Common Machining Processes

Transcription

1 Common Machining Processes Tool (a) Straight turning (b) Cutting off Tool Cutter End mill (c) Slab milling (d) End milling FIGURE 8.1 Some examples of common machining processes.

2 Orthogonal Cutting t c Rough surface Chip Shear plane t o! - + " V Shiny surface Tool face Tool Rake angle Flank Relief or clearance angle Workpiece Shear angle (a) t c Rough surface Primary shear zone Chip t o - + " V Tool face Tool Rake angle Flank Relief or clearance angle Rough surface FIGURE 8.2 Schematic illustration of a two-dimensional cutting process, or orthogonal cutting. (a) Orthogonal cutting with a well-defined shear plane, also known as the Merchant model; (b) Orthogonal cutting without a well-defined shear plane. (b)

3 Chip Formation Rake angle, Chip Tool ( ) d Workpiece A B C ( - ) V c (90 - ) V Vs Shear plane A O B C ( - ) (a) (b) FIGURE 8.3 (a) Schematic illustration of the basic mechanism of chip formation in cutting. (b) Velocity diagram in the cutting zone.

4 Tool Secondary shear zones Chip Primary shear zone Workpiece Chip Tool Primary shear zone BUE Types of Chips (a) (b) (c) Low shear strain High shear strain (d) FIGURE 8.4 Basic types of chips produced in metal cutting and their micrographs: (a) continuous chip with narrow, straight primary shear zone; (b) secondary shear zone at the tool-chip interface; (c) continuous chip with built-up edge; (d) segmented or nonhomogeneous chip; and (e) discontinuous chip. Source: After M.C. Shaw, P.K. Wright, and S. Kalpakjian. (e) FIGURE 8.5 Shiny (burnished) surface on the tool side of a continuous chip produced in turning.

5 Hardness in Cutting Zone Chip Built-up edge Workpiece Hardness (HK) (b) 230 (a) FIGURE 8.6 (a) Hardness distribution in the cutting zone for 3115 steel. Note that some regions in the built-up edge are as much as three times harder than the bulk workpiece. (b) Surface finish in turning 5130 steel with a built-up edge. (c) Surface finish on 1018 steel in face milling. Source: Courtesy of Metcut Research Associates, Inc. (c)

6 Chip Breakers Chip breaker Chip After Before Tool Rake face of tool Clamp Chip breaker Tool Rake face Workpiece (a) (b) FIGURE 8.7 (a) Schematic illustration of the action of a chip breaker. Note that the chip breaker decreases the radius of curvature of the chip. (b) Chip breaker clamped on the rake face of a cutting tool. (c) Grooves on the rake face of cutting tools, acting as chip breakers. Most cutting tools now are inserts with built-in chip-breaker features. Radius Positive rake (c) 0 rake FIGURE 8.8 Various chips produced in turning: (a) tightly curled chip; (b) chip hits workpiece and breaks; (c) continuous chip moving radially outward from workpiece; and (d) chip hits tool shank and breaks off. Source: After G. Boothroyd. (a) (b) (c) (d)

7 Oblique Cutting z a Top view Tool t c Chip y i o a Tool i = 0 x Chip i o Workpiece Workpiece (a) (b) (c) i = 15 i = 30 FIGURE 8.9 (a) Schematic illustration of cutting with an oblique tool. (b) Top view, showing the inclination angle, i. (c) Types of chips produced with different inclination angles.

8 Right-Hand Cutting Tool Axis Side-rake angle, + (SR) End-cutting edge angle (ECEA) Axis Shank Axis Face Side-relief angle Cutting edge Back-rake angle, + (BR) Nose radius Flank Side-cutting edge angle (SCEA) Clearance or end-relief angle Toolholder Clamp screw Clamp Insert Seat or shim (a) (b) FIGURE 8.10 (a) Schematic illustration of a right-hand cutting tool for turning. Although these tools have traditionally been produced from solid tool-steel bars, they are now replaced by inserts of carbide or other tool materials of various shapes and sizes, as shown in (b).

