View
243
Download
5
Category
Preview:
Citation preview
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
1/33
Cutting-tool Materials & Cutting
Fluids
Dr. Ouzhan YILMAZ (Assoc.Prof.)
Room: 319
oyilmaz@gantep.edu.tr
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
2/33
Introduction
The selection of cutting tool materials is the most important factors in machiningoperations.
Cutting tools are generally recommended. There is no tool that fits exactly.
In the selection of cutting tool materials, the followings should be bear in mind:
Cutting tools are subject to high temperatures
High contact stresses
Rubbing along the tool-chip interface and machined surface
Cutting tool materials must possess the following characteristics:
- Hot Hardness: the cutting tool should maintain its hardness, strength and wearresistance at the high temperatures during machining.
- Toughness and impact strength: Cutting tools must resist the impact forces dueto interrupted cutting (milling or some turning operations) and forces due to
vibration and chatter without chipping or fracture.- Thermal shock resistance: Cutting tools should withstand the rapid temperature
cycling in interrupted cutting.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
3/33
Introduction
- Wear resistance: An acceptable tool life is
obtained before replacement is necessary.
- Chemical stability and inertness: Cutting
tool is to avoid or minimize any adverse
reactions, adhesions and tool-chip diffusion
that would contribute to tool wear.
Properties for determining desirable tool-
material characteristics:
Hardness and strength (wrt wp material)
Impact strength (interrupted cut, milling)
Melting temperature (tool material)
Physical properties (thermal conductivity,
thermal expansion)
Figure 1. Hot hardness variations
for different cutting tool materials
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
4/33
Introduction
The cutting tool materials (listed according to developing and implementing order):
1. High-speed steels
2. Cast-cobalt alloys
3. Carbides
4. Alumina-based ceramics
5. Cubic-boron nitride
6. Silicon-nitride-based ceramics
7. Diamond
8. Whisker-reinforced materials and nano-materials
Carbon steels are the oldest tool materials and they have been used widely for drills,taps, broaches, and reamers.
They are inexpensive, easily sharpened, not have sufficient hot hardness, wear resistancefor high cutting speeds and hard materials. They are not preferred in modernmachining operations.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
5/33
Introduction
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
6/33
Introduction
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
7/33
Introduction
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
8/33
High-speed Steel (HSS)
HSS tools were developed to machine at higher speeds.
HSS are the most highly alloyed of the tool steels.
They are hardened in various depth in order to have a good wear resistance.
Due to their toughness (high resistance to fracture), HSS are suitable for:
High positive rake angle tools
Interrupted cuts
Vibration and chatter due to low machine tool stiffness
Complex and single piece tools (drills, reamers, taps, and gear cutters)
HSS has lower hot hardness and theircutting speed are low compared to carbide tools.
The are two basic types of HSS:
- Molybdenum (M-series): %10Mo, Cr, V ,W and Co
- Tungsten (T-series): 12 to 18%W, Cr, V and CoM-series has higher abrasion resistance and less expensive. 95% HSS are M-series.
HSS are available in rolled, forged, cast, sintered (pm), coated, surface treated
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
9/33
Cast-cobalt alloys
Composition: 53% Co, 30-33% Cr, and 10-20 W
They have good hardness and resist elevated temperatures.
They are not as tough as HSS and sensitive to impact forces.
They are used for special operations, involving deep, continuous roughing cuts at high
feeds and speeds.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
10/33
Carbides
Cemented and sintered carbides were introduced to meet the challenge for increasingly
higher cutting speed (not possible using with HSS and cast-cobalt tools)
Carbides have high hardness over a wide range of temperatures, high elastic modulus,
high thermal conductivity, and low thermal expansion.
Therefore, they are among the most important, versatile, and cost-effective tool and die
materials for a wide range of applications.
1. Tungsten Carbide (WC):
- Tungsten carbide particles bonded together in a cobalt matrix
- They are manufactured bypowder metallurgy technique (sintered)
- They are used for cutting steels, cast irons, and abrasive nonferrous materials.
Micro grain Carbides and Functionally Graded Carbides
2. Titanium Carbide (TiC): consists of a nickel-molybdenum matrix. It has higher wear
resistance than WC but not as tough.
TiC can machine hard materials(steels and cast irons) and at higher cutting speed than WC.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
11/33
Inserts
Inserts are individual cutting tools with several
cutting points.
A square insert has eight cutting points, and a
triangular insert has six.
Inserts are usually clamped on the tool holder with
various locking mechanisms.
Each inserts has a number of cutting points and after
one edge is worn, it is indexed (rotated in its holder)to make another cutting point available. Quick
insertion and removal features are available.
