Roll Forming Handbook / Edited by George T. Halmos

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(b) Lead-In Flange Design for Curved Edges.If

the furthermost edge of the section is already

formed, then the lead-in surface may startfrom a

tangent point to the outermost element (Figure

5.132). This method is frequently used when the

lead is also used to “push”the leg inwards,

especially when forming ablind corner.

If the lips are already formed and the roll

opposite to the rollwiththe lead-in ﬂange cannot

reachinto the bend line, then those rolls can be

relieved as shown in Figure5.133a. However,if

the bend line to be formed is a“blind corner”

(Figure5.133b), then it is more prudent to

“contain”(boxin) the section by pressing down

the lips (Figure5.133c).

Thediameterincreasecausedbythe lead in both

the“trap”and “lead” rollsmakes it frequently

more economical to splitthe rollsasshown in

Figure 5.134. Thesplit linesonthe drawings are

indicatedwithtriangles.Thissplitting allows the

rollsmarkedT1, T3,and B2 to be madefrom

smallerdiameterblanks, savinginmaterialcost.

This arrangementalsomakes rework,adjustment,

or replacementeasierand less expensive. Further-

more,splitting makesiteasiertoadjustorreplace

rollsifthe blanksizehas to be modiﬁed.

ﬂanges are often not required when the bending of

the section commences at the center partofthe

strip,not at the edges, such as forming of wide

panels and similar products with relatively loose

toleranceonthe lips (last elements at the edges).

Typicalexamplesare showninFigure5.135a–c.

Becausebuildingpanel rollsdonot requirelead

surfaces,the roll diametersdonot have to be

increased.

FIGURE 5.130 Occasionally, theextension of the

forming angle can serve as alead-in.

FIGURE 5.131 Part of the radius at the end of the lead surface can be used for lead. Large radius tangent to one

surface (a) is better than smaller radius tangent to two surfaces.

FIGURE 5.132 Lead can be tangential to the outermost

curved surface.

Roll Forming Handbook5 -82

Traps or leads are frequently omitted for certain

types of forming,especially over a40to50 8 angle.

However,lead-in ﬂange may be incorporated

occasionally even at these angles when the edge of

the strip has to be pushed inwards or downwards

when forming blind corners(Figure5.136a). In

case of blind corners, the application of cluster-

rollsissometimes more effectivethan the lead-in

ﬂanges (Figure5.136b).

5.12.4 Finalizing Roll Edge Radii at

Bend Lines

Twoalternativesare available to ﬁnalize the radii

at the convex and concave partofthe rolls at the

bend lines.

(a) MatchingRadii on Both Topand Bottom Rolls.Manyrollsare designed to fully envelope

(surround) the section at each bend line (Figure5.137a). The rolls are machined to havetheir

forming radii identical to the inside and outside bend-line radii of the section. Rolls designed in

this wayhavetobeturned and set up with morecare; small discrepancies can create problems at

the bend-lines.

(b) Radii on the Convex Rolls Only.During forming,the strip is wrapped around the male die and

the bend lines will be thinner.The outside of the strip at the bend line may not even touch the

FIGURE 5.133 When male roll does not reaches the bend line (blind corner), then it is recommended to forcethe

edge (lip) down to avoid unwanted deformation.

FIGURE 5.134 Rolls are split by necessity as well as to

reducetool material cost.

FIGURE 5.135 Lead-in ﬂanges are not required when forming at the center of section, away from the edge.

Roll Design 5 -83

bend line radiionthe femalerolls.

Therefore, theconcave rolls are fre-

quently machined to the tangent point

at each bend line. Rolls designed to

tangent points can be moreeasily split

(Figure 5.137b) and turned easily manu-

ally.Most manual lathe operators prefer

drawings showing tangents point with

an indication of the radii required for

the corners(Figure5.138).

The effect of the two differentroll

designs (all rolls with radii or convex

rolls to tangent point only) on the ﬁnal

product is not clear.The author assumes

that because of the small roll misalign-

ments in the mill, the “all rollswith

radii” will apply some “cold forming”to

the corners, thus reducing springback.

Rolls turned to their tangent point are

more“forgiving”tosimilar misalign-

ments (Figure5.139). However,ifthe edges are trapped or pushed, then radii of both rolls will

provide abetter radii control to the ﬁnished section. If the straight element adjacent to aradius

is forced towards the curvedelement (across the strip), then it is possible that the strip “moves

FIGURE 5.136 Lead-in ﬂanges are required when it is prudent to “push”the strip inwards(a) to help forming.In

some cases, side-rolls or cluster-rolls would be moreefﬁcient (b).

