Forming diagrams and roll-passes in roll-forming of sections with middle rigidity elements Текст научной статьи по специальности «Строительство и архитектура»

A.V.Filimonov

Ltd Co «New Industrial technologies», city of N. Novgorod

S.V.Filimonov

Ltd Co «Spetstechnology», town of Ulyanovsk

FORMING DIAGRAMS AND ROLL-PASSES IN ROLL-FORMING OF SECTIONS WITH MIDDLE RIGIDITY ELEMENTS

Abstract. There are discussed forming diagrams for roll-formed profiles with middle rigidity elements adopted in traditional roll-forming and in intensive deformation method. A manufacture technology based on the intensive deformation method for a symmetrical profile with middle double thickness rigidity elements is offered.

Key words: roll-forming, roll-formed profile, middle rigidity element, number ofpasses, forming length zone, forming roll.

Modern thermally separated and non-separated systems of doors, windows, façades, glazed roofs, rails and gates largely use various roll-formed sections (profiles) with middle rigidity elements. Thus, the range of Foerster profiles includes dozens of such semi-closed profiles [1] to be preferably produced through intensive deformation method (owing to minimum number of passes and compact technological equipment) [2, 3]. Nevertheless, their technology is far to be a trivial task. The further limitations come out during the implementation of the method to manufacture the above nomenclature of sections: rather large number of passes, peripheral element edge waviness, flange kink or flange plastic collapse, spring-back, profile surface defects in contact zones, warpage, twist (of an asymmetric profile) [4].

The paper goal consists in revealing the most general laws in forming and pass design for the above sections on the basis of a profile with middle rigidity elements.

The cross-section of the mentioned Foerster profile is given in fig. 1. General requirements towards the profile and to the appropriate roll-forming machine are given in table 1. The patented equipment shown in table 1 is developed and being produced in Ltd Co «Spetstechnology» (town of Ulyanovsk). In column 3 there are indicated two types of roll-forming machines for the case of insufficient number of passes revealed during the technology development. The analysis of the two first columns in table 1 shows that the profile tolerances are rather tight for roll-formed sections.

Fig. 1. Initial configuration of profile 90*20*1.5 mm with middle double thickness rigidity elements (material - steel of group 08 or stainless steel)

In small-lot roll-forming it is wise to use the technology based on intensive deformation method [2], since the traditional roll-forming technologies are not sufficiently efficient for small-lot production due to the following grounds: 1) for small-lot production the forming rolls and guidance devices will not be repaid; 2) considerable expenditures related to the powerful equipment use (energy consumption, working area, etc.) will decrease the competitiveness of the profiles having small cross-section dimensions; 3) the use of guidance devices will substantially increase the rolls change-over time, let alone the requirement of high qualification of the profiler; 4) the high number of passes involves a prolonged period of tooling cost recovery; 5) the use of unclosed roll opening requires the use of guidance devices not only for forming itself but also for blank positioning; 6) the force locking of the rolls may cause nun-uniform blank deformation across its cross-section and de-

fects of profile shape such as twisting, warping and camber; 7) the blank cutting-in into the upper roll on the last passes may cause some profile surface defects; 8) slipping forces applied to the blank may increase contact friction provoking non-uniform deformation and defects; 9) during the manufacturing reorganization and diversification the bulky and costly equipment for traditional roll-forming may become illiquid.

Table 1

General requirements toward the profile bearing middle rigidity elements and specifications of roll-forming machines

Requirements toward the profile dimensions Value Roll-forming machines specifications (SPU-400K12-65/50 and SPU-400K8-65/50) Value

Unspecified limit deviations of dimensions Н14, h14, IT14/2 Working shaft diameter, mm 65/50

Unspecified inner radii, mm 1.5(±0,5) Number of working stands, pc. 12 (8)

Camber, mm/m 1.0 at most Inter-stand distance, mm 400 (285)

Twist angle, m/mm 2° at most Inter-axle distance, мм 130/190 (120/150)

Edge waviness, mm ±0.8 at most Working shaft length, mm 400 (250)

Limit angle deviation, deg. ±1 Key groove dimensions in the shafts (Bxt), mm (key height -10/9 mm) 16x6 (14x5.5)

Limit deviations of elements in height, mm ±0.1 Roll-forming speed, m/min 20/10

Limit deviations of elements in width, mm ±0.2 Lower and upper shaft speed ratio Lower shafts are driven

The roll-forming of profiles with middle rigidity elements turned inward through intensive deformation method usually causes less problems than that relating to the profiles with rigidity elements turned outward (see case study of roll-forming of the profile type «stringer» with dimensions 85^25x1.0 mm or profiles Knauf in the same book [2]). The technology development on the basis of intensive deformation method includes the following stages: feasibility analysis of a given profile configuration, profile cross-section location in the last stand, choice of base element and tracking axis, number of passes calculation, development of forming diagram, equipment choice, process design and tooling design, tooling manufacturing and its setting-up, technology and equipment implementation. These technology development stages will be further associated with roll-forming of profile Foerster 90x20x1.5 mm with middle rigidity elements (see fig. 1).

