آناليز سه‌بعدي برشكاري با ليزر متحرك CO2در حالت پالسي به‌كمك روش اجزا محدود

3D FINITE ELEMENT ANALYSIS OF CUTTING WITH A MOVING CO2 PULSED LASER

در اين مقاله يك مدل اجزا محدود سه‌بعدي بر پايه‌ي معادلات انتقال حرارت گذرا، براي شبيه‌سازي ماشين‌كاري با ليزر CO2 به‌طول موج ?m 6/10 مورد استفاده قرار گرفته است. موج ليزر به‌صورت گوسي فرض شده و محاسبات بر روي ماده‌يي از جنس فولاد St.37 براي بررسي تعيين نرخ برداشت ماده و توزيع حرارت در جسم انجام شده است. ليزر در حالت پالسي در نظر گرفته شد و عمق شيارها براي مقادير مختلف قدرت، سرعت و همچنين فركانس پالس ليزر تعيين ‌شد. براي شبيه‌سازي برداشت ماده از روش تولد و مرگ المان استفاده شد. در نهايت نتايج حاصل از شبيه‌سازي با نتايج ساير محققين مورد مقايسه قرار گرفت. تطابق جواب‌ها نشان‌دهنده‌ي صحت شبيه‌سازي و قابليت اطمينان روش اجزا محدود در مقايسه با ساير روش‌هاي به كار گرفته شده براي شبيه‌سازي برشكاري با ليزر است.

Laser beam cutting has received increased attention for a wide variety of applications in industry due to its excellent cut quality with high productivity and flexibility. High intensity laser beams can be directed to narrow regions to instantly melt material with very small heat affected zones. This ability to cut instantly with an extremely narrow laser beam distinguishes it from other cutting methods. The key to success in precision cutting by laser depends on many factors, such as laser power, cutting speed and pulse frequency. Mathematical modeling is a useful tool to investigate the range of processing parameters that leads to successful cutting. In the present study, a 3D finite element model using unsteady heat transfer equations for simulation of the laser cutting process has been developed, using a CO2 laser with a 10.6 ?m wavelength (TEM00) in a pulsed mode. The analysis allows the investigation of groove depth for a variety of laser powers, cutting speeds and pulse frequency. The heat source modeling is considered to be the most important aspect of the cutting thermal analysis. In order to simulate the heat distribution and flow in the cutting direction, the laser beam was modeled as a three-dimensional moving heat source. The heat flux assumed to be in Gaussian mode and was implemented into the FE code by developing a FORTRAN subroutine. The laser that is employed for this study is 0.15 mm in beam radius at an intensity range of 200-1000 W and repetition rate of 5000-10000 Hz. The pulse duration is 10 ?s and cutting speed varies from 1 to 2 m/min. The target is a supposed rectangular cubic and only half of the target is simulated because of the axial symmetry of the problem. The calculation for prediction of material removal rate and temperature distribution in the target was done on St.37 steel. In order to define the thermal behavior of the material, phase change, enthalpy, internal energy per unit mass and its variation with temperature and spatial gradients of temperature, the ABAQUS subroutine was employed. Thermal properties of the material were assumed temperature dependent, and the birth and death technique of elements was employed for simulation of material removal. Thus, during the cutting process, if the temperature of any element is greater than the melting point, then, the element is deactivated and does not participate in the calculation. The temperature of the remaining material is corrected to take into account the latent heat of fusion. The applicability of the model under consideration was verified by comparing the result of simulation with experimental data in the relevant literature. The results show the validity of the simulation and applicability of the developed finite element model for modeling of the laser cutting process.