FIGURE 5.137 Concavecorners of the rolls are fre-

quently cut to the tangent points.

FIGURE 5.138 In the case of manual turning,the lathe operators prefer drawings showing tangent points.

Roll Forming Handbook5 -84

away”fromthe male roll.This movement can result in asharper than intended corner radius

(Figure5.140).

If concaverollsare not split at the tangent point, then the application of asmall radius is

recommended, especially for rolls with thin wall ﬂanges exposed to large side pressure

(Figure5.141). Sharp corners are potential starting points for cracks.

Followingthe “constantarc length”theory,

whenever abendlineis“overbent,”then

thebendradiuswillbecome smaller.

Although some roll designersignorethis

fact becausethe change in radius is small, it

is proper to apply the correct radius

(Figure5.142). Thecorrect radius canbe

calculatedwith the equation usedfor

constant arclengthbending (Equation

5.15)orbythe propersoftware.

5.12.5 Applying AdditionalRadii to

the Rolls

(a) Radii on Split Rolls and Rolls Ending with aFlat Surface.The radius at the edge of asplit roll

should be sufﬁciently large to minimize marking of the product. Marking can be caused by the

FIGURE 5.139 Both top and bottom rolls with corner radii (a) requiremore careful alignment along the mill than

rolls with concave corners machined to tangent points (b).

FIGURE 5.140 The trap forcing down strip edge into the corner may deform the radius if the concave roll is

machined to the tangent point.

FIGURE 5.141 Leaveasmall radius at the tangent point

of the concave rolls to avoid roll edge cracking.

Roll Design 5 -85

slight differences in thematingroll

diameters, outofroundness,out of

center,too big gap between roll bore

and shaft diameter (Figure 5.143).

Rolls that havetobesplit at atapered

partofasection, because they are used

for avarietyofpurposes or because of

their weight, may require large radii at

the sharp edges to avoid damage to the

rolls and marking of the product (see

Figure5.144,right-hand side).

(b) Other Roll Edge Radii.Applying asmall

radius to allsharp edgesisrec-

ommended for safe roll handling and

to minimize edge damages. (A general

note,e.g., “brake corner”0.030 in.

[0.75 mm] R can be an instruction on

all rolldrawings).

To avoid chipping of verysharp,

shallowangle edges, aradius may have

to be included on rollswhich otherwise

do not requireradii. However,ifthe roll

is already made with asharp tip,the tip

cannot be remachined without reducing

the material required to achieve the ﬁnal

height. In this and similar cases, it is

recommended to change the roll design

and apply additional false bends adjacent

to the ﬁnal radius (see Section 5.9.6 and

Figure5.97band Figure 5.144). The arc

of the ﬁnal radius plus the twofalse

bends will provide alarger radius at the

tip of the rollateach pass. Eventually,the

arcsofthe false bends will be ﬂattened at the last pass. The section will havethe correct shape,

height, and will less likely split (crack) at the 1808 bend.

FIGURE 5.142 Usethe correct radius for overbending;

the radius at overbending is smaller than the ﬁnished

radius.

FIGURE 5.143 Small radius ð r Þ should be placed at each

split roll edge to avoid marking of the productand damage

to the rolls.

FIGURE 5.144 To avoid sharp tips on rolls, the roll design can be modiﬁed by using false bends.

Roll Forming Handbook5 -86

Designs incorporating traps can leave

verysharp roll edges. These edges can be

easily damaged. It is recommended to

either avoid them or add asmall radius

to them (Figure5.145a).

Asmall radius is recommended at the

peak of the scoring(grooving) rolls used

when the product must be formed with

sharp inside radius (Figure5.145b).

For rolls forming sine wave corruga-

tions,adifferent kind of radiusis

recommended. The sinusoidal shape is

usually “air bent”and the roll designer

speciﬁes therequiredradiustobe

incorporated onto the outer edges of

the “donut” shaped rolls. This method

workscorrectlyinmostcases

(Figure5.146a). However, to reduce

springback the forming depth maybe

increased by lowering the top shafts. If

the rolls are pushed deeper in between

each other,the material is no longer

tangential to the rolls. This can create

unacceptable sharp forming lines adja-

cent to the radii in the panels (Figure

5.146b). To avoid the sharp lines, it is

recommended to placeadditional radii at

the edges of the rolls, tangential to both

the large forming surface and the ﬂat

ends of the roll (Figure 5.146c).

therolls can damagethe shafts and

make installation difﬁcult. Therefore, it

is recommended to specify asmall radius

at both ends of the bores. The radius can

be 0.030 to 0.060 in. (0.75 to 1.5 mm) in

rolls up to 10 in. (250 mm) in diameter.

