Fabrication of plate metals is the irreplaceable component of mechanical treatment in such areas as automobile, aviation, elevator as well as household devices. Bending is the key procedure while working out plate metals the quality of which has a direct effect on shaping dimensions and the form of products. That is why ensuring the shaping sizes and bevel of the piece being processed is vital in the procedure of bending.
The attractiveness of products largely depends on its design and fancy style. The more intricate the form of plate design bend, the more attractive it seems. Only this is not enough, though. The pieces should correspond to the industrial demands as well, which assumes the circular arch radius to be small, smooth piece face with no bending signs and scratches.
Press brake machines of traditional types could not manage to correspond to the specific industrial demands, thus grooving technology came out.
Traditional Bending Technique and Its Restrictions
Bending by the means of traditional method implies sheet bending through enforcement of top and below die. Sheet bending is carried out by two opening ridges of the below die and the upper ridge of the top one. Sheet metals pass through the procedure of resilient distortion to a flexible one.
The depth of the top die into the below die defines the curve bevel and the curve semi-diameter R may be more than or the same as the sheet density. (See Fig.1)
The requirements on appearance of work pieces are gradually increasing. Bending by traditional method is not always workable for intricate pieces (see fig. 2). It is impossible for the curve semi-diameter to be controlled in the case of the traditional bending. This has led to the advent of a new method, that is groove bending.
Groove Bending Specifications
What does groove bending suggest?
This technique implies grooving V shaped notched line upon plate metal at which point it has to be bent and bending it on the press brake according to requirements. These particular features are typical of groove bending:
The ridge arch semi diameter is not big and performs without leaving bending signs on produced pieces.
Bending technique suggests that the utmost edge arch semi-diameter of processed pieces is equal to the sheet density in the aftermath of bending.
When a V notch line has been grooved on plate metals, the density equals the half or less than that of its original state. Thus, the arch semi-diameter considerably reduces in the aftermath of bending. So the point being bent becomes thin and the enforcement while bending decreases allowing unbent surface not to be affected. As a result, no signs are left on the produced piece after bending.
Bending requires low press brake burden of tons.
Curve strength necessary for metal plates bending depends on its own density. If the sheet is thicker, the demanded strength for curving process is higher. In that case the burden of the press brake increases. Prior to bending, a V shaped groove has to be made on the sheet at the point where it is intended to be bent. This considerably decreases sheet density, which in its turn reduces bend enforcement resulting in curving with little burden. And all this supports less power consumption.
This technique ensures bending of intricate pieces and the plasticity control.
A traditional bending machine is incapable of flexing and shaping the section depicted in Fig.2. Its bending can be realized manually in the aftermath of grooving on the area being bent. Moreover, this method enables to manage the bouncing strength and bevel.
Method of Notching a V shape.
Grooving machine is frequently applied to shape a V form on metal plates.
Put crooked sheet in the grooving device and later set proper sheet density to groove automatically. Mind these tips:
Deepness of grooving and residual density.
In accordance with bending standards, the remaining density is placed first and must be no more than 0.3 mm. Afterwards adjust groove deepness considering sheet density. As the blades must be kept safe, it is not advisable to feed excessively. In general groove deepness should not surpass 0.8 mm. Realize grooving by two acts.
For instance, in the aftermath of grooving stainless plates of 1.2 mm, the residual density is 0.5 mm.
Adjusting the groove bevel.
Plate metals have got various extent of bouncing deformity while bending leading to bending bevel deflection. Grooving should be realized in accordance with the work piece bending bevel while grooving a V shape. Generally V groove bevel is 1 or 2 degrees bigger compared to bending bevel.
For instance, while bending a work piece of 90 degrees, V groove bevel should be adjusted at 92 degrees. See fig. 4. By this means it is possible to prevent bevel distortion brought about by bouncing backwards. See fig. 5.
Kinds of groove blades and their selection
Types of groove blades are rhombus upper bevel blades, square groove blades, triangular, circular groove blades and so on. See fig. 6. Blades are chosen taking into consideration V grooving bevel and form. The blade bevel must be no more compared to the V slit bevel. For instance in case of V grooving of 45-60 degrees, rhombus blades of 35 degrees upper bevel are suitable.
In case of 60-80 degrees V groove triangular ones are proper. In case of 80-90 degrees rhombus blades of 80 degrees upper bevel are suitable. If V shape is grooved with more than 90 degrees, square blades are advisable. For circular form grooving circular blades are suitable.
The times of adjusting blades.
During groove process of long and deep plates,blades are to be damaged as a result of overheat in case of operating permanently just one blade piece. This will also bring on bad grooving outcomes and various burrs on plates.
In case blade feed quantity is 0.2 mm, the realization of grooving of 2 mm dense plate can be finished in ten times.
In fig. 7 3 or 4 blades are applied to operate at the same time. Feeding quantity of blades varies by 2 mm. This will ensure proper quality and enhance task effectiveness.
Prevention of bending bevel and size deflection.
Bending bevel and size determine bending efficiency. To gain them properly note these tips:
Not centered upper notch and beneath mold will result in improper bending size. So the top and bottom molds have to be centered prior to bending process.
The placement of sheet metal and bottom mold might change in the aftermath of left movement of back stopper. So check their breadth prior to bending.
If the work piece and bottom mold are not parallel bending bounce backwards is possible, which will damage bending bevel.
Bending bevel of each time bending should be accurate to prevent further errors.
While bending a work piece after V grooving, make sure that the top double ridge, V shape down ridge of the work piece as well as the V shape lower ridge of the down mold are parallel to one another.
The top mold bevel has to be set at 84 degrees to prevent mold pressing.
Estimating the metal plate unfolding length
It is shown in the figure that the sheet density is 3 mm. The ridge sizes are also shown. In case the residual density is 0.5 mm, the unfolding length will be L=(40-0.5) +(30-2×0.5) + (10-0.5)=107 mm.
Bending with no groove:
L= (40-3+0.25) + (30-6=2×0.25) + (30-6+2×0.25)+(10-3+0.25)=93.5 mm.
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