The needs of those who bend are different from those who design and from those who cut, but with a few simple steps, the various departments can collaborate to increase the efficiency of the entire shop.
More often than not, press brake operators aren’t pleased with the quality of the laser cut pieces that arrive at their machines. The issue is that the two production processes require different approaches that don’t always match up. Fortunately, there are a few simple tricks that allow laser cutters to work more in sync with downstream bending operations.
Matters of material
Sheet metal is an anisotropic material, meaning its properties are not the same in all directions. As all press brake operators worth their salt know, sheet metal’s behavior changes depending on the direction of rolling.
Knowing that, it’s useful to laser cut all of the pieces in the same direction or to divide them into pieces that should either be cut parallel to the fiber or perpendicular to the fiber. Nesting with variable orientation is not recommended, however. While some material might be saved by fitting an extra piece in the sheet, there is a risk of wasting parts and time when it then becomes difficult to get the right angle when bending at the press brake.
The first rule of thumb is to divide the pieces according to the characteristics of the sheet. For example, the internal tensions of the sheet change between the center and the edges due to the stresses introduced by the rolling. Additionally, it’s not recommended to mix pieces cut from different batches of sheet metal because there are inevitable differences between one casting and another, causing variable hardness and elasticity, which can affect the final bend.
In these cases, a real-time angle control system and adaptive crowning system can help press brake operators obtain constant angles even if the pieces have been laser cut in a different direction.
Joints, jigs and lines
In certain cases, especially with small pieces, it is mandatory to leave micro junctions, sometimes referred to as micro joints, in place to prevent cut pieces from falling into the bed or from tipping over, with the risk of collision with the laser cutting head. It’s important to know, however, that these micro joints can leave small spikes on the edge of the piece, which can make it difficult to properly rest it (G) on the press brake’s back gauge fingers. When possible, place micro joints where they do not cause difficulties (H), as seen in Figure 1.
Creating alignment jigs can be helpful for a press brake operator. If the press brake does not have the X5 and X6 axes for oblique bends or, if the piece (A) has an irregular shape that makes it difficult to rest it safely, the laser operator can cut a piece of the scrap (D) and attach it to the back gauge stops (C). In this way, the piece can be placed on the opposite shape, ensuring an optimal alignment with the bending axis (C), as referenced in Figure 2.
Another method for helping with the lack of the relative X axes on the press brake is by marking the bending lines with the laser. If it is not possible to trace the surface, marks can be placed on the edges ([F), as seen in Figure 3. They should preferably face outward rather than inward to avoid cracking. If forced to use inward-facing marks, avoid sharp notches (E).
When unloading cut pieces from the laser bed, keeping them well stacked and in order helps the press brake operator significantly. And it also reduces damage, such as distorted or scratched pieces, especially on pieces made with delicate materials or finishes.
Although it may sound trivial to count the pieces before handing them over for bending, it can help avoid any potential headaches. With large lots, a piece or two may easily come up missing, especially if they are small. Stopping and resuming the laser cutting later may also cause an operator to lose count. In the end, less time is wasted on re-cutting a missing piece on the fly while the drawing is still in the machine and the sheet is still on the bed, rather than having to do so maybe days later with the risk of no longer having sheet available.
Furthermore, before sending an entire lot to the press brake, check that the cut pieces correspond to what is indicated on the order sheet or in the technical drawing. By doing so, problems and setbacks can be avoided.
Finally, split orders and associate each order with its drawing or worksheet instead of heaping all of the drawings together or, worse still, without any drawing at all.
For laser operators, it’s essential to correctly calculate the bend deduction and the correct cut length according to the material and tools. Here, it’s essential to discuss with the press brake operator to calculate the specific K-factor of a bend, doing preliminary tests.
For assistance calculating bend allowance, bend deduction and the K-factor, Gasparini developed a tool that can be found on the company website in the Calculators section.
Insert the necessary bend reliefs into the drawing to avoid cracks and tears. Maintain adequate distances (the bend radius plus two times the thickness) between the bending line and holes, ridges, louvers and threads. And, of course, don’t forget the corner reliefs.
Take into account the need for over-bending to compensate for springback. If a flange comes into contact with another part of the piece, it must be taken into account to achieve the desired angle. In some cases, operators should bend to a more closed angle to avoid the risk of collision.
When laser cutting and press brake operations work in tandem, the end results will ultimately be of a higher quality – a higher quality that is achieved with less rework, less scrap and, in turn, higher profits.