Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 23: Machining Processes: Turning and Hole Making Presentation slide for courses,

Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 23: Machining Processes: Turning and Hole Making Presentation slide for courses, classes, lectures et al. Copyright © 2010 Pearson Education South Asia Pte Ltd

Chapter Outline Introduction The Turning Process
Lathes and Lathe Operations Boring and Boring Machines Drilling, Drills, and Drilling Machines Reaming and Reamers 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 Turning is performed at various:
Rotational speeds, N, of the workpiece clamped in a spindle Depths of cut, d 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

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

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

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

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 Components
Bed 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

Tailstock 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 Specifications Max diameter of the workpiece that can be machined Max distance between the headstock and tailstock centers Length of the bed 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

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 Lathes
Bench 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

Automatic 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

EXAMPLE 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: Turning-process Capabilities
Relative production rates in turning are important on productivity in machining operations Copyright © 2010 Pearson Education South Asia Pte Ltd

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

General design guidelines:
Lathes and Lathe Operations: Design Considerations and Guidelines for Turning Operations General design guidelines: Parts should be designed to be fixtured and clamped easily into work-holding devices Dimensional accuracy and surface finish should be as wide as permissible for the part to still function properly Sharp corners should be avoided Blanks should be as close to final dimensions as possible Parts should be designed so that cutting tools can travel across the workpiece without obstruction Design features should be commercially available Copyright © 2010 Pearson Education South Asia Pte Ltd

Guidelines for Turning Operations
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: Minimize tool overhang Support the workpiece rigidly Use machine tools with high stiffness and high damping capacity 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: Gravity drop Dragging the chips from a settling tank Using augers with feed screws Using magnetic conveyors 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

Design Considerations for Screw Thread Machining Design considerations must be taken into account: Designs should allow for the termination of threads Attempts should be made to eliminate shallow, blind tapped holes Chamfers should be specified at the ends of threaded sections Threaded sections should not be interrupted Standard threading tooling and inserts should be used 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

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

Design Considerations for Boring: Through holes should be specified Greater the length-to-bore-diameter ratio, the more difficult it is to hold dimensions 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

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

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: Point angle Lip-relief angle Chiseledge angle Helix angle Copyright © 2010 Pearson Education South Asia Pte Ltd

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

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

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: Strength of the workpiece material Feed Rotational speed Drill diameter Drill geometry Cutting fluid Copyright © 2010 Pearson Education South Asia Pte Ltd

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

EXAMPLE 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: 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: Numerical Letter Fractional 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 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

Drill 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

Measuring 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: Designs should allow holes to be drilled on flat surfaces and perpendicular to the drill motion Interrupted hole surfaces should be avoided Hole bottoms should match standard drill-point angles Through holes are preferred over blind holes Dimples should be provided Parts should be designed with a minimum of fixturing Blind holes must be drilled deeper Copyright © 2010 Pearson Education South Asia Pte Ltd

Reaming and Reamers Reaming is an operation used to:
Make existing hole dimensionally more accurate Improve surface finish Most accurate holes in workpieces are produced by: Centering Drilling Boring 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:
Drilling machines Lathes Automatic screw machines Vertical CNC milling machines One system for the automatic tapping of nuts is shown Copyright © 2010 Pearson Education South Asia Pte Ltd

Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 23: Machining Processes: Turning and Hole Making Presentation slide for courses,

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Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 23: Machining Processes: Turning and Hole Making Presentation slide for courses,

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Presentation on theme: "Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 23: Machining Processes: Turning and Hole Making Presentation slide for courses,"— Presentation transcript:

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