Material – Removal Processes - Cutting

Material – Removal Processes - Cutting
Chapter 8 Material – Removal Processes - Cutting

Manufacturing Process 2
DEPARTMENT OF INDUSTRIAL ENG. Manufacturing Process 2 FACULTY: Dr. Mazin Obaidat Room: 3079 Office Hours: 12:00-1:00 (Mo.,We.) TEXTBOOKS: Manufacturing Processes for Engineering Materials, Serope Kalpakjian and Steven R. Schmid, Prentice Hall, 5th Edition, 2008 Fundamentals of Modern Manufacturing – materials, processes and systems, Mikell P. Groover, Wiley, 2nd Edition, 2002 References: Materials and Processes in Manufacturing, E. Degarmo, J.T. Black and R.A. Kohser, Wiley, 9th Edition, 2002. Mechanical Metallurgy, G.E. Dieter, McGraw-Hill, 3rd Edition, 1986

Manufacturing Process I
Handouts: are available at Moodle Assessment1: Mid Exam 30 % Project % others % Final Exams: %

Manufacturing Process I
Handouts: are available at Moodle Assessment2: First Exam 30 % Second Exam % Final Exams: 40%

introduction The manufactured by bulk deformation and forming processes are taken in manufacturing process I, often require further processing or finishing operations to impart specific characteristics such as dimensional accuracy and surface finish, before the product is ready to use..

introduction Because not all manufacturing operations produce finished products or products to desired specifications, additional finishing operations may be necessary. For example, a forged part may not have the desired dimensional accuracy; thus additional operations such as machining may be necessary. Likewise, it may be difficult to produce a product using only one manufacturing process, a part that, by design, has a number of holes in it, necessitating additional process such as drilling. Also, the holes produced by drilling process may not have the proper roundness, dimensional accuracy, or surface finish, thus necessitating the need for additional operations, such as honing. These additional operations can contribute significantly to the cost of a product

introduction In this course we will describe in details the various operations that are employed to obtain these characteristics. These processes are generally classifies as material-removal processes and they are capable of producing competitive shapes with those produced with other methods.

Definition of Material Removal Processes
Material-removal processes is a family of shaping operations through which undesired excess material is removed from a starting workpart so the remaining part become closer to the desired shape. Although machining is generally term used to describe material removal process.

Material Removal Processes Classification
It covers several processes, which are usually divided into the following categories : Conventional Machining (cutting) – material removal by a sharp cutting tool which generally involves single-point or multipoint cutting tools and processes, e.g., turning, milling, drilling Abrasive processes – material removal by hard abrasive particles, e.g., grinding, honing Nontraditional processes - various energy forms other than sharp cutting tool to remove material (which use electric, chemical, thermal, hydrodynamic and optical sources of energy, as well as the combinations of these energy sources, to remove material from workpiece surface)

classifications OR Machining Or Cutting

Conventional Machining: – Material removed from the surface of the workpart by means of sharp cutting tools. Examples are turning, milling, drilling, etc. Turning Milling Drilling

Abrasive operations: – Material removed from the surface of the workpart by means of hard abrasive particles. e.g. grinding Grinding

Nontraditional operations: – Various energy forms other than sharp cutting tool to remove material e.g. electro-discharge machining, water jet cutting etc. Electro-discharge machining

Material Removal Processes- Machining
It is important to view machining as a system consisting of Workpiece Cutting tool Tool holder Workpiece holding device And machine tool. These operations cannot carried out efficiently and economically without a fundamental knowledge of the often complex interaction among these critical elements. As the fact that, in the USA alone, labor and overhead costs for the machining operations are estimated to a bout $300 billion per year

A shearing process in which excess materials is removed by cutting tools. – A variety of work materials – Close tolerance (<0.025μm) – Smooth surface finish (0.4μm) – Waste, Expensive: Cost and Time – Other processes such as casting, forging, and bar drawing create the general shape – Machining provides the final shape, dimensions, finish, and special geometric details

Why Machining is Important
Variety of work materials can be machined Most frequently applied to metals Parts may possess external and internal geometric features(Variety of part shapes and special geometry features possible), that cannot be produced by forming and shaping processes such as: Screw threads Accurate round holes Very straight edges and surfaces Sharp corners Engine Blocks have special geometry features Good dimensional accuracy and surface finish. For example, in a forged crankshaft, the bearing surfaces and the holes cannot be produced with good dimensional accuracy and surface finish by forming and shaping process alone.