9 Cutting Forces F n Chip F s R R F N Workpiece F t F c Tool V F t F c Chip F s R N F Tool Workpiece V FIGURE 8.11 (a) Forces acting on a cutting tool in two-dimensional cutting. Note that the resultant forces, R, must be collinear to balance the forces. (b) Force circle to determine various forces acting in the cutting zone. Source: After M.E. Merchant. (a) (b) Cutting force F c = Rcos(β α) = wt oτcos(β α) sinφcos(φ + β α) Friction coefficient µ = tanβ = F t + F c tanα F c F t tanα

10 Cutting Data F t (lb) mm/rev ! = (N) TABLE 8.1 Data on orthogonal cutting of 4130 steel. (in.-lb/in 3 u f /u t α φ γ µ β F c (lb) F t (lb) 10 3 ) u s u f (%) t o = in.; w = in.; V = 90 ft/min; tool: high-speed steel. u t Feed (in./rev) FIGURE 8.12 Thrust force as a function of rake angle and feed in orthogonal cutting of AISI 1112 cold-rolled steel. Note that at high rake angles, the thrust force is negative. A negative thrust force has important implications in the design of machine tools and in controlling the stability of the cutting process. Source: After S. Kobayashi and E.G. Thomsen. TABLE 8.2 Data on orthogonal cutting of 9445 steel. u f /u t α V φ γ µ β F c F t u t u s u f (%) t o = in.; w = 0.25 in.; tool: cemented carbide.

11 Shear Force & Normal Force mm mm F s (lb) = 20 to 40 = 50,000 psi (N) F t (lb) (N) A s (in 2 x 10-3 ) A s (in 2 x 10-3 ) (a) (b) FIGURE 8.13 (a) Shear force and (b) normal force as a function of the area of the shear plane and the rake angle for brass. Note that the shear stress in the shear plane is constant, regardless of the magnitude of the normal stress, indicating that the normal stress has no effect on the shear flow stress of the material. Source: After S. Kobayashi and E.G. Thomsen.

12 Shear Stress on Tool Face Tool face Sliding Sticking! " Tool Stresses on tool face Tool tip Flank face FIGURE 8.14 Schematic illustration of the distribution of normal and shear stresses at the tool-chip interface (rake face). Note that, whereas the normal stress increases continuously toward the tip of the tool, the shear stress reaches a maximum and remains at that value (a phenomenon known as sticking; see Section 4.4.1).

13 Shear-Angle Relationships 50 Shear angle, # (deg.) Tin Aluminum Lead Eq. (8.21) Eq. (8.20) Copper Mild steel (! - ") # (deg.) " = 0! = (deg.) µ= FIGURE 8.15 (a) Comparison of experimental and theoretical shear-angle relationships. More recent analytical studies have resulted in better agreement with experimental data. (b) Relation between the shear angle and the friction angle for various alloys and cutting speeds. Source: After S. Kobayashi. (a) (b) Merchant [Eq. (8.20)] φ = 45 + α 2 β 2 Shaffer [Eq. (8.21)] φ = 45 + α β Mizuno [Eqs. (8.22)-(8.23] φ = α for α > 15 φ = 15 for α < 15

14 Specific Energy Specific Energy Material W-s/mm 3 hp-min/in 3 Aluminum alloys Cast irons Copper alloys High-temperature alloys Magnesium alloys Nickel alloys Refractory alloys Stainless steels Steels Titanium alloys At drive motor, corrected for 80% efficiency; multiply the energy by 1.25 for dull tools. TABLE 8.3 Approximate Specific-Energy Requirements in Machining Operations

15 Chip Workpiece Temperature ( C) Tool FIGURE 8.1 Typical temperature distribution in the cutting zone. Note the severe temperature gradients within the tool and the chip, and that the workpiece is relatively cool. Source: After G. Vieregge. T = 1.2Y f ρc 3 Vto K Flank surface temperature ( F) Temperatures in Cutting mm V = 550 ft/min Work material: AISI Annealed: 188 HB Tool material: K3H carbide Feed: in./rev (0.14 mm/rev) Distance from tool tip (in.) (a) C Local temperature at tool-chip interface ( F) ft/min Fraction of tool-chip contact length measured in the direction of chip flow FIGURE 8.2 Temperature distribution in turning as a function of cutting speed: (a) flank temperature; (b) temperature along the tool-chip interface. Note that the rake-face temperature is higher than that at the flank surface. Source: After B.T. Chao and K.J. Trigger. (b) C FIGURE 8.18 Proportion of the heat generated in cutting transferred to the tool, workpiece, and chip as a function of the cutting speed. Note that most of the cutting energy is carried away by the chip (in the form of heat), particularly as speed increases. Energy (%) Tool Workpiece Chip Cutting speed

16 Terminology in Turning Feed (mm/rev or in./rev) Depth of cut (mm or in.) Chip Tool FIGURE 8.19 Terminology used in a turning operation on a lathe, where f is the feed (in mm/rev or in./rev) and d is the depth of cut. Note that feed in turning is equivalent to the depth of cut in orthogonal cutting (see Fig. 8.2), and the depth of cut in turning is equivalent to the width of cut in orthogonal cutting. See also Fig

