manufacturing lecture

Manufacturing Technology – IME 307

Chapter 22

©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e

References:

Fundamentals of Modern Manufacturing: materials, processes, and systems, 3nd Ed., by Mikell P. Groover, JOHN WILEY & SONS, INC., 2007. (Chapter 22, pages 523-530)


MACHINING OPERATIONS AND MACHINE TOOLS

• Turning and Related Operations• Drilling and Related Operations• Milling• Machining Centers and Turning Centers• Other Machining Operations• High Speed Machining


Machining Processes Used to Produce Various Shapes: Milling, Broaching, Sawing, and

Filing; Gear Manufacturing


FIGURE 22.2 (d) plain milling, and (e) profile milling.

Generating shape in milling


Parts Made with Millining Processes

Figure 24.1 Typical parts and shapes that can be produced with the machining processes described in this chapter.


MillingMachining operation in which work is fed past a

rotating tool with multiple cutting edges (fly-cutter with single cutting edge is rarely used)

Axis of tool rotation is perpendicular to feed (parallel in drilling)

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


Figure 21.3 Two forms of milling: (a) peripheral milling, and (b) face milling.

Two Forms of Milling



Peripheral Milling vs. Face Milling

Peripheral milling (plain milling) Cutter axis parallel to surface being

machined Cutting edges on outside periphery of cutter

Face milling Cutter axis perpendicular to surface being

milled Cutting edges on both the end and outside

periphery of the cutter


Milling Cutters and Milling Operations

Figure 24.2 Some basic types of milling cutters and milling operations. (a) Peripheral milling. (b) Face milling. (c) End milling. (d) Ball-end mill with indexable coated-carbide inserts machining a cavity in a die block. (e) Milling a sculptured surface with an end mill, using a five-axis numerical control machine. Source: (d) Courtesy of Iscar. (e) Courtesy of The Ingersoll Milling Machine Co.


Fig 22.18 Peripheral milling: (a) slab milling, (b) slotting, (c) side milling, (d) straddle milling, and (e) form milling.


Basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides

Figure 22.18 (a) slab milling

Slab Milling


Width of cutter is less than workpiece width, creating a slot in the work

if the cutter is very thin, the operation can mill narrow slots or cut workpart in two. (saw milling)

Figure 22.18 (b) slotting

Slotting (Slot milling)


milling teeth have a special profile that determines the shape of the slot

Form milling is therefore classified as a forming operation

Figure 22.18 (e) form milling

Form milling


Fig 22.19 Two forms of milling with a 20-tooth cutter: (a) up milling, and (b) down milling.

(a) up milling (conventional milling) the direction of motion of the cutter teeth is opposite the feed direction. (milling against the feed)

(b) Down milling (climb milling) the direction of cutter motion is the same as the feed direction. (milling with the feed)


up milling and down milling

up milling down milling

the chip starts out very thin and increases in thickness during the sweep of the cutter.

the chip starts out thick and reduces in thickness throughout the cut

The length of a chip is slightly large The length of a chip is less

The cutter is engaged in the work for more time per volume of material cut.

The cutter is engaged in the work for less time per volume of material cut,

this tends to reduce tool life this tends to increase tool life

tendency to lift the workpart as the cutter teeth exit the material.

the cutter force direction is downward,tending to hold the work against the milling machine table.

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

ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Cutters

Figure 24.11 Cutters for (a) straddle milling, (b) form milling, (c) slotting, and (d) slitting with a milling cutter.



Milling Operations

Figure 24.3 (a) Schematic illustration of conventional milling and climb milling. (b) lab-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.


Figure 22.20 Face milling


Cutter overhangs work on both sides

Figure 22.20 (a) conventional face milling

Conventional Face Milling


the cutter overhangs the work on only one side

Figure 22.20 (b) conventional face milling

Partial Face Milling


High speed face milling using indexable inserts (photo courtesy of Kennametal Inc.).


