Roll Forming Handbook / Edited by George T. Halmos

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outside dimension mayalso be noted on the drawing if the partmust ﬁt into the inside of another

component.

Owing to variation in material thickness, it is preferable to use the same product surfacefor

dimensioning.

In most cases, it is preferred to dimension roll formed components to the intersect points rather

than to the center,ortothe starting point of the radius. The distances between the intersect points

and the enclosed angle can be used for dimensioning,but maylead to mistakesand errors

(Figure 9.35).

So-called “base line” dimensioning is rarely used to deﬁne roll formed sections (Figure9.36).

9.6.2 Tolerancing

Tolerancecan be deﬁned as the total amount by which aspeciﬁc dimension is permitted to vary. The

toleranceisthe difference between the maximum and minimum limits. In other words, tolerancing

speciﬁes the total permissible variation in the size

of adimension and it basically describes the

difference between the limits of size.

“Bilateral tolerance” is atolerancethat is

expressed as plus and minus values to denote

permissible variations in both directions from

the speciﬁc size.

“Unilateraltolerance” is atolerance that

applies only in one direction from the speciﬁed

size, so that the toleranceinthe other direction

will be zero (for explanation, see Figure 9.37).

“Standardtolerances” formanufacturing

plants can be achieved at standard production

rates, at speciﬁed costs, without much extra

precaution. Therefore,changing or modifying

the equipment or tooling can inﬂuence these

established tolerances.“Standardtolerances,”

however, canbespeciﬁedbygovernment,

industry,orother trade standards.To manufacture

FIGURE 9.36 Base line dimensioning is not used for roll formed product.

±p

− n

− 0

FIGURE 9.37 Bilateral and unilateral tolerances on

drawings.

Roll Forming Handbook9 -24

products within these “standard tolerances”the manufacturer must havethe right qualityequipment,

tooling and properly trained personnel.

Tolerances applied to roll formed parts can be assigned into ﬁve groups.

Length and related tolerances

Tolerances on section dimensions

Toleranceondeviation from straightness

Tolerances applied to other featuressuch as holes, dimples, and so on

Other tolerances such as burr,appearance,and so on.

9.6.3 Length and Cutting Tolerances

The length toleranceofparts made from precut blanks depends on the accuracy of the precutting process

but rollpressure, rolldesign and other factors can alter the precut length.

If the partiscut to length in the roll forming line, then the most critical factors inﬂuencing the length

toleranceare the type and condition of the cutoffpress, the method of die accelerating and length

measuring.The length tolerancewillbealso inﬂuencedbythe speed of roll forming,roll forming tooling,

shape of the product, lubrication, location of holes, skill of operator,temperature, and afew other factors

[223]. Therefore,the partdesigner should realize that the length tolerancedepends on the capabilityof

the line used to produce the partatoptimum speed. If the partlength tolerance must be tighter than the

line capability, than either the line has to be run slower, or parts of the line (e.g., die accelerator) has to be

replaced, or acompletely new line, capable of producing parts within the speciﬁed tolerance, has to be

acquired.

Squarenessofthe cutend is seldom speciﬁedbecause it is expected that deviationfrom

perpendicularityofthe cutoffdie to the direction of rollforming is usually better than normally

required. There are cases, however, especially in wide panels, wherethe inaccurate mounting of die rails

or location of the press or other factors will create an “off squareness”problem.

Offsquarecuts are occasionally speciﬁed, such as in the case of gable ends or tapered or curved

products. In these cases, the angular toleranceshould be speciﬁed on the drawing.

9.6.4 Section Dimension Tolerances

ASME Y14.5M or other national standards and the previously mentioned examples provide aguideline

for the tolerancing of roll formed proﬁles. Afew additional examples are shown in Figure 9.38.

Figure9.39aand Figure9.39bshow panels with multiple cells. Both the cell center distance(pitch) and

the coverage haveatolerance.