Carbide inserts are available in a variety of shapes,
such as square, triangle, diamond and round.
The strength of the cutting edge of an insert dependson its shape.
The smaller the included angle, the lower the
strength of the edge.
Typical inserts with chip-breaker
features.
Figure 3 Methods of attaching inserts to toolholders:
(a) Clamping, and (b) Wing lockpins. (c)Examples of
inserts attached to toolholders with threadless
lockpins, which are secured with side screws
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
12/33
Inserts
The smaller the included angle, the lower the strength of the edge.
Figure 4 Relative edge strength and tendency for
chipping and breaking of insets with various
shapes. Strength refers to the cutting edge shown
by the included angles.
Figure 5 Edge preparation of inserts
to improve edge strength
Chip-breaker features on inserts are for the
purpose of;
(a) Controlling chip flow during machining
(b) Eliminating long chips
(c) Reducing vibration and heat generated
The selection of a particular chip-breakerfeature depends on the feed, depth of cut,
workpiece material, type of chip produced
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
13/33
Classification of Carbides Carbides grades are classified using the letters P,M and Kfor a range of applications.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
14/33
Classification of Carbides
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
15/33
Coated Tools Coatings on cutting tools have such
properties:
Lower friction
Higher adhesion
Higher resistance to wear and cracking
Acting as a diffusion barrier
Higher hot hardness and impact resistance
Coated tools can have lives 10 times longer
than those of uncoated tools, allowing for
high cutting speeds and thus reducing both
the time requiring for machining operations
andproduction costs.
Coated tools are used in 40% to 80% of all
machining operations (turning, milling,drilling)
Decreasing machining time also leads to
decreasing machining cost.
Figure Development of cutting tool materials
and improvement cutting speed year-by-year.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
16/33
Coating materials and coating methods
Commonly used coating materials are:
Titanium nitride (TiN)
Titanium carbide (TiC)
Titanium carbonitride (TiCN)
Aluminum oxide (Al2O3)
These coatings generally in the thickness range from 2 to 15 m, are applied on
cutting tools and inserts by two-techniques:
(1) Chemical-vapor deposition (CVD)(2) Physical-vapor deposition (PVD)
The CVD process is the most commonly used method for carbide tools with
multiphase and ceramic coatings.
PVD-coated carbides with TiN coatings have higher cutting edge strength, lowerfriction and lower tendency to form built-up edge.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
17/33
Coating materials and coating methods
Coatings forcutting tools and dies should have the following general characteristics:
High hardness at elevated temperatures
Chemical stability and inertness to the workpiece materials
Low thermal conductivity to prevent temp rise in the substrate
Compatibility and good bonding to the substrate
Little or no porosity in the coating, to maintain its integrity and strength
The effectiveness of coatings is enhanced by the hardness, toughness and high thermal
conductivity of the substrate (carbide or HSS)
Titanium-nitride Coatings (gold color): It provides low friction coefficient, high
hardness, resistance to high temp and good adhesion to the substrate.
They improve life of HSS and carbide, drill bits and cutter.
They perform well at higher cutting speeds and feeds.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
18/33
Coating materials and coating methods Titanium-carbide coatings: are on tungsten carbide inserts which have high-flank
wear resistance in machining abrasive materials.
Ceramic coatings: Because of their chemical inertness, low thermal conductivity,resistance to high temperature, and resistance to flank and crater wear. The mostcommonly used ceramics is aluminum oxide (Al2O3)
Multiphase coatings: Carbide tools are now available with two or three layers of suchcoatings and particularly effective in machining cast irons and steels.
For example, one could first deposit TiC over the substrate, followed by Al2O3 and then
TiN. The first layer should bond well, the outer layer should resist wear and have lowthermal conductivity and intermediate layer should bond well and be compatible bothlayers.
Typical applications of multiple-coated tools are as follows:
1. High-speed, continuous cutting: TiC/ Al2O3
2. Heavy-duty, continuous coating: TiC/ Al2O3 /TiN
3. Light, interrupted cutting: TiC/TiC+TiN/TiN
The thickness of these layers is on the order of2 to 10m. Thinner coatings increasehardness with decreasing grain size. Thin layers are harder than thick layers.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
19/33
Coating materials and coating methods A typical multi-phase-coated carbide tool may consists of the following layers, starting
from the top, along with their primary function:
1. TiN: low friction2. Al2O3 : high thermal stability
3. TiCN: fiber reinforced with a good balance of resistance to flank wear and crater wear,
particularly for interrupted cutting.
