Bulk Deformation Rolling Processes Forging Processes Extrusion Processes Wire and Bar Drawing Sheet Metal Forming Bending Operations Deep or Cup

Transcription

1 Metal Forming

2 Bulk Deformation Rolling Processes Forging Processes Extrusion Processes Wire and Bar Drawing Sheet Metal Forming Bending Operations Deep or Cup Drawing Shearing Processes Miscellaneous Processes

3 [1]Groover, M. P., Fundamentals of Modern Manufacturing, 2th Edition, ISBN= , John Wiley & Sons, Inc., 2002.

4 Bulk Deformation

5 Bulk Deformation Processes Characterized by significant deformations and massive shape changes "Bulk" refers to workparts with relatively low surface area to volume ratios Starting work shapes include cylindrical billets and rectangular bars

6 Bulk Deformation Rolling: 兩 輪 度 來 行 更 Forging( ): 利 兩 (Mold) 行 狀金 Extrusion: 金 利 (Die) Wire and Bar Drawing: 利 拉 金 (Die)

7 Bulk Deformation Rolling Forging Extrusion Drawing

8 Plastic Behavior in Metal Forming Plastic region of stress-strain curve is primary interest because material is plastically deformed In plastic region, metal's behavior is expressed by the flow curve: σ = where K = strength coefficient; and n = strain hardening exponent Stress and strain in flow curve are true stress and true strain K ε n

9 Flow Stress For most metals at room temperature, strength increases when deformed due to strain hardening Flow stress = instantaneous value of stress required to continue deforming the material Yf = Kε n where Y f = flow stress, that is, the yield strength as a function of strain

10 Average Flow Stress Determined by integrating the flow curve equation between zero and the final strain value defining the range of interest _ Y f K = 1 + ε n n _ where Y f = average flow stress; and ε = maximum strain during deformation process

11 Temperature in Metal Forming For any metal, K and n in the flow curve depend on temperature Both strength and strain hardening are reduced at higher temperatures In addition, ductility is increased at higher temperatures Any deformation operation can be accomplished with lower forces and power at elevated temperature Three temperature ranges in metal forming: Cold working Warm working Hot working

12 Cold Working Performed at room temperature or slightly above Many cold forming processes are important mass production operations Minimum or no machining usually required These operations are near net shape or net shape processes

13 Advantages of Cold Forming Better accuracy, closer tolerances Better surface finish Strain hardening increases strength and hardness Grain flow during deformation can cause desirable directional properties in product No heating of work required

14 Disadvantages of Cold Forming Higher forces and power required Surfaces of starting workpiece must be free of scale and dirt Ductility and strain hardening limit the amount of forming that can be done In some operations, metal must be annealed to allow further deformation In other cases, metal is simply not ductile enough to be cold worked

15 Warm Working Performed at temperatures above room temperature but below recrystallization temperature Dividing line between cold working and warm working often expressed in terms of melting point: 0.3T m, where T m = melting point (absolute temperature) for metal

16 Advantages of Warm Working Lower forces and power than in cold working More intricate work geometries possible Need for annealing may be reduced or eliminated

17 Hot Working Deformation at temperatures above recrystallization temperature Recrystallization temperature = about one half of melting point on absolute scale In practice, hot working usually performed somewhat above 0.5T m Metal continues to soften as temperature increases above 0.5T m, enhancing advantage of hot working above this level

18 Advantages of Hot Working Workpart shape can be significantly altered Lower forces and power required Metals that usually fracture in cold working can be hot formed Strength properties of product are generally isotropic No strengthening of part occurs from work hardening Advantageous in cases when part is to be subsequently processed by cold forming

19 Disadvantages of Hot Working Lower dimensional accuracy Higher total energy required (due to the thermal energy to heat the workpiece) Work surface oxidation (scale), poorer surface finish Shorter tool life