Under other conditions, the accumulated stackedtoleranceiscalculated as

acc

ﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ

þ t

þ ···þ t

In the case of roll forming, however,the toleranceoncoverage is not necessarily the mathematical

function of the accumulated tolerances of the cells. According to the interpretation used by the industry,

anycell-to-cell distanceshould be within the speciﬁed tolerance, but the toleranceofthe overall coverage

is independently speciﬁed. Figure9.39 shows adifferent wayofdimensioning the cell distance, coinciding

with the most frequently used method to measurecelldistances. The toleranceofcell distance, however,

should not be incompatible with the dimensions and tolerances shown on the section drawing.

The dimensions and tolerances on the cross section of a“U” channel shown on Figure9.40 will also be

affected by the manufacturing method, tools and equipment. The dimensions will be inﬂuenced by the

factors shown in Table 9.7.

During rollforming, the material is “wrapped around” the male roll. Because the inside dimension ð a

cannot be changed (unless the rollissplit), the outside dimension will usually be affected by changes in

the material thickness. Forexample, a0.078-in. (2-mm) thick steel may haveacommercial thickness

Designing Products for Roll Forming 9 -25

toleranceof ^ 0.005 in. (0.13 mm). If the inside “U” channel is 1.0 in. (25.4 mm), then as aresult of

changes in material thickness, the outside dimension ﬂuctuates between 0.990 and 1.010 in. (29.14 and

29.66 mm). This ﬂuctuation will be in addition to the tolerancerequired for forming,springback, set up

variations, tool wear,and so on. Therefore, it is not correct to specify,for example, a ^ 0.004 in.

( ^ 0.1 mm) toleranceonthe outside dimension ð a

Þ when the two thicknesses of the material alone

require atoleranceof ^ 0.010 in. ( ^ 0.26 mm). Even arestrictedthickness toleranceof ^ 0.002 in.

( ^ 0.05 mm) will requirea^ 0.004 in. ( ^ 0.1 mm) tolerancefor thickness variation, plus all the

5.39

5.41

5.39

product within

9.38(i) dimensions

incorrect

dimensioning

1.70

2.2

2.50

product within

9.38(g) dimensions

correctly

dimensioned

dimensioning

acceptable

dimension X

not acceptable

acceptableacceptableas shown on

drawing

(a)

(e) (f) (g)

(h) (i) (j)

(b) (c)

(d)

5.40

±.01

90°

88°

92°

75°

±2°

TYP

1.70 (ref.)

insufficient

dimensions

2.20

±.01

2.50

±.01

2.50

±.01

2.20

±.01

2.50

2.20

1.70

FIGURE 9.38 Interpretation of tolerances.

Dimensioning the

center of cell

(a)

(b)

6.00±0.05

18.00±0.05

Typ. not accumulative

6.00±0.05

Dimensioning at the corner

of cell (seldom used)

FIGURE 9.39 Typical dimensioning of building panel cells.

Roll Forming Handbook9 -26

additional tolerances mentioned above.One must remember,however,that an extra pricemust be paid

for restrictedthickness and width or other tolerances.

9.6.5 Deviation from Straightness and Flatness

Products, which are within the speciﬁed cross-sectional tolerances, are not necessarily acceptable unless

they are within the required straightness and ﬂatness tolerances.

Longitudinal bow, cross bow, twist and ﬂare(see Figure4.1 and Figure10.38c–l)should be speciﬁed to

be tested on aﬂat surface, with one end of the product ﬁrmly held down against ahorizontal surface.

Longitudinal bowisoccasionally checked against astraight edge or twoproducts are held against each

other with bows facing each other.

Some standardsspecify the maximum height of waviness and, occasionally,the minimum distanceof

peaks from each other but in most cases edge or center waviness, ripples, and herringbone effects are

checked and judged visually.

9.6.6 Tolerances Applied to Other Features (Curvatures, Holes, Notches,

Embossments, etc.)

