turning mfg chapter23
TRANSCRIPT
Manufacturing Engineering Technology in SI Units, Manufacturing Engineering Technology in SI Units,
66thth Edition Edition Chapter 23: Chapter 23:
Machining Processes: Turning and Hole Machining Processes: Turning and Hole MakingMaking
Copyright © 2010 Pearson Education South Asia Pte Ltd
Chapter Outline
1. Introduction
2. The Turning Process
3. Lathes and Lathe Operations
4. Boring and Boring Machines
5. Drilling, Drills, and Drilling Machines
6. Reaming and Reamers
7. Tapping and Taps
Copyright © 2010 Pearson Education South Asia Pte Ltd
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
Copyright © 2010 Pearson Education South Asia Pte Ltd
Introduction
Copyright © 2010 Pearson Education South Asia Pte Ltd
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
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Majority of turning operations use simple single-point cutting tools, which is a right-hand cutting tool
Important process parameters have a direct influence on machining processes and optimized productivity
Tool Geometry Rake angle control both the direction of chip flow and
the strength of the tool tip Side rake angle controls the direction of chip flow Cutting-edge angle affects chip formation, tool
strength and cutting forces
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Tool Geometry Relief angle controls interference and rubbing at the
tool–workpiece interface Nose radius affects surface finish and tool-tip strength
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Tool Geometry
Material-removal Rate The material-removal rate (MRR) is the volume of
material removed per unit time (mm3/min)
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Material-removal Rate The average diameter of the ring is
Since there are N revolutions per minute, the removal rate is
Since the distance traveled is l mm, the cutting time is
The cutting time does not include the time required for tool approach and retraction
Copyright © 2010 Pearson Education South Asia Pte Ltd
20 f
avg
DDD
dfVMMRdfNDMMR avg toreduceor
fN
lt
The Turning Process
Material-removal Rate
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Forces in Turning The 3 principal forces acting on a cutting tool are
important in the design of machine tools, deflection of tools and workpieces for precision-machining operations
Cutting force acts downward on the tool tip and deflect the tool downward and the workpiece upward
Thrust force (or feed force) acts in the longitudinal direction
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Roughing and Finishing Cuts First practice is to have one or more roughing cuts at
high feed rates and large depths of cut Little consideration for dimensional tolerance and
surface roughness Followed by a finishing cut, at a lower feed and depth
of cut for good surface finish
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Tool Materials, Feeds, and Cutting Speeds The range of applicable cutting speeds and feeds for a
variety of tool materials is shown
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Tool Materials, Feeds, and Cutting Speeds
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Tool Materials, Feeds, and Cutting Speeds
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Cutting Fluids Recommendations for cutting fluids appropriate to
various workpiece materials
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
EXAMPLE 23.1
Material-removal Rate and Cutting Force in Turning
A 150-mm-long, 12.5-mm-diameter 304 stainless steel rod is being reduced in diameter to 12.0 mm by turning on a lathe. The spindle rotates at N 400 rpm, and the tool is travelling at an axial speed of 200 mm/min. Calculate the cutting speed, material-removal rate, cutting time, power dissipated, and cutting force.
Copyright © 2010 Pearson Education South Asia Pte Ltd
The Turning Process
Solution
Material-removal Rate and Cutting Force in Turning
The maximum cutting speed is
The cutting speed at the machined diameter is
The depth of cut is
Copyright © 2010 Pearson Education South Asia Pte Ltd
mm 25.02
0.125.12
d
m/min 7.15
1000
4005.120
NDV
m/min 1.15
1000
4000.120
NDV
The Turning Process
Solution
Material-removal Rate and Cutting Force in Turning
The feed is
The material-removal rate is
The actual time to cut is
Copyright © 2010 Pearson Education South Asia Pte Ltd
mm 75.04005.0
150t
mm/rev 5.0400
200f
/minm 102/min mm 19244005.025.025.12 363 MMR
The Turning Process
Solution
Material-removal Rate and Cutting Force in Turning
The power dissipated is
Since W=60 N•m/min, power dissipated is 7680 N m/min.
