manufacturing lecture

Manufacturing Technology – IME 307

Material Removal Processes

©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

THEORY OF METAL MACHINING

1. Overview of Machining Technology

2. Theory of Chip Formation in Metal Machining

3. Force Relationships and the Merchant Equation

4. Power and Energy Relationships in Machining

5. Cutting Temperature


References:

Fundamentals of Modern Manufacturing: materials, processes, and systems, 3nd Ed., by Mikell P. Groover, JOHN WILEY & SONS, INC., 2007. (Chapter 21, pages 481-486)


Material Removal Processes

A family of shaping operations, the common feature of which is removal of material from a starting workpart so the remaining part has the desired geometry

Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling

Abrasive processes – material removal by hard, abrasive particles, e.g., grinding

Nontraditional processes - various energy forms other than sharp cutting tool to remove material


Fig 21.1 Classification of material removal processes


Schematic illustration of the cutting processAfter K. Holmberg, A. Matthews. Coating Tribology: Properties, Techniques and

Applications in Surface Engineering, Elsevier, Amsterdam, 1994. (fig.7. 9)

Machining is a manufacturing process in which a sharp cutting tool is used to cut away material to leave the desired part shape.


Cutting action involves shear deformation of work material to form a chip As chip is removed, new surface is exposed

Figure 21.2 (a) A cross‑sectional view of the machining process, (b) tool with negative rake angle; compare with positive rake angle in (a).

Machining


Why Machining is Important

Variety of work materials can be machined Most frequently used to cut metals

Variety of part shapes and special geometric features possible, such as: Screw threads Accurate round holes Very straight edges and surfaces

Good dimensional accuracy (tolerances of ±0.025 mm are achievable)

Good surface finishes (Roughness values less than 0.4 microns achievable in conventional machining)



Disadvantages with Machining

Wasteful of material Chips generated in machining are wasted

material, at least in the unit operation 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


Machining in Manufacturing Sequence

Generally performed after other manufacturing processes, such as casting, forging, and bar drawing Other processes create the general shape

of the starting workpart Machining provides the final shape,

dimensions, finish, and special geometric details that other processes cannot create


Machining Operations

Most important machining operations: Turning Drilling Milling

Other machining operations: Shaping and planing Broaching Sawing


Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape rotating workpiece to generate a cylindrical shape,Tool feed is parallel to the axis of rotation of the workpiece.

Figure 21.3 Three most common machining processes: (a) turning,

Turning

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.

The Turning Operation

Figure 21.2 Schematic illustration of the turning operation showing various features.


Basic principles of the turning operation



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

Tool feed is parallel to its axis of rotation.

Figure 21.3 (b) drilling,

Drilling


Drilling OperationAfter Ghosh, A. and Mallik, A.K. Manufacturing Science



Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface

Two forms: peripheral milling and face milling Tool feed is perpendicular to its axis of

rotation.

Figure 21.3 (c) peripheral milling, and (d) face milling.

Milling



Machining with multipoint toolsAfter Ghosh, A. and Mallik, A.K. Manufacturing Science




Cutting Tool Classification

1. Single-Point Tools One dominant cutting edge Point is usually rounded to form a nose

radius Turning uses single point tools

2. Multiple Cutting Edge Tools More than one cutting edge Motion relative to work achieved by rotating Drilling and milling use rotating multiple

cutting edge tools


Figure 21.4 (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 Tools


Cutting Conditions in Machining

Three dimensions of a machining process: Cutting speed v – primary motion Feed f – secondary motion Depth of cut d – penetration of tool

below original work surface For certain operations, material removal

rate can be computed as

RMR = v f d (mm3/s)

where v = cutting speed m/s; f = feed mm (mm/rev for turning); d = depth of cut mm


Cutting Conditions for Turning

Figure 21.5 Speed, feed, and depth of cut in turning.


Roughing vs. Finishing

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 starting workpart Creates shape close to desired geometry,

but leaves some material for finish cutting High feeds and depths, low speeds

Finishing - completes part geometry Final dimensions, tolerances, and finish Low feeds and depths, high cutting speeds


For Turning: Roughing cuts f = 0.4---1.25 mm/rev;

d = 2.5---20 mm Finishing cuts f = 0.125---0.4 mm/rev;

d = 0.75---2.0 mm

Cutting Fluid

is often applied to the machining operation to cool and lubricate the cutting tool.

Determining whether to use a cutting fluid

choosing the proper cutting fluid,


Characteristics of the typical operation of machining

Operation Sectional area of cut off layer, mm2

Energy for material removing10-3, J./cm3

Cutting speed, m/s

Productivity, sm3/sMRR

Turning 1,0 0,5…0,7 1,5…7,5 5∙10-2…5∙10

Broaching 0,5 2,5…3,7 0,01…0,1 4∙10-3…1∙10-1

Milling 0,3 5,0…7,5 2…6 2∙10-3…1,0

Reaming 0,1 12…30 0,15…1,6 5∙10-3…5∙10-1

Grinding 0,00005 55…70 25…50 5∙10-3…2∙10-2


Machine Tools

A power‑driven machine that performs a machining operation, including grinding

Functions in machining: Holds workpart Positions tool relative to work Provides power at speed, feed, and depth

that have been set The term is also applied to machines that

perform metal forming operations


Conventional Machine Tools Used for the Three Common Machining Operations

Operation

Machine tool Definitions of speed, feed, and depth of cut

Turning Lathe Work rotates for speed motion.Tool is fed parallel to work axis.Depth of cut is tool penetration beneath original work surface.

Drilling Drill press Work is held stationary.Tool rotates and feeds in direction parallel to tool axis. Drill bit diameter determines hole diameter.Depth of cut is depth of hole.

Milling Milling machine

Tool rotates for speed motion.Work is fed in direction perpendicular to tool axis.Depth of cut is tool penetration beneath original surface.



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