In case of curved(swept) products, either the radius, the apex (height of the center of the product above

astraight line between the ends), or adeviation from acurvedtemplate is speciﬁed with appropriate

tolerances. The sweep number used by the automotive industryisusually transferredinto achecking

template or ﬁxture.

It is recommended that each drawingindicates these tolerances and often the method of measuring

them, or refers to acompanystandard.

TABLE 9.7 Factors Inﬂuencing Dimensions in Figure 9.40

Dimension Inﬂuenced by

(preferred) Tooling, springback,ﬂare, height of leg, and dimension b

(avoid)Same as above, plus variation in material thickness

(preferred) Tooling, toleranceonstrip width, movement of coil, camber

(avoid) As b

plus twice the variation in material thickness

(preferred) Method of piercing, gaging, camber,and so on

(avoid) As c

plus variation in material thickness

e (preferred) Method piercing and gaging

(preferred) To oling and springback

(avoid) Tooling, springback and variation in material thickness

b Springback and tooling

FIGURE 9.40 Dimensioning cross section of a“U” channel.

Designing Products for Roll Forming 9 -27

Dimensioning and tolerancing of holes, notches, embossings, and other features may followthe ANSI

514.5M Standard. The importanceofhow the dimensions and tolerances are applied is demonstrated

in Table 9.2 to Table 9.6 on asimple roll formed “U” channel with six holes on the web.

The application of dimensioning in these examples shows how the manufacturing method and tooling

affects the wayofdimensioning and tolerancing.These examples also illustrate how the manufacturing

personnel are directed to select technology, equipment, tooling,production speed, material, and

inspection gages by the occasionally arbitraryselected application of dimensioning and tolerancing.

The “U” channel shown in the above-mentioned tables could be manufactured by forming precut

blanks or cutting the product after roll forming. The holes can be pierced individually or by two,three,

or six at atime, prior to,during,orafter forming. The tables show the correlation between manufacturing

methods, dimensioning and tolerancing.Manufacturing processes based on piercing one hole at atime

or forming the channel in apress are not included in the tables.

Tolerancewillbeinﬂuenced by:

“ a ”: Length toleranceofprecut line

“ b ”: Length toleranceofprepiercingpress

“ c ”: Length toleranceofrollforming line

“ d ”: Length toleranceofroll forming line (with pick-up mechanism)

“ e ”: Punch position in die set

“ f ”: Forming tolerance

“ g ”: Gaging fromcut edge

“ h ”: Gaging from hole

“ i ”: Gaging from formed edge

“ j ”: Accuracy of strip feeder

“ p ”: Uniform but accumulating, tolerances of “ e ”

“ r ”: Dimension “ r ”iseither random or related to dimension “ e ”tolerance if the ﬁrst case is not

applicable, in the second case, it depends on the accuracyofthe cutoffdie equipped with pick-up

pin.

“ w ”: width tolerance(slitting)

“ x ”: camber of blank

“ y ”: camber of formed product

The top illustration in Table 9.2 showsthe manufacturing process where the “U” channel is roll formed

from precut sheets or strips having acamber.When twoadjacent holes in the web are pierced in one hit,

the location of the twoholes from the edge is usually set by gaging the pieceatthe end. The location of the

other pair of holes can be set by gaging the holes from the piercedholes or from additional end gages.

The toleranceinthe longitudinal direction will depend on the method of the gaging.During piercing,the

strip is usually pushed against one longitudinal edge; therefore, the holes in the blank will follow the

curvatureofthe precut strip.

During rollforming, however,the forming rollswill straighten out the section and the holes will be an

even distance from the formed corners.

When three holes are pierced at atime, the toleranceofthe ﬁrst hole from the edge will depend on the

accuracy of end gauging,but the tolerancebetween the threeholes will be verytight. If the second rowof

three holes is gaged from the same side of the strip,then the tolerance between the tworowsofholes will

be better,but if it is gaged fromthe opposite side, then the strip width tolerancehas to be added to the

tolerancebetween the rows of holes. The holes will be in one line in the precut blank but after roll

forming they will be out of line as much as the starting strip bowed.

