Experimental investigation of suspension-type abrasive water jet machining of nitrile rubber for positive displacement motor applications

Abstract

The lightweight elastomers (such as nitrile rubber) frequently used in the Positive Displacement Motor (PDM) stator assembly are subjected to harsh environmental conditions. These elastomeric components are manufactured by primary casting/shaping methods, followed by secondary manufacturing/machining processes. The production of intricate shapes/sizes in single or batch-size elastomeric components using primary casting methods requires a customized mould to fulfil the requirement of sudden breakdown conditions, which is uneconomical. It necessitates an alternate production method that can satisfy the need for the elastomeric component at the stage of failure. The current research focuses on the possibility of producing nitrile rubber components using a non-conventional machining method, Suspension-type Abrasive Water Jet Machining (AWJM), suitable for batch production with better dimensional stability and versatility in shape/size. This work presents the experimental investigation of Suspension-type AWJM of nitrile rubber specimens (15 mm thick) using a custom-designed Tungsten Carbide (WC) nozzle under room-temperature condition. The top surface of the machined slot is analyzed to determine the mineral composition and abrasive particle embedding through Energy Dispersive Spectroscopy (EDX) and Backscatter Electron (BSE) detector. The Taguchi Orthogonal Array (OA) is employed to study the effect of the process parameters (Water Jet Pressure (WJP), Traverse rate (V_f), and Stand-Off Distance (SOD)) on the performance parameters (Kerf Taper Ratio (KT_R), and Material Removal Rate (MRR)). The Analysis of Variance (ANOVA) is applied to check the statistical significance and percentage contribution of each process parameter on the performance of Suspension-type AWJM. The uniformity in the geometry of the machined slot is analyzed by the waviness patterns observed in the profile images of the cut specimen. The analysis of the EDX results reveals the presence of Manganese (Mn) and an increased percentage of Silicon (Si) particles near the top surface of the machined slot. The SOD influences KT_R the most, whereas V_f highly influences MRR. It is observed that the waviness pattern is minimal at high WJP experimental runs. The outcome of this research work provides a quick and economical method of producing the PDM bushings instead of the casting/moulding method.