OPTIMIZATION OF MACHINING PARAMETERS OF TITANIUM … · OPTIMIZATION OF MACHINING PARAMETERS OF TITANIUM ... which all possible combinations of k factors at all the levels are used

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OPTIMIZATION OF MACHINING PARAMETERS OF

TITANIUM ALLOY (GRADE 2) IN ELECTRO CHEMICAL

MACHINING PROCESS BY USING RSM METHOD

V.P.Krishnamurthy, E.R.Sivakumar, M.Manikandan

Department of Mechanical Engineering, Sasurie College of Engineering, Tirupur.

Abstract

Electrochemical machining (ECM) has inaugurated itself as one of the major other possible way to conventional methods for machining hard materials and complicated outlines not having the residual stresses and

tool wear. Electrochemical machining has vast application in automotive, Aircrafts, petroleum, aerospace, textile,

medical and electronic industries. Studies on Material Removal Rate (MRR) are of extremely important in ECM Use

of optimal ECM process parameters can significantly reduce the ECM operating, tooling, and maintenance cost and

will produce components of higher accuracy. This paper investigates the effect and parametric optimization of

process parameters for Electrochemical machining of Titanium alloy (Grade 2).

The process parameters considered are Current, Voltage, Flow rate, Gap and are optimized in consideration of

material removal rate and Surface Roughness.

Keywords - Electrochemical machining; Material removal rate; Design of Experiments; Response surface

methodology; process parameters; etc.,

Keywords: Electrochemical machining

1.Introduction

Electrochemical machining (ECM) was developed to machine difficult-to cut materials, and it is

an anodic dissolution process based on the phenomenon of electrolysis, whose laws were established by Michael

Faraday [1]. In ECM, electrolytes serve as conductors of electricity. The rate of machining does not depend on the

hardness of the metal. ECM offers a number of advantages over other machining methods and also has several

disadvantages:

Advantages: there is no tool wear; machining is done at low voltage compared to other processes with high metal removal rate; no burr formation; hard conductive materials can be machined into complicated profiles; work-piece

structure suffer no thermal damages; suitable for mass production work and low labour requirements.

Disadvantages: a huge amount of energy is consumed that is approximately 100 times that required for the turning

or drilling of steel; safety issues on removing and disposing of the explosive hydrogen gas generated during machining; not suited for nonconductive materials and difficulty in handling and containing the electrolyte [2].

* Corresponding author. Tel.: +91-9865461948; fax: +0-000-000-0000 .

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E-mail address:[email protected]

Applications: ECM is widely used in manufacturing for making moulds and dies; also used for making complicated shape of turbine blades and it is now routinely used for the machining of aerospace components, critical deburring,

Fuel injection system components, ordnance components etc.

The shaped tool (cathode) is connected to the negative polarity and the work-piece (anode) is connected to the

positive polarity. The electrolyte flow through the small inter-electrode gap, thus flushing away sludge and heat

generated during machining process.

EXPERIMENTAL SETUP AND TOOL DESIGN:

Experimental Objectives:

To study the material removal rate (MRR), surface roughness of ECM, it is necessary to identify and understand the factors affecting the responses. The factors effecting the responses have been studied by conducting

series of machining experiments using titanium alloy (Grade 2) as work-piece.

Titanium Alloy (Grade 2) is a medium-carbon low-alloy steel and finds its typical applications in the manufacturing

of automobile and machine tool parts. Give rise to certain problems in its machining such as large cutting forces,

high cutting tool temperatures, poor surface finish and built-up edge formation. This material is thus difficult to

machine. Schematic diagram of ECM is shown in Figure 3.1. The effect of the different process parameters such as

the voltage, feed rate, electrolyte concentration and electrode diameter has been studied and has been reported in the

following chapters.

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Experimental Setup:

The whole experimental conducted on Electrochemical Machining set up from Metatech Industry, Bangalore. Which is having input Supply of - 415 v +/- 10%, 3 phase AC, 50 HZ. Output supply is 0-300A DC at

any voltage from 0-25V and efficiency is better than 80% at partial and full load condition. The cable insulation

resistance is not less than 10 Mega ohms with 500V DC. And consist of three major sub systems which are being

discussed in this chapter. The set up consists of three major sub systems.

