Question: I have been dealing with a complex workpiece (shown in Fig. 1 and 2) which is a steel of 3/16 inch thickness. The workpiece bears stiffening ribs on the left as well as the right sides, which are descending flanges of 90 degrees with 4 inner bends. Inner bends stretch obliquely, rather than parallel to the blank edges. 

Fig. 1
Fig. 2

The central trapezoidal formation produced by the 2 inmost bends has to touch the table, so do the edges of triangular grooves, thus, the incline is 8 to 10 degrees down from the backside to the head (grooves at the front). The greater part of the piece is possible to mold sequentially, still, the form of trapezoidal fails to touch the table and gets fluctuations.

I mostly make my bends with a particular stamp of 0.65-inch aperture (Fig. 3) dealing with stiffening ribs of 90 degrees. I first make the outside down bend, next, turn it over to make the inside upper bending. The same thing is done on the opposite side. (Fig. 4) The workshop draft instructs making 150-degree bends (outer angles of 30 degrees) for inside bends and 152-degree bends (outer angles of 28 degrees) for outside bends. 

Fig. 3
Fig. 4

Unluckily, when the outside bend has been performed, it becomes too hard to perform the 2nd bending without the 1st bend in contact with the stamp. Thus, I apply a V-shaped die with an aperture of 0.65 inches to make the 2nd bending.

Currently, I have around sixty of such kinds of parts fluctuating, rather than flat. I have no idea about the correct ways. Should these parts be flattened and re-bent through a wide die? If they are re-bent as flat parts, should the inside bend be first made? Will this contribute to the flattening of the trapezoidal shape so that it will not lean back? 

Answer: The way you think is mainly right. The die used by you is one of the promoting factors, that is easy to fix. The trouble you have is related to the bending succession and gauging.

Attempts of flattening and reworking will not give satisfactory results even if you perform this in the most perfect conditions. It will bring about poorly marked areas on your workpiece. It becomes impossible to gain flatness for the part, thus it gets damaged. Besides, the part being exposed to flattening gets weaker along the bending lines. Performing bends in the same area is not easy as it may cause cracks on the outer side of bending radii. 

The bending direction shifts at the weak spot. It will not be upright along the bending direction. You will get a flat W-shape on your part. Certain sections on the flat bending run will get thinner producing weaker parts inside the piece.

What is more, holding the required measures will be impossible, as flattening makes dimensional changes. Bending deductions get changed as well. The entire size expands in length. As a result of flattening and re-bending the workpiece gets weaker, causing the material entirety to suffer. The piece will get damaged after the device installed in the area.

While avoiding re-striking several parts, you can aggravate the wobble. You may not like this, but reworking apart from a new blank is the right thing to do. This can help you to avoid deterioration, particularly when it comes to your profits.

Improving Formation Sequence

As you start with down bending of 90 degrees for stiffening flanges, then the inmost up-bending, you have to perform bending down from flanges. This brings you beneath the zone parallel to the die. Changing the order of the bending succession improves the case and helps solve the problem associated with trapezoidal vibrations and allows saving sizes according to the draw.

I advise beginning from the 2 inmost bends ending with the bending of 90 degrees. In particular, I`d begin from the inmost up-bending, turn the part over for external bending, next do the downward bending of 90 degrees for stiffening flanges.  Then, rotate the piece to make the same 3 bends on the opposite face.

Blank Gauging

Any change in bending angles changes the ratio of the part to the back gauge, as a result of which the position of the bending lines moves off the location in which they should appear. How can successive measurement strategics be developed to have the same position for all bending lines, alongside?

The measurement strategics is dependent on the style of your back gauge. The upgraded multi-axle back gauge system has flexible stops meant to deal with the back gauge fingers.

The alternative solution is adding break-away material for gauging, cutting the surplus material at the same angles as the bending line in the workpiece. (Fig. 5) It must be noted that here the angles of the bending lines are referred concerning the workpiece edges rather than the bending angle itself. The additional material provides parallelism for bending lines and measures. After having the bend performed, the additional material could be removed.

Fig. 5

As inner bending lines are of 2 different angularities, 2 break-away parts will be needed. To perform this, cut the blanks with 2 laser-stitch lines on sides. There must be parallelism between each edge and inmost bending lines (for angles of 150 degrees), the external laser-stitched lines must be parallel to the outer bending lines (for angles of 150 degrees). The internal laser-stitched lines should be the edges for the finished piece.

Start with 150-degree bending, next tear off the material alongside the external laser-stitch lines and you will find edges parallel to the bending of 152 degrees. Following the bending formation, tear the inmost laser-stitched lines to identify the actual workpiece edge. This is used to measure the down flanges of 90 degrees. At last, tip the piece over to perform the same succession on the opposite face.

Bend Die Alteration

Your die seems slightly overhauled. In case of troubles related to the gap or enforcement to change the part dynamics, you can remove a portion of the tooling. The removal of some material should have no effect on the force or functions of the tooling.

Excellence With Experience and Endurance

Gauging and formation sequence continues to be a matter of practice. It takes particular periods of time and effort to master the process. One can learn from mistakes, still, some of them might turn rather costly, particularly if you happen to re-make the whole bending succession.

Over time you will gain all the required skills and mastery. Remember that the efficient management of the press brake takes a rigorous training period. Mastering press brakes is one of the key challenges in the workshop.