Laser-assisted forming is a method based on contactless shaping of profiles with the use of a laser beam impact. This method has been developed from the early 1980s by the Centre for Laser Technology of Metals at the Kielce University of Technology (PŚk) and the Polish Academy of Sciences (PAN), among others [1-7]. In general, the mechanism allowing for changing the shape of profiles is the material’s thermal expansion. Suitable profile heating (on programmed paths with an adequately selected temperature, etc.) allows for obtaining the planned shapes.
Despite certain areas of application (electrical mechanics, precision mechanics, micro-positioning and others), this method is ineffective [4-5]. When changing the shape of large-diameter profiles, this method is power and time consuming, thereby eliminating it from industrial applications. Thus, the concept of a hybrid method was created, i.e. laser forming with mechanical assistance. I
n 2015, PŚk established co-operation with the Metal Forming Institute (INOP) in Poznań, PAN’s Institute of Fundamental Technological Research, and the Rzeszów University of Technology in terms of research in the aforementioned topic. The above consortium commenced the execution of the project titled “Laser forming of thinwalled profiles with mechanical assistance, financed by the National Centre for Research and Development as part of subsidy no. PBS3/A5/47/2015.
The paper’s authors will present, among other things, the main concept of hybrid laser and mechanical forming, one of the concepts selected for the execution, design and construction of a station for bending thin-walled tubes and cone diffusers used in the construction of aircraft engines. The target materials of the research are Inconel 618 and Inconel 625 refractory nickel superalloys, as well as AISI 410 and AISI 325 heat-resistant Martensitic steels. These materials, due to their good mechanical properties when working at higher temperatures, are used for building turboprop engines. For economic reasons, the testing was conducted on X5CrNi18-10 acid-resistant austenitic steel. The hybrid method (assumptions, concept, design) presented in the paper was subjected to validation in laboratory conditions. The testing featured measurements of the forces required to obtain plastic deformations in the profile, bending angle, and determination of the process temperature. Furthermore, the paper will feature a presentation of future plans concerning the work executed as part of the said project.
KEYWORDS: Control systems, Laser processing, Fuzzy logic, Control systems design, Beam controllers, Error control coding, Actuators, Process control, Automatic control, LabVIEW
The article presents a developed, proprietary system of automatic temperature control of the workpiece surface for a laser processing. In the control system, a regulator based on fuzzy logic algorithms has been developed. The system is based on a RT real time system with a frequency of 1 kHz. In order to implement the system, the reconfigurable NI CompactRio microprocessor system together with the appropriate input modules was used. The control application was created based on the LabView software. The feedback signal for the control system was realized with usage of a fiber optic pyrometer observing the area of the laser beam. In order to implement the system in the existing, dedicated control system of the Trumpf TruCell 1005 laser device, a number of integration works were carried out. During the preliminary tests, the settings of the developed regulator were selected empirically and the correctness of its operation was checked for various working conditions. The article also presents the time series of the temperature control value and the control error combined with the course of the modulated laser device power during the laser machining process.
Tube bending locally heated by a laser beam is analysed. This heating reduces the yield stress and prevents stress hardening thus making easier the process of plastic deformation. In the present work simple model of elasto-plastic bending of circular tubes is developed and some experimental results of laser assisted bending are shown.
Laser-assisted forming techniques have been developed in recent years to aid plastic working of materials, which are difficult in processing at normal temperatures due to a high brittleness, effects of high work-hardening or a high spring-back phenomenon. This paper reports initial experimental investigations and numerical simulations of a mechanically-assisted laser forming process. The research is aimed at facilitating plastic shaping of thin-walled parts made of high temperature resistant alloys. Stainless steel plate, 1 mm thick, 20 mm wide, was mounted in the cantilever arrangement and a gravitational load was applied to its free end. A CO2 laser beam with rectangular cross-section traversed along the plate, towards the fixed edge. Laser spot covered the whole width of the plate. Experiments and simulations using the finite element method were performed for different values of mechanical load and with constant laser processing parameters. Experimentally validated numerical model allowed analysis of plastic deformation mechanism under the hybrid thermo-mechanical processing. The revealed mechanism of deformation consists in intense material plastic flow near the laser heated surface. This behavior results mainly from the tension state close to the heated surface and the decrease of material yield stress at elevated temperature. Stress state near the side edges of the processed plate favored more intense plastic deformation and the involved residual stress in this region.
The absorption coefficient of the surface of a workpiece is of importance in laser treatment, particularly in the treatment where the temperature of an element must be strictly controlled. Laser surface treatment (such as hardening, metallic glazing) and laser forming can be primarily included in this type of technology. In another case, surface temperature must be precisely controlled, especially if structural changes are to be avoided. There are a number of ways to increase the absorption coefficient of the surface of an element. Since the laser forming is the research subject of the authors of the presented paper, it was necessary to determine the absorption coefficient for the different surfaces preparation of workpieces. Raw surface, oxidized surface, sandblasted surface, black enamel covered surface and waterglass covered surface were examined, respectively. The experiment was performed using a CO2 laser with a head for a surface treatment which generates a rectangular beam of dimensions 2x20 mm, and the samples were made of X5CrNi18-10 stainless steel.
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