MEE4001-TOOL DESIGN
Latest developments on Cutting tools and coatings
NAME:SHREY S JAIN
REGNO:18BME1225
FACULTY:Dr. UMASANKAR
SLOT:F1
INTRODCUTION
Trends in the manufacturing industry drive trends in metal cutting
insert development. Changes in workpiece materials, manufacturing
processes and even government regulations catalyse parallel
advances in metal cutting tooling technology.
As manufacturers continually seek and apply new manufacturing
materials that are lighter and stronger—and therefore more fuel
efficient—it follows that cutting tool makers must develop tools that
can machine the new materials at the highest possible levels of
productivity.
According to the sold value, 40% of all cutting tools are coated in
industry today. The most important application field of conventional
and new coatings for cutting tools will be discussed. There are two
opposing development trends in the cutting industry today: (1) in dry
machining the user wants to work without coolant to save the
environment and production costs; (2) in high speed machining (HSC)
the cutting parameters can be increased by a factor of 4–10. Aside
from increasing productivity, multi-spindle heads can be replaced by
one spindle, increasing the flexibility enormously. With both
technologies much greater heat is produced than under normal
cutting conditions. The cutting materials must have a high warm
hardness and cannot work without a good heat isolation coating
between the hot chips and the tool body. The overview of the latest
industrial applications of different coatings for dry and HSC cutting
and characterizes the most important requirements of future
coatings for cutting tools will be discussed.
The recent developments in the field of PVD coating for
manufacturing tools.
The studies have shown that in the manufacturing industry a 30%
reduction of tool costs, or a 50% increase in tool lifetime results only
in a 1 % reduction of manufacturing costs. But an increase in cutting
data by 20% reduces manufacturing costs by 15%. In order to
achieve higher productivity different approaches such as high
performance cutting (HPC) and high-speed cutting (HSC) can be
chosen.
The introduction of PVD coatings for cutting tools in the metal
cutting industry is one of the main success stories in the industrial
application of modern coating technology over the last 40 years. The
first PVD coating material that have a commercial application on
cutting tools was TiN in the early 1980s and since the 1990s most
cutting tools are PVD coated, particularly in applications where sharp
edges are required (threading, grooving, end-milling) and in cutting
applications that have a high demand for a tough cutting edge
(drilling). In solid carbide cutting tools (end-mills and drills) PVD is the
standard coating technology. The TiAlN PVD coating is currently the
most widely deposited PVD coating for cutting tools, but other
coatings such as TiCN and CrN offer better solutions in certain
applications.
The development of PVD coatings followed the steps:
• first generation (1970): pseudo ceramic materials based on
binary compounds (TiN, TiC, TiB2, etc.);
• second generation (1985): ternary and quaternary interstitial
solid solutions (Ti-AlN, Ti-Al-N-C, etc.);
• third generation (1990): multilayer structures, superlattices
(M/MN/M and MN/MC/MN, etc., where M – metallic
component);
• fourth generation (2002): nano laminated structures and
nanocomposite structures, nanostructures doped with solid
components as dry lubricant;
• present generation (2008-2010): DLC and OXI coatings
Advances in manufacturing technologies (increased cutting speeds,
dry machining, etc.) triggered the fast-commercial growth of PVD
coatings for cutting tools. On the other hand, technological
improvements in coating types (TiAlN, AlTiN, AlCrN, multilayer
coatings, nanocomposite coatings, DLC and OXI coatings) enabled
these advances in manufacturing technologies
The use of new materials (high temperature aerospace alloy, higher
strength ductile iron used in automotive, silicon aluminium and
magnesium alloys, composite materials) will increase over time and
the development of new cutting tools, machine tools, and metal
cutting processes, under dry machining conditions will offer many
opportunities to tooling and machine tool manufacturers in the years
to come
In the areas of machining and tooling PVD coatings are widely used
to increase the life and productivity of production cutting tools
saving companies milliards of euro worldwide. The use of PVD
coatings on cutting tools saves money in three ways:
• PVD coated cutting tools can be run faster reducing cycle times
and enabling the production of more components in less time;
• PVD coatings on cutting tools reduce wear; in metal cutting
different wear processes exist depending on the cutting tool,
crater wear on the rake face, caused by chemical interaction
between the cut chip and the tool surface, built-up edge on the
cutting edge and depth-of-cut notching caused by abrasion by
the outer edge of the chip; none of these wear mechanisms
exists in isolation however one usually predominates; PVD
coatings are resistant to all forms of wear increasing the life of
cutting tools reducing tool-changing costs.
• PVD coatings on cutting tools reduce the need for cutting fluid;
cutting fluids cost companies today up to 15% of their total
production costs. High speed cutting and dry machining involve
extremely high temperatures at the cutting edge; some PVD
coatings have incredible thermal stability, hot hardness and
oxidation resistance; PVD coatings can therefore be run dry or
with very limited amount of cutting fluid.
