Roll Forming Handbook / Edited by George T. Halmos

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During the Industrial Revolution of the eighteenth and nineteenth centuries, manyofthe handtools

used in metal manufacturing were gradually replaced by power-driven machinery. Water wheels, steam

engines, and, later on, electrical motors provided an abundant quantityofpower. In 1855, Bessemer

patented the ﬁrst modern steel-making method in England, aprocess that provided large quantities of

better qualitysteel. Originally,steel was intended for castings (canons), but eventually most of it was

processed by forging, using big,powered presses.

One of the most signiﬁcant and least-heralded achievements of the Industrial Revolution was

the replacement of the ancient artofhammering (forging) with pairs of rotating rollstochange the shape

or the thickness of the metals. Based on the forging experience, and knowing that steel is more

pliable when it is hot, the rolling process was completed at hightemperatures. Rolling reduced

the thickness and increased the surface area in contact with air.The rapid cooling of the large

surfaceslimits the minimum thickness achievable by hot rolling.The introduction of ﬂywheels, clutches,

reversible steam engines, and electrical motors contributed to faster steel forming processes, permitting

further reduction of the minimum thickness of the rolled products. However,the thinner the metal gets,

the larger its surface and the faster the rate of cooling. Therefore,evenwiththe most modern equipment,

the minimum thickness of commercially available hot rolled steel is still about 0.060 to 0.070 in.

(1.5 to 1.8 mm).

Rolling at room temperatureisnot anew technology. Primitivecold rolling was used in the

fourteenth centuryfor gold and silver. The ﬁrst true rolling mills of which anyrecordexists were

pairs of rolls were used to rollﬂats from soft materials such as gold, lead, and tin, probably at room

temperature.Cold rolling was also used to planish tin plates. Room temperature (cold) rolling of steel

commenced in the late eighteenth centuryand became more widely used in the nineteenth century. By

the late nineteenth and in the twentieth centuries, an immense varietyofhot and cold rolled

aluminum,copper,brass,lead, tin, titanium,zirconium,and specialtyalloys sheetbecame

commercially available. Without these rolled ﬂat products, our current life and our living standard

would be unimaginable.

1.1.2 Forming of Sheet Metals

The name “manufacturing”originates from the Latin manu (hand) and factura (making). When ﬂat-

rolled sheets became commercially available,for along time, the ﬁnal products were manufactured,

formed, and shaped by hand. Gradually,machines, particularly presses, substituted for most of the hand

forming.

Avarietyofmechanical presses (single-action screw,friction, link-and-crank, and different double-

action drawpresses)and hydraulic presses were used almost exclusively to blank, form, or drawall sheet

metal products until the early twentieth century. Other processes, such as curving, proﬁledrawing,

stretch bending, spinning, winding,beading,explosiveforming,electromagnetic forming, and hydro

forming are also used for forming sheets and plates. However,the combined output of these processes is

considerably less than that produced by the presses and later on by roll formers.

Althoughroll forming was already used in the early 1900s, it was only after the Second Word Warwhen

it took over asigniﬁcant percentage of the fabrication of sheet metal products from press brakes and

other types of forming.Owing to the highefﬁciency of roll forming,the labor content of manyproducts

was drastically reduced.

Rooﬁng,siding,farm buildings, grain storage bins (silos), shelving,storage racks, ﬂuorescent light

ﬁxtures, electrical products, refrigeration, heating,ventilation, railwaycars, powerplants, doors,

windows, toilet partitions, bicyclewheels, ﬁreplaces, furniture, appliances, airplanes, spacecraft,

swimming pools, and countless other products haveall been efﬁciently roll formed.

In the 1950s and 1960s, rotaryencoders were introduced and the applications of pneumatic presses,

in-line welding, prepunching, and rollforming prepainted metals spread widely.Eventually,moreand

moreother operations were incorporated into the roll forming lines.

Roll Forming Handbook1 -2

In the 1970s and 1980s, prepunching became moresophisticated through the use of differentcontrols

and gagged punches. Innovations wereintroduced to reduce tool changeover time using rafted

construction,

side-by-side rolls and other devices. Die accelerating systems became more sophisticated

and lengths moreaccurate. Steels with up to 200,000 psi (1960 MPa) yield strength and manyexotic

metals were successfully rollformed. In the late 1970s and early 1980s, computer-aided rolldesign

systems were introduced.

