Abstract
Inconel 718 (IN718) is a precipitation hardened nickel-base super-alloy exhibiting high strength and good corrosion resistance at elevated temperatures and on the downside; it is characterized by poor machinability. Abrasive water jet (AWJ) process offers a potential method to machining difficult-to-cut materials such as IN718. The present work investigates the influence of AWJ parameters on surface roughness, topography, depth of cut, and residual stress when milling IN718. Surface characterization was conducted through 3D optical microscopy and SEM techniques. Residual stresses were measured in longitudinal and transverse directions with respect to the machining path using X-ray diffraction (XRD) technique. The obtained results showed that milled surfaces have a homogeneous texture with embedded abrasive particles and high surface roughness. AWJ process introduced high compressive residual stresses with similar order of level in both directions (X and Y). In addition, it was observed that jet pressure is the most influencing parameter on roughness and depth of cut, whilst traverse speed and step-over distance had a significant effect on the residual stress. Based on the experimental analysis, an empirical model to predict the depth of cut was proposed. The validation of the proposed model has shown around 5% error in the predicted and actual pocket depth.
Highlights
Nickel-based super alloys are widely used for aircraft engines, gas turbines, and in industries like petrochemical and oil refineries
In the works conducted by Flower et al and Gupta et al [13, 14] it was shown that the increase in abrasive particle size favors the increase in the material removal rate; it leads to degradation of machining quality giving a very poor surface roughness
When milling is conducted with conventional cutting tool, the average roughness surface roughness (Sa) reported is around 1 μm when machining with new tool and up to 3.9 μm when machining with a worn tool
Summary
Nickel-based super alloys are widely used for aircraft engines, gas turbines, and in industries like petrochemical and oil refineries. AWJ is characterized by a large number of process parameters [16], viz., jet pressure, traverse speed, abrasive flow rate, abrasive grit size, stand-off distance, step-over distance, nozzle diameter, orifice diameter, and length of the focusing tube. These parameters influenced the characteristics of the machined surface, for example, in the work conducted by previous studies [17, 18], when machining stainless steel, authors proved that the impact of abrasive flow rate as well as the vibration phenomenon that occur during the cutting process affect the machining quality. To counter this problem, the works conducted by Xavier et al and Hejjaji et al [19, 20] recommend a medium mesh size of (#120) abrasive particles to strike a balance between surface quality and material removal rate
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