17 Rake face Crater wear depth (KT) Tool Rake face R Nose radius Crater wear Flank wear Depth-of-cut line VB max VB Flank face Tool Wear Flank wear Flank face Depth-of-cut line (a) Taylor tool life equation: Rake face Flank wear Flank face Rake face Crater wear Flank face V T n = C (b) (c) Thermal cracking BUE Rake face (d) Flank face FIGURE 8.20 Examples of wear in cutting tools. (a) Flank wear; (b) crater wear; (c) chipped cutting edge; (d) thermal cracking on rake face; (e) flank wear and built-up edge; (f) catastrophic failure (fracture). Source: Courtesy of Kennametal, Inc. (e) TABLE 8.4 Range of n values for various cutting tools. High-speed steels Cast alloys Carbides Ceramics

18 Effect of Workpiece on Tool Life Tool life (min) m/min e a 80 b c d Cutting speed (ft/min) Tool life (min) m/s Martensitic Pearlite-ferrite Spheroidized a. As cast b. As cast c. As cast d. Annealed e. Annealed Hardness (HB) Ferrite Pearlite (a) 20% % _ Cutting speed (ft/min) (b) FIGURE 8.21 Effect of workpiece microstructure on tool life in turning. Tool life is given in terms of the time (in minutes) required to reach a flank wear land of a specified dimension. (a) Ductile cast iron; (b) steels, with identical hardness. Note in both figures the rapid decrease in tool life as the cutting speed increases.

19 Tool-Life Curves Tool life (min) m/min High-speed steel Cast alloy Carbide Ceramic n 3000 Tool life (min) C Feed constant, speed variable Speed constant, feed variable Cutting speed (ft/min) (a) 10, Temperature ( F) Work material: Heat-resistant alloy Tool material: Tungsten carbide Tool life criterion: in. (0.6 mm) flank wear (b) FIGURE 8.22 (a) Tool-life curves for a variety of cutting-tool materials. The negative inverse of the slope of these curves is the exponent n in tool-life equations. (b) Relationship between measured temperature during cutting and tool life (flank wear). Note that high cutting temperatures severely reduce tool life. See also Eq. (8.30). Source: After H. Takeyama and Y. Murata.

20 Crater wear rate (in 3 /min x 10-6 ) C a b c Average tool-chip interface temperature ( F) 0.15 mm 3 /min Tool Wear Rake face FIGURE 8.23 Relationship between craterwear rate and average tool-chip interface temperature in turning: (a) high-speed-steel tool; (b) C1 carbide; (c) C5 carbide. Note that crater wear increases rapidly within a narrow range of temperature. Source: After K.J. Trigger and B.T. Chao. Crater wear TABLE 8.5 Allowable average wear lands for cutting tools in various operations. Allowable Wear Land (mm) Operation High-Speed Steels Carbides Turning Face milling End milling Drilling Reaming Chip Flank face FIGURE 8.23 Interface of chip (left) and rake face of cutting tool (right) and crater wear in cutting AISI 1004 steel at 3 m/s (585 ft/min). Discoloration of the tool indicates the presence of high temperature (loss of temper). Note how the crater-wear pattern coincides with the discoloration pattern. Compare this pattern with the temperature distribution shown in Fig Source: Courtesy of P.K. Wright.

21 Acoustic Emission and Wear Mean flank wear mm in Crater wear Flank wear in mm Maximum crater depth Mean RMS (mv) Elapsed machining time (min) FIGURE 8.25 Relationship between mean flank wear, maximum crater wear, and acoustic emission (noise generated during cutting) as a function of machining time. This technique has been developed as a means for continuously and indirectly monitoring wear rate in various cutting processes without interrupting the operation. Source: After M.S. Lan and D.A. Dornfeld.

22 Roughness (R a ) µm Process µin Rough cutting Flame cutting Average application Snagging (coarse grinding) Less frequent application Sawing Casting Sand casting Permanent mold casting Investment casting Die casting Forming Hot rolling Forging Extruding Cold rolling, drawing Roller burnishing Machining Planing, shaping Milling Broaching Reaming Turning, boring Drilling Advanced machining Chemical machining Electrical-discharge machining Electron-beam machining Laser machining Electrochemical machining Finishing processes Honing Barrel finishing Electrochemical grinding Grinding Electropolishing Polishing Lapping Superfinishing Surface Finish FIGURE 8.26 Range of surface roughnesses obtained in various machining processes. Note the wide range within each group, especially in turning and boring. (See also Fig. 9.27).

