chapter22 - CHAPTER 22 MACHINING PROCESSES USED TO PRODUCE...

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Unformatted text preview: CHAPTER 22 MACHINING PROCESSES USED TO PRODUCE ROUND SHAPES 22-1 The workpiece (part) is rotating While being machined (a) Straighttuming (bl Taper turning (c) Profiling Ill! 18E 13 ESE; O . L.— . Tool .— td‘.‘ Turning and external grooving (3) Facing (0 Face g'rwving '1 a . /. | / 4. ~ '- ‘ (5;) Form tool (h) Boring and internal grooving (i) Drilling m 7/ ymm O // m (j) Cutting off (k) Threading (I) Knurling _ E. I ‘~ I 51 FIGURE 22.1 Various cutting operations that can be performed on a fathe. 22-2 Lathes are the oldest machine tools (1000 BC) Metalworking lathes with lead screws (1700’s) Figure 22.2 Lathe specifications Swing (max diameter of workpiece) Distance between headstock and tailstock, Length of bed Type or style Horsepower 22-3 Spindle soeed selector —_ Spindle \ [with chuck l _f Headstock \ ’ fl / Ways assemblv / rCompound . gr- . Dead center /" “35‘ / Tallstock qunll / Cross Tailstock assembly ‘ [ slide / r0, . : 1" 'v ' .19“ I '— TOOJ post ,_ Carnage Lt _ v- - Handwheel ApronJ pan .1 Split-nut “— Clumh Lead screw Feed rod Longitudinal & transverse feed control FIGURE 22.2 Components of a lathe Source: Courtesy of Heidenreich & Harbec: _—————————— TYPICAL CAPACITIES AND MAXIMUM WORKPIECE DIMENSIONS FOR MACHINE TOOLS MAXIMUM DIMENSION POWER MAXIMUM MACHINE TOOL (m) " (kW) rpm Lathes (swing/length) Bench 0.3/1 <1 3000 Engine 3/5 70 4000 Turret 0.5/1.5 60 3000 Automatic screw 0.1/0.3 20 10,000 Boring machines (work diameter/length) Vertical Spindle 4/3 200 300 Horizontal spindle 1.5/2 70 1000 Drilling machines Bench and column (drill diameter) 0.1 10 12,000 Radial (column to spindle distance) 3 — — Numerical control (table travel) 4 Nate: Larger capacmes are available for special applications, Workholding Devices Chuck 3-j aw, self centering 4-jaW, independent Collet Tapered bushing Face plates Used with clamps/fixture for irregularly shaped parts Mandrels For ID support of tubular workpieces 22-6 End view Top view 20' r Side rake angle d /"\ End cutting-edge angle 14"-\ I / 1“ *- A Side relief i Side clearance 3.2mm('lsin.) ‘A , .' . R Nose radius 15 Side cutting-edge angle End section A-A Side view Flank '- 1 o face ' l 6“ Normal ‘4 6’ End relief angle Normal side J E side relief E ‘- i clearance angle 12°; angle 3126‘?" End clearance angle Tool Signature Dimensions Abbreviation 8 . . . . . . . . . . . . . . . Back rake angle BR 14 . . . . . . . . . . . . . . . Side rake angle SR 6 . . . . . . . . . . . . . . . End relief angle ER l2 . . . . . . . . . , . . . . . End clearance angle . . . 6 . . . . . . . . . . . . . . . Side relief angle SRF 12 . . . . . . . . . . . . . . . Side clearance angle . . . 20 . . . , . . . . . . . . . . . End cutting-edge angle ECEA 15 . . . . . . . . . . . . . . . Side cutting-edge angle SCEA 'lu . . . . . . . . . . . . . . . Nose radius NR (13) Top view Toolholder Side view FIGURE 22.4 (a) Designations and symbols for a right-hand cutting tool; solid high-speed-steel tools have a similar designation. Right-hand means that the tool travels from right to left as shown in Fig. 22.1a. (b) Square insert in a right-hand toolholder for a turning operation. A wide variety of toolholders are available for holding inserts at various angles. Source: Kennametal Inc. 22-7 I TAB LE 22.2 GENERAL RECOMMENDATIONS FOR TURNING TOOLS __—-—__—______fl______——__~___ HIGH-SPEED STEEL CARBIDE (INSERTS) SIDE AND SIDE AND BACK SIDE END SIDE END CUTTING BACK SIDE END SIDE END CUTTING MATERIAL RAKE RAKE RELIEF RELIEF EDGE RfiKE RAKE RELIEF RELIEF EDGE _.