If six holes are pierced at the same time, then the relative location of the holes to each other can be kept

at averytight tolerance. They will be out of line again (the center hole will be closer or further from the

formed corner)bythe amount of bow in the starting strip.

Roll Forming Handbook9 -28

Table 9.3 shows the effect of the manufacturing process on the piercing tolerancewhen two or six holes

are pierced in atight line (with ﬂying die), or in aloose line (using astrip feeder and stationarydie), with

loop between press and roll forming line, when the holes are prepierced.

Table 9.4 shows the different possibilities of punching the holes and cutting the product to length in the

line, after forming.

Table 9.5 showsthe possibilities of piercing two, three or six holes at atime after cutting the formed

channel to lengths.

Table 9.6 is based on rotary punching of strip beforeroll forming.

The examples above show that there are 17 different ways, with 17 different groups of tolerances, to

pierce and form such asimple product. Additional holes and notches and different shapes can complicate

the issue further.Therefore, if the designer expects that his or her speciﬁcations be followed in the plant,

then he or she must apply the dimensions or tolerances in away that is best suited to the manufacturing

method.

9.6.7 Other Tolerances Such as Burr and Appearance

The most difﬁcult is to establish standards for appearance,scratch or other marks, waviness and other

characteristic that cannot be measured at the manufacturing plants. Manyofthese featuresare judged

by eye, inﬂuencedbythe available light, eyesight, anticipated reaction from aspeciﬁc customer,orother

factors.

In the case of burr,itisimportant to specify the direction of the burr on the drawings but burr size or

other featuresare seldom speciﬁed on the drawings because at most rollforming plants they can be

measured only with difﬁculties or not at all.

9.6.8 Inﬂuence of the Applied Tolerances on Cost

The designer’sdream is to manufactureeverything to exact dimensions or at least to verytight tolerances.

Tighttolerances can reduce product cost and simplify assembly.They can also reducewaste material and

scrap,and improvethe qualityofthe product.

Manufacturing to tight tolerances, however,usually costs more. It requires moreexpensiveand better

qualityequipment, better tooling,with morefrequent and thorough maintenance. To achieve tight

tolerance, the production speed may havetobesloweddown, and larger number of products must be

checked and possibly scrapped. More precise and expensive measuring instruments and gages are

required, operators havetobebetter trained and the whole organization must be gearedto

manufacturing products to tight tolerances.

Manufacturing products to loose tolerances, on the other hand mayalso cost more. Additional

material is wasted, assembly and erection costs can increase, and quality, most probably,willbeinferior.

(for additional comments, see Chapter 4.)

With an increased complexityofshape and hole patterns and other requirements, additional thought

should be directed to the method of dimensioning and tolerancing.Properly dimensioned and

toleranced product drawings can save from $1000 to $100,000 or moreinequipment, tooling,material

and manufacturing costs compared with the drawing of identical parts with improper dimensions and

tolerances.

Dimensions and tolerances should suit requirements, available equipment, tooling and among others,

manufacturing methods. Therefore, it is strongly recommended that the use or reference to the general

“machining tolerances” preprinted on the drafting paper is avoided.

References

[223] Halmos, G., Length tolerancefor roll formed parts, Prec. Met.,December,33–36, 1981.

[382] AISI (American Ironand Steel Institute). Appropriate Standards and Guides.

Designing Products for Roll Forming 9 -29

[420] Canadian StandardAssociation. Appropriate Standard and Guides.

[421] Dimensioning and Tolerancing,ASME National StandardY14.5A.

Further Reading

[341] Roll forming looks for ways to educate designers, Prec. Met.,March, 38–39, 1976.

[342] Production design techniques for coldroll forming, Mach. Des.,December,106–112, 1956.

[343] Halmos, G.T.1980. Design for manufacturability. Fifth International Conference on ColdFormed

Steel Structure,November 1980, St. Louis, MO.