20 Strain Rate Sensitivity Theoretically, a metal in hot working behaves like a perfectly plastic material, with strain hardening exponent n = 0 The metal should continue to flow at the same flow stress, once that stress is reached However, an additional phenomenon occurs during deformation, especially at elevated temperatures: Strain rate sensitivity

21 Strain Rate Strain rate in forming is directly related to speed of deformation(speed of Deformation) v Deformation speed v = velocity of the ram or other movement of the equipment Strain rate is defined: ε ε = where = true strain rate; and h = instantaneous height of workpiece being deformed v h

22 Strain Rate Sensitivity Flow stress is a function of temperature At hot working temperatures, flow stress also depends on strain rate As strain rate increases, resistance to deformation increases This effect is known as strain rate sensitivity

23 Strain Rate Sensitivity Log-Log Scale

24 Strain Rate Sensitivity Yf = Cε m where C = strength constant (similar but not equal to strength coefficient in flow curve equation), and m = strain rate sensitivity exponent

25 Strain Rate Sensitivity Effect of temperature on flow stress for a typical metal. The constant C, indicated by the intersection of each plot with the vertical dashed line at strain rate = 1.0, decreases, and m (slope of each plot) increases with increasing temperature

26 Rolling Processes

27 Flat Plate Rolling Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls

28 The Rolls The rotating rolls perform two main functions: Pull the work into the gap between them by friction between workpart and rolls Simultaneously squeeze the work to reduce cross section

29 By geometry of work: Types of Rolling Flat rolling - used to reduce thickness of a rectangular cross section Shape rolling - a square cross section is formed into a shape such as an I beam By temperature of work: Hot Rolling most common due to the large amount of deformation required Cold rolling produces finished sheet and plate stock

30 Steel Products by Rolling Mill

31 Side View of Flat Rolling

32 Flat Rolling Draft = amount of thickness reduction d = t t o f where d = draft; t o = starting thickness; and t f = final thickness Reduction = draft expressed as a fraction of starting stock thickness: r where r = reduction = d t o

33 Shape Rolling Work is deformed into a contoured cross section rather than flat (rectangular) Accomplished by passing work through rolls that have the reverse of desired shape Products include: Construction shapes such as I beams, L beams, and U channels Rails for railroad tracks Round and square bars and rods

34 Rolling Mill

35 Rolling Mills Equipment is massive and expensive Rolling mill configurations: Two-high two opposing large diameter rolls Three-high work passes through both directions Four-high backing rolls support smaller work rolls Cluster mill multiple backing rolls on smaller rolls Tandem rolling mill sequence of two-high mills

36 Rolling Mills 2 high 3 high 4 high Cluster mill Tandem rolling mill

37 Thread Rolling Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies Most important commercial process for mass producing bolts and screws Performed by cold working in thread rolling machines Advantages over thread cutting (machining): Higher production rates Better material utilization Stronger threads due to work hardening Better fatigue resistance due to compressive stresses introduced by rolling

38 Thread Rolling with Flat Dies Start of Cycle End of Cycle

39 Ring Rolling Deformation process in which a thick walled ring of smaller diameter is rolled into a thin walled ring of larger diameter As thick walled ring is compressed, deformed metal elongates, causing diameter of ring to be enlarged Hot working process for large rings and cold working process for smaller rings Applications: ball and roller bearing races, steel tires for railroad wheels, and rings for pipes, pressure vessels, and rotating machinery Advantages: material savings, ideal grain orientation, strengthening through cold working

40 Ring Rolling Ring rolling used to reduce the wall thickness and increase the diameter of a ring. Start Completion

41 Forging Processes

42 Forging Deformation process in which work is compressed between two dies Oldest of the metal forming operations, dating from about 5000 B C Components: engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts In addition, basic metals industries use forging to establish basic form of large components that are subsequently machined to final shape and size

