TY JOUR TI PRODUCTION OF TEES FROM PIPE BLANKS USING MULTIPASS STAMPING METHOD KW multi-stage stamping KW pipe blank KW tee KW punch KW neck KW mathematical modeling JO Bulletin of Belgorod State Technological University named after. V. G. Shukhov AU Gavrilov, R.V. AU Duyun, T.A. PY 2026 IS 11 PB Belgorod State Technological University named after V.G. Shukhov