Innovations in Cutting Tool
Technology: Implications for Manufacturing and Industrial Technology Programs
By
Dr. Samuel C. Obi and Dr.
Nicholas Akinkuoye
Introduction
Machine
tools help to make any industrialized nation. They are used for different
industrial processes, particularly in the manufacturing industry. But machine
tools are of little use without cutting tools. Cutting tools have been the
lifeblood of manufacturing industry since the Industrial Revolution. They are
the tools used to transform raw materials into quality finished products,
employing processes such as drilling, milling, turning, sawing, blanking etc.
Since their discovery, cutting tools have undergone numerous changes, which
have made them more effective.
Modern
cutting tools as we know them today actually were introduced around the turn of
the 20th century, but have witnessed tremendous metamorphosis since
then. In recent years metamorphosis in cutting tools has grown steadily as a
result of global and domestic competition. Intense Global competition and the
demand for maximum productivity at minimal cost and better quality of
manufactured products has been the catalyst for the recent innovations in
cutting tools.
This paper examines the changes
and innovations in cutting tool materials, design, geometry, applications and
management; their effectiveness in continuous quality production; and what all
this means to the manufacturing programs offered by Industrial Technology.
Emphasis will be on reasons why these changes are taking place and their
implications for Industrial Technology programs in the new millennium. It is
imperative that students in Technology Programs are made aware of these
innovations, and how they impact the manufacturing industry.
Innovations
in Cutting Tool Materials
Cutting
tools are made of hard materials. The story of the many innovations in cutting
tool materials actually parallels their history. Carbon steel was the first
cutting tool material to appear at the turn of the 20th century (Kalpakjian
1995). It was almost immediately followed (and nearly replaced) by high-speed
steel cutters which were more wear resistant. But the proliferation of
different harder-to-machine workpiece materials posed a serious challenge to
metal working industry even to this day, when research on newer and better
cutting tool materials is carried out more than at any other time in history.
According to Quinto (1996), newer, harder-to-machine workpiece materials have
become the driving force in the research for new cutting tool materials,
because they tend to be lightweight, stronger, and more difficult to machine.
Every metal cutting business knows that unrestrained wear on tools results in
constant replacement of worn tools, constant tool resharpening, loss of
accuracy and tolerances, more machine downtime, and tool changes half-way
through the part. Thus, cutting tool materials like cemented carbides (coated
and uncoated), silicon nitride, diamonds, cermets, ceramic and most recently
cubic boron nitride (CBN) followed in the resulting evolution.
In
their search for newer and better cutting tool materials, researchers have
investigated different grades of materials. This helps them to determine the
best application for such materials. For example, according to researchers at
Kennametal (1998), diamonds and cubic boron nitride, which are the hardest
natural material known to man, actually belong to a group of materials known as
polycrystalline (or PCD and PCBN) grades. Similarly, ceramic grades are divided
into two families known as alumina based (Al2O3) and silicon nitride based
(Si3N4). Cermet grades are comprised of mostly titanium carbonitride (TiCN)
with nickel binder.
The
list of cutting tool materials is not likely to diminish as long as
metalcutting business remains a major portion of manufacturing industry.
Industry observers like Quinto (1996) predicted that the developments that will
most likely add to the arsenal of current tool materials would include a) more
PVD coatings, b) superhard PCD and PCBN product extensions, c) superhard
diamond and CBN coatings, and d) tougher alumina-based ceramics. Already most
of these predictions are being implemented, as will be seen in the next
section.
Innovations
in Cutting Tool Coatings
For
most machining applications, coated grades are the best choice because coatings
reduce frictional forces at the cutting tip, add chemical stability, and have
hot hardness at elevated temperatures often encountered in metalcutting
(Kennametal, 1998). Coatings can literally extend a tool’s life many times its
original uncoated life (Smith, 1999). By definition, coating is simply applying
a thin layer of another (often harder, more wear resistant) material on the
surface of a cutting tool material. Coatings can be thin or thick, with thin
coatings defined as “anything less than 50 microns thick” (Vasilash,
1995). For most hard cutting
applications, coating materials currently include thin films of diamond,
titanium nitride (TiN), titanium aluminum nitride (TiAlN) and titanium
carbonitride (TiCN).
According
to Jindal et al (1999) coatings, while primarily increasing wear resistance,
may also reduce cutting forces and temperatures at the tool’s edge and thereby
indirectly affect the deformation and fracture behavior of the tool. Since the
introduction of this critical innovation to the metal-cutting industry in the
mid 1980s, coating technology has gone from single coating to multiple
coatings, usually described as “double” and triple “coatings”. Researchers have
discovered that application of multiple layers of the coating materials
increases the cutting life of the material substrate of the cutter.
