A. hot push forming  

The forming process of hot push elbow is the process of using elbow pushing machine, core die and heating device, so that the blank on the die moves forward under the push of the pushing machine, and is heated, expanded diameter and bent forming in the movement.  Hot push bend deformation characteristics are based on volume before and after plastic deformation rule of metal materials determine the pipe diameter, pipe diameter bend diameter, through the core module and control the deformation of the process, make the inner arc compressed metal flow, the compensation to other parts of the thinned by hole diameter, wall thickness uniform Angle is obtained.  

The forming process of hot push elbow has the characteristics of beautiful appearance, uniform wall thickness and continuous operation, suitable for mass production, so it has become the main forming method of carbon steel and alloy steel elbow, and is also used in the forming of some specifications of stainless steel elbow.  

The heating method of forming process has medium frequency or high frequency induction heating (heating ring can be multiple or single ring), flame heating and reflector furnace heating, which heating method depends on the requirements of forming products and energy conditions.  

B. Stamping forming  

Stamping forming elbow is the earliest forming process applied in batch production of seamless elbow. At present, it has been replaced by hot push method or other forming process in the production of elbow in common specifications, but in some specifications of elbow due to the production of less quantity, wall thickness is too thick or too thin.  The product is still in use when there are special requirements.  The forming of elbow is made of pipe blank equal to the outside diameter of the elbow, which is directly pressed by press in the die.  

Before stamping, the tube blank is placed on the lower die, the inner core and end die are loaded into the tube blank, and the upper die begins to press down, and the elbow is formed through the constraint of the outer die and the support of the inner die.  Compared with the hot push process, the appearance quality of stamping is not as good as the former.  The outer arc of the punching elbow is in the stretching state when forming, and there is no excess metal in other parts to compensate, so the wall thickness of the outer arc is reduced by about 10%.  However, due to its applicability to single production and low cost, the stamping elbow process is mostly used in the manufacture of small batch, thick wall elbow.  

Stamping elbow is divided into cold stamping and hot stamping, usually according to the nature of the material and equipment capacity to choose cold stamping or hot stamping.  

Cold extrusion elbow forming process is the use of elbow forming machine, put the tube billet into the outer die, the upper and lower die after the die, under the push rod, the tube billet along the inner die and the outer die reserved clearance movement and complete the forming process.  The elbow made by the internal and external die cold extrusion process has beautiful appearance, uniform wall thickness and small size deviation, so the stainless steel elbow, especially the thin-walled stainless steel elbow forming is made by this process.  The precision of internal and external die used in this process is high;  The wall thickness deviation of the billet is also strict.