43 Cold vs. hot forging: Forging Operations Hot or warm forging most common, due to the significant deformation and the need to reduce strength and increase ductility of work metal Cold forging - advantage is increased strength that results from strain hardening Impact vs. press forging: Forge hammer - applies an impact load Forge press - applies gradual pressure

44 Types of Forging Dies Open die forging - work is compressed between two flat dies, allowing metal to flow laterally without constraint Impression die forging - die surfaces contain a cavity or impression that is imparted to workpart, thus constraining metal flow - flash is created Flashless forging - workpart is completely constrained in die and no excess flash is produced

45 Types of Forging Dies Open Die Forging Impression Die Forging Flashless Forging

46 Open Die Forging Compression of workpart with cylindrical cross section between two flat dies Similar to compression test Deformation operation reduces height and increases diameter of work Common names include upsetting or upset forging

47 Open Die Forging Without Friction If no friction occurs between work and die surfaces, then homogeneous deformation occurs, so that radial flow is uniform throughout workpart height and true strain is given by: h ε = ln o h where h o = starting height; and h = height at some point during compression At h = final value h f, true strain is maximum value

48 Open Die Forging Without Friction ε = ln h h0 F = Y A f

49 Open Die Forging With Friction Friction between work and die surfaces constrains lateral flow of work, resulting in barreling effect In hot open-die forging, effect is even more pronounced due to heat transfer at and near die surfaces, which cools the metal and increases its resistance to deformation

50 Open Die Forging With Friction F = KYA f f K f = µ D h

51

52 Open Die Forging

53 Impression Die Forging Compression of workpart by dies with inverse of desired part shape Flash is formed by metal that flows beyond die cavity into small gap between die plates Flash must be later trimmed from part, but it serves an important function during compression: As flash forms, friction resists continued metal flow into gap, constraining material to fill die cavity In hot forging, metal flow is further restricted by cooling against die plates

54 Impression Die Forging

55 Flashless Forging Compression of work in punch and die tooling whose cavity does allow for flash Starting workpart volume must equal die cavity volume within very close tolerance Process control more demanding than impression die forging Best suited to part geometries that are simple and symmetrical Often classified as a precision forging process

56 Flashless Forging

57 Forging Hammers (Drop Hammers) Apply an impact load against workpart - two types: Gravity drop hammers - impact energy from falling weight of a heavy ram Power drop hammers - accelerate the ram by pressurized air or steam Disadvantage: impact energy transmitted through anvil into floor of building Most commonly used for impression-die forging

58 Drop Hammer

59 Drop Hammer

60 Forging Presses Apply gradual pressure to accomplish compression operation - types: Mechanical presses - converts rotation of drive motor into linear motion of ram Hydraulic presses - hydraulic piston actuates ram Screw presses - screw mechanism drives ram

61 Upsetting and Heading Forging process used to form heads on nails, bolts, and similar hardware products More parts produced by upsetting than any other forging operation Performed cold, warm, or hot on machines called headers or formers Wire or bar stock is fed into machine, end is headed, then piece is cut to length For bolts and screws, thread rolling is then used to form threads

62 Upset Forging Operation for Heading

63 Swaging Accomplished by rotating dies that hammer a workpiece radially inward to taper it as the piece is fed into the dies Used to reduce diameter of tube or solid rod stock Mandrel sometimes required to control shape and size of internal diameter of tubular parts

64 Swaging Swaging process to reduce solid rod stock; the dies rotate as they hammer the work In radial forging, the workpiece rotates while the dies remain in a fixed orientation as they hammer the work

65 Trimming Cutting operation to remove flash from workpart in impression die forging Usually done while work is still hot, so a separate trimming press is included at the forging station Trimming can also be done by alternative methods, such as grinding or sawing