4. A thin-carbide substrate: high fracture toughness
5. A thick-carbide substrate: hard and resistant to plastic deformation at high temperatures.
Figure 7 Multiphase coatings on a tungsten-carbide
substrate. Three alternating layers of aluminum
oxide are separated by very thin layers of titanium
nitride. Inserts with as many as thirteen layers of
coatings have been made. Coating thicknesses are
typically in the range of 2 to 10 m.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
20/33
Coating materials and coating methodsDiamond Coatings: Polycrystalline diamond is being used widely as a coating for cutting
tools, particularly on tungsten-carbide and silicon-nitride inserts.
They are effective in machining nonferrous metals, abrasive materials such asaluminum alloys containing silicon, fiber-reinforced and metal-matrix composite
materials, and graphite.
Diamond-coated inserts: Thin films are deposited on substrates through PVD or CVD
techniques.
Thick films are obtained by growing a large sheet ofpure diamond, which is then lasercut to shape and brazed to a carbide insert.
Multilayer nanocrystal diamond coatings are used to give strength to the coating.
Good adherence of the diamond film to the substrate and minimize the difference in
thermal expansion between diamond and substrate materials.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
21/33
Coating materials and coating methodsMiscellaneous Coating Materials:
- Titanium carbonitride (TiCN) and Titanium-aluminum nitride (TiAlN) are effective in
cutting stainless steels.- TiCN is harder and tougher than TiN and used on carbides and HSS.
- TiAlN is effective in machining aerospace alloys
- Chromium carbide (CrC) is used for cutting softer metals that tend to adhere to the
cutting tool, such as aluminum, copper and titanium
- Zirconium Nitride (ZrN)- Hafnium Nitride (HfN)
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
22/33
Alumina-based Ceramics Ceramic tool materials consist primarily offine-grained, high purity aluminum oxide.
They are cold pressed into insert shapes underhigh pressure and sintered at high
temperatures. Additions oftitanium carbide and zirconium oxide help improve properties such as
toughness and thermal shock resistance.
Alumina-based ceramic tools have very high abrasion resistance and hot hardness.
Chemically, the are more stable than HSS and carbides, so they have less tendency to
adhere to metals and lower tendency to form a build-up edge. Ceramics lack toughness, and their use may result in premature tool failure by
chipping or in catastrophic failure.
Ceramic inserts are effective in high-speed, uninterrupted cutting operations.
Ceramic tool shape and set-up are important. Negative rake angles (large included
angles) generally are preferred in order to avoid chipping due to the poor tensilestrength of ceramics.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
23/33
Cerments (ceramic and metal) They consist ofceramic particles in a metallic matrix.
A typical cermet consists of70% aluminum oxide and 30% titanium carbide; other
cermets contain molybdenum carbide, niobium carbide, and tantalum carbide.
Cermets have chemical stability and resistance to built-up edge formation.
Brittleness and high cost are limitations.
Figure 8 Ranges of properties for
various groups of tool materials.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
24/33
Cubic Boron Nitride
Cubic boron nitride (cBN) is the hardest material available.
cBN is made by bonding a 0.5 to 1 mm layer of polycrystalline cubic boron nitride to a
carbide substrate by sintering under high pressure and high temperatures.
While the carbide provides shock resistance the cBN layerprovides very high wear
resistance and cutting edge strength
At elevated temperatures, cBN is chemically inert to iron and nickel (no wear due to
diffusion)
Because cBN tools are brittle, stiffness of the machine tool and fixturing is importantto avoid vibration and chatter.
Figure 9 Construction of a
polycrystalline cubic boron nitride
or a diamond layer on a tungsten-
carbide insert
Figure 10 Inserts with polycrystalline
cubic boron nitride tips (top row) and
solid polycrystalline cBN inserts (bottom
row).
Di d
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
25/33
Diamond
Of all known materials, the hardest substance is diamond.
As a cutting tool, it has highly desirable properties, such as low friction, high wear
resistance, and the ability to maintain a sharp cutting edge.
Diamond is used when a good surface finish and dimensional accuracy are required,
particularly with soft nonferrous alloys and abrasive nonmetallic and metallic
materials.
Synthetic or industrial diamonds are widely used.
Because diamond is brittle, tool shape and sharpness are important. Low rake angles are generally used to provide strong cutting edge.
Wear may occur through microchipping (caused by thermal stresses and oxidation) and
through transformation to carbon.
Diamond tools can be used satisfactorily at almost any speed, but are most suitable for
light, uninterrupted finishing cuts. Diamond is not recommended for machining plain-carbon steels or titanium, nickel,
and cobalt-based alloys.