Also, power is the product of torque:
Since , we have Copyright © 2010 Pearson Education South Asia Pte Ltd
2avgcDFT
W128
60
19244Power
Nm 1.34002
7680
T
N 506
2/25.12
10001.3cF
Lathes and Lathe Operations Lathes are considered to be the oldest machine tools Speeds may range from moderate to high speed
machining Simple and versatile But requires a skilled machinist Lathes are inefficient for repetitive operations and for
large production runs
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Lathe ComponentsBed Supports all major components of the lathe
Carriage Slides along the ways and consists of an assembly of
the cross-slide, tool post, and apron
Headstock Equipped with motors, pulleys, and V-belts that supply
power to a spindle at various rotational speeds
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Lathe ComponentsTailstock Slide along the ways and be clamped at any position,
supports the other end of the workpiece
Feed Rod and Lead Screw Powered by a set of gears through the headstock
Lathe Specifications1. Max diameter of the workpiece that can be machined2. Max distance between the headstock and tailstock
centers3. Length of the bed
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Lathe ComponentsLathe Specifications
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Workholding Devices and Accessories Workholding devices must hold the workpiece securely Chuck is equipped with three or four jaws Three-jaw chucks used for round workpieces Four-jaw (independent) chucks used for square,
rectangular, or odd-shaped workpieces Power chucks are used in automated equipment for
high production rates Chuck selection depends on the type and speed of
operation, workpiece size, production and dimensional accuracy requirements and the jaw forces required
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Workholding Devices and Accessories
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Workholding Devices and Accessories A collet is a longitudinally-split, tapered bushing Used for round workpieces and shapes like square or
hexagonal It can grips the entire circumference of the part,
suitable for parts with small cross sections Face plates are used for clamping irregularly shaped
workpieces Mandrels used to hold workpieces that require
machining on both ends or on their cylindrical surfaces
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Lathe Operations Cutting tool removes material by travelling along the
bed Facing operations are done by moving the tool radially
with the cross-slide and clamping the carriage for better dimensional accuracy
Form tools are used to produce various shapes on solid, round workpieces by moving the tool radially inward while the part is rotating
Boring on a lathe is similar to turning Drilling can be performed on a lathe by mounting the
drill bit in a chuck in the tailstock quill
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesBench Lathes Have low power, operated by hand feed, and are used
to machine small workpieces
Special-purpose Lathes Used for applications such as railroad wheels, gun
barrels, and rolling-mill rolls
Tracer Lathes Cutting tool follows a path that duplicates the contour of
a template
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesAutomatic Lathes For fully automatic lathe, parts are fed and removed
automatically For semiautomatic machines, functions are performed
by the operator
Automatic Bar Machines Designed for high-production-rate machining of screws
and similar threaded parts
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesTurret Lathes Perform multiple cutting operations, such as turning,
boring, drilling, thread cutting, and facing
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesComputer-controlled Lathes Movement and control of the machine tool and its
components can be achieved
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesComputer-controlled Lathes Each turret is equipped with a variety of tools and
performs several operations on different surfaces of the workpiece
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesEXAMPLE 23.2
Typical Parts Made on CNC Turning Machine Tools
The capabilities of CNC turning-machine tools are illustrated as shown. The material and number of cutting tools used and the machining times are indicated for each part. These parts also can be made on manual or turret lathes, although not as effectively or consistently.
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesEXAMPLE 23.2
Typical Parts Made on CNC Turning Machine Tools
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesEXAMPLE 23.3
Machining of Complex Shapes
The capabilities of CNC turning are shown
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Types of LathesEXAMPLE 23.3
Machining of Complex Shapes
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Turning-process Capabilities Relative production rates in turning are important on
productivity in machining operations
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Turning-process Capabilities High-removal-rate machining has two requirements: (a)
high machine tool and (b) high power The surface finish and dimensional accuracy depend
on the characteristics of the machine tool, stiffness, vibration and chatter, process parameters, tool geometry and wear, the use of cutting fluids, the machinability of the workpiece material, and operator skill
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Turning-process Capabilities
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Turning-process Capabilities
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Design Considerations and Guidelines for Turning Operations
General design guidelines:
1. Parts should be designed to be fixtured and clamped easily into work-holding devices
2. Dimensional accuracy and surface finish should be as wide as permissible for the part to still function properly
3. Sharp corners should be avoided
4. Blanks should be as close to final dimensions as possible
5. Parts should be designed so that cutting tools can travel across the workpiece without obstruction