In the 1990s, an increased number of programmable controllers and computers havebeen added to

control the lines. The product, as well as the material tolerances, has become tig hter and the demand for

manufacturing ﬂexibilityhas increased. Customers pressed equipment suppliers for better qualityand

moreefﬁcient lines, including automated ﬁnished-product handling.Competitiveness has necessitated

the reduction of the number of operators and in some cases one operator to run two or more lines, at an

increased speed, and at ahigher utilization rate.

By the 1970s, about 35 to 40% of all sheet products produced by the NorthAmerican steel mills were

processed through roll formers. In the last decades of the twentieth century, rollforming of automotive

products became the fastest growing segment of the industry.

The roll forming industryisstill growing strongly in the twenty-ﬁrst century.

1.1.3 What is Roll Forming?

It is not asimple task to describe or explain the concept of rollforming.Afrequently used deﬁnition

demonstrates the complexity:

To form sheet metal strip along straight, longitudinal, parallel bend lines with multiple pairs of

contoured rolls without changing the thickness of the material at room temperature.

Similar to manyother deﬁnitions, the above one also has exceptions.

To form sheet metal strip along straight, longitudinal, parallel bend lines, but

The products often exit the roll former curvedorinaspiral form

The products can havebend lines 908 to the longitudinal bend line

The bend lines are not always parallel (intentionally)

The bend lines are not always straight (occasionally unintentionally)

with multiple pairs of contoured rolls, but

To achieve the desiredshape, the roll formers mayapply bronze shoes, plastic guides and,

especially during setup,2£ 4s. If the wood pieces are effective during the setup,then they are

clamped to the machine. Once the clamps are taken away ,the 2 £ 4s are strapped to the

equipment. If they are still functioning well after amonth or so,then they are painted in green and

became partofthe line [431]

without changing the thickness of the material, but

The thickness is almost always reduced at the bend lines

In thin curvedproducts, the outside ﬁbers are thinner than the inside ones

Mills are built with special passes to reducethe strip thickness at speciﬁed locations

Contrarytogood practice, the thickness of the material is occasionally

reduced by bent shafts, and far too frequently by the operators

Raftedw Rollformer is aregisteredtrade name of The BradburyGroup.

Introduction to Roll Forming 1 -3

at room temperature, but

To eliminate the cracking of paint at the bend lines, the material can be preheated just before

forming

Plastic can be roll formed at elevated temperature

In-line soldering, brazing, or annealing requires elevating the temperature of metal while

processingthrough the equipment

Titanium was hot roll formed in the late 1960s

Hot rollforming is apotential new technology.

Rollforming is aﬂexible process, whereboth the fundamental rules and the exceptions can be utilized. It

has been provenseveral times that even seemingly impossible roll forming tasks can be accomplished,

althoughitmay take alonger time and much moremoney.Onthe other hand, it has also been shown

that plans to roll form simple shapes can create disastrous results if the basic rules of rollforming are not

followed.

1.1.4 Basic Requirements

1.1.4.1 Satisfying Customers

Rollformed products are sold to customers in an extremely competitive market. Customers are always

looking for manufacturers who can repeatedly meet with their basic requirements. They are expecting to

receive:

The right quality

The right quantity of products

At the right time

Forthe right price

Companies not able to supply the right qualityorthe right quantity, at the right time for the right price

will lose their customers. However,not consistently meeting customers’expectations or having

manufacturing problems is not always the plant’s fault. The plant cannot manufacturegood-quality

products at the right time for the right price if they are not provided with the basic mechanisms to fulﬁll

their obligations.

1.1.4.2 Basic Requirements of the Manufacturing Plant

To successfully meet the demands and outperform the competitors, manufacturing plants must have:

Good design (product drawings) to be manufactured

Sufﬁcient run quantities

The right material to be formed

Proper equipment

Good tooling and

Knowledgeable, motivated workforce

Good design (products that can be manufactured without extreme hardship).Most plants haveexperience

with products that cannot be efﬁciently roll formed, or sometimes not roll formed at all. The product can

be too complicated for the available equipment, or the dimensions or tolerances are beyond the

capabilities of the equipment or tooling.

Sufﬁcient run quantities.Ifthe run quantities are belowaneconomical minimum level, then highsetup

cost can reduceefﬁciency unless the plant has aspecial-purpose line set up for that speciﬁc product. Very

highrun quantities may reduceproduct costs but can increase inventory, product-handling cost, and

storage space requirement.

