Non-Conventional Machining of Titanium and Nickel Based Alloys
Abstract
This review article provides consolidated information about various conventional and non-conventional techniques that are being implemented over the years to machine Ni (Nickel) and Ti (Titanium) based alloys. In the initial section of this review, the applications of various Ni and Ti-based alloys are presented. The discussion is then extended to various conventional methods of machining followed by the difficulties in working on these alloy using traditional methods of machining. Further various non-conventional methods of machining such as cryogenic, EDM (Electro Discharge Machining), ECM (Electro Chemical Machining), WJM (Water jet Machining), UAT (Ultrasonic Assisted Turning), etc have been reviewed. Different output responses such as material removal rate, surface roughness, tool wear rate during the machining processes are highlighted. A consolidated data of various researchers and their studies connect to this topic has been offered. Finally, the article has been concluded by indicating some key points observed during the review process.
Nickel alloys are used extensively in the field of
aerospace mainly due to their excellent chemical and physical properties. These
alloys are used in the manufacture and development of aircraft wings and gas
turbine blades. However, manufacturing or working on these alloys with
conventional machining processes has not been very productive due to the
disappointing results of surface integrity and surface roughness obtained after
machining. Similarly, Titanium-based
alloys are also highly valued materials in the manufacturing sector due to
their biocompatible properties and also due to their ability to resist
corrosion and wear. These alloys are considered as advanced materials with a
wide span of applications in the multi-disciplinary fields of engineering such
as medicine, marine, automobile, gas-turbine engines, military ballistic armor, etc. These alloys are present in such a wide spectrum of engineering
applications mainly due to their ability to exhibit excellent properties such
as superplasticity, good ductility, high specific strength and modulus, and
excellent fatigue properties. Nickel and titanium-based alloys have various
potential applications in various fields.
However, in spite of all these characteristics, manufacturers are not satisfied with the results obtained when nickel and titanium-based alloys are machined using conventional methods. This is mainly because these alloys are challenging to machine due to their high chemical reactivity which ultimately results in high tool wear rates and also high values of surface roughness and improper surface integrity. A high-temperature rise can be observed at the interface of the workpiece and the machining tool which ultimately affects the tool life by increasing the wear rate. This is due to its low thermal conductivity. Hence, these factors have resulted in the shift of manufacturing methods for these alloys from conventional to non-conventional machining processes. This articles discusses the various applications of nickel and titanium-based alloys, their machining difficulties through the conventional process, and usage of non-conventional machining processes for the same.
FIGURE 1. Potential applications of Nickel and Titanium base alloys
Figure 1 presents some of the popular applications of
Titanium and Nickel based alloys. From Fig 1, one can identify the wide-span
applications of Ti alloys in medical and marine fields. Ti alloys are
extensively used to develop and manufacture artificial hip joints, knee joints,
bone plates, pacemakers, etc. Ti alloys are one of the most biocompatible
alloys. Ti alloys further find their application in the manufacture of heat
exchange equipment, high-pressure vessel equipment, flexible pipes, pumps, and
filters. Nickel alloys are known for their robust applications in the aerospace
industry. Ni alloys are also used in the manufacturing of wings and gas turbine
blades of the aircraft. Adding on, these are used in many energy generation and
process industries such as petrochemicals, chemicals, etc.
Conventional Machining of Ni and Ti
Based Alloys
The basic machining operations that are widely implemented in the manufacturing industry are drilling, milling, cutting, turning, abrasive machining, and boring. The process of drilling is implemented when there is a need to drill holes into a workpiece. Milling is another process that is employed to remove a predetermined amount of material from the surface of the workpiece to be machined. The cutting process is employed to modify the geometry of the workpiece based on the products or manufacturer’s needs. Turning is a form of cutting that subtracts material by contacting the sharp edge of the tool with the workpiece rotating at high speeds in order to provide a smoother cutting process. Another form of machining which employs abrasive particles to eliminate material from the workpiece is known as abrasive machining. Finally, Boring is another machining process employed when there is a need to enlarge the already drilled holes.
