The document discusses cutting tool technology, including tool materials, geometry, and failure modes. It describes how tool life is influenced by cutting speed and material properties. Common tool materials include high-speed steel, cemented carbides, ceramics, and coatings. Tool geometry depends on the operation, with single-point and multiple-point tools discussed. Twist drills are a type of multiple-point tool used for hole making.
Chronological developments in Cutting Tool MaterialsBilal Syed
This is ap resentation showing the developments of cutting tools materials used from early life to present. their materials, properties, advantages, etc.
In this report the basic design principles and the current state-of-the-art for cutting tools specially designed to be applied on difficult-to-cut materials are described. One by one, the main aspects involved in tool design and construction will be explained in depth over the following sections, completing a general view of the tool world, to provide easy comprehension of the whole book. Materials for the substrates, coatings, and geometry are explained, with special attention to recent developments. A section is devoted to new machining techniques such as high-feed and plunge milling, turn milling and trochoidal milling.
Chronological developments in Cutting Tool MaterialsBilal Syed
This is ap resentation showing the developments of cutting tools materials used from early life to present. their materials, properties, advantages, etc.
In this report the basic design principles and the current state-of-the-art for cutting tools specially designed to be applied on difficult-to-cut materials are described. One by one, the main aspects involved in tool design and construction will be explained in depth over the following sections, completing a general view of the tool world, to provide easy comprehension of the whole book. Materials for the substrates, coatings, and geometry are explained, with special attention to recent developments. A section is devoted to new machining techniques such as high-feed and plunge milling, turn milling and trochoidal milling.
This slide describes two essential elements in machining operations:
cutting-tool materials and cutting fluids.
° The slide opens with a discussion of the types and characteristics of cutting tool materials.
° The properties and applications of high-speed steels, carbides, ceramics, cubic boron nitride, diamond, and coated tools are described in detail.
The types of cutting fluids in common use are then described, including their functions and how they affect the machining operation.
° Trends in near-dry and dry machining are also discussed, and their importance with respect to environmentally friendly machining operations are explained.
The selection of cutting-tool materials for a particular application is among the most important factors in machining operations, just as the selection of mold and die
materials was critical for forming and shaping processes . We will discuss throughout this slide the relevant properties and performance characteristics of all major types of cutting-tool materials, which will help us in tool selection.
However, as it will become apparent, the complex nature of this subject does not always render itself to the determination of appropriate tool materials; hence, we also must rely on general guidelines and recommendations that have been accumulated in industry over many years.More detailed information on tool material recommendations for specific workpiece materials and machining operations will be presented.
As noted, the cutting tool is subjected to
(a) high temperatures,
(b) high contact stresses, and
(c) rubbing along the tool-chip interface and along the machined surface.
Consequently, the cutting-tool material must possess the following characteristics:
° Hot hardness, so that the hardness, strength, and wear resistance of the tool are maintained at the temperatures encountered in machining operations. This property ensures that the tool does not undergo any plastic deformation and thus retains its shape and sharpness.
Toughness and impact strength (or mechanical shock resistance), so that impact forces on the tool that are encountered repeatedly in interrupted cutting operation (such as milling and turning a splined shaft on a lathe) or forces due to vibration and chatter during machining do not chip or fracture the tool.
Thermal shock resistance, to withstand the rapid temperature cycling encountered in interrupted cutting.
Wear resistance, so that an acceptable tool life is obtained before replacement is necessary.
Chemical stability and inertness with respect to the material being machined, to avoid or minimize any adverse reactions, adhesion, and tool-chip diffusion that would contribute to tool wear.
Classification of Tool Materials.
For More Details
Subscribe to My YOUTUBE CHANNEL
Engineering Study Materials : https://www.youtube.com/channel/UC8vigo0VxccfcGnmJnf-ESA
Cutting of hardened steel is a topic of high interest for toda 's industrial production and scientific research.
Machine parts consisting of hardened steel are high peiormance components which are often loaded
near their physical limits. The functional behavior of machined parts is decisively influenced by the fine
finishing process which represents the last step in the process chain and can as well be undertaken by
cutting as grinding. An overview of the mechanisms of chip removal in hard cutting and the thermomechanical
influence of the work area is presented. Furthermore, several models of chip removal in hard
turning are introduced and discussed summarizing the metallurgical fundamentals and giving an overview
on stress and temperature distributions in the work area. Boundary conditions for hard cutting as e.g.
machine tools, cutting materials and others are subject to discussion to determine the achievable
workpiece quality and economic efficiency of hard cutting processes in comparison with grinding.
