The forming limit curve (FLC) is an important parameter for sheet metal simulations of autobody metals. Every material has its own individual forming limit curve that is generally calculated in accordance with Nakajima or Marciniak using cupping tests on sheet metal specimens. In addition to hydraulic sheet metal testing machines, ZwickRoell offers a special test fixture that is integrated into an electromechanical testing machine for these tests. Voestalpine uses this machine in its factory in Linz.
The suppliers for the autobody are under constant pressure from automobile manufacturers to increase production efficiency, minimize costs, and optimize quality, i.e. especially the precision of the manufactured parts.
A static materials testing machine (Fmax 600 kN) in conjunction with a deep draw test fixture allows ZwickRoell to offer a flexible testing solution for all deep draw tests: e.g., cupping tests to Erichsen (DIN EN ISO 20482), earing tests to DIN EN 1669, hole expansion tests (ISO 16630), FLC or cupping tests (ISO 12004) to Nakajima or Marciniak. The latter test is used at Voestalpine to manufacture specimens for testing the surface waviness to VW factory standard PV 1054. These specimens are subsequently checked for their waviness. The waviness characteristic is used to record the long waviness of the sheet metal surface on the unpainted parts. The long waviness is not visible on more heavily formed component areas until they are painted.
A special feature of the testing system is the laserXtens extensometer with eight measurement axes. It measures the surface strain without making contact and stops the sheet metal forming at the set value. The advantage of this solution is that there are no markings on the sheet metal specimen so that the preparation time and thereby the clock cycle are reduced to a minimum.
The testing machine at Voestalpine is used during production and can be expanded to include an automatic specimen feeding system if there is increased demand for testing. Voestalpine is the first to implement this test solution.