Influence of the hydraulic press system on advanced high-strength steel formability

In sheet-forming operations, it has been sought to always obtain the maximum elongation of the material without the occurrence of defects, a condition that is of fundamental importance to know the performance of the sheet metal in industrial processes. In view of this need, the FLCs (forming limit curves) of the used metal sheets are determined, which provide an excellent condition for the evaluation of the material stamping limit. Deformation levels lower than FLC, considering a safety margin, are considered satisfactory in industrial operations. Based on this, the objective of this work was the adequacy of a test machine and the development of a method to obtain the FLC of sheet metal at the beginning of the material’s bonding, thus seeking a more precise result of the formability of the main steels used in the industry, advanced high strength steels. For this, an initial analysis of the hydraulic press was carried out where, taking advantage of the displacement and oil pressure sensors present, a new control program was determined in the PLC (programmable logic controller), to parameterize the points that precede the rupture of the sheet during the stamping test. Under these conditions, the FLC of the dual-phase steel DP600 was determined until its rupture and, later, until the point of its beginning, which allowed the definition of the real limit of formability of this material. In addition to the conclusion regarding the behavior of the material, considering the industrial processes, the results obtained also allow the determination of set points of machines more adequate to the limits of deformation of the sheet metal used. The FLC presented a variation, characterized by a small increase in the formability limit for the tests with hydraulic press temperature control conditions. The results highlighted higher temperatures on the pump, followed by the distributing block and the pressure sensor, concluding that the major influence critical point on the FLC result was the hydraulic pump.