Toolarge boreradius can create problems

because of the reduced contact area between the rolls and the spacers or shaft shoulders

(see Section 5.7.2).

5.12.6 Relief

The inevitable surface speed differential along the contour of each roll, caused by the different roll

diameters (Figure5.147), create manyproblems. Different diameter roll segments forming or just

contacting either side of the strip surfacewill create friction, maymark the surface of the product, wear

the rolls, make the productspeed unevenand increase the torque (horsepower) requirement for forming.

To minimize the friction, the rollsare often designed with a“relief.”The example shown on

Figure5.148 shows the top roll relieved by 2to38 .This change eliminates the friction between the top roll

and the product, and by driving the product at the peak of the section provides amorepositive and even

driveatthe pass line height.

FIGURE 5.145 To avoid “chipping” of roll edges,

applying asmall radius is suggested at the critical points.

FIGURE 5.146 Asingle radius at the working surface of

the donut-shape rolls (a) can mark product (b). Added

corner radii eliminate this problem (c).

Roll Design 5 -87

Similar relief is recommended at blind corner

rolls as shown on the right-hand side of aroll in

Figure5.149. Theextensiverubbing action

between the section edge and the roll (Figure

5.149a) will be reduced by the relief to ashort

distance(Figure5.149b).

Theapplicationofsimilar relief is rec-

ommended for panel rolls (Figure5.150). It will

havethe same beneﬁcial effects mentioned above

without changing the section dimensions. A

similar but deeper and parallel cutout is used to

provide spacefor embossed compositedeck webs

(Figure5.151).

Because this type of roll relief works, then the

application of disk rolls (Figure5.152), utilized

by several designers, should also work. Cautious

designers mayplacefull (not relieved) rolls in

passes in which grooves are stretched into the

panel to avoidslipping offthe bend lines. Full

rolls are usually used at the last passes.

5.12.7 Interlocking

Interlocking or “gating”keeps the top and bottom rolls aligned in the horizontal direction and it is highly

recommended. Interlocking requires extra rollmaterial but it savesaconsiderable amount of setup time,

reduces scrap and eliminates some of the troubleshooting requirements.

Typical interlocks (occasionally called “locks”or“gates”) are shown in Figure 5.153.After the rolls are

placed on the shafts and the operator sets the gap at both ends of the rolls, the rollsare properly set. The

gap at both ends of the rollsatall passes should be equal to the material thickness gap between the rolls.

However,afew plants prefer to havea“standard” gap at the interlocks for all tooling.For example,

FIGURE 5.147 Surfacespeed differential exists at everydiameter in contact with the material, except at the pass line.

FIGURE 5.148 The original top rolls are “rubbing”

against the section at different speeds at full contact line

(a). Relieve top rolls (b) are in contact only at one point

with the material, running at the same speed.

Roll Forming Handbook5 -88

a0.100 in. (2.5 mm) gap at the both ends of the

rollsateach pass sets all the rolls in this set to the

proper,say,0.020 in. (0.5 mm) roll gap.

The interlock can go up or down at both ends

of the rolls at anypass, but should not go up at

one end and down at the other end at one pass.

The interlock direction is usually dictated by

economy.Ifthe rolls on one shaft are “forced

apart” during forming,then some designers

incorrectly plan to keep them together by the

rollsonthe other shaft, especially if the female

roll is not split. This is not agood practice

because the top and bottom rolls should never

touch each other.Occasionally,when forming is

not forcing split rolls apart, only the bottom rolls

will havespacers and the top rolls will be

positionedbythe “locks”(“gates”) before

material enters between them. Once the material is between the rolls, it will“self position”the rolls

installed on the other shaft without spacers.

The width of the interlock (“w ”) is determined by its strength required in case of unexpected problems.

The interlock should always be conveniently wide, approximately 0.5 in. (12 mm), to permit the

insertion of afeeler gauge horizontally.The height of the interlock (“h ”) is less critical, it should be at

least 0.4 to 0.6 in. (10 to 15 mm) to facilitate installation. It is advisable to haveasmall taper or radius at

the opposite mating corners (Figure5.154)toassist the installation of the interlocking surfacesduring

setup.

