The reduction forming process for reducing elbows involves placing a tube blank with a diameter equal to the large end of the reducing elbow into a forming die. By compressing along the axial direction of the tube blank, the metal moves within the die cavity and shrinks into shape. Depending on the degree of reduction of the reducing elbow, it is categorized as single-stage or multi-stage forming.

2. The expanding forming process utilizes a billet with a diameter smaller than the large end diameter of the reducing elbow, and expands the billet internally using a mandrel. This technique primarily addresses the issue of reducing elbows with significant size changes, which are difficult to form through reduction. Occasionally, depending on material and product shaping requirements, the expanding and reduction methods are combined.

In the process of reducing or expanding diameter deformation pressing, cold pressing or hot pressing is determined based on different materials and varying diameters. Generally, cold pressing is preferred, but in cases of severe work hardening caused by multiple diameter changes, thick wall thickness, or materials like alloy steel, hot pressing is advisable.