Unit 2 Machinability, Cutting Fluids, Tool Life & Wear, Tool MaterialsMechbytes
Concept of machinability, machinability index, factors affecting machinability
Different mechanism of tool wear types of tool wear (crater, flank etc.), Measurement and control of tool wear
Concept of tool life, Taylor's tool life equation (including modified version)
Different tool materials and their applications including effect of tool coating
Introduction to economics of machining
Cutting fluids: types, properties, selection and application methods
Presentation on steel, fabrication & erection Munger Ganga BridgeAshish Kumar Yadav
Presentation on Steel Fabrication work and Erection of girder by Cantilever erection method.
One of the largest bridge in India (Bridge Length 3.690 Km)
Similar Bridge 1. Patna- Sonpur (Digha Bridge) across the river Ganga, Bihar
2. Bogibeel across river Brahmaputra in Assam
This slide describes two essential elements in machining operations:
cutting-tool materials and cutting fluids.
° The slide opens with a discussion of the types and characteristics of cutting tool materials.
° The properties and applications of high-speed steels, carbides, ceramics, cubic boron nitride, diamond, and coated tools are described in detail.
The types of cutting fluids in common use are then described, including their functions and how they affect the machining operation.
° Trends in near-dry and dry machining are also discussed, and their importance with respect to environmentally friendly machining operations are explained.
The selection of cutting-tool materials for a particular application is among the most important factors in machining operations, just as the selection of mold and die
materials was critical for forming and shaping processes . We will discuss throughout this slide the relevant properties and performance characteristics of all major types of cutting-tool materials, which will help us in tool selection.
However, as it will become apparent, the complex nature of this subject does not always render itself to the determination of appropriate tool materials; hence, we also must rely on general guidelines and recommendations that have been accumulated in industry over many years.More detailed information on tool material recommendations for specific workpiece materials and machining operations will be presented.
As noted, the cutting tool is subjected to
(a) high temperatures,
(b) high contact stresses, and
(c) rubbing along the tool-chip interface and along the machined surface.
Consequently, the cutting-tool material must possess the following characteristics:
° Hot hardness, so that the hardness, strength, and wear resistance of the tool are maintained at the temperatures encountered in machining operations. This property ensures that the tool does not undergo any plastic deformation and thus retains its shape and sharpness.
Toughness and impact strength (or mechanical shock resistance), so that impact forces on the tool that are encountered repeatedly in interrupted cutting operation (such as milling and turning a splined shaft on a lathe) or forces due to vibration and chatter during machining do not chip or fracture the tool.
Thermal shock resistance, to withstand the rapid temperature cycling encountered in interrupted cutting.
Wear resistance, so that an acceptable tool life is obtained before replacement is necessary.
Chemical stability and inertness with respect to the material being machined, to avoid or minimize any adverse reactions, adhesion, and tool-chip diffusion that would contribute to tool wear.
Classification of Tool Materials.
For More Details
Subscribe to My YOUTUBE CHANNEL
Engineering Study Materials : https://www.youtube.com/channel/UC8vigo0VxccfcGnmJnf-ESA
Cutting of hardened steel is a topic of high interest for toda 's industrial production and scientific research.
Machine parts consisting of hardened steel are high peiormance components which are often loaded
near their physical limits. The functional behavior of machined parts is decisively influenced by the fine
finishing process which represents the last step in the process chain and can as well be undertaken by
cutting as grinding. An overview of the mechanisms of chip removal in hard cutting and the thermomechanical
influence of the work area is presented. Furthermore, several models of chip removal in hard
turning are introduced and discussed summarizing the metallurgical fundamentals and giving an overview
on stress and temperature distributions in the work area. Boundary conditions for hard cutting as e.g.
machine tools, cutting materials and others are subject to discussion to determine the achievable
workpiece quality and economic efficiency of hard cutting processes in comparison with grinding.
