Roll Forming Handbook / Edited by George T. Halmos
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[57] Gradous, F.,Rollform design —driving diameters, Tool. Prod.,June, 92, 1967.
[58] Gradous, F.,Roll form design —strip width calculations and the section flower, Tool. Prod.,
February, 95–110, 1968.
[59] Gradous, F.,Rollformdesign—roll-passdesign—making thecurl, Tool.Prod.,April,79–83,1969.
[60] Gradous, F.,Roll form design —roll-pass design —placement of bend allowance, Tool. Prod.,
February, 61–64, 1969.
[61] Vanderploeg, E.J., Roll forming —simple method for designing rolls, Tool Eng.,October,59–65,
1953.
[62] Angel, R.T., Designing tools for cold roll-forming, The Iron Age ,November,83–88, 1949.
[63] VonBonhumil Pocta, Die Herstellung Kaltgefertigter Profile aus Stahl fu
¨
rden Leichtbau, Neue
Hu
¨
tte,10.Jg.Heft3,156–161, Ma
¨
rz, 1965.
[64] Halmos, G.T.and Dobrev, A. 1993. Roll design. SME Conference Proceeding,December.
[65] Li, H., Developing adesign for coldroll forming, Fabricator,April, 28–37, 1998.
[66] Li, H. and Li, K.-X., Predicting slit width in coldroll forming parts, Fabricator,April, 28–31,
1999.
[67] Benson, S.D., Kfactors, bend deductions, and bend angles past 908 (a look at some
misunderstood areas of bending), Fabricator,90, February, 32–35, 1999.
[70] Trainer,D., Preparing for roll form tooling design, Roll Form.Ind.Quart.,9,2,7–12, 1995.
[71] Sedlmaier,A., Simulating the roll forming process on the computer,October, Fabricator,1996.
[72] Sedlmaier,A., CAD development for roll formed products, Sheet Met. Ind.,November,1997.
[73] Heislitz, F.,Livatyali, H., Ahmetoglu, M.A., and Altan, T.,Simulating roll forming by computer,
Fabricator,April, 1997.
[74] Halmos, G., Computer aided roll design —anart or ascience? Fabricator,November/December,
22–24, 1985.
[75] Ona, H., Jimma, T.,and Kozono,H., Acomputer aided design system for cold roll forming,
Adv.Technol. Plast.,1,508–513, 1984.
[76] Yuen, W.Y. D. and Ellen, C.H., Newdevelopments in CAD for roll forming, Adv.Technol. Plast.,1,
514–519, 1984.
[77] Profil, CAD construction in der Blechverarbeitung, Blech Rohre Profile,34, 6, 476–477, 1987.
[79] Milner,D.A. and Deeley,G.W., Computer aided design and manufactureofrollforms, Met. Ind. ,
November,1983.
[80] Bhattacharyya, D.,Smith, P. D.,Yee, C.H., and Collins, I.F., The prediction of deformation length
in coldroll-forming, J. Mech. Work. Technol.,9,181–191, 1984.
[81] Jorgens,L., Computerized tooling for roll forming, Prec. Met.,June, July,August, 1977.
[82] Rhodes, A., Computer-aided design and manufactureofrolls for cold roll forming machines,
Sheet Met. Ind. ,August, 643–650, 1982.
[83] Rhodes, A., Boardman, A.S., and McIntos, D.H. 1979. Computer-aided design and manufacture
of rolls for cold rollforming machines, First International Conference on RotaryMetal-Working
Processes,London, UK, November 20–22.
[84] Marklew,J.J., An importantjob for the computer in coldroll-forming, Mach. Prod. Eng.,9,June,
530–534, 1976.
[85] Miller,D.A., CAD/CAM for coldroll-forming tools, Prod. Eng.,November,52–55, 1983.
[86] Editorial, CAD/CAM cuts rollform tooling time, Prec. Met.,April, 37–40, 1985.
[87] Krause, F.J.,Computer speeds roll design, Prec. Met.,July,29–34, 1981.
[88] Editorial, Roll form die design time slashed from days to hours, Mod. Met.,May,38–40, 1980.
[90] Stauffer,R.J., CAD/CAM comes to precision roll production, Manuf. Eng.,June, 67–68, 1978.
