Sheet metal bending process

Bend formation is realized in plate metal elements formation and it is efficient, suitable in terms of performance, time saving and costs needed to process elements.

Nevertheless, because of inproper understanding of bend procedure working staff usually use traditional methods to finalize element formation, for inctance manual or hydraulic formation. These methods raise processing costs because of formation tool. The more are the human factors, the less stable elements are. This may affect element processing effectiveness as well.

So, proper understanding of bend formation techniques is essential. There are lots of factors that have to be taken into consideration in bend formation technique selsction. Nonchalence in this matter may bring about processing collapse and element improvement gets affected. Herein we are going to bring forward such issues as extended material size calculating, choosing of bend tools, ceratin elements processing examination, troubles and their keys often occuring in bend processing, all these are going to be a manual for plate metal elements processing preparations.

Technical Processing Examination 

Plate extension length calculating.

Plate metal extension size depends on its density, stuff, bend angle, bend tools and so on. There are two widely applied techniques to calculate plate metal extension length. They are neutral coat calculating technique and empirical calculating technique.

1. Neutral coat calculating technique.

This is workable in case bend angle is not right-angled at all. In bend procedure the external coat is exposed to extensile compression, the inside coat is exposed to compress pressure. So, transit coat in the midst of inside and outside coats does not appear in extensile or compress pressure. That is why it is reffered to as neutral coat.

This coat is not changed until bend process and becomes base coat to calculate bend element length. Neutral coat location depends on the plate density. Generally the space in the midst of neutral coat and bend element inside face is 0.5 t in case of no more than 4 mm density plate. In case sheet density exeeds 5 mm, space is 0.34 t. Neutral coat extension length is the sheet extension length.

2. Empirical calculating technique.

This technique is workable if element bend angle is right-angled and sheet density is t≤3 mm. The proposed technique assists operators in elements extension length calculation.

Formula is as the following L=A+B-2t

In the formula L is plate extension length, A/B is element bend or material size and t is thickness or density.

Choosing of bend tools.

1. Press brake tool selecting principles.

Choosing proper tooling for bending is an essential issue. Bend tooling consists of upper and lower tools, called punch and die. They are picked in accordance with elements density, bend sizes to escape deformity brought about through impact in the midst of bend elements and punching dies. Press brakes have got miltipurpose bottom and specific dies, notches in case of V form and slit bevel is 60 degrees. In general, if the sheet is thick the slit appears bigger and its breadth is 8 t. Punches of press brakes contain direct, goose-necked, little bend hem punches and the like. They are able to suit specific tooling in accordance with each particular condition.

Direct punch is applicable in case of t ≤ 3 mm plates. Little goose-necked punch is for less deep U form bend. Goose-necked one is suitable for deep U form bend and the hem one is for flattening elements.

2. Choosing appropriate punch and die.

Bend tool is chosen in accordance with element bend semidiameter. However, bottom die is ignored by us from time to time. Sometimes when bend punches and dies appear inproper, both parts of bend semidiameter are exposed to pressure in the aftermath of bend formation, which makes repairing impossible.

Figure 3 depicts that the model element density is 1.6 mm, bend semidiameter is R4, bend is 8.9 mm high. In the result of consideration, bottom die slit is chosen through V12 or a less one. For this specific element V 12 is the proper option due to certain conditions shown in fig. 3. Leftside is V10 slit. Rightside is V 12 slit. Elements bend resiliency must be taken into consideration, so bend angle inlet into controller must not exceed 90 degrees. In case of 90 degrees bend edge in the figure, it is apparent that when punches lower, V 10 displacement is inevitable, on the other hand V 12 slit does not have displacement. That is why bottom die together with V 12 slit is more suitable than V 10 or even a less one. If so, both sides of bend semidiameter in the aftermath of bending are deprived of pressure, so, high quality elements are gained.

Technichal examination of typal bend elements.

While bending ridge highness and web breadth must be considered. In case of excessively little web breadth and excessive ridge highness, previously shaped ridge and bend tooling get interfered in bending formation. Further bend process becomes impossible. In case of no correction actions, the complete pack of material may scrap, bringing on increasing costs.

Now let us note U form and Z form elements bend process.

