Altan T. Metal Forming Handbook

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Deep drawingis a method of forming under compressive and tensile

conditions whereby a sheet metal blank is transformed into a hollow

cup, or a hollow cup is transformed into a similar part of smaller dimen-

sions without any intention of altering the sheet thickness (cf.Sect. 4.2.1).

Using the single-draw deep drawing techniqueit is possible to produce

a drawn part from a blank with a single working stroke of the press

(Fig. 2.1.10).

In case of large deformations, the forming process is performed by

means of redrawing,generally using a number of drawing operations.

This can be performed in the same direction by means of a telescopic

punch (Fig. 2.1.11)or by means of reverse drawing,which involves the

second punch acting in opposite direction to the punch motion of the

previous deep-drawing operation (Fig. 2.1.12).

Methods of forming and cutting technology

punch

workpiece

sinkingdie

Fig. 2.1.9 Can ironing

punch

blankholder

blank

drawnpart

die

Fig. 2.1.10 Single-draw deep drawing with blank holder

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

The most significant variation of deep drawing is done with a rigid

tool (Fig.2.1.10). This comprises a punch, a bottom die and a blank

holder, which is intended to prevent the formation of wrinkles as the

metal is drawn into the die. In special cases, the punch or die can also

be from a soft material.

There are deep drawing methods which make use of active media

and active energy. Deep drawing using active media is the drawing of a

blank or hollow body into a rigid die through the action of a medium.

Active media include formless solid substances such as sand or steel

balls, fluids (oil, water) and gases, whereby the forming work is per-

formed by a press using a method similar to that employed with the

rigid tools. The greatest field of application of this technique is hydro-

mechanical drawing,for example for the manufacture of components

from stainless steel (Fig.2.1.13,cf. Sects. 4.2.4 and 4.2.5).

Basic principles of metal forming

punchfor2draw

punchfor1draw

asblankholder

forredraw

initialhollow

body

2drawnpart

die

Fig. 2.1.11 Multiple-draw deep drawing with telescopic punch

die for 1draw

blank holder for 1draw

punch for1draw as

die for reverse draw

blank holder for reverse draw

punch for reverse draw

Fig. 2.1.12 Reverse drawing

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Flanging is a method of forming under combined compressive and

tensile conditions using a punch and die to raise closed rims (flanges or

collars) on pierced holes (Fig. 2.1.14). The holes can be on flat or on

curved surfaces. Flanges are often provided with female threads for the

purpose of assembly.

Spinning is a combined compressive and tensile forming method used

to transform a sheet metal blank into a hollow body or to change the

periphery of a hollow body. One tool component (spinning mandrel,

spinning bush) contains the shape of the workpiece and turns with

the workpiece, while the mating tool (roll head) engages only locally

(Fig. 2.1.15). In contrast to shear forming, the intention of this process

is not to alter the sheet metal thickness.

Wrinkle bulgingor upset bulging is a method of combined tensile and

compressive forming for the local expansion or reduction of a general-

ly tubular shaped part. The pressure forces exerted in the longitudinal

direction result in bulging of the workpiece towards outside, inside or

in lateral direction (Fig. 2.1.16).

Methods of forming and cutting technology

punch

blankholder

seal

pressuremedium

container

pressure medium

workpiece

Fig. 2.1.13 Hydromechanical deep drawing

punch

blankholder

workpiece

die

Fig. 2.1.14 Flanging with blank holder on a flat sheet

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Forming under tensile conditions

Extending by stretching is a method of tensile forming by means of a ten-

sile force applied along the longitudinal axis of the workpiece. Stretch

forming is used to increase the workpiece dimension in the direction of

force application, for example to adjust to a prescribed length. Tensile

test is also a pure stretching process. Straightening by stretching is the

process of extending for straightening rods and pipes, as well as elimi-

nating dents in sheet metal parts.

Basic principles of metal forming

spinning mandrel

spinning roller

circular blank

workpiece

Fig. 2.1.15 Spinning a hollow body

pressure ring

workpiece

punch

container

ejector

Fig. 2.1.16 Wrinkle bulging to the outside

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Expanding is tensile forming to enlarge the periphery of a hollow

body. As in case of deep drawing, rigid (Fig. 2.1.17)as well as soft tools,

active media and active energies are also used.

Stretch formingis a method of tensile forming used to impart impres-

sions or cavities in a flat or convex sheet metal part, whereby surface

enlargement – in contrast to deep drawing – is achieved by reducing the

thickness of the metal.