[91] Kiuchi,M., Koudabashi,T., andEto,F., Developmentofsimulationmodel of roll-forming processes
—multi-purpose CADsystemfor roll-forming processI, J. JSTP,27, 306, 874–881, 1986–7.
[92] Kiuchi, M. and Koudabashi, T.,Computer aided simulation of roll-forming process of section
steels —multi-purpose CAD system for rollforming process II, J. JSTP,27, 308, 1091–1098,
1986–9.
Roll Forming Handbook5 -112
[93] Kiuchi, M. and Koudabashi, T.,Computerized design system of roll flower —development
of generalized CAD system for cold roll-forming process III, J. JSTP,27, 311, 1349–1355,
1986-12.
[94] Kiuchi, M. and Koudabashi, T.,Application of computerized design system of roll flower —
development of generalized CAD system for cold roll-forming process —IV, J. JSTP,28, 312,
49–57, 1987-1.
[96] Baranowski,D., Whyflexibilityisimportantinrollformsoftware, Roll Form.Ind.Quart. ,9,4,1995.
[97] Ahmetoglu, M., Software supportfor rollformers, Form.Fabricating,May,32–34, 1995.
[98] Li, H., Bal, G., and Haller,M., Producing aflower diagram for cold roll forming, Fabricator,
April, 18–21, 1996.
[188] Hill, D.R., Flying dies: their design and economic impact (partI), Fabricator,January/February,
1987.
[189] Hill, D.R., Flying dies: their design and economic impact (partII), Fabricator,March, 18–21,
1987.
[190] Hill, D.,1975. Flying Dies (Prenotch and Cut-off) Measuring Systems Their Design and Economic
Impact.FMA Inc.
[408] Gradous, F.,Roll form design —section orientation, Tool. Prod.,September,83, 1966.
[409] Vantura, D.,Examining roll form tooling, Fabricator,April, 1996.
[410] Baranowski, D.,Automating rollform layout, Fabricator,September,1989.
[414] Srnec, A., Reducing springback and flare, unpublished communication.
[581] Srnec, A. Minimizing roll split marks on products, unpublished communication.
Further Reading
[10] Levy,B.S., Empirically derived equations for predicting springback in bending, J. Appl.
Metalwork.,3,2,January, 135–141, 1984.
[16] Davies, R.G., Springback in high-strength steels, J. Appl. Metal Work.,1,4,45–52.
[24] McClure, C.K. and Li, H., Roll forming simulation using finite element analysis, Manuf. Rev.,8,
2, 114–119, 1995.
[31] Kiuchi, M., Shintani, K., and Tozawa, M. 1979. Investigation into pass-schedule. Experimental
Study on RollForming Process of Non-circular Pipe —10th Report, Vo l. 31, No.1,Institute of
Industrial Science, The UniversityofTokyo.
[32] Kiuchi, M. 1975. Data Book for Roll Forming Clinic,Institute of Industrial Science, University of
TokyoProgrammed by SME, February1975.
[36] Kimura, H. 1974. The edge waves of thin wall roll-formed product. Fundamental Study on Roll
Forming Process (Rep.3), Vol. 15, No.4.
[37] Monid, V.A., Podyminogin, V. S., Zhemaitis, P.P. ,and Kornilov, G.G., Characteristics of the roll
pass design for cold bending of No.40channels, Metallurgia,8,29–30, 1974.
[41] Fukaya, N., Experiments into the cold roll-forming of straight asymmetrical channels, J. Mech.
Work. Technol.,8,273–291, 1983.
[42] Bhattacharyya, D. and Smith, P.D.,The development of longitudinal strain in cold roll forming
and its influence on product straightness, Adv.Technol. Plast.,1,422–427, 1984.
[53] Cain, E. 1976. Abasic approach to coldroll-forming. FMA 1976,Technical Paper No.F-2500 and
Fabricator,Mar/April.
[54] Gutowski,T.A. 1976. Alogical approach to roll form tooling.FMA Te chnical Paper #F-2000.
[56] Gradous, F.,Roll form design —locating the vertical guideline, Tool. Prod.,November,103, 1966.
Roll Design 5 -113
6
Materials
GeorgeT.Halmos
Delta Engineering Inc.
