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Metal folding’s place in the forming department

How a folder complements the press brake in a metal fabrication shop

metal folding

Figure 1 Segmented upper beam tools are grouped to provide clearance for previously formed flanges.

Walk into most commercial or precision sheet metal operations with CNC metal folders on the floor and you’ll probably find a collection of CNC press brakes too. Sure, press brakes have a longer history in U.S. metal fabrication than folders do, but that’s often not why fabricators keep both types of forming machines on the floor. They have both because in many ways metal folders and press brakes aren’t competitive technologies. In fact, they’re complementary.

Having both presents opportunities, but to take advantage of them, you need to understand how exactly folders work and what their inherent benefits and limitations are. While some limitations remain, folders can do so much more than they could even a decade ago. They also add much needed forming capacity to fabrication operations that, thanks to the fiber laser, have more blanking capacity than ever.

Folding Basics

CNC folding occurs in a variety of machines, from those that require full operator involvement to fully automated, lights-out operation. It all depends on the task at hand.

Many shops take a hard look at metal folding for not only efficiency, but also worker ergonomics. Can you imagine the operator not having to support the weight of the part as he moves through the bend sequences? Do some large or heavy parts require several operators to manipulate through bending? Eliminating these concerns is one of folding’s most basic inherent advantages.

When you invest in a press brake, you consider bed length, tools, and tonnage capacity for the machine and tools you choose. When you invest in a folder, tonnage doesn’t enter the conversation, just material gauge. Machines are designed to handle up to a specific material thickness, with carbon steel as the typical baseline. Material thickness capacity is a few gauges thicker (lower gauge) for softer aluminum and should be a few gauges thinner (higher gauge) for stainless.

For instance, when you are folding 14-ga. carbon steel on a machine rated for 14 ga., the machine should be able to fold that material along the entire length of the bed. Bend length is a factor, though. Folders can bend some material that is thicker than the rated capacity in shorter lengths as long as the tooling is rated for the heavier material. Most machine manufacturers will provide a performance graph reflecting the tooling’s capability.

In a typical metal folding setup, sheet metal is positioned on a gauging table behind the work envelope. This includes an upper beam with upper beam tools, a lower beam with lower beam tools, and, finally, the folding beam with folding beam tools.

During air bending on a press brake, the punch descends into the die space, the material drags over the die shoulders, and the inside radius forms as a percentage of the die width.

A metal folder also “air-bends”—in the sense that the material is not bottomed or coined—and because of this, there is little to no wear in tooling for most folding applications. But the machine’s approach to bending is entirely different. For the most part, folders incorporate servo technology to drive and position all axes. This results in the most accurate product.

With integrated sheet support and backgauging systems, the part is positioned flat on the table, and only the flange is bent. The operator doesn’t need to balance or support the part in any way during the forming cycle. Segmented upper beam tools are grouped to accommodate bend lengths and necessary clearances for previously formed flanges (see Figure 1). The upper beam tools descend, and the workpiece is clamped between the upper and lower beam tools. The folding beam tool then moves into position, contacts the material, and rotates to form the first flange.

bidirectional metal folding

Figure 2 Bidirectional folding systems can bend both positive and negative flanges, no flipping of the part required.

Entry-level upacting-only folders require operators to flip the part to achieve a negative bend. In semiautomated folders, the folding beam can bend both positive and negative, no flipping of the material required, greatly reducing run times. Specifically, these bidirectional folders can rotate the beam upward for positive bends, then reposition itself to a new pivot point before swinging downward for a negative bend (see Figure 2). Hybrid gauging and suction cup gauging can reduce operator involvement and part positioning problems (see Figure 3).

The distance between two points of contact on the workpiece—the edge of the lower beam tool and the tip of the folding beam tool—determines the inside bend radius. Although a 1-to-1 inside-bend-radius-to-material-thickness relationship might be achievable, typical setups maintain a 1.25-to-1 relationship between the inside bend radius and material thickness depending on the machine’s clamping force and the workpiece’s material type and thickness. On some folding systems, the beam can move outward slightly; like having a larger die opening on a press brake, this allows for a larger inside radius on some material thicknesses. On some thicknesses a larger than 1.25X thickness radius bend can be achieved. If a workpiece requires a larger radius, the folder usually turns to incremental bending, or bumping. The lower beam is programmable to accommodate different material thicknesses automatically up to the rated capacity of the machine.

In fact, most folding machines automatically adjust for material thickness changes. After the program has been developed and proven via offline software, the machine is ready to run. And because programming occurs offline, the machine can produce other parts while the new program is being generated.

Levels of Folding Automation

CNC folding machines are sold with varying levels of automation. In a semiautomated machine, the operator’s involvement is limited to loading, positioning, rotating, and unloading the part.

