Roll Forming Handbook / Edited by George T. Halmos

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×10

− 3

#1 23456

D.H.=0

D.H.=(1/4)H

B.L:Horizontal

#1 23456

Roll No. Roll No.

t 4.5 × f 101.6

(

)

MAX

∆ q (deg)

×10

− 3

#1 23456

12 3456

Roll No.

(

)

MAX

D.H.=(1/4)H

(Downhill)

t 4.5 × f 101.6

(b)

(a)

23456

(c)

3456

∆ q (deg)

( e

)

MAX

t 4.5 × f 101.6

Roll No.

D.H.=0

D.H.=(1/2)H

× 10

− 3

FIGURE 11.40 Optimizedrollproﬁles correspondingtodifferent descending pass linesfor manufacturingERW pipes.

Roll Forming Handbook11-32

following fact: as D becomessmall, the transversal bending deformation incurred by the metal sheet

becomes large and the transversal bending strain occurring in it increases. At the same time,

the strain hardening of the metal sheet becomes moreand morecritical. These effects increase the

W : On

the other hand, as D becomes small, the volumeofthe metal strip decrease, which decreases

W : In the

B.L.:Horizontal

#1 23456

120

100

∆ q (deg)

W (Kgf·m/sec)

(Kgf·m/sec)

∆ q (deg)

t 4.5 × f 48.6

t 2.3 × f 101.6

( ∆ q ):Increment of Profle Angle

( W ):Power of Deformation at Inter-Stand Stage

Roll No.Roll No.

FIGURE 11.41 Designed roll proﬁles (roll ﬂowers for ERWpipes). They are optimized so that the power of

deformation “

W ”dissipated at everyinterstand stage becomes equal to each other.

CAD

SYSTEM

EWS

2 − D

EWS

MAIN

FRAME

ANALYSIS

ROLL DESIGN

USER

PASS -

SCHEDULE

DESIGN

RESIDUAL

STRESS

BENDING AT

ROLL GAP

SPRINGBACK

ANALYSIS

3-D

ANALYSIS

2-D

ANALYSIS

CURVATURE

WIDTH

EDGE

ELONGATION

( e

)max

1+I

FIGURE 11.42 Framework of CAE system for roll forming.

Behavior of Metal Strip During Roll Forming 11-33

usual cases, the effects of the increased strain and strain hardening are larger than those of the decreased

volume.

As mentioned already,when the diameter of tube D is ﬁxed, the power of deformation

W given to

the strip by each proﬁle roll increases proportionally to (2.1 , 2.2)th powerofwall thickness as

follows:

W / t

2 : 1 , 2 : 2

ð 11: 13Þ

11.6 CAE for Roll Forming

Developed design systems can be used to design roll positions as well as optimal rollproﬁles.They also

can be used for the design of equipment, and the diagnosis and correction of conventional rolls.

Figure11.42 shows the basic concept of one of those developed CAE systems.

Roll Forming Handbook11-34

Acquiring Roll Forming

Lines, Education, and

Training

GeorgeT.Halmos

Delta Engineering Inc.

12.1 WhyRollFormProducts? ............................................... 12-1

Reducing Manufacturing Cost

†

Additional

Manufacturing Capacity Required because of

Increased Sales Volume of an Existing Product

†

Introducing New Products

12.2 Different Paths to StartRollForming ............................ 12-2

Custom Roll Forming

†

Roll Form with Existing

Equipment

†

Acquiring aNew Line

†

Purchasing

Used Line

12.3 Evaluating the Product .................................................... 12-3

12.4 Selecting Line Components ............................................ 12-4

Entry Section

†

Roll Forming Mills

†

Presses

†

Length Measuring

†

Finished Product Handling

12.5 Procuring Roll Forming Tooling .................................... 12-7

12.6 Equipment and Tool Speciﬁcations ............................... 12-7

12.7 AcceptanceTest ................................................................ 12-7

12.8 Education and Training .................................................. 12-7

Education and Training is aKey to Success

†

Roll

Forming Line Operators

†

Maintenance Personnel

†

Setup Person, Line Supervisor, and Plant Manager

†

Product Designer

†

Purchase Agents and Schedulers

†

Managers and Executives

†

Tool and Equipment

Designers

12.9 Motivation ........................................................................ 12-11

References ..................................................................................... 12-11

12.1 Why Roll FormProducts?

The most frequent reasons to consider roll forming are:

Reducing manufacturing cost of aproduct or group of product

Increase in sales volume of an existing product requires additional manufacturing capacity

Introducing anew product

12-1

12.1.1 Reducing Manufacturing Cost

Products manufactured with rollforming lines usually cost less than those made by other methods.

