machining processes

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CHAPTER 23

Machining Processes Used to ProduceVarious Shapes

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Examples of Parts Produced Using theMachining Processes in the Chapter

Figure 23.1 Typical parts and shapes produced with the machining processes described in thischapter.


Examples of Milling Cutters and Operations

Figure 23.2 Some of the basic types of milling cutters and milling operations.


Example of Part Produced on a CNC MillingMachine

Figure 23.3 A typical part that can beproduced on a milling machine equippedwith computer controls. Such parts canbe made efficiently and repetitively oncomputer numerical control (CNC)machines, without the need forrefixturing or reclamping the part.


Conventional and Climb Milling

Figure 23.4 (a) Schematic illustration of conventional milling and climb milling. (b) Slab milling operation,showing depth of cut, d, feed per tooth, f, chip depth of cut, tc, and workpiece speed, v. (c) Schematicillustration of cutter travel distance lc to reach full depth of cut.


Summary of Milling Parameters and Formulas

TABLE 23.1N = Rotational speed of the milling cutter, rpmf = Feed, mm/tooth or in./tooth

D = Cutter diameter, mm or in.n = Number of teeth on cutterv = Linear speed of the workpiece or feed rate, mm/min or in./minV = Surface speed of cutter, m/min or ft/min

=D Nf = Feed per tooth, mm/tooth or in/tooth

=v /N nl = Length of cut, mm or in.t = Cutting time, s or min

=( l+lc ) v , where l

c =extent of the cutter’s first contact with workpiece

MRR = mm3/min or in.

3/min

=w d v , where w is the width of cutTorque = N-m or lb-ft

( Fc ) (D/2)

Power = kW or hp= (Torque) (ω ), where ω = 2π N radians/min

Note: The units given are those that are commonly used; however, appropriate units mustbe used in the formulas.


Face Milling

Figure 23.5 Face-milling operation showing (a)action of an insert in face milling; (b) climbmilling; (c) conventional milling; (d) dimensions inface milling. The width of cut, w, is not necessarilythe same as the cutter radius. Source: IngersollCutting Tool Company.

Figure 23.6 A face-milling cutterwith indexable inserts. Source:Courtesy of Ingersoll CuttingTool Company.


Effects of Insert Shapes

Figure 23.7 Schematic illustration of the effect of insert shape on feed marks on a face-milled surface:(a) small corner radius, (b) corner flat on insert, and (c) wiper, consisting of a small radius followed by alarge radius which leaves smoother feed marks. Source: Kennametal Inc. (d) Feed marks due to variousinsert shapes.


Face-Milling Cutter

Figure 23.8 Terminology for a face-milling cutter.


Effect of Lead Angle

Figure 23.9 The effect of lead angle on the undeformed chip thickness in facemilling. Note that as the lead angle increase, the chip thickness decreases, but thelength of contact (i.e., chip width) increases. The insert in (a) must be sufficientlylarge to accommodate the contact length increase.


Cutter and Insert Position in Face Milling

Figure 23.10 (a) Relative positionof the cutter and insert as it firstengages the workpiece in facemilling, (b) insert positionstowards the end of the cut, and (c)examples of exit angles of insert,showing desirable (positive ornegative angle) and undesirable(zero angle) positions. In allfigures, the cutter spindle isperpendicular to the page.


Cutters for Different Types of Milling

Figure 23.11 Cutters for (a) straddlemilling, (b) form milling, (c) slotting,and (d) slitting with a milling cutter.


Other Milling Operations and Cutters

Figure 23.12 (a) T-slot cuttingwith a milling cutter. (b) Ashell mill.


Arbors

Figure 23.13 Mounting amilling cutter on an arbor foruse on a horizontal millingmachine.


Capacities and Maximum WorkpieceDimensions for Machine Tools

TABLE 23.2 Typical Capacities and Maximum Workpiece Dimensions forSome Machine Tools

Machine toolMaximum dimension

m (ft)Power(kW)

Maximumspeed

Milling machines (table travel) Knee-and-column 1.4 (4.6) 20 4000 rpm Bed 4.3 (14) Numerical control 5 (16.5)Planers (table travel) 10 (33) 100 1.7Broaching machines (length) 2 (6.5) 0.9 MNGear cutting (gear diameter) 5 (16.5)Note: Larger capacities are available for special applications.