In fully automated folding systems, once the material is loaded, the machine inspects the part to provide its identity. For instance, some systems use infrared light that focuses on specific areas of a sheet metal blank. With the piece identified, the machine automatically changes to the required tools, and a manipulator positions and rotates the part during the bend cycle.

Automated folding systems can be integrated with material load towers, shuttle load systems, and robot load/unload. In essence, material handling is driven by the application requirements.

Offline programming software has also helped automate and streamline folding even further. Today some software can import CAD-generated STEP files, along with a variety of other formats. It automatically generates a 3D model for viewing, creates a recommended bend sequence for review, and runs a simulation of the product being formed. From there it converts the job into machine tool language. All this can be done offline, effectively eliminating the need for on-machine programming.

Crowning on a Folder

Crowning systems also enhance overall accuracies. Depending on the level of folding technology you consider, manual, automated, and engineered crowning systems are all available.

In a typical press brake, crowning occurs on the surface of the lower beam, just below where the dies are seated. In wedge-style crowning systems, the wedges slide against one another to provide a crown that counteracts deflection during bending.

On a folder, crowning occurs in the folding beam tooling or in the beam itself, just below where the folding beam tooling seats. In manual crowning systems, operators use a special folding beam tool that allows them to dial in a specific crown. This is common for architectural shops that might need to bump-form gutters or similar products.

gauging for metal folding

Figure 3 Suction-based gauging systems help eliminate part positioning inconsistencies.

Commercial and precision sheet metal shops often use CNC folders with intelligent crowning integrated into the folding beam. The mechanism itself is similar to the wedge-style systems seen on press brakes, but the folder’s crowning system as a whole is distinctly different. The folding beam swings up 10 degrees, detects the material, engages the crowning where needed, then commences the folding cycle.

Tooling Factors

In metal folding, the folding beam tool moves upward in an arc during the form and, as such, maintains constant contact with the workpiece’s outside surface. This makes the process well-suited for surface-sensitive material.

The process is also well-suited for high-product-mix, even kit-based production because, again, it uses a toolset that’s universal for most applications. In fact, usually one set of tools is enough for most formed parts. Tools are precision-ground and clamped in place, so no alignment is required except for positioning along the length of the bed of the machine to accommodate for the size of the part. There’s no punch that needs to be centered with a bottom V die.

Over a typical shift, a standard folding beam tool is used for multiple material thicknesses, though various upper beam tool segments can be staged across the beam length to provide necessary clearances for the job mix at hand. The segmented upper beam tools might need to be rearranged to accommodate different bend lengths and required clearances.

Some operations stage these tools across the length of the machine to accommodate all or most jobs over a shift, complete with tools designed to bend certain common forms, like an upper tool with rotating foot corners that provides clearance for adjacent return flanges. Many manual tool positioning systems, such as those in semiautomated machines, offer pneumatic clamping. Some advanced folding systems have automatic tool changing, which reduces setup times even further.

Flange Factors

A folder has no flange height limitation for open bends, but at 90 degrees or more the flange height limit depends on the upper beam tooling shut height, at least on certain machines.

That said, many folders do have significant tool height for deep box bending. Moreover, some folders have slanted upper beams that give clearance for very tall flanges (see Figure 4). Material handling and integrity (bowing of large, flimsy parts, etc.) are the only practical limitations.

Yes, You Can Fold That

Some parts that were actually considered impossible to form on a folder not too many years ago are now being formed on a folding machine. This is thanks in large part to special tooling. For instance, a folding beam might require a narrower tool to access tight Z forms and channels (see Figure 5). An application might also use a special folding beam tool that approaches the workpiece at an angle, making the folding of certain internal flange geometries possible.

The lower beam tools usually remain where they are, but special lower beam tools allow clearance for certain geometries, such as when the bend line is interrupted by weld tabs. The tools stay low to maintain the necessary clearances for other bends, then rise up so the remaining tabs can be bent. Other special tools allow for clearances of negative flanges on certain machines. “Certain machines” is the operative phrase here. These days folding machines can be designed and customized for certain part families.

Some commercial and precision fabricators might choose to fold a workpiece and then complete forming on a press brake, where an operator might, say, bend a few internal flanges that couldn’t be folded. Yes, it sounds counterintuitive; adding a secondary operation breaks the traditional efficiency rules. But the cycle time math often adds up. This might be especially true for large, unwieldy workpieces that are slow, arduous, or even dangerous to manipulate entirely on a press brake.

metal folding flange clearance

Figure 4 The upper beam orientation of this folding machine provides clearance for very tall bends. Note also how the setup gives clearance for the narrow down-flanges on each side of the workpiece.