1. Machining setup

2. Control Panel

3. Electrolyte Circulation

Machining Setup:

This electro-mechanical assembly is a sturdy structure, associated with precision machined components, servo motorized vertical up/down movement of tool, an electrolyte dispensing arrangement, illuminated machining

chamber with see through window, job fixing vice, job table lifting mechanism and sturdy stand. All the exposed

components, parts have undergone proper material selection and coating/plating for corrosion protection. ECM setup

is shown in Figure.

ECM Setup 19

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Control Panel :

Through control panel we adjust the current (I), voltage (V), feed rate (F) and time (T) for duration of

experiment. The power supply is a perfect integration of, high current electrical, power electronics and precision

programmable microcontroller based technologies. Since the machine operates at very low voltage, there are no

chances of any electrical shocks during operation. Control Panel shown in Figure 3.3.

Control Panel

Tool Setup:

The purpose of the experimental investigation was to find out the Material removal rate, surface roughness

of plane work pieces made of Titanium alloy grade 2.

The tools were made up of copper. It is an abridged general view of the experimental system. The experimental

conditions are: the electrolyte is sodium chloride, the electrode gap between the tool and work piece is 0.1 to 0.3

mm, the work piece is 10 mm diameter and 6 mm thickness and the cathode is copper. When the experiment is

carried out, the electrolyte should be at room temperature each time and after the experiment the conductivity of

electrolyte must be checked. And while doing the experiment some overcuts are occurred so that overcut diameter

and depth is taken with the help of Coordinate Measurement Machine (CMM).

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METHODOLOGY:

DESIGN OF EXPERIMENTS:

Design of experiments is a standard tool to conduct the experiment in an optimum way to investigate the effects

of process parameters on the response or output parameter. The various steps involved in the design of experiments are identifying the important process parameter, finding the upper and lower limit of selected process parameter and

developing the box ben hen design matrix. The design matrix for three factors involves three blocks in which each

of two factors are varied through the four possible combinations of higher and lower limits. In each block a certain

number of factors are put through all combinations for the three factorial designs, while the other factors are kept at

central values.

In this study, three machining parameters were selected as control factors, and each parameter was

designed to have three levels, denoted 1, 2, and 3.The experimental design was according to an L27 array based on

Taguchi method, while using the Taguchi orthogonal array would markedly reduce the number of experiments. A

set of experiments designed using the Taguchi method was conducted to investigate the relation between the process

parameters and determination factor. DESIGN EXPERT @ 16 mini tab software was used for regression and

graphical analysis of the obtained data.

RESPONSE SURFACE METHODOLOGY:

Response surface designs are employed in the empirical study of relationship between one or more

measured response variable sand a number of independent or controllable variables of a process. Response surface

designs are employed to investigate and predict the following conditions of a process. RSM methodology is

practical, economical and relatively easy for use.They are the effect on a particular response by a given set of input

variables over some specified region of interest. The required values of variables to obtain desirable or acceptable

levels of a response. The required values of variables to achieve a minimum or maximum response and the mature

response surface near this minimal or maximal value. To describe the response surface method by second order

polynomials, the factor in the experimental design should have three levels. A three level factorial experiment in

which all possible combinations of k factors at all the levels are used is called 3k full factorial design which is

employed.

MATERIAL SELECTION:

TITANIUM ALLOY (GRADE 2)

INTRODUCTION

The work material used for the present investigation is AISI 316. The diameter of the material is 10mm and

machined length is 10mm for all trials. The chemical composition of the work material is given in an output as the

reflection of local information stored in connections. The output of each neuron is determined by the level of the

input signals in relation to the threshold value. These signals are modified by the connection weights between the

neurons. The output of a neuron is intake and supplied to other neurons of adjacent layers as input signals via

interconnections.

Chemical Composition

The following table shows the chemical composition of titanium alloy

Element Content (%)

C 0.1

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Fe 0.3

H 0.015

N 0.03

O 0.25

Ti 99.2

MATERIAL HARDNESS TEST REPORT:

HARDNESS TEST REPORT:TEST REPORT NO HT / 260/ 08.10.13

SAMPLE ID Dia-22mm ROD

Hardness Value 234,BHN

Indentor 2.50mm BALL

Load applied 187.5,Kgf

PGP COLLEGE OF ENGG & TECH 14

Hardness test report

TESTING THE HARDNESS OF METALS:

BRINELL HARDNESS TEST:

The Brinell test for determining the hardness of metallic materials consists of applying a known load to the

surface of the material to be tested through a hardened steel ball of known diameter. The diameter of the resulting

permanent impression in the metal is measured and the Brinell Hardness Number (BHN) is then calculated from the

following formula in which D = diameter of ball in millimeters, d = measured diameter at the rim of the impression in millimeters, and P =applied load in kilograms.