66 Trimming Trimming operation (shearing process) to remove the flash after impression die forging

67 Extrusion Processes

68 Extrusion Compression forming process in which the work metal is forced to flow through a die opening to produce a desired cross sectional shape Process is similar to squeezing toothpaste out of a toothpaste tube In general, extrusion is used to produce long parts of uniform cross-sections Two basic types of extrusion: Direct extrusion - 料 Die Indirect extrusion - Die 料 Die

69 Direct Extrusion As ram approaches die opening, a small portion of billet remains that cannot be forced through die opening This extra portion, called the butt, must be separated from extruded product by cutting it just beyond the die exit Starting billet cross section usually round, but final shape is determined by die opening

70 Direct Extrusion Hollow Semi Hollow

71 Indirect Extrusion Solid Hollow

72 Hot vs. Cold Extrusion Hot extrusion - prior heating of billet to above its recrystallization temperature This reduces strength and increases ductility of the metal, permitting more size reductions and more complex shapes Cold extrusion - generally used to produce discrete parts The term impact extrusion is used to indicate high speed cold extrusion

73 Extrusion Ratio Also called the reduction ratio, it is defined as r x = A A where r x = extrusion ratio; A o = cross-sectional area of the starting billet; and A f = final crosssectional area of the extruded section Applies to both direct and indirect extrusion o f

74 Die Angle and Ram Force

75 Die Angle Low die angle - surface area is large, leading to increased friction at die billet interface Higher friction results in larger ram force Large die angle - more turbulence in metal flow during reduction Turbulence increases ram force required Optimum angle depends on work material, billet temperature, and lubrication

76 A Complex Extruded Cross Section

77 Extrusion Presses Either horizontal or vertical Horizontal more common Extrusion presses - usually hydraulically driven, which is especially suited to semi continuous direct extrusion of long sections Mechanical drives - often used for cold extrusion of individual parts

78 Wire and Bar Drawing

79 Wire and Bar Drawing Cross section of a bar, rod, or wire is reduced by pulling it through a die opening Similar to extrusion except work is pulled through die in drawing (it is pushed through in extrusion) Although drawing applies tensile stress, compression also plays a significant role since metal is squeezed as it passes through die opening

80 Drawing of Bar, Rod, or Wire

81 Area Reduction in Drawing Change in size of work is usually given by area reduction: r = A o A f A o where r = area reduction in drawing; A o = original area of work; and A r = final work

82 Wire Drawing vs. Bar Drawing Difference between bar drawing and wire drawing is stock size Bar drawing - large diameter bar and rod stock Wire drawing - small diameter stock - wire sizes down to 0.03 mm (0.001 in.) are possible Although the mechanics are the same, the methods, equipment, and even terminology are different

83 Drawing Practice and Products Drawing practice: Usually performed as cold working Most frequently used for round cross sections Products: Wire: electrical wire; wire stock for fences, coat hangers, and shopping carts Rod stock for nails, screws, rivets, and springs Bar stock: metal bars for machining, forging, and other processes

84 Bar Drawing Accomplished as a single draft operation the stock is pulled through one die opening Beginning stock has large diameter and is a straight cylinder This necessitates a batch type operation

85 Hydraulically Operated Draw Bench

86 Wire Drawing Continuous drawing machines consisting of multiple draw dies (typically 4 to 12) separated by accumulating drums Each drum (capstan) provides proper force to draw wire stock through upstream die Each die provides a small reduction, so desired total reduction is achieved by the series Annealing sometimes required between dies

87 Continuous Drawing of Wire

88 A Draw Die Entry region - funnels lubricant into the die to prevent scoring of work and die Approach - cone shaped region where drawing occurs Bearing surface - determines final stock size Back relief - exit zone - provided with a back relief angle (half angle) of about 30 Die materials: tool steels or cemented carbides

89 Draw Die for Drawing of Round Rod or Wire

90 Sheet Metal Forming

91 Sheet Metalworking Forming and related operations performed on metal sheets, strips, and coils High surface area to volume ratio of starting metal, which distinguishes these from bulk deformation Often called pressworking because presses perform these operations Parts are called stampings Usual tooling: punch and die

