Sivasrinivasu Devadula

Kerf profile generated by abrasive waterjet (AWJ) machining process has always been an interesting area as it dictates the quality of the part. However, due to the non-deterministic nature of the process, it is a challenging task to predict it. On the other hand, understanding and controlling the kerf profile in multi-layered structures (MLSs) is a further difficult task as various layers made of different materials respond to erosion in a different manner and results in a completely different kerf shape (barrel or x-shaped kerf profile) due to the material removal mechanisms dependency on the material property of the specific layers, jet divergence and position of specific layer. Therefore, it is important to understand and develop predictive models of resulting kerf profile in MLSs so that they can be used in controlling the accuracy of the resulting kerf which in turn dictates the final part accuracy. The attempts in this direction are very limited although some modeling efforts are reported in homogeneous materials (metals, ceramics). For the first time, an analytical model for predicting the kerf profile generated in MLS machining with AWJ was presented in this research work. Discretized form of Hashish model was used for determining depth of cut. The effect of jet divergence from the experimentally obtained values, upon passing through the upper layer has been considered. The developed predictive model was validated by the kerf shapes obtained from the experimental trials on metal-adhesive-rubber MLS. Kerf profiles obtained from the simulations have captured the resulted convergent-divergent (X-shaped) profile, while cutting metal-rubber laminate composite, effectively. Furthermore, the effectiveness of the proposed analytical model was demonstrated by generating the various kerf shapes generated at various jet traverse rates.

Abrasive waterjet (AWJ) milling is suitable for generating pockets in difficult-to-machine ductile materials as the material removal is through local erosion with the exertion of minimal forces. However, the surface generated is non-uniform. The surface quality characterisation based on 2D profile parameters is insufficient to characterise the whole-milled surface. In this work, a region-wise surface characterisation approach is proposed and validated on Al6061-T6 material. The varying depth at jet start/stop (region 1), and jet traverse direction change (region 2) are qualitatively analysed. Following this, relatively flat central surface (region 3) is quantitatively characterised by 2D/3D surface roughness and waviness parameters. From the qualitative analysis, the mean depth at region 1 and region 2 is observed higher than the mean depth at region 3. The quantitative analysis at region 3 reveals that the surface quality improved in terms of surface waviness by ten times at lower waterjet pressures (P) and by two times at higher jet traverse rates (vf). The surface roughness improved by 2.5 times at lower P, and roughness parameters found less sensitive to vf. Finally, from the results, it is concluded that the 3D characterisation with surface waviness as parameter suits better for AWJ milled surfaces.