Unit 2 Machinability, Cutting Fluids, Tool Life & Wear, Tool MaterialsMechbytes
Concept of machinability, machinability index, factors affecting machinability
Different mechanism of tool wear types of tool wear (crater, flank etc.), Measurement and control of tool wear
Concept of tool life, Taylor's tool life equation (including modified version)
Different tool materials and their applications including effect of tool coating
Introduction to economics of machining
Cutting fluids: types, properties, selection and application methods
Presentation on steel, fabrication & erection Munger Ganga BridgeAshish Kumar Yadav
Presentation on Steel Fabrication work and Erection of girder by Cantilever erection method.
One of the largest bridge in India (Bridge Length 3.690 Km)
Similar Bridge 1. Patna- Sonpur (Digha Bridge) across the river Ganga, Bihar
2. Bogibeel across river Brahmaputra in Assam
Please refer this file just as reference material. More concentration should on class room work and text book methodology.
Thermal aspects of Machining, Tool materials, Tool wear Cutting fluids and Machinability.
Numerical simulation of friction stir butt welding processes for az91 magnesi...eSAT Journals
Abstract Friction Stir Welding (FSW) is a solid state welding process. In particular, it can be used to join high-strength aerospace magnesium and other metallic alloys that are hard to weld by conventional fusion welding. It was performed on 4 mm thickness AZ91 Magnesium alloy. Magnesium alloy have more advantage than aluminum such as light weight, softer, tendency to bend easily, cost effective in terms of energy requirements so magnesium alloy has selected in this FSW technique. In friction stir welding (FSW), a momentous residual stress is present in weld due to complex nature of fixturing system compared to fusion welding. These residual stresses can affect properties of welded components during service. Therefore, for estimating magnitude of welding residual stresses and their nature of distribution along with thermal history, a three dimensional non- linear thermo-mechanical finite element (NLTMFE) model using ABAQUS/ CAE package was developed for butt welded magnesium alloy AZ91. The objective of this work is to predict the temperature distribution in both materials and evaluate the mechanical properties during the friction stir welding on magnesium alloy. Keywords: Fsw, Nltmfe, Abaqus, Cae, Az91.
Numerical simulation of friction stir butt welding processes for az91 magnesi...eSAT Publishing House
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
Determining the influence of cutting fluids on tool wear and surface roughnes...Lepuufu
Knowledge of the performance of cutting fluids in machining different work materials is
of critical importance in order to improve the efficiency of any machining process. The
efficiency can be evaluated based on certain process parameters such as flank wear, surface
roughness on the work piece, cutting forces developed, temperature developed at the tool
chip interface, etc. The objective of this work is to determine the influence of cutting fluids
on tool wear and surface roughness during turning of AISI 304 with carbide tool. Further
an attempt has been made to identify the influence of coconut oil in reducing the tool
wear and surface roughness during turning process. The performance of coconut oil is also
being compared with another two cutting fluids namely an emulsion and a neat cutting oil
(immiscible with water). The results indicated that in general, coconut oil performed better
than the other two cutting fluids in reducing the tool wear and improving the surface finish.
Coconut oil has been used as one of the cutting fluids in this work because of its thermal
and oxidative stability which is being comparable to other vegetable-based cutting fluids
used in the metal cutting industry.
Unit 8 - Information and Communication Technology (Paper I).pdfThiyagu K
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This will be used as part of your Personal Professional Portfolio once graded.
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2. Cutting Tool Technology
Two principal aspects:
1. Tool material
2. Tool geometry
ISE 316 - Manufacturing
Processes Engineering
3. Three Modes of Tool Failure
Fracture failure
◦ Cutting force becomes excessive and/or
dynamic, leading to brittle fracture
Temperature failure
◦ Cutting temperature is too high for the tool
material
Gradual wear
◦ Gradual wearing of the cutting tool
ISE 316 - Manufacturing
Processes Engineering
4. Preferred Mode of Tool Failure:
Gradual Wear
Fracture and temperature failures are
premature failures
Gradual wear is preferred because it leads
to the longest possible use of the tool
Gradual wear occurs at two locations on
a tool:
◦ Crater wear – occurs on top rake face
◦ Flank wear – occurs on flank (side of tool)
ISE 316 - Manufacturing
Processes Engineering
5. Figure 23.1 - Diagram of worn cutting tool, showing the principal
locations and types of wear that occur
ISE 316 - Manufacturing
Processes Engineering
6. Figure 23.2 (a)
Crater wear, and
(b)
flank wear on a cemented
carbide tool, as seen
through a toolmaker's
microscope
(Courtesy Manufacturing
Technology Laboratory,
Lehigh University, photo by J.
