Contrary to popular belief, press brake tooling plays an essential part in the formation of metal as well as is not merely an accessory.The tooling is all that ever comes into contact with the item when bending, even though press brakes have developed into multiaxes, very precise devices with self-stabilizing characteristics (see Figure 1).
The distinctions between RFA, New Standard, European, and American standard tooling are no longer as clear. Numerous attributes required for high-performance bending have been transferred to every kind of tooling. Choose a tooling and clamping style, but make sure it satisfies a few basic requirements.
High precision: Tolerances within the range of 0.0004 inches should be used in the manufacturing of the tools. To attain part precision without shimming or requiring further setup adjustments, this is essential.
Divided portions: These let you construct different lengths using multiple precut pieces. Additionally safer and simpler to handle are little parts.
Self-retaining installation: With the RAM up, you ought to be able to load the tools. Multiple components should be held in position by the tool-holding system until the clamping pressure is applied (see Figure 2).
Front loading: Installing tools ought to be possible from the machine’s front. Because you don’t have to spend time sliding tools from the end of the press brake, this reduces setup time. Front loading also typically removes the requirement for overhead cranes and forklifts.
Standard sizes: When switching projects, common-height tools can minimize the requirement for machine changes. Safety devices, backgauge heights, and front support arms all stay in the same place. Additionally, you may add off-the-shelf components and be sure they will match your current tools because all tools are constructed to the same heights.
Many standards are used in the manufacture of several premium press brake tools. Consequently, a nominal 0.250-in. in actuality, the V opening is 6mm, or 0.236 in. Furthermore, the corner radii of bends in sheet metal are slightly elliptical, thus accuracy is achieved by just getting close. In this article, imperial measurements are rounded for ease.
You’ll see that the following discussion is justified in concentrating on air bending. The current trend is to prefer air bending over bottoming or coining wherever it is feasible. But keep in mind that not every item can be made with traditional air bending methods.
Die Selection
Select a minimum quantity of lower dies that will accommodate the full range of metal thicknesses that your company forms in order to obtain the most value for your money. Shops with limited funds, unplanned uses, and little tribal knowledge should attempt to use the 8×2 rule to select lower dies.
Choose the range of metal thicknesses that you wish to bend first. For instance, material that is 0.250 in thick through 0.030 in. may need to be bent.
Second, multiply the thinnest metal by 8 to determine the smallest V die required. The lowest die would be required in this instance for 0.030-in. material, therefore we’ll round it to 0.25 (0.030 × 8 = 0.24).
Third, double the thickest metal by eight to determine the greatest V die required. Here, the largest die would be required for the thickest material, which is 0.250 in. (0.250 × 8 = 2).
You now know that you require the smallest and largest dies, which are 0.25 and 2 inches. Start with the smallest V die and double its size to fill in everything you need in between. This provides you with a 0.5-inch die in this instance (0.25 × 2 = 0.5). Then, to produce 1.0 in. and 2.0 in., double the 0.5-in. die twice. This allows you to bend material ranging from 0.030 to 0.250 inches in four distinct V-die openings at minimum: 0.25, 0.5, 1.0, and 2.0 in.
Punch Selection
The minimum number of upper punches is also determined by the thickness of the material. You can use an acute offset knife punch with a 0.04-in. radius for material 0.187 in. and thinner. Bending past 90 degrees is possible due to the acute angle, and forming J forms is made possible by the offset. When shaping material that is between 0.187 and 0.5 inches thick, use a straight punch with a radius of roughly 0.120 inches to manage the increased forces.
It should be noted that when utilizing normal industry bending standards, the workpiece has a tendency to fold, crack, or even split in two for certain applications, especially those involving thicker and high-tensile material. It is a matter of physics. More force is applied to the bend line by a thin punch tip; when combined with a narrow V-die opening, the forces increase even more. For difficult applications, it is best to speak with your material supplier about the appropriate punch tip radius, particularly if the material thickness is more than 0.5 inches.
The 8 Rule
The ideal situation would be one in which you could choose the V-die opening by applying what is known as the “rule of 8,” which states that the V-die aperture should be eight times the thickness of the material. Multiply the material thickness by 8 to find this, then select the closest die that is available. Therefore, a 0.5-inch die is required for material that is 0.060 inches thick (0.060 × 8 = 0.48; the closest die width is 0.50 inches); a 1-inch die is required for material that is 0.125 inches thick (0.125 × 8 = 1). This ratio is often referred to as the “sweet spot” for V-die choosing since it provides the best angular performance. The majority of bending charts that are published revolve around this principle.
Easy enough, huh? If sheet metal designers always adhered to the rule of eight, then yes, it would be in an ideal world, and you could live in that wonderful world. Unfortunately, there are many exceptions in the actual world.
Radius is determined by the V-die Opening
The inside bend radius of mild steel formed by air bending occurs at about 16 percent of the V-die opening. Thus, your inside bend radius will be approximately 0.16 inches if you air-bent material over a 1-inch V die.
Let’s say a print calls for 0.125-inch material. In an ideal scenario, you would utilize a 1-in. V die and multiply that thickness by 8. Fairly easy. However, a lot of sheet metal designers like to give a bend radius that matches the thickness of the metal. What happens if the inside radius of the print is 0.125 inches?
Once more, the material air-bends with an interior radius equal to around 16% of the die opening. Thus, a radius of 0.160 in can be produced using your 1-in. die. What happens next? Simply utilize a smaller V die. An inside radius of 0.125 inches can be obtained with a 0.75-inch die (0.75 × 0.16 = 0.12).
The same reasoning holds true for prints that call for greater bend radii. Let’s say you have to shape mild steel that is 0.125 inches thick to an inner bend radius of 0.320 inches, which is more than double the thickness of the material. Using a 2-inch die in this situation would result in an inner bend radius of roughly 0.320 inches (2 × 0.16).
This has its bounds. For instance, you will jeopardize angular precision, maybe damage the machine and its tooling, and place yourself in grave danger if you discover that, in order to accomplish the desired inside bend radius, you need a V-die opening that is less than five times the thickness of the metal.
Punch Selection Rules
The regulations are… there are no rules for L shapes. You can use almost any shape of punch. Because these L-shaped components can be punched with almost any punch shape, you should always choose punches for them last when choosing punches for a group of parts.
Instead of adding extraneous tools to the library, utilize a punch that can also be used to produce other pieces when creating these L shapes. Recall that less is always better when it comes to tooling specifications. This applies not just to minimizing tooling costs but also to saving setup time by minimizing the number of tool shapes required on the shop floor (see Figure 3).
There are principles for punch selection that apply to other shapes. For example, the following guidelines apply for creating J shapes (see Figure 4):
- When the small up-leg is longer than the bottom leg, you need a gooseneck punch.
- When the small up-leg is shorter than the bottom leg, any punch shape will work.
- When the small up-leg is equal to the bottom leg, you need an offset acute punch.
As you can see, workpiece interference is the main topic covered by the punch selection criteria. Bending simulation software can be very helpful in this regard. You can manually check for punch-part interference using the drawings with grid backgrounds provided by your tooling supplier if you do not have access to bend simulation software. (see Figure 5)
