In particular, sheet metal was used extensively for roofing and building cladding. These applications were well-suited to the swing bending machine’s geometry, and the modern metal folding industry was born.
A number of German manufacturers began adding powered backgauges with rudimentary numerical controls in the ’60s. By the ’80s, fully multiaxis computer numerical controllers (CNCs) were applied, and automatic backgauges were added. Folding technology continued to dominate architectural metal fabricating in Europe.
As folding technology developed, it was found to be useful for bending large parts, because whip up, sometimes associated with press brakes, was not a problem.
The backgauge is integrated into a sheet support system so that operators don’t have to support the weight of a large part. Also, the whole part is gauged, not just the flange, so blank intolerances are folded into the first flange. This is useful for secondary process assembly.
Furthermore, development of the capability to change positions of the three tool sets (upper beam, lower beam, and folding beam) relative to the material thickness allowed for the use of universal tool sets. This eliminated most of the setup usually associated with changing material thicknesses. As a result, the machines started to be used for short-run production.
The advent of modern motion control technology to control the folding beam swing made it possible to