C. Keefe)
ISE 316 - Manufacturing
Processes Engineering
7. Figure 23.3 - Tool wear as a function of cutting time
Flank wear (FW) is used here as the measure of tool wear
Crater wear follows a similar growth curve
ISE 316 - Manufacturing
Processes Engineering
8. Figure 23.4 - Effect of cutting speed on tool flank wear (FW) for three
cutting speeds, using a tool life criterion of 0.50 mm flankwear
ISE 316 - Manufacturing
Processes Engineering
9. Figure 23.5 - Natural log-log plot of cutting speed vs tool life
ISE 316 - Manufacturing
Processes Engineering
10. Taylor Tool Life Equation
This relationship is credited to F. W. Taylor
n
(~1900)
vT C
where v = cutting speed; T = tool life; and n and C are parameters that
depend on feed, depth of cut, work material, tooling material, and the
tool life criterion used
• n is the slope of the plot
• C is the intercept on the speed axis
ISE 316 - Manufacturing
Processes Engineering
11. Tool Life Criteria in Production
failure of cutting edge
Visual insComplete pection of flank wear (or crater
wear) by the machine operator
3. Fingernail test across cutting edge
4. Changes in sound emitted from operation
5. Chips become ribbony, stringy, and difficult to dispose
of
6. Degradation of surface finish
7. Increased power
8. Workpiece count
9. Cumulative cutting time
1.
2.
ISE 316 - Manufacturing
Processes Engineering
12. Tool Materials
Tool failure modes identify the important
properties that a tool material should
possess:
◦ Toughness - to avoid fracture failure
◦ Hot hardness - ability to retain hardness at
high temperatures
◦ Wear resistance - hardness is the most
important property to resist abrasive wear
ISE 316 - Manufacturing
Processes Engineering
13. Figure 23.6 - Typical hot hardness relationships for selected tool
materials. Plain carbon steel shows a rapid loss of hardness as
temperature increases. High speed steel is substantially better, while
cemented carbides and ceramics are significantly harder at elevated
temperatures.
ISE 316 - Manufacturing
Processes Engineering
14. Typical Values of n and C in
Taylor Tool Life Equation
Tool material
n
C (m/min)
C (ft/min)
High speed steel:
Non-steel work 0.125
Steel work
0.125
120
70
350
200
900
500
2700
1500
Cemented carbide
Non-steel work
Steel work
0.25
0.25
Ceramic
Steel work
0.6
3000
ISE 316 - Manufacturing
Processes Engineering
10,000
15. High Speed Steel (HSS)
Highly alloyed tool steel capable of maintaining
hardness at elevated temperatures better
than high carbon and low alloy steels
One of the most important cutting tool
materials
Especially suited to applications involving
complicated tool geometries, such as drills,
taps, milling cutters, and broaches
Two basic types (AISI)
1. Tungsten-type, designated T- grades
2. Molybdenum-type, designated M-grades
ISE 316 - Manufacturing
Processes Engineering
16. High Speed Steel Composition
Typical alloying ingredients:
◦
◦
◦
◦
Tungsten and/or Molybdenum
Chromium and Vanadium
Carbon, of course
Cobalt in some grades
Typical composition:
◦ Grade T1: 18% W, 4% Cr, 1% V, and 0.9% C
ISE 316 - Manufacturing
Processes Engineering
17. Cemented Carbides
Class of hard tool material based on
tungsten carbide (WC) using powder
metallurgy techniques with cobalt (Co)
as the binder
Two basic types:
1. Non-steel cutting grades - only WC-Co
2. Steel cutting grades - TiC and TaC added to
WC-Co
ISE 316 - Manufacturing
Processes Engineering
18. Cemented Carbides – General
Properties
High compressive strength but
low-to-moderate tensile strength
High hardness (90 to 95 HRA)
Good hot hardness
Good wear resistance
High thermal conductivity
High elastic modulus - 600 x 103 MPa (90
x 106 lb/in2)
Toughness lower than high speed steel
ISE 316 - Manufacturing
Processes Engineering
19. Non-steel Cutting Carbide Grades
Used for nonferrous metals and gray cast
iron
Properties determined by grain size and
cobalt content
◦ As grain size increases, hardness and hot
hardness decrease, but toughness increases
◦ As cobalt content increases, toughness
improves at the expense of hardness and
wear resistance
ISE 316 - Manufacturing
Processes Engineering
20. Steel Cutting Carbide Grades
Used for low carbon, stainless, and other
alloy steels
◦ For these grades, TiC and/or TaC are
substituted for some of the WC
◦ This composition increases crater wear
resistance for steel cutting, but adversely
affects flank wear resistance for non-steel
cutting applications
ISE 316 - Manufacturing
Processes Engineering
21. Cermets
Combinations of TiC, TiN, and titanium
carbonitride (TiCN), with nickel and/or
molybdenum as binders.