6.1 Design Considerations ...................................................... 6 -1
6.2 Mechanical Properties ....................................................... 6 -2
Elastic and Plastic Deformation
†
Testing Material,
Yield and Ultimate Strengths, Elongation
6.3 Crystalline Structure of Metals ......................................... 6 -7
6.4 Forming Metals .................................................................. 6 -7
6.5 Increasing the StrengthofMetals by Cold Working ...... 6 -10
6.6 Hot Rolling ......................................................................... 6 -10
6.7 H.R. and H.R.P.O.Steels ................................................... 6 -12
6.8 Cold Rolled Steel ............................................................... 6 -12
6.9 Carbon Steel ....................................................................... 6 -12
6.10 Alloyed Steel ....................................................................... 6 -13
HSLA (High-Strength Low Alloy) and UHSS (Ultra
High-StrengthSteels)
†
Aging and Drawing Quality Steels
6.11 Stainless Steel ..................................................................... 6 -15
Austenitic Stainless Steels
†
Ferritic Stainless Steels
†
Martensitic Stainless Steels
†
FormabilityofStainless Steels
6.12 Metallic Coatings ............................................................... 6 -16
6.13 Nonmetallic Coating and Laminating ............................. 6 -17
6.14 Joining DifferentMaterials in the Roll
Forming Process ................................................................. 6 -18
6.15 Aluminum .......................................................................... 6 -18
Wrought Aluminum Alloy Designations
†
Basic Temper
Designations
†
Temper Designations
†
Cladding
†
Bimetals
†
Roll Forming of Aluminum
6.16 Other Metals and Materials .............................................. 6 -20
6.17 Influence of PrimaryMetal Processeson
Roll Forming ...................................................................... 6 -20
Metallurgical Process
†
Hot and Cold Rolling
†
Tension Leveled Metal
†
Slitting
6.18 Guideline to Steel Prices ................................................... 6 -24
Reference ........................................................................................ 6 -24
6.1 Design Considerations
Owing to the highefficiency of rollforming lines, material may represent 65 to 95% of the manufacturing
cost.
To manufacturethe right product at the right price, it is important to select the right material.
6 -1
The designer or the person who selects and specifies the material must take anumber of factors into
consideration, such as:
1. Mechanical properties
2. Manufacturability(formability)
3. Appearance
4. Price
5. Availability of material
6. Equipment and tool capacity
7. Weight of product
8. Customer’sspecification
9. Supplier’s or other specifications
10. Corrosion resistance(application, environment, storage, discoloration, cathodic resistance)
11. Heat and wear resistance
12. Weldability, acceptance of coatings
13. Susceptibility of surface (scratch, mar)
14. Market acceptance
15. Electrical, magnetic, or other properties
Only the relevant requirements are considered when material is selected. However,missing just one of the
above factors may result in technical, marketing or financial problems.
6.2 Mechanical Properties
Safely withstanding the expected maximum load without permanent deformation (or to staywithin
the specified deflection) is abasic requirementfor anyproduct. The “resistance”against the load is a
function of the cross-section and the mechanical properties (or in loose terms the “strength”) of the
material.
The most importantmechanical properties are the yield strength, tensile strength, and elongation.
6.2.1 Elastic and Plastic Deformation
Astraight piece of steel wire or strip,rigidly held at one end, bent by asmall load to afew degrees, will
“spring back” to its original shape when the load is released. By placing adouble load at the end of the
steel specimen, the rate of deflection will be twice as highbut the specimen will still return to its original
shape when the load is taken off. In other words, the specimen is loaded within its “elastic” range
(Figure6.1).
After increasing the load and the deflection to acertain limit, the specimen willnot return to its
original shape upon the removal of the load. At that load, the wire will remain “permanently” deformed
because the stresses in the material exceeded the yield strength limit.
Similar occurrences can be observedwithsprings (Figure6.1). The linear relation between load and
deflection is utilized in the fish scale but the load is always kept safely within the elastic range of the
spring.Ifaspring is stretched over its elastic range (over yield limit), then it will not spring back to its
original shape.
6.2.2 Testing Material, Yield and Ultimate Strengths, Elongation
Materials are tested for their mechanical properties by applying tension (pulling force) on the test
specimens. The test (tensile) specimens are cut and machined out from the material to be tested. After
measuring their cross-section and marking aspecified length, the specimens are placed between the jaws
of atesting machine (Figure6.2). The gradually increasing load and the elongation are accurately
checked.