The most important application for stretch forming makes use of a

rigid die. This type of process includes also stretch drawingand emboss-

ing.Stretch drawing is the creation of an impression in a blank using

a rigid punch while the workpiece is clamped firmly around the rim

(Fig. 2.1.18). Embossing is the process of creating an impression using a

punch in a mating tool, whereby the impression or cavity is small in

comparison to the overall dimension of the workpiece (Fig. 2.1.19).

Methods of forming and cutting technology

mandrel

workpiece

collet

punch

workpiece

s<s

Fig. 2.1.18 Stretch forming

Fig. 2.1.17 Expanding by stretching

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Forming by bending

In bending with a linear die movementthe die components move in a

straight line (cf. Sect. 4.8.1). The most important process in this sub-

category is die bending,in which the shape of the part is impacted by the

die geometry and the elastic recovery (Fig. 2.1.20). Die bending can be

combined with die coining in a single stroke. Die coining is the restrik-

ing of bent workpieces to relieve stresses, for example in order to reduce

the magnitude of springback.

Bending with rotary die movementincludes roll bending, swivel bend-

ing and circular bending. During roll bending, the bending moment is

applied by means of rolling. Using the roll bending process, it is possi-

ble to manufacture cylindrical or tapered workpieces (Fig. 2.1.21). The

roll bending process also includes roll straightening to eliminate unde-

sirable deformations in sheet metal, wire, rods or pipes (Fig. 2.1.22and

cf. Sect. 4.8.3) as well as corrugating and roll forming (Fig. 2.1.23and

cf. Sect. 4.8.2).

Basic principles of metal forming

punch

die

workpiece

Fig. 2.1.19 Embossing

punch

workpiece

bendingdie

Udie Vdie

Fig. 2.1.20 Die bending

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Swivel bendingis bending using a tool which forms the part around

the bending edge (Fig. 2.1.24). Circular bendingis a continuous process

of bending which progresses in the direction of the shank using strip,

profile, rod, wire or tubes (Fig. 2.1.25). Circular bending at an angle

greater than 360°, for example is used in the production of springs and

is called coiling.

Forming under shear conditions

Displacementis a method of forming whereby adjacent cross-sections of

the workpiece are displaced parallel to each other in the forming zone

by a linear die movement (Fig. 2.1.26). Displacement along a closed die

edge can be used for example for the manufacture of welding bosses

and centering indentations in sheet metal components.

Methods of forming and cutting technology

workpiece

straighteningrollers

Fig. 2.1.22 Roll straightening

workpiece

rollers

Fig. 2.1.21Roll bending

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Twistingis a method of forming under shearing conditions in which

adjacent cross-sectional surfaces of the workpieces are displaced relative

to each other by a rotary movement (Fig. 2.1.27).

Basic principles of metal forming

Fig. 2.1.23 Roll forming

clampingjaws

workpiece

cheek

Fig. 2.1.24Swivel bending

workpiecesupport

workpiece

bendingmandrel

clampingfixture

Fig. 2.1.25Circular bending

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

2.1.3Dividing

Dividingis the first subgroup under the heading of parting, but is gen-

erally categorized as a “forming technique” since it is often used with

other complementary production processes (cf. Fig. 2.1.2). According

to the definition of the term, dividing is taken to mean the mechani-

cal separation of workpieces without the creation of chips (non-cut-

ting). According to DIN 8588, the dividing category includes the sub-

categories shear cutting, wedge-action cutting, tearing and breaking

(Fig. 2.1.28). Of these, the shear cutting is the most important in indus-

trial application.

Methods of forming and cutting technology

punch

workpiece

blank holder

Fig. 2.1.26Displacement

workpiece

Fig. 2.1.27Twisting

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998

Shear cutting– known in practice as shearing for short – is the separa-

tion of workpieces between two cutting edges moving past each other

(Fig. 2.1.29and cf. Sect. 4.5).

During single-stroke shearing, the material separation is performed

along the shearing line in a single stroke, in much the same way as using

a compound cutting tool. Nibbling, in contrast, is a progressive, multi-

ple-stroke cutting process using a cutting punch during which small

waste pieces are separated from the workpiece along the cutting line.

Fine blankingis a single-stroke shearing method that uses an annular

serrated blank holder and a counterpressure pad. Thus the generated

blanked surface is free of any incipient burrs or flaws, which is fre-

quently used as a functional surface (Fig.2.1.30and cf. Sect. 4.7).

Basic principles of metal forming

parting

dividing

breakingtearingwedge-actioncutting

shear cutting

Fig. 2.1.28 Parting techniques classified under forming

openshearing

blankingcontour

punch

die

Fig. 2.1.29 Shearing

Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998