Altan T. Metal Forming Handbook

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1 Introduction

Technology has exerted a far greater influence on the development of

our past than most history books give credit for. As late as the 19th cen-

tury, craftmanship and technology were practically synonymous. It is

only with the advent of mechanisation – through the use of machines –

that the term technology took on a new meaning of its own.

Today, technology is one of the bastions of our modern lifestyle and

the basis for our prosperity, in which metal forming technology plays a

central role. Alongside the manufacture of semi-finished products

through rolling, wire drawing and extrusion, the production of discrete

components using sheet metal and solid forming techniques is of major

significance. Its fields of application range from automotive engineer-

ing, production line and container construction through to the build-

ing construction, household appliance and packaging industries.

The machine tool, with its capacity to precisely guide and drive one

or more tools for the machining of metal, has become a symbol of eco-

nomic metalworking. In the past, the work processes typically seen in

metal forming technology used to be executed in a series of individual

operations on manually operated machine tools. Today, however, auto-

matic production cells and interlinked individual machines through to

the compact production line with integrated feed, transport, monitor-

ing and finished part stacking systems are the state of the art. Develop-

ments in this field created the technological basis to allow the benefits

of formed workpieces, such as a more favorable flow line, optimum

strength characteristics and low material and energy input, to be com-

bined with higher production output, dimensional control and surface

quality.

As a reputed German manufacturer of machine tools, the company

SCHULER has played a determining role in this development over a period

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

of more than 150 years: From the manually operated sheet metal shear

to the fully automatic transfer press for complete car body side panels.

Over the millenniums, the handworking of metal by forming reached

what may still today be considered a remarkable degree of skill, result-

ing in the creation of magnificent works in gold, silver, bronze, copper

and brass. It was only in around 1800 that iron sheet produced in

rolling plants began to find its way into the craftsmen’s workshops,

requiring completely new processing techniques: In contrast to non-

ferrous metals, the much harder and more brittle new material could be

more economically worked with the aid of machines.

In 1839, master locksmith Louis Schuler founded a modest workshop

comprising primarily a tinsmith’s shop, as well as a blacksmith’s forge

and a smithy. Driven by his Swabian business sense, he considered the

possibilities opened up by the newly available, cheaper iron sheet. He

was quick to realize that the increased input required in terms of phys-

ical strength and working time, and thus the manufacturing costs

involved in producing the finished article were far too high to benefit

from the favorable price of the iron sheet itself. Step by step, Louis

Schuler accordingly began to replace manual work processes by mechan-

ical fixtures and devices. He began to mechanise his workshop with

sheet shears, bending machines and press breaks, which were consider-

able innovations in those days.

Inspired by the World Exhibition in London in 1851, Louis Schuler

decided to concentrate his activities entirely on producing machines for

sheet metal working. His production range was continuously extended

to include sheet metal straightening machines, metal spinning and

levelling benches, eccentric presses, spindle presses, turret, crank and

drawing presses, both mechanically and hydraulically powered, notch-

ing presses as well as cutting and forming tools and dies. As early as

1859, he exported his first sheet metal forming machines.

At the end of the 1870s, Schuler registered his first patent for “Inno-

vations in punching dies, shears and similar”. In 1895, he patented

“Hydraulic drawing presses with two pistons fitted into each other”,

and in the same year was also awarded first prize at the Sheet Metal

Industry Trade Exhibition in Leipzig. With expansion of the production

program, the workforce as well as the company premises had under-

gone continuous growth (Fig.1.1). The Schuler machine tool company

Metal Forming Handbook

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

was one of the foresighted enterprises of the day to pioneer the process

of differentiation taking place in the field of machine tool engineering.

As a supplier of machines and production lines for industrial man-

ufacture – in particular series production – the company’s reputation

increased rapidly.

The increasing export volume and a consistent process of diversifica-

tion in the field of forming technology led to an early process of glob-

alisation and to the development of the internationalSCHULER Group of

Companies.

The SCHULER Group’s process of globalisation got under way at the

beginning of the sixties with the founding of foreign subsidiaries. To-

day, SCHULER runs not only eight manufacturing plants in Germany but

also additional five production facilities in France, the US, Brazil and

China. Alongside its world-wide network of sales agencies, SCHULER has

also set up its own sales and service centers in Spain, India, Malaysia

and Thailand.

An internationally-based network of production facilities coordinat-

ed from the parent plant in Goeppingen permits rapid response to the

changes taking place in the targeted markets. Production in overseas

locations brings about not only a reduction in costs but also creates

Introduction

Fig. 1.1 L.Schuler, Machine tool factory and foundry, Goeppingen, around 1900

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

major strategic benefits by increasing “local content” and so ensuring

an improved market position.