Roll Forming Handbook6 -2
Under anyload (stress), the test specimen will elongate (strain). Doubling the load (stress) will
double the elongation (strain) —uptoacertain load. If the load is released beforethe specimen starts
to yield, then the specimen will return (“shrink back”) to its original length (Figure6.3). At aspecific
stress, the strain willincrease without increasing the stress. In other words, the material will “yield”
under the load. If the load is released after yielding,then the specimen will not regain its original length
but will remain“permanently” longer.Wherethis yielding of material occurs, the stress is called the
“yield stress.”
To eliminate the influence of the specimen size on the load, for stress calculations the test load
is divided by the area of the original specimen’s cross-section. The load (lb or N) divided by the area
(sq. in. or mm
2
)isthe “stress.”For example, a2000 lb load on atest specimen having across-section of
FIGURE 6.2 Te sting tensile strength. (Courtesy Tinius Olsen T.M. Co.)
no load
f
2P
3P
4P
P=0
2f
3f
6f
load released
load released
load released
g
permanent deformation
0ver yield strength
f
2f
3f
6f
g
2P
P
0 l 0 l 0 l 0 l 0
3P
4P
0-noload (load released)
l-under load
P=0
FIGURE 6.1 Loading and unloading abeam and aspring.
Materials 6 -3
0.1 in.
2
will create a20,000 psi stress (2000 4 0.1 ¼ 20,000). In manycases, the yield limit is clearly
recognizable on stress –strain graphs made by plotting the loads (stress) and the corresponding
elongations (strain; Figure 6.4 and Figure6.5).
After acertain amount of “yield,”tofurther increase the elongation, the load has to be increased. Under
the gradually increased stress, the specimen elongates further,and at the same time, its cross-section
reduces evenly.Atone point, however,the test specimen startstoreduce its cross-section visibly at one
localized area. In technical terms, it will start to “neck.”Because of the reduced cross-section at the necking,
elongation will further increase even at areduced load. Finally,the specimen will break. The maximum load
divided by the original cross-section gives the maximum or ultimate “tensile strength”ofthe material.
If the load is released at anypoint during the test, then “permanent elongation”(strain) of the
unloaded specimen can be measured. The permanent elongation willbeequal to the elongation under
load “minus” the elastic elongation (Figure6.4). After loading the specimen again, the stress–strain
graph will continue its original path.
Comparing the stress–strain diagrams of different materials (Figure6.5), it became obvious that the
low strength, highelongation material (Material #1 in this Figure) will have adifferent diagram than a
higher strength, less ductile material (Material #2). An even higher strength and lowerelongation
material will again provide adifferent stress–strain graph (Material #3).
Figure6.5 also shows that, assuming both are steels, Material #2 and Material #3 havethe same “slope”
up to the yield point. This means that the elongation created by agiven load is the same for both the low
strength and highstrength steel. Of course, the highstrength material will accept alarger load than the
low strength material beforeityields and permanently deforms. The slope representing the ratio between
strain and stress expresses the elastic modulus ( E ), and is almost identical for all steels, approximately
30 £ 10
6
psi (2056 GPa). Therefore, amild steel wire and aspring steel wire, with the same cross-section,
will deflect the same amount under the same load, regardless of their yield or tensile strength.
However,higher strength steels can carryhigher loads and will remainelastic under loads, which would
permanently deform lower strength steels.
Assume that Material #1 in Figure 6.5 is aluminum and has adifferent stress–strain slope from steel.
The different angle of the slope means that the elastic modulus of aluminum is different from steel.
Actually,the elastic modulus of aluminum is about 1/3 of that of steel (Table 6.1). Therefore, under the
same load, aluminum specimens (regardless of their type) will deflect about threetimes as much as steel
specimens of the same cross-section.
e(elastic)
2e (elastic)
permanent plus
elastic elongation
permanent
elongation
before
testing
load=L
unload
L=0
load=2L
unload
L=0
load over
yield
unload
L=0
FIGURE 6.3 Te st specimen loaded below yield will regain its original length when unloaded, but loaded over the
yield limit will cause permanent deformation.