Some chemistries are more complex
Applications: high speed finishing and
semifinishing of steels, stainless steels, and
cast irons
◦ Higher speeds and lower feeds than steel-cutting
carbide grades
◦ Better finish achieved, often eliminating need for
grinding
ISE 316 - Manufacturing
Processes Engineering
22. Coated Carbides
Cemented carbide insert coated with one or
more thin layers of wear resistant materials,
such as TiC, TiN, and/orAl2O3
Coating applied by chemical vapor deposition
or physical vapor deposition
Coating thickness = 2.5 - 13 m (0.0001 to
0.0005 in)
Applications: cast irons and steels in turning
and milling operations
Best applied at high speeds where dynamic
force and thermal shock are minimal
ISE 316 - Manufacturing
Processes Engineering
23. Ceramics
Primarily fine-grained Al2O3, pressed and
sintered at high pressures and temperatures
into insert form with no binder
Applications: high speed turning of cast iron
and steel
Not recommended for heavy interrupted
cuts (e.g. rough milling) due to low
toughness
Al2O3 also widely used as an abrasive in
grinding
ISE 316 - Manufacturing
Processes Engineering
24. Synthetic Diamonds
Sintered polycrystalline diamond (SPD) - fabricated
by sintering very fine-grained diamond crystals
under high temperatures and pressures into
desired shape with little or no binder
Usually applied as coating (0.5 mm thick) on
WC-Co insert
Applications: high speed machining of
nonferrous metals and abrasive nonmetals
such as fiberglass, graphite, and wood
◦ Not for steel cutting
ISE 316 - Manufacturing
Processes Engineering
25. Cubic Boron Nitride
Next to diamond, cubic boron nitride (cBN)
is hardest material known
Fabrication into cutting tool inserts same
as SPD: coatings on WC-Co inserts
Applications: machining steel and
nickel-based alloys
SPD and cBN tools are expensive
ISE 316 - Manufacturing
Processes Engineering
26. Tool Geometry
Two categories:
Single point tools
◦ Used for turning, boring, shaping, and planing
Multiple cutting edge tools
◦ Used for drilling, reaming, tapping, milling,
broaching, and sawing
ISE 316 - Manufacturing
Processes Engineering
27. SinglePoint
Tool
Geometry
Figure 23.7 - (a)
Seven elements of
single-point tool
geometry; and (b) the
tool signature
convention that
defines the seven
elements
ISE 316 - Manufacturing
Processes Engineering
28. Figure 23.9 - Three ways of holding and presenting the cutting edge for a
single-point tool:
(a) solid tool, typical of HSS;
(b) brazed insert, one way of holding a cemented carbide insert; and
(c) mechanically clamped insert, used for cemented carbides, ceramics, and other
very hard tool materials
ISE 316 - Manufacturing
Processes Engineering
29. Figure 23.10 - Common insert shapes: (a) round, (b) square, (c) rhombus
with two 80 point angles, (d) hexagon with three 80 point angles, (e)
triangle (equilateral), (f) rhombus with two 55 point angles, (g)
rhombus with two 35 point angles. Also shown are typical features of
the geometry.
