Question: I have been an intern in a workshop for a while and I have been contributing to the optimization of bending procedures. At first, both I and the operator were less experienced at handling the press brake. Looking over the articles from harsle.com equipped me with the necessary tips and guidance on making sheet bend process come off. I managed to come to the proper determination on bending lines upon the circular blanks bent by us. However, there still exist certain items that leave me in confusion. 

Fig. 1

We have got a die and a punch of 0.125-inch together with a 0.25-inch die and punch. My task was to make bending, which meant I could come up with a bending of 0.125 or 0.25 inner radii. I succeed in achieving the necessary measuring, but the tooling we possess is too old. Moreover, the 0.125 dies cleft. (Fig.1). We have been in search of newer tools for some time, something that can meet the requirements of our tasks.

Generally, we make up to ninety-degree bends. For this purpose, the piece is first bottom-bent, which requires 5 times as much tonnage as the air-bend putting more strain on punches and dies. Now I seek ways to possibly escape a situation like this.  

In case of moving to the air-bend, are 85-degree-angle dies needed? Do the bending radii of dies matter in the air-bend process? How important are punches and V-slot sizes? How can we achieve bending of 90 degrees, meanwhile keeping the inner radii measures as well as get the post-bend measuring to take the required course?    

Answer: To begin with, I will reflect on the die photo sent by you. The dies are obviously outworn, they have served their best. They carry burns of severe wear, at some points between-die slot is larger in comparison with the rest length of dies. It may appear the effect of tool overloading. Without bottom-bend or coin formation, the possibility of achieving permanent bend is limited or even improbable. 

Judging by the appearance of the dies, I see a high probability that the press brake plunger undergoes a plunger disorder – a situation when the plunger or the base of the press brake gets exposed to constant deflection. (Fig. 2) As you have bottomed for a considerable period, you had better make use of a magnetic basis with dial indicators along with the plunger and bed. Check whether the indicator raises just as you come to the central area. The ram disorder needs checking, as well. If these are the cases, then the press brake needs serious correction or you may at least turn it off. There is no point in fighting anymore. You surely should get new tools, or even a newer press brake considering the caused faults.

Radius Is Decisive

Fig. 2

No matter what technique you apply; air-bend, bottom or coin, the inner bend radii appear decisive in the bending process. This point is crucial as it comes to calculating K factor, bending resolution, external set-back or bend deduction. Thus, the workpiece inner radius does matter a great deal.

Now I suggest clarifying certain terms. Punch radii are clear: it appears to be radii of punch tips. Radii of dies mostly refer to the radii of dying shoulders upon both sides of the die slot. Taking your question as a basis, I am assuming you refer to V-die base radii.

In the case of air-bend or bottom, sharp corners near the V base are technical “radii”. If your coin, you will make use of dies bearing significant radii at the V base. Those radii and bending external radii have to coincide just the way the stamp dies work.

In the beginning, you implied 0.125-inch radii punches and 0.125-inch radii near the die base. Thus, you are going to ensure 0.125-inch inner radii in any material of 0.108-0.375 inch thick. Besides, you are going to create 0.25-inch radii with 0.25-inch punch radii as well as 0.25 radii near the die base.

The external bending radii appear no less important point. The external bending radii should be counted through adding the inner bending radii to the sheet thicknesses. So 0.125-inch inner bending radii for materials of 0.125-inch density gains 0.25-inch outer radii. (0.125+0.125= 0.25)

As for your task (Fig. 3), in case of bending materials of 0.125-inch density through 0.125-inch punches, the result will be 0.125-inch inner bending radii and 0.25-inch outer bending radii, which you are going to push in dies with just 0.125-inch radii at the base. What is the way to make it work?

Here is an illustration of the result when the breadth of a die and the V base radii happen to be smaller for your task. The appearance of the bend is going to be less satisfactory.

Formation of radii.

Bend methods are decisive in the radius formation process. In case of using punches with the same nose radii as those of the inner radii we strive to gain, then the parts nay be bottom-bent or air-bent. An excellent bending is like this. In case of air bending the breadth of die slots is the most crucial factor, for the radii is going to float as the breadth proportion. The proportion varies depending on materials. Proper die breadth can provide you with the bending radii required.

The next decisive factor while air bending appears the radii of punching noses. In case there is no need for greater punching noses as compared with the natural radii, floating in parts, or smaller, compared to the sharp bending or the least inner radii, then you can gain it by avoiding the crease of the bending center. Based upon the required inner radii, consider these factors to choose suitable die openings or punch radii proper for your task. If the radii of punching noses appear close to the natural floating radii, your bending will be of more consistency and stability from the point of dimensional and angular views.

Tool Consideration Upon Air Bending

In case of air bend angles, radii of dies, as well as die base radii, make no influence on the workpiece floating inner radii. One more time dies breadth is responsible for this. 

To sum up, in case of air bend, a die of 85 degrees is a suitable decision, as far as its breadth produces the required inner bending radius in the workpiece, besides, it is capable of handling the needed formation tonnages. Yet it should be noted that bottom forming is impossible to perform or attempt through this tool. Sharp dies are designed exclusively for air formation. Matching any die of sharp angles with load pressures in the bottom will produce so much lateral traction over the die that it will split the tooling in the center.

Tools are consumable materials

Most manufacturers purchase the newest, modern press brakes just to keep using their old shabby tools and outworn modes, and later wonder when their newest, modern press brakes do not live up to expectancy!

The press brake tools must be considered as consumables; They serve long, of course, but they are not eternal. They outwear. The additional periods spent on resolving problems concerning outworn tools will significantly exceed the cost of newer, top-quality tools.

Sometimes special tools might be required to operate, still, you may make use of adapters (with conventional planing with accuracy or accurate to conventional planing) to install them on your newer press brakes. This generally comes down to human nature and the need to get out of our comfort zone.

We have to change our way of thinking: the newest tools make wonders in the industry.