October 2011

ICS 77.140.50 SupersedesDIN 693522010-O1

Cold bending of flat rolled steel,English translation of DIN 6935:2011-10

Kaltbiegen__von Flacherzeugnissen aus Stahl,Englische Ubersetzung von DIN 6935:2011-10Cintrage a froid des produits plats en acier,Traduction anglaise de DIN 6935:2011-10

Document comprises 13 pages

Translation by DIN-Sprachendienst.In case of doubt, the German-language original shall be considered authoritative.

DIN 6935:2011-10

A comma is used as the decimal marker.

Contents

PageForeword ....................................................................................................................................................... .. 31 Scope ............................................................................................................................................... .. 42 Normative references ..................................................................................................................... .. 43 Bending radii ................................................................................................................................... .. 43.1 General ............................................................................................................................................. .. 43.2 Bending angle 04 and thickness s .................................................................................................. .. 44 Key to materials .............................................................................................................................. .. 65 Minimum leg length ........................................................................................................................ .. 66 Permissible deviations for angular positions on bending sections .......................................... .. 67 Calculation of developed lengths ................................................................................................. .. 78 Representation and position of bend lines for developments ................................................. .. 109 Dimensioning and calculation of developed lengths (examples) ............................................ .. 1010 Development and marking of bend line position (example) .................................................... .. 12Bibliography ............................................................................................................................................... .. 13

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DIN 6935:2011-10

Foreword

This standard has been prepared by Working Committee NA 026-00-03 AA Stanzteile of the Normen-ausschuss Federn, Stanzteile and Blechformteile (NAFS) (Springs, Stamped Parts and Moulded PartsStandards Committee).

For more information on NAFS, visit our website at www.nafs.din.de.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patentrights. DIN shall not be held responsible for identifying any or all such patent rights.

Amendments

This standard differs from DIN 6935:2010-01 as follows:

a) the scope has been updated;b) normative references have been updated;c) figures have been provided with titles;d) Clause 3 has been changed;e) Tables 1 to 3 have been revised;f) the standard has been editorially revised.

Previous editions

DIN 6935: 1958-01, 1967-05, 1969-05, 1975-10, 2010-01

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DIN 6935:2011-10

1 Scope

This standard applies for bent parts made of flat steel products for application in steel construction andmechanical engineering.

For standards on flat steel products, see DIN EN 10025-2.

2 Normative references

The following referenced documents are indispensable for the application of this document. For datedreferences, only the edition cited applies. For undated references, the latest edition of the referenceddocument (including any amendments) applies.

DIN 250, Radii

DIN EN 10025-2, Hot-rolled products of structural steels Part 2: Technical delivery conditions for non-al/oystructural steels

3 Bending radii

3.1 General

When bending flat rolled steel such as sheets, strips, wide flats etc., the rolling direction shall be taken intoconsideration, since bending should be carried out transverse to the rolling direction, because this is moresuitable for bending.

The suitability of the rolled steel for bending shall be agreed with the manufacturers works when ordering. Toguarantee bending suitability, the rolled surface shall be flawless and the sheared edges straight. For flatrolled steel, the sheared edges on the outside of a bend shall also be de-burred at the bending location toprevent cracks from spreading from the cut edges.

3.2 Bending angle a and thickness s

The bending angle a can have any value between 0 and 180. Thickness s decreases by approximately 20 %in the rounded portion (see Figure 1).

1;). -'1?

-_- I.. .. I ~'= E< 1Keyr Bending radius0: Bending angle Opening angle

Figure 1 Bending radius (notation)

To obtain uniform bends on bending rails, it is recommended that only bending radii from the series below beselected. The values printed in bold are to be preferred.

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DIN 6935:2011-10

Dimensions in millimetres

IIIEEHHIHHEHEEEEEMThese bending radii comply with the radii according to DIN 250.

Table 1 gives the minimum permissible bending radii to be chosen for given sheet thicknesses and materialsand for the applicable bending machines. The indicated values apply for bending angles as 120. Forbending angles 04> 120 the next higher value in the table shall be used, e.g. if sheets of S 275 JR accordingto DIN EN 10025-2 are to be bent transverse to the rolling direction, with a thickness S = 6 mm, the minimumpermissible bending radius is r : 10 mm for as 120 and r = 12 mm for 04> 120.

