ch16 sheet metal forming

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.

Chapter 16Sheet-Metal Forming Processes


Sheet-Metal Parts

(a) (b)

Figure 16.1 Examples of sheet-metal parts. (a) Die-formed and cut stamped parts.(b) Parts produced by spinning. Source: (a) Courtesy of Aphase II, Inc. (b)Courtesy of Hialeah Metal Spinning, Inc.


Characteristics of Sheet-Metal Forming Processes


Shearing with aPunch and Die

Figure 16.2 (a) Schematic illustration ofshearing with a punch and die, indicatingsome of the process variables.Characteristic features of (b) a punchedhole and (c) the slug. (Note: The scalesof the two figures are different.)

!

Punch force, F = 0.7TL UTS( )


Shearing

Figure 16.3 (a) Effect of the clearance, c, between punch and die on the deformation zonein shearing. As the clearance increases, the material tends to be pulled into the die ratherthan be sheared. In practice, clearances usually range between 2 and 10% of the thicknessof the sheet. (b) Microhardness (HV) contours for a 6.4-mm (0.25-in.) thick AISI 1020 hot-rolled steel in the sheared region. Source: After H.P Weaver and K.J. Weinmann.


Die-Cutting Operations

Figure 16.4 (a) Punching (piercing) and blanking.(b) Examples of various die-cutting operations onsheet metal.


Conventional Versus Fine-Blanking

Figure 16.5 (a) Comparison of sheared edges produced by conventional (left) andby fine-blanking (right) techniques. (b) Schematic illustration of one setup for fineblanking. Source: Courtesy of Feintool U.S. Operations.


Slitting with Rotary Knives

Figure 16.6 Slitting with rotary knives. This process is similar to opening cans.


Tailor-Welded Blanks

Figure 16.7 Production of an outer side panel of a car body by laser butt-welding and stamping. Source: After M. Geiger and T. Nakagawa.


Examples of Automotive ComponentsProduced from Tailor-Welded Blanks

Figure 16.8 Examples of laser butt-welded and stamped automotive-body components.Source: After M. Geiger and T. Nakagawa.


The Shaving Process

Figure 16.9 Schematic illustrations of the shaving process. (a) Shaving a shearededge. (b) Shearing and shaving combined in one stroke.


Shear Angles

Figure 16.10 Examples of the use of shear angles on punches and dies.


CompoundDie and

ProgressiveDie

Figure 16.11 Schematic illustrations: (a) before and (b) after blanking a common washer in acompound die. Note the separate movements of the die (for blanking) and the punch (forpunching the hole in the washer). (c) Schematic illustration of making a washer in aprogressive die. (d) Forming of the top piece of an aerosol spray can in a progressive die.Note that the part is attached to the strip until the last operation is completed.


Characteristics of Metals Used in Sheet-Forming


Sheet Metal

Figure 16.12 (a) Yield-point elongation in a sheet-metal specimen. (b) Luder’s bandsin a low-carbon steel sheet. (c) Stretcher strains at the bottom of a steel can forhousehold products. Source: (b) Courtesy of Caterpillar Inc.


Cupping Test and Bulge-Test

Figure 16.13 (a) A cupping test (the Erichsen test) to determine the formability of sheetmetals. (b) Bulge-test results on steel sheets of various widths. The specimen farthestleft is subjected to, basically, simple tension. The specimen farthest right is subjected toequal biaxial stretching. Source: Courtesy of Inland Steel Company.


Forming Limit Diagram

Figure 16.14 (a) Strains indeformed circular gridpatterns. (b) Forming-limitdiagrams (FLD) for varioussheet metals. Although themajor strain is always positive(stretching), the minor strainmay be either positive ornegative. In the lower left ofthe diagram, R is the normalanisotropy of the sheet, asdescribed in Section 16.4.Source: After S .S Hecker andA. K. Ghosh.


Deformation and Tearing in Sheet Metal During Forming

Figure 16.15 The deformation of the grid pattern and the tearing of sheet metal duringforming. The major and minor axes of the circles are used to determine the coordinateson the forming-limit diagram in Fig. 16.14b. Source: After S. P. Keeler.


Bending Terminology

Figure 16.16 Bending terminology. Note that the bendradius is measured to the inner surface of the bent part.


Effect of Elongated Inclusions

Figure 16.17 (a) and (b) The effect of elongated inclusions stringers) oncracking as a function of the direction of bending with respect to the originalrolling direction of the sheet. (c) Cracks on the outer surface of an aluminumstrip bent to an angle of 90 degrees. Note also the narrowing of the top surfacein the bend area (due to Poisson effect).


