Top Sheet Metal Forming Processes & Equipment

FIGURE 1 Examples of sheet-metal parts.

(a) Stamped parts.
(b) Parts produced by spinning.

TABLE 1 General Characteristics of Sheet-metal Forming Processes (in alphabetic order)

FIGURE 2

(a) Schematic illustration of shearing with a punch and die, indicating some of the process variables.
Characteristic features of
(b) a punched hole and
(c) the slug.
(Note that the scales of (b) and (c) are different.)

FIGURE 3

(a) Effect of the clearance, c, between punch and die on the deformation zone in shearing. As the clearance increases, the material tends to be pulled into the die rather than be sheared. In practice, clearances usually range between 2 and 10% of the thickness of the sheet.
(b) Microhardness (HV) contours for a 6.4-mm (0.25-in.) thick AISI 1020 hot-rolled steel in the sheared region.

FIGURE 4

(a) Punching (piercing) and blanking.

(b) Examples of various die-cutting operations on sheet metal.

Lancing involves slitting the sheet to form a tab.

FIGURE 5

(a) Comparison of sheared edges produced by conventional (left) and by fine blanking (right) techniques.

(b) Schematic illustration of one setup for fine blanking.

FIGURE 6 Slitting with rotary knives.

This process is similar to opening cans.

FIGURE 7 An example of Taylor-welded blanks

Production of an outer side panel of a car body by laser butt welding and stamping.

FIGURE 8 Examples of laser butt-welded and stamped automotive-body components.

FIGURE 9 

Schematic illustrations of the shaving process.

(a) Shaving a sheared edge.

(b) Shearing and shaving combined in one stroke.

FIGURE 10 Examples of the use of shear angles on punches and dies.

FIGURE 11  Schematic illustrations

(a) before and (b) after blanking a common washer in a compound die.

Note the separate movements of the die (for blanking) and the punch (for punching the hole in the washer).

(c) Schematic illustration of making a washer in a progressive 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.

TABLE 2  Important Metal Characteristics for Sheet-forming Operations

FIGURE 12

(a) Yield-point elongation in a sheet-metal specimen.

(b) Lüder’s bands in a low-carbon steel sheet.

(c) Stretcher strains at the bottom of a steel can for household products.

FIGURE 13 

(a) A cupping test (the Erichsen test) to determine the formability of sheet metals.

(b) Bulge-test results on steel sheets of various widths. The specimen farthest left is subjected to, basically, simple tension. The specimen that is farthest right is subjected to equal biaxial stretching.

FIGURE 14 

(a) Strains in deformed circular grid patterns.

(b) Forming-limit diagrams (FLD) for various sheet metals. Although the major strain is always positive (stretching), the minor strain may be either positive or negative. R is the normal anisotropy of the sheet, as described in Section 4.

FIGURE 15 

The deformation of the grid pattern and the tearing of sheet metal during forming. The major and minor axes of the circles are used to determine the coordinates on the forming-limit diagram in Fig. 14b.

FIGURE 16 

Bending terminology. Note that the bend radius is measured to the inner surface of the bent part.

FIGURE 17 

(a) and (b) The effect of elongated inclusions (stringers) on cracking as a function of the direction of bending with respect to the original rolling direction of the sheet.

(c) Cracks on the outer surface of an aluminum strip bent to an angle of 90°. Note also the narrowing of the top surface in the bend area (due to the Poisson effect).

TABLE 3  Minimum Bend Radius for Various Metals at Room Temperature

FIGURE 18 

Relationship between R/T and tensile reduction of area for sheet metals. Note that sheet metal with a 50% tensile reduction of area can be bent over itself in a process like the folding of a piece of paper without cracking.

FIGURE 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 final bend angle to be smaller than the original angle (negative springback).

FIGURE 20  Methods of reducing or eliminating springback in bending operations.

FIGURE 21 

Common die-bending operations showing the die- opening dimension, W, used in calculating bending forces.

FIGURE 22  Examples of various bending operations.

FIGURE 23  (a) through (e) Schematic illustrations of various bending operations in a press brake. (f) Schematic illustration of a press brake.

FIGURE 24   (a) Bead forming with a single die. (b) through (d) Bead forming with two dies in a press brake.

FIGURE 25  Various flanging operations.

(a) Flanges on flat sheet.

(b) Dimpling.

(c) The piercing of sheet metal to form a flange. In this operation, a hole does not have to be pre-punched before the punch descends. Note, however, the rough edges along the circumference of the flange.

(d) The flanging of a tube.

Note the thinning of the edges of the flange.

FIGURE 26 

(a) Schematic illustration of the roll-forming process.

(b) Examples of roll-formed cross sections.

FIGURE 27  Methods of bending tubes.

Internal mandrels or filling of tubes with particulate materials such as sand are often necessary to prevent collapse of the tubes during bending.