1. U form elements technical analysing.

To bend U form the relation of highness (H) of element both ridges and web breadth (B) has to be considered. In case H≤B form can be shaped. However, bending may be disturbed as element bend ridge and device frame may get interfered. In case of common press brakes, if bend highness is H≥B mm, element gets interferedwith bend device in element bend process. Two keys are suggested to solve these troubles:

1. Prior to element bending, make an obtuse bevel upon web and adverse the ridge direction. Thus, you can avoid element interference with device frame in bend process. If ridges bend into direct angles, hem tooling is applicable for flattening obtuse angle of element web. Such kind of technique leaves pressure on bend location.

2. If the element bend breadth does not exceed 200 mm, a specific top die can be selected, which is the suspending punch and is suitable to bend element ridges.(See fig. 4) Element flange gets fully protected and does not interfere with dies. As there is some restriction in top die framework or force, such technique is applicable in case of elements the breadth of which does not exceed 200 mm.

2. U form element technical analysing.

Z curve ridge part on plate metal elements has features of little size and big amount. In case operator adopts traditional manual formation to gain the required form, effectiveness drops and the outcome is not stable. Elements have to be modelized, analised prior to chossing any bend technique, as element web and bend die sizes are limited. In accordance with specifications needed in modelizing chart 1 shows categories.

Chart 1. Model specifications

According to this chart operators may precisely choose proper bend method and get ensured in correct outcome. If L + P > T/2, realize element bending formation.

Troubles occuring often while bending and suggested keys.

1. Element flange bend.

Due to punch and die restriction of press brakes all flanges possessing different highness cannot be shaped. That is why it is important to analyse, modelize forming elements prior to choosing any bend technique. While analizing or modelizing, make use of CATIA to check the possibility of the element bend highness. Note these tips in simulation process:

1. Element stuff density as well as off-set factor K of neutral coat.

2. Choose the very or at least resembling punches appropriate to element bend semidiameter.

3. In accordance with element stuff density and gating compression punches, chhose proper bottom die slot.

4. Consider neutral coat for calculation position ending upon bottom die while bending.

5. In simulation process consider little R on V-groove tips.

Fig. 5 depicts modelizing process appropriate to the given specifications.

In the shape depicted in fig. 5 black line is the element neutral coat, a is neutral coat line measure, b is neutral coat arch length at bend semidiameter, c is the space in the midst of tooling centre as well as ending border of V slot R. Bendinh is possible in case (a + b)/2>c. In case (a + b)/2≤c bending is not possible. It may be concluded that in case element sizes are excessively little, general flanging sizes of elment must be enlarged in simulation process.

2. Bend of big elements.

Press brakes are influenced by machineray tooling framework in bend process of big elements in order to make it possible for each bend bead to get exposed to deformity. In the aftermath of bend process direct lines are turned int curved lines and operators are required to accomplish bend process through a set of operations. In case of these problems an equipment attached to press brakes, called crowning may be adjusted in the aftermath of bend process to remove element deformities (see fig. 6), this reduces workers` efforts, improves element features as well as product effectiveness.

3. Bend of elements thinning in parts.

Sometimes ceratin elements get decreased in parts to diminish heft. Elements are possible to form through hydraulic formation or bendprocess. But in case of material unstable density for proper bend  process bending is impossible to realize by the same punches or dies through one operation. In this case thin pads are added to thin areas of stuff, adjust pads in the aftermath of bend process in accordance with upper punch. During bend formation, pad makes R offset for upper punch, so the stuff bend in case of various density is possible to form through one operation.

4. Bend process of formed flange element.

Normally back positioned stopper is of direct line. Manyfold rear stoppers appear in direct lines. That is why they are capeable of bending equal-highedflange elements. Traditional rear stoppers are not able to bend unevenly high flanged elements and formed elements. Here are two suggested solutions.

1. Rear stopper has got a screw to make positioning and this is different from traditional position methods and solves the trouble to bend unevenly high flanged and formed elements. Fig. 7 and 8 show processing prior to and after bending.

2. During blank process adjust assisting positional ear piece to bend elements. Ear piece is at the utmost height with elements, and elements with earing plate positionings contribute to bend and formation process. Take away ear piece in the aftermath of bend process to carry out element bending formation. This also boosts producing effectiveness.

5. Element breakage at bend area.

It may happen so that elements break at bending place. Affecting factors can be:

• Element stuff state.
• Extended stuff texture direction. In case of ruptures, the stuff fiber direction should be changed and made vertical to bend direction. Adopting anneal procedure upon bend elements will also work.

Conclusion

For efficient and proper bend formation appropriate bend tool should be chosen. In case of various errors, cosider the tips and solutions given above. This will improve production efficiency as well, and will save labour efforts and time ensuring high quality outcome.

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