Table 1 Minimum permissible bending radius rDimensions in millimetres

For Minimum permissible bending radius r for thicknesses 5bending Up Over Over Over Over Over Over Over Over Over Over Over Over Over Overtransverse toSteel

grades to the 1 1 1,5

S 235S 235S 235

.RB-0

.2

or parallel2,5 3 4 5 6 7 8 10 12 14 16 18

rolling upto upto upto upto upto upto upto upto upto upto upto upto upto uptodirection

Transverse1,5 2,5 3 4 5 6 7

1,6 2,5 3 5 6 8 "

12 14 16 18 20

20 25 28 36 40

Parallel 1,6 2,5 3 6 8 O 25 28 32 40 45

S 275S 275S 275

.RB-0

.2

Transverse 2 3 4 5 8 O 25 28 32 40 45

Parallel 2 3 4 6 10 2 32 36 40 45 50

S 355S 355S 355

Table 2 gives permissible deviations for minimum bending radii which are to be expected for various sheetthicknesses and materials.

Steel grades

S 235S 235S 235

.RB-0

.2

RO2

Transverse 2,5 4 5 6 8 O 25 32 36 45 50Parallel 2,5 4 5 8 10 2 32 36 40 50 63

Table 2 Permissible deviations for minimum bending radii rDimensions in millimetres

Permissible deviations for minimum bending radii r for thicknesses sUp to 3 Over 3 up to 8 Over 8 up to 20

+0,5 +1

I3 O

+1,5

0

S 275S 275S 275 |\>o;U

+0,8 +1,5I3 O

+2

0

S 355S 355S 355 |\>o;U

+1 +2

0 0

+3

0

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DIN 6935:2011-10

4 Key to materials

Table 3 provides examples of materials for which suitability for cold bending, cold flanging and cold curling isguaranteed, taking into account the minimum permissible bending radii specified in Table 1.

Table 3 Key to materials (examples)

Steel grade with a minimum tensile strength TYP f 519 Over 360 MPa Over 430 MPa Over 510 MPa

up to 510 MPa up to 580 MPa up to 680 MPaHot-rolled products of

structural steels according S 235 JR S 275 JR S 355 J2to DIN EN 10025-2

5 Minimum leg length

When mechanically bending sections of sheet metal, the leg length b is approximately 4 - r (see Figure 2).

Q J

1

Figure 2 Minimum leg length (notation)

6 Permissible deviations for angular positions on bending sections

Table 4 provides an overview of permissible deviations of bending angles in relation to leg lengths.

Table 4 Permissible deviations of angular positionsDimensions 'n millimetres

Leg lengths a and b(wherethe ShQfte|'|eg Upto 30 Over 30 up to Over 50 up to Over 80 up to Over 120length is regarded as the 50 80 129nominal length)

E:;'Li';':LgfIe;'t'" f + 2 + 1 45' + 1 30' + 1 15' + 1

6

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DIN 6935:2011-10

ti-

? I I I -

El

Figure 3 Permissible deviations for angular positions (notation)

Values apply for a ratio up to r : s : 4. For a larger (r : s) ratio, a larger deviation due to spring back is to beexpected (see Figure 3).

7 Calculation of developed lengths

Developed length:a+b+v. Depending on the value of the bending angle, v varies and represents acompensating value which, at an opening angle ,6 of 0 up to 65 (calculated value 65 24' 30"), can benegative or positive, and at an opening angle over 65 can only be negative.

Developed lengths shall be rounded up to the nearest full millimetre.

Opening angle ,60 up to 90

Compensating value u = 1; - {I810;0_ '8) ( 2 k) 2 (r + s) (1)

4.5

'RI

.t~~aIFI

3

Figure 4 Opening angle ,6 0 up to 90 (notation)

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DIN 6935:2011-10

Opening angle ,690 up to 165

Compensating value 0 : 1c- I800 _ '8 S k 2 (r + s)- tanE (2)180 2 2

/I?

mlI0.

Sggl? u-

Figure 5 Opening angle ,690 up to 165 (notation)

Opening angle ,6165 up to 180Compensating value 0 : 0

The values for 0 are negligibly small in this case and sufficiently accurate for practical applications.

,5

. b ElIAA

_'Ii__

5

---in-I-|-I|

Figure 6 Opening angle ,6165 up to 180 (notation)

Correction factor k to determine the cut lengths of bent workpieces

The correction factor k gives the deviation of the position of the neutral line; and can be calculated asfollows:

k:0,65+lIg (3)2 s

or can be taken from the following graphical representation in Figure 7, which represents the equation. Forr : s > 5, Equation (3) is no longer valid so that k: 1 applies.