Incorporating other operations in the line, such as punching,notching,embossing,welding,adhesive

bonding,painting,packaging,and others can further reduce the total manufacturing cost. The elimination

of the material handling and inventorybetween different operations are additional contributors to the

production cost reduction.

12.1.2 Additional Manufacturing Capacity Required because of Increased

Sales Volume of an Existing Product

When the volume of brake formed, press formed, welded, extruded, or purchased componentsreaches a

critical level; usually,roll forming is the most economical method to manufacturethe increased product

volume. The purchase of aroll forming line can frequently be justiﬁed with the reduction of labor and

material cost, together with the elimination of the need for investment for additional press brakes,

punches, press, or similar equipment.

12.1.3 Introducing New Products

Forsome new products, the only practical manufacturing technologyisroll forming.For other products,

alternative methods such as press brake or punch press forming or extrusion are available, but the

product volumeishighenoughtojustify roll forming .Roll forming can also be the only practical way to

fabricate products from hightensile or special materials, producing variable lengths and hole patterns or

manufacturing the producttoverytight tolerances.

12.2 Different Paths to StartRoll Forming

When adecision is reached that aproduct should be roll formed, then the manufacturer has several

alternative approaches:

Have the product custom roll-formed by other companies

Roll form it with the existing equipment

Acquire anew roll forming line

12.2.1 Custom Roll Forming

To haveaproductmanufactured by acustom roll former is arelatively easy decision. There are many

reputable custom roll formers with suitable equipment to makethe product once the product design and

the anticipated volume are established. Slight design modiﬁcations suggested by the custom rollformer

can often reduce the price of the product and tooling .These modiﬁcations can either be general in nature

or designed speciﬁcally to suit the product to the existing equipment of the custom roll former.

12.2.2 Roll Formwith Existing Equipment

To roll form products with the customer’sown, existing equipment is also arelatively simple decision,

assuming that the equipment is suitable to form the product and enoughmanufacturing capacityis

available. The decision can be more difﬁcult if the mill does not havethe capacitytoform all of the

required thickness and lengths.

12.2.3 Acquiring aNew Line

The decision to buy aroll forming line is not asimple one. Capital investment can be signiﬁcant, but on

the other hand, the total sales value of the products manufactured during the ﬁrst 20 to 25 year life of a

good line is incredibly high. Therefore, purchasinganinappropriate line can cause difﬁculties.

Roll Forming Handbook12-2

Oncethe decision to acquirearoll forming line has been made, it is important to follow afew basic

guidelines.

All aspects of the products to be rollformed must be considered.Some of the important parameters

are: expected quantities in the ﬁrst year;anticipated yearly and run quantities in the next 3to5years; all

variations of the products such as thickness, length, width, material ty pes, tolerance, and appearance

requirements; method of material handling; and packaging and availabilityofoperators. Input from

sales, marketing, production, inventorycontrol, material handling,and other personnel can be just as

important as the recommendations from the plant and ﬁnancial management.

When all of the information is collected, it is highly recommended to have a“roll forming line

speciﬁcation”prepared by aperson knowledgeable in roll forming.The 5to15pages of the speciﬁcation,

depending on the complexit yofthe line, is agood basis fromwhich to obtain quotations. The input of

the suppliers should be taken into consideration and the speciﬁcation modiﬁed if needed. The supplier’s

standardsizes, technology, and experience in the ﬁeld can reduce the equipment, tooling as well as

product costs without sacriﬁcing quality. Suppliers can also recommend minor or relatively inexpensive

changes to the rollforming line speciﬁcations, such as width of line, number of forming stations, and so

forth that will make it feasible to utilize the new line to agreater extent. On the other hand, if only one

product is to be formed on the line, then simpliﬁcation and reduction in capital expenses are possible.