92 Sheet Metalworking Bending Drawing Shearing

93 SHEET METALWORKING Cutting Operations Bending Operations Drawing Other Sheet Metal Forming Operations Dies and Presses for Sheet Metal Processes Sheet Metal Operations Not Performed on Presses Bending of Tube Stock

94 Sheet Metalworking Defined Cutting and forming operations performed on relatively thin sheets of metal Thickness of sheet metal = 0.4 mm (1/64 in) to 6 mm (1/4 in) Thickness of plate stock > 6 mm Operations usually performed as cold working

95 Sheet and Plate Metal Products Sheet and plate metal parts for consumer and industrial products such as Automobiles and trucks Airplanes Railway cars and locomotives Farm and construction equipment Small and large appliances Office furniture Computers and office equipment

96 Advantages of Sheet Metal High strength Parts Good dimensional accuracy Good surface finish Relatively low cost For large quantities, economical mass production operations are available

97 Sheet Metalworking 1. Punch and die Terminology Tooling to perform cutting, bending, and drawing 2. Stamping press Machine tool that performs most sheet metal operations 3. Stampings Sheet metal products

98 Three Major Categories of 1. Cutting Sheet Metal Processes Shearing to separate large sheets; or cut part perimeters or make holes in sheets 2. Bending Straining sheet around a straight axis 3. Drawing Forming of sheet into convex or concave shapes

99 Cutting Shearing between two sharp cutting edges Figure 20.1 Shearing of sheet metal between two cutting edges: (1) just before the punch contacts

100 Figure 20.1 Shearing of sheet metal between two cutting edges: (2) punch begins to push into work, causing plastic

101 Figure 20.1 Shearing of sheet metal between two cutting edges: (3) punch compresses and

102 Figure 20.1 Shearing of sheet metal between two cutting edges: (4) fracture is initiated at the opposing cutting edges which

103 Shearing, Blanking, and Punching Three principal operations in pressworking that cut sheet metal: Shearing Blanking Punching

104 Shearing Sheet metal cutting operation along a straight line between two cutting edges Typically used to cut large sheets into smaller sections for subsequent operations

105 Figure 20.3 Shearing operation: (a) side view of the shearing operation (b) front view of power shears equipped with inclined upper cutting blade Symbol v indicates motion

106 Blanking and Punching Blanking - sheet metal cutting to separate piece from surrounding stock Cut piece is the desired part, called a blank Punching - sheet metal cutting similar to blanking except cut piece is scrap, called a slug Remaining stock is the desired part

107 Figure 20.4 (a) Blanking and (b) punching

108 Clearance in Sheet Metal Cutting Distance between the punch and die Typical values range between 4% and 8% of stock thickness If too small, fracture lines pass each other, causing double burnishing and larger force If too large, metal is pinched between cutting edges and excessive burr results

109 Clearance in Sheet Metal Cutting Recommended clearance can be calculated by: c = at where c = clearance; a = allowance; and t = stock thickness Allowance a is determined according to type of metal

110 Allowance a for Three Sheet Metal Groups Metal group 1100S and 5052S aluminum alloys, all tempers 2024ST and 6061ST aluminum alloys; brass, soft cold rolled steel, soft Cold stainless rolled steel, half hard; stainless steel, half hard and full hard a

111 Punch and Die Sizes for Blanking and Punching For a round blank of diameter D b : Blanking punch diameter = D b 2c Blanking die diameter = D b where c = clearance For a round hole of diameter D h : Hole punch diameter = D h Hole die diameter = D h + 2c where c = clearance

112 Figure 20.6 Die size determines blank size D b ; punch size determines hole size D h.; c = clearance

113 Angular Clearance Purpose: allows slug or blank to drop through die Typical values: 0.25 to 1.5 on each side Figure 20.7 Angular clearance