FIGURE 5.149 Relief reduces the contact areabetween the roll and the section.

FIGURE 5.150 Relieved panel rolls reduce friction,

pick-up and horsepower requirements.

FIGURE 5.151 Forming rolls relieved to accommodate composite deck embossments.

Roll Design 5 -89

The 0.002 to 0.003 in. (0.05 to 0.075 mm) gap

(marked“b ”inFigure5.153 and Figure5.154)

should be checked after each setup with amirror.

The interlocking surfacesshould never touch each

other;they are theretohelp setup only.Toavoid

the contact between the interlocking surfaces, it is

better to have all the usual spacers in both top and

bottom shafts.

5.12.8 End Gap

The horizontal surfacesatboth ends of each pass

of rolls can greatly help the setup procedure. The

end gaps, explained aboveinthe interlock section,

can be applied to all roll sets even if they are not

supplied interlocked. End gaps may require some

extra roll material and moreprecise machining of

the rolls, but it willbeasubstantial setup time

saver during the life of the rolls.

5.12.9 Roll Length

(a) Narrow Sections.The rolllength at the ﬁrst

pass is calculated as the strip width plus roll

material required for trap or lead in ﬂange

surfaces at both ends. The ﬁgure is usually

rounded up to the nearest 0.25 to 0.5 in. (5

to 10 mm). As forming progresses and the

sectionnarrows, designers frequently

reduce the roll length to saveroll material.

This reductioniseconomical, but the

simplicity in setup and checking should

also be considered.

For example,the simplest way to

check the vertical alignment of the top

and bottom shoulders as well as the roll

alignments is to placeashortstraight

edge (ruler) to the ends of the rollsatthe

operator side (Figure5.155). If they are

aligned, then the shoulders and the rolls

are most probably aligned properly.To

accommodatethis simple checking,both

top and bottom rolls in apass shall have

the same total length within 0.0005 in.

(0.125 mm).

Thealignment in thelongitudinal

direction can also be simply checked by

placing astraight edge to the outside

surfaceofthe rolls (Figure5.156). One or twolength reductions in 10 to 12 passes can be made, but

the change should be in round ﬁgures such as 0.5 or 1in. (10, 20, or 30 mm) at each side. This will

allowthe placement of the straight edge against the ﬁrst several passes and the next two or three

passes can be checked with an additional 0.5- or 1-in. wide gauge block (Figure5.157). Onceafew

FIGURE 5.153 Interlockingaligns top and bottom

rolls. Gap and parallelness can be easily set at both sides.

FIGURE 5.154 Small taper at both top and bottom lock

helps roll installation.

FIGURE 5.152 Disk rolls are used to form panels by

some designers.

Roll Forming Handbook5 -90

passes of the shorter rolls are checked,

then the straight edge can be movedover

to these and so on.

It is highly recommended not to make

the top and bottom rolls to different

lengths or to reduce the roll length in

everytwo or threepasses to save tooling

cost. The little extra cost will be paid back

manytimes by the ease of setup and

checking.

(b) Adjustable Roll Lengths.Multiple-purpose

rolls used to form products with variable

widths or other dimensions may consist

of complete set of rolls or mixtures of rolls

and spacers. In both cases, the location of

the rolls and the section dimensions are

changed by relocating rolls or spacers.

completeset of top and bottom rolls. Figure5.158,Figure5.77,and Figure5.100fshow atypical

panel rolling mill. The forming starts at the middle and after afew passes, the adjacent corrugations

(cells) are formed. In the ﬁrst pass, only the center rolls are used, the rest of the roll space is ﬁlled

with spacers. Occasionally,some supporting (not forming) rolls are used to guide the ﬂat partof

the panel close the edges. Some setup technicians prefer to havethese supporting rolls mounted on

the spacers with set screws. This will allow them to be movedtothe right location during testing of

the rollset.

FIGURE 5.155 Vertical alignment of rolls can be easily

checked with asmall straight edge if roll lengths are the

same within 0.0005 in. (0.01 mm).

FIGURE 5.156 It is easy to check the shoulder misalignment in the longitudinal direction with astraight edge if all

rolls are the same lengths.

FIGURE 5.157 To save1to 2in. (25 to 50 mm) or more of roll material, aone or two length reduction maybe

made.

Roll Design 5 -91