The updated “roll forming line speciﬁcation”should be par tofthe purchase orderand line acceptance

test requirements.

12.2.4 Purchasing Used Line

Alarge number of roll forming mills, presses,and uncoilers are available most of the time at used

machine dealers, auctions, or at the sellers’ plant. It is not easy to ﬁnd the exact line required, and

compromises often havetobemade. Used lines havenowarranties, and drawings, manuals, and backups

are frequently not available. Finding aline with the right tooling is also ararity.

Financial considerations and quick availabilityare the main reasons of buying used equipment. Prices

of the used machines depend greatly on their type, make, age, condition of the equipment, and market

conditions. However,occasionally,good bargains are available. There are times that companies would

pay highprices to get the equipment in order to market the product 5to6months sooner than the

anticipated deliveryofanew line.

Beforepurchasing the used line, it is essential to check the line thoroughly and estimate the repair cost.

Some used lines can be installed quickly and are readyfor production, while others may require major

maintenanceand overhaul, which could cost more than the purchase priceofthe new equipment.

12.3 Evaluating the Product

To gain the most beneﬁt from roll forming, it is highly recommended that the product be designed

speciﬁcally for roll forming [342–345,347,348].Products previously brake formed, press formed,

extruded, or rollformed by others can usually be adapted to the new line, but the design should be

reviewed in detail before equipment and tooling are ordered. Even minor modiﬁcations can reduce

production cost or add to partstrength and marketing features. Other design changes maypermit

incorporating secondaryoperations into the line to reduce product cost. Hence, not only should the

cross-section be considered; all holes, notches, cutouts, embossments, welding, painting,and packaging

should be appraised as well.

The selection of material for the product is affected by its application, strength, and price. Formability

of the material, however,may inﬂuence the number of forming stands and thus the length of the mill.

Type of paint or coating may haveabearing on roll tool material, surface ﬁnish, and lubrication

speciﬁcations.

Product tolerancerequirements can be importantfactors affecting the priceofanew line. Length

tolerances usually dictate the type of length measuring and die accelerating devices. Tolerances on

Acquiring Roll Forming Lines, Education, and Training 12-3

section dimensions and appearance requirements inﬂuence the number of stands, and thus, the length

of the line. Other tolerances such as location of holes, notches, straightness, and ﬂarehaveasimilar effect

on priceand size.

If the product is roll formed in different sizes, for example, different widths, or if different products are

roll formed in the line in small run quantities, then it is important to reduce the changeover time. In these

cases, quick changeover lines are recommended. On the other hand, if runs are long and the quantities

are high, then asimpler single-purpose line maybesufﬁcient.

To produceacceptable products, the rollshaft deﬂection must be kept within the speciﬁed limits. Shaft

deﬂection is inﬂuenced by the shaft diameter and distance between the supportbearings, the thickness

and yield strength of the material to be formed, number of bends formed at each station, distanceofbend

lines from supportbearings, type of forming (air bending or coining), as well as the gap between the

upper and the lowerrollsset by the operator.

Alarger shaft diameter will reduce deﬂection and can improveproduct appearance and tolerances, but

the tool material requirements for all future rolls will be higher (because tool weig ht is asquare function

of the diameter). Larger shaft diameters usually call for increased bearing and head sizes, horizontal

distances, and consequently,ahigher mill price. Alarger mill, on the other hand, may be used for a

greater variety of products and can extend the life of the mill.

12.4 Selecting Line Components

The rollforming line usually consists of four major parts; namely,the entrysection, rollforming mill,

cutoffpress, and exit section, but auxiliaryequipment and tooling may also be included.

12.4.1 EntrySection

Asmall percentage of all rollforming lines are manually or automatically fed with aprecut sheet, or the

product may be transferreddirectly from aprevious operation such as piercing, notching,orbrake

forming.Inmost cases, however,the material is fed into the roll forming line in coil form.

Small lines mayuse coil cradles, but most coilsare placed on uncoilers (reels). Occasionally,when

small custom orders are produced, the partially used coils have to be removed from the uncoiler.