23 Surfaces in Machining FIGURE 8.27 Surfaces produced on steel in machining, as observed with a scanning electron microscope: (a) turned surface, and (b) surface produced by shaping. Source: J.T. Black and S. Ramalingam. (a) (b) FIGURE 8.28 Schematic illustration of a dull tool in orthogonal cutting (exaggerated). Note that at small depths of cut, the rake angle can effectively become negative. In such cases, the tool may simply ride over the workpiece surface, burnishing it, instead of cutting. Increasing depth of cut Workpiece Tool Machined surface

24 Inclusions in Free-Machining Steels (a) (b) (c) FIGURE 8.29 Photomicrographs showing various types of inclusions in low-carbon, resulfurized freemachining steels. (a) Manganese-sulfide inclusions in AISI 1215 steel. (b) Manganese-sulfide inclusions and glassy manganese-silicate-type oxide (dark) in AISI 1215 steel. (c) Manganese sulfide with lead particles as tails in AISI 12L14 steel. Source: Courtesy of Ispat Inland Inc.

25 Hardness of Cutting Tools 95 C Ceramics Carbides Hardness (HRA) Carbon tool steels Cast alloys High-speed steels Temperature ( F) HRC FIGURE 8.30 Hardness of various cutting-tool materials as a function of temperature (hot hardness). The wide range in each group of tool materials results from the variety of compositions and treatments available for that group.

26 Tool Materials TABLE 8.6 Typical range of properties of various tool materials. Carbides Cubic Single High-Speed Cast Boron Crystal Property Steel Alloys WC TiC Ceramics Nitride Diamond Hardness HRA HRA HRA HRA HRA HK HK Compressive strength MPa psi Transverse rupture strength MPa psi Impact strength J < 0.1 < 0.5 < 0.2 in.-lb < 1 < 5 < 2 Modulus of elasticity GPa psi Density kg/m ,000-15, lb/in Volume of hard phase (%) Melting or decomposition temperature C F Thermal conductivity, W/mK Coefficient of thermal expansion, 10 6 / C The values for polycrystalline diamond are generally lower, except impact strength, which is higher.

27 Properties of Tungsten-Carbide Tools Wear (mg), compressive and transverserupture strength (kg/mm 2 ) Compressive strength Hardness Transverse-rupture strength Wear HRA Vickers hardness (HV) Cobalt content (% by weight) FIGURE 8.31 Effect of cobalt content in tungsten-carbide tools on mechanical properties. Note that hardness is directly related to compressive strength (see Section 2.6.8) and hence, inversely to wear [see Eq. (4.6)].

28 Inserts Toolholder Insert Shank Clamp screw Clamp Insert Seat or shim Lockpin Seat (a) (b) (c) FIGURE 8.32 Methods of mounting inserts on toolholders: (a) clamping, and (b) wing lockpins. (c) Examples of inserts mounted using threadless lockpins, which are secured with side screws. Source: Courtesy of Valenite.

29 Insert Strength Increasing strength Increased chipping and breaking FIGURE 8.33 Relative edge strength and tendency for chipping and breaking of inserts with various shapes. Strength refers to that of the cutting edge shown by the included angles. Source: Courtesy of Kennametal, Inc. Negative with land and hone Negative with land Negative honed Negative sharp Positive with hone Positive sharp Increasing edge strength FIGURE 8.34 Edge preparations for inserts to improve edge strength. Source: Courtesy of Kennametal, Inc.

30 Historical Tool Improvement 100 Carbon steel Machining time (min) High-speed steel Cast cobalt-based alloys Cemented carbides Improved carbide grades First coated grades First double-coated grades First triple-coated grades 0.5 Functionally graded triple-coated 1900!10!20!30!40!50!60!70!80!90!00 Year FIGURE 8.35 Relative time required to machine with various cutting-tool materials, with indication of the year the tool materials were introduced. Note that, within one century, machining time has been reduced by two orders of magnitude. Source: After Sandvik Coromant.

31 Coated Tools Rake face Tool TiN coated Uncoated TiN TiC + TiN Al 2 O 3 TiN Al 2 O 3 TiN Al 2 O 3 TiC + TiN Carbide substrate Flank wear FIGURE 8.36 Wear patterns on high-speed-steel uncoated and titanium-nitride-coated cutting tools. Note that flank wear is lower for the coated tool. FIGURE 8.37 Multiphase coatings on a tungsten-carbide substrate. Three alternating layers of aluminum oxide are separated by very thin layers of titanium nitride. Inserts with as many as 13 layers of coatings have been made. Coating thicknesses are typically in the range of 2 to 10 µm. Source: Courtesy of Kennametal, Inc.

