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Machining Processes and Machine
Tools
• Machining is the removal of material and modification
of the surfaces of a workpiece
• Machining involves secondary and finishing operations
Copyright © 2010 Pearson Education South Asia Pte Ltd
Machining Processes and Machine
Tools
• Parts can be manufactured by casting, forming and
shaping processes
• They often require further operations before the
product is ready for use
Copyright © 2010 Pearson Education South Asia Pte Ltd
Machining Processes and Machine
Tools
• Major types of material removal processes:
1. Cutting
2. Abrasive processes
3. Advanced machining processe
• Machining operations is a system consisting of the
1. Workpiece
2. Cutting tool
3. Machine tool
4. Production personnel
Copyright © 2010 Pearson Education South Asia Pte Ltd
Common Machining Processes
Some examples of common machining processes.
Characteristics of Machining
General characteristics of machining processes.
Introduction
• Machining processes has the capability of producing
parts that are round in shape
• Such as miniature screws for the hinges of eyeglass
frames and turbine shafts for hydroelectric power plants
• Most basic machining processes is turning where part
is rotated while it is being machined
• Turning processes are carried out on a lathe or by
similar machine tools
• Highly versatile and produce a wide variety of shapes
Copyright © 2010 Pearson Education South Asia Pte Ltd
Introduction
• In the turning process, the cutting tool is set at a certain
depth of cut (mm) and travels to the left as the
workpiece rotates
• Feed, or feed rate, is the distance the tool travels
horizontally per unit revolution of the workpiece
(mm/rev)
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathe Operations
Variety of machining operations that can be
performed on a lathe.
Introduction
• Turning is performed at various:
1. Rotational speeds, N, of the workpiece clamped in a
spindle
2. Depths of cut, d
3. Feeds, f, depending on the workpiece materials,
cutting-tool materials, surface finish, dimensional
accuracy and characteristics of the machine tool
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The Turning Process
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Cutting Speeds for Turning
The range of applicable cutting speeds and
feeds for a variety of cutting-tool materials.
Approximate Ranges of Recommended Cutting
Speeds for Turning Operations
Tool Angles
Designations and symbols for a
right-hand cutting tool. The
designation “right hand” means that
the tool travels from right to left
General recommendations for
tool angles in turning.
Types of Chips
Basic types of chips produced in metal cutting and their micrographs: (a)
continuous chip with narrow, straight primary shear zone; (b) secondary
shear zone at the tool-chip interface; (c) continuous chip with built-up edge;
(d) segmented or nonhomogeneous chip; and (e) discontinuous chip.
FIGURE 8.5 Shiny (burnished)
surface on the tool side of a
continuous chip produced in turning.
Chip Breakers
FIGURE 8.7 (a) Schematic illustration of the action of a chip
breaker. Note that the chip breaker decreases the radius of
curvature of the chip. (b) Chip breaker clamped on the rake
face of a cutting tool. (c) Grooves on the rake face of cutting
tools, acting as chip breakers. Most cutting tools now are
inserts with built-in chip-breaker features.
FIGURE 8.8 Various chips produced in
turning: (a) tightly curled chip; (b) chip hits
workpiece and breaks; (c) continuous chip
moving radially outward from workpiece;
and (d) chip hits tool shank and breaks off.
Source: After G. Boothroyd.
Lathe
FIGURE 8.44 General view of a typical lathe, showing various major components. Source: Courtesy
of Heidenreich & Harbeck.
CNC Lathe
(a) A computer-numerical-control lathe, with two turrets; these machines have higher power and spindle
speed than other lathes in order to take advantage of advanced cutting tools with enhanced properties;
(b) a typical turret equipped with ten cutting tools, some of which are powered.
Typical CNC Parts
Typical parts made on computer-numerical-control machine tools.
Typical Production Rates
Typical production rates for various cutting operations.
Boring Mill
Schematic illustration of the components of a vertical boring mill.
Drilling, Drills, and Drilling Machines
• Holes are used for assembly with fasteners, for design
purposes or for appearance
• Hole making is the most important operations in
manufacturing
• Drilling is a major and common hole-making process
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drills Two common types of drills: (a)
Chisel-point drill. The function of the
pair of margins is to provide a
bearing surface for the drill against
walls of the hole as it penetrates into
the workpiece. Drills with four
margins (double-margin) are
available for improved drill guidance
and accuracy. Drills with chip-
breaker features are also available.