The North and South American markets are supplied locally. The

NAFTA area is coordinated by Schuler Inc. in Ohio, while South Ameri-

ca’s common market, the Mercosul, is supervised from Brazil. The high

standard of quality achieved by the SCHULER plant in Brazil has opened

up even the most demanding markets.

In the growing market of China, the SCHULER Group runs two joint

venture corporations in cooperation with Chinese partners for the man-

ufacture of mechanical presses and hydraulic presses.

Today, we stand on the threshold to a new millennium marked by

increasing market globalisation and rapidly changing organizational

and producing structures. Under these rapidly changing conditions, it

is SCHULER’s workforce which remains the single most important deter-

mining factor between success and failure. The technological orienta-

tion of the staff provides the innovative impetus which will secure the

company’s development as it moves into the 21st century.

This Metal Forming Handbook reflects the technical competence, the

rich source of ideas and the creativity of the SCHULER Group’s workforce.

The book takes an in-depth look at the pioneering stage of development

reached by today’s presses and forming lines, and at related production

processes, with particular emphasis on the development of control

engineering and automation. Developments in the classical fields of

design, mechanical engineering, dynamics and hydraulics are now

being influenced to an ever greater degree by more recently developed

technologies such as CAD, CAM, CIM, mechatronics, process simula-

tion and computer-aided measurement and process control technology.

In today’s environment, the main objective of achieving enhanced

product quality and productivity is coupled with lower investment and

operating costs. In addition, questions of reliability, uptime, accident

prevention, process accounting, economical use of resources and envi-

ronmental conservation play also a central role.

In view of the fundamental importance of metal forming technology

today, this Handbook offers the reader a reference work whose useful-

ness stretches to practically every branch of industry. The book provides

an in-depth analysis of most of the important manufacturing tech-

nologies as a system comprising the three elements: process, production

line and product.

Metal Forming Handbook

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

2 Basic principles of metal forming

2.1Methods of forming and cutting technology

2.1.1Summary

As described in DIN8580, manufacturing processes are classified into

six main groups: primary shaping, material forming, dividing, joining,

modifying material property and coating (Fig.2.1.1).

Primary shaping is the creation of an initial shape from the molten,

gaseous or formless solid state. Dividing is the local separation of mate-

rial. Joining is the assembly of individual workpieces to create sub-

assemblies and also the filling and saturation of porous workpieces.

Coating means the application of thin layers on components, for exam-

ple by galvanization, painting and foil wrapping. The purpose of modi-

fying material property is to alter material characteristics of a workpiece

coating

dividing

joining

modifyingmaterial

property

primaryshaping

forming

Fig. 2.1.1

Overview of production processes

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

to achieve certain useful properties. Such processes include heat treat-

ment processes such as hardening or recrystallization annealing.

Forming– as the technology forming the central subject matter of this

book – is defined by DIN 8580 as manufacturing through the three-

dimensional or plastic modification of a shape while retaining its mass

and material cohesion. In contrast to deformation, forming is the mod-

ification of a shape with controlled geometry. Forming processes are

categorized as chipless or non-material removal processes.

In practice, the field of “forming technology” includes not only the

main category of forming but also subtopics, the most important of

which are dividingand joining through forming (Fig.2.1.2). Combinations

with other manufacturing processes such as laser machining or casting

are also used.

2.1.2Forming

Forming techniques are classified in accordance with DIN8582

depending on the main direction of applied stress (Fig.2.1.3):

–forming under compressive conditions,

–forming under combined tensile and compressive conditions,

–forming under tensile conditions,

–forming by bending,

–forming under shear conditions.

Basic principles of metal forming

forming under compressive

conditions

forming under shear conditions

forming under compressive

and tensile conditions

forming under tensile conditions

forming

parting

joining

forming by bending

joining through forming

dividing

Fig. 2.1.2

Production

processes

used in

the field

of forming

technology

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

The DIN standard differentiates between 17 distinct forming processes

according to the relative movement between die and workpiece, die

geometry and workpiece geometry (Fig.2.1.3).

Forming under compressive conditions

Cast slabs, rods and billets are further processed to semi-finished prod-

ucts byrolling. In order to keep the required rolling forces to a mini-

mum, forming is performed initially at hot forming temperature. At

these temperatures, the material has a malleable, paste-like and easily

formable consistency which permits a high degree of deformation

without permanent work hardening of the material. Hot forming can

be used to produce flat material of the type required for the production

of sheet or plate, but also for the production of pipe, wire or profiles. If

the thickness of rolled material is below a certain minimum value, and

where particularly stringent demands are imposed on dimensional ac-

curacy and surface quality, processing is performed at room tempera-

ture by cold rolling. In addition to rolling semi-finished products, such

as sheet and plate, gears and threads on discrete parts are also rolled

under compressive stress conditions.