32 Properties of Cutting Tool Materials Hot hardness and wear resistance Diamond, cubic boron nitride Aluminum oxide (HIP) Aluminum oxide + 30% titanium carbide Silicon nitride Cermets Coated carbides Carbides HSS Strength and toughness FIGURE 8.38 Ranges of properties for various groups of cutting-tool materials. (See also Tables 8.1 through 8.5.) Tungsten-carbide insert Braze Polycrystalline cubic boron nitride or diamond layer Carbide substrate FIGURE 8.39 Construction of polycrystalline cubicboron-nitride or diamond layer on a tungsten-carbide insert.

33 Characteristics of Machining Commercial tolerances Process Characteristics (±mm) Turning Turning and facing operations are performed on all types of materials; requires skilled labor; low production rate, but medium to high rates can be achieved with turret lathes and Fine: Rough: 0.13 Skiving: automatic machines, requiring less skilled labor. Boring Internal surfaces or profiles, with characteristics similar to those produced by turning; stiffness of boring bar is important to avoid chatter. Drilling Round holes of various sizes and depths; requires boring and reaming for improved accuracy; high production rate, labor skill required depends on hole location and accuracy specified. Milling Variety of shapes involving contours, flat surfaces, and slots; wide variety of tooling; versatile; low to medium production rate; requires skilled labor. Planing Flat surfaces and straight contour profiles on large surfaces; suitable for low-quantity production; labor skill required depends on part shape. Shaping Flat surfaces and straight contour profiles on relatively small workpieces; suitable for low-quantity production; labor skill required depends on part shape. Broaching External and internal flat surfaces, slots, and contours with good surface finish; costly tooling; high production rate; labor skill required depends on part shape. Sawing Straight and contour cuts on flats or structural shapes; not suitable for hard materials unless the saw has carbide teeth or is coated with diamond; low production rate; requires only low skilled labor. 0.8 TABLE 8.7 General characteristics of machining processes.

34 Depth of cut Lathe Operations Feed, f Tool (a) Straight turning (b) Taper turning (c) Profiling (d) Turning and external grooving (e) Facing (f) Face grooving (g) Cutting with a form tool (h) Boring and internal grooving (i) Drilling Workpiece (j) Cutting off (k) Threading (l) Knurling FIGURE 8.40 Variety of machining operations that can be performed on a lathe.

35 Tool Angles Side rake angle (RA) Side relief angle (SRA) Back rake angle (BRA) Wedge angle End relief angle (ERA) Shank Flank face Nose radius End cutting-edge angle (ECEA) Side cutting-edge angle (SCEA) Nose angle Rake face FIGURE 8.41 Designations and symbols for a right-hand cutting tool. The designation right hand means that the tool travels from right to left, as shown in Fig (a) End view (b) Side view (c) Top view T A B L E 8. 8 G e n e r a l recommendations for tool angles in turning. High-speed steel Carbide inserts Material Back Side End Side Side and end Back Side End Side Side and end rake rake relief relief cutting edge rake rake relief relief cutting edge Aluminum and magnesium alloys Copper alloys Steels Stainless steels High-temperature alloys Refractory alloys Titanium alloys Cast irons Thermoplastics Thermosets

36 Turning Operations N N d Workpiece F t F c F r Chuck D f D o Feed, f Tool Feed, f Tool (a) (b) FIGURE 8.42 (a) Schematic illustration of a turning operation, showing depth of cut, d, and feed, f. Cutting speed is the surface speed of the workpiece at the tool tip. (b) Forces acting on a cutting tool in turning. Fc is the cutting force; Ft is the thrust or feed force (in the direction of feed); and Fr is the radial force that tends to push the tool away from the workpiece being machined. Compare this figure with Fig for a two-dimensional cutting operation.

37 Cutting Speeds for Turning Cutting speed (ft/min) mm/rev Uncoated carbides Cubic boron nitride, diamond, and ceramics Cermets Coated carbides Feed (in./rev) m/min Cutting Speed Workpiece Material m/min ft/min Aluminum alloys Cast iron, gray Copper alloys High-temperature alloys Steels Stainless steels Thermoplastics and thermosets Titanium alloys Tungsten alloys Note: (a) The speeds given in this table are for carbides and ceramic cutting tools. Speeds for high-speed-steel tools are lower than indicated. The higher ranges are for coated carbides and cermets. Speeds for diamond tools are significantly higher than any of the values indicated in the table. (b) Depths of cut, d, are generally in the range of mm ( in.). (c) Feeds, f, are generally in the range of mm/rev ( in./rev). FIGURE 8.43 The range of applicable cutting speeds and feeds for a variety of cutting-tool materials. TABLE 8.9 Approximate Ranges of Recommended Cutting Speeds for Turning Operations

38 Lathe Tool post Spindle (with chuck) Headstock assembly Spindle speed selector Compound rest Carriage Ways Dead center Tailstock quill Tailstock assembly Handwheel Cross slide Clutch Feed selector Apron Longitudinal & transverse feed control Bed Lead screw Split nut Feed rod Chip pan Clutch FIGURE 8.44 General view of a typical lathe, showing various major components. Source: Courtesy of Heidenreich & Harbeck.