However,
conventional machining of Nickel and Titanium-based alloys are considered to be
a poor choice because these alloys have a low thermal conductivity which leads to
the development of heat between the surface of the tool and the surface of the
workpiece that comes in contact with each other during machining thus
resulting in a high rate of tool wear and abrasive along with a high rate of
chemical reactivity with the cutting tool material, hence making the process of
machining more challenging. Hence in order to overcome these, several
modifications in tools, coolants, and processes have been made to facilitate the
machining of these alloys. These modifications include the usage of Cubic
Nitride Boron (CBN), Physical Vapour Deposition (PVD), and Polycrystalline
Diamond Cutting Tool (PCD)tools used CBN tools at high-pressure coolant
supplies during the turning of Ti–6Al–4V alloy. A machining experiment was
conducted to evaluate the different CBN tool grades. Three designated grades of
CBN tools namely T1, T2, and T3, and uncoated carbide inserts namely T4 were used
for the experimental trials. Three different coolants, that is, one
conventional coolant and two high-pressure coolants at respective pressures of
11Mpa and 20.3Mpa were used to perform the comparative study on tool life, wear
rate, and surface finish characteristics. From the experimental observations, it
was concluded that the tool with the highest CBN content affects the tool life
adversely by increasing the wear rate. Hence uncoated carbide tool (T4) gave
better performance than CBN tools (T1, T2, T3) as T4 has the least CBN content.
Finally, it was witnessed that the surface finish of Ti–6Al–4V alloy was not
affected significantly when CBN tools were used to study the effect of
PVD-coated carbide tools on the finish machining of Ni-base Inconel 718 alloy
under conventional and high-pressure coolant supplies. After the machining of
these alloys, it was noted that CBN tools operated at high speeds under high
coolant pressures can drastically improve the tool's life. However, machining at
pressures higher than the critical coolant pressure will adversely affect the
tool life. Adding on, it was also observed that, due to the effect of dynamic
forces, an increase in coolant pressure and cutting speeds increases the reactive
forces generated at high-pressure coolant jet studied the surface integrity of
finished turned Ti–6Al–4V alloy with PCD tools using conventional and high-pressure
coolant supplies. A sample bar of Ti-6Al-4V alloy was taken into consideration
which was then turned on a CNC lathe. Acceptable results of surface finish were
obtained after machining the alloy with the PCD tool. Adding on, the PCD machined
surfaces were found to be softened at high speeds of machining and high-pressure
coolant supplies.
Difficulties in Conventional
Machining of Ni and Ti Based Alloys
It
has been found that, generally, conventional methods of machining advanced
engineering materials are challenging as they exhibit properties of high
strength, high toughness, severe strain hardening, and excessive heat
generation. Ni and Ti-based alloys also fall into this category. These alloys
are found to be very sensitive to temperature changes, exhibit a high strain
rate, and also undergo a transformation of phase. Excessive heat affects the
transformation of phase, which has proven to be one of the major challenges in
machining Ni and Ti-based alloys. Furthermore, the machinability of Ti and Ni-based alloys are also considered poor when conventional methods are used. This
is mainly because Titanium and Nickel are chemically very reactive which
ultimately leads to early tool failure. Adding on, the tool life is also
affected adversely due to the low thermal conductivity of Ti alloys which leads
to an increase in temperature at the tool and workpiece interface.
As reviewed the machining difficulties of Ni and Ti-based shape memory alloys. Tool wear, high ductility, work hardening, and viscosity in the cutting process are some of the parameters that have made the machining of these alloys highly challenging. In conventional machining, Ni and Ti-based alloys exhibit many forms of surface defects. Chip redeposition to the surface worsens the surface quality because these redeposited particles cause unwanted disturbances on the surface during machining. Residual stresses are another major reason for the failure of these machined components because these stresses have the potential to cause crack initiation, crack propagation, and fatigue failure. Adding on, plastic deformation is another major hurdle. This is a direct threat to the surface integrity of the workpiece alloy. Hence, in an effort to overcome these hurdles, various non-conventional approaches of machining were adopted such as cryogenic, EDM, ECM, WJM, UAT, etc. Some of these are discussed briefly in the next section.