[344] Designer’sguide to roll forming, Prec. Met.,April, 44–46, 1976.

[345] Halmos, G.T.Thin-walled structures; inﬂuenceofmanufacturing technologyondesign.

Unpublished paper.

[347]Halmos, G.,Practical design guidefor brake&rollformedproducts, Fabricator,July/August,1982.

[348] Halmos, G. 1980. Design for manufacturability. Fifth International Conference on Cold Formed

Steel Structures Proceeding,November,1980.

[349] Halmos, G., Rollforming to tight tolerances, Fabricator,March/April, 1988.

[350] Halmos, G. 1982. Practical grain bin design-manufacturing and erection considerations. Inter-

national Conference on Cold Formed Steel Structures Proceeding,November,1982.

[351] Halmos, G. 1982. Inﬂuenceofforming technologyonproduct design. Second International

Conference RotaryMetalworking Proceeding,October,p.187, 1982.

[352] Halmos, G. 1986. Rollforming to tight tolerances. SME Conference Proceeding,September 1986.

[415] Halmos, G. 1986. Designing automotive products for rollforming. SME Conference Proceeding.

[418] Yu,W.W.1979. Cold Formed Steel Structures Design Analysis Construction.Robert E. Krieger

Publishing,Huntington.

[419] Schuster,R.M. 1974. Design in Cold Formed Steel.UniversityofWaterloo Press, Waterloo.

Roll Forming Handbook9 -30

Equipment Installation,

Roll Setup,

Maintenance, and

Troubleshooting

GeorgeT.Halmos

Delta Engineering Inc.

10.1 Installation of Roll Forming Lines ................................. 10-1

Plant Layout

†

Service Lines (Electrical, Compressed Air,

Water etc.)

†

Space RequirementsAround the Roll Forming

Mill

†

Foundations, FoundationBolts, and Leveling

†

Installing Roll Forming Mills

†

Aligning and Installing

Uncoilers

†

Aligning Presses

†

Aligning Other Equipment

in the Line

†

Start-Up and Training

10.2 Roll Installation and Setup ............................................. 10-8

Considerations for Roll Installation

†

Installing Rolls on the

Shaft

†

CheckingRoll Gaps

†

Setting up Straighteners

10.3 Maintenanceand Spare Parts......................................... 10-14

Manuals

†

General, Preventive, Predictive Maintenance

Program

†

Lubrication Program

†

Lubrication Instruction

†

Mill Maintenance

†

MaintenanceofMechanical Presses

†

Maintenance of Hydraulic and Pneumatic Presses

†

Maintenance of Other Equipment in the Line

†

Aligning

Mill Shaft Shoulders

†

Handling and Storing of Rolls

and Tools

†

Spare Parts

10.4 Troubleshooting and Trouble Prevention ...................... 10-32

The Root of Troubles

†

Problems Created by Design and

Drawings

†

Problems Created by the Material

†

Problems

Caused by Equipment

†

Problems Caused by Tooling

†

Troubles with the Know-How of the Workforce

†

Troubleshooting

†

Trouble Prevention

10.1 Installation of Roll Forming Lines

10.1.1 Plant Layout

It is expensivetoinstall arollforming line and costly to move it; therefore, they generally stay in place for

manyyears or even decades. At that location, during the rollforming operations, thousands of coils

are loaded on to the uncoiler and millions of pieces of ﬁnished product are transportedfrom the end of

10-1

the line. To minimize material handling costs, it is essential to haveagood plant layout with an efﬁcient

ﬂowofmaterial.

To layout the inside of aplant properly,some of the factors listed below(among others) must be

considered:

1. Areaoccupied by the line

2. Spacerequired to operate, maintain, and repair the line safely and comfortably

3. Arearequiredfor the incoming material, ﬁnished products, and spareparts

The methods of handling coils and ﬁnished products are also importantconsiderations. Toomuch

unnecessaryspacewill increase operating costs (indirectly increasing the overhead cost, which includes

heating,maintenance, taxes, etc.). On the other hand, too little ﬂoor areawillrestrictthe efﬁciency of the

line, and possibly affect the safetyofthe operators. For additional details, see Chapter 8.

