Important parameters in rolling operation

Q-2.Consider any one of the metal forming operations and list out the important parameters involved during the process.

Ans: Rolling is a metal working process. In rolling, the metal stock or billet is passed through a pair of rolls to reduce the thickness. During the rolling process, the width of the stock remains constant.

The important parameters involved during the rolling process are,

Diameter of rolls.
Friction generation between workpiece and roll surface & Neutral plane position.
Deformation resistance of metal and temperature of billet, etc.

Diameter of rolls:

In the rolling process, rolling force is directly proportional to the diameter of roll. Rolling force increases as the roll diameter.
As a decrease in diameter of roll, length of arc of contact also decreases. Hence, smaller diameter roll provides uniform reduction in thickness of billet. Hence, small diameter rolls are generally used in rolling purposes.
Larger rolls are used as back up rolls, hence it provides back support to smaller rolls against deformation and maintain the smaller roll in the axis of roll.

Friction generation between workpiece and roll surface & Neutral plane position:

As shown in fig 2.2, at entry of material, the velocity of material is less than the velocity of roll. So, the friction will act in the forward direction.
At exit of roll, velocity of material increased due to plastic deformation. Hence, friction acts in backward direction. So, there is a plane where the velocity of roll and material velocity are equal, that plane is called the neutral plane.
By increasing a coefficient of friction, the neutral plane can be shifted towards the left side. But, by increasing the thickness of the incoming billet, external pressure is applied at the entry zone and the neutral plane shifts toward the right side.
Shifting the neutral plane toward the right is not favorable. Because if the neutral plane consists with vertical axis (axis passes through the roll center), there will be no deformation in material and the roll will slip over the material.

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