Machining of titanium alloys and composites for aerospace applications

172 Pages·2013·13.27 MB·English

Machining of
Titanium Alloys and
Composites for
Aerospace Applications
Edited by
R. Zitoune
V. Krishnaraj
J. Paulo Davim
Machining of Titanium
Alloys and Composites
for Aerospace Applications
Special topic volume with invited peer reviewed papers only
Edited by
R. Zitoune, V. Krishnaraj and J. Paulo Davim
Copyright  2013 Trans Tech Publications Ltd, Switzerland

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Volume 763 of
Materials Science Forum
ISSN print 0255-5476
ISSN cd 1662-9760
ISSN web 1662-9752

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Preface 
A  growing  concern  in  the  aerospace,  automotive  and  biomedical  industrial  segments  of  the 
manufacturing industry is to build absolute reliability with maximum safety and predictability of the 
performance of all machined components. This requires development and deployment of predictive 
models  for  detailing  the  effects  of  varying  machining  parameters  on  fatigue  life  of  machined 
components.  The  fatigue  life  is  mainly  affected  by  the  residual  stresses  developed  during  the 
machining.  Residual stresses are produced due to plastic deformation material while machining. The 
plastic deformation generates cracks and micro structural changes, as well as large micro hardness 
variations. Residual stresses have consequences on the mechanical behaviour, especially on the 
fatigue life of the workpieces. Residual stresses are also responsible for the machining distortion 
phenomenon  of  the  machined  parts  which  lead  to  difficulties  during  assembly.  The  literature 
detailing the effects of varying operating parameters on tool life when machining Titanium alloy is 
comprehensive, however, relatively little of this data refers to their effects on machined workpiece 
surface integrity particularly, residual stress generation and distortion created. Greater knowledge of 
the  effects  of  operating  parameters  on  surface  integrity  is  critical  to  the  acceptance  of  new 
environment, cutting path and cutting sequence strategies on machining of Ti6Al4V aerospace alloys 
to increase the functional requirements and fatigue life of the milled thin components. In this book 
four chapters have been included to address the above reported issues.  
The use of polymer matrix composite materials has significantly increased in the last few years. The 
aerospace, naval and automotive are the industry’s highly interested in this material, because of its 
strength/weight ratio which made it very attractive. Edge trimming, cut‐outs and holes exist in most 
of the composite structures. For example in an aircraft fuselage structure, around 10 million holes 
are required for joining purposes. However due to their laminated constructions several types of 
damages like matrix cratering and thermal alterations, fibre pullout and fuzzing, are introduced 
during machining.  Trimming the edges of the composite part is the first and mandatory machining 
operation  carried  out  after  the  composite  parts  are  demoulded.  This  operation  is  done  using 
conventional  machining  widely,  or  in  some  cases  by  using  abrasive  water  jet  cutting.  The 
heterogeneity and anisotropy of the composite materials made their machining difficult. This has 
lead to the propagation of many defects. Damages are located at the free edges of the laminate or 
through the thickness (fibres pull‐out and resin degradation). Few chapters have been dedicated to 
address the issues of edge trimming and drilling of composite materials.
Particularly, the influence of the quality of the machined surfaces (drilling and trimming) on the 
mechanical  behaviour  is  analysed  for  different  processes  of  machining.    A  chapter  has  been 
dedicated to address the challenges in drilling of multimaterials. This book will be a useful guide to 
those  who  would  like  to  understand  the  issues  in  machining  of  titanium  alloys  and  polymer 
composite materials. The editors express their sincere thanks to the authors, who contributed papers 
for this book. 
Redouane Zitoune 
Vijayan Krishnaraj 
J P Davim
Table of Contents
Preface
Turning Investigations on Machining of Ti64 Alloy with Different Cutting Tool Inserts
S. Ramesh and L. Karunamoorthy 1
Multi-Objective Optimization on Drilling of Titanium Alloy (Ti6Al4V)
A. Prabukarthi, V. Krishnaraj and M. Senthil Kumar 29
Experimental Study on Tool Wear when Machining Super Titanium Alloys: Ti6Al4V and
Ti-555
M. Nouari and H. Makich 51
Statistical Approach for Modeling Abrasive Tool Wear and Experimental Validation when
Turning the Difficult to Cut Titanium Alloys Ti6Al4V
F. Halila, C. Czarnota and M. Nouari 65
Laser Assisted Machining of Titanium Alloys
M.W. Norazlan, Z. Mohid and E.A. Rahim 91
Influence of Tool Geometry and Machining Parameters on the Surface Quality and the
Effect of Surface Quality on Compressive Strength of Carbon Fibre Reinforced Plastic
M. Haddad, R. Zitoune, F. Eyma and B. Castanié 107
Analysis of Stresses in CFRP Composite Plates Drilled with Conventional and Abrasive
Water Jet Machining
M. Saleem, H. Bougherara, L. Toubal, F. Cénac and R. Zitoune 127
Challenges in Drilling of Multi-Materials
V. Krishnaraj, R. Zitoune, F. Collombet and J.P. Davim 145
Materials Science Forum Vol. 763 (2013) pp 1-27
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/MSF.763.1
Turning Investigations on machining of Ti64 alloy with different cutting
tool Inserts
S.Ramesh1,a, L.Karunamoorthy2,b
1Department of Mechanical Engineering, Sona College of Technology, Salem – 636 005, INDIA
2Department of Mechanical Engineering, College of Engineering Guindy Campus, Anna University,
Chennai-600 025, INDIA
[email protected] (corresponding author) [email protected],
Keywords: Machining, Titanium Alloy, Microstructure Studies, Cutting Force, Cutting temperature,
Tool wear, Surface roughness, Machining Optimization, Grey Relational Analysis
Abstract: Turning operation is fundamental in the manufacturing industry to produce cylindrical
parts especially for producing near-nett shape, and aesthetic requirements with good dimensional
accuracy. This present research chapter, an attempt has been made to investigate the machining
characteristics of titanium alloys. The investigation has been carried out to measure the effect of
tool flank wear, surface roughness, cutting force and temperature on different cutting tools by
adopting Taguchi’s design of experiment concept. This investigation was set to analyse and develop
a mathematical model using response surface methodology, fuzzy logic. The observed responses
were optimized using grey relational grade algorithm. Except for a few cases, the experimental
results have close proximity (95%) to the predicted value. This validates the model developed in
this work. Orthogonal array with grey relational analysis has been successfully implemented for the
optimization of the machining parameters. The optimized cutting conditions evolved in this
research study will help to achieve better machinability of these advanced materials like titanium
alloy.
Introduction
Titanium is one of the important metals and is used in various fields of engineering and medical
sciences. Titanium (Ti), named after the Greek god Titan, was first discovered in 1791 (McQuillan
and McQuillan [1]). Although it has been available more than two hundred years, it has only been
produced commercially since the 1950s. Titanium is a member of the tin group of the periodic
tables. Titanium is a very expensive structural material compared to steel. Titanium shows very
good strength to weight ratio at elevated temperatures, and it has exceptional corrosion resistance.
These characteristics have been the main cause for the rapid growth of the titanium industry over
the last 55 years. The specific weight of titanium is only 2/3rd that of steel and only 60% greater
than aluminium. The major application of this material is in aerospace industry, both in air frames
and engine components. Non-aerospace applications mainly due to their excellent strength
properties as in the case of steam turbine blades, superconductors, missiles etc., or corrosion
resistance as in the case of marine services, chemical and petrochemical industries, electronics
industry, biomedical instrumentation etc. However, the production and usage of titanium are
expensive when compared to many other metals, because of the complexities of the extraction
process, difficulty of melting and associated problems during fabrication. On the other hand, the
longer service lives and higher property levels counterbalance the high production costs.

