Research On Process Of Penetration Welding In Several Fe-C Auto Materials With High Power CO₂ Laser

High power CO2 laser in Lulea University of Technology of Sweden and thatimported from Germany with three-direction, five-axis laser machine (maximumoutput power 6KW and 3KW respectively) were used to weld Fe-C auto materialsincluding thin steel plate with and without zinc coating for car body, thick steel forrear bridge case with advanced welding method such as single-beam welding,double-beams welding, laser welding with wire and hybrid, laser-MIG welding,process of laser welding of Gear materials, microstructure and properties of weld,influence of zinc coating on Zinc-coated steel plate of laser welding, mechanismsof laser welding with wire, feeding, were studied. The method for fast optimizingparameters of laser welding was investigated. The feasibility of laser welding ofgears for first rate in rate charging case was shown, followed by heat treatment.The laser welding was successfully applied to process top roof of heave trackdriving room in spinning off. In addition, austenite transformation as well as temperature field numericalsimulation and testing compare of laser welding under laser rapid heating, based onequilibrium and non-equilibrium original structure of steels were investigated. Thestudy on development and application of laser processing technology in our country,practical problems and their solving ways were also investigated through theapplication of laser remelting of brake shoes made of cast iron as well as theadoption project of "ready-engineering". It was showed by theoretical study that there are influences of joint shape, jointgap and MIG parameters variations on weld shape, effect throat of weld in hydridelaser MIG welding. Laser welding with wire feeding apparently dramaticallyincreases ability of "overlap" in laser butt welding. The mechanism of laserwelding with wire feeding is different from laser butt welding, but it is the same ashydride laser-MIG welding. The laser welding processes can be stimulated andoptimized by using single steel plate with and without zinc coating at a high speed.Like butt welding, gas holes will be produced, leasing to fracture of weld ifparameters are not correctly selected. There is a sensitive region of laser power andwelding rate for gas holes formation. Double beams welding with transversemovement has better ability for joint gap filling than single beam welding does.However, this ability will be decreased when the laser beam is deviated from thecentre line of weld.There are two ways for austenite formation in non-equilibrium original structuresteel, i.e. needle-like austenite (γα′) and ball-like austenite (γg). γα′ nucleis inoriginal α′ plate boundary at the point over As in the forms on non-diffusion anti-transformation, followed by diffusion growth and incorporated, showingmicrostructure hereditary. γg austenite is diffusively nuclei and grew. γg isdominately formed on crystal grain boundary and then followed by nuclei in theboundary of α′ plates and the boundary of α′ and carbide. The nucleationtemperature of γα′ is higher than that for γg.The temperature field of laser welding was numerically modulated overlap usingGass distribution surface heating source and double ellipsoid heating source model.The results are good in agreement with profile of welding pool obtained in practicallaser welding. It is shown by practical application that laser welding can be utilizedto weld covering part of heave track with the charge shape. As a result, the weldedheave track is characterized with high precision, short testing period, low cost. Thisprocess can be used to weld covering parts of heave track with the charged shapefor production in a small quantity by adopting available hardening tools for laserwelding with soft three-direction.The gears for first rate in rate charging case after heat treatment can be weldedby laser through protection of weld butt during carbonizing. The welded gears areapplicable, processed with suitable parameters of laser welding: laser powerP=2.8KW～3.0KW;welding rate V=2.5m/min～2.8m/min;focus distance △ F=-1mm～0mm;N2 protection with flowing amount of 8L/min～12 L/min, flow fromside.Laser remelting technology was used to solve problem of low hardness ofCA1092 brake shoes which cannot satisfy the requirement of standard. The wearresistance of laser-treated parts is increased by a factor of over 3 times comparedwith that used before.