Roll Forming Handbook6 -4
STRESS
Max load
Fracture
Total elongation (strain)
at L
1
stress
start of
necking
breaking
before
after
l
1
no load
l
0
no load
Permanent Elastic
STRAIN
L
1
FIGURE 6.4 The shape of test specimen at different stress/strain points during testing.
Material #3
Material #2
Material #1
STRAIN
STRESS
FIGURE 6.5 Stress–strain diagram of different metals.
Materials 6 -5
Notall types of materials display adefinite “yield” point. It is generally accepted that for these
materials, the stress, which creates 0.2% elongation, will be the yield stress (Figure6.6).
Total elongation ( e )isthe ratio of the increase in length divided by the original specimen length
(Figure6.7). The elongation is normally expressed in percentage.
NorthAmerican standards specify that elongation should be measured in 2or8in. lengths.
The measured permanent elongation includes the increased elongation at the “neck”; therefore, the 2-in.
long specimens of the same material displayarelatively larger elongation than the 8-in. long.
TABLE 6.1 Elastic Modulus Guideline
Metal AlloyGPa 10
3
psi
Steel Low carbon and high strength 202 to 205 29.5 to 30
Maraging Steel 18 Ni 186 27
Stainless Steel 302, 316 190 28
Aluminum 1100 69 10
Aluminum 2024 72 10.6
Aluminum 3003 70 10
Aluminum 6061 68 10
Copper 115 17
Elongation
Load
0.2% elongation
Load
Elongation
Lüder's strain
(Yield elongation)
Lower
yield point
Upper
Proportional
limit
Lower
yield point
FIGURE 6.6 Stress–strain diagrams showing discontinuous and continuous yield points.
l
0
l
1
before testing
after testing
elongation (in percentage)
e=
l
1
− l
0
l
0
×100 (%)
FIGURE 6.7 Elongation is calculated from the permanent deformation of the test specimen (after fracturing).
Roll Forming Handbook6 -6
6.3 Crystalline Structure of Metals
Metals havecrystalline structure. Most crystals are so small that they can only be observedunder
microscope. Crystals havedifferent mechanical, electrical, and other properties depending on the
direction of their axis.
Impurities, alloying elements, and rate of cooling are some of the reasons whythe crystals of the
commonly used metals are not “perfect.”Perfect crystals haveextremely highstrength, but imperfections
can create “slip planes”along dislocations in the regular rows of atoms. These dislocations usually move
along aplane, within acrystal to its boundaries or to other obstacles and then they stop.By“using up”
these dislocations during plastic deformation, the material “work hardens.”After acertain amount of
deformation, therewill be no more dislocation planes left and the metal loses its plasticity. Metals can
also be hardened by blocking the slip planes with impurities, with alloying elements, by creating small
crystals or by heat treatment.
Dislocations are not visible on roll formed products, but they may create visible marks during deep
drawing (Lu
¨
ders lines).
6.4 Forming Metals
In well-designed products wherea“safety factor” was used in the calculations, the actual stresses will
neverreachthe yield stress. Therefore, products shall not permanently deform under the maximum load.
Only accidental overloads such as crashing acar or overloading astructure will create permanent
deformation.
Forming anymetals, however,must be achievedwith stresses abovethe yield stress. Material formed
with astress belowyield would spring back to its original shape. The forming stress should not exceed the
maximum tensile stress, otherwise the productwillcrack or tear during forming.
Aquick glance at the stress–strain diagrams (Figure 6.8) reveals that the larger the differencebetween
the yield and the ultimate tensile stresses, and the larger the elongation, the better the chanceistoform
the metal. It is more difficult (even impossible) to form metals withextremely highyield and tensile
stresses and having anear zeroelongation. These materials willcrack at the sharp bend lines because the
elongation in the outside fibers, created by the bending, would be larger than the maximum elongation of
that material.
high strength -low elongation material
low strength -high elongation material
USEFUL RANGE OF FORMABILITY
STRAIN
STRESS
YS 2
UTS 1
YS 1
UTS 2
e
U2
e
T2
e
U1
e
T1
YS -Yield Strength
UTS -Ultimate Tensile Strength
e
U
-Uniform elongation
e
T
-Total elongation
FIGURE 6.8 Assessing formabilityfrom stress–strain diagram.
Materials 6 -7