10.1.2 Service Lines (Electrical,Compressed Air,Water,etc.)

Rollforming lines usually require only electricityand compressed air.Water and drainage are only

needed for seldom-used water-cooled brakes or for special equipment such as resistant welders.

Each rollforming line is connected to amain electrical switch box, which contains the main

disconnectingswitch. The power(industrial voltage to the motors, 110 or 220 volts for controls, lights,

etc.) is fed through conduits from the main electrical boxtothe line. Compressed air is supplied by pipes

to the uncoiler,mill, die accelerator,and other equipment.

Installing the conduits and the pipes on the ﬂoor is less expensivethan to burythem, but they create a

safetyhazard. They can be covered with formed checkered plates, but this method is not recommended

for areas with forklift truck trafﬁc. The best waytoprevent ahazardous situation is to install the conduits

and the air pipes into trenches, covered with ﬂat checkered plates (Figure10.1).

Electrical and air connectionsbetween the mill, the press and other components, which are not

located in the regular walking area, can be made above the ﬂoor surface. Air and water lines are

occasionally fed directly from the ceiling into the machine, but this method is not practical if cranes

are used in that area.

It is very helpful if the supplier of the roll forming line provides aﬂoor layout showing the electrical,

air and other requirements well before the installation. Atypical example is shown in Figure10.2.Itis

prudent to install larger diameter conduits and air pipes than those needed at the time of installing

the line. During installation, and sometimes manyyears afterwards, additional wireshavetobepulled

through those conduits and more air could be required for the retroﬁt pneumatic devices.

RECOMMENDED

(a) (b)

PNEUMATIC

HYDRAULIC

ELECTRICAL

RECOMMENDED

NOT RECOMMENDED

AVOID

FIGURE 10.1 Power conduits, compressed air,and hydraulic pipes run in covered trenches.

Roll Forming Handbook10-2

10.1.3 Space Requirements around the Roll Forming Mill

Arollforming line layout usually shows only the spaceoccupied by the equipment itself, but in aplant

layout additional space requirements havetobeincluded to ensure efﬁcient and safe operation.

In the plant layout, the following space requirements should be considered:

Asafe walkwayfor the operators at the operator side of the line

Extra working space around the consoles and control panels

Sufﬁcient space for paperwork (workorders,drawings, etc.)

An areaorabench for the hand and powertools required for operating/maintaining the line

Awalkway at the back of the line

Awalkway between the equipment to the back of long lines

Safe distances from electrical switch boxes, as speciﬁed by law

Sufﬁcient space to ensurethat the equipment can be maintained and parts can be replaced safely

withthe aid of the required lifting equipment

Spacefor forklift truck trafﬁc

Spacefor crane attachments

Coil storage space at the uncoiler

Finished products handling,marking,marshaling, and packaging area

Spacefor ﬁnished product qualitycontrol (table, lights, measuring ﬁxtures, ﬂoor area to check

waviness, etc.)

Spacefor the packaging material (tote boxes, lumber,strapping,etc.) for use during production

Spacefor scrap and offcuts

Spacetostorerolls and roll-storage devices

Spacetostorerafts (plates) for other sections

Spacetostorecutoff, prepunching,and other dies

Spacetokeepthe equipment used for the secondaryoperations that are temporarily removed

from the line

Spacefor lubricant for forming

The abovespacerequirements are directly related to the rollforming line, but do not include: coil storage,

coil upenders, ﬁnished product storage, and other commonareas speciﬁed in the plant layout.

FIGURE 10.2 Typical trench layout for power and air lines.

Equipment Installation, Roll Setup, Maintenance, and Troubleshooting 10-3