Profile design feasibility analysis

Such an analysis is carried out on the contractual stage aiming at the technology development according to paper [5] containing 34 criteria. In necessary cases the profile design may be changed upon the Customer approval. Particularly, for some profiles with large peripheral elements there may be induced constructive or technological rifts to raise the peripheral elements rigidity. These rifts should not contradict the profile functionality. In the actual case, the horizontal flanges width is equal to ten-fold of the blank thickness, thus, the above mentioned measures are not necessary.

Profile locating in the last pass opening

Symmetric multi-element profiles are usually located so as their open part be turned upward (their bottom being horizontal), while asymmetric profile bottom should be tilted at a calculated angle. The upper position of the profile «mouth» allows the operator to observe the process and makes

it easy to set up the tooling. The profile location in the last stand involves the notions of «base element» choice and «tracking axis» choice.

Definition of «base element» and «tracking axis»

In traditional roll-forming both of these two notions are mostly related to the speed mode of manufacturing. In several cases the base element was not associated physically with the blank body. This may be illustrated through the consideration of different methods of tube forming, when the tracking axis was alternatively «fastened» to the lower point, center of gravity or unified edge level [6]. In the second and third cases the base element has no connection with physical body, although it is thought geometrically in terms of a point or segment (connecting the bland edges) respectively. In intensive deformation method the situation is different [2]. The notion «base element» is associated with a physical element of the blank (rectilinear element or bending zone), which is usually in contact with the lower part of the roll opening.

The tracking axis usually passes through the base element middle which is liable to minimum displacements in the space during roll-forming in contrast to other profile elements. The fig. 2, shows the flower forming diagram, where the base element is the profile bottom, while the tracking axis passes through its middle, just in intersecting point of the bottom line and profile axial line.

Fig. 2. Flower forming diagram for profile Foerster 90*20*1.5 mm with its edge displacement trajectory: 1-8 - numbers of technological passes

In whole, the choice of base element and tracking axis may affect the forming speed mode (difference of speeds in cross-section height), especially for high profiles. It also may be sensible when selecting technological bases at forming rolls manufacturing.

Number of passes calculation

The traditional roll-forming uses several approaches due to the traditions adopted in some scientific schools [2]. In intensive deformation method, the procedure of number of passes determination is formalized and given by the following equation [7]:

N = (1)

LM-pi W U. T n '

where A - edge displacement in vertical plane containing the working shafts axis in the last pass with reference to the appropriate points of a flat blank, mm; Lm - roll-forming machine interstand distance, mm; p - limit angle of blank «constraint», rad.; H, W - height and width of the profile cross-section respectively, mm; s - profile reduced thickness; k - profile quality class; T - cross-section size allowance for quality class k, mm; as, ob - bland material yield stress and its ultimate stress, MPa; n - number of bending zones in the profile; - total folding angle of the flange carrying the rigidity element, rad.; n - dimensionless form-modifier depending on the ratio «forming roll base diameter to forming height».

The calculation error according to formula (1), as usual, does not exceed 0,7 [7]. Yet, for asymmetric profile, the calculations should be made for both parts (carrying flanges) of the profile with reference to the tracking axis. The edge displacement and total bending angles of the carrying

flanges may be different, giving thus different values of numbers of passes, the greatest of which should be declared sought-for. To illustrate the above, the fig. 3 shows the program and diagrams used to determine the number of passes for profile 90*20* 1.5 mm being fabricated to match the 11th quality class.

Number of steps calculation program Profile Forster 90x20x1,5 mm rProfiTe~data iQuality"

Blank data

oS := 200 oii:=260

ГтесИпо data

p==n

n :-6

W := 90

I data

I

I k:= 11

I.

