theoretical model of forming limit is obtained by using upper bound theory.By programming calculation and analysis,the effect of various parameters（the original blank thickness to diameter ratio,friction coefficient,die cone angle） on the forming limit is put forward.With the increase of die angle,the limit reduction（forming limit） first increases and then decreases,i.e.the limit reduction has a maximum and obtains the optimal die angle in the range of 15°～20°.With the increase of friction coefficient,the limit reduction decreases.Comparing the theoretical calculation result with the experimental result shows that the error is less than 8%,which meets the engineering requirement.The research contents and results have important guiding function in mapping out the process of thick-walled tube open-die cold extrusion forming with mandrel.