Fundamentals of Metal cutting and Machining Processes CUTTING TOOL TECHNOLOGY Tool Life Tool Materials Tool Geometry Cutting Fluids

2. 1.
2.
3.
4.
Tool Life
Tool Materials
Tool Geometry
Cutting Fluids

3. Two principal aspects:
1. Tool material
2. Tool geometry

4. 1.
Fracture failure
◦
1.
Temperature failure
◦
1.
Cutting force becomes excessive and/or dynamic,
leading to brittle fracture
Cutting temperature is too high for the tool material
Gradual wear
◦
Gradual wearing of the cutting tool

5. 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)

6. Tool Wear
Diagram of worn cutting tool, showing the principal locations and
types of wear that occur.

7. Crater wear, (above), and flank
wear (right) on a cemented
carbide tool, as seen through a
toolmaker's microscope

8. Tool Wear vs. Time
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.

9. Effect of Cutting Speed
Effect of cutting speed on tool flank wear (FW) for three cutting
speeds, using a tool life criterion of 0.50 mm flank wear.

10. Tool Life vs. Cutting Speed
Natural log‑log plot of cutting speed vs tool life.

11. vT = C
n
Relationship is credited to F. W.
Taylor
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 at one
minute tool life

12. 1.
2.
3.
4.
5.
6.
7.
8.
9.
Complete failure of cutting edge
Visual inspection of flank wear (or crater
wear) by the machine operator
Fingernail test across cutting edge
Changes in sound emitted from operation
Chips become ribbon-like, stringy, and
difficult to dispose off
Degradation of surface finish
Increased power
Workpiece count
Cumulative cutting time

13. 
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 abrasion

14. Tool Tip Temperatute vs Cutting Speed
900
600
300
200
400
600
Ft/Min

15. Hot Hardness
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.

16. Tool material
High speed steel:
Non-steel work
Steel work
Cemented carbide
Non-steel work
Steel work
Ceramic
Steel work
n
C (m/min)
C (ft/min)
0.125
0.125
120
70
350
200
0.25
0.25
900
500
2700
1500
0.6
3000
10,000

17. 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

18. 
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

19. 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

20. •
•
•
•
•
•
•
High compressive strength but low‑to‑moderate
tensile strength
High hardness (90 to 95 HRc)
Good hot hardness
Good wear resistance
High thermal conductivity
High elastic modulus ‑ 600 x 103 MPa
Toughness lower than high speed steel

21. 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

22. Used for low carbon, stainless, and other
alloy steels
 TiC and/or TaC are substituted for some of
the WC
 Composition increases crater wear
resistance for steel cutting

◦ But adversely affects flank wear resistance for
non‑steel cutting applications

23. 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

24. Cemented carbide insert coated with one or more
thin layers of wear resistant materials, such as
TiC, TiN, and/or Al 2 O 3
•
•
•
•
Coating applied by chemical vapor deposition or
physical vapor deposition
Coating thickness = 2.5 ‑ 13 µm (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

25. Photomicrograph
of cross section of
multiple coatings
on cemented
carbide tool

26. 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

27. 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

28. 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


29. 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

31. The "business end" of a twist drill has two cutting
edges
 The included angle of the point on a conventional
twist drill is 118°
 Margins are the outside tip of the flutes and are
always ground to the drill diameter


32. •
•
An essential feature of drilling is the variation in
cutting speed along the cutting edge. The
speed is maximum at the periphery, which
generates the cylindrical surface, and
approaches zero near the center-line of the drill
where the cutting edge is blended to a chisel
shape.
Drills are slender, highly stressed tools, the
flutes of which have to be carefully designed to
permit chip flow while maintaining adequate
strength.

33. 
Chip removal
◦ Flutes must provide sufficient clearance to allow chips
to be extracted from bottom of hole during the cutting
operation

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
opposite direction

34. 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 and friction zones
2. Friction at 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

35. 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

36. 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)


37. Usually oil‑based fluids
 Most effective at lower cutting speeds
 Also reduce temperature in the operation


38. No cutting fluid is used
 Avoids problems of cutting fluid contamination,
disposal, and filtration
 Problems with dry machining:

◦ Overheating of 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

39. 



Gear cutting is the process of creating a gear. The most
common processes include hobbing , broaching, and
machining; other processes include shaping, forging,
extruding, casting, and powder metallurgy.
Hobbing is a machining process for making gears, on a
hobbing machine,
The teeth or splines are progressively cut into the workpiece
by a series of cuts made by a cutting tool called a hob .
Compared to other gear forming processes it is relatively
inexpensive but still quite accurate, thus it is used for a broad
range of parts and quantities

41. •
•
•
The two shafts are rotated at a proportional
ratio, which determines the number of teeth on
the blank; for example, if the gear ratio is 40:1
the hob rotates 40 times to each turn of the
blank
The hob is then fed up into workpiece until the
correct tooth depth is obtained.
Finally the hob is fed into the workpiece parallel
to the blank's axis of rotation

42. 
Hobbing uses a hobbing machine with
two non-parallel spindles, one mounted
with a blank workpiece and the other with
the hob.

The angle between the hob's spindle and
the workpiece's spindle varies,
depending on the type of product being
produced.

If a spur gear is being produced, then
the hob is angled equal to the helix angle
of the hob; if a helical gear is being
produced then the angle must be
increased by the same amount as the
helix angle of the helical gear

43. •
•
•
The hob is the cutter used to cut the
teeth into the workpiece.
It is cylindrical in shape with helical
cutting teeth. These teeth have
grooves that run the length of the hob,
which aid in cutting and chip removal.
The cross-sectional shape of the hob
teeth are almost the same shape as
teeth of a rack gear that would be used
with the finished product