ApproximateCost of

Selected Toolsfor Machining

TABLE 23.3 Approximate Cost of Selected Tools for Machining*Tools Size (in.) Cost ($)Drills, HSS, straight shank 1/4 1.00–2.00

1/2 3.00–6.00Coated (TiN) 1/4 2.60–3.00

1/2 10–15Tapered shank 1/4 2.50–7.00

1 15–452 80–853 2504 950

Reamers, HSS, hand 1/4 10–151/2 10–15

Chucking 1/2 5–101 20–251 1/2 40–55

End mills, HSS 1/2 10–151 15–30

Carbide-tipped 1/2 30–351 45–60

Solid carbide 1/2 30–701 180

Burs, carbide 1/2 10–201 50–60

Milling cutters, HSS, staggered tooth, wide 4 35–758 130–260

Collets (5 core) 1 10–20*Cost depends on the particular type of material and shape of tool, its quality,and the amount purchased.


GeneralRecommendations

for MillingOperations

TABLE 23.4General-purpose starting

conditions Range of conditions

Workpiecematerial Cutting tool

Feedmm/tooth(in./tooth)

Speedm/min

(ft/min)

Feedmm/tooth(in./tooth)

Speedm/min

(ft/min)Low-C and free-machining steels

Uncoated carbide,coated carbide,cermets

0.13–0.20(0.005–0.008)

120–180(400–600)

0.085–0.38(0.003–0.015)

90–425(300–1400)

Alloy steels Soft Uncoated, coated,

cermets0.10–0.18

(0.004–0.007)90–170

(300–550)0.08–0.30

(0.003–0.012)60–370

(200–1200) Hard Cermets, PCBN 0.10–0.15

(0.004–0.006)180–210

(600–700)0.08–0.25

(0.003–0.010)75–460

(250–1500)Cast iron, gray Soft Uncoated, coated,

cermets, SiN0.10–10.20

(0.004–0.008)120–760

(400–2500)0.08–0.38

(0.003–0.015)90–1370

(300–4500) Hard Cermets, SiN,

PCBN0.10–0.20

(0.004–0.008)120–210

(400–700)0.08–0.38

(0.003–0.015)90–460

(300–1500)Stainless steel,austenitic

Uncoated, coated,cermets

0.13–0.18(0.005–0.007)

120–370(400–1200)

0.08–0.38(0.003–0.015)

90–500(300–1800)

High-temperaturealloys, nickel base

Uncoated, coated,cermets, SiN,PCBN

0.10–0.18(0.004–0.007)

30–370(100–1200)

0.08–0.38(0.003–0.015)

30–550(90–1800)

Titanium alloys Uncoated, coated,cermets

0.13–0.15(0.005–0.006)

50–60(175–200)

0.08–0.38(0.003–0.015)

40–140(125–450)

Aluminum alloys Free machining Uncoated, coated,

PCD0.13–0.23

(0.005–0.009)610–900

(2000–3000)0.08–0.46

(0.003–0.018)300–3000

(1000–10,000)High silicon PCD 0.13

(0.005)610

(2000)0.08–0.38

(0.003–0–015)370–910

(1200–3000)Copper alloys Uncoated, coated,

PCD0.13–0.23

(0.005–0.009)300–760

(1000–2500)0.08–0.46

(0.003–0.018)90–1070

(300–3500)Thermoplastics andthermosets

Uncoated, coated,PCD

0.13–0.23(0.005–0.009)

270–460(900–1500)

0.08–0.46(0.003–0.018)

90–1370(300–4500)

Source: Based on data from Kennametal Inc.Note: Depths of cut, d , usually are in the range of 1–8 mm (0.04–0.3 in.). PCBN: polycrystalline cubic boron nitride;PCD: polycrystalline diamond.Note: See also Table 22.2 for range of cutting speeds within tool material groups.


General Troubleshooting Guide for MillingOperations

TABLE 23.5Problem Probable causesTool breakage Tool material lacks toughness; improper tool angles; cutting

parameters too high.Tool wear excessive Cutting parameters too high; improper tool material; improper tool

angles; improper cutting fluid.Rough surface finish Feed too high; spindle speed too low; too few teeth on cutter; tool

chipped or worn; built-up edge; vibration and chatter.Tolerances too broad Lack of spindle stiffness; excessive temperature rise; dull tool; chips

clogging cutter.Workpiece surfaceburnished

Dull tool; depth of cut too low; radial relief angle too small.

