1Cr18Ni9Ti不锈钢小相对弯曲半径整体弯头内高压成形壁厚变化规律

Wall thickness variation of 1Cr18Ni9Ti stainless steel integral elbow with small reative bending radius during hydroforming

针对航空航天装备对大径厚比(D/t>60)、小相对弯曲半径(R/D<1)不锈钢弯头整体制造技术的迫切需求,以及传统工艺无法整体成形的技术难题,提出一种管件推弯与内高压成形的两步成形工艺方法。理论推导出管坯与整体弯头的尺寸对应关系,有限元仿真分析了两步成形过程整体弯头壁厚变化规律。发现推弯后整体弯头外侧壁减薄、内侧壁增厚;模具间隙和摩擦因数是影响推弯壁厚变化的主要因素,间隙过小或摩擦力过大会加剧外侧壁减薄及内侧增厚。内高压成形时整体弯头外侧壁先贴模,内侧壁工艺补充段圆角区后贴模;整体弯头内、外侧壁均减薄,最大减薄位置在外侧壁中心区域。实验成形出直径Φ200 mm,径厚比67,相对弯曲半径0.76的1Cr18Ni9Ti不锈钢整体弯头,壁厚分布均匀。

Aiming at the urgent demand of aerospace equipment for integral manufacturing technology of stainless steel elbow with large diameter to thickness ratio(D/t>60)and small relative bending radius(R/D<1),and the technical problem that traditional process can not be integral forming,a two-step forming process method of push-bending and hydroforming of tube fittings was proposed.The relationship between the size of the tube billet and the integral elbow was deduced theoretically,and the change law of the wall thickness of the integral elbow during the two-step forming process was analyzed by finite element simulation.It is found that the outer wall of the integral elbow decreases and the inner wall thickens after push-bending.Die clearance and friction factor are the main factors affecting the change of push-bending wall thickness.Too small clearance or too large friction force can aggravate the thinning of outer wall and the thickening of inner wall.During hydroforming,the outer wall of the integral elbow is pasted first,and the round corner area of the inner wall is pasted later.The inner and outer walls of the integral elbow are thinning,and the greatest thinning is located in the center area of the outer wall.The 1Cr18Ni9Ti stainless steel integral elbow with diameter of Φ200 mm,diameter to thickness ratio of 67 and relative bending radius of 0.76 is formed.The wall thickness distribution is uniform.