沉积路径对激光立体成形钛合金T型缘条热/应力场的影响

Effects of Scanning Patterns on the Thermal/Stress Field during Laser Solid Forming T-Shape Chord of Ti-6Al-4V Alloy

分别建立了基于轮廓偏置、长光栅、短光栅三种沉积路径的Ti-6Al-4V合金T型缘条激光立体成形过程热/应力场有限元模型。结果表明熔池最大温度梯度沿竖直方向的分量GYmax比扫描方向的分量GXmax大得多,随成形高度的增加,二者都先下降后快速趋于稳定,最终稳定的GYmax约是GXmax的三倍。短光栅沉积时瞬时最大温度梯度GTmax呈现小幅度的振荡变化,且整体小于另外两种沉积路径。长光栅路径的应力增长速率略大于轮廓偏置路径,短光栅的最小。成形结束后,采用轮廓偏置路径的横、纵向缘条连接处的背面出现应力集中,长光栅沉积的缘条端部存在大范围的应力集中,而采用短光栅沉积的缘条整体应力分布最均匀。沉积结束后,三种沉积方式基板上各个方向的残余应力分布规律基本相同,但是,采用短光栅沉积的基板上应力值比其他两种路径小。

Finite-element models of the thermal/stress field for three different scanning patterns,i.e.contour offsetting,long raster and short raster patterns,during laser solid forming（LSF）processes for T-shaped chord of Ti-6Al-4V alloy are developed respectively.It is shown that the component along the vertical direction GYmaxof the maximum temperature gradients in the melting pool is much bigger than its component along the scanning direction GXmax.Both GYmaxand GXmaxdecrease in first few layers and then become almost constant with the increase of cladding height.Finally GYmaxis about three times as great as GXmax.The instantaneous maximum temperature gradient GTmaxfor short raster pattern always presents a fluctuation with a small amplitude range and which is smaller than those for other patterns as a whole.The increasing velocity of stress for long raster pattern is somewhat larger than that for contour offsetting,the increasing velocity of stress for short raster pattern is the smallest.When the deposition of the T-shape chords are finished,there exists a residual stress concentration at the back of conjunction of horizontal and vertical parts of the T-shape chord for contour offsetting pattern,at the two ends of the chord for long raster pattern.And the residual stress distribution in T-shape chord formed by short raster pattern is uniform.The residual stresses in different directions on the substrate for these three scanning patterns show the same distribution regularity,but the residual stress of short raster is smaller than others.