Machining is important in metal-manufacturing process to achieve near-nett shape, good
dimensional accuracy and for aesthetic requirements. The machining of titanium poses many
problems. The problems encountered when machining titanium have usually originated in shops
working with aircraft alloys. In 1955, Siekmann pointed out that machining of titanium and its
alloys would always be a problem. The poor machinability of titanium has led many large
companies (such as General Electric) to invest large amount of money in developing techniques in
2 Machining of Titanium Alloys and Composites for Aerospace Applications
order to minimize machining costs. Similarly, tool makers are looking for new tool materials which
would extend tool life in the presence of such a challenge. The inherent properties of the material
make it more difficult to machine. The heat resistance property of the metal proves to be
detrimental to the tool life of the cutting tool. Due to its low thermal conductivity, the heat produced
during metal cutting accumulates at the small area of the tool-workpiece contact point, resulting in
high thermal stresses and frictional forces. At high cutting forces and high cutting temperatures the
workpiece material develops higher residual stresses (Guo et al [2] and Manouchehr Vosough [3],
Ramesh et al [4])

The chemical reactivity of the material at elevated temperatures makes it easily react with the
surrounding atmosphere. Ordinary cutting tools may fail prematurely under these adverse
conditions. So, alternate cutting tools which can serve effectively at these severe cutting conditions
are to be considered. Cutting parameters have to be carefully selected so as to produce machined
surfaces with high level of surface finish at reasonable production rates. The temperature gradients
in the tools used for cutting titanium alloys are similar in character to those found when cutting the
commercially pure metal (Edward et al [5] and Milton C. Shaw [6]).

The present work is aimed at studying the performance of different cutting tool inserts in the
machining of Titanium alloy (Ti-64). The work material used for the present investigation is with
characteristic microstructures of α + β phase. The machining tests were carried out on lathe. The
operations carried out on lathe for the present investigation is turning. Turning is one of the
important operations and is backbone of many industrial manufacturing operations. The cutting
performance in turning of titanium alloy is evaluated by using the performance investigators such as
tool flank wear, surface roughness, and cutting force.

