Introduction to Hot Forming

The principal methods of hot working are extrusion, drawing, forging and rolling. Rolling is the most extensive employed forming process, though some limitations may apply to the process. Rolling mainly consists of three major sub-categories: flat rolling, shape rolling (with specifically designed roll grooves) and pipe rolling (including piercing). Forging may be sub-categorized as hamming, pressing, etc.

Forging may be performed under hammers, in mechanical presses and upsetters or by a method known as roll forging. Pressing generally includes the manufacture of forged articles in hydraulic presses. Extrusion usually is performed in hydraulic presses which force the hot steel through a die. Rolling is performed in rolling mills of a variety of types.

The two principal reasons for perform metal forming at elevated temperatures (hot working) are to reduce the forming loads through the reduction of the resistance of the steel to deformation, and to develop preferred metallurgical structures for strength and ductility of the finish products.

The most appropriate manufacturing method of a product will be decided with consideration of its material, sizes, shape, use, standards and other properties.

There are numerous processes for manufacturing butt weld fittings, several examples listed as follows.

TEES: Extrusion method (Hot Forming)

The hot-extrusion process consists of enclosing a piece of metal, heated to forging temperature, in a chamber called a “container” having a die at one end with an opening of the shape of the desired finished section, and applying pressure to the metal through the opposite end of the container. The metal is forced through the opening, the shape of which it assumes in cross-section, as the metal flows plastically under the great pressures used.

Tees using raw material with a bigger diameter than the finished product, the branch outlet is extruded from pipe while the main body is being pressed. The outlet’s wall thickness can also be adjusted as needed. Applied to Tees with large diameters, heavy wall thickness and/or special material with challenging workability that cannot be manufactured using the hydraulic bulge method.

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ELBOWS: Mandrel method (Hot Forming)

One of the most common manufacturing methods for manufacturing Elbows from pipes. After heating the raw material, it is pushed over a die called “mandrel” which allows the pipe to expand and bend simultaneously. Applicable to a wide size range.

Elbows of steel pipe joints are used in the industrial plants and are mainly manufactured by the hot mandrel bending from raw material of straight steel pipe. Elbows are generally manufactured at elevated temperature by means of pushing, expanding and bending of pipes simultaneously, using the inner tool of mandrel. Characteristics of mandrel bending strongly depend on the integrated shape and dimensions of the mandrel.

Elbows manufactured by using hot mandrel bending have advantages of small thickness deviation and shorter bending radius than those of any other bending method type.

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CAPS: Deep Drawing method

One of the most common manufacturing methods for caps, where plate is cut out in a circle and formed by deep drawing.
Deep drawing is the manufacturing process of forming sheet metal stock, called blanks, into geometrical or irregular shapes that are more than half their diameters in depth. Deep drawing involves stretching the metal blank around a plug and then moving it into a moulding cutter called a die.
A drawing press can be used for forming sheet metal into different shapes and the finished shape depends on the final position that the blanks are pushed down in. The metal used in deep drawing must be malleable as well as resistant to stress and tension damage.