Proceedings of SerbiaTrib '13

Serbian TribologySocietySERBIATRIB ‘1313 th International Conference onTribologyKragujevac, Serbia, 15 – 17 May 2013Faculty of Engineeringin KragujevacUSE FRACTAL GEOMETRY TO DESCRIBE FRICTION OFROBOT LASER HARDENED SPECIMENSM. Babič 1 , P. Kokol 2 , M. Milfelner 3 , P. Panjan 4 , Igor Belič 51 Emo-Orodjarna d.o.o., Slovenia, babicster@gmail.com2University of Maribor, Faculty of Health Sciences, Slovenia,3 Tic-Lens d.o.o., Slovenia,4 Institute Jozef Stefan, Slovenia,5 Institute of Materials and Technology, Slovenia,Abstract: This paper describes some of our experience in laser surface remelting, consolidating, andhardening of steels. The process of laser hardening with remelting of the surface layer allows us to veryaccurately determine the depth of modified layers. In this procedure, we know the exact energy input into thematerial. Heating above the melting temperature and then rapidly cooling causes microstructural changes inmaterials, which affect the increase in hardness. Mathematics and Computer Science are very useful in manyother Science. We use mathematical method, fractal geometry in engineering, exactly in laser technics.Moreover, with fractal geometry we analize complexity of robot laser hardened specimens. We analizespecimens hardened with different parameters of robot laser cell. So we changed two parameters speed v ∈[2, 5] mm/s and temperature T ∈ [1000, 1400] °C. In this work, we have used a scanning electronicmicroscope (SEM) to search and analyse the fractal structure of the robot laser hardened specimens.Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements slidingagainst each other. The present study is intended to use new method, fractal geometry to describe completelyfriction of robot laser hardened specimens. Finally, concept of fractal geometry is applied to characterizethe microstructure and derive the useful relationship between fractal dimension and microstructuralfeatures. The modeling of the relationship was obtained by the four layer neural network.Keywords: Friction, fractal geometry, robot, laser, hardening,1. INTRODUCTIONFriction is the force resisting the relative motionof solid surfaces, fluid layers, and material elementssliding against each other.In nature we have many geometrical objectswhich are irregular and cannot be described withclassical Euclidian geometry. Thus we need a newmethod for describing the complexity andirregularity of objects. A relatively new method isfractal geometry. Recently, a concept of fractalgeometry which was originally developed for theanalysis of irregular features in nature has beenfinding increased applications in the fields ofmaterials science for the characterization ofmicrostructures. The key to fractal geometry is thefractal dimension, which describes the complexityof a fractal and geometrically irregularmicrostructure. Measuring fractal dimensions hasbecome a common practice for describing thestructural properties of roughness and hardness ofheat-treated materials. We use fractal geometry inlaser techniques. Laser hardening is a metal surfacetreatment process that is complementary toconventional aim and induction hardeningprocesses. A high-power laser beam is used to heata metal surface rapidly and selectively so as toproduce hardened case depths of up to 1.5mm withthe hardness of a martensitic micro-structure,providing improved properties such as wearresistance and increased strength.First, we hardened tool steel standard label DINstandard 1.7225 with a robot laser cell. Thechemical composition of the material contained0.38 to 0.45% C, 0.4% maximum Si, 0.6–0.9% Mn,0.025% maximum P, 0.035% maximum S and13 th International Conference on Tribology – Serbiatrib’13 351