Why Machining is Important
Some parts are heat treated for improved hardness and wear resistance, and since heat –treated parts may undergo distortion and surface discoloration, they generally required additional finishing operations. It may be more economical to machine the parts than manufacture it by other process, particularly if the number of parts required is relative small. Metal working processes typically required expensive dies and tooling, the cost of which can only be justified if the number of parts made is high enough

Disadvantages with Machining
Wasteful of material Machining processes inevitably waste material and generally require more energy and labor than other metal working operations; thus, machining should be avoided or minimized whenever possible. Time consuming A machining operation generally takes more time to shape a given part than alternative shaping processes, such as casting, powder metallurgy, or forming Removing a volume of material from a workpiece generally takes more time than other processes Unless carried out properly, material-removal processes can have adverse effects on the surface integrity of the product, including fatigue life (disturbing residual stresses equilibrium)

Relative motion between the cutting tool and the workpiece develops a cutting action. Cutting action involves shear deformation of work material to form a chip. As chip is removed, a new surface is exposed.

Chip formation due to shear

Each machining operation produces a characteristic part geometry due to two factors: Relative motions between tool and workpart Generating – part geometry determined by feed trajectory of cutting tool Shape of the cutting tool Forming – part geometry is created by the shape of the cutting tool

Generating Shape Generating shape: (a) straight turning, (b) taper turning, (c) contour turning, (d) plain milling, (e) profile milling.

Forming to Create Shape
Forming to create shape: (a) form turning, (b) drilling, and (c) broaching.

There is relative motion between the workpiece and the cutting tool, these are: Primary motion: Cutting motion (defined by cutting speed) Secondary motion: Feed motion (defined by the feed rate) Depth of cut (defines the amount of plunging of the tool into the workpiece) Any machining operation involves these quantities.

Cutting Conditions in Machining
The three dimensions of a machining process: Cutting speed v (m/s) – (primary motion)– Surface speed Feed f (m)– (secondary motion) the lateral distance traveled by the tool during one revolution Depth of cut d (m) – penetration of tool below original work surface [The depth of cut is always perpendicular to the direction of feed motion.] For certain operations, material removal rate can be found as MRR = v f d where v = cutting speed; f = feed; d = depth of cut

Example of Cutting Conditions for Turning
Cutting speed, feed, and depth of cut for a turning operation

Conventional Machining Operations
Most important conventional machining operations: Turning Drilling Milling Other machining operations: Shaping and planing Broaching Sawing

Turning A single point cutting tool removes material from a rotating workpiece to form a cylindrical shape.

Drilling Used to create a round hole, usually by means of a rotating tool (drill bit) that has two cutting edges.

Milling Rotating multiple-cutting-edge tool is moved slowly relative to work to generate plane or straight surface. There are two forms of milling; Peripheral milling Face milling

Milling Two forms: peripheral milling and face milling (a) (b) (a) peripheral milling, and (b) face milling

Classification of the cutting tools
Conventional Machining Operations Classification of the cutting tools Single-Point Tools One cutting edge Turning uses single point tools Point is usually rounded to form a nose radius Multiple Cutting Edge Tools More than one cutting edge Motion relative to work usually achieved by rotating Drilling and milling use rotating multiple cutting edge tools.

Classification of the cutting tools
(a) A single-point tool showing rake face, flank, and tool point; and (b) a helical milling cutter, representative of tools with multiple cutting edges

Cutting Conditions in Machining(turning)
the three dimensions of a machining process: Cutting speed v (m/s) – (primary motion)– Surface speed Feed f (m/rev)– (secondary motion) the lateral distance traveled by the tool during one revolution Depth of cut d (m) – penetration of tool below original work surface [The depth of cut is always perpendicular to the direction of feed motion]. For certain operations, material removal rate can be found as MRR = v f d where v = cutting speed; f = feed; d = depth of cut

Cutting Conditions in Machining (Turning)
Cutting speed (V) m/min D: Diameter in mm of workpiece. N: rev/min. of workpiece. V: cutting speed of workpiece in m/min 1 RPM = 1/60 RPS Feed (F) m/rev Depth of cut m

Cutting Conditions in conventional Machining

Roughing vs. Finishing in Machining
In production, several roughing cuts are usually taken on the part, followed by one or two finishing cuts: Roughing - Removes large amounts of material from the starting workpart. Creates shape close to desired geometry, but leaves some material for finish cutting High feeds and depths, low cutting speeds Finishing - completes part geometry Achieves final dimensions, tolerances, and finish. Low feeds and depths, high cutting speeds A roughing operation is used to remove large amounts of material rapidly and to produce a part geometry close to the desired shape. A finishing operation follows roughing and is used to achieve the final geometry and surface finish

Machine Tools A power-driven machine that performs a machining operation Holds workpart Positions tool relative to work Provides power and controls speed, feed, and depth. Pumps a Cutting fluid

Turning Single point cutting tool removes material from a rotating workpiece to generate a cylinder Performed on a machine tool called a lathe Variations of turning performed on a lathe: Facing Contour turning Chamfering Cutoff Threading

Turning operation. cutting speed (N) in revolution per minute

Turning operation. Close-up view of a turning operation on steel using a titanium nitride coated carbide cutting insert (photo courtesy of Kennametal Inc.)