Back striking Dull cutting tools; cutter spindle tilt; negative tool angles.Chatter marks Insufficient stiffness of system; external vibrations; feed, depth, and

width of cut too large.Burr formation Dull cutting edges or too much honing; incorrect angle of entry or

exit; feed and depth of cut too high; incorrect insert geometry.Breakout Lead angle too low; incorrect cutting edge geometry; incorrect angle

of entry or exit; feed and depth of cut too high.


Surface Features and Corner Defects

Figure 23.14 Surface features and corner defects in face milling operations; see also Fig. 23.7. Fortroubleshooting, see Table 23.5. Source: Kennametal Inc.


Horizontal- and Vertical-Spindle Column-and-Knee Type Milling Machines

Figure 23.15 Schematic illustration of a horizontal-spindle column-and-knee type milling machine. Source:G. Boothroyd.

Figure 23.16 Schematic illustration of a vertical-spindlecolumn-and-knee type milling machine (also called a kneemiller). Source: G. Boothroyd.


Bed-Type Milling Machine

Figure 23.17 Schematicillustration of a bed-typemilling machine. Note thesingle vertical-spindle cutterand two horizontal spindlecutters. Source: ASMInternational.


Additional Milling Machines

Figure 23.18 A computer numerical control,vertical-spindle milling machine. Thismachine is one of the most versatile machinetools. Source: Courtesy of BridgeportMachines Division, Textron Inc.

Figure 23.19Schematicillustration of afive-axisprofile millingmachine. Notethat there arethree principallinear and twoangularmovements ofmachinecomponents

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Examples of Parts Made on a Planer and byBroaching

Figure 23.20 Typical parts that can bemade on a planer.

Figure 23.21 (a) Typical parts made by internalbroaching. (b) Parts made by surface broaching. Heavylines indicate broached surfaces. Source: GeneralBroach and Engineering Company.


Broaches

Figure 23.22 (a) Cutting action of a broach, showing various features. (b) Terminology for a broach.


Chipbreakers and a Broaching Machine

(a)

(b)

(c)

Figure 23.23 Chipbreaker features on (a) a flat broach and (b) a round broach. (c) Verticalbroaching machine. Source: Ty Miles, Inc.


Internal Broach and Turn Broaching

Figure 23.24 Terminology for a pull-type internal broachused for enlarging long holes.

Figure 23.25 Turn broaching of a crankshaft. The crankshaftrotates while the broaches pass tangentially across thecrankshaft’s bearing surfaces. Source: Courtesy of IngersollCutting Tool Company.


Broaching Internal Splines

Figure 23.26


Sawing Operations

Figure 23.27 Examplesof various sawingoperations. Source:DoALL Company.


Types of Saw Teeth

Figure 23.28 (a) Terminology for saw teeth. (b) Types of tooth set on saw teeth, staggered toprovide clearance for the saw blade to prevent binding during sawing.


Saw Teeth and Burs

Figure 23.29 (a) High-speed-steel teeth welded on steel blade. (b) Carbide inserts brazedto blade teeth.

Figure 23.30 Types of burs. Source:The Copper Group.


Spur Gear

Figure 23.31 Nomenclature for an involute spur gear.


Gear Generating

Figure 23.32(a) Producinggear teeth on ablank by fromcutting. (b)Schematicillustration ofgear generatingwith a pinion-shaped gearcutter. (c)Schematicillustration ofgear generatingin a gear shaperusing a pinion-shaped cutter.Note that thecutterreciprocatesvertically. (d)Gear generatingwith rack-shaped cutter.


Gear Cutting With a Hob

Figure 23.33 Schematicillustration of three views of gearcutting with a hob. Source: AfterE. P. DeGarmo and Society ofManufacturing Engineers


Cutting Bevel Gears

Figure 23.34 (a) Cutting a straight bevel-gear blank with two cutters. (b) Cutting aspiral bevel gear with a single cutter. Source: ASM International.


Gear Grinding

Figure 23.25 Finishing gears by grinding: (a) form grinding with shaped grinding wheels;(b) grinding by generating with two wheels.


Economics of Gear Production

Figure 23.36 Gearmanufacturing cost as afunction of gear quality.The numbers along thevertical lines indicatetolerances. Source:Society of ManufacturingEngineers.

machining processes

Documents

face milling b

milling operations

facemilling cutter figure

straddle milling

prenticehall page

examples of milling

b form milling

horizontal milling machine