a. Hot push forming

The hot push elbow forming process uses a special elbow pushing machine, a mandrel and a heating device, so that the blank placed on the mold is pushed It moves forward under the push of the machine and is heated, expanded and bent into shape during the movement. The deformation characteristic of the hot-pushed elbow is to determine the diameter of the tube blank based on the rule that the volume of the metal material does not change before and after plastic deformation. The diameter of the tube blank used is smaller than the diameter of the elbow. The deformation process of the blank is controlled by the mandrel so that the inner arc is compressed. The metal flow compensates for other parts that are thinned 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 mass production. Therefore, it has become the main forming method of carbon steel and alloy steel elbows, and is also used in certain specifications of stainless steel elbows. is taking shape. The heating methods used in the forming process include medium-frequency or high-frequency induction heating (the heating circle can be multi-turn or single-turn), flame heating and reverberatory furnace heating. The heating method used depends on the requirements of the formed product and the energy situation.

b. Stamping

Stamping elbow is the earliest forming process used in mass production of seamless elbows. At present, it has been popular in the production of elbows with common specifications. method or other forming processes, but in certain specifications of elbows due to the small production quantity and the wall thickness is too thick or too thin. The product is still used when there are special requirements. The stamping forming of the elbow uses a tube blank that is equal to the outer diameter of the elbow and is directly pressed into the mold using a press. 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. The elbow is formed through the constraints of the outer mold and the support of the inner mold. Compared with the hot pushing process, the appearance quality of stamping forming is not as good as the former; the outer arc of the stamping 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 manufacture of small batch, thick-walled elbows. Stamping elbows are divided into cold stamping and hot stamping. Cold stamping or hot stamping is usually selected according to the material properties and equipment capabilities. The forming process of cold extrusion elbow is to use a special elbow forming machine to put the tube blank into the outer mold. After the upper and lower molds are closed, under the push of the push rod, the tube blank is pushed along the reserved areas of the inner mold and the outer mold. Clearance movement completes the forming process. The elbow made by the cold extrusion process of internal and external dies has beautiful appearance, uniform wall thickness and small size deviation. Therefore, this process is often used for the forming of stainless steel elbows, especially thin-walled stainless steel elbows. The internal and external molds used in this process require high precision; the wall thickness deviation requirements of the tube blanks are also strict.

c. Other forming methods

In addition to the above three commonly used forming processes, seamless elbow forming also uses extruding the tube blank into the outer mold and then passing it through The forming process of ball shaping inside the tube blank. However, this process is relatively complex, troublesome to operate, and the forming quality is not as good as the aforementioned process, so it is rarely used.

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