Cutting process is one of the most important metal forming processes. Utilizing guillotine cutting process, Reduces the required process force and consequently required mechanical work. Cutting processes modeling needs advanced material models like damage mechanics and fracture mechanics model. Today, damage mechanics model is an efficient tool for successfully simulation and evaluation fracture behaving for ductile materials. Damage mechanics models are capable to simulate the crack growth and propagation and cavity integration using continuum mechanics. Applying damage mechanics model on the metal forming processes analysis gives more precise estimations and prediction of the critical process forces, cracking commencement and failure points, respectively. Johnson-Cook damage model is one of the most widely used models in ABAQUS software. This model is one of the ductile damage models which can predicts ductile fracture. In this model, the fracture strain considered as a function of triaxial stress, strain rate and temperature. Strain rate dependent models used for relatively fast processes like dynamic processes as well as metal forming processes. Since the target of this study is to simulate the cutting process by Halden cutting machine which applied in cold rolling part of Fulad e Mobarake Complex, Isfahan, Iran, which its cutting process is relatively fast, damage mechanics model has been chosen for required process force estimation. In this study, after mentioning studies done about well-known damage mechanics models and their applications, Johnson-Cook damage model is discussed. For applying this model, at the first step the input parameters for the simulation of cutting with Johnson-Cook model has been determined. Then In order to determine the parameters needed in the Johnson-Cook damage simulation, special experiments designed and conducted on St12. after simulating the guillotine cutting proce and calculating the process force, the effect of some parameters including angle and radius of blade has been studied on the required force .Comparison between the standard tensile test results obtained from laboratory tests and simulations by these determined coefficients, shows the accuracy of these extracted coefficients. Also, the results shows that the blade angle increasing lowers the required process force and radius increasing raises it. Applied torque determining on every one of Halden Cutting machine’s gears based upon cutting force in critical condition as well as plate buckling evaluation due to difference between blades’ speed and Mandrel speed in Halden cutting machine which is one of the major machine’s challenges, are other problems discussed in this study. Keywords : Damage mechanics, Guillotine, Johnson-Cook damage model, Fracture strain, Triaxiality stress, Damage parameters, Buckling