__-—_—_..____——__________—__________ Aluminum and magnesium alloys 20 15 12 10 ' 5 0 5 5 5 15 Cepper alloys 5 10 8 8 5 O 5 5 5 15 Steels 10 12 5 5 15 —5 -5 5 5 15 Stainless steels 5 8—1 0 5 5 15 — 5-0 — 5—5 5 5 1 5 High -t-emperature alloys 0 1 0 5 5 1 5 5 0 5 5 45 Refractory alloys 0 20 5 5 5 0 0 5 5 15 _ Titanium alloys 0 5 5 5 15 -5 -5 5 5 5 Cast irons 5 1O 5 5 15 — 5 —5 5 5 15 Thermoplastics 0 0 20—30 1 5—20 10 0 0 20—30 1 5-20 10 Thermclsets O 0 20—30 1 5—20 10 O 1 5 5 5 15 Material Removal Rate (MRR) MRR = 7T(Davg)(d)(i)(1‘T ) Where: Davg = (D0 + 2 d = Depth of cut (in.) f = feed (in/rev) N = Rotational speed/unit time Schematic illustration of a turning operation showing depth of cut. d, and feed, 2'. Cutting speed is the surface speed of the workpiece. . Component Design Guidelines Parts should be designed so that they can be fixtured and held in workholding devices with relative ease. Thin, slender workpieces are difficult to support properly to withstand clamping and cutting forces Dimensional accuracy and surface finish specified should be as wide as permissible for the part to function properly. Sharp corners, tapers, and major dimensional variations in the part should be avoided Blanks to be machined should be as close to final dimensions as possible, so as to reduce production cycle time. 22-10 Component Design Guidelines (cont.) Parts should be designed so that cutting tools can travel across the workpiece without obstruction. Design features should be such that standard, commercially available cutting tools and inserts can be used. Materials should, as much as possible, be selected for their machinability. 22-4 1 Roughness iR”! Process um 50 25 12.5 6.3 3.2 1.0 0.5 0.40 0.20 0.10 0.05 0.025 0.012 Rns +001. 2000 1000 500, 250 125 63 :32 16 3 4 2 1 0.5 Flame cutting - Average application t I ‘ Less frequent application 1 Snzigging (coarse grinding) Sawing Planing, shaping Drilling Chlemicai machining Electrical-discharge machining Milling Broaching Rea ming Electron-beam machining Laser machining Electrochemical machining Turning. boring Barrel finishing Electrochemical grinding Roller bumiahing Grinding Honing Electropolishing Polishing Lapping Superfinishing FIGURE 22.14 Range of surface roughnesses obtained in various machining processes. Note the wide range within each group. See also Fig. 26.4. —...._ 22-12 5 10 ' 20 100 250 Tolerance (in) 6 4 0.1 2 10“ ' 0.1 0.5 1.0 10 20 Diameter or length ( in.) - - FIGURE 22,15 # Range of tolerances obtained in various machining processes as a function of workpiece size. Source: Adapted from Manufacturing Planning and Estimating Handbopk, McGraw-Hill, 1963. Design Considerations Whenever possible, through holes rather than blind holes should be specified The greater the length—to-bore- diameter ratio, the more difficult it is to hold dimensions because of the deflections of the boring bar from cutting forces. Interrupted internal surfaces should be avoided. 