11:= 20 j j T := 0.2

Tooling data

D := 90 TTm:=

' Imashine 11 data

l|

И

I ! L:=400

II

2 ■ Hm I I I

D

f Program body and cycle parameter

P(n) :=-

1

.p-.-s.r-

L p 4 к T dft

d := 20,30.. 100

Г

40 60 A. mm -

Insert graph of N

a)

b)

Fig. 3. Program to calculate the number of passes in application MathCad2000Pro (shaded rectangles conceal the data referring to technology «know-how») (a) and diagram for number of passes determination (b): 1, 2, 3 - = 180, 135 and 90 degrees respectively

The calculating and graph generating program (fig. 3 a) includes the data blocks for: a) blank; b) profile cross-section overall dimensions; c) required quality class; d) secondary parameters (technological); e) tooling; f) roll-forming machine. The program body includes the calculating dependencies and cycle parameter. The computing is ended by the graph generation for the number of passes determination (fig. 3b). For the profile under consideration the required number of passes is eight (round-off included).

Forming diagram development and equipment selection

The forming diagram development is started with the blank calculation on the basis of neutral line by adding a calculated blank width increment to provide for its transversal compression by the rolls to prevent the thinning in bending zones and to reduce the spring-back [2]. In a 3-D application the profile cross-section is located in the last pass taking into consideration the number of passes and inter-stand distance of the eventual roll-forming machine. They select the trajectory of reference points (blank edges and future bending zones), then, the 3-D model is created to deliver the roll opening for each step as a result of intersection of the model and an appropriate vertical plane. Sometimes it requires corrections to match the profile peculiarities and specific requirements towards it. At 2-D designing, a preliminary forming diagram should be created. In this diagram, be it linear (fig. 4a) or flower type (see fig. 2), the folding angles are determined on the basis of equal

longitudinal strains of flanges per step. To do so, we have previously to calculate the reduced thickness for the profile side walls bearing rigidity elements and further to obtain the folding angles with the aid of an iteration procedure [2]. To make the calculations easier, one may approximate the reduced thickness per steps, taking its values in the first and in the last pass into consideration.

Fig. 4. Linear forming diagram (a) and roll openings (b) for profile 90*20*1.5 mm

It is clear, that the preliminary forming of future bending zones should occur on the first steps with radii matching the profile drawing. This differs the intensive deformation method from the traditional roll-forming where the bending radii variations are monotonous with the step number increase.

On setting the folding angles, one should calculate the deformation length Lk (k - step number) for each step according to the formula [8]:

L

(2)

GT 0 +^пр,

where b - side wall width; Cto - blank yield stress; X - linear hardening module, r, C - relative radius and relative bottom width respectively; s - bland thickness; Snp - known value of the ultimate elastic strain [7].

The relation (2) is to be used to precise the folding angles 0k according to the criterion (3), where the right side gives ultimate folding angles:

ek < root(L(9)- Lm ,0), (3)

where L(0) - function defined by formula (2); LM - roll-forming machine inter-stand distance.

If the condition (3) is not satisfied, it means that on the previous step the blank would be reformed. That's why the folding angle of the previous step should be diminished. In whole, the limit abilities of the intensive roll-forming are established in paper [8].

As soon as the forming diagram development is over, the final choice of the roll-forming machine should be made. This is important since the roll-forming machines of the same type may have different lengths of their working shafts (see table 1). The calculated blank width may prompt you the required value of the working shafts [7]. As it follows from table 1, the 8-stand roll-forming machine SPU-400K8-65 is suitable to manufacture the profile under consideration.

Process and tooling design, tooling manufacturing and its setting-up

Depending on the Customer's order, the technology may include auxiliary operations (e.g., coil shearing, packing, etc.), so the technology development should be in parallel with the forming rolls manufacturing.

The tooling of the intensive roll-forming should be designed, manufactured and set up according to papers [2, 7]. The electronically designed forming rolls (see fig. 4b) are to be manufactured on the CNC turns adopting electronic drawings without dimensioning.

As shows fig. 4b, the roll openings of all the passes are closed, with horizontal and vertical bases of the lower roll ledges. There is used geometric closing thanks to the use of swing (hinged) links of the roll-forming machine. The blank cutting-in on the first steps is performed into the upper roll, while on the last steps the blank cutting-in is executed into the lower roll. The first and second pairs of rolls give the blank its final bending zones radii. The level of roll opening locking is chosen to ensure favorable forming conditions and to minimize the rolls mass. The upper rolls of the sixth and seventh pairs are split-face to give access to the cutters to the roll working surfaces. The described tooling for the intensive roll forming is very distinct from that of traditional roll-forming.

At the tooling setting-up the blank and profile parameters should be thoroughly monitored according to table 1. The main parameters of profile 90*20*1.5 mm (fig. 5) are given in table 2.