Cutter diameter is less than work width, so a slot is cut into part

Figure 22.20 (c) end milling

End Milling


Form of end milling in which the outside periphery of a flat part is cut

Figure 22.20 (d) profile milling

Profile Milling


Another form of end milling used to mill shallow pockets into flat parts

Figure 22.20 (e) pocket milling

Pocket Milling


Ball‑nose cutter fed back and forth across work along a curvilinear path at close intervals to create a three dimensional surface form

Figure 22.20 (f) surface contouring

Surface Contouring

Manufacturing, Engineering & Technology, Fifth Edition, by Serope Kalpakjian and Steven R. Schmid.ISBN 0-13-148965-8. © 2006 Pearson Education, Inc., Upper Saddle River, NJ. All rights reserved.

Face-Milling Operation

Figure 24.4 Face-milling operation showing (a) action of an insert in face milling; (b) climb milling; (c) conventional milling; (d) dimensions in face milling. The width of cut, w, is not necessarily the same as the cutter radius.


After Materials and Processes in

Manufacturing. 8th ed. By E. Paul

DeGarmo, J.T. Black, Ronald A. Kohser. 1997 by Prentice-

Hall.


After G. Ghryssolouris. Manufacturing Systems. Theory and Practice. – Springler-Verlag New York, Inc., 1992. – 419 p.


CUTTING CONDITIONS IN MILLING

The cutting speed is determined at the outside diameter of a milling cutter.

The feed given as a feed per cutter tooth; (chip load) it represents the size of the chip formed by each cutting edge. The feed rate is:

where fr = feed rate,mm/min; N = spindle speed, rev/min; nt = number of teeth on the cutter; and f = chip load in mm/tooth.


CUTTING CONDITIONS IN MILLING

Material removal rate is determined using the product of the crosssectional area of the cut and the feed rate.

RMR = wd fr

The feed given as a feed per cutter tooth; (chip load) it represents the size of the chip formed by each cutting edge. The feed rate is:

where fr = feed rate, mm/min; N = spindle speed, rev/min; nt = number of teeth on the cutter; and f = chip load in mm/tooth.


Time required for Milling (slab)

Fig 22.21 Slab (peripheral) milling showing entry of cutter into the workpiece

the approach distance

Time required to Mill


Time required for Milling (face centered)

FIGURE 22.22 Face milling showing approach and overtravel distances for: (a) when cutter is centered over the workpiece




Time required for Milling (face offset)

FIGURE 22.22 Face milling showing approach and overtravel distances for: (b) when cutter is offset to one side over the work.




Fig 22.22 Face milling showing approach and overtravel distances for two cases: (a) when cutter is centered over the workpiece, and (b) when cutter

is offset to one side over the work

• In all of the milling scenarios of the previous slides Tm represents the time the cutter teeth are engaged in the work, making chips.

• Approach and overtravel distances are added at the beginning and end of each cut to allow access to the work for loading and unloading. Thus the actual duration is greater than Tm.


Position of Cutter and Insert in Face Milling

Figure 24.9 (a) Relative position of the cutter and insert as it first engages the workpiece in face milling. (b) Insert positions towards the end of cut. (c) Examples of exit angles of insert, showing desirable (positive or negative angle) and undesirable (zero angle) positions. In all figures, the cutter spindle is perpendicular to the page and rotates clockwise.



Ball Nose End Mills

Figure 24.10 Ball nose end mills. These cutters are able to produce elaborate contours and are often used in the machining of dies and molds. (See also Fig. 24.2d.) Source: Courtesy of Dijet, Inc.



T-Slot Cutting and Shell Mill

Figure 24.12 (a) T-slot cutting with a milling cutter. (b) A shell mill.


Face-Milling Cutter with Indexable Inserts

Figure 24.5 A face-milling cutter with indexable inserts. Source: Courtesy of Ingersoll Cutting Tool Company.


