The method of making sheet metal 90 degree elbow:
1：Hot pressing forming
The hot push elbow forming process uses a dedicated elbow pushing machine, core mold, and heating device to move the billet placed on the mold forward under the push of the pushing machine, and during the movement, it is heated, expanded, and bent into shape. The deformation characteristics of a hot push elbow are determined based on the law that the volume of the metal material remains unchanged before and after plastic deformation. The diameter of the pipe blank used is smaller than the diameter of the elbow. The deformation process of the blank is controlled by a core mold, so that the compressed metal at the inner arc flows and compensates for the thinning of other parts due to diameter expansion, thereby obtaining an elbow with uniform wall thickness.
The hot push elbow forming process has the characteristics of beautiful appearance, uniform wall thickness, and continuous operation, which is suitable for large-scale production. Therefore, it has become the main forming method for carbon steel and alloy steel elbows, and is also applied in the forming of certain specifications of stainless steel elbows.
The heating methods used in the forming process include medium frequency or high-frequency induction heating (the heating coil can be multiple or single coil), flame heating, and reflector heating. The choice of heating method depends on the requirements of the formed product and the energy situation.
2：Stamping forming
Stamping forming sheet metal 90 degree elbow is the earliest forming process applied to mass production of seamless elbows. It has been replaced by hot pressing or other forming processes in the production of commonly used specifications of elbows. However, in some specifications of elbows, the production quantity is small, and the wall thickness is too thick or too thin.
Still in use when there are special requirements for the product. The stamping forming of the elbow adopts a pipe blank with the same outer diameter as the elbow, and is directly pressed and formed in the mold using a press machine.
Before stamping, the tube blank is placed on the lower mold, and the inner core and end mold are loaded into the tube blank. The upper mold moves downward to start pressing, and the elbow is formed by the constraint of the outer mold and the support of the inner mold.
Compared with the hot pressing process, the appearance quality of stamping forming is not as good as the former; The outer arc of the stamped elbow is in a stretched state during forming, and there is no excess metal in other parts to compensate, so the wall thickness at the outer arc is reduced by about 10%. However, due to its suitability for single piece production and low cost, the stamping elbow process is mostly used for the manufacturing of small batch, thick walled elbows.
Stamping sheet metal 90 degree elbow are divided into two types: cold stamping and hot stamping. Cold stamping or hot stamping is usually chosen based on material properties and equipment capabilities.
The forming process of cold extrusion elbow is to use a dedicated elbow forming machine to place the pipe blank into the outer mold. After the upper and lower molds are closed, the pipe blank moves along the gap reserved by the inner and outer molds under the push of the push rod to complete the forming process.
The elbow manufactured by internal and external cold extrusion process has a beautiful appearance, uniform wall thickness, and small dimensional deviation. Therefore, this process is often used for the forming of stainless steel elbows, especially thin-walled stainless steel elbows. The precision requirements for the inner and outer molds used in this process are high; The requirements for wall thickness deviation of the pipe blank are also quite strict
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