Tubes also can be bent by a technique in which a stiff, helical tension spring is slipped over the tube. The clearance between the outer diameter of the tube and the inner diameter of the spring is small; thus, the tube cannot kink and the bend is uniform.

FIGURE 28 

(a) The bulging of a tubular part with a flexible plug. Water pitchers can be made by this method.

(b) Production of fittings for plumbing by expanding tubular blanks under internal pressure. The bottom of the piece is then punched out to produce a “T.”

FIGURE 29  Schematic illustration of a stretch-forming process. Aluminum skins for aircraft can be made by this method.

FIGURE 30  The metal-forming processes involved in manufacturing a two-piece aluminum beverage can.

FIGURE 31 

(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 parameters indicated in the figure are independent variables.

FIGURE 32 

Strains on a tensile-test specimen removed from a piece of sheet metal. These strains are used in determining the normal and planar anisotropy of the sheet metal.

TABLE 4  Typical Ranges of Average Normal Anisotropy, Ravg for Various Sheet Metals

FIGURE 33 

The relationship between average normal anisotropy and the limiting drawing ratio for various sheet metals.

FIGURE 34 

Earing in a drawn steel cup, caused by the planar anisotropy of the sheet metal.

FIGURE 35 

(a) Schematic illustration of a draw bead.

(b) Metal flow during the drawing 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.

FIGURE 36 

An embossing operation with two dies. Letters, numbers, and designs on sheetmetal parts can be produced by this process.

FIGURE 37 

(a) Aluminum beverage cans. Note the excellent surface finish.

(b) Detail of the can lid, showing the integral rivet and scored edges for the pop-top.

FIGURE 38 

Examples of the bending and embossing of sheet metal with a metal punch and with a flexible pad serving as the female die.

FIGURE 39 

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

FIGURE 40 

(a) Schematic illustration of the tube-hydroforming process.

(b) Example of tube-hydroformed parts. Automotive-exhaust and structural components, bicycle frames, and hydraulic and pneumatic fittings are produced through tube hydroforming.

FIGURE 41  

Hydroformed automotive radiator closure.

FIGURE 42 

Sequence of operations in producing a tubehydroformed component:

(1) tube as cut to length;

(2) after bending;

(3) after hydroforming.

FIGURE 43 

Schematic illustration of expansion of a tube to a desired cross section through (a) conventional hydroforming and (b) pressure sequence hydroforming.

FIGURE 44  

View of the tube-hydroforming press, with bent tube in place in the forming die.

FIGURE 45 

(a) Schematic illustration of the conventional spinning process.

(b) Types of parts conventionally spun. All parts are axisymmetric.

FIGURE 46 

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

FIGURE 47 

(a) Illustration of an incremental-forming operation. Note that no mandrel is used and that the final part shape depends on the path of the rotating tool.

(b) An automotive headlight reflector produced through CNC incremental forming. Note that the part does not have to be axisymmetric.

FIGURE 48 

Types of structures made by superplastic forming and diffusion bonding of sheet metals. Such structures have a high stiffness-to-weight ratio.

FIGURE 49 

(a) Schematic illustration of the explosive-forming process.

(b) Illustration of the confined method of the explosive bulging of tubes.

FIGURE 50 

(a) Schematic illustration of the magnetic-pulse- forming process used to form a tube over a plug.

(b) Aluminum tube collapsed over a hexagonal plug by the magnetic pulse- forming process.

FIGURE 51 

(a) A selection of common cymbals.

(b) Detailed view of different surface textures and finishes of cymbals.

FIGURE 52 

Manufacturing sequence for the production of cymbals.

FIGURE 53 

Hammering of cymbals.

(a) Automated hammering on a peening machine;

(b) hand hammering of cymbals.

FIGURE 54 

Methods of manufacturing honeycomb structures:

(a) expansion process;

(b) corrugation process;

(c) assembling a honeycomb structure into a laminate.

FIGURE 55 

Efficient nesting of parts for optimum material utilization in blanking.

FIGURE 56 

Control of tearing and buckling of a flange in a right angle bend.

FIGURE 57 

Application of notches to avoid tearing and wrinkling in right-angle bending operations.

FIGURE 58 

Stress concentrations near bends.

(a) Use of a crescent or ear for a hole near a bend.

(b) Reduction of severity of tab in flange.

FIGURE 59 

Application of (a) scoring or (b) embossing to obtain a sharp inner radius in bending. Unless properly designed, these features can lead to fracture.

FIGURE 60 

(a) through (f) Schematic illustrations of types of press frames for sheet forming operations. Each type has its own characteristics of stiffness, capacity, and accessibility.

(g) A large stamping press.

FIGURE 61 

Cost comparison for manufacturing a round sheet- metal container either by conventional spinning or by deep drawing.

Note that for small quantities, spinning is more economical.

P.S: we just prepared you the PDF version of the sheet metal forming process, you can download it here.