A Brief Discussion on the Forming Process of Titanium Three-way Pipe Fittings

For the common titanium three-way pipe fittings, due to their small diameter and thin wall, the parts need to withstand high pressure. Manufacturing them by casting method is not only difficult but also the quality cannot be guaranteed. If two straight pipes are welded to form the shape, the weld seam is the spatial intersection line of two cylinders, and both the cutting and welding operations are difficult to control. Moreover, the part size is small, and it can only be welded from the outside, making it difficult to maintain the inner wall welding quality. Even if casting and welding can complete the shape manufacturing, since they are inevitable to have pores and slag during the process, this is not allowed for medium and high-pressure pipelines due to process defects.

The technicians initially considered using the die forging or radial extrusion process to first produce a solid T-shaped blank. Then, they planned to drill holes in both the horizontal and vertical directions separately. However, the experimental results showed that the quality of the titanium three-way pipe fittings could not be maintained. Moreover, this process had several drawbacks such as a large number of processing steps, a large amount of equipment required, and low utilization rate of the metal materials. Finally, it was decided to use either a straight pipe or an extrusion forming process. The straight pipe blank filled with the packing material was placed in the mold cavity. The upper and lower molds were closed together. Then, using two rods of the same diameter size (two pieces), they were pushed from both sides at the same speed. Under the action of the pressure at both ends, the titanium pipe in the mold cavity was inevitably subjected to plastic deformation; either being extruded by bulging or being extruded radially along the radial hole of the mold.

Since the pipe is already filled with incompressible filler, upsetting deformation is impossible. Therefore, the straight pipe, together with the filler, is extruded from the radial hole on the mold under the pressure. To prevent the extruded radial pipe from bursting under the internal pressure of the filler, a stopper is installed in the radial hole of the mold, applying sufficient compressive stress to the extruded radial branch pipe.

When the extruded branch pipe reaches the size requirement, the mold is opened to remove the part, and the packing material is cleared out. Thus, the required titanium three-way pipe fittings can be obtained. Practice has shown that the three-way pipe fittings produced by extrusion have the same wall thickness in all three directions, and the deformation during upsetting is very small. The extruded part height is 2 to 3 times the pipe diameter. In addition, because the packing material and the titanium pipe move synchronously in the mold cavity, there are no mechanical scratches on the inner wall of the pipe fitting, and the size and quality meet the requirements of the drawings.