Forging Hammers

FORGING HAMMERS

Hammers are the most common types of machine tool used in forging. They are often preferred for small to medium batches because of quicker tool setups and lower overheads. They are also used for elongated and branch-type forgings because die areas can be provided for the larger number of preform dies required for such shapes.

The various types of hammers used in forging are described here.

1. Gravity Drop Hammers

Gravity drop hammers are the oldest type of forging equipment available. The upper die and ram are raised by friction rolls gripping the board when the rolls rotate. After releasing the board, the ram falls under gravity to produce the blow energy. This potential energy is converted into kinetic energy as the die block falls and it is then dissipated as the deformation of the workpiece. Various lifting mechanisms are used which include frictional means with boards, band brakes or belts or a lifting cylinder employing steam, compressed air or hydraulic fluid as shown in Figure 3.18. These machines are available in the range of blow energies from 0.6 kN-m to 400 kN-m. The hammer can strike between 60-150 blows per minute depending on the size and capacity.

2. Power Hammers.

Power hammers are similar to gravity hammers in lifting cylinder that raises the upper die but power is also applied to the downward-movement of the upper die to increase the energy capacity. Energy ratings for similar die weights are considerably more than gravity hammers and the die closing speeds are also high. Power comes from double-acting steam, compressed air or hydraulic cylinders as shown in Figure 3.19.

Steam hammer is operated by using a high pressure steam for the movement of a ram. When the compressed air from the compressor is supplied for obtaining the ram movement through the piston and cylinder arrangement, the hammers are called pneumatic hammer. In hydraulic hammers, the compressed air is replaced by hydraulic oil which is supplied by a pump under high pressure.

Double-acting hammers are manufactured in the range of energy ratings from 3 kN-m to 825 kN-m.

3. Vertical Counterblow Hammers

In these machines, two rams with nearly equal masses are driven by double-acting cylinders towards each other and impact at the center of the machine. More energy is` dissipated into the workpiece than in the foundations and subsoil compared to single-acting hammers. Very high energy capacities are available in the largest machines with the range from 30 kN-m to 2000 kN-m.

4. Horizontal Counterblow Hammers

These machines are also called impactors and two rams are actuated by double acting cylinders. Heated stock is positioned vertically between dies by an automatic transfer mechanism. Typical energy ranges from 4 kN-m to 54 kN-m.