39 CNC Lathe CNC unit Chuck Round turret for OD operations Drill Multitooth cutter Tool for turning or boring Reamer Individual motors End turret for ID operations (a) Tailstock (b) Drill FIGURE 8.45 (a) A computer-numerical-control lathe, with two turrets; these machines have higher power and spindle speed than other lathes in order to take advantage of advanced cutting tools with enhanced properties; (b) a typical turret equipped with ten cutting tools, some of which are powered.

40 Typical CNC Parts 67.4 mm (2.654") 87.9 mm (3.462") 98.4 mm (3.876") mm (9.275") 50.8 mm (2") 23.8 mm (0.938") 85.7 mm (3.375") 32 threads per in. Material: Titanium alloy Number of tools: 7 Total machining time (two operations): 5.25 minutes (a) Housing base 78.5 mm (3.092") Material: alloy steel Number of tools: 4 Total machining time (two operations): 6.32 minutes (b) Inner bearing race 53.2 mm (2.094") Material: 1020 Carbon Steel Number of tools: 8 Total machining time (two operations): 5.41 minutes (c) Tube reducer FIGURE 8.46 Typical parts made on computer-numerical-control machine tools.

41 Typical Production Rates Operation Rate Turning Engine lathe Very low to low Tracer lathe Low to medium Turret lathe Low to medium Computer-control lathe Low to medium Single-spindle chuckers Medium to high Multiple-spindle chuckers High to very high Boring Very low Drilling Low to medium Milling Low to medium Planing Very low Gear cutting Low to medium Broaching Medium to high Sawing Very low to low Note: Production rates indicated are relative: Very low is about one or more parts per hour; medium is approximately 100 parts per hour; very high is 1000 or more parts per hour. TABLE 8.10 Typical production rates for various cutting operations.

42 Boring Mill Cross-rail Tool head Workpiece Work table Bed Column FIGURE 8.47 Schematic illustration of the components of a vertical boring mill.

43 Drills Shank diameter Tang Tang drive Neck Straight shank Shank length Taper shank Flutes Helix angle Overall length Flute length Body Point angle (a) Chisel-point drill Lip-relief angle Drill diameter Chisel-edge angle Lip Margin Body diameter clearance Land Clearance diameter Web Chisel edge FIGURE 8.48 Two common types of drills: (a) Chisel-point drill. The function of the pair of margins is to provide a bearing surface for the drill against walls of the hole as it penetrates into the workpiece. Drills with four margins (double-margin) are available for improved drill guidance and accuracy. Drills with chip-breaker features are also available. (b) Crankshaft drills. These drills have good centering ability, and because chips tend to break up easily, they are suitable for producing deep holes. (b) Crankshaft-point drill Drilling Core drilling Step drilling Counterboring Countersinking Reaming Center drilling Gun drilling High-pressure coolant FIGURE 8.49 Various types of drills and drilling operations.

44 Speeds and Feeds in Drilling Surface Feed, mm/rev (in./rev) Spindle speed (rpm) Speed Drill Diameter Drill Diameter Workpiece 1.5 mm 12.5 mm 1.5 mm 12.5 mm Material m/min ft/min (0.060 in.) (0.5 in.) (0.060 in.) (0.5 in.) Aluminum alloys (0.001) 0.30 (0.012) , Magnesium alloys (0.001) 0.30 (0.012) , Copper alloys (0.001) 0.25 (0.010) , Steels (0.001) 0.30 (0.012) Stainless steels (0.001) 0.18 (0.007) Titanium alloys (0.0004) 0.15 (0.006) Cast irons (0.001) 0.30 (0.012) , Thermoplastics (0.001) 0.13 (0.005) , Thermosets (0.001) 0.10 (0.004) , Note: As hole depth increases, speeds and feeds should be reduced. Selection of speeds and feeds also depends on the specific surface finish required. TABLE 8.11 General recommendations for speeds and feeds in drilling.