Minimum Bend Radius

Figure 16.18 Relationship between R/T ratio and tensile reduction of area for sheet metals.Note that sheet metal with 50% tensile reduction of area can be bent over itself in a processlike the folding of a piece of paper without cracking. Source: After J. Datsko and C. T.Yang.


Springback in Bending

Figure 16.19 Springback in bending. The part tends to recover elastically after bending,and its bend radius becomes larger. Under certain conditions, it is possible for the finalbend angle to be smaller than the original angle (negative springback).

!

Ri

Rf

= 4RiY

ET

"

# $

%

& ' 3

( 3RiY

ET

"

# $

%

& ' +1


Methods of Reducing or Eliminating Springback

Figure 16.20 Methods of reducing or eliminating springback in bendingoperations. Source: After V. Cupka, T. Nakagawa, and H. Tyamoto.


Common Die-Bending Operations

Figure 16.21 Common die-bending operationsshowing the die-opening dimension, W, used incalculating bending forces.

Bending Force

!

P =kYLT

2

W

where

k = 0.3 for wiping die,

k = 0.7 for a U - die,

k =1.3 for a V- die


Bending Operations

Figure 16.22 Examples of various bending operations.


Press Brake

Figure 16.23 (a) through (e) Schematic illustrations of various bending operations in apress brake. (f) Schematic illustration of a press brake. Source: Courtesy of VersonAllsteel Company.


Bead Forming

Figure 16.24 (a) Bead forming with a single die. (b) and (c) Beadforming with two dies in a press brake.


Flanging OperationsFigure 16.25 Variousflanging operations. (a)Flanges on a flat sheet.(b) Dimpling. (c) Thepiercing of sheet metal toform a flange. In thisoperation, a hole doesnot have to be pre-punched before thepunch descends. Note,however, the roughedges along thecircumference of theflange. (d) The flangingof a tube. Note thethinning of the edges ofthe flange.


Roll-Forming Process

Figure 16.26 (a) Schematic illustration of the roll-forming process. (b)Examples of roll-formed cross-sections. Source: (b) Courtesy of SharonCustom Metal Forming, Inc.


Methods of Bending Tubes

Figure 16.27 Methods of bending tubes. Internal mandrels or filling of tubes withparticulate materials such as sand are often necessary to prevent collapse of the tubesduring bending. Tubes also can be bent by a technique consisting if a stiff, helical tensionspring slipped over the tube. The clearance between the OD of the tube and the ID of thespring is small, thus the tube cannot kick and the bend is uniform.


Tubular Parts

Figure 16.28 (a) The bulging of a tubular part with a flexible plug. Water pitcherscan be made by this method. (b) Production of fittings for plumbing by expandingtubular blanks under internal pressure. The bottom of the piece is then punchedout to produce a “T.” Source: After J. A. Schey.


Manufacturing of Bellows

Figure 16.29 Steps in manufacturing a bellows.


Stretch-Forming Process

Figure 16.30 Schematic illustration of a stretch-forming process. Aluminum skinsfor aircraft can be made by this method. Source: Courtesy of Cyril Bath Co.


CanManufacture

Figure 16.31 The metal-forming processesinvolved in manufacturinga two-piece aluminumbeverage can.


Deep-Drawing

Figure 16.32 (a) Schematic illustration of the deep-drawing process on a circular sheet-metal blank. The stripper ring facilitates the removal of the formed cup from the punch.(b) Process variables in deep drawing. Except for the punch force, F, all the parametersindicated on the figure are independent variables.

!

Fmax

= "DpT UTS( )Do

Dp

#

$ %

&

' ( ) 0.7

*

+ , ,

-

. / /


Normal and Average Anisotropy

Figure 16.33 Strains on atensile-test specimenremoved form a piece ofsheet metal. These strainsare used in determining thenormal and planaranisotropy of the sheetmetal.

!

Normal anisotropy, R =Width strain

Thickness strain="w

"t

Average anisotropy, Ravg =R0 + 2R45 +R90

4


Relationship between Average Normal Anisotropyand the Limiting Drawing Ratio

Figure 16.34 The relationship betweenaverage normal anisotropy and the limitingdrawing ratio for various sheet metals. Source:After M. Atkinson.

!

LDR =Maximum blank diameter

Punch diameter=Do

Dp


Earing and Planar Anisotropy

Figure 16.35 Earing in a drawn steel cup causedby the planar anisotropy of the sheet metal.

!

Planar anisotropy, "R =R0 # 2R45 +R90

2

Note: If ΔR=0, no ears form.The height of ears increases asΔ R increases.


Drawbeads

Figure 16.36 (a) Schematic illustration of a draw bead. (b) Metal flow during thedrawing of a box-shaped part while using beads to control the movement of the material.(c) Deformation of circular grids in the flange in deep drawing.


