Analysis of laser cutting parameters with finite element method

In history of science, development of laser has been an important chapter. History of laser technology began with Albert Einstein in 1917. Stimulated emission concept which is utilized in lasers, was developed by Einstein. The word " laser" stands for " Light Amplification by Stimulated Emission of Radiation" The light emitted by a laser is electromagnetic radiation. Properties of laser light specify the application area of lasers. These properties are monochromaticty, directionality, the spatial and temporal charastics of laser beams, coherence properties, radiance, the capability to focus to a small spot, very limited heat affected zone occurrence, high efficiency and the high power levels. Conventional lasers are well developed and widely available. These inculude gas lasers such as helium-neon, argon, CO2, solid state lasers like Nd: YAG and semi conductor lasers. Although a laser was a fragile device, requiring considerable care and maintance. At the present time, lasers became durable, reliable and reasonably economical to operate. Intense pulses of light energy produced by laser leads to many applications involving heating, melting and vaporization. Lasers used in metal working is able to deliver very high values of irradiance to a workpiece. The knowledge of physical processes that occur during the interaction of high power laser radiation with materials is important to understanding the capabilities and limitations of laser based material processing. When laser radiation strikes a target surface, part of laser beam is absorbed and part is reflected. The energy that is absorbed begins to heat the surface. The heating effects due to absorption of high power beams can occur very rapidly. The surface quickly rises to its melting temprature. Laser – induced melting is of interest because of welding applications. Material processing refers to a variety of industrial operations. In these operations the laser operates on a workpiece to modify it, for example, by melting it or removing material from it. Some of the possible applications include welding, hole drilling, cutting, trimming of electronic components, heat treating, brazing and alloying. Properties of laser light that enable material processing applications are its collimation, radiance, and focusability. Because of these properties, laser light can be concentrated by a lens to achieve extremely high irradiance at the surface of a workpiece. Lasers may be used to cut or shape a wide variety of materials. Cutting means vaporization of material along a line, so as to separate the workpiece into separate parts. This method generally is used to cut plastic, wood, paper and ceramic metarials. Because these materials do not have observable melting point. For metal materials cutting means melting of metarial with high efficency. In this study, firstly literature research including generation of laser beam , transfer of the laser beam from resonator to workpiece and laser beam properties, optical properties and interaction of laser radiation with materials is done. After then laser technology efficently used manufacturing processes are investigated. Among this process laser cutting process was focused on. When laser cutting method investigated particularly, lots of parameters affect cutting process considered and the most important parameters are defined as material properties, workpiece thickness, cutting velocity and cutting power. After investigated effect of this parameter and a 3D laser cutting model generated by using finite element method (FEM). The aim was to develop cutting surface quality and define the parameter values to obtain an efficient cutting process. Different sheet metal thickness is used in industry because of different requirements. In this study, 1 mm and 2 mm material thickness is used as industrial demand. If only material thickness is changed (fix cutting velocity, cutting power and same material), cutting process is completed without problem for thiner work piece. Under same condition, Some problems can be observed for thick work piece cutting. Cutting surface angle can be bigger than thiner work piece cutting surface angle or laser can not be completely removed material. To solve these problems cutting power or cutting velocity can be increased. But at that time, heat affected zone and removed material will be increased. In this study, only 2 different metarial thickness is used to compare each other. But analysis model can produce sufficeient results to support different metarial thickness. Another important parameter which used in analysis is laser cutting velocity. Cutting velocity must be fastest to increase efficiency and reduce unit cost. High velocity also decerase heat effected zone. All parameters are choosen as fix, only cutting velocity is changed from 1 m / min to 2 m / min for some analysis to understand effect of the cutting velocity. If cutting velocity is increased, heat affected zone and removed material will be decreased. But higher cutting velocity has bad effect on the cutting surface angle. Cutting velocity very important parameter on the laser cutting performance. To decrease cutting time, higher cutting velocity should be choseen. But cutting surface angle should be taken precaution. In this study, only two different velocity is used, but model can support different cutting velocities which used in the industry. Laser cutting power is another important parameter. It affects efficency, unit cost , heat effected zone and cutting angle directly. All parameters are choosen as fix, only cutting power is changed from 1000W to 2000W in some analysis to show affect of cutting power. Only According anaysis, when higher laser power is used, removed material and heat affected zone are larger than other. To increase efficency and reduce removed material value, lower cutting power level should be used. But lower cutting power increases angel on the cutting surface. So an optimisation is necccesary between efficiency and cutting angle. 1000W and 2000W cutting powers are used to define effect of cutting power. But different cutting powers can be used in this model. Extra analysis (8 different analysis) are performed from 100 W to 2000W to show model capability. And model solved all of the analysis with sufficient results. Different materials are used in the industry as a machine part. So laser cutting process must be applicable method for different materials to support industrial demands. Otherwise laser cutting method can be used for only special purpose applications. St-37, AISI304 and Al 2024 are the most preferred materilas in the industry. St-37, AISI 304 and Al 2024 materials have been used to analysis for investigate material effect on the laser cutting operation. Those materials have different melting temprature, coefficient of thermal conduction, specific heat and density. According to analysis results, material heat conductivity, density, specific heat cutting surface have been directly affected on the heat affected zone and material cutting ratio. Additonal analysis are performed to understand effect of power change on the cutting surface angle. Analysis are repeated for 100 W, 250 W, 300 W, 400 W, 500 W, 900W, 1000 W and 2000 W. All of the other parameters were same to compare analysis results. When we compare analysis results, effect of the cutting power is observed clearly.