basic roll + strip width

8/11/2019 BASIC ROLL + strip width

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Roll form tooling design for air bending

Selecting a techique for reduced distortion

By Hanhui LiApril 10, 2007

Several techniques are used commonly to reduce profile distortion when air bending with aroll former. hese include small!radius forming, false bending, vertical side rolls, and angle

side rolls.

"hen a bend is formed with the air bending process #air bend$, the interior of the bending corner can%t bereached by either the top roll or the bottom roll, ma&ing it difficult to control the part%s profile and dimensions.'igure 1 illustrates a typical air bend. he theoretical formed profile is the desired profile. he actual formedprofile is the finished part, which was distorted because the top roll couldn%t reach the interior corner to holdit in position. he bottom roll flange lifted the section and distorted the profile. Several techniques canreduce such distortion in parts formed by air bending.

The Small-radius Forming Technique

Figure 1Scoring, grooving, beading, perforating, and interruptive slitting are techniques that can reduce distortion in air

bending.

'orming a radius smaller than the metal thic&ness is a suitable technique for the air bend in Figure 1.Scoring, grooving, beading, perforating, or interruptive slitting wea&ens the bending trac&. Scoring is themost commonly used technique. he score depth should not be deeper than one!third the metal thic&ness incold roll forming applications. (f the score is deeper than one!third the metal thic&ness, the metal may brea&at the scored trac&. (n hot roll forming, a grooving trac& is easy to form and prevents corner crac&ing.

he beading technique is suitable for thin metal applications. )eading doesn%t brea& the protective coatingand doesn%t reduce the thic&ness at the bent section.

A rotary punch performs perforating or interruptive slitting.

The False-bend Technique


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Figure 2wo e*amples of the false!bend technique show how the bottom section is curved to allow the top roll to ma&e the

+0!degree angle at the left side of the part.

he false!bend technique e*poses the blind bend #the air bend$ to the top roll or bottom roll by curving astraight section #see Figure 2$. After the section is curved, the top roll can physically reach the interior bend

and form it to +0 degrees precisely. he station after the false!bend station flattens the curve. sually thefalse!bend design needs an additional station.

The Vertical Side Roll Technique

Figure A single vertical side roll #A$ is better than using conventional rolls. wo vertical side rolls #) and -$ provide more

precision than a single side roll does.

he vertical side roll located at the outside of the bend is the outer side roll. he forming force from the outerside roll has the same direction as the bending action. (t forms a better!quality bend than the conventionalrolls in 'igure 1. he vertical side roll located at the inside of the bend is the inner side roll. he function ofthe inner side roll is forming the desired radius at the bend.

he single roll design in Figure ! cannot control the radius dimension because tooling cannot reach theinner corner. he double side roll design in Figure B forms the profile and the dimension more accuratelythan the roll design in A.

he side rolls, which are mounted in the same central line plane as the conventional rolls, are calledstationary side rolls, as shown in 'igure A and 'igure ). he stationary side rolls and conventional rollsform a rotational e*trusion head that squee/es the formed section from all directions up, down, left, andright. his e*trusion process provides strict control over the profile and dimension.

Single side rolls and double side rolls can be mounted before the conventional roll station #see Figure "$.his arrangement allows more space for large side rolls.


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The !ngle Side Roll Technique

Figure #Angle side rolls can reach the inside corner #A$ and the outside corner #)!$ for precise bending.

he inner angle side roll can contact the inner bend on both the vertical and hori/ontal surfaces to form asmall and accurate bending radius. he single side roll in Figure #!is referenced to the bottom roll. wo!angle side rolls are shown in Figure #B. he concave top roll in Figure #"provides more forming contactsurface, if needed.

he double angle side rolls can be mounted before the conventional roll station, as shown in Figure #$.his is similar to 'igure - in that it provides more space for large side rolls.

Stationary %andrel

Figure &

A roller mandrel is mounted to the roll stand. (t is inset into a conventional roll to form an air bend.(n many cases an air bend can be accomplished effectively with a stationary solid mandrel mounted in aconventional roll #see Figure &$. (t combines both the roll and mandrel features. he roller and mandrel areattached to the roll stand. he roller is captive. he hole on the mandrel is more than a half circle, which&eeps it in place hori/ontally, and the set screw prevents the roller from escaping vertically.

