ENB331 Lecture Materials and Manufacturing 2
Cutting Tool Technology
Cutting Tool Failure: Preferred Mode: Gradual Wear
Fracture Failure Fracture and temperature are premature failures;
Cutting force becomes excessive and/or dynamic leading to gradual wear is preferred because it leads to the
brittle fracture longest possible use of the tool. Gradual wear occurs
Thermal Failure at two locations on a tool:
Cutting temperature is too high for the tool material 1. Crater Wear – occurs on top rake face
Gradual Wear 2. Flank wear – occurs on flank
Gradual wearing of the cutting tool
Crater Wear Flank Wear
Wear Patterns on Tools (a) Flank wear and crater wear in a cutting tool;
the tool moves to the left.
(b) View of the rake face of a turning tool,
showing various wear patterns
(c) View of the flank face of a turning tool,
showing various wear patterns.
(d) Types of wear on a turning tool:
a. Flank wear
b. Crater Wear
c. Chipped Cutting Edge
d. Thermal Cracking on rake Face
e. Built up Edge
f. Catastrophic Failure
Dull tool in Orthogonal Machining
Schematic illustration of a dull tool with respect to the depth of cut in
orthogonal machining (exaggerated). Note that the tool has a positive rake
angle, but as the depth of cut decreases, the rake angle effectively can
become negative. The tool then simply rides of the workpiece (without
cutting) and burnishes its surface; this action raises the workpiece
temperature and causes surface residual stress.
1 Week 3 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2
Tool Wear vs Time
Effect of Cutting Speed on Tool Wear
Effect of Cutting Speed on Tool Life
Taylors Tool Life Equation
n and C are parameters that depend V = cutting speed
on feed, depth of cut, work material, T = Tool life
tooling material and the tool life N = Slope of the plot
criterion used. C = the intercept on the speed axis at one minute tool life (i.e. cutting speed
required for one min tool life)
Tool life criteria in production
Cumulative Cutting time Increased Power Chips become ribbon-like, stringy, and
Workpiece Count Degradatino of surface finish difficult to dispose of
Changes in sound emitted from Fingernail test across cutting edge Visual inspection of flank wear (or
operation Complete failure of cutting edge crater wear) by the machine operator)
2 Week 3 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2
Single point tools Multiple Cutting Edge Tools
Used for turning, shaping and planing, threading, boring Drilling, reaming, tapping, milling, broaching and sawing.
Holding the tool Typical Insert Shapes
Feed Marks on a Turned Surface
Most common cutting tools for hole-making, usually made of high speed steel.
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 into the hole
3 Week 3 Tuesday, 27 August 2013 ENB331 Lecture Materials and Manufacturing 2
Twist Drill Operation Problems
Chip Removal: Flutes must provide sufficient clearance to allow chips to be extracted from bottom of hole during the
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.
Milling Cutters – Principal Types
1. Plain milling cutter: used for peripheral or slab milling
2. Face milling cutter: Teeth cut on side and periphery of the cutter
3. End milling cutter: Small diameter plain milling tool
Plain Milling Cutter Face Milling Cutter
End Milling Cutter
Looks like a drill but but designed for primary cutting with its peripheral teeth, applications include; Face milling,
profile milling and pocketing, cutting slots, engraving, surface contouring, die sinking.
Tool failure modes identify the important properties
that a tool material should possess:
(a) Toughness – to avoid failure
(b) Hot Hardness – ability to retain hardness at
(c) Wear resistance – hardness is the most
important property to resist abrasive wear.
High Speed Steel (HSS) Two basic types (AISI)
Highly alloyed tool steel capable of maintain hardness (a) Tungsten-type, designated T-grades
at elevated temperatures better than high carbon and (b) Molybdenum-type, designated M-grades
low alloy steel. (c) Alloying elements – C,Si,Cr,V,W,Mo,Co
One of the most important cutting tool materials Typical alloying ingredients: Tungsten, Molybdenum,
Especially suited to applications involving complicated Chromium, Vanadium, Carbon, Cobalt.
tool geometries such as drills, taps, milling cutters andTypical Composition