However,most of the time, the coils are “run out” (used up). If the coil is usually runout, then it is

economical to use the largest possible coil size to minimize coil handling and changing time. Maximum

coil size is restricted by the capacityofmaterial handling equipment and availability.

To utilize the potential of arollformer,itisimportant to keep the line running; in other words,

minimize the nonoperating time. Because loading and threading the new coil takes usually the longest

“nonproductive”time, the application of the double, rotating uncoilers, coil cars, turnstiles, or other

material handling devices coupled with in-line storage of threetoﬁve coils and sometimes strip end

joining (welding) are recommended. Productivityboosting equipment at the entryend can be fully

utilized only if provisions are made to removeﬁnished products without interruption at the exit end of

the line. Mechanized product removal at the exit end can often greatly increase the output of the line.

An in-line coil accumulator,combined with strip-end joiner is the ultimate approach to continuous

line operation. However,the highcost of the accumulators usually prohibits its use for roll forming lines,

unless the continuous run is atechnological requirement.

12.4.2 Roll Forming Mills

The mills can be classiﬁed in twobasic categories; outboardorinboardtypes. In the outboardor

cantilevered mill, the rolls are placed on shafts supported at one end only.Inboard mills haveshafts

supported at both ends, as described in details in Chapter 2.

Cantilevered shafts deﬂect more than those supported at both ends; therefore, outboard mills are

usually used for thinner material and forming only the strip edges. The outboardmills haveagreat

Roll Forming Handbook12-4

advantage for products with avarietyofwidths. Twooutboard mills facing each other (duplex roll

former) with at least one adjustable side can be set to different blank widths in about 1min.

Inboardmills fall into several categories. The method of supporting the shaft (spindle) ends at the

stands, the adjustabilityofthe stands, tool interchangeabilityand variation in drive, and other features

determine the type of mill.

Conventional, standard mills provide easy removal of outboardstands and access to change rolls one

by one. However,changing to anew product maytake 4to8hr.

Avariation of the conventional mill, supplied with outboard bearings matching the shaft diameters,

permits moving the outboardstand closer to the inboardstand. This position reduces the shaft deﬂection.

Mills with universal coupler-driven shafts provide larger vertical shaft adjustments, which is required

for deeper sections. It is also simple to disconnect the upper shaft driveifrequired. Mills equipped with

universal couplers can be somewhat more expensivethan conventional lines.

To increase rollforming line utilization, avarietyofmethods are offered to reduce the changeover

time. In the case of “mechanically assisted” tool change applicable to conventional, universal, and other

mills, the rolls are manually slid over to apaciﬁer shaft, which is also used to storerolls.

In other cases, the rollsare “locked-on”atthe required position on the shaft. Removing the complete

tooling withthe shaft not only reduces the changeover time, but also makes the setup less dependent on

the skill of the setup personnel, allowing improvedrepeatabilityofthe cross-section. In an early “quick

changeover” system, the shafts and the locked on rolls were removed or replaced in pairs. In most cases,

the outboard stand had to be removed for this type of change.

The next moresophisticated (and moreexpensive) method was to replacerolls, shafts and bearings

altogether.This required only disconnecting the driveand swinging the bridge out at each stand.

The above early technologies havebeen replaced with moreadvanced, subplated or rafted mills, which

provide aconsiderably shorter changeover.Several stands, fastened to aplate (raft), complete with shafts

and tooling can be removed together by acrane. It is expensivebut acomplete line changeover can take

less than 30 to 45 min.

As an alternative to the shaft and tool changes, there are mills wit hmultiple setup capabilities. The

double highmill

consists of twoindependent sets of rollsatdifferent levels. Changing the shape can be

accomplished by feeding the material either to the bottom or to the top rowofrolls.

Another simple and frequently used method to reduce changeover time is to install two or amaximum of

threesets of rolls on each shaft. Each set has its own entryguide and straightener.The uncoiler and cutoff

press remains in the same position, and the mill is movedsideways when the other set of rollsisoperated.

Another approach to adouble setup,especially for wider sections, is the “side-by-side” rollformer.

