Among the various applications of lasers, laser cutting is one of the main businesses of this technology and is becoming more and more widespread thanks to its level of precision, speed and quality compared to traditional cutting processes. However, laser cutting cannot be performed on any type of material. The main requirement of this technology is that the material to be cut must have excellent flatness and no internal stresses. This is because the release of these stresses at the time of cutting can cause the piece to not meet the required flatness tolerances. It is also detrimental to the cutting process itself.
The requirements in terms of flatness tolerances and absence of stresses that the current market demands for materials to be laser cut are very demanding, and may vary depending on the final destination of the material. The main steelmakers provide minimum values that must be guaranteed in the formats in order to be able to carry out an adequate laser cutting. These maximum permissible flatness values are usually approximately 3 or 4 mm/m depending on the required final flatness quality. Achieving these tolerances will depend to a large extent on the quality of the material and flattening process, which will have a great influence on the final result.
When talking about sheet flatness, two aspects must be considered: the sheet must not have local defects such as edge waves, central buckles, cross bow, etc., but it must also have as few internal stresses as possible in the material. The first point is easy to assess and measure. However, the level of internal stresses in a material requires complex techniques which, at present, would be unfeasible to perform in an industrial process due to their lack of precision. In fact, one of the usual ways of validating the level of internal stresses in a material, given the complexity of the experimental techniques, is to check its state of flatness after having been cut by a laser cutting process.
If the material has a high level of internal stresses, this could not only affect the laser cutting, but also future processes such as welding, stamping or bending. Therefore, proper flattening of the materials is necessary to ensure that they remain flat even after subsequent processing.
Fagor Arrasate has have been manufacturing straightening and leveling machines for over 60 years. Like everything else, materials also evolve and their machines have had to evolve to adapt to them. In the last two decades, the upward trend in the increase of the yield strength of steels is what has pushed us to adapt to the new requirements and to deepen the study of the behavior of the different families of material. This has allowed to determine the optimal way to process these materials and thus become a worldwide reference in laser quality leveling.
In recent years, the company has been working on a new leveling concept with which can guarantee an adequate degree of leveling, even in materials with high yield strength. In addition, we have further studied new line configurations that have proven to be optimal for minimizing internal stress in materials.
On the one hand, the latest generation of levelers with the new multi-drive concept (I-MOTION) has been used with 3rd generation high-strength steels with excellent results. The optimized configuration of the cassettes, together with the great robustness of these levelers, ensures a high and homogeneous plasticization across the width of the strip without structural deflections, even with materials with high yield strength or with large thicknesses with very demanding load stresses. Furthermore, thanks to this technology, the distribution of torques between the rolls of the leveler is controlled, which makes it a much more efficient process and minimizes the risk of breakage in the most critical rolls.
Moreover, Fagor Arrasate has developed new optimal line configurations to minimize internal stresses in the material (LASERFLAT), without the need for the large investments required by other flattening methods. These lines provide an agile response of the equipment to the variations of the input product, ensuring repeatability in the final quality of the formats. The adjustment of the rolls in this type of lines is key to achieve the desired objective of minimizing the stress of the material. For this reason, the company has studied in depth the roll adjustment models to reach the optimal configurations for each type of material in order to obtain a minimized internal stress profile at the exit of the leveler. The leveling assistant (LSA) incorporated in these levelers will recommend the operator the optimum setting of the rolls to properly process the different work materials, depending on their thickness and their yield strength.
This type of line combined with a state-of-the-art has been validated by several of our customers in a wide range of thicknesses. The blanks obtained on the cutting lines have been laser cut to subsequently evaluate their flatness in pieces with complex geometry, and therefore their level of internal stress. In this way, our customers have been able to see that the improvement is evident and that they have managed to be recognized for their quality in the laser cutting market thanks to our lines.
These results in different installations and with different material and thickness conditions, reaffirm Fagor Arrasate as a worldwide reference in the manufacture of levelers suitable for processing advanced materials and with a leveling quality suitable for laser cutting applications.