(b) Crankshaft drills. These drills
have good centering ability, and
because chips tend to break up
easily, they are suitable for producing
deep holes.
Various types of drills and drilling operations.
Drilling, Drills, and Drilling Machines:
Material-removal Rate in Drilling
• The material-removal rate (MRR) in drilling is the
volume of material removed per unit time
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fND
MMR
4
2
Speeds and Feeds in Drilling
General recommendations for speeds and feeds in drilling.
Reamers and Taps
Terminology for a helical reamer.
(a) Terminology for a tap; (b)
illustration of tapping of steel nuts in
high production.
CASE STUDY
Bone Screw Retainer
• A cervical spine implant
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Introduction: Milling
Typical parts and shapes produced by the machining processes
Milling and Milling Machines
• Milling is machining operation for a variety of
configurations with the use of a milling cutter
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Conventional and Climb Milling
(a) Illustration showing the difference between conventional milling and climb milling.
(b) Slab-milling operation, showing depth of cut, d; feed per tooth, f; chip depth of cut,
tc and workpiece speed, v. (c) Schematic illustration of cutter travel distance, lc, to
reach full depth of cut.
Milling and Milling Machines:
Peripheral Milling
Milling Parameters
• The cutting speed in peripheral milling is the surface
speed of the cutter is
Copyright © 2010 Pearson Education South Asia Pte Ltd
DNV
Milling and Milling Machines:
Peripheral Milling
Milling Parameters
Copyright © 2010 Pearson Education South Asia Pte Ltd
Milling Operations
Cutters for (a) straddle milling; (b) form
milling; (c) slotting; and (d) slitting
operations.
Approximate range of recommended cutting speeds for
milling operations.
Milling Machines
(a) Schematic illustration of a horizontal-spindle column-and-knee-type milling machine. (b)
Schematic illustration of a vertical-spindle column-and-knee-type milling machine.
Broaching
(a) Typical parts finished by internal broaching. (b) Parts finished by surface broaching.
The heavy lines indicate broached surfaces; (c) a vertical broaching machine. Source:
(a) and (b) Courtesy of General Broach and Engineering Company, (c) Courtesy of Ty
Miles, Inc.
Broaches
FIGURE 8.61 (a) Cutting action of a
broach, showing various features. (b)
Terminology for a broach.
Terminology for a pull-type internal
broach, typically used for enlarging long
holes.
Saws and Saw Teeth
FIGURE 8.63 (a) Terminology
for saw teeth. (b) Types of saw
teeth, staggered to provide
clearance for the saw blade to
prevent binding during sawing.
(a) High-speed-steel teeth welded on a steel
blade. (b) Carbide inserts brazed to blade
teeth.
Gear
Manufacture
(a) Schematic illustration of gear
generating with a pinion-shaped gear
cutter. (b) Schematic illustration of
gear generating in a gear shaper,
using a pinion-shaped cutter; note that
the cutter reciprocates vertically. (c)
Gear generating with a rack-shaped
cutter. (d) Three views of gear cutting
with a hob.
Machining Centers
Schematic illustration of a computer
numerical-controlled turning center. Note
that the machine has two spindle heads and
three turret heads, making the machine tool
very flexible in its capabilities.
A horizontal-spindle machining center, equipped with
an automatic tool changer. Tool magazines in such
machines can store as many as 200 cutting tools,
each with its own holder.
Reconfigurable Machines
Schematic illustration of a reconfigurable modular machining center, capable of
accommodating workpieces of different shapes and sizes, and requiring different machining
operations on their various surfaces. Source: After Y. Koren.
Reconfigurable Machining Center
Schematic illustration of assembly of different components of a reconfigurable
machining center.
Machining of Bearing Races
Sequences involved in machining outer bearing races on a turning center.
Hexapod
(a) A hexapod machine tool, showing its major components. (b) Closeup view of the cutting tool
and its head in a hexapod machining center. Source: National Institute of Standards and
Technology.
Machining Mechanics: Orthogonal
Cutting
Schematic illustration of a two-dimensional cutting
process, or orthogonal cutting. (a) Orthogonal cutting with
a well-defined shear plane, also known as the Merchant
model; (b) Orthogonal cutting without a well-defined shear
plane.
