Optimization of stir casting and drilling process parameters of hybrid composites

Abstract

AA2219 alloy is widely used in aerospace and automobile applications, wherein the properties can be enhanced with 15% wt. of B4C reinforcement particles. Assembly task in aerospace application requires drilling millions of holes, and it is often challenging to obtain good-quality drilled holes due to the presence of hard B4C particle reinforcements. The self-lubricating capability of molybdenum disulfide (MoS2) and Graphene (Gr) materials was used as secondary reinforcements to improve the drilled hole quality characteristics. The stir-casting route fabricates the hybrid composites (AA2219 alloy/B4C/Gr/MoS2). The hardness and wear resistance properties of hybrid composites are affected by the influencing process variables such as percent reinforcement of Gr and MoS2, stirring speed, and pouring temperature. Taguchi L9 matrix is used for experimentation and performs statistical analysis. All stir-casting variables are found to make significant contributions toward hardness and wear resistance. The limitation of the Taguchi method to solve multiple objective optimizations is solved by applying Data Envelopment Analysis Ranking (DEAR) method. A DEAR method determined optimal conditions (Gr and MoS2: 1.5 wt%, stir speed: 400 rpm, and pouring temperature: 760 °C) resulted in a reduced wear rate of 1.65 × 10−3 mm3/min and 128 HV hardness in hybrid composites. The hybrid composites were prepared for the determined optimal stir casting conditions. Drilling experiments were carried out to analyze the variables such as feed rate (FR), drilling speed (DS), and drill tool material (DM): high-speed steel: HSS, carbide: C, and coated carbide: CC that affect the hybrid composite hole quality characteristics such as burr height: BH, material removal rate: MRR, and thrust force: TF. A DEAR method determined optimal drilling conditions (FR: 0.25 mm/rev; DS: 20 m/min; DM: coated carbide drill tool) resulted in 645 mm3/min of MRR, 2.95 kN for TF, and 0.16 mm for BH, respectively. The self-lubricating capability of Gr and MoS2 reinforcement particles in hybrid composites ensures excellent composite properties and drilled-hole quality characteristics. Taguchi and DEAR methods employ simple mathematical steps which can be used by novice industry personnel to perform optimization for other output characteristics.