Fig. 5. Specimen of profile 90*20*1.5 mm (produced in Ltd Co «Spetstechnology»)

Table 2

Measured and processed parameters of profile 90*20*1.5 mm

Monitored parameter and its nominal value according to the drawing Mean value, mm Standard deviation for universal set Confidence interval at significance level 0.05 Confidence interval at significance level 0.02 Extreme deviations IT14/2

C = 90 mm 90.29 0.094 0.024 0.066 ±0.35

Delta = 30 mm 29.88 0.106 0.062 0.074 ±0.25

HR = 20 mm 20.24 0.080 0.048 0.056 ±0.21

HL = 20 mm 20.25 0.054 0.032 0.038 ±0.21

bL = 15 mm 15.79 0.027 0.016 0.019 ±0.18

bR = 15 mm 14.93 0.040 0.024 0.028 ±0.18

rsL = 1,5 mm 1.18 0.079 0.061 0.073 ±0.5

rsR = 1,5 mm 1.10 0.070 0083 0.049 ±0.5

riL = 1,5 mm 1.40 0.104 0.061 0.073 ±0.5

riR = 1,5 mm 1.35 0.114 0.061 0.073 ±0.5

aL = 90° 89°21' 17.7' 10.5' 12.4' ±60'

aR = 90° 89°09' 13.0' 10.5' 12.4' ±60'

Notes: C - bottom width; Delta - gap between horizontal flanges; HR - leight of the right side wall;

HL - height of the left side wall; bL - width of the left horizontal flange; bR - width of the right horizontal flange; rsL, rsR, riL, riR - bending radii at the left and right horizontal flanges and at the bottom (on the left and on the right) respectively; aL, aR - angles between the bottom and vertical side walls (left and right respectively)_

The dimensions of the bottom, flanges, the height and gaps between horizontal flanges were measured with the help of an electronic caliper to within 0,01 mm on the length 200 mm with a step of 20 mm; the angles between the vertical walls and the bottom were measured at spaced intervals of 20 mm with the aid of an angular gauge with vernier 5UM (GOST 5378-88) with main error ±3'; the bending radii were measured on the section scans with 10-fold selection of approximating circumferences and scaling via the wall thickness in its middle part using the application MS-VISIO; the bending zone quality and thickness variations were assessed with the help of device MPB-2 with magnification 20x. The results were processed using the application MS-EXCEL-2007.

The analysis of table 2 shows that the parameters of the profile being produced are in full conformity with the drawing requirements. Minor deviations slightly beyond the drawing restraints are observed on the left flange, but they do not affect the profile functionality, thus the profile is compatible with assembly requirements. The bending radii which are somewhat lower than those specified in the drawing are also within the allowable limits. Although the mean values of the angles between elements are close to the admissible limit, they do still stay within the allowable boundaries. The camber, twisting and edge waviness were not observed. The comparison of the confidence intervals with allowable extreme deviations allows to state that the roll-forming process stability is rather high.

Industrial implementation

The developed technology is realized on the basis of an automated roll-forming line developed by Ltd Co «Spetstechnology» and is being used on the Customer's industrial premises.

References

1. Catalogue Forster: Schweiz: Forster Profilsysteme AG, 2016. 37 S.

2. Filimonov S.V., Filimonov V.I. Intensive roll-forming of sheet-metal profiles. - Ulyanovsk: Publ. house of UlSTU, 2008. 444 p.

3. Filimonov V.I. Classification and trends in roll-forming equipment evolution // Rolled metal production, 2008, №4. P. 37-43.

4. Lapin V.V., Filimonov S.V., Filimonov V.I. Defects of roll-formed profiles with rigidity elements: requirements and employed materials // Sheet-metal profiles roll-forming: theory and practice (2015): collected scientific papers / edited by D.T.S., professor V.I.Filimonov. - Ulyanovsk, 2015. 161 p. P. 18-26.

5. Filimonov V.I., Filimonov S.V., Karpov S.A., Kokorina I.V. Manufacturability and design of roll-formed profiles // Handbook. Engineering journal, 2015, №8. P. 11-17.

6. Danchenko V.N., Kolikov A.P., Romatsev B.A., Samusev S.V. Tube manufacturing technology. Moscow: Intermet Engineering, 2002. 640 p.

7. Filimonov A.V., Filimonov S.V. Semi-closed roll-formed profile fabrication using intensive deformation method / edited by prof. V.I.Filimonov. Ulyanovsk: Publ. house of UlSTU, 2010. 206 p.

8. Filimonov S.V., Filimonov A.V., Filimonov V.I. Deformation length model at intensive roll-forming of strain-hardening material // Rolled metal production, 2008, №10. P. 26-32.