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The forming limit diagram (FLD) is one of useful parameters for evaluating the formability of sheet metal, and has been currently used in the development of forming processes of autobody panels. Also FLD plays an important role for the prediction of fracture in the analyses by numerical forming simulation. In this paper the influencing factors on FLD were examined experimentally. The experimental results of FLD depend on the experimental conditions such as tool shape and dimension, lubricant, gauge length and measuring preciseness. The effect of straining path on FLD is seemed large, but it is complicated to obtain FLD in complex straining paths experimentally. For efficient application of FLD in tool design and making, and stamping shops, there are still remained some problems to be solved.

In automobile companies new techniques of sheet metal forming have been developed and some of them are applied practically in order to solve the social demands to automobile. Sheet materials makers have also developed new materials with good formability in response to the requests of automobile companies. Current topics of sheet metal forming techniques in Japan are; (1) Stamping of high strength steel and aluminum alloy sheets for weight reduction of autobody, (2) Stamping of tailored blanks, (3) Application of new forming techniques such as hydro-mechanical forming and blank holding force control, and (4) Practical application of FEM simulation to die making and stamping processes for the reduction of preparation time and the optimization of forming processes.

The practical application of high strength steel sheets to autobody parts has been increased year by year in order to promote weight reduction and ensuring safety. New types of high strength steels with good formability have been developed and the average weight ratio of high strength steel in a whitebody is over 20 % in Japan. In the near future the weight ratio of high strength steel in a whitebody is estimated as over 40 %. In the forming of high strength steel sheets it is difficult to suppress geometrical failures and dimensional inaccuracy. The developments of forming techniques and their suitable application are required to succeed the forming of high strength steel sheets.