Seamless elbow: elbow is a kind of pipe fitting used for pipe turning. 1 accounts for 80% of all fittings used in the pipeline system. Usually, for elbows with different materials or wall thicknesses, different forming processes are selected. The common forming processes of seamless elbow are hot pushing, stamping and extrusion. The forming process of hot-push forming hot-push elbow is a process in which the blank sleeved on the mold moves forward under the push of the pusher by using a special elbow pusher, mandrel and heating device, and is heated, expanded and bent during the movement. The deformation characteristic of hot push elbow is to determine the diameter of tube blank according to the law of constant volume of metal material before and after plastic deformation, and the diameter of tube blank used is smaller than the diameter of elbow. The deformation process of the blank is controlled by the mandrel, so that the compressed metal at the inner arc flows and is compensated to other parts with enlarged diameter and thinner thickness, thus obtaining an elbow with uniform wall thickness. Hot-push elbow forming process has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, which is suitable for mass production. Therefore, it has become the main forming method of carbon steel and alloy steel elbows, and is also applied to the forming of stainless steel elbows with certain specifications. Draw a top view according to the curvature radius and pipe diameter of the elbow; Draw the end section according to the number of sections. For the three sections, the two end sections are 22.5, and the middle section is 45, that is, the whole 90 is divided into four parts, and then the elbow is simplified into a combination of cylindrical truncated platforms by tangent from the arc where the two ports intersect with 45; Based on the obtained end section, the end section is expanded by the parallel line method, and the middle section expansion diagram is the synthesis of the end section expansion diagram after rotating180 around the horizontal line. The development steps of parallel line method of cylindrical truncated platform: draw a semi-circular arc connecting the two ends of horizontal line with the midpoint of truncated platform as the center and the radius of circular tube as the radius; Divide that semi-circular arc into six to obtain five intersections on the circular arc, and the vertical line of the five intersections intersect with the oblique line of the truncated platform as horizontal lines to obtain five parallel line of the truncated platform, and the sum of the five contour lines of the truncated platform and seven parallel line segments are all real long lines of the truncated platform; Seven parallel lines are used as extension lines of the horizontal line, starting from a certain point, arranged in parallel at intervals of one-sixth and a half arc length, and then the vertices of the seven parallel lines are connected into smooth arcs to obtain a half development diagram of the end joint, and the development diagram is flipped left or right 180 to obtain a complete development diagram of the end joint.