With this type of equipment, two rows of stands, shafts, and tooling are mounted on one common base

and driven by acommon drive. The mill base can be moved sideways to line up the desired set of tools

with the material feeding and runout sections.

One companyhas introduced adifferent approach to fast changeover [160]. Up to six sets of rolls,

mounted on shafts, are cantilevered from acommon turret type magazine. By rotating the magazine

along the axis parallel to the direction of rolling,the desiredset can be positioned. However,this type of

mill has yettogain widespread acceptance.

All but afew roll forming mills are driven by 2- to 200-hp electric motors. The horsepower is usually

determined by experience —based on the number and size of stands, thickness and strength of material

to be formed, depth of section, number of bends, rolling speed, and availability of coolant lubricant. An

oversized driveincreases initial capital expenditure and uses moreenergythan necessary. Undersized

drives obviously limit the capacityofthe mill.

Manyolder mills still in service are driven directly by less than a20- to 30-hp motor.For 30-hp or

larger motors, aclutch was normally applied to reducepower surges and shock on the line when jogging

Double high roll former is aregistered trademark of The BradburyGroup.

Side-by-side roll former is aregisteredtrademark of The BradburyGroup.

Acquiring Roll Forming Lines, Education, and Training 12-5

or operating with frequent stops and starts. Since the last decades of the twentieth century, variable

frequency AC motors or DC motors havereplaced these older methods.

When power is turned offorthe clutch is disengaged, the product will still coast an average distance

of 6to30in. (150 to 750 mm), depending on the speed, type of line, type of material formed, friction,

inertia of tooling,and other factors. If coasting is to be minimized, then amorepositive stop has been

attained. In the past, brakes stopped the drivetrain; lately the AC or DC motor controls the deceleration.

The early,simple, small mills usually ran at asingle speed, while larger mills often featuredmultiple

speeds. The change in speeds was either incremental (gearbox) or inﬁnitesimal (often called “variable”).

Most of the time, the variable speeds havebeen accomplished by mechanical devicesand lately by

electrical means. The advantages of variable speeds are simplicity and safetywhile threading anew coil

end into the line, abilitytoproduceshortpieces, capabilityofimproving length toleranceatlower speeds,

and rolling heavier thicknesses without overloading the motor.Ifthe line is coupled with apaint line,

then plastic extrusion, welding,orsimilar operations whereprecise speed control is critical, the inﬁnitely

adjustable speed selection is imperative.

It is highly recommendedthatall millsbeequippedwithacoolant/lubricantsystem, even if at thetime

of procuringit, theﬁrstproductstoberollformeddonot requirelubrication.Noone canforeseewhat willbe

produced withthe mill in thenext15to25years andretroﬁttingacoolant/lubricantsystem is more expen-

sive than ordering it withthe mill.The properly appliedcoolant/lubricant will reduce tool wear andenergy

requirement, eliminatematerial pick-uponthe rolls, improvesurface appearance,and wash away dirt.

Inevitably,every plant manager wants spacefor afew morestands on the mill bed. Extra mill bed

length is relatively inexpensive. It is recommended that in addition to the spacerequired for the entry

table and the other equipment, the mill bed should be ordered wi th extra spacefor at least twomore

stands than initially required.

12.4.3 Presses

The prepunch and cutoffpresses are critical pieces of equipment in the line. Incorrectly designed or

speciﬁed presses can be the cause of manyshutdownsand problems. The presses should havethe

necessarycapacitytopunch, shear,notch, or emboss the maximum material width and thickness with

the maximum shear strength at the maximum production rate. The stroke of the cutoffpress should be

long enoughtocut the deepest section that the mill can produce. The presses should also haveenough

clearance between the posts to accommodate the widest die. To olittle clearance between posts may result

in weaker,inferior,ormoreexpensivedies. It is recommended that the prepunching and cutoffpresses

and all the dies be designed for quick changeover.Operators should be able to change dies without

removing the runout conveyor or other mechanisms around the press.

The presses can be powered mechanically,through clutch and brake,orpneumatically or hydraulically.