Two
major processes of applying the coating materials are physical vapor deposition
(PVD) and chemical vapor deposition (CVD). While a detailed explanation of the
principles of the two processes is beyond the scope of this paper, it should be
mentioned that PVD coated inserts are generally ideal for low speed, low
temperature applications, while the reverse tends to be the case for CVD coated
inserts. Moreover, while both PVD and CVD coatings increase wear resistance,
researchers at Kennametal, Inc have found that CVD coatings tend to reduce the
fracture strength of the tool material due to the presence of grown-in cracks
due to tensile residual stresses in the coating (Jindal, 1999).
Innovations in Cutting Tool Applications
For
industrial applications, the traditional calculations of machining speeds and
feeds have practically changed dramatically. Those calculations appear to be
for small shops and educational institutions, where carbon and high speed steel
cutters are still used on small jobs and academic projects. But the robust
nature of modern industrial machining demands and the increasing domestic and
foreign competition have literally changed the rules.
Because
of the drastic deviations in modern machining speed and feed calculations,
cutting tool manufacturers have now recognized the need for guidelines in
proper tool selection procedure. For example, Kennametal (1998) has recommended
a 3-step process for properly selecting their inserts for just about any
machining application. For a particular workpiece material, the company
recommends the following steps in selecting the most ideal insert: a) select
insert geometry, b) select the insert grade, and c) select the starting speed.
These data are published in their manuals where engineers and machinists use
them for their various machining applications.
Because
of the differences in their hardness, and hence the need to apply a specific
cutting tool material to each machining task, workpiece materials have been
grouped into six major categories or families of similar hardness groups by
engineers at Kennametal, Inc. Table 1 contains these six groups. It can easily
be understood that a tool selected for machining materials in group 5, for
instance, will not be an ideal tool for machining the materials in group 2.
Table 1*
Six workpiece Machinability
Groups
____________________________________________________________________________
Group # Materials
____________________________________________________________________________
1 Low carbon steels, medium
carbon steels, alloy and tool steels (48 and less
HRc), ferritic, martensitic, and PH stainless steels
2 Hardened steels and hardened
irons
3 Austenitic stainless steels
4 Ductile and malleable cast
irons, gray irons
5 Free-machining and
low-silicon aluminum alloys, high-silicon aluminum alloys, miscellaneous
non-ferrous work materials
6 Iron-base, heat-resistant
alloys; cobalt-base, heat resistant alloys
nickel-base,
heat-resistant alloys; titanium and titanium alloys
__________________________________________________________________________
* Adapted from Kennametal (1998)
Coated
carbide grades find the most applications in modern machining in just about
every process, i.e. milling, turning boring, drilling etc. They are excellent
for general machining applications. Caution should, however, be exercised when
they are used, since their coating materials have a tendency to chemically
contaminate some workpiece materials in high temperature cutting operations.
For this reason, uncoated grades are sometimes used, to avoid the risk of
contamination, but at the expense of more frequent tool changes as a result of
increased wear on the cutter.
Ceramics
and cermets are good candidates for high-speed, high-temperature applications.
Polycrystalline (diamonds and CBN) grades are more expensive but can withstand
wear longer than other cutting tools at very high speeds. They are also
excellent candidates for obtaining mirror finish surfaces and for operations
that have interrupted cuts.
Innovations in Cutting Tool Management
Traditional
tool management system (which is basically a tool crib, attendant(s) and manual
information entry etc.) is too laborious and prone to mistakes, which every
manually operated process is noted for. It also wastes time, results in
carrying too much inventory, and can cause unnecessary spending on tools, which
can be as high as 30% or more (Hogan, 2000). Many metalworking companies
(especially the big ones) with ever expanding files and literally thousands of
cutting tools need a system that will not only facilitate the management of
their tools, but also will integrate the database with other company systems.
According to Hogan (2000) such a system will provide full information on tool
allocation, availability, usage, cost etc. Such a system will also provide a
tracking capability and tool quality support efforts in the company’s quality
standard requirements.
Modern
tool inventory control systems provide an easy solution to these challenges.
These systems are being implemented in major companies at an alarming rate. The
system has basically same components which many inventory systems have. Some
companies, perhaps to replace the crib attendant or to save time, are also
installing tool dispensing machines, where an operator inputs some code and the
required tool is dispensed, much like a coke machine.
