(1) Correction of eccentricity during punching: Uneven anvil, skewed punch ends, and uneven heating of the billet can all cause eccentricity in the hole diameter during punching. The correction method can be the water immersion method: during operation, immerse the thinner side of the hole wall in water to lower its temperature, then use the punch to enlarge the hole. The thicker side, due to its higher temperature and better plasticity, will become thinner, making the entire forging wall thickness uniform and correcting the eccentricity. This method is suitable for materials with good plasticity.
(2) Billet distortion during punching: This means that the metal under the punch is squeezed outwards, reducing the billet height, increasing the diameter, causing the upper end face to be concave and the lower end face to be convex. The degree of distortion is related to the billet diameter D0, height H0, and hole diameter d1 before punching. The smaller the D0/d1 ratio, the more severe the distortion. The correction method is to control D0/d1 to be ≥2.5~3. If the diameter of the hole to be punched is large, such as D0/dl<2.5, a small hole is usually punched first, and then the hole is enlarged to obtain the required hole diameter [1].
