直写铸造蜡沉积成型数值模拟分析与实验

Numerical Simulation Analysis and Experiment of the Extrusion and Deposition for Casting Wax with Direct Ink Writing

熔模铸造工艺中蜡模制作周期长、开模费用高,而且不适合单铸件或中小规模生产,将基于快速成型的热辅助直写技术(DIW)应用于蜡模制造可以实现对零件研发的快速响应。熔丝质量是保证蜡模成型质量的前提,因此,探究挤出压力、挤出速度、打印速度、喷嘴内径、喷嘴与热床间隙等工艺参数对熔丝成型的影响。对铸造蜡直写挤出沉积过程进行流体动力学建模,利用数值分析法详细研究上述5个工艺参数对熔丝成型的影响,采用纵横比、紧凑度两个指标对熔丝进行评价,得出在不同速度比v/u下可选择的最优间隙比h/d。通过实验验证了计算模型的正确性。结果表明:相较于理想截面模型,所提出的计算模型可以更准确地预测熔丝的截面几何特性,为铸造蜡直写成型过程最优工艺参数的选择提供参考。

In investment casting, wax mold production has a long production cycle, high mold cost, and is not suitable for single casting or small-scale production.Heat-assisted direct ink writing(DIW) based on rapid prototyping is applied to wax mold manufacturing, by which the efficiency of prototyping parts can be improved.The fuse quality is the premise to ensure the molding quality.Hence, it is significant to explore the influence of printing parameters on strand forming, which contains extrusion pressure, extrusion speed, printing speed, nozzle inner diameter and gap between nozzle and hot bed.The hydrodynamic model of DIW extrusion deposition process was established for casting wax.The effects of printing parameters on strand forming were studied.Aspect ratio and compactness were used to evaluate the strand.Based on these, the optimal matching of speed ratio v/u and gap ratio h/d was obtained.Finally, the calculation model was verified by experiments.Compared with the ideal cross section model, the proposed model can be used to predict the cross section of the strand more accurately.The results provide a theoretical basis for selecting the optimal printing parameters in DIW process for casting wax.