扫描路径对激光立体成形TC4构件热-力场的影响

Effect of scanning path on thermo-mechanical field of laser solid forming TC4 part

为减缓激光立体成形过程中由于大的热梯度导致的残余应力和变形,首先采用原位测量监测成形过程中基板的温度及变形演化,并以此校验有限元模型,然后利用校准模型研究不同扫描路径对激光立体成形TC4钛合金构件热-力场演化行为的影响。结果表明:模拟结果与实验吻合良好。最大热梯度和最大拉应力均出现在第一层扫描过程中,温度梯度随沉积层数增加而逐渐减小。长边单向扫描方式下基板的变形量最大,而采用短边往复扫描方式下残余应力和变形最小;采用棋盘格扫描方式能有效减小基板的变形,但不能减小构件的残余应力。另外,基板的横向弯曲变形能有效抑制基板的纵向弯曲,而相变诱导的应力释放对激光立体成形构件的残余应力和变形具有显著的影响。

In order to mitigate both residual stress and distortion induced by large thermal gradient in laser solid forming(LSF)process,the in-situ measurement first was used to monitor the thermal and distortion evolutions of the substrate during LSF and to calibrate the finite element model.Using the validated model,the effect of different scanning paths on the evolution of thermo-mechanical fields in LSF was analysed.The results show that good agreement is obtained between the numerical results and the experimental measurements.The maximum thermal gradient and the maximum tensile stress occur in the deposition of the first layer,and with the increasing of the layers,the temperature gradient is reduced gradually.The largest distortion is resulted from the long edge unidirectional scanning mode while the minimum residual stress and distortion is produced by short edge reciprocating scanning.The checkerboard scanning method can effectively reduce distortion of the substrate while hardly reduce the residual stress.In addition,the transverse bending of the substrate can notably curb the longitudinal bending of the substrate.Stress relaxation induced by the phase transformation has a significant effect on both residual stress and distortion of LSF part.