ISO 12004-1:2020 pdf download – Metallic materials — Determination of forming-limit curves for sheet and strip — Part 1: Measurement and application of forming-limit diagrams in the press shop.
7 Procedure The procedure for the determination of the forming limit is as follows: 1) Take a representative sample of the material to be evaluated. 2) Apply a suitable grid pattern, that has been checked for accuracy of the initial gauge lengths, to the surface of a test piece in areas of the part to be formed which are known, or have been established by investigation, to be critical. 3) Any test device that satisfies Clause 6 may be used to form the test piece, such as a universal tensile testing machine, a stamping press, a cupping press, a hydraulic bulge machine and their combinations or any other equipment capable of clamping the test piece and applying a plastic deformation force in an area remote from the edge. A universal testing machine may be employed and forming limits established using a tensile test. 4) Test pieces shall be tested while clamped around the whole of their periphery or shall be cut into strips of varying widths to give a range of strain conditions. The surface between the punch and the specimen shall be suitably lubricated using a standard product for the operation. A combination of polyethylene sheet and lubricant can be used. 5) Stop the test at the first occurrence of fracture. 6) Determine the engineering strains e 1 and e 2 as follows: a) Measure (for example with calliper or optical measurement system) three adjacent gauge lengths in the direction of e 1 that were originally in a straight line. Repeat until the three values obtained are the same to within ±10 %. Record the average of these three values as l 1 . A more accurate method may be prescribed as provided for in ISO 12004-2 [2] . NOTE Although engineering strain is specified in this document, true strain is specified in the forming limit determination for ISO 12004-2 [2] . b) If it is not possible to obtain three values within ±10 %, form a new test piece and repeat the measurements.