Yes, You Can Gauge That

Some machines can accommodate challenging gauging requirements. Along with specialized backstops on the table, the folding beam itself can act as a kind of frontgauge.

When part blanks are sheared at an angle to create a tapered edge, some systems have a folding beam with limited travel (about 6 in.) for use as a kind of frontgauge. Again, only certain machines can perform this function, and the folding beam can move only so far to gauge a workpiece. But for the right situations, frontgauging with the folding beam can introduce a host of folding opportunities.

Where the Press Brake Excels

Folders have two primary limitations, and the second is more straightforward than the first. The first limitation is part geometry. The folding beam needs to be able to access the bend without colliding with other areas of the workpiece—hence the challenge of internal flanges located in the middle of very large workpieces. In automated folders especially, workpieces do need to be of a certain size. Tiny brackets or pieces involving intricate acute bends are difficult or impossible to form on a traditional folder.

Not only do manipulators need somewhere to grasp the piece, but the piece also needs enough surface area for the upper and lower beam tools to grasp. If a piece can’t be securely clamped, it can’t be reliably folded. Special circumstances aside, the piece also needs to be able to sit flat on the backgauge table for forming.

“Special circumstances” is an important aside, though, because quite often, special tools combined with a little creative thinking can make the previously unfoldable foldable. For instance, the folder might not be able to fold one tiny bracket, but could those brackets be tabbed together on a nest, folded as a single unit, then snapped apart after folding? And again, even certain internal flanges might not be a problem if the folding beam has a special tool to make the form.

The second primary folder limitation is far more straightforward, and it has to do with tonnage. Consider a typical hemming operation on a folder. The folding beam forms an acute bend that is then positioned under the upper beam tool. The upper beam tool descends to form a hem—open, closed, or teardrop—no special tool required.

However, the folder cannot coin the hem. Why? Because a coined hem is driven by high tonnage, and forming through tonnage is where the press brake really excels. True, some folding machine models use hydraulics to boost the servo-driven clamping force between the upper and lower beams, and doing that extends folding capacity to some plate material. But beyond that, the machine simply can’t exert enough force. For the most part, the folder is not a plate bending machine.

If an operation requires a forming strategy based on tonnage—be it coining a hem, bottoming a sharp radius in sheet, or air forming plate—the press brake is ideal. Consider air-bending armor plate. To reduce the application’s forming tonnage level, you simply choose a wider V die. Doing so might solve forming and cracking problems too. As long as the generated forming tonnage doesn’t exceed the tonnage capacity of the machine or tooling, and the bend radius the wider die produces meets the job requirements, you’re good to go. Similarly, if a part design requires a sharp bottomed radius in sheet metal, a press brake can do the job.

Complementary Forming Operations

Imagine a forming department with both metal folders and press brakes. The greatest volume of parts might run through a series of folders. The fabricator might even send some seemingly challenging parts through the folders, including jobs that call for flanges in internal windows (which use a special tool). It also might fold small parts that share a bend line, tabbing them all together for folding efficiency. Some pieces are formed first on the folder, then sent to a brake for a single quick bend—still much faster than if the entire piece were formed on the press brake.

But some parts just aren’t suited for the folders at all. Small and complex parts—those that take advantage of custom or unusual backgauge sequences as well as bend sequences that leave no flat surface for the folder—go to a press brake. Another large press brake has the required tonnage to bend plate and perhaps perform a few coined hems and radii in sheet.

narrow folding beam tools

Figure 5 Narrow folding beam tools allow for the folding of Z forms and other tight geometries.

This hypothetical arrangement would likely be a very flexible and especially productive forming department. With highly productive lasers sending the industry’s blanking capacity through the roof, the time is ripe for new approaches to forming productivity.


Another Option for Small Parts

Many fabricators that have both folding machines and press brakes might relegate small, complex parts to the press brake. But there is another, fully automated option. Specifically, there are a few systems on the market for lights-out bending of small parts. The machines don’t use folding beams or clamp material like a typical folding system does. Again, they can’t, because these parts are simply too small for a folder’s tools to grasp. Instead, a very small, specialized part manipulator holds the middle of the small blank, clamping it from above and below. It then carries the blank to the work envelope and positions it in between a set of upper and lower clamping tools. Behind these are two bending tools, one that moves upward for positive bends, another downward for negative bends. To bend another side, the clamping tools open, the manipulator rotates the piece, and the process starts again.

Small Part folding

Certain systems for lights-out bending of small parts use small manipulators and narrow clamping tools to grasp and manipulate the part through a bending cycle.

About the Author

Bill Kennedy

Vice President

1135 Dividend Court

Peachtree City, GA 30269

770-487-7300