Lubrication in tube hydroforming (THF): Part I. Lubrication mechanisms and development of model tests to evaluate lubricants and die coatings in the transition and expansion zones

The lubrication mechanisms that occur at the tool–workpiece interface for the transition and expansion zones are discussed. Suitable lubrication systems for the transition and expansion zones are reviewed based on the mechanics of deformation and material flow at the interface. Details of two model tests for evaluating the performance of tube hydroforming (THF) lubricants and die coatings are given. The optimization of die geometries for the model tests is based on sensitivity analysis through the finite element method together with experimental verification. The details of these tests are given and their development is discussed.