Tool
inventory control systems help tool managers to have updated information on all
tools, a key factor in tasks like locating a missing tool, accounting for
broken tools, knowing when to recondition (sharpen) a tool, knowing when to
purchase new tools, maintaining important files on tool calibration data and
such like. Herko (1999) sums it all up when he noted that:
Tool
management systems add value to manufacturing operations by supplying information about how tools are used, reused,
reworked, and maintained. They capture information
about tool usage, consumption, and usage patterns as well as track tooling. They facilitate everything from tool
kitting to presetting and pregaging so that setup time at the machine tool is dramatically reduced. They must be
flexible enough to manage the inventory
within a variety of tool storage systems, including automated storage and retrieval systems, tool dispensing
units, open tool storage, multiple tool storage cribs, point of use tool storage, central tool storage, and
cellular storage aided by the latest in bar-coding
and data collection devices.
The list of the type of
information to be stored in a tool inventory control system is endless. The
systems are so broad that the needs of each user manufacturer can be served
adequately.
Innovations in Cutting tool Geometry and Conditioning
It
has already been noted that machine tools will be of little use without cutting
tools. But to perform an efficient cutting of materials, cutting tools must be
conditioned or ground to the right configuration, much like sharpening a knife
before it can be used to peel an orange. This given configuration of cutting
tools is what is called their geometry. If the cutter is not given the proper
geometry, it simply will not function well. For the sake of simplicity and
because of the different types of cutters in the metalworking business today,
this discussion will be limited to single-point cutters only.
Six
cutting angles and one radius can adequately describe the geometry of a
single-point-cutting tool (Wakil, 1998). They are: back rake angle, side rake
angle, end relief angle, side relief angle, end cutting-edge angle, side cutting-edge
(or lead) angle, and a nose radius. The standard recommended angles for each
one of these, together with the purposes they serve are contained in Table 2.
Table 2
Standard Geometry of a
Single-Point Cutter
__________________________________________________________________________
Angle Purpose Recommended Angle in degrees
__________________________________________________________________________
Back rake Determines direction of chip flow 0
Side rake Determines direction of chip flow 0-15
End relief Eliminates rubbing
b/w work and tool 5-15
Side relief Eliminates rubbing
b/w work and tool 5-15
End cutting-edge Eliminates rubbing b/w work and
tool 15-30
Side cutting-edge (lead) Provides actual cutting & shoulder
angle 5-15
___________________________________________________________________________
Cutting
tool manufacturers modify these angles and their corresponding radii to meet
their specific needs. However, changing any one of these angles will result in
a number of things, such as tool chattering, more force requirement, frequent
tool breakages etc. Because modern machine tools have more power, tool
manufacturers can modify these angles to minimize or avoid tool breakage, and
increase machine rigidity without really taking a lot out of the machine. As a
result, traditional speed and feed calculations as we know them do not really
hold in today’s industrial applications, when spindle speeds can reach
something in the excess of 40,000 rpm and work tables travel faster than ever.
More sophisticated formulas for aggressive machining applications such as those
derived by Isakov (1996) are being developed.
Another
aspect of cutting tools that has experienced some remarkable innovation is
reconditioning and/or resharpening of tools. Tool resharpening is gaining some
momentum among many tool users, because cutting tool costs tend to be rising as
their level of sophistication increases. The premise is that it is cheaper to
regrind a used tool than to buy a new one. Sophisticated grinding machines
designed exclusively for grinding cutting tools are now on the market. These
machines come with devices that make angular settings possible so that proper
tool geometry can be achieved during tool restoration. Some companies have
dedicated their operations to grinding tooling cutters for other metalworking
businesses.
Implications for Industrial/Manufacturing Technology
This
paper has discussed innovations in cutting tool technology, a key component of
manufacturing, which in turn is one of the major programs offered by Industrial
Technology. Since students of this program will eventually graduate and work
for employers who are already using modern technologies, it makes a lot of
sense to argue that manufacturing programs should be equipped with similar
technologies so that these students will be better prepared. Presently, many
manufacturing programs are still equipped with much of the old concepts and
technologies, a situation that can easily deny graduates of critical
information and proper preparation for their new job roles.
Although
modern technologies are very expensive, manufacturing educators still can make
a great impact if proper steps are taken. In an era of shrinking manufacturing
equipment monies in many colleges and universities, one possible step is to
seek outside grants (monies and/or equipment grants). Today, many organizations
are willing to help educators who approach them for such help. That is why it
is very important that higher education and industry form a closer partnership.
But in the absence of that, industry will always be ahead of education, when
the reverse should have been the case. The situation needs an urgent attention.
References
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Jindal, P. C.; Santhanam, A. T.; Shuster, A. F.; Marsh B. K; & Schleinkofer, U. (February, 1999). PVD
Coatings for Turning. Cutting
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