Design and Optimization Process Analysis of Aluminum Hybrid Composites

Abstract

ABSTRACT Aluminum Metal Matrix composites (AMMC) refer to a relatively recent class of aluminum alloy-based composites having an emphasis on lightweight and high performance. Compared to other MMC composites, AMMC has advantages like improved strength, higher stiffness, high-temperature properties, wear resistance, increased damping capacity coupled with a reduction in density. Applications of AMMC encompass a wide range of industrial components for automobile, aerospace, nuclear and electronic industries due to their above mentioned attractive properties. In this context, reinforcing the AMMC with suitable particulate materials such as chromium carbide (Cr3C2), an abrasive and graphite (Gr), a soft lubricant, can be advantageous over reinforced aluminum alloy due to their improved property combination, particularly high specific strength and elastic modulus coupled with good machinability, enhanced hardness and wear resistance. Hence, an attempt has been made in the present investigation to fabricate LM4/Cr3C2/Gr hybrid aluminum composites and to study their microstructure, hardness and machining characteristics. Al LM4 alloy reinforced with Cr3C2 / Gr particles were fabricated using the stir casting method since it is an economical and welltested fabricating technique for particulate matrix composites. LM4 alloy was selected as the matrix material and reinforced with Cr3C2 in varying amounts (3, 6, 9 and 12 wt. %) along with constant 3 wt. % Gr to produce hybrid composites. Optical Microscopy (OM) studies of the hybrid LM4 composites revealed the uniform distribution of Cr3C2 and Gr in the matrix. Measured densities of aluminum, Cr3C2, and Gr respectively were 2.70, 6.68 and 2.26 g/cm3 , the overall density of composites increased with increasing Cr3C2 iv addition to the aluminum alloy matrix. The lowest density of the aluminum matrix composites was observed for LM4+3wt% Cr3C2+3wt% Gr composite. Machining of composites with good surface finish and minimum Cylindricity is essential for good product quality. Hence a conventional technique, namely drilling was used to study the machinability of the material with respect to Surface Roughness and Cylindricity. WEDM, a nontraditional technique was used to assess the MRR and Surface Roughness of the machined composite. The main objective of this research work is to carry out machining process following Central Composite Design method (CCD) to study the Surface Roughness and Cylindricity using uncoated carbide drilling tool and uncoated high-speed steel drilling tool, through Burr Height and Burr Thickness measurement as well as the nature of chip formed. Wire Electrical Discharge Machining (WEDM) of composites was carried out and MRR and Surface Roughness were analyzed. With reference to the drilling process, process parameter optimization was carried out taking into account the influence of the cutting parameters and the drill geometry. Optimization was performed to achieve minimum Surface Roughness (SR), Cylindricity (CY), Burr Height (BH) and Burr Thickness (BT) using process parameters including spindle speed, wt% of Cr3C2, feed rate and depth of cut. A detailed experimental plan based on the Design of Experiments (DOE) was adopted to minimize the number of experiments as well as reduce the cost and time of experimentation. Drilling experiments were performed as per the design matrix and corresponding Surface Roughness and Cylindricity values were obtained. v The experimental values were analyzed Minitab 17 software using ANOVA (Two-level factorial design) techniques, mathematical models, Response Surface Methodology (RSM), response optimization and composite desirability functions. Mathematical models were developed for Surface Roughness, Cylindricity, Burr Height and Burr Thickness using Response Surface Methodology (RSM). WEDM is one of the best machining methods for composite specimens because of its accuracy. ANOVA was used to identify the parameters having a significant influence on the chosen responses. The selection of optimum machining parameter combinations for obtaining desired MRR, Surface Roughness, and higher dimensional accuracy is a challenging task in WEDM due to the involvement of a large number of process variables. Hence, there is a need for research to establish a systematic approach to find out the optimum parameter combinations to achieve desired characteristics. This work attempts to develop an appropriate machining strategy for the WEDM machining of LM4 composites. The four important process parameters, pulse-on time (T-on), pulse-off time (T-off), peak current (A) and spark gap voltage (SV) were taken as input parameters while MRR and Surface Roughness were taken as the responses. Design of Experiments using Central Composite Design was employed for WEDM studies. Machined surface characteristics were analyzed by Scanning Electron Microscope (SEM) to get a better understanding of the machining characteristics of LM4 hybrid composites on machining using uncoated highspeed steel drilling tool, carbide drilling tool, and WEDM. v