Press Brake

Sheet Metal Design Guide

Bending is a process of stamping that compels any material to disfigure elastically through pressure shaping a particular angle and gradient form.

V-bend, Z-bend, offset and hemming bend are the ones that are in common use.

Bending Height

The flexing height of a plate material should be twice as thick as the sheet metal along with flex radius, which H ≥ 2t + R.

As it is seen below flexing height of plate metal is rather low and the metal can be disfigured easily and deformed while curving. This creates difficulty to get a particular desired form and accurate size.

While curving a beveled ridge bend deformation will most probably happen for bending level is rather small.

According to the depiction in the principle design twisting distortion is most possible during flexing process as the left crook spread is rather small. This will lead to decreased bending quality.

In the improved design the flex level on left side may be raised or minimum portion of crook elevation may be eliminated so as not to expose certain plate metal to deformation and come to a high quality bending. 

Bending Radius 

To secure strong bending the flex offshoot of plate metals have to be bigger compared to the minimum bending offshoot of sheet metals. Different plate metals may vary in minimum bending radius as shown in the following table.

Aluminum Alloy06t
Magnesium Alloy5t13t
Stainless Steel0.5t6t
Low Carbon Steel / Low Alloy Steel0.5t4t
Titanium Alloy2.6t4t

Bigger plate metal flex radius does not make the business better. The greater bending offshoot, the greater bend bounce. This makes it harder to control the crook angle and height.

Consequently, plate metal radius has to be calculated correctly.

Moreover, most sheet metal producers are inclined to have a zero flex offshoot in order to prevent sheet materials from recoiling after bending. Besides the crook angle and spread will be easier to control.

Nevertheless, zero bending offshoot increases the risk of damaging or breaking plate materials and flex durability decreases particularly in case of solid plate metals. What is more, the right side angle of the mold increasingly becomes plain after a period of operation making the crook size difficult to control.

To reduce the flex strength and secure the size, the plate metal mold producer works out a different method, which makes possible processing process prior to bending.

Nonetheless, a design like this does not exclude such defects as weak flex strength and cracking or even breaking sheet metals.

The pressing process allows to press a groove on plate metal materials to alleviate flexing and gain accurate bending.

Bending Direction

Bending should be utmost upright in accordance with metal fiber direction. If the plate metal material flex is parallel to the course of metal fiber, fractures tend to appear at the fold of a particular plate metal, and the flex force is low and breaking is quite easy as it is seen in the picture.

 Bending Failure Escape

While bending sheet metals may sometimes fail to be pressed or crooked. The density of plate metals should be no less than twice as much as the bending radius at the base of sheet metals in order to avoid a problem like this. See in the figure below.

In the preliminary sample the refund straightening location appears too close to the metal base, which was the main  cause of pressing and bending failure.

Bending process may also fail if plate metal budding and flex root are rather close to each other. In case of this, the bud should be located at the base of plate metal as shown in the modified sample. 

However, if any design requests do not permit to move the bud and bend location, you may make a gap at the flex root according to the bud to secure the process of bending as shown in the modified sample.

Secure Smooth Bending and Escape Bending Obstacles

Owing to plate metal crooking resistance a particular bending cut has to be made to prevent bending collapse.

The upper side of plate metals should be crooked first and later the right one should be bent.

As shown in the first figure, there is no space between the flex tips. While bending, the existence of metal crooking resistance makes barriers during bending.

In the modified sample there is a cleft of 0.2 mm between the right and upper sides, which brings about smooth bending.

Secure Flex Force

While bending  certain plate metal the flex force has to be secured. The longer and narrower the flex force, the lower it is and vice versa. Consequently, the metal bend has to be fixed to the longer part as depicted in the below design.

Minimizing Bending Process and Escape Intricate Twists 

In case of bending many parts of the sheet metal, the mold cost will be higher and the exactness will be lower. That is why the design of any plate metal should be drawn in a way to decrease the folding points. See in the below sample.

You can see double bending in the first figure. In the second one just a single bending is needed to accomplish the process.

If the plate metal design is intricate, wastes are expected to be more.   

The more complicated a design, the more accurate calculations should be. This will ensure reduced production costs and better quality.

You can see in the following figure that the metal design requiring intricate bending is divided into two parts, both of which are joint by spikes or welding.

Pores on Numerous Bends Are Hard to Aline 

Not a few workers may have experienced the difficulty of aligning nail and screw pores on plate metals and spikes and screws cannot be attached. The reason for this is that bending resistance is high, particularly when metal has to be bent multiply.

One bend0.15
Two bend0.25
Three bend0.36
Four bend0.44
Five bend0.51
Six bend0.59

It can be inferred that the greatness of bending resistance depends on how many times the sheet is flexed. Ensuring size precision of multiple bends is quite hard. This makes it difficult to align screw, nail or other holes on the metal.

Meanwhile, an optimized design should be made to escape the assembly misalignment. Here is an offered solution: 

Turn a pore in a bend into a circular hole.

Make two inside locating punctures, decrease bending resistance and secure the hole alignment on both bends.

Size precision of two pores is possible to guarantee by first crooking and later punching. Though this in its turn may cause stamping die complicacy and cost rise. Actually, it cannot be absolutely recommended.

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