Acceptable quality material.Running across “bad material” is not arare occurrence. Perhaps the

supplied material was either unsuitable for the product, or it could havebeen incorrectly speciﬁed.

Roll Forming Handbook1 -4

However,when troubleshooting of the equipment and tooling does not yield quick results,the material is

far too frequently,and often incorrectly,blamed for the bad products.

Proper equipment suitable for for ming the product.There is no plant without complaints about the roll

forming lines. Frequently,the complaints are justiﬁed; sometimes, it is the results of procuring aline of

insufﬁcient capacityorbad quality, or of neglected maintenanceorabusive usage by the operator.The life

of agood-quality, reasonably well-maintained rollformer can be over 50 years. Most malfunctioning

equipment problems are corrected in the ﬁrst year,and the mill will operate with reasonable reliability.

However,incorrectly speciﬁed, slow,weak, or low-qualitylines cannot be made competitive against faster

and better lines.

Good tooling.Roll forming lines are equipped with several sets of tooling during their lifetime. Good-

quality, operator-friendly,properly set up tooling is essential to produce good-qualityproducts at

reasonable price.

Knowledgeable, motivated work force.Ithas been stated repeatedly that the greatest asset of acompany

is its people. Acompanycan haveanexcellent product, good material, the best equipment and tooling,

but is still unable to produce competitivelywithout knowledgeable people. Continuous education of the

operators and other employees, combined with motivation, is crucial to good productivityand proﬁt.

Introduction to Roll Forming 1 -5

Roll Forming Mill

GeorgeT.Halmos

Delta Engineering Inc.

2.1 General ................................................................................ 2 -1

2.2 Mill Types ........................................................................... 2 -1

Cantilevered Mills

†

Duplex Mills

†

Through-Shaft

Duplex Mills

†

Standard (Conventional) Mills

†

Double-High

Mills

†

Rafted (Plated, Cassetted) Mills

†

Side-by-Side

Mills

†

Pull-ThroughMills

†

Spiral-Tube Mills

†

Truck-Mounted Mills

†

Special Mills

2.3 Mill Components ............................................................... 2 -18

Mill Bed

†

Stands

†

Shafts

†

Power Train

†

Side-Roll and

Cluster-Roll Stands

†

Guides Between Passes

†

Straightener

†

Lubrication System

†

Shaft Shoulder

Alignment

†

Installation of Other Units in the Mill

References ....................................................................................... 2 -32

2.1 General

The heartofthe roll forming line is the mill. The mill provides the power and supporttothe tooling

that forms the metal. The completeroll forming line is aligned withthe shaft shoulders of the roll

forming mill.

The variations in mill design are unlimited, but mills can be classiﬁed as cantilevered, duplex, through-

shaft duplex, standard (conventional), or rafted (plated). Those not ﬁtting into anyofthese categories

may be considered as “special mills.”

2.2 Mill Types

2.2.1 CantileveredMills

The shafts of the cantilevered mills are supported at one end only;hence, they are sometimes called

“overhanging”orstub-typemills (Figure2.1).

Cantilevered mills, producing lock-forms at the edge of sheets, havebeen popular with sheet metal

workers for along time. They are low-cost, nonsophisticated machines, and require little adjustment. The

cantilevered mills become morepopular and havebeen used to form manysimple, narrowsections

(Figure2.2).

To utilize the mill for two sections, the opposite side of the “cantilevered” shaft ends can be tooled to

form another section (Figure2.3).

The advantages of the cantilevered mills are:

Relatively low cost

Capabilitytoform the edge of sheets of anywidth

2 -1

FIGURE 2.1 Cross-section of cantilever mill.

TABLE 2.1 Shaft Diameter Selection Examples

Roll Space(in.) Yield (ksi) Thickness (in.) Factors Revised Thickness Shaft Diameter (in.)

12 50 0.036 1N/A 1.5

36 50 0.036 1N/A 2.75

36 50 0.020 1N/A 2.5

48 50 0.020 1N/A 3.0

48 100 0.020 £

ﬃﬃﬃﬃﬃﬃ

100

ð 100 ksi yieldÞ¼0.022 in. 3.0

48 50 0.020 £ 2(stretched groove) ¼ 0.040 in. 3.5

12 50 0.375 1(check bearing) N/A 4.25

48 50 0.020 £ 0.6 (edge forming) ¼ 0.012 in. 2.75

FIGURE 2.2 Cantilever mill. (Courtesy of Metform International Ltd.)

