4.8. Hammering

Hammering, or forging is the method of hot metal forming in which metals are deformed by universal tools, such as hammer, anvils, block heads and others.

There are two types of hammering:

- hand (smith) forging;

- machine forging.

Only the second type of hammering is used in machine industry. A half-finished product of hammering is named a forging. Mass of forgings ranges from a few grams to 250 ton. The main advantages of hammering are:

- simple universal tools are used for manufacturing of different articles;

- heavy forging may be produced only by hammering.

Main Hammering Operations (Fig. 4.17). Upsetting is conducted under impact loading P of a billet located an the anvil. As a result the height of a billet is reduced.

Degree of deformation is determined by the following formula:

(4.6)

where F₀ and F₁ are initial and final cross sections correspondingly;

H and h are initial and final heights correspondingly.

Heading (Fig. 4.17d) is local upsetting of the upper part of a billet (e.g. to produce head of a bolt).

Spreading is a process of making the billet wider and correspondingly thinner.

Drawing (Fig. 4.17a) is a forging operation for elongation of the billet or a part of it.

Ring rolling or paying out (Fig. 4.17c) means increasing in diameter of a ring, which undergoes hammering by block head and a rotation around cylindrical mandrel.

Piercing (Fig. 4.17e) is making a hole in the billet.

Fig. 4.17. The main hammering operations: a, b – drawing; c – ring rolling; d – heading;

e – piercing; f – bending; g – twisting; h – cutting off

Chopping or cutting off (Fig. 4.17h) is separating of one part of half-finished article from another one.

Bending and twisting operation are shown in Fig. 4.17f and 4.17g correspondingly.

Hammers (smith forging hammers) and hydraulic presses are used in forging process. The forging hammer is a machine of impact action. The impact is produced by mass of falling parts. A compressed air, steam and electrical energy are used in forging hammers.

Let us consider design of a pneumatic forging hammer (Fig 4.18). When compressed air is given through hole 4 a piston 6 moves up in a cylinder 5. The piston lifts a piston rod 8, a slider 10 and a block head 11, which are assembled together.

Fig. 4.18. Forging hammer: 1 – handle; 2 – traction; 3 – valve; 4 – hole (pipe); 5 – cylinder; 6 – piston;

7 – sliding surface; 8 – rod; 9 – body; 10 – slider; 11 – block head; 12 – smithy; 13 – anvil block

During the next part of the working cycle compressed air is released away and all moving parts named falling parts (the piston, the rod, the slider and the block head) fall down to perform deformation of a workpiece. This workpiece is placed on a smithy (swage anvil) 12, which is mounted on anvil block 13, located, in turn, on a basement. In steam-air hammer a bedframe 9 is mounted separately from the anvil.

The higher the mass of the anvil block is, the higher the efficiency of an impact and work of the hammer will be. The capacity of hammers is defined by mass of the falling parts. It ranges from 50 to 1000 kg. Forge hammers are used for producing forgings that have mass up to20kg.

Hydraulic presses (Fig. 4.19) are machines of static action. When oil is given into a main cylinder 10 under pressure from 20 to 30 MPa a plunger 6 with traverse 3 and head block 2 is moved down and the head block deforms a work. The plunger 6 and the head block 2 are raised by cylinders 9 and pistons 5.

Hydraulic presses have deforming force from 5 to 600 MN.

Forging manufacturing process. Process of manufacturing a forging comprises the following operations (steps):

- drawing of the forging is developed on the base of drawing of a finished part;

- the machining allowances, laps and tolerances are point out on the forging’s drawing (Fig.4.20);

- the shape and weight of required billet is determined;

- the necessary equipment is selected;

- the sequence of forging operations should be specified.

Let's assume that the part be done has shape of a lever with a jaw ( Fig. 4.21a) and the billet has shape of a cube (Fig. 4.21.b). The sequence of operations to manufacture a part are shown in Fig. 4.21c…i. As a result, the required forging is received.