Terminology in Turning
FIGURE 8.19 Terminology used in a turning operation on a lathe, where f is the feed (in mm/rev or
in./rev) and d is the depth of cut. Note that feed in turning is equivalent to the depth of cut in orthogonal
cutting (see Fig. 8.2), and the depth of cut in turning is equivalent to the width of cut in orthogonal
cutting. See also Fig. 8.42.
Chip Formation
(a) Schematic illustration of the basic mechanism of chip formation in cutting. (b) Velocity diagram
in the cutting zone.
Oblique Cutting
FIGURE 8.9 (a) Schematic illustration of cutting with an oblique tool. (b) Top view, showing the
inclination angle, i. (c) Types of chips produced with different inclination angles.
Right-Hand Cutting Tool
(a) Schematic illustration of a right-hand cutting tool for turning. Although these tools have
traditionally been produced from solid tool-steel bars, they are now replaced by inserts of
carbide or other tool materials of various shapes and sizes, as shown in (b).
Chip Mechanics
Cutting Forces
FIGURE 8.11 (a) Forces acting on a
cutting tool in two-dimensional cutting.
Note that the resultant forces, R, must
be collinear to balance the forces. (b)
Force circle to determine various
forces acting in the cutting zone.
Source: After M.E. Merchant.
Cutting force Friction coefficient
Cutting Forces
Specific Energy
Approximate Specific-Energy Requirements in
Machining Operations
Tool Wear
Examples of wear in cutting tools. (a) Flank wear; (b)
crater wear; (c) chipped cutting edge; (d) thermal
cracking on rake face; (e) flank wear and built-up edge;
(f) catastrophic failure (fracture). Source: Courtesy of
Kennametal, Inc.
Taylor tool life equation:
Range of n values for various cutting tools.
Surface Finish
FIGURE 8.26 Range of surface roughnesses
obtained in various machining processes. Note
the wide range within each group, especially in
turning and boring. (See also Fig. 9.27).
Hardness of Cutting Tools
Hardness of various cutting-tool materials as a
function of temperature (hot hardness). The wide
range in each group of tool materials results from
the variety of compositions and treatments available
for that group.
Tool Materials Typical range of properties of various tool materials.
Properties of Tungsten-Carbide Tools
Effect of cobalt content in tungsten-carbide tools on mechanical properties. Note that
hardness is directly related to compressive strength (see Section 2.6.8) and hence,
inversely to wear [see Eq. (4.6)].
Inserts
Methods of mounting inserts on toolholders: (a) clamping, and (b) wing lockpins. (c) Examples
of inserts mounted using threadless lockpins, which are secured with side screws. Source:
Courtesy of Valenite.
Insert Strength
FIGURE 8.33 Relative edge strength and tendency for
chipping and breaking of inserts with various shapes.
Strength refers to that of the cutting edge shown by the
included angles. Source: Courtesy of Kennametal, Inc.
FIGURE 8.34 Edge preparations for inserts to improve
edge strength. Source: Courtesy of Kennametal, Inc.
Historical Tool Improvement
Relative time required to machine with various cutting-tool materials, with indication of the
year the tool materials were introduced. Note that, within one century, machining time
has been reduced by two orders of magnitude. Source: After Sandvik Coromant.
Properties of Cutting Tool Materials
Ranges of properties for various groups of cutting-tool materials. (
Construction of polycrystalline cubic-boron-nitride
or diamond layer on a tungsten-carbide insert.
Machining Economics
FIGURE 8.75 Qualitative plots showing (a) cost per
piece, and (b) time per piece in machining. Note that
there is an optimum cutting speed for both cost and time,
respectively. The range between the two optimum speeds
is known as the high-efficiency machining range.
Process Planning
Processes Planning
Case Study: Ping Golf Putters
FIGURE 8.76 (a) The Ping Anser® golf putter; (b) CAD model of rough machining of the putter outer surface; (c) rough
machining on a vertical machining center; (d) machining of the lettering in a vertical machining center; the operation
was paused to take the photo, as normally the cutting zone is flooded with a coolant; Source: Courtesy of Ping Golf, Inc.