Facing Tool is fed radially inward [feeding tool parallel to axis of rotation] Figure 22.6 (a) facing

Contour Turning Instead of feeding tool parallel to axis of rotation, tool follows a contour that is other than straight, thus creating a contoured shape

Chamfering Cutting edge cuts an angle on the corner of the cylinder, forming a "chamfer"

Cutoff Tool is fed radially into rotating work at some location to cut off end of part

Threading Pointed form tool is fed linearly across surface of rotating workpart parallel to axis of rotation at a large feed rate, thus creating threads

Engine Lathe Diagram of an engine lathe, showing its principal components

Methods of Holding the Work in a Lathe
Holding the work between centers Chuck Collet Face plate

Holding the Work Between Centers
Figure : (a) mounting the work between centers using a "dog”

Figure : three‑jaw chuck

Collet Figure : (c) collet

Face Plate Figure 22.8 (d) face plate for non‑cylindrical workparts

Chucking Machine Uses chuck in its spindle to hold workpart
No tailstock, so parts cannot be mounted between centers Cutting tool actions controlled automatically Operator’s job: to load and unload parts Applications: short, light‑weight parts

Bar Machine Similar to chucking machine except collet replaces chuck, permitting long bar stock to be fed through headstock At the end of the machining cycle, a cutoff operation separates the new part Highly automated (automatic bar machine) Applications: high production of rotational parts

Automatic Screw Machine
Same as automatic bar machine but smaller Applications: high production of screws and similar small hardware items

Multiple Spindle Bar Machines
More than one spindle, so multiple parts machined simultaneously by multiple tools Example: six spindle automatic bar machine works on six parts at a time After each machining cycle, spindles (including collets and workbars) are indexed (rotated) to next position

Multiple Spindle Bar Machine
Figure : (a) Part produced on a six‑spindle automatic bar machine; and (b) sequence of operations to produce the part: (1) feed stock to stop, (2) turn main diameter, (3) form second diameter and spotface, (4) drill, (5) chamfer, and (6) cutoff.

Boring Difference between boring and turning:
Boring is performed on the inside diameter of an existing hole Turning is performed on the outside diameter of an existing cylinder In effect, boring is internal turning operation Boring machines Horizontal or vertical - refers to the orientation of the axis of rotation of machine spindle

Vertical Boring

Drilling Creates a round hole in a workpart
Compare to boring which can only enlarge an existing hole Cutting tool called a drill or drill bit Machine tool: drill press

Through Holes vs. Blind Holes-Drilling
Through‑holes - drill exits opposite side of work Blind‑holes – does not exit work opposite side Figure : Two hole types: (a) through‑hole, and (b) blind hole.

Reaming-Drilling Used to slightly enlarge a hole, provide better tolerance on diameter, and improve surface finish Figure : (a) Machining operations related to drilling: reaming

Tapping-Drilling - Used to provide internal screw threads on an existing hole Tool called a tap Tapping Figure : (b)

Counterboring Provides a stepped hole, in which a larger diameter follows smaller diameter partially into the hole Figure :(c) counterboring

Drill Press Upright drill press stands on the floor
Bench drill similar but smaller and mounted on a table or bench Figure Upright drill press

Work Holding for Drill Presses
Workpart in drilling can be clamped in any of the following: Vise - general purpose workholder with two jaws Fixture - workholding device that is usually custom‑designed for the particular workpart Drill jig – similar to fixture but also provides a means of guiding the tool during drilling

Work Holding for Drill Presses
Vise Fixture Drill jig

Milling Machining operation in which work is fed past a rotating tool with multiple cutting edges Axis of tool rotation is perpendicular to feed Creates a planar surface Other geometries possible either by cutter path or shape Other factors and terms: Interrupted cutting operation Cutting tool called a milling cutter, cutting edges called "teeth" Machine tool called a milling machine

Milling Three Forms of Milling
Machining operation in which work is fed past a rotating tool with multiple cutting edges Axis of tool rotation is perpendicular to feed Creates a planar surface Three Forms of Milling (c) Three forms of milling: (a) peripheral milling. and (b) face milling (c) end milling

Peripheral Milling vs. Face Milling
Cutter axis parallel to surface being machined Cutting edges on outside periphery of cutter Face milling Cutter axis perpendicular to surface being milled End milling Three forms of milling: (a) peripheral milling. and (b) face milling (c) end milling

Slab Milling slab milling (a) Figure (a) :
Basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides (a) slab milling Figure (a) :

Conventional Face Milling
Cutter overhangs work on both sides Figure : (a) conventional face milling

Slotting slotting (b) Figure (b) :
Width of cutter is less than workpiece width, creating a slot in the work (b) slotting Figure (b) :

End milling (c) Cutter diameter is less than work width, so a slot is cut into part Figure (c) End milling

End milling in which the inside periphery of a flat part is cut just leaving an open side.