Roll Forming Handbook2 -2

The disadvantages of the cantilevered mills are:

Singular adjusting screwmakes it difﬁcult

to set the required rollgap.

Double-adjustingscrewsmakes it very

difﬁcult to adjust the shafts up or down,

while keepingthe top shaft parallel to the

bottom shaft.

The deﬂection of the two opposing shafts

under the same load is approximately four

timesthe deﬂectionofthe same shaft

supported at both ends (Figure 2.4).

Owingtothe largerdeﬂectionofthe

cantilevered shaft, the shaft length (and

the maximum formed width) is limited.

The ﬁrst twoshortcomings can be eliminated by

usingdouble-adjusting screwsconnected with

gears (one shaft-height adjusting screwrotates

the other one). The deﬂection can be reduced by

FIGURE 2.3 Cantilever mill with rolls at both ends of the shafts.

(a) supported at one ends

(b) supported at both ends

defl

=4defl

defl

FIGURE 2.4 Cantilevered shaft deﬂects four times

more than ashaft supported at both ends.

Roll Forming Mill 2 -3

FIGURE 2.5 Connecting the operator side of the cantilevered shafts reduces deﬂection.

FIGURE 2.6 Rafted cantilever mill stand. (Courtesy of CompuRoll Inc.)

Roll Forming Handbook2 -4

using larger shaft diameter shafts or by applying aconnector (yoke) between the top and bottom shafts

at the operator side (Figure2.5). This connecting unit can be applied to form narrow sections only.

Using cantilevered mills, the maximum width of the formed partofthe product seldom exceeds 4in.

(100 mm).

To facilitate fast proﬁle changes, rafted (plated) cantilevered mills havebeen developed (Figure2.6).

The plate, supporting the stands, shafts, and tools, can be lifted offand exchanged with another one

within afew minutes.

2.2.2 Duplex Mills

Twocantilevered mills facing each other are called

aduplex mill. Duplex mills have one common

base and drive(Figure 5.47). They can form both

edges of narroworwide products leaving the

center ﬂat. The minimum strip widths depend on

how close the opposing rolls can be pushed

together, andthe maximum widthsusually

depend on how far the two mills can be moved

from each other. Thewidth of theformed

products can be changed quickly by adjusting

one or both sides of the duplex mill in or out

(Figure2.7).

Duplex mills havethe same advantages and disadvantages as the cantilevered mills, except that the

shaft end connecting pieces cannot be used. Some duplex mills haveshafts extended at the other side of

the mill, which can be used to form narrow sections.

Duplex mills either haveone side ﬁxed and the other one adjustable, or both sides adjustable.

Adjustment of aside is usually accomplished by placing all stands on one plate, which, with proper

guides, can be moved in and out, thus changing the gap between the twocantilevered mills.

Forduplex mills with one adjustable rowofstands, the centerline of the product changes with width

change.

In the case of duplex mills with twoadjustable rows of stands, the centerline of the products remains in

the same position. This arrangement is used when holes are prepunched at or around the centerline,

either when the cutoffdie has to be kept symmetrical or for other reasons when it is advantageous to keep

the centerline in the same position (Figure2.8).

The width adjustment can be manual or motorized. The most sophisticated lines haveprogrammable

controller or computer-controlled width adjustment. Forming rolls installed in acantilevered or duplex

mill are seldom exchanged to produce different proﬁles.

It is highly recommended that rolls are installed with the same length throughthe mill. This makes it

very easy to check shoulder alignment (by placing a“straight edge”tothe end of the rolls) and to check

whether the tworowsofstands are parallel

(by checking the gap between the tooling).

Both the single cantilevered and duplex mills

must have long entryand reasonably long exit

guides (Figure2.9). The unevenrollpressure,

unevenorasymmetric forming,and bent shafts

can generate uneven driving forces, resulting in a

skewed entryorexit of the product(Figure 2.10).

Firmly attaching the entryand exit guides to

the entryand exit stands eliminate the individual

adjustment of the guides when the width is

changed. Both the entryand exit guides should

fixed adjustable adjustable adjustable

FIGURE 2.7 Duplex mill with one or two adjustable row

of stands.

1,2,3

12 43

134

(a) one side adjusted (b) both sides adjusted

FIGURE 2.8 Channels with variable widths produced in

duplex mill with one or two adjustable rowofstands.

Roll Forming Mill 2 -5