Liquid filling and external extrusion composite forming tiny size spiral tube with equal wall thickness

Positive displacement motor is a widely used downhole power drilling tool. In order to solve the problems of short life of conventional positive displacement motors and difficulty in processing micro-sized positive displacement motors with equal wall thickness, this paper proposes to use the liquid filling and external extrusion composite forming process to process the tiny size spiral tube with equal wall thickness. Based on the tensile test of 304 stainless steel and the liquid-filled and external extrusion composite forming process, a finite element model of the 5LZ54 type equal-wall spiral tube by liquid-filled and external extrusion composite forming was established. We use the finite element method to study the composite forming of liquid-filled and externally extruded metal spiral pipes with equal wall thickness. The reasonable process parameters are that the outer diameter of the tube is 51 mm, the wall thickness of the tube is 5.5 mm, the friction coefficient is 0.125, the hydraulic pressure is 700 MPa, the extrusion speed of die is 0.167 m/s, and the hydraulic pressure loading path is path 5. The spiral tube completely fits the die. The variance of the wall thickness is 0.00846, and the wall thickness is more concentrated. The minimum wall thickness is 4.948 mm, the design wall thickness is 5 mm, the maximum wall thickness is 5.353 mm, and the average wall thickness is 5.15 mm. The maximum wall thickness error of the spiral section is 0.275 mm. The wall thickness at the convex arc is larger, and the wall thickness at the concave arc is smaller. Studies have shown that it is feasible to form a spiral tube with a small size and equal wall thickness by liquid filling and external extrusion forming process.