BHN = load on indenting tool in kilograms/ surface area of indentation in sq. mm.

If the steel ball were not deformed under the applied load and if the impression were truly spherical, then the

preceding formula would be a general one, and any combination of applied load and size of ball could be used.

Hence, for a standard Brinell test, the size and characteristics of the ball and the magnitude of the applied load must

be standardized. In the standard Brinell test, a ball 10 millimeters in diameter and a load of 3000, 1500, or 500

kilograms is used. It is desirable, although not mandatory, that the test load be of such magnitude that the diameter

of the impression be in the range of 2.50 to 4.75 millimeters.

The following test loads and approximate Brinell numbers for this range of impression diameters are: 3000 kg, 160

to 600 BHN; 1500 kg, 80 to 300 BHN; 500 kg, 26 to 1making a Brinell test, the load should be applied steadily and

without a jerk for at least 15 seconds for iron and steel, and at least 30 seconds in testing other metals.

COPPER (tool materials):

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Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a

ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; a freshly exposed

surface has a reddish-orange color. It is used as a conductor of heat and electricity, a building material, and a

constituent of various metal alloys. The metal and its alloys have been used for thousands of years. In the Roman

era, copper was principally mined on Cyprus, hence the origin of the name of the metal as сyprium (metal of

Cyprus), later shortened to cuprum. Its compounds are commonly encountered as copper (II) salts, which often

impart blue or green colors to minerals such as azurite and turquoise and have been widely used historically as

pigments. Architectural structures built with copper corrode to give green verdigris (or patina). Decorative art

prominently features copper, both by itself and as part of pigments.

Properties of Copper:

Copper is an excellent electrical conductor. Most of its uses are based on this property or the fact that it is also a

good thermal conductor. However, many of its applications also rely on one or more of its other properties. For

example, it wouldn't make very good water and gas pipes if it were highly reactive. On this page, we look at these

other properties:

a good electrical conductor

a good thermal conductor

corrosion resistant

antibacterial

easily joined

ductile

tough

non magnetic

attractive colour

Applications of Copper:

Copper and copper alloy can be used in an extraordinary range of applications. Some of these applications

include:

Power transmission lines

Architectural applications

Cooking utensils

Spark plugs

Electrical wiring, cables and busbars

High conductivity wires

Electrodes

Heat exchangers

Refrigeration tubing

Plumbing

ELECTRO CHEMICAL MACHINE SELECTION:

Working principal of ECM:

Electro chemical machining (ecm) is a method of removing metal by an electrochemical process. It is normally

used for mass production and is used for working extremely hard materials or materials that are difficult to machine

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using conventional methods. Its use is limited to electrically conductive materials; however, this includes all metals.

Ecm can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals such

as titanium, hastelloy, kovar, inconel and carbide.

Ecm is often characterized as "reverse electroplating," and is similar in concept to electrical discharge

machining in that a high current is passed between an electrode and the part, through an electrolyte material removal

process having a negatively charged electrode (cathode), a conductive fluid (electrolyte), and a conductive work

piece (anode); however, in ecm there is no tool wear. the ecm cutting tool is guided along the desired path very close

to the work but it does not touch the piece. unlike edm however, no sparks are created. very high metal removal

rates are possible with ecm, along with no thermal or mechanical stresses being transferred to the part, and mirror

surface finishes are possible.

ECM SETUP 19

MATERIAL: TITANIUM ALLOY

Definition:

Titanium alloys are metals which contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness (even at extreme temperatures). They are light in weight, have

extraordinary corrosion resistance and the ability to withstand extreme temperatures.

APPLICATIONS OF TITANIUM ALLOY

The high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft,

medical devices, connecting rods on expensive sports cars and some premium sports equipment and consumer

electronics. Auto manufacturers Porsche and Ferrari also use titanium alloys in engine components due to its durable

properties in these high stress engine environments.

Although "commercially pure" titanium has acceptable mechanical properties and has been used

for orthopedic and dental implants.

