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    工具凸包结构对非圆孔冷挤压强化效果的影响

    Influence of Tool Convex Hull Structure on Cold Expansion Strengthening Effect of Non-Round Holes

    • 摘要: 设计了适用于镍基高温合金非圆孔的弧形凸包芯棒与梯形凸包芯棒的2种凸包结构的直接芯棒往复冷挤压工具,利用Abaqus有限元软件建立不同芯棒往返冷挤压的有限元模型,模拟2种类型凸包芯棒往返冷挤压强化后GH4169高温合金孔壁的残余应力分布;采用试验方法对2种类型凸包芯棒往返冷挤压强化后非圆孔壁的表面形貌、硬度和残余应力进行表征。结果表明:模拟与试验得到2种挤压工具冷挤压强化后孔壁残余压应力随距孔壁表面距离的变化趋势相吻合,残余压应力极值附近的残余应力相对误差小于20%,验证了有限元模拟方法的准确性。与弧形凸包芯棒往返冷挤压强化相比,梯形凸包芯棒往返冷挤压强化后孔壁的表面残余压应力高约200 MPa,残余压应力层深度大150~200 μm,残余压应力极值相差不大,孔壁长边、短边和拐角的残余压应力层深度、残余压应力极值、表面残余压应力的极差更小,挤压过程所受到的轴向力变化更加平缓。梯形凸包芯棒冷挤压强化后的表面粗糙度更低,轴向与周向表面粗糙度的极差更小,孔壁不同位置的轴向硬度提升层深度(1 020~1 035 μm)明显高于弧形凸包芯棒冷挤压强化后(720~920 μm),且其极差更小。梯形凸包芯棒在改善非圆孔残余应力分布均匀性、提升孔壁表层硬度、降低孔壁表面粗糙度方面均优于弧形凸包芯棒。

       

      Abstract: Two types of direct hull mandrel reciprocating cold expansion tools suitable for non-circular holes of nickel-based superalloys, namely arc-shaped and trapezoidal convex hull mandrels, were designed. The finite element models of different hull mandrel reciprocating cold expansion were established by Abaqus finite element software, and the residual stress distribution on the hole wall of GH4169 superalloy after reciprocating cold expansion strengthening of the two types of convex hull mandrels was simulated. The surface morphology, hardness and residual stress of the non-round hole walls of two types of convex hull mandrels after reciprocating cold expansion strengthening were characterized by experimental methods. The results show that the changes of residual compressive stress vs the distance from the hole wall surface on the hole wall after cold expansion strengthening with the two expansion tools by simulation and test was consistent. The relative error of the residual stress near the extreme value of the residual compressive stress was less than 20%, verifying the accuracy of the finite element simulation method. Compared with those after reciprocating cold expansion strengthening with arc-shaped convex hull mandrels, the surface residual compressive stress of the hole wall after reciprocating cold expansion strengthening with trapezoidal convex hull mandrels was about 200 MPa higher, the depth of the residual compressive stress layer was 150–200 μm greater, and the extreme values of the residual compressive stress were not much different; the depth of the residual compressive stress layer, the extreme value of the residual compressive stress, and the range difference of the surface residual compressive stress on the long side, short side and corner of the hole wall was smaller, and the axial force change during the expansion was more gentle. The surface roughness after cold expansion strengthening with the trapezoidal convex hull mandrels was lower, and the range difference between the axial and circumferential surface roughness was smaller; the depth of the axial hardness enhancement layer at different positions of the hole wall (1 020–1 035 μm) was significantly higher than that after cold expansion strengthening with the arc-shaped convex hull mandrels (720–920 μm), and the range difference was smaller. Trapezoidal convex hull mandrels were superior to arc-shaped convex hull mandrels in improving the uniformity of residual stress distribution in non-round holes, enhancing the surface hardness of the hole wall, and reducing the surface roughness of the hole wall.

       

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