Non-Conventional Machining of Ni and Ti Based Alloys
As indicated in the previous sections, surface integrity, surface roughness, and excessively large tool-wear rate are known to be some of the major challenges in machining Ni and Ti-based alloys, and hence these have ultimately resulted in the shift from conventional machining processes to non-conventional machining processes. As conducted a study related to the surface integrity characteristics of a nickel-based alloy in cryogenic machining. The machining experiment was conducted in such a way that it consisted of four conditions pertaining to the usage of four different coolants. The four conditions were namely: dry machining, minimum quantity lubrication machining (MQL), cryogenic machining, and an amalgam of cryogenic and MQL machining. The machining was done to an Inconel 718 round bar of diameter 32mm and length 150mm on a CNC lathe machine. After the machining experiment, it was found that the surface with the lowest roughness value was obtained in the cryogenic machining process. It was also noted that cryogenic machining slightly influences the microstructure of the final product and induces the least plastic deformation among the four on the sample’s machined surface. As studied the behavior of Ti6Al4V alloy when machined under dry, minimal quality lubrication, and cryogenic cooling conditions using coated tools at varying cutting speeds and feed rates. A CNC lathe was used to perform the orthogonal cutting operation wherein the alloy disks were turned at three different speeds. The experiment showed that the measurements of surface roughness obtained by cryogenic machining are largely superior to those obtained by dry and MQL machining. Also, there was no significant influence of feed rate on SR values. As performed a comparative study of cryogenic and traditional cooling methods on turning off the Ti-based alloy. Tool wear, SR, cutting forces, coefficient of friction, and chip morphology were the parameters under consideration for the experiment. With the help of the ANOVA table, the results of the experiment were statistically analyzed after which it was found that the cryogenic machining method gives superior results for all parameters under consideration as opposed to traditional methods of machining. As studied the effects on tool wear and cutting force components in dry, preheated, and cryogenic machining of Ni & Ti shape memory alloys. Round bars of 10mm diameter were used for the experiment. The length of cut in all machining conditions was 26mm. Liquid Nitrogen was used as the cryogenic coolant which was applied at a pressure of 1.5Mpa. The tool wear rate was measured using an optical microscope while the cutting force components were measured using a piezo-electric dynamometer. The experimental results showed that phase control of the shape memory alloy during machining can have a significant impact on the tool wear rate and hence improve the cutting performance of the tool. Also, the results showed that the phase of work material does not depend on the thickness of the chip during machining.
As
studied the influence of machining parameters on EDM of Ni & Ti shape
memory alloys. The input parameters of EDM were chosen such that they have the
highest impact on the output parameters, that is, the discharge current,
voltage, pulse on time, and pulse off time. MRR, SR, tool wear rate, and relative
electrode wear were the output parameters. Furthermore, in this study, the
design of the experimental approach was implemented. This approach has proven to be
very useful because the input parameters can be controllably varied and their
impact on the output parameters can be studied. By this technique, it was found
that pulse current and pulse on time are the most significant parameters that
impact the MRR. An increase in these two parameters increases the MRR. Also, it
was found that a rise in pulse current results in a rise in SR. Adding on, it was also witnessed that the
tool wear rate increases along with an increase in pulse on time only up to a
certain threshold, after which the tool
wear rate starts diminishing. Furthermore, it was also noted that an increase
in pulse off time results in a reduction of MRR and SR. As studied the machinability of a Ni-based alloy
by AWJM. Water jet pressure, traverse speed of jet nozzle, and standoff distance
were the three parameters that were taken under consideration. The performance
of these parameters was judged by measuring the variation in kerf width, kerf
wall inclination, and MRR. This study was conducted on Inconel 600 alloy. This
experiment showed that with an increase in the pressure of the water jet and speed
of traversal, the inclination of the kerf wall also increases. The MRR and SR
depend heavily on the water jet pressure. It was also found that at low jet
pressures, MRR reduces consistently.
As
studied one of the novel techniques of machining known as hot ultrasonically
assisted turning (HUAT) to understand its effect on a Ti alloy. A bar of aged
and solution-treated Ti-15333 alloy was used for the experiment. Cement carbide
cutting tools were employed for all turning processes. The bar was mounted on a
modified lathe on which the turning operation was carried out in the presence
of a band resistance heater. The experiment showed a reduction in force
components during the turning of the alloy using HUAT as opposed to
conventional methods of turning. A thermal analysis was carried out to study
the temperature development in the machined component during conventional
turning (CT), hot conventional turning (HCT), and HUAT. The experiment showed
that the temperature in the machining component increases as the heat
transferred to the workpiece during machining increases. It was further
discovered that the cutting tool of HUAT results in the highest temperature
rise in the workpiece. Furthermore, a significant reduction in SR was found in
HUAT and HCT as compared to CT with HUAT posing the least SR values. Therefore,
this experiment demonstrated a significantly improved machining quality of
HUAT.