Embossing with Two Dies

Figure 16.37 An embossing operation with two dies. Letters, numbers,and designs on sheet-metal parts can be produced by this process.


Aluminum Beverage Cans

Figure 16.38 (a) Aluminum beverage cans. Note the excellent surface finish.(b) Detail of the can lid showing integral rivet and scored edges for the pop-top.

(a)


Bending and Embossing of Sheet Metal

Figure 16.39 Examples of the bending and embossing of sheet metal with a metalpunch and with a flexible pad serving as the female die. Source: Courtesy ofPolyurethane Products Corporation.


Hydroform Process

Figure 16.40 The hydroform (or fluid-forming) process. Note that in contrast to theordinary deep-drawing process, the pressure in the dome forces the cup walls against thepunch. The cup travels with the punch; in this way, deep drawability is improved.


Tube-Hydroforming

Figure 16.41 (a) Schematic illustration ofthe tube-hydrofroming process. (b) Exampleof tube-hydroformed parts. Automotiveexhaust and structural components, bicycleframes, and hydraulic and pneumatic fittingsare produced through tube hydroforming.Source: Courtesy of Schuler GmBH.

(b)


Conventional Spinning

Figure 16.42 (a) Schematic illustration of the conventional spinning process.(b) Types of parts conventionally spun. All parts are axisymmetric.


Shear-Spinning and Tube-Spinning

Figure 16.43 (a) Schematic illustration of the shear-spinning process for makingconical parts. The mandrel can be shaped so that curvilinear parts can be spun. (b)and (c) Schematic illustrations of the tube-spinning process


Structures Made by Diffusion Bonding and SuperplasticForming of Sheet Metals

Figure 16.44 Types of structures made by diffusion bonding and superplastic forming ofsheet metals. Such structures have a high stiffness-to-weight ratio. Source: Courtesy ofRockwell International Corp.


Explosive Forming

Figure 16.45 (a) Schematic illustration of the explosive forming process.(b) Illustration of the confined method of the explosive bulging of tubes.


Magnetic-Pulse Forming Process

Figure 16.46 (a) Schematic illustration of the magnetic-pulse forming process used to forma tube over a plug. (b) Aluminum tube collapsed over a hexagonal plug by the magnetic-pulse forming process.


CymbalManufacture

Figure 16.47 (a) A selection of commoncymbals. (b) Detailed view of differentsurface textures and finishes of cymbals.Source: Courtesy of W. Blanchard, SabianLtd.

(a)

(b)


Cymbal Manufacture(cont.)

Figure 16.48 Manufacturing sequence forthe production of cymbals. Source:Courtesy of W. Blanchard, Sabian Ltd.


Hammering of Cymbals

Figure 16.49 Hammering of cymbals. (a) Automated hammering on a peening machine;(b) hand hammering of cymbals. Source: Courtesy of W. Blanchard, Sabian Ltd.

(a) (b)


Manufacturing Honeycomb Structures

Figure 16.50 Methods of manufacturing honeycomb structures: (a) expansion process;(b) corrugation process; (c) assembling a honeycomb structure into a laminate.


Efficient Part Nesting for Optimum Material Utilization

Figure 16.51 Efficient nesting of parts for optimum material utilization in blanking.Source: Courtesy of Society of Manufacturing Engineers.


Control of Defects in a Flange

Figure 16.52 Control of tearing and buckling of a flange in a right angle bend.Source: Courtesy of Society of Manufacturing Engineers.


Application of Notches

Figure 16.53 Application of notches to avoid tearing and wrinkling in right-anglebending operations. Source: Courtesy of Society of Manufacturing Engineers.


Stress Concentration Near Bends

Figure 16.54 Stress concentration near bends. (a) Use of a crescent or ear for a holenear a bend. (b) Reduction of severity of tab in flange. Source: Courtesy of Society ofManufacturing Engineers.


Obtaining a Sharp Radius in Bending

Figure 16.55 Application of scoring or embossing to obtain a sharp inner radius inbending. Unless properly designed, these features can lead to fracture. Source:Courtesy of Society of Manufacturing Engineers.


Presses

Figure 16.56 (a) through (f)Schematic illustrations oftypes of press frames forsheet-forming operations.Each type has its owncharacteristics of stiffness,capacity, and accessibility. (g)A large stamping press.Source: (a) through (f)Engineer’s Handbook, VEBFachbuchverlag, 1965. (g)Verson Allsteel Company.


Cost of Conventional Spinning Versus Cost of Deep Drawing

Figure 16.57 Cost comparison for manufacturing a round sheet-metal container either byconventional spinning or by deep drawing. Note that for small quantities, spinning is moreeconomical.

ch16 sheet metal forming

Engineering

engineering technology

serope kalpakjian

upper saddle river

pearson education

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