Hanhui Li is senior engineer with Worthington Armstrong Venture (WAVE), 9 Old Lincoln Highway, Suite2, !al"ern, #A $9%&&, '$22$2%2, hanhui*li+armstrongcom

Reference


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-eorge . Halmos, /oll 0orming Hand1oo (.oronto3 .aylor 4 0rancis -rou5, 2')

anhui 3iSenior 4ngineer,"orthington Armstrong 5enture

anhui 3i is senior engineer with "orthington Armstrong 5enture #"A54$, + 6ld 3incoln ighway, Suite 200,alvern, 8A 1+99, :10!722!122.'orthingtonindustries(com

hanhui)li*armstrong(com

BASIC ROLL-FORM TOOLING

DESIGN:

PROCESS OVERVIEW, INSTRUCTION

AND TIPS

1.0 INTRODUCTION

This paper is intended to provide

basic roll tooling design instructionand tips for the beginning or novice

designer. In my experience, the ideasexpressed in this report can be applied

to many situations but I will stop

short of claiming that these are the only solutions. Many roll designers have differentapproaches to both design and development (testing of tooling, and ama!ingly enough,

there is more than one way to successfully form a profile. "owever, there are common

design practices that must be understood and applied to the design process, coupledwith a certain degree of magic (gained through previous experiences.

In other words, a mixture of science and art is still very prevalent today in this industry.#or a roll design, considering all the variables and applying theory whenever possibleis vital in producing a good running product, with minimal start$up problems. %ecause

the roll forming process has a seemingly limitless capacity to produce complex profiles

with &ust as many variables, a high percentage of designs are one$of$a$'ind. This is whytheory can only go so far. ast experiences, correctly applied, are still the 'ey ingredients

to the design and development of

these applications.
http://www.worthingtonindustries.com/http://www.worthingtonindustries.com/mailto:[email protected]:[email protected]://www.worthingtonindustries.com/


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More commonly formed, or basic shapes, tend to have fewer variables and limitations,

which in turn have higher levels of results which are both theoretical and repeatable. )iththis in mind, we will only scratch the surface in this basic design guide. The basics are

essential for the beginning designer.

2.0 DESIGN PROCESS OVERVIEW

#or each new tooling re*uirement, the designer should use the following steps+

. -evelop a cross$sectional drawing (with part, material and mill specifications

tolerances./. 0alculate the 1stimated 2trip )idth.

3. roduce a %end rogression or #lower.

4. 5ayout and design the roll tooling around the flower.6. Incorporate fixtures, guides, side rolls and straightening devices where applicable.

7fter the cross$section has been finali!ed, and before the rolls can be designed, the proper

number of passes and rolling mill must be determined. 7t the same time, other *uestions

need to be answered such as+

. 2teel type and grade./. re$notching, pre$cut lengths, multiple gages.

3. 0ombination sets.

4. 2econdary processes, which can limit roll design options.

3.0 CALCULATING THE ESTIMATED STRIP WIDTH

robably the most common problem associated with designing roll tooling is predictinghow a forming bend will react during the rolling process. 8sing the proper 9 factor or

%end 7llowance is the main item the designer must consider when calculating a strip

width. :arious factors contribute to the bend allowance such as, material type and yield

strength, profile characteristics such as large radii or ;


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#irst, consider the material to be formed. 8sing steels with yield strengths of 3


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or box forming. )hen this occurs, forming the remaining angle from bend C/ helps to

reduce distortion in the radius of bend C.

FIG #2: EAMPLES OF AIR FORMING AND FLOWER WITH ROLL

CONTACT

If the bend corner of C/ has a pre$punched slot or hole, it would be better to finish the

bend while C is flat (


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4 / OUTS WITH DESCRIPTIONS


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T>PES OF /TRAP ROLLS:


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?.0 ROLL DESIGN TIPS

)hen forming a bend which has a t or less inside radius and when box forming, acoining or bead pass is very effective in setting the corner. %y coining the material a

slight thinning will occur. "owever, the finished bend corner will be crisp.

FIG #: COINING PASS

7nother tip to reduce material scuffing is to idle flange rolls so they are not driven. The


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speed at which these idled rolls spin is dictated by the section (at or near the highest point

of the leg rather than the millsK drive. Jenerally this method is necessary when the

formed legs of the profile are greater than D


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2ide rolls, or rolls which are mounted on a vertical axis and located between passes is anexcellent way to help a profile enter the main roll passes. These are especially good for

light and heavy gage materials ali'e. Thinner gages tend to spring while heavy gages

have high lateral forces against the flanges. In addition to smoothing out the formingtransition between passes, side rolls also reduce scuffing of the vertical legs because they

spin on the same axis that the profile travels.

FIG #11: T>PICAL SIDE STAND CUSTOM DESIGN BETWEEN PASS SIDE

ROLL STAND


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contain all of the same steps that are needed to complete a roll design. There is much

more that could be added in this report detailing other areas of a design. 7gain it is only

meant to give the beginning designer a guide and hopefully it will be used as a referenceto help you. Jood luc'L

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basic roll + strip width

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