Numerical Simulation And Experimental Study Of Fiber Laser Composite Texture

Laser surface texturing technique is used to improve the friction between the friction pair which can reduce wear of mechanical parts and increase longevity.Among several surface texture technique,laser texture is applied more because of many advantages,roll,disk,mechanical seal,mold,tool,engine cylinder,bearings are all applying the technique.Previous works more concentrated in the dimple,the theory and experimental researches on bulge are short of systematicness and innovation.Different materials or same material applications are different,these differences caused requirements of friction pair are different,so the bulge morphology,size,distribution are different.In view of this,with the aim of engineering application,numerical simulation and experimental study on 45 steel,Cr12 steel were carried out.The main researches and conclusions are as follows:?1?The three-dimensional mathematical model of laser surface texturing was established by FLUENT based on the interaction mechanism of laser and metal material.The effects of pulse width and laser power density on the temperature field and flow field of 45 steel and Cr12 die steel were investigated.The results show that the flow direction of the pool are both from the edge to the center in these two materials,which leads to form bulge.For 45 steel,When the pulse width is larger than 500 us,the maximum temperature of the pool center exceeds boiling point and causes material gasification.The above conclusion was experimentally verified: when the pulse width is smaller,larger than 500 us,it tends to form spherical crown and concave crown,respectively.The rate of pool diameter and depth firstly increases with the increase of pulse width then decreases.By analyzing the flow field and the temperature field,it is found that the large temperature gradient can promote the rapid growth of the molten pool,while the small temperature gradient makes slow growth rate of the molten pool.The conclusion was also experimentally verified: the turning point of bulges diameter and height rate from large to small is pulse width of 500 us.The liquid convection between Cr12 and 45 steel due to differences in material properties is different.The profile metallographic diagram illustrates Cr12 diameter/depth is greater than 45 steel by simulation.The temperature field of the two kinds of materials was analyzed by the metallographic point,which is followed by the gasification zone,the fusing zone,the heat affected zone and the substrate zone from the inside to the outside.Themicrostructure and hardness of each zone were measured.It is believed the hardness of surface tecturing is larger than substrate.?2?The quantitative characterization of the morphology of these bulges were carried out.The parameters are as follows: T is depression rate,and Pb is the inner and outer diameter ratio.T of spherical crown is 0;T of concave crown is between 0 and 0.33;T of M-shape is between0.33 and 1;and crater's T is larger than 1,and 0 <Pb <0.83.The approximate calculation formula of convex and concave was given,V-convex reflects the wear resistance of the point,V-concave represented abrasion resistance and V-shape represented the ability to store lubricants and abrasive particles.?3?Based on the guidance given by the simulation calculation,the fiber laser was used to study the texturing.The spherical crown was produced,and depending on the 45 steel gasification and the recoil pressure of the gasification process,the concave crown formed.Because the chromium boiling point of Cr12 is low and the content is high,as well as the molten pool center material gasification and thus induced recoil pressure,within the selection of parameters,M-shape was produced.And due to the role of plasma shielding,concave crown wad produced.?4?High quality dimple could be produced at a low power density of 1.02 * 104 W / mm2.This paper carried out a preliminary analysis of the strange phenomen,and explored the processing technology of dimple systematically.?5?To explore bulge morphology and size changes under the different auxiliary gas and different pressure.Adding N₂ as auxiliary gas,45 steel in the given processing parameters appeared M-shape?concave crown?spherical crown in turn;Cr12 formed concave crown,both materials' bulge diameter bigger than the diameter and height is smaller than the height that without auxiliary gas.With O₂ as the auxiliary gas,45 steel bulge morphology changes without regular,Cr12 bulge randomly appear in the M-shape and crater under condition of 0.05 MPa.Two kinds of material molten pool were blown,which unable to form bulge under the condition of 0.1 MPa.?6?In the processing surface coating a layer of sodium silicate,changing laser absorption rate,to explore the change rule of bulge morphology and size.When the coating conditions,high asp ect ratio of two materials bulge morphology larger than high aspect ratio of uncoated.?7?Adding a magnet on the side of the specimen expect to work out tited bulge.Two material s as ferromagnetic material.When the temperature exceeds Curie temperature,materila will beco me a paramagnetic material.Therefore,the magnetic field can't influence on the liquid metal,so bulge morphology without changing.?8?The active element S influence the molten pool convection,in the processing surface coa ting a layer of 5um diameter sulfur powder for laser texuring.Although crater morophology did not appear,forming ellipsoid shape.And,long and short axis is inconsistent between every bulges.Thisphenomenon confrim that the S element does have an impact on metal liquid convect ion in the experiment.