22-14 Drilling (a) Twist drill (c) Straight-flute drill (b) Step drill (d) Spade drill m3} 3‘, (e) Gun drill (f) Drill with brazed carbide tip Carbide insert body indexable carbide inserts flow-alloy Braze steel) Figure 22.22 22-15 (a) Chisel-point drill . A (b) Crankshafbpoint drill , ‘4‘ D ' Taper shank l l 1' diarrllleller Tang/ I /r\ . Point anelé Tang drive “ Body diameter Clearance \ ' clearance diameter [D m Lip relief_ Chisel edge I / angle angle “\ Flutes ' J / .x Helix angle r ,‘sl‘ Chi-561VWW ~ Neck—e ; \N ~ \ ll I ( I — i ‘ edge ‘ , » K ‘ / Shank T 7 Jag diameterL_ I I‘ I .. l‘ _ MFlute length*———g Maren] l : Body ————. ‘Lip Mm Overall length (‘3) 3 1 2 ur margins (double-margin) are available uidance and accuracy. Drills with chip-breaker features are also available. (b) Crankshaft-point drill. (cl Various drill points Four-facet split point, by Komet of America 2 SE pomt b Mitsubishi Materials. 4. Hosoi point, 22-lfo [0 TABLE 22,} W GENERAL RECOMMENDATIONS FOR DRILL GEOMETRY FOR HIGH-SPEED STEEL TWIST DRILLS LIP- CHISEL- WORKPIECE POINT RELIEF EDGE HELIX MATERIAL ANGLE ANGLE ANGLE ANGLE POINT Aluminum alloys 90—1 18 12—1 5 125—135 24—48 Standard Magnesium alloys 70—1 18 12—1 5 120—135 30—45 Standard Copper alloys 1 18 12—1 5 125—135 10~30 Standard Stee=s 118 10—1 5 125—135 24-32 Standard High-strength steels 1 18—135 7—1 0 125—135 24—32 Crankshaft Stainless steels, 118 10—1 2 125-135 24—32 Standard low strength Stainless steels, 1 18-135 7—1 0 120-130 24—32 Crankshaft high strength High-temp. alloys 118—135 9—1 2 125—135 15—30 Crankshaft Refractory alloys 1 18 7—1 0 125—135 24—32 Standard Titanium alloys 118-135 7—1 0 125—135 15—32 Crankshaft Cast irons 118 8—1 2 125—135 24—32 Standard Plastics 60-—90 7 120—135 29 Standard /’ 22-17 Material Removal Rate for Drilling MRR= JEDZ N 4 (f) Where: D = Drill OD f = feed rate (in/rev) N = rpm of drill 22-18 Tool Life for twist drills and taps Tool life Force or torque 1., Number of holes drilled or tapped FIGURE 22: m Determination of drill life by monitoring the rise in force or torque as a function of the number of holes drilled. This test is also used for determining tap life. __—_.__—_________—_.__________ 22-19 Machining Precision Holes ELIE 19L; Centering 125 Drilling :I:0.005” 63 Reaming . i0.001” Boring 12 Honing :l:0.0001” 6 Lapping 22-20 Design Considerations for Drilling, Reaming, and Tapping Some of the design guidelines for drilling, reaming, and tapping operations are as follows: a) Designs should allow holes to be drilled on flat surfaces, perpendicular to the drill motion; otherwise the drill tends to deflect and the hole will not be located accurately. Exit surfaces for the drill should also be flat b) Interrupted hole surfaces should be avoided or minimized for better dimensional accuracy c) Hole bottoms should match standard drill-point angles. Flat bottoms or odd shapes should be avoided 22—21 d) As in boring operations, through holes a) are preferred over blind holes. Hole depth should be minimized for good dimensional accuracy. If holes with large diameters are required, the workpiece should have preexisting holes, preferably made during fabrication of the part by forming or casting Parts should be designed so that all drilling can be done with a minimum of fixturing or without repositioning the workpiece Reaming blind or intersecting holes may be difficult because of possible tool breakage. Extra hole depth should be provided. Blind holes must be drilled deeper than subsequent reaming or tapping operations that may be performed. 22-22 ...
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This note was uploaded on 10/13/2010 for the course INDS 354 taught by Professor Shell during the Summer '05 term at University of Cincinnati.

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chapter22 - CHAPTER 22 MACHINING PROCESSES USED TO PRODUCE...

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