ISE 316 - Manufacturing
Processes Engineering
30. Twist Drills
By far the most common cutting tools for
hole-making
Usually made of high speed steel
Figure 23.12 - Standard geometry of a twist drill
(old:Fig.25.9)
ISE 316 - Manufacturing
Processes Engineering
31. Twist Drill Operation
Rotation and feeding of drill bit result in
relative motion between cutting edges
and workpiece to form the chips
◦ Cutting speed varies along cutting edges as a
function of distance from axis of rotation
◦ Relative velocity at drill point is zero, so no
cutting takes place
◦ A large thrust force is required to drive the
drill forward into hole
ISE 316 - Manufacturing
Processes Engineering
32. Twist Drill Operation - Problems
Chip removal
◦ Flutes must provide sufficient clearance to
allow chips to be extracted from bottom of
hole
Friction makes matters worse
◦ Rubbing between outside diameter of drill bit
and newly formed hole
◦ Delivery of cutting fluid to drill point to
reduce friction and heat is difficult because
chips are flowing in the opposite direction
ISE 316 - Manufacturing
Processes Engineering
34. Plain Milling Cutter
Used for peripheral or slab milling
Figure 23.13 Tool geometry elements
of an 18-tooth plain
milling cutter
ISE 316 - Manufacturing
Processes Engineering
35. Form Milling Cutter
Peripheral milling cutter in which cutting
edges have special profile to be imparted
to work
Important application
◦ Gear-making, in which the form milling cutter
is shaped to cut the slots between adjacent
gear teeth, thereby leaving the geometry of
the gear teeth
ISE 316 - Manufacturing
Processes Engineering
36.
Face Milling Cutter
Teeth cut on side and periphery of the cutter
Figure 23.14 - Tool geometry elements of a four-tooth face
milling cutter: (a) side view and (b) bottom view
ISE 316 - Manufacturing
Processes Engineering
37. End Milling Cutter
Looks like a drill bit but designed for
primary cutting with its peripheral teeth
Applications:
◦
◦
◦
◦
◦
◦
Face milling
Profile milling and pocketing
Cutting slots
Engraving
Surface contouring
Die sinking
ISE 316 - Manufacturing
Processes Engineering
38. Cutting Fluids
Any liquid or gas applied directly to machining
operation to improve cutting performance
Two main problems addressed by cutting
fluids:
1. Heat generation at shear zone and friction
zone
2. Friction at the tool-chip and tool-work
interfaces
Other functions and benefits:
◦
◦
◦
Wash away chips (e.g., grinding and milling)
Reduce temperature of workpart for easier
handling
Improve dimensional stability of workpart
ISE 316 - Manufacturing
Processes Engineering
39. Cutting Fluid Functions
Cutting fluids can be classified according
to function:
◦ Coolants - designed to reduce effects of heat
in machining
◦ Lubricants - designed to reduce tool-chip and
tool-work friction
ISE 316 - Manufacturing
Processes Engineering
40. Coolants
Water used as base in coolant-type
cutting fluids
Most effective at high cutting speeds
where heat generation and high
temperatures are problems
Most effective on tool materials that are
most susceptible to temperature failures
(e.g., HSS)
ISE 316 - Manufacturing
Processes Engineering
41. Lubricants
Usually oil-based fluids
Most effective at lower cutting speeds
Also reduces temperature in the
operation
ISE 316 - Manufacturing
Processes Engineering
43. Dealing with Cutting Fluid
Contamination
Replace cutting fluid at regular and
frequent intervals
Use filtration system to continuously or
periodically clean the fluid
Dry machining
ISE 316 - Manufacturing
Processes Engineering
44. Cutting Fluid Filtration
Advantages:
Prolong cutting fluid life between changes
Reduce fluid disposal cost
Cleaner fluids reduce health hazards
Lower machine tool maintenance
Longer tool life
ISE 316 - Manufacturing
Processes Engineering
45. Dry Machining
No cutting fluid is used
Avoids problems of cutting fluid
contamination, disposal, and filtration
Problems with dry machining:
◦ Overheating of the tool
◦ Operating at lower cutting speeds and
production rates to prolong tool life
◦ Absence of chip removal benefits of cutting
fluids in grinding and milling
ISE 316 - Manufacturing
Processes Engineering
46. Tooling
Very hard materials that need other
characteristics
◦ Hard – wear resistance
◦ Impact – high impact resistance
◦ Low elasticity