Keywords: cutting, drilling, FE modelling, cutting forces, material model, damage material modelling.

The paper presents a finite element (FE) model of the process of drilling. The paper takes into account all aspects related to the technique of a modelling cutting process: boundary conditions (cutting velocity, speed of feed, the way of the supporting work material); material models of the workpiece and tool; a model of friction; heat generation (which is due to plastic deformation and friction forces); and heat transfer. The paper shows that the feed force component and the cutting torque are the main goal of the simulation results.

The FE modelling of the drilling process was performed using the explicit code Abaqus which offers the possibility of making a thermomechanical simulation. This permits mechanical events and heat transfer to be combined. The modelling includes the modelling of heat generation due to plastic work and friction forces.

The paper shows a chip formation process during the cutting of carbon steel. This steel was modeled as an isotropic elastic-plastic material. The Young's modulus changes with temperature was used in the simulation. Flow stress was calculated according to the Johnson-Cook equation [1,2], giving a description of flow material as a function of strain, strain rate and temperature. Similar to mechanical properties, thermal properties of the work material (conductivity of heat, specific heat) depending on temperature were specified as well.

The model considers also an initiation of material damage when losing material cohesion. For that purpose d_i coefficients connected with the Johnson-Cook equation were used. These coefficients take into account the state of material (strain, strain rate, temperature and a relation between normal stress and reduced stress) when the carrying loads start to loose capacity.

In Abaqus the state of material after the onset of the damage can be described in terms of an effective plastic displacement or energy dissipated during the damage evolution. In this paper a description related to the dissipated energy was used [3].

The research has shown that the friction coefficient in cutting conditions depends on the normal stress between surfaces being in contact (rake face and chip) [4]. It has been shown that the friction coefficient decreases exponentially when normal stress increases. According to this study a friction model was used in the simulation.

As a result of applied simulation there were have been obtained values of feed force component and torque when drilling.

The modelling presented demonstrates the possibility of determining the field of temperature, stress, strain etc. of chips and workpiece. The tool is modeled as a rigid body with heat transfer.

1

S.P.F.C. Jaspers, J.H. Dautzenberg, "Material behaviour similar to metal cutting: flow stress in the primary shear zone", Journal of Material Processing Technology 122, 2002. doi:10.1016/S0924-0136(01)01228-6

2

H. Zhao, "A constitutive model for metals over a large range of strain rates. Identification for mild-steel and aluminum sheets", Materials Science and Engineering A230, 1997. doi:10.1016/S0921-5093(97)00024-5

3

ABAQUS 6.7 documentation.

4

M.F. Polietika, "Interaction on cutting tool areas", Maszinostrajenie, Moscow, 1969, (in Russian).

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