6. Design features should be commercially available
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Design Considerations and Guidelines for Turning Operations
Guidelines for Turning Operations Some guidelines have to be implemented on a trial-
and-error basis:
1. Minimize tool overhang
2. Support the workpiece rigidly
3. Use machine tools with high stiffness and high damping capacity
4. When tools begin to vibrate and chatter, modify one or more of the process parameters
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Chip Collection Systems Chips produced during machining must be collected
and disposed properly Chip management involves collecting chips from their
source in the machine tool in an efficient manner and removing them from the work area
Chips can be collected by:
1. Gravity drop
2. Dragging the chips from a settling tank
3. Using augers with feed screws
4. Using magnetic conveyors
5. Employing vacuum methods of chip removal
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Cutting Screw Threads Screw thread defined as a ridge of uniform cross
section that follows a helical or spiral path on the outside or inside of a cylindrical (straight thread) or tapered surface (tapered thread)
Threads can be machined externally or internally with a cutting tool called thread cutting or threading
Screw-thread Cutting on a Lathe The cutting tool, the shape depends on the type of
thread to be cut
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Cutting Screw ThreadsScrew-thread Cutting on a Lathe A number of passes are required to produce threads
with good dimensional accuracy and surface finish
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Cutting Screw ThreadsScrew-thread Cutting on a Lathe The production rate in cutting screw threads can be
increased with tools called die-head chasers
Copyright © 2010 Pearson Education South Asia Pte Ltd
Lathes and Lathe Operations:Cutting Screw ThreadsDesign Considerations for Screw Thread Machining Design considerations must be taken into account:
1. Designs should allow for the termination of threads
2. Attempts should be made to eliminate shallow, blind tapped holes
3. Chamfers should be specified at the ends of threaded sections
4. Threaded sections should not be interrupted
5. Standard threading tooling and inserts should be used
6. Thin-walled parts should have sufficient thickness and strength
Copyright © 2010 Pearson Education South Asia Pte Ltd
Boring and Boring Machines
The cutting tools are mounted on a boring bar to reach the full length of the bore
Boring bars have been designed and built with capabilities for damping vibration
Large workpieces are machined on boring mills
Copyright © 2010 Pearson Education South Asia Pte Ltd
Boring and Boring Machines
In horizontal boring machines, the workpiece is mounted on a table that can move horizontally in both the axial and radial directions
A vertical boring mill is similar to a lathe, has a vertical axis of workpiece rotation
Copyright © 2010 Pearson Education South Asia Pte Ltd
Boring and Boring Machines
Design Considerations for Boring:
1. Through holes should be specified
2. Greater the length-to-bore-diameter ratio, the more difficult it is to hold dimensions
3. Interrupted internal surfaces should be avoided
Copyright © 2010 Pearson Education South Asia Pte Ltd
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
Drilling, Drills, and Drilling Machines: Drills
Drills have high length-to-diameter ratios, capable of producing deep holes
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines: Drills
Drills are flexible and should be used with care in order to drill holes accurately and to prevent breakage
Drills leave a burr on the bottom surface upon breakthrough, necessitating deburring operations
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines: Drills
Twist Drill The most common drill is the conventional standard-
point twist drill The geometry of the drill point is such that the normal
rake angle and velocity of the cutting edge vary with the distance from the center of the drill
Main features of this drill are:
1. Point angle
2. Lip-relief angle
3. Chiseledge angle
4. Helix angle
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines: Drills
Twist Drill Drills are available with a chip-breaker feature ground
along the cutting edges Other drill-point geometries have been developed to
improve drill performance and increase the penetration rate
Other Types of Drills
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines: Drills
Gun Drilling Gun drilling is used for drilling deep holes and requires
a special drill
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines: Drills
Trepanning The cutting tool produces a hole by removing a disk-
shaped piece (core) from flat plates Trepanning can be carried out on lathes, drill presses,
or other machine tools using single-point or multipoint tools
Copyright © 2010 Pearson Education South Asia Pte Ltd
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
Copyright © 2010 Pearson Education South Asia Pte Ltd
fND
MMR
4
2
Drilling, Drills, and Drilling Machines:Thrust Force and Torque Thrust force acts perpendicular to the hole axis Excessive thrust force can cause the drill to break,
distort the workpiece and cause the workpiece to slip into the workholding fixture
The thrust force depends on:
1. Strength of the workpiece material
2. Feed
3. Rotational speed
4. Drill diameter
5. Drill geometry
6. Cutting fluid Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Thrust Force and TorqueTorque A knowledge of the torque in drilling is essential for
estimating the power requirement Due to many factors involved, it is difficult to calculate Torque can be estimated from the data table
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Thrust Force and TorqueEXAMPLE 23.4
Material-removal Rate and Torque in Drilling
A hole is being drilled in a block of magnesium alloy with a 10-mm drill bit at a feed of 0.2 mm/rev and with the spindle running at N = 800 rpm. Calculate the material-removal rate and the torque on the drill.