Titanium Alloy (CP-Ti)

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Grade 2: Titanium alloy

Product form: Titanium Bar

Market: Aerospace, Chemical Processing, Motor sport, Medical, Oil & Gas, Defence DiameterRange:5mm–254mm

Specifications: AMS4928, BS2TA11, ASTM B 348 GR 2, ISO5832/3

TITANIUM ALLOY CP-Ti (Grade 2)

Its usability lies in its many benefits. Cp-ti may be heat treated to increase its strength. It can be used in welded construction at service temperatures of up to 600° F. This alloy offers its high strength at a light weight,

useful formability and high corrosion resistance.

Cp-ti usability makes it the best alloy for use in several industries, like the aerospace, medical, marine and chemical

processing industries. It can be used in the creation of such technical things as:

Aircraft turbines

Engine components

Aircraft structural components

Aerospace fasteners High-performance automatic parts

Marine applications

Sports equipment.

EXPERIMENTAL DETAILS

A set of experiments were conducted on Lathe machine to determine effect of machining parameters

namely table speed (rpm),feed(mm/rev),depth of cut (mm) and material (Al alloy and Resin) on output responses

namely surface roughness and metal removal rate and burr height.

The machining conditions were listed below. Three levels for first three factors and two for the fourth,

taken as category are used to give the design matrix by using Response Surface Methodology (RSM) and relevant

ranges of parameters as shown in runs to conduct the experiments is shown in the Table along with the output

responses, MRR and surface roughness. MRR was calculated as the ratio of volume of material removed from the

work piece to the machining time. The surface roughness, Ra was measured in perpendicular to the cutting direction

using Profilometer. These results will be further used to analyze the effect of input machining parameters on output

responses with the help of RSM and design expert software.

EXPERIMENTAL PROCEDURE

Test Specimen

This research conducted a cutting test with an automatic machine called PINACHO, RAYO 180 model,

using an Insert of KENNAMETAL-KC5010 with Nose Radius of 0.4 millimeter, and SHELLDROMUS OIL B for

heat ventilation. The material used in the cutting is Titanium alloy (Grade 2)

Tool life measurement

The cutting for calculating the working life of tool life is shown as the table of orthogonal array L9 by

cutting the part at 10 rounds of one piece to get the cutting length at1,000 millimeter and stopping watch and

checking the wearing out by the Toolmaker’s Microscope of TM 505which the lenses of 30 times and measure

every 1,000millimeter until the size of the Flank Were are more than0.6 millimeter(VB max>0.6 millimeter)

Taguchi Method and design of experiment The Taguchi method is a quality tool that helps improve the work efficiently. It is possible to select suitable

factors, which indicates factors and their levels in the cutting experiment with CNC machine, which contains 3

factors, and each factor has 3 levels.

As mentioned earlier, Taguchi method is used for tuning the turning process by optimizing the process

parameters for best tool life.

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In general, the parameter optimization process of the Taguchi method is based on 8-steps of planning,

conducting and evaluating results of matrix experiments to determine the best levels of control parameters.

Those eight steps are given as follows:

Identify the performance characteristics (responses) to optimize and process parameters to control (test).

Determine the number of levels for each of the tested parameters.

Select an appropriate orthogonal array, and assign each tested parameters into the array.

Conduct an experiment randomly based on the arrangement of the orthogonal array.

Calculate the S/N ratio for each combination of the tested parameters.

Analysis the experimental result using the S/N ratio and ANOVA test.

Find the optimal level for each of the process parameters.

Conduct the confirmation experiment to verify the optimal process parameters.

Determination of cutting parameters Test result collection according to the order of the experiment and analyze S/N ratio of tool life is as

follows;

This section provides the results of S/N ratio, main effect plot and ANOVA. From the results of mean S/N

ratio and ANOVA analysis, the optimal combination of cutting parameters is achieved and verification tests have

been performed to predict the improvement.

Analysis of the signal-to-noise(S/N) ratio In Taguchi method, the term signal represents the desirable value, and noise represents the undesirable

value. Process parameters with the highest S/N ratio always give the best quality with minimum variance [10]. The

S/N ratio for each parameter level is calculated by finding the average of S/N ratios at the corresponding level. Fig 2 shows the response table for S/N ratio of tool life for larger is better obtained for different parameter levels.

APPLICATIONS:

It is used in the following fields

Pigments, additives and coatings

Aerospace and marine

Industrial

Consumer and architectural

Jewelry

Medical

Nuclear waste storage

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