Open die formingis the term used for compressive forming using tools

which move towards each other and which conform either not at all or

only partially to the shape of the workpiece. The shape of the work-

piece is created by the execution of a free or defined relative movement

Methods of forming and cutting technology

forming under compres-

sive conditions DIN 8583

forming under compres-

sive and tensile

conditions DIN 8584

forming under

tensile conditions

DIN 8585

forming under shearing

conditions DIN 8587

forming by bending

DIN 8586

forming

rolling

open die forming

closed die forming

coining

stripping

deep drawing

flanging

spinning

wrinkle bulging

extending by stretching

expanding

displacement

twisting

stretch forming

bending with linear

die movement

bending with rotary

die movement

forming by forcing through

an orifice

Fig. 2.1.3 Classification of production processes used in forming in accordance with DIN 8582

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

between the workpiece and tool similar to that used in the hammer

forging process (Fig.2.1.4).

Closed die formingis a compressive forming process, where shaped

tools (dies) move towards each other, whereby the die contains the

workpiece either completely or to a considerable extent to create the

final shape (Fig.2.1.5).

Coiningis compressive forming using a die which locally penetrates

a workpiece. A major application where the coining process is used is in

manufacturing of coins and medallions (Fig.2.1.6).

Forming by forcing through an orificeis a forming technique which

involves the complete or partial pressing of a material through a forming

die orifice to obtain a reduced cross-section or diameter. This technique

includes the subcategories free extrusion, extrusion of semi-finished prod-

ucts and extrusion of components(cf. Sect. 6.1).

Basic principles of metal forming

die

workpiece

Fig. 2.1.4 Open die forming

upper die

workpiece

lower die

Fig. 2.1.5 Closed die forming

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

During free extrusion, a billet is partially reduced without upsetting

or bulging of the non-formed portion of the workpiece (Fig.2.1.7and

cf. Sect. 6.5.4). Free extrusion of hollow bodies or tapering by free extru-

sion involves partial reduction of the diameter of a hollow body, for

example a cup, a can or pipe, whereby an extrusion container may be

required depending on the wall thickness.

In extrusion of semi-finished productsa heated billet is placed in a con-

tainer and pushed through a die opening to produce solid or hollow

extrusions of desired cross-section.

Cold extrusion of discrete partsinvolves forming a workpiece locat-

ed between sections of a die, for example a billet or sheet blank (cf.

Sects. 6.5.1 to 6.5.3 and 6.5.7). In contrast to free extrusion, larger

deformations are possible using the extrusion method.

Methods of forming and cutting technology

embossingpunch

workpiece

Fig. 2.1.6 Coining

punch

workpiece

pressbush

Fig. 2.1.7

Free extrusion

of shafts

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

Extrusion is used for the manufacture of semi-finished items such as

long profiles with constant cross sections. Cold extrusion is used to pro-

duce individual components, e.g. gears or shafts. In both methods,

forming takes place using either rigid dies or active media. In addition,

a difference is drawn depending on the direction of material flow re-

lative to the punch movement – i.e. forwards, backwards or lateral –

and the manufacture of solid or hollow shapes (cf. Fig. 6.1.1). Based on

the combination of these differentiating features, in accordance with

DIN 8583/6 a total of 17 processes exist for extrusion. An example of a

manufacturing method for cans or cups made from a solid billet is back-

ward cup extrusion (Fig. 2.1.8).

Forming under combination of tensile and compressive conditions

Drawingis carried out under tensile and compressive conditions and

involves drawing a long workpiece through a reduced die opening. The

most significant subcategory of drawing is strip drawing. This involves

drawing the workpiece through a closed drawing tool (drawing die,

lower die) which is fixed in drawing direction. This allows the manu-

facture of both solid and hollow shapes. In addition to the manufacture

of semi-finished products such as wires and pipes, this method also

permits the production of discrete components. This process involves

reducing the wall thickness of deep-drawn or extruded hollow cups by

ironing, and has the effect of minimizing the material input, particu-

larly for pressure containers, without altering the dimensions of the can

bottom (Fig. 2.1.9and cf. Sect. 6.5.5).

Basic principles of metal forming

punch

workpiece

press bush

blank

ejector

Fig. 2.1.8

Backward

can extrusion

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