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DIN 6935:2011-10

if I1,2

1,1

1

0,9

0,8

0,?

0,6

0,5

0,11 L

0,3 I

0,2

0,1

-00 " 2 3 L 5

Pl 5

Figure 7 Graphical representation of correction factor

If only minimum requirements are set for the determination of cut lengths, rounded values as grouped togetherin Table 5 may be used for the correction factor k.

Table 5 Correction factor k, rounded values

Inte_maI bendIn9' Over 0,65 Over 1 Over 1,5 Over 2,4 Over 3,8radius r as a .Rat|O r ' sfunction of sheet 'thickness S up to 1 up to 1,5 up to 2,4 up to 3,8

C t' f t korrec ion ac or 0,6 0,7 0,8 0,9 1(rounded values)

For any value for ,6, r and s, the corresponding compensating values 0 can also be identified by the use of thecorrection factor ktogether with the graphical representations of factors in DIN 6935, Supplement 1.

For calculated compensating values 0 for several opening and bending angles based on the above formula forcorrection factor k, see DIN 6935, Supplement 2.

9

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DIN 6935:2011-10

8 Representation and position of bend lines for developments

The bend line indicates the middle of the bending radius and shall be represented by a thin continuous line.The position of the bend line results from the abutting leg lengths a and b, with half of the positive or negativecompensating value 0 taken into account (see Figure 8).

_ .-l+0+v I

0+-'72 W2 +3

Figure 8 Representation and position of the bend line (notation)

Developments shall only be explicitly drawn if the shape of the cut sheet is not unambiguously determined bydimensioning and indication of the bend line.

9 Dimensioning and calculation of developed lengths (examples)

All dimensions in millimetres

EXAMPLE 1

Material: S 235 JR

Sum of leg lengths .. ..................... .. 50 + 200 + 80 = 330FOI,B=9(),r= 6,s=4then .......... ..v=8,26FOI,B=9(),r=2(),s=4[hen .......... .. v=13,44=21,7Developed length ........................................ .. 308,3

z 309

Dimensions in millimetres200

s -;>,_,. Q35 E

1+

Figure 9 Example 1 (notation)

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EXAMPLE 2

Material: S 235 JR

Sum of leg length .. ....................... .. 50+ 170+246+50=516For,6= 9(),r=20,s=12[hen ......... ..v=25,41For,6= 45,r=2(),s=12[hen .......... ..v= 6,12For,6= 135, r: 32, S: 12 then ......... .. 0: 7,25=38,78Developed length ........................................ .. 477,22

_l

_l

z 478

A I? 8fa

Figure 10 Example 2 (notation)

{ 1;; 935.

3 ,1: /9 bf].L-.1 9

5U

DIN 6935:2011-10

Dimensions in millimetres

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DIN 6935:2011-10

10 Development and marking of bend line position (example)

Material: S 355 J2

All dimensions in millimetres

Development:Sum of leg lengths .. ........................... .. 45 + 50 + 32 = 127For,6= 45,r=1(),s=5[hen ......... ..v= 1,72For,6=135,r=10,s=5then ......... ..v= 3,00 = 4,72Developed length ........................................ .. = 122,28

~ 123 Dimensions in millimetres

I-+5

I 111

DIN 6935:2011-10

Bibliography

DIN 1623, Cold rolled strip and sheet Technical delivery conditions General structural steels

DIN 6935 Supplement 1, Cold bending of flat rolled steel Supplement 1: Factors determining the correctionvalue 0 for calculating length of flats prior to bending

DIN 6935 Supplement2, Cold bending of flat steel products Supplement 2: Calculated compensatingvaluesv

DIN 59200, Flat products of steel Hot rolled wide flats Dimensions, mass, tolerances on dimensions,shape and mass

DIN EN 10048, Hot-rolled narrow steel strip Tolerances on dimensions and shape

DIN EN 10058, Hot rolled flat steel bars for general purposes Dimensions and tolerances on shape anddimensions

DIN EN 10131, Cold rolled uncoated and zinc or zinc-nickel electrolytically coated low carbon and high yieldstrength steel flat products for cold forming Tolerances on dimensions and shape

DIN EN 10139, Cold rolled uncoated mild steel narrow strip for cold forming Technical delivery conditions

DIN EN 10140, Cold rolled narrow steel strip Tolerances on dimensions and shape

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