MILLING MACHINES

Milling machines must provide a rotating spindle for the cutter and a table for fastening, positioning, and feeding the workpart.Classified on the base spindle orientation:

1. horizontal milling machine

2. vertical milling machineOther types are

– knee-and-column,

– bed type,

– planer type,

– tracer mills, and

– CNC milling machines.


Figure 22.23 Two basic types of knee-and-column milling machine.

• It is a versatile machine due to its capability for worktable feed movement in any of the x–y–z axes.

• The worktable can be moved in the x-direction, the saddle in the y-direction, and the knee vertically to achieve the z-movement.



Column-and-Knee Type Milling Machines

Figure 24.15 Schematic illustration of (a) a horizontal-spindle column-and-knee type milling machine and (b) vertical-spindle column-and-knee type milling machine. Source: After G. Boothroyd.


Figure 22.23 (a) horizontal knee-and-column milling machine.

Horizontal Milling Machine


Figure 22.23 (b) vertical knee‑and‑column milling machine

Vertical Milling Machine


Figure 22.24 Special types of knee-and-column milling machine: (a) universal – overarm, arbor, and cutter omitted for clarity

Universal Milling Machine (knee & column type)

It has a table that can be swiveled in a horizontal plane (about a vertical axis) to any specified angle. This facilitates the cutting of angular shapes and helixes on workparts.


Figure 22.24 Special types of knee-and-column milling machine: (b) ram type

Ram Mill (knee & column type)

The ram can be adjusted in and out over the worktable to locate the cutter relative to the work. The tool head can also be swiveled to achieve an angular orientation of the cutter with respect to the work.


Fig 22.25 Simplex bed-type milling machine horizontal spindle


Bed-type Milling Machine

Designed for high production.

Constructed with greater rigidity than knee-and-column machines,

this permits them to achieve high material removal rates by heavier

feed rates and

depths of cut


Bed-type Milling Machine

Simplex mills:

Single spindle bed machines are called simplex mills, and are available in either

horizontal or

vertical models.

Duplex mills

use two spindle heads.

The heads are usually positioned horizontally on opposite sides of the bed to perform simultaneous operations during one feeding pass of the work.

Triplex mills

add a third spindle mounted vertically over the bed to further increase machining capability.


Planer type Mills

Planer type mills are the largest milling machines.

The general appearance and construction is that of a large planer with the difference

milling is performed instead of planing.

One or more milling heads are substituted for the single-point cutting tools used on planers, and

the motion of the work past the tool is a feed rate motion rather than a cutting speed motion.

built to machine very large parts.

The worktable and bed of the machine are heavy and relatively low to the ground, and


FIGURE 22.31 Open-side planer.


Tracer Mills

Also called a profiling mill, is designed to reproduce an irregular part geometry that has been created on a template.

Uses either

manual feed by a human operator or

automatic feed by the machine tool

a tracing probe is controlled to follow the template while a milling head duplicates the path

Tracer mills are of two types:

1.x-y tracing

2.x-y-z tracing


CNC Vertical-Spindle Milling Machine

Figure 24.17 A computer numerical-control (CNC) vertical-spindle milling machine. This machine is one of the most versatile machine tools. The original vertical-spindle milling machine iused in job shops is still referred to as a “Bridgeport”, after its manufacturer in Bridgeport, Connecticut. Source: Courtesy of Bridgeport Machines Dibision, Textron Inc.


Five-Axis Profile Milling Machine

Figure 24.18 Schematic illustration of a five-axis profile milling machine. Note that there are three principal linear and two angular movements of machine components.


After Manufacturing Technology. Metal Cuting & Machine Tools. By P N RAO. 2002 by McGRAW-HILL.


Fig 25-6 Sketch of an arbor (two views) used on a horizontal spindle milling machine

After Materials and Processes in Manufacturing. 8th ed. By E. Paul DeGarmo, J.T. Black, Ronald A. Kohser. 1997 by Prentice-Hall.


After Manufacturing Technology. Metal Cuting & Machine Tools. By P N RAO. 2002 by McGRAW-HILL.


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