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Thrust Force and TorqueSolution
Material-removal Rate and Torque in Drilling
The material-removal rate is
The power required is
The torque is
Copyright © 2010 Pearson Education South Asia Pte Ltd
/smm 210min/mm 570,12)800)(2.0(4
)10( 332
MMR
W1055.0210 Power
Nm 25.18.83
105T
Drilling, Drills, and Drilling Machines:Drill Materials and Sizes Drills are made of high-speed steels and solid carbides
or with carbide tips Drills are coated with titanium nitride or titanium carbon
nitride for increased wear resistance Standard twist-drill sizes consist of:
1. Numerical
2. Letter
3. Fractional
4. Millimeter
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling Practice Drill does not have a centering action, tends to “walk”
on the workpiece surface at the beginning of the operation
A small starting hole can be made with a center drill before drilling
Or the drill point may be ground to an S shape which has a self-centering characteristic and produces accurate holes with improved drill life
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling PracticeDrilling Recommendations The speed is the surface speed of the drill at its
periphery
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling PracticeDrilling Recommendations The feed in drilling is the distance the drill travels into
the workpiece per revolution Chip removal during drilling can be difficult for deep
holes in soft and ductile workpiece materials
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling PracticeDrill Reconditioning Drills are reconditioned by grinding them either
manually or with special fixtures Hand grinding is difficult and requires considerable skill
in order to produce symmetric cutting edges Grinding on fixtures is accurate and is done on special
computer controlled grinders
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling PracticeMeasuring Drill Life Drill life is measured by the number of holes drilled
before they become dull and need to be re-worked or replaced
Drill life is defined as the number of holes drilled until this transition begins
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling Machines Drilling machines are used for drilling holes, tapping,
reaming and small-diameter boring operations The most common machine is the drill press
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Drilling Machines The types of drilling machines range from simple bench
type drills to large radial drills The drill head of universal drilling machines can be
swiveled to drill holes at an angle Numerically controlled three-axis
drilling machines are automate in the desired sequence using turret
Drilling machines with multiple spindles (gang drilling) are used for high-production-rate operations
Copyright © 2010 Pearson Education South Asia Pte Ltd
Drilling, Drills, and Drilling Machines:Design Considerations for Drilling Basic design guidelines:
1. Designs should allow holes to be drilled on flat surfaces and perpendicular to the drill motion
2. Interrupted hole surfaces should be avoided
3. Hole bottoms should match standard drill-point angles
4. Through holes are preferred over blind holes
5. Dimples should be provided
6. Parts should be designed with a minimum of fixturing
7. Blind holes must be drilled deeper
Copyright © 2010 Pearson Education South Asia Pte Ltd
Reaming and Reamers
Reaming is an operation used to:
1. Make existing hole dimensionally more accurate
2. Improve surface finish Most accurate holes in workpieces are produced by:
1. Centering
2. Drilling
3. Boring
4. Reaming For even better accuracy and surface finish, holes may
be burnished or internally ground and honed
Copyright © 2010 Pearson Education South Asia Pte Ltd
Reaming and Reamers
Hand reamers have a tapered end in the first third of their length
Machine reamers are available in two types: Rose reamers and Fluted reamers
Shell reamers are used for holes larger than 20 mm Expansion reamers are adjustable for small variations
in hole size Adjustable reamers can be set for specific hole
diameters and therefore are versatile
Copyright © 2010 Pearson Education South Asia Pte Ltd
Tapping and Taps
Internal threads in workpieces can be produced by tapping
A tap is a chip-producing threading tool with multiple cutting teeth
Tapered taps are designed to reduce the torque required for the tapping of through holes
Bottoming taps are for tapping blind holes to their full depth
Collapsible taps are used in large-diameter holes
Copyright © 2010 Pearson Education South Asia Pte Ltd
Tapping and Taps
Tapping may be done by hand or with machines:
1. Drilling machines
2. Lathes
3. Automatic screw machines
4. Vertical CNC milling machines One system for the automatic tapping of nuts is shown
Copyright © 2010 Pearson Education South Asia Pte Ltd
Tapping and Taps
CASE STUDY 23.1
Bone Screw Retainer A cervical spine implant
Copyright © 2010 Pearson Education South Asia Pte Ltd