Diamond is also used as an abrasive in grinding and polishing operations and coatings.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
26/33
Whisker-reinforced Materials and Nanomaterials
In developing new tool materials, the followings are concered:
- High fracture toughness
- Resistance to thermal shock
- Cutting-edge streghth
- Creep resistance
- Hot hardness
Whiskers as reinforcing fibers in composite cutting tool materials
Examples of whisker-reinforced cutting tools include:
(a) silicon-nitride based tools
(b) Aluminum-oxide based tools
Suitable nanomaterials are carbides and ceramics.Nanomaterials are applied as a thin coating and able to machine at higher speeds
T l C d R di i i f T l
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
27/33
Tool Costs and Reconditioning of Tools
Tool costs vary widely, depending on the tool material, size, shape, chip breaker
features and quality.
Tooling costs in machining have been estimated to be on the order of2 to 4 % of themanufacturing costs.
Cutting tools can be reconditioned by resharpening them, using tool and cutter
grinders with special fixtures.
Reconditioning of coated tools is also done by recoating them.
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
28/33
Cutting Fluids Cutting fluids have been used extensively in machining operations to achieve the
following results:
(a) Reduce friction and wear, thus improving tool life and the surface finish(b) Cool the cutting zone, thus improving tool life and reducing the temperature and
thermal distortion of the wp
(c) Reduce forces and energy consumption
(d) Flush away the chips from the cutting zone
(e) Protect the machined surface from environmental corrosion.
Cutting fluid could be a coolant, a lubricant or both.
The effectiveness of cutting fluid depends on:
(1) Type of machining operation
(2) Tool and workpiece materials
(3) Cutting speed
(4) Method of application
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
29/33
Cutting Fluids Water: excellent coolant, but not a lubricant. Results oxidation.
Cutting fluids are used for turning, milling, drilling, gear cutting, thread cutting,
tapping, and internal broaching. In some cases, cutting fluids may cause: curly chip which lead to heat concentration
on tool tip, reducing tool life, thermal cycling (interrupted cutting) and thermal
cracks.
Cutting fluid has a capillary action that seeping the tool-chip interface.
T f C tti Fl id
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
30/33
Types of Cutting Fluids
Four general types of cutting fluids are commonly used in machining operations:
(1) Oils: mineral, animal, vegetable, compounded, and synthetic oils, typically used for
low-speed operations where temp rise is not significant.(2) Emulsions (soluble oils): a mixture of oil and water and additives, generally used for
high-speed operations. Water makes it effective coolant. Oil eliminates the oxidation
and supply lubrication.
(3) Semisynthetics are chemical emulsions containing little mineral oil, diluted in water,
and with additives that reduce the size of oil particles, making them more effective.(4) Synthetics: are chemicals with additives, diluted in water and containing no oil.
Methods of Cutting fluid Application
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
31/33
Methods of Cutting-fluid Application
There are four basic methods of cutting fluid applications in machining:
(1) Flooding: flow rates are from 10L/min for single-point tools to 225L/min per cutter
for multiple-tooth cutters as in milling. For drilling and milling, flushing pressure is700 to 14000 kPa.
(2) Mist: cooling of inaccessible areas. It is effective with water-based fluids at air
pressures from 70 to 600kPa.
(3) High-pressure systems: Delivering cutting fluid via specially designed nozzles that
aim a powerful jet of fluid to the zone, into the clearance or relief face of the tool.
Pressure is 5.5 to 35MPa. Used in high-speed applications and CNC machines
(4) Through the cutting tool system: Cutting fluids is passed through the passages
produced in the cutting tool.
The aim is to supply fluid into cutting zone for specific machining operations
(a) gun drilling: a long small hole through the body of the drill
(b) boring bars: a long hole through the shank (tool holder)
Flooding applications
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
32/33
Flooding applicationsFigure 11 Schematic illustration of
proper methods of applying
cutting fluids in various
machining operations: (a) turning,(b) milling, (c) thread grinding,
and (d) drilling
Mist Cooling
Effects of Cutting Fluids
7/27/2019 Cutting Tool Materials and Cutting Fluids by Dr. Ouzhan YILMAZ
33/33
Effects of Cutting Fluids
The selection of a cutting fluid, the followings should also be considered:
Workpiece material and machines tool
Biological considerations
The environments
Cutting fluids containing sulfurshould not be used with nickel-based alloys
Fluids containing chlorine should not be used with titanium
Machined parts should be cleaned and washed to remove any cutting fluid residue.
Since additional process can easily be applied, such as coating, painting, welding,
brazing etc. See surface cleaning section 34.16
Operator health concern due to mist, fumes, smoke and odors of cutting fluids.
Cutting fluid also environmental effects after used
Proper techniques should be used forfiltering cutting fluids to be reused
Disposal of cutting fluids must obey environmental laws of the government.
Recommended