Methods of Establishing Forming Limit Diagram of Tube Hydroforming

Forming severity is one of the significant indexes to assess formability of tube hydroforming. The state of strain can be accurately reflected when tube reaches forming limit, mechanical rules during forming processes can be revealed as well by using the forming limit diagram (FLD). By contrast with FLD of sheet metal, the FLD of tube hydroforming is seen as different. In this paper, the importance of FLD of tube hydroforming was discussed briefly; typical methods established to FLD of tube hydroforming were listed and classified; characteristics and insufficiencies of those methods were pointed out; advantages of forming limit stress diagram (FLSD) were introduced simply. Furthermore, the main problem and the trend of development in FLD of tube hydro-forming were summarized.