Titanium-based alloys were studied more than Ni-based alloys. This is mainly due to the wide range of applications of Ti alloys such as in biomedicine wherein these alloys are used for the development and manufacture of artificial hip joints, artificial knee joints, bone plates, pacemakers, etc. Adding on, by observing the trend of studies over the years, it can be seen that most of the researchers deviated their field of interest from conventional machining processes to non-conventional machining processes mainly due to the unsatisfactory results obtained by conventional machining of Ni and Ti-based alloys. Over the years, various non-conventional techniques such as cryogenic, WEDM, AWJM, LBM, ECM, and HUAT were employed to manufacture Ni and Ti-based alloys. WEDM is the most heavily employed non-conventional machining process for these alloys. This is mainly because WEDM gives better results of SR, surface integrity, and MRR. Kerf loss in a WEDM machined component is very insignificant as compared to other non-conventional techniques. Its high MRR is attributed to high pulse on time of WEDM. However, pulse off time cannot be neglected as insufficient pulse off time and high pulse on time can ultimately result in the formation of recast layers and thus reduce the MRR. Proper flushing time should also be provided to avoid the formation of a white layer. One more advantage of WEDM is that depending on the application and the material of the workpiece, the wire of the WEDM can be selected. Standard wires made up of Brass, ZnBr, Copper (Cu), and ZnCu are available. Depending on the purpose of manufacturing, a suitable wire for WEDM is chosen out of the four. The table also presents work on laser beam machining (LBM). This is another form of non-conventional machining in which the heat of a laser is used to cut the workpiece. Another form of laser beam machining is a plasma cutter which is essentially more powerful than a typical laser beam since plasma is capable of generating temperatures a lot higher than laser beams. In LBM, the machine is first fed with data of the profile of the cut. The laser pointer then traverses the path of the profile while imparting the high-temperature laser beam onto the workpiece. As a result of extremely elevated temperatures, the workpiece material (metal or acrylic) starts to melt and cuts out of the body of the workpiece. The key advantage of using LBM is that there won’t be any tool wear rate since there is no actual tool that comes in contact with the workpiece during machining. Hence, depending upon the requirement, any of the above-mentioned non-conventional machining techniques can be implemented.
Conclusions
In this article, various methods of conventional and non-conventional machining of Ni and Ti-based alloys along with their applications have been briefly summarized. The difficulties in machining these smart alloys conventionally have also been discussed. Various works on non-conventional methods of machining such as WEDM, EDM, LBM, AWJM, ECM, and cryogenic machining are some of the emphasized processes in this study. Finally, the various machining processes and the work material used by the researcher have been presented. The following observation has been made based on the article.
1. High
chemical reactivity, highly sensitive to temperature changes, chip formation
and phase transformation during machining of Ni and Ti-based alloys are some of
the reasons for industries to adopt non-conventional methods of machining as
they avoid high wastage of material and has proven to be very economical as
opposed to conventional methods of machining.
2. WEDM the process is the dominant choice in non-conventional machining of Ni and Ti-based
alloys as it is clearly evident from the number of studies carried out on this method by numerous researchers.
3. Change
in minute parameters such as the coolant used or the speed of machining has a major influence on the surface integrity of the workpiece.
4. Titanium
alloys are extensively used in biomedical applications for the development of
artificial hip joints, artificial knee joints, bone plates, pacemakers, etc.
while Nickel-based alloys are used extensively for aerospace applications.
5. Nickel
based alloys are also used for industrial applications such as petrochemicals,
chemicals and process industries.
6. Today’s
researchers are using Nickel Titanium as shape memory alloys in many
applications, which gives the benefit of both Nickel and Titanium along with
extra added features. These alloys are termed Nitinol alloys. These nitinol alloys can also be machined using various non-conventional machining processes,
out of which Wire EDM being the most preferred machining process by the
researchers.
7. Many
researchers have concentrated on machining Ni and Ti-based alloys and
concerned parametric studies, whereas further the studies on surface integrity
and related aspects have to be worked on in the future.
References
4. Maurotto, A., Roy, A., Babitsky, V. I., & Silberschmidt, V. V. (2012). Analysis of Machinability of Ti- and Ni-Based Alloys. Solid State Phenomena, 188, 330–338.
5. Ezugwu, E. O., & Wang, Z. M. (1997). Titanium alloys and their machinability—a review. Journal of Materials Processing Technology, 68(3), 262–274.
6. Maurotto, A., Muhammad, R., Roy, A., Babitsky, V. I., & Silberschmidt, V. V. (2012). Comparing Machinability of Ti-15-3-3-3 and Ni-625 Alloys
7. Yang, X., & Richard Liu, C. (1999). MACHINING TITANIUM AND ITS ALLOYS. Machining Science and Technology
8. Gupta, K., & Gupta, M. K. (2018). Developments in nonconventional machining for sustainable production: A state-of-the-art review. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science
Comments
Post a Comment