Profile Milling profile milling (d) Figure (d) :
Form of end milling in which the outside periphery of a flat part is cut (d) profile milling Figure (d) :

Pocket Milling Another form of end milling used to mill shallow pockets into flat parts (e) Figure (e) : pocket milling

Surface Contouring Ball‑nose cutter fed back and forth across work along a curvilinear path at close intervals to create a three dimensional surface form Figure (f) surface contouring

Horizontal Milling Machine
Cutter axis is parallel to surface being milled Figure (a) horizontal knee-and-column milling machine.

Vertical Milling Machine
Cutter axis is perpendicular to surface being milled Figure (b) vertical knee‑and‑column milling machine

Machining Centers The term “machining center” describes almost any CNC milling and drilling machine that includes an automatic toolchanger and a table that clamps the workpiece in place. On a machining center, the tool rotates, but the work does not. Highly automated machine tool can perform multiple machining operations under CNC control in one setup with minimal human attention Typical operations are milling and drilling Three, four, or five axes Other features: Automatic tool‑changing Automatic workpart positioning CNC means Computer Numerical Control. This means a computer converts the design produced by Computer Aided Design software (CAD), into numbers ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Figure Universal machining center; highly automated, capable of multiple machining operations under computer control in one setup with minimal human attention (photo courtesy of Cincinnati Milacron). ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Figure CNC 4‑axis turning center (photo courtesy of Cincinnati Milacron); capable of turning and related operations, contour turning, and automatic tool indexing, all under computer control. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Mill-Turn Centers Highly automated machine tool that can perform turning, milling, and drilling operations General configuration of a turning center Can position a cylindrical workpart at a specified angle so a rotating cutting tool (e.g., milling cutter) can machine features into outside surface of part Conventional turning center cannot stop workpart at a defined angular position and does not include rotating tool spindles

Operation of Mill-Turn Center
Figure Operation of a mill‑turn center: (a) example part with turned, milled, and drilled surfaces; and (b) sequence of operations on a mill‑turn center: (1) turn second diameter, (2) mill flat with part in programmed angular position, (3) drill hole with part in same programmed position, and (4) cutoff.

Shaping and Planing Similar operations
Both use a single point cutting tool moved linearly relative to the workpart Figure (a) Shaping, and (b) planing.

Shaping and Planing A straight, flat surface is created in both operations Interrupted cutting Subjects tool to impact loading when entering work Low cutting speeds due to start‑and‑stop motion Typical tooling: single point high speed steel tools

Broaching Moves a multiple tooth cutting tool linearly relative to work in direction of tool axis Figure Broaching operation. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Broaching Advantages: Good surface finish Close tolerances
Variety of work shapes possible Cutting tool called a broach Owing to complicated and often custom‑shaped geometry, tooling is expensive

Internal Broaching Performed on internal surface of a hole
A starting hole must be present in the part to insert broach at beginning of stroke Figure Work shapes that can be cut by internal broaching; cross‑hatching indicates the surfaces broached.

Sawing Cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth Tool called a saw blade Typical functions: Separate a workpart into two pieces Cut off unwanted portions of part

Power Hacksaw Figure (a) power hacksaw –linear reciprocating motion of hacksaw blade against work.

Band Saw Figure (b) bandsaw (vertical) – linear continuous motion of bandsaw blade, which is in the form of an endless flexible loop with teeth on one edge.

Circular Saw Figure (c) circular saw – rotating saw blade provides continuous motion of tool past workpart.

High Speed Machining (HSM)
Cutting at speeds significantly higher than those used in conventional machining operations Persistent trend throughout history of machining is higher cutting speeds At present there is a renewed interest in HSM due to potential for faster production rates, shorter lead times, and reduced costs

Indexable tools (face mills)
High Speed Machining Conventional vs. high speed machining Indexable tools (face mills) Work material Conventional speed High speed m/min ft/min Aluminum 600+ 2000+ 3600+ 12,000+ Cast iron, soft 360 1200 4000 Cast iron, ductile 250 800 900 3000 Steel, alloy 210 700 Source: Kennametal Inc.

High Speed Machining Applications
Aircraft industry, machining of large airframe components from large aluminum blocks Much metal removal, mostly by milling Multiple machining operations on aluminum to produce automotive, computer, and medical components Quick tool changes and tool path control important Die and mold industry Fabricating complex geometries from hard materials ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Material – Removal Processes - Cutting

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