114 Cutting Forces Important for determining press size (tonnage) F = S t L where S = shear strength of metal; t = stock thickness, and L = length of cut edge

115 Bending Straining sheetmetal around a straight axis to take a permanent bend Figure (a) Bending of sheet metal

116 Metal on inside of neutral plane is compressed, while metal on outside of neutral plane is stretched Figure (b) both compression and tensile elongation of the metal occur in bending

117 Types of Sheetmetal Bending V bending - performed with a V shaped die Edge bending - performed with a wiping die

118 V-Bending For low production Performed on a press brake V-dies are simple and inexpensive Figure (a) V bending

119 Edge Bending For high production Pressure pad required Dies are more complicated and costly Figure (b) edge bending

120 Stretching during Bending If bend radius is small relative to stock thickness, metal tends to stretch during bending Important to estimate amount of stretching, so that final part length = specified dimension Problem: to determine the length of neutral axis of the part before bending

121 Bend Allowance Formula BA = A 2π ( R + Kbat) 360 where BA = bend allowance; A = bend angle; R= bend radius; t = stock thickness; and K ba is factor to estimate stretching If R < 2t, K ba = 0.33 If R 2t, K ba = 0.50

122 Springback in Bending Springback = increase in included angle of bent part relative to included angle of forming tool after tool is removed Reason for springback: When bending pressure is removed, elastic energy remains in bent part, causing it to recover partially toward its original shape

123 Figure Springback in bending shows itself as a decrease in bend angle and an increase in bend radius: (1) during bending, the work is forced to take the radius R b and included angle A b ' of the bending tool (punch in V bending), (2) after punch is removed, the work springs back

124 Bending Force Maximum bending force estimated as follows: F = K bf TSwt D 2 where F = bending force; TS = tensile strength of sheet metal; w = part width in direction of bend axis; and t = stock thickness. For V- bending, K bf = 1.33; for edge bending, K bf = 0.33

125 Figure Die opening dimension D: (a) V die, (b) wiping die

126 Drawing Sheet metal forming to make cup shaped, box shaped, or other complex curved, hollow shaped parts Sheet metal blank is positioned over die cavity and then punch pushes metal into opening Products: beverage cans, ammunition shells, automobile body panels

127 Figure (a)drawing of a cup shaped part: (1)start of operation before punch contacts work (2)near end of stroke

128 Clearance in Drawing Sides of punch and die separated by a clearance c given by: c = 1.1 t where t = stock thickness In other words, clearance = about 10% greater than stock thickness

129 Drawing Ratio DR Most easily defined for cylindrical shape: DR = D D b p where D b = blank diameter; and D p = punch diameter Indicates severity of a given drawing operation Upper limit = 2.0

130 Reduction r Again, defined for cylindrical shape: r = D b D D b p Value of r should be less than 0.50

131 Thickness to Diameter Ratio Thickness of starting blank divided by blank diameter Thickness-to-diameter ratio = t/d b Desirable for t/d b ratio to be greater than 1% As t/d b decreases, tendency for wrinkling increases

132 Blank Size Determination For final dimensions of drawn shape to be correct, starting blank diameter D b must be right Solve for D b by setting starting sheet metal blank volume = final product volume To facilitate calculation, assume negligible thinning of part wall

133 Shapes other than Cylindrical Cups Square or rectangular boxes (as in sinks), Stepped cups, Cones, Cups with spherical rather than flat bases, Irregular curved forms (as in automobile body panels) Each of these shapes presents its own unique technical problems in drawing

134 Other Sheet Metal Forming on Presses Other sheet metal forming operations performed on conventional presses Operations performed with metal tooling Operations performed with flexible rubber tooling

135 Ironing Makes wall thickness of cylindrical cup more uniform Examples: beverage cans and artillery shells Figure Ironing to achieve a more uniform wall thickness in a drawn cup: (1) start of process; (2) during process Note thinning and elongation of walls