PVD processes have the fastest market growth in the latest years,
replacing the CVD technologies. This is due to their certain
advantages upon other surface engineering technologies:
• the high vacuum employed makes it possible to achieve coating
properties that are not available with gases and baths at
atmospheric pressure (thermal spraying, nitriding, electro or
chemical deposition); the resulting coatings offer high
hardness, good adhesion and wear resistance, and these
properties can tailor for every specific application;
• PVD processes are used for component coating operate at
relatively low coating temperatures of 250...500°C; these
temperatures are chosen to lie at or below the tempering
temperature of steels in order to avoid the altering the
fundamental material properties;
• PVD coatings are thin, typically 0,5...4 µm; this feature, in
conjunction with close tolerances, means that the component
retains its form, fit and dimensions after coating, without the
need of costly refinishing;
• PVD processes are environmentally benign and do not entail
the use of emulsions or pollutants; the gases used are noble
ones, as argon together with working gases such are hydrogen
or acetylene; no toxic reactions occurs
Types of coatings
1) Monoblock coatings:
The first generation of hard PVD coatings was single metal nitrides
such as TiN, CrN and ZrN. They have been commercially exploited
since the middle of the 1980s in cutting applications (because of
their higher hardness compared to high speed steel and cemented
carbide) and for decorative purposes because of their attractive
appearance: TiN has a distinctive yellow gold colour, CrN looks like
silver, ZrN has a white gold colour. Alloyed coatings improve
hardness, wear resistance, toughness and oxidation resistance by
introducing other elements such as C, Al and Cr into the TiN lattice.
2) Multilayer coatings:
Further improvements of the properties of hard PVD coatings were
achieved by the deposition of multilayer structures. By selecting a
suitable combination of materials for the multilayer structure it is
possible to improve the resistance against wear, corrosion, oxidation.
Multilayer structure has higher toughness and lower hardness
comparable with mono block coatings. The “sandwich” structure
absorbs the crack by sublayers; therefore, a multilayer coating is
usually preferred for high dynamical load, e.g. for roughing.
3) Nanocomposite coatings:
Nanocomposite structures represent a new class of materials,
consisting in two or more phases coexisting in a very low volume,
crystals having dimensions of 3...10 nm. In the case of
nanocrystalline materials the number of atoms in a crystal grain is
comparable, or even less, than the number of atoms that are in the
grain limits. In such conditions the formation of dislocations is
inhibited by the grain limits, and mechanical deformation takes place
by the mechanism of slipping at the grain limits, not by dislocation
movement, which is the mechanism of deformation in conventional
materials. This leads to a significant increasing of hardness of
nanocrystalline materials and to the development of super hard
materials . By depositing different kinds of materials, the
components (like Ti, Cr, Al, and Si) are not mixed, and two phases are
created. The nanocrystalline TiAlN or AlCrN grains become
embedded in an amorphous Si3N4 matrix. Nanocomposite coatings
are commercially available since 2003 and they have outstanding
properties and applications
4) DLC and OXI coatings:
Diamond Like Coating (DLC) is a metastable form of amorphous
carbon with a high percentage of cubic sp3 elements. DLC coatings
improve the running-in characteristics of chip removal and forming
tools and play an important role in the treatment of soft and
adhesive materials which cause built-up edges. Today, DLC coatings
are mainly used in component mass production to protect against
wear and tear through less friction. Oxide and oxinitride coatings
serve to separate tool/component and workpiece and to achieve a
low affinity between the two, especially in dry cutting processes
where high temperatures are reached. They offer the following
advantages:
• high resistance against adhesive wear, abrasive wear,
oxidation, oxygen diffusion (the layer already is as an oxide)
• chemical and thermal isolation and chemical indifference
• reduced friction even at temperatures of more than 1000 °C
• fewer built-up edges and less material interdiffusion in the trio
contact zone
Developments of cutting tools for high performance cutting of
rolling components
The process of manufacturing critical parts of railway rolling stock is
accompanied by:
• high removal of withdrawn allowance at cutting depth a=520mm,feed f=0.8-1.5 mm/rev and cutting speed V=30-50
m/min.
• high variation of cutting allowance
• inclusion of non-metallic particles with increased abrasive
properties on the machined surface of forged slab
Edge machining of workpieces under the above conditions products
elevated heating of the cutting area, which results in high
concentration of thermal stresses directly at the constant areas of
carbide inserts used in this process of manufacturing products for rail
transport. The studies of wear mechanisms of cutting carbide inserts
with coatings of various compositions have shown that the process
of wear of inserts under conditions of the high thermal stresses is
accompanied by thermoplastic deformation of cutting edge. This in
turn is connected with the subsequent intense failure of coating and
high adhesion and fatigue wear, which is accompanied by chipping of
cutting edges or complete failure of fragile cutting part of a tool.
