High Strength Temperature Resistance Research Articles

Generation of high aspect ratio complex micro-features by micro-electrochemical milling employing novel flushing technique

Fabrication of high aspect ratio (HAR) complex micro features on high strength temperature resistant (HSTR) alloys is challenging by any conventional or non-conventional machining methods. In this study blind, HAR and complex micro features have been fabricated by micro electrochemical milling (MEM) on HSTR Cobalt alloy (Haynes-188) introducing a new strategic approach with novel flushing technique which could get rid of the need of pulsed DC power supply. Multiphysics simulation of the rotating micro-tool at different rpm and its impact on effective sludge removal has been analyzed and verified experimentally. In this study, most influencing parameters of MEM like voltage, feed rate, rpm of tool and milling layer depth have been selected to investigate their effects on the machining responses like width overcut, machined depth and surface roughness on Haynes-188 alloy. Comparison has also been made with constant and pulsed DC power source to know the influence of these process parameters on the MEM responses. Finally, several linear and non-linear blind, HAR (AR > 11) and intricate micro features have been fabricated successfully on cobalt alloy at the most suitable parametric combination, i.e., 7.5 V of machining voltage, feed rate of 0.3 mm/min, and tool rotation of 750RPM with 0.5 M of NaNO3 electrolyte.

Parametric optimization of process parameters for Electric discharge Machining of Tungsten carbide (93% WC and 7%Co)

Abstract Nowadays there is a huge demand of High Strength Temperature Resistance (HSTR) alloys such as titanium, carbide, nimonics and ceramics in aerospace, defence and electronics. Among these alloys machining of tungsten carbide alloy is of interest, because of its numerous applications. Complex shapes of tungsten carbide are not generally made by traditional manufacturing process. To machine tungsten carbide with high accuracy, non-traditional machining process like Laser beam machining, Electron beam machining and Electrical discharge machining are a proper choice. In the present paper, the authors have machined Tungsten carbide (93% WC and 7%Co) with copper electrode. The machining is performed on EDM MODEL 500 X 300 ENC with VELVEX EDMVEL-2 as dielectric oil. The 17 experiments are carried out based on RSM (Box-Behnken) method. Further, in order to find the optimum combination grey relational approach is used. The results showed that pulse-on-time of 40μs, pulse-off-time of 2μs and current of 8A are optimum combination for machining of Tungsten carbide (93% WC and 7%Co). Lastly, the confirmation experiment has been conducted.

Problematic areas in micro-electrochemical milling of HSTR alloys

Micro-electrochemical milling has capability to fabricate intricate micro-features for fulfilling the rising needs of modern manufacturing industries. Electrochemical milling is an advanced version of the ECM process, and micro-electrochemical milling is just a scaled-down approach of it. Due to the formation of a passive oxide layer on the machinable surface, electrochemical dissolution of titanium and its alloy is very much difficult and it is much more challenging with this downscaled approach. Since the last few years, researchers are trying to get the best solution for successful machining of different high-strength temperature-resistant (HSTR) alloys, e.g. titanium, nickel and cobalt alloys, etc. In this research, an attempt has been made to identify the issues that arise during micro-electrochemical milling of three different HSTR alloys which are now-a-days extensively used in the modern manufacturing industries. Furthermore, this study also deals with the best possible remedial approaches for minimizing these problems. Finally, considering all the problematic areas and their best possible remedial approaches in this study, high aspect ratio (> 10) 3D micro-features have been successfully fabricated on HSTR alloys, e.g. nickel (Nimonic-263) and cobalt alloy (Haynes-188) at the most suitable parametric combination of 7.5 V of constant DC voltage, 0.4 mm/min of feed rate and 750RPM of tool rotation.

Generation of Stepped Profiles on Ti6Al4V by Electrochemical Milling

Generation of accurate complex-shaped products on various high-strength temperature-resistant (HSTR) alloys such as titanium and nickel alloys is a key feature for many kinds of machine parts widely used in diverse industries starting from biomedical to defence industries. Being free of tool wear, thermal stresses and residual stresses, electrochemical machining has great potential of machining those HSTR metal structures. The process of EC milling is similar to conventional ECM, where the material is removed by a simple geometric tool following a predefined path in a layer-by-layer fashion. EC milling avoids complex electrode design which is often a burden in sinking ECM. In this paper, attempts have been made to investigate the influence of different process parameters on various performance characteristics of EC milling of Ti6Al4V by generating stepped profiles, and then, optimization of process parameters have been done using Taguchi and grey relation analysis (GRA). Experiments were conducted based on Taguchi’s L27 orthogonal array with five important process parameters, i.e. electrolyte concentration, milling layer depth, feed rate, frequency and duty ratio. From analysis of variance, it was observed that electrolyte concentration and milling layer depth are the significant process parameters that mostly affect the responses. The experimental results show that for successful machining of Ti6Al4V by EC milling process, the optimal parametric combinations are 0.5 M electrolyte concentration, 0.15 mm milling layer depth, 0.04 mm/s feed rate, 5 kHz frequency and 50% duty ratio; and milling layer depth has a major influence on all the responses of EC milling of Ti6Al4V.

