Testing with no ifs or buts – hole expansion to ISO 16630 successfully automated
09.12.2019 | Initiative Automotive
The automatic hole expansion system of Salzgitter Flachstahl GmbH (SZFG) was presented for the first time to a specialist audience from research and industry at a materials testing conference on 4 December.
Most of the sheet steel supplied by Salzgitter Flachstahl is shear cut in the process of manufacturing components. Depending on the type of steel and the cutting parameters, the formability of the edge can be significantly reduced as a result by comparison with the base material. This effect must be taken into account when designing components if, for example, high-performance materials are to be exploited to the limit of their formability. To ensure that the customer can rely on high formability in production in spite of the cut, Salzgitter Flachstahl guarantees minimum formability for the shear cut edge on request. Such products are furnished with the suffix xpand®. The formability of the shear cut edge is determined by measuring the hole expansion ratio in accordance with ISO 16630. To do so, a hole is first cut in the sheet to be tested using defined process parameters. The hole is then widened with a reamer until a crack runs through the entire thickness of the sheet. The hole expansion ratio is calculated from the diameter of the initial hole cut and that of the expanded hole.
The time and effort expended on testing has increased with the growing demand for xpand® steels. The cutting and widening performed manually with a sheet metal testing machine was becoming more and more of a bottleneck in the evaluation of relevant coils. For this reason, Salzgitter Flachstahl decided to significantly increase its testing capacity with an automatic hole expansion system. Salzgitter Mannesmann Forschung GmbH (SZMF) provided support from the design to commissioning of the system. The results of previous research and development activities in the determination and evaluation of measurements were incorporated in the process.
The newly installed testing process continues to meet ISO 16630 and besides increasing capacity, it also reduces the possibility of errors. The sample measuring approx. 100 mm in width and 500 mm in length is furnished with a barcode for identification and later allocation of the process data and results. A cutting tool perfectly adapted to fit the application was built to cut the holes in the first stage of the process. It allows the cutter blades to be easily swapped while at the same time guaranteeing the necessary stiffness for high, consistent cutting quality.
At the same time, a sample strip is furnished with five holes with one stroke of the 700 kN servo-electric press. This cutting process is controlled by an intuitively operated LabView interface. Numerous sensors and plausibility checks reduce the possibility of errors.
The perforated samples are then stacked in the hole expansion system feed. The sheets are automatically withdrawn and fed to the expansion unit. In order to run hole expansion testing without an operator, automatic crack detection is required. For this, the surface of the sample must be evenly lit with low reflections. A high-resolution digital camera generates a series of individual images of the material area around the cut hole. These are analyzed directly by a LabView Vision program and cropped to the cut edge. If the resulting ring is completely severed by a crack, the expansion process is halted and the hole expansion ratio can be calculated on the basis of the images.
In commissioning the automatic hole expansion system, Salzgitter Flachstahl is adapting its testing capacity to meet rising demand and redefining the state of the art in this field.
If you have any questions, your contacts in technical customer service will be happy to help you.