Wear Mechanism And Prediction Of Mandrel For Hot Bending Forming Of High Strength Steel Tubes

Hot bending forming of high strength steel tubes has a wide application prospect in automotive lightweight,aerospace and other fields.In the process of machining,as a part of the mold,the mandrel faces huge wear under the bad working conditions of high temperature and high pressure.The study of mandrel wear is helpful to guide the design and manufacture of mandrel for hot bending of high strength steel pipe,prolong the service life of mandrel,further stabilize the hot bending forming process of high strength steel pipe and improve the forming quality of pipe.In this paper,theoretical analysis,finite element simulation and experimental verification are used to study the wear process of the mandrel used for hot bending of high strength steel pipes,which can provide a reference for the design of the mandrel used for hot bending of high strength steel pipes.The common models and development rules of mandrel used for hot bending forming of pipes are summarized,and a new design structure is proposed.According to the existing experimental conditions,non-core ball mandrel,circular head mandrel and vertical head mandrel were designed respectively for numerical simulation calculation.The different mandrel structures and the different gaps between the mandrel and the pipe wall were simulated by ABAQUS.For mandrel wear,ABAQUS was redeveloped,and Archard wear model was embedded into the subroutine.The wear amount was expressed in the form of ALE adaptive grid.The wear condition of mandrel with different shape is predicted.The mandrel was designed and manufactured according to the type of pipe used in the experiment,and the mandrel wear experiment was carried out.The cooling water channel and temperature measuring thermocouple were built in the mandrel to measure the temperature of the mandrel in the machining process.It is found that the temperature of the mandrel increases rapidly in the absence of cooling water,up to 1200?,while in the presence of cooling water,the temperature of the mandrel is stable at about 200?.Through metallographic experiment,it is found that the surface of mandrel changes.Under the condition of cooling water,the austenite crystal cell locally appears twinning due to the action of external force.Without cooling water,lattice distortion occurs,and the grain becomes coarser,so that the wear on the macro level occurs locally.