Finite element modelling of abrasive waterjet milled footprints

It is well-known that it is difficult to perform controlled-depth in abrasive waterjet (AWJ) milling, due to the dependency of the milled footprint not only on the jet kinematic parameters (e.g. jet traverse speed) but also on the jet energy parameters (e.g. pressure, abrasive mass flow, etc.). In this paper, an attempt has been made for modelling, simulation and validation of the AWJ footprint working in controlled depth (i.e. milling) mode at various jet traverse speeds and pump pressures at 90°incidence angles by using the finite element (FE) method. The proposed model is validated by comparing the material erosion rates and the profiles of the milled kerfs obtained by FE simulation to those generated from the experiments. The current model also simulates the effect of mass flow rate of the abrasive particles as well as the traverse rate of the AWJ plume across the workpiece. The abrasive particles (i.e. garnet) are modelled with various non-spherical shapes (rhombic, triangular and trapezoidal) and sharp cutting edges, while the workpiece material modelled is a titanium based superalloy (Ti-6Al-4V) extensively used in the aerospace industry. The workpiece material is modelled as elastic-plastic with a Johnson-Cook failure criterion, while a tensile failure criterion is used for the impacting garnet particles rather than considering them as rigid. The particles are arranged in a Gaussian distribution above the target surface to control the shape of the eroded footprint. To emulate the real interaction between the AWJ plume on the target surface, the material description in the FE model incorporates the effects of strain rate sensitivity, adiabatic heating and friction during the particles-workpiece interaction. The proposed modelling approach is capable of simulating the maximum depth of the AWJ footprint and the erosion rate at an acceptable level of accuracy (errors < 10%) when compared with experimentally generated data. Considering the possible sources of errors within the experimental data (e.g. non-constant traverse speed, particle flow and shapes), the results of this research are encouraging.