In the present work, an attempt has also been made to analyze and optimize the machining
parameters in the machining of titanium alloys. Statistics and optimization techniques are important
tools used for modeling the machining characteristics and performing the optimization of cutting
parameters for achieving the selected objectives. The modeling of machining parameters is carried
out using response surface methodology (RSM) and validation of model is done by using fuzzy
logic. Grey relational analysis has been used to optimize the machining characteristic with multiple
performance characteristics. The effect of temperature on machining of titanium alloy has also been
investigated in the present study.
2. Literature Review
The demand for machining of titanium alloy has been increased in recent years (Klaus Gebauer [7]
and Kennametal [8]). In order to understand and access the current status of research in machining
of titanium alloys, an extensive literature review has been carried out. The selected literature
reviews for the present investigations are given hereunder:
2.1. Machining of Titanium Alloys
The present study is focused on the machining characteristics of titanium alloy. In general, a finish
machining of a titanium component will be necessary, because of the requirement of exact
dimensional accuracy, surface quality and material homogeneity. Machining of titanium alloy poses
considerable problem due to its poor machinability (Komanduri [9] and Awopetu [10]). The poor
machinability of titanium has led many large companies (for example Rolls-Royce and General
Electric) to invest large amount of money in developing techniques to minimize machining costs.
Similarly, tool makers are looking for new tool materials which can extend tool life in the presence
of such a challenge (Machado and Wallbank [11], Ramesh et al [12, 13]).
Materials Science Forum Vol. 763 3
From the available literature, it has been noticed that the first literature on machining of titanium
alloy was presented by Siekmann [14]. It has been pointed out that machining of titanium and its
alloys will always be a problem no matter what technique is employed to transform this metal into
chips. Komanduri and Reed [9] have commented that the machining difficulty of titanium alloy is
still true as far as cutting tool materials are concerned. While improving the machining rates will go
a long way towards increasing the usage of the material, it must be noted that this is only one of the
number of factors affecting the use of the material. Others, which include material cost, must also
be considered in any specific application.

The Metals Handbook [15] gives detailed information about the alpha-beta alloy, Ti-64 which
accounts for about 45% of the total titanium production while unalloyed grades comprise about
30%. All the other alloys comprise of the remaining 25%. Michael Field [16] has set some
guidelines for improving surface integrity as a new requirement for improving reliability of
Aerospace hardware.

Komanduri et al [17] presented some new observations on the mechanism of chip formation to
increase productivity when machining Titanium alloys and reported interesting findings towards the
goal. Hartung et al [18] have investigated turning test on Ti-64 with conventional (Carboloy 820
and Kennametal K68) grade cemented carbides. They analyzed and suggested that tool wear rate of
tool materials, which maintain a stable reaction layer, is limited by the diffusion rate of tool
constituents from the tool-chip interface. The diffusion flux correlates well with the observed wear
rate.

Bhaumik et al [19] has developed a wurtzite boron nitride–cubic boron nitride (wBN-cBN)
composite tool obtained by high pressure/high temperature sintering for machining Ti-64 alloys. In
their investigation they indicated that this composite tool can be used economically to machine
titanium alloys. Bayoumi et al [20] have studied the behavior of chip formation using various
metallurgical analysis techniques.

Obikawa et al [21] has studied the computational machining of titanium alloy using finite element
analysis. They have used finite element modeling to simulate the serrated chip formation similar to
that found by actual cutting. Kitagawa et al [22] have carried out high speed machining on Inconel
718 and Ti-6Al-6V-2Sn alloys from a thermal point of view. They have studied the temperature and
wear of the cutting tools by means of cutting experiments and numerical analysis up to a cutting
speed of around 600 m/min.

Toru Okabe et al [22] have explored the present status of titanium castings in the field of
biomaterials as dental casting. Zoya and Krishnamurthy [24] have discussed the factors that affect
the machining of titanium and its alloys. They have stated that the machining of titanium alloys is a
thermally dominant process. With the increase in cutting speed, the temperature produced also
increased. They observed that surface roughness increased with increasing cutting speed in the
range of 150-350 m/min at 0.5 mm depth of cut.

Barry et al [25] have carried out some observations on chip formation and acoustic emission in
machining Ti-64 alloy. They have found that the degree of welding between the chip and the tool
increases with cutting speed. Shane et al [26] have reported how the temperature affects Ti-64 alloy
properties and they have proposed a new economical cryogenic cooling approach.

Shuting Lei et al [27] have invented a new generation driven rotary lathe tool for high-speed
machining of titanium alloy, Ti-64. They have found that the tool can significantly increase tool life
and achieved more than 60 times. Corduan et al [28] have presented the interactions between
Polycrystalline Diamond (PCD), Cubic Boron Nitride (cBN) and TiB2 -coated carbide with