Mechanical, underslung presses are most frequently used, but their limited strokes per minute capacity

often represent the bottleneck of the line. Pneumatic presses operate faster and are lower in price, but

they are too noisy,create excessivevibrations, and consume relatively expensiveshop air.The new,fast

acting,and quiet hydraulic presses are increasingly applied for both prepunching and cutoff.

12.4.4 Length Measuring

Length sensing andpresstriggeringmechanismsare freq uent ly part of counting andlength

predetermining systems. Electronic, microprocessor and computer controlled systems are taking a

larger shareofthe market. These systems can also be used to govern other functions such as prepunching

or producing avarietyofpatterns.

12.4.5 Finished Product Handling

The exit end of the line is often neglected in spite of the fact that the bottleneck created by the slow

removal of the ﬁnished product affects the productivityofthe whole line. At most rollforming lines,

the ﬁnished product runs out on asteel roller conveyor table and is manually removedbythe operator.

Roll Forming Handbook12-6

Belted conveyor tables are commonly used but they are not recommended for wide, heavy pieces, which

havetobedragged sideway by the operator.For nestable building products or heavy structural sections,

drop tables are often employed. Mechanized or computer-controlled product removal, combined with

bundling and packaging,are available for manyproducts.

Serious consideration should always be given to the removal of ﬁnished pieces or bundles to avoid

interference withthe productivityofthe line.

12.5 Procuring Roll Forming Tooling

Without goodtooling, the plantcannot produce goodproducts at competitiveprices. However,purchasing

inferiortooling based on pricealone is one of the most common mistakesmadebythe roll forming industry.

Supplying rolls is acompetitivebusiness. Asupplier can reducethe tool pricebyreducing the qualityof

the tool steel, offering fewer passes, smaller roll diameters, avoiding side-rollstands or simply not meeting

the customer’sproduct tolerance, quantity, and qualityrequirements. Fewer passes, smaller “guide ﬂanges”

(not interlocking rollsand other shortcuts) can save afew thousand dollars at the time of purchasingbut

can result in tens or hundreds of thousands of dollar losses in increased setup time, increased scrap,reduced

productivity, inferior product, and loss of customers. In extreme cases, after months of testing and scraping

40 to 50 tons of material, the complete set of rolls can end up in the garbage bin.

Pressing the tool supplier to reduce the number of passes is not recommended. Once the number of

passes is established, it is wise to specify one morelast pass, which does not do anyforming.Two identical

passes at the end provide better qualityproducts.

12.6 Equipment and Tool Speciﬁcations

When new equipment and tooling is purchased, precise and detailed speciﬁcations preparedbyaroll

forming expertare highly recommended. The speciﬁcations should be discussed with the prospective

suppliers prior to quotation. The supplier can provide good ideas or suggestions to reduce equipment,

tooling,and product cost without scarifying qualityorequipment/tooling life.

It is prudent to ask the supplier to provide alist of their recently supplied equipment and tooling,

complete with contact names for checking references. The time and cost invested in the thorough

preparation would only be asmall fraction of the time and cost in correcting or solving problems that

would ensue if inferior equipment and tooling are acquired.

Selecting reliable tool suppliers with experienced roll designers, is the primaryrequirement when rolls

are purchased. The same rule applies to all other tools (cutoff, punching) and equipment (e.g., welding).

12.7 Acceptance Test

Acceptancetest at the supplier’spremises is preferredbut it is not always feasible. The acceptancetest

requirements and procedures should be discussed with the supplier and be incorporated into the

purchase order. It is highly recommended that the test should be carried out with the extreme material

thicknesses, widths, and qualities speciﬁed in the purchase order. If only asingle product is manufactured

from one type of material, then coils from at least three different heats should be supplied for testing.

The acceptancetests are often late, behind schedule. Even then, it should not be rushed and shortcuts

should not be taken. Afew daysofextra work and improvements can prevent aseveral years of headaches

and loss of thousands of dollars.

12.8 Education and Training

12.8.1 Education and Training is aKey to Success

Ever ycompanycan buy the same material at more or less for the same price as their competitors. Every

companycan buy the same equipment and tooling that was sold to other companies making the same or

Acquiring Roll Forming Lines, Education, and Training 12-7