National University of Science and Technology (NUST) MISiS, Moscow, Russia:

N. M. Vavilkin, Dr. Eng., Prof., Dept. of Metal Forming
A. S. Budnikov, Cand. Eng., Associate Prof., Dept. of Metal Forming, e-mail: budnikov.as@misis.ru

Vyksa branch of NUST MISiS, Vyksa, Russia:
N. V. Kholodova, Senior Lecturer, Dept. of Technology and Equipment for Metal Forming

The piercing plug is one of the most important elements of a technological tool operating under conditions of high force and significant heating, especially in the process of piercing extra-thickwalled shells with a D/S < 5.5 ratio. The results of the joint solution of the thermal problem of the plug and shell using the QForm 3D program, operating on the basis of finite element and control volumes methods have been presented. Based on the simulation results, the temperature field of the non-watercooled plug and shell was considered in the process of modeling the piercing of a billet of 2 m long and 250 mm in diameter into a shell of 270 mm in diameter with a wall thickness of 70 mm under conditions of a mini 70–270 pipe rolling plant. According to the calculations, the piercing process proceeded for 13 s, which practically corresponds to the experimental estimates of the machine time, while there is a significant inhomogeneity of the temperature field of the shell and plug both along the length and in the cross section. The temperature of the inner surface of the shell, which is in direct contact with the plug, changes dramatically. The temperature of the inner part of the shell at the front end is 800 °C, the middle and rear ends is 1200 °C. This behaviour of the thermal state of the shell is associated with the plug state. When piercing a long billet, the temperature of the mandrel toe increases to 1200 °C, and its spherical part to 1120 °C. These values are critical and show that in the absence of water cooling, the mandrel operates in extremely difficult conditions, which significantly reduces its durability.

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