In this regard, the decrease of thermal stress of the cutting area by
the deposition of nanoscale multilayer composite coatings (NMCCs)
on the working surfaces of the tool, which reduce friction and
capacity of heat sources. as well as the general improvement of the
conditions of heat transfer out of the cutting area improves the tool
life and the efficiency of the HPV processes. The studies of the effect
of wear-resistant coatings on the thermal state of the cutting system
under severe cutting conditions have shown that they reduce
thermal and mechanical loads on the tool and increase its efficiency.
The standard method for reducing thermal stress of the cutting
process includes the use of cutting fluids. However, under heavy
conditions of machining, the efficiency of cutting fluids decreases
significantly. Besides, specialized machine equipment (including
wheel turning machines and vertical turning machines), intended for
manufacturing of products (wheel sets, wheel bands, axles, etc.)
used in rail transport, does not use the systems of supply of liquid
fluids because of high probability of their intense damage. Thus, the
main objective of this study was to develop a tool system improving
the efficiency of the technology of heavy machining of workpieces of
rail rolling stock products by reducing the thermal stress of the
cutting process and cutting tools.
Deposition of nanoscale composite multilayer coatings (NMCC).
Nanoscale composite multilayer coatings were deposited on carbide
inserts using filtered cathodic vacuum arc deposition (FCVAD) with
the vacuum. The study used a three-component NMCC system,
comprising outer (wear-resistant) layer, intermediate layer, and
adhesive layer. The developed three-component NMCCS meet at
best the dual nature of coatings as an intermediate process medium
between the tool material and the material being machined. The
coating should at the same time increase the physical and
mechanical properties of the cutting tool (hardness, heat resistance,
wear resistance) and reduce thermal and mechanical effect on the
contact pads, resulting in their wear. The analysis of the influence of
the synthesis process parameters on various properties of composite
coatings (e.g. Ti-TIN-TICFAIN) has shown that the most important
parameters are as follows: current of titanium cathode arc is
nitrogen pressure in vacuum chamber P. and bias potential on the
substrate (tool during condensation of wear-resistant layer U. These
parameters were taken as major ones for the deposition of NMCCs
The investigation into the microstructure of NMCCS were carried out
on a Jeol electron scanning microscope JSM 6480LV. The
macroscopic properties of NMCCS, such as thickness, hardness,
friction coefficient, and strength of coating adhesion to substrate,
were determined by standard methods.
Using a portable computer tomography UPUC-2000, the
temperature gradient of the developed tool system was obtained as
shown in Fig. 2. Here a reduction in the intensity of the heat source
in the NMCC can be seen with a better heat dissipation through the
thermal pad.
Cutting properties of the developed tool system:
This study revealed a high efficiency of the developed tool system
based on double-sided T14K8 carbide inserts, with dense contact
with tool holder, provided by elastic pads of reinforced ceramic
polymer material with high thermal conductivity. Tool life and
coefficient of tool life variation for the developed tool system were
compared with commercial tool equipped with carbide inserts with
multilayer coating of the modem generation. The tool life coefficient
T (Fig 4) was determined as the ratio of tool life of coated insert to
tool life of an uncoated insert; and the tool life variation v was
determined as the ratio of standard deviation of tool life to its
arithmetic mean value.
The study showed that the developed tool system based on inserts
of carbide T14K8 with Ti-TiN-TiCrAIN NMCCS outperformed the
commercial version of carbide insert with coating of the modern
generation during hard reconstruction turning of running surfaces of
wheel sets . In particular, the study has shown not only the higher
average tool life value (88.1 min) and tool life coefficient 7 (2.1% but
also the decrease of the coefficient of tool life variation = 0.355). The
latter indicates the significant increase in the reliability of the
developed tool system for rough turning of wheelsets.
The results of production tests of carbide cutting tools with the use of
thermal pads made of NOMAKON KPTD-2 are shown in Table 2.
The analysis of the results of the production tests also shows the
increase in tool life in the developed tool system.
The effect of applied thermal pad on the nature of the wear of rake
and flank faces is illustrated below:
Conclusion:
The analysis of the results of laboratory and industrial tests has shown
that the use of the developed tool system, including carbide inserts
with NMCCs and set of structures for mounting the insert on the tool
holder, including high heat conducting ceramic polymer pads with
high thermal conductivity increased the actual contact bearing surface
between the carbide insert and the holder intensifies the effective heat
transfer along bearing surface of the insert. The combined effect of
the increase in heat transfer and reduction of frictional heat sources
due to application of the developed NMCCs showed a significant
reduction of the thermal stress of the cutting system during roughing
of rolling stock products. This new approach has positively
transformed the character of the tool wear, and brought in an
improvement of the tool life up to 4 times by increasing the reliability
of the tool due to reduction of the coefficient of tool life variation.