A Review on Copper and its alloys used as electrode in EDM

In 21st century, the demand of HSTR (High Strength Temperature Resistant) material is steadily increasing due to its numerous industrial applications. These materials are machined efficiently by Electro discharge machining (EDM) process. EDM process largely depends upon the electrode used, as different electrode material will have different properties and these properties affect the performance of the EDM process. Thus the selection of proper electrode material plays a very important role in EDM process. Different electrodes frequently used are Copper, Brass, Graphite, Copper Tungsten etc. In the present paper a detail study has been done over different copper and copper based electrodes used in EDM process.

Experimental investigation into electrochemical milling of Ti6Al4V

Electrochemical milling (EC milling) avoids complex electrode design which is often a burden in sinking ECM. In this process material is removed by a simple geometric tool following a predefined path in a layer-by-layer fashion. High strength temperature resistance (HSTR) material like Ti6Al4V is extensively used in different field starting from the defense to bio-medical industry. Study of comparative effects of different electrolytes on various performance characteristics on titanium alloy, is the soul of this paper. Commencement of making simple shape grooves to complex shape i.e ‘L’ shaped feature was machined by means of electrochemical milling process with layer by layer fashion. In each layer, the tool was controlled to move along a predefined path with a multi downward step. ‘L’ shaped features were machined on Ti6Al4V using three different electrolytes by varying feed rates and frequency followed by the corresponding effects on various performance characteristics were studied. It was observed that NaCl(0.5M)+NaNO3(0.5M) mixed electrolyte gave better result compare to the other two electrolyte as far as accuracy and surface finish of the features were concerned. It was also observed that performance characteristics other than depth and surface finish was improved with increasing feed rate and frequency up to a certain limit and after that short circuit was occurred. After analysing all the graphs and figures, it was concluded that to achieve better accuracy and surface finish, type of electrolytes, feed rate and frequency are the major important factors of EC milling.

Selection of EDM Process Parameters Using Biogeography-Based Optimization Algorithm

Amongst the nontraditional machining processes, electric discharge machining (EDM) is considered to be one of the most important processes for machining intricate and complex shapes in various electrically conductive materials, including high-strength, temperature-resistant (HSTR) alloys, especially in aeronautical and automotive industries. For achieving the best performance of the EDM process, it is imperative to carry out parametric design which involves characterization of multiple process responses, such as material removal rate, tool wear rate, surface finish and surface integrity, heat affected zone, etc., with respect to different machining parameters, like peak current, pulse-on time, duty factor, gap voltage, and dielectric flushing pressure, followed by parametric optimization of the process. This article focuses on the application of the biogeography-based optimization (BBO) algorithm for single and multiobjective optimization of the responses of two EDM processes. The optimization performance of the BBO algorithm is compared with that of other population-based algorithms, e.g., genetic algorithm (GA), ant colony optimization (ACO), and artificial bee colony (ABC) algorithm. It is observed that the BBO algorithm performs better than the others with respect to the optimal process response values.

Selection of non-traditional machining processes using analytic network process

Non-traditional machining (NTM) processes are now being widely used to generate intricate and accurate shapes in materials, like titanium, stainless steel, high strength temperature resistant (HSTR) alloys, fiber-reinforced composites, ceramics, refractories and other difficult-to-machine alloys having higher strength, hardness, toughness and other diverse material properties. Generation of complex shapes in such materials by the traditional machining processes is experienced to be difficult. For effective utilization of the capabilities of different NTM processes, careful selection of the most suitable process for a given machining application is often required. Selection of the best suited NTM process for a work material and shape feature combination requires the consideration of several criteria. In this paper, an analytic network process (ANP)-based approach is proposed to select the most appropriate NTM process for a given machining application taking into account the interdependency and feedback relationships among various criteria affecting the NTM process selection decision. To avoid the difficult and time consuming mathematical calculations of the ANP, a computer program is also developed in Visual Basic 6.0 with graphical user interface to automate the entire NTM selection decision process. It simply acts as an ANP solver. The observed results from the ANP solver are quite satisfactory and match well with those obtained by the past researchers.

A combined TOPSIS-AHP-method-based approach for non-traditional machining processes selection

With the introduction and increased use of newer and harder materials such as titanium, stainless steel, high-strength temperature-resistant (HSTR) alloys, fibre-reinforced composites, and ceramics in the aerospace, nuclear, missile, turbine, automobile, tool, and die-making industries, a different class of machining processes has emerged. Instead of employing the conventional cutting tools, these non-traditional machining (NTM) processes use energy in its direct form to remove materials from the workpiece. Selection of the most suitable NTM process for machining a shape feature on a given work material requires consideration of several factors. A combined method using the ‘technique for order preference by similarity to ideal solution’ (TOPSIS) and an analytical hierarchy process (AHP) is proposed to select the most appropriate NTM process for a specific work material and shape feature combination, while taking into account different attributes affecting the NTM process selection decision. This paper also includes the design and development of a TOPSIS-AHP-method-based expert system that can automate the decision-making process with the help of a graphical user interface and visual aids. The expert system not only segregates the acceptable NTM processes from the list of the available processes, but also ranks them in decreasing order of preference. It also helps the user as a responsible guide to select the best NTM process by incorporating all the possible error-trapping mechanisms.