136 Embossing Used to create indentations in sheet, such as raised (or indented) lettering or strengthening ribs Figure Embossing: (a) cross section of punch and die configuration during pressing; (b) finished part with embossed ribs

137 Guerin Process Figure Guerin process: (1) before and (2) after Symbols v and F indicate motion and applied force

138 Advantages of Guerin Process Low tooling cost Form block can be made of wood, plastic, or other materials that are easy to shape Rubber pad can be used with different form blocks Process attractive in small quantity production

139 Dies for Sheet Metal Processes Most pressworking operations performed with conventional punch and die tooling Custom designed for particular part The term stamping die sometimes used for high production dies

140 Figure Components of a punch and die for a blanking operation

141 Figure (a)progressiv e die; (b)associated strip developme nt

142 Figure Components of a typical mechanical drive stamping press

143 Types of Stamping Press Frame Gap frame configuration of the letter C and often referred to as a C frame Straight sided frame box-like construction for higher tonnage

144 Figure Gap frame press for sheet metalworking (photo courtesy of E. W. Bliss

145 Figure Press brake with bed width of 9.15 m (30 ft) and capacity of 11,200 kn (1250 tons); two workers are positioning

146 Figure Several sheet metal parts produced on a turret press, showing variety of hole shapes possible (photo courtesy of Strippet, Inc.)

147 Figure Computer numerical control turret press (photo courtesy of Strippet, Inc.)

148 Figure Straight sided frame press (photo courtesy Greenerd Press & Machine

149 Power and Drive Systems Hydraulic presses - use a large piston and cylinder to drive the ram Longer ram stroke than mechanical types Suited to deep drawing Slower than mechanical drives Mechanical presses convert rotation of motor to linear motion of ram High forces at bottom of stroke Suited to blanking and punching

150 Sheet Metal Operations Not Performed on Presses Stretch forming Roll bending and forming Spinning High energy rate forming processes.

151 Stretch Forming Sheet metal is stretched and simultaneously bent to achieve shape change Figure Stretch forming: (1) start of process; (2) form die is pressed into the work with force F die, causing it to be stretched and bent over the form. F = stretching force

152 Force Required in Stretch Forming F = LtY f where F = stretching force; L = length of sheet in direction perpendicular to stretching; t = instantaneous stock thickness; and Y f = flow stress of work metal Die force F die can be determined by balancing vertical force components

153 Roll Bending Large metal sheets and plates are formed into curved sections using rolls Figure Roll bending

154 Roll Forming Continuous bending process in which opposing rolls produce long sections of formed shapes from coil or strip stock Figure Roll forming of a continuous channel section: (1) straight rolls (2) partial form (3) final form

155 Spinning Metal forming process in which an axially symmetric part is gradually shaped over a rotating mandrel using a rounded tool or roller Three types: 1. Conventional spinning 2. Shear spinning 3. Tube spinning

156 Figure Conventional spinning: (1) setup at start of process; (2) during spinning; and (3) completion of process

157 High Energy Rate Forming (HERF) Processes to form metals using large amounts of energy over a very short time HERF processes include: Explosive forming Electrohydraulic forming Electromagnetic forming

158 Explosive Forming Use of explosive charge to form sheet (or plate) metal into a die cavity Explosive charge causes a shock wave whose energy is transmitted to force part into cavity Applications: large parts, typical of aerospace industry

159 Figure Explosive forming: (1) setup, (2) explosive is detonated, and (3) shock wave forms part and plume escapes water surface

160 Electromagnetic Forming Sheet metal is deformed by mechanical force of an electromagnetic field induced in workpart by an energized coil Presently the most widely used HERF process Applications: tubular parts

161 Figure Electromagnetic forming: (1) setup in which coil is inserted into tubular workpart surrounded by die; (2) formed part

162 論

163 論 金 狀 金 狀 狀 輪 拉 金 狀 切 度 冷 金