45 Reamers and Taps Chamfer angle Chamfer length Chamfer relief Radial rake Margin width Land width FIGURE 8.50 Terminology for a helical reamer. Helix angle, - Primary relief angle FIGURE 8.51 (a) Terminology for a tap; (b) illustration of tapping of steel nuts in high production. Chamfer angle Heel Cutting edge Land Chamfer relief Flute Rake angle Tap Nut (a) Hook angle (b)

46 Typical Machined Parts (a) (b) (c) Stepped cavity Drilled and tapped holes (d) (e) (f) FIGURE 8.52 Typical parts and shapes produced by the machining processes described in Section 8.10.

47 Conventional and Climb Milling Cutter D D N t c d Cutter d Conventional milling Workpiece Climb milling v f l c v Workpiece l (a) (b) (c) FIGURE 8.53 (a) Illustration showing the difference between 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) Schematic illustration of cutter travel distance, lc, to reach full depth of cut.

48 Face Milling l c Insert f Cutter Workpiece v D w l f Cutter Workpiece v d l v w Machined surface FIGURE 8.54 Face-milling operation showing (a) action of an insert in face milling; (b) climb milling; (c) conventional milling; (d) dimensions in face milling. l c (a) (b) (c) (d) End cutting-edge angle Peripheral relief (radial relief) Axial rake, 1 Corner angle FIGURE 8.55 Terminology for a facemilling cutter. End relief (axial relief) Radial rake, 2

49 Cutting Mechanics Insert Undeformed chip thickness Depth of cut, d Feed per tooth, f (a) (b) f Lead angle FIGURE 8.56 The effect of lead angle on the undeformed chip thickness in face milling. Note that as the lead angle increases, the undeformed chip thickness (and hence the thickness of the chip) decreases, but the length of contact (and hence the width of the chip) increases. Note that the insert must be sufficiently large to accommodate the increase in contact length. FIGURE 8.57 (a) Relative position of the cutter and the insert as it first engages the workpiece in face milling, (b) insert positions at entry and exit near the end of cut, and (c) examples of exit angles of the insert, showing desirable (positive or negative angle) and undesirable (zero angle) positions. In all figures, the cutter spindle is perpendicular to the page. Workpiece Cutter (a) Exit Entry (b) Re-entry Exit Cutter Milled surface + Desirable (c) - Undesirable

50 Milling Operations (a) Straddle milling (c) Slotting (b) Form milling (d) Slitting FIGURE 8.58 Cutters for (a) straddle milling; (b) form milling; (c) slotting; and (d) slitting operations. Arbor Cutting Speed Workpiece Material m/min ft/min Aluminum alloys ,000 Cast iron, gray Copper alloys High-temperature alloys Steels Stainless steels Thermoplastics and thermosets Titanium alloys Note: (a) These speeds are for carbides, ceramic, cermets, and diamond cutting tools. Speeds for high-speed-steel tools are lower than those indicated in this table. (b) Depths of cut, d, are generally in the range of 1-8 mm ( in.). (c) Feeds per tooth, f, are generally in the range of mm/rev ( in./rev). TABLE 8.12 Approximate range of recommended cutting speeds for milling operations.

51 Milling Machines Overarm Column Head Work table Arbor Column Workpiece T-slots Work table Saddle T-slots Workpiece Saddle Base Knee Base Knee (a) (b) FIGURE 8.59 (a) Schematic illustration of a horizontal-spindle column-and-knee-type milling machine. (b) Schematic illustration of a vertical-spindle column-and-knee-type milling machine. Source: After G. Boothroyd.

52 Broaching (a) (b) (c) FIGURE 8.60 (a) Typical parts finished by internal broaching. (b) Parts finished by surface broaching. The heavy lines indicate broached surfaces; (c) a vertical broaching machine. Source: (a) and (b) Courtesy of General Broach and Engineering Company, (c) Courtesy of Ty Miles, Inc.

53 Broaches Cut per tooth Chip gullet Rake or hook angle Tooth depth Pitch Land Backoff or clearance angle FIGURE 8.61 (a) Cutting action of a broach, showing various features. (b) Terminology for a broach. Workpiece Root radius (a) (b) Semifinishing teeth Pull end Front pilot Roughening teeth Finishing teeth Rear pilot Follower diameter FIGURE 8.62 Terminology for a pull-type internal broach, typically used for enlarging long holes. Root diameter Shank length Overall length Cutting teeth

54 Saws and Saw Teeth Tooth face Tooth back (flank) Tooth spacing Back edge Tooth back Gullet clearance angle depth Tooth rake angle (positive) Width Straight tooth Raker tooth Wave tooth Tooth set FIGURE 8.63 (a) Terminology for saw teeth. (b) Types of saw teeth, staggered to provide clearance for the saw blade to prevent binding during sawing. (a) (b) FIGURE 8.64 (a) High-speed-steel teeth welded on a steel blade. (b) Carbide inserts brazed to blade teeth. M2 HSS HRC Electron-beam weld Flexible alloy-steel backing Carbide insert (a) (b)

55 Gear cutter Base circle Pitch circle Cutter spindle Spacer Gear Manufacture Gear blank Pitch circle Base circle Pinion-shaped cutter Gear blank Gear teeth (a) (b) Top view Gear blank Rack-shaped cutter Gear blank Hob Gear blank Hob FIGURE 8.65 (a) Schematic illustration of gear generating with a pinion-shaped gear cutter. (b) Schematic illustration of gear generating in a gear shaper, using a pinion-shaped cutter; note that the cutter reciprocates vertically. (c) Gear generating with a rack-shaped cutter. (d) Three views of gear cutting with a hob. Source: After E.P. DeGarmo. (c) (d)

56 Machining Centers Tool storage Tools (cutters) Tool-interchange arm Traveling column Spindle Spindle carrier Computer numerical-control panel FIGURE 8.66 A horizontal-spindle machining center, equipped with an automatic tool changer. Tool magazines in such machines can store as many as 200 cutting tools, each with its own holder. Source: Courtesy of Cincinnati Machine. Index table Pallets Bed 1st Turret head 2nd Turret head 1st Spindle head FIGURE 8.67 Schematic illustration of a computer numerical-controlled turning center. Note that the machine has two spindle heads and three turret heads, making the machine tool very flexible in its capabilities. Source: Courtesy of Hitachi Seiki Co., Ltd. 2nd Spindle head 3rd Turret head

57 Reconfigurable Machines Magazine unit Rotational motion Arm unit Functional unit Linear motion Rotational motion Linear motion Bed unit Base unit Arm unit FIGURE 8.68 Schematic illustration of a reconfigurable modular machining center, capable of accommodating workpieces of different shapes and sizes, and requiring different machining operations on their various surfaces. Source: After Y. Koren.

58 Reconfigurable Machining Center (a) (b) (c) FIGURE 8.69 Schematic illustration of assembly of different components of a reconfigurable machining center. Source: After Y. Koren.

59 Machining of Bearing Races Tube Form tool 1. Finish turning of outside diameter 2. Boring and grooving on outside diameter 3. Internal grooving with a radius-form tool Form tool Bearing race 4. Finish boring of internal groove and rough boring of internal diameter 5. Internal grooving with form tool and chamfering 6. Cutting off finished part; inclined bar picks up bearing race FIGURE 8.70 Sequences involved in machining outer bearing races on a turning center.

60 Hexapod Hexapod legs Spindle Cutting tool Workpiece (a) (b) FIGURE 8.71 (a) A hexapod machine tool, showing its major components. (b) Closeup view of the cutting tool and its head in a hexapod machining center. Source: National Institute of Standards and Technology.

61 Chatter & Vibration FIGURE 8.72 Chatter marks (right of center of photograph) on the surface of a turned part. Source: Courtesy of General Electric Company V Cast iron s (a) 10-1 V Epoxy/graphite s FIGURE 8.73 Relative damping capacity of (a) gray cast iron and (b) epoxy-granite composite material. The vertical scale is the amplitude of vibration and the horizontal scale is time. (b) Increasing damping Bed only Bed + carriage Bed + headstock Bed + carriage + headstock Complete machine FIGURE 8.74 Damping of vibrations as a function of the number of components on a lathe. Joints dissipate energy; thus, the greater the number of joints, the higher the damping. Source: After J. Peters.

62 Total cost Machining Economics Cost per piece Machining cost Tool-change cost Nonproductive cost Tool cost Cutting speed (a) High-efficiency machining range Time per piece Cutting speed (b) Total time Machining time Tool-changing time Nonproductive time FIGURE 8.75 Qualitative plots showing (a) cost per piece, and (b) time per piece in machining. Note that there is an optimum cutting speed for both cost and time, respectively. The range between the two optimum speeds is known as the high-efficiency machining range.

63 Case Study: Ping Golf Putters FIGURE 8.76 (a) The Ping Anser golf putter; (b) CAD model of rough machining of the putter outer surface; (c) rough machining on a vertical machining center; (d) machining of the lettering in a vertical machining center; the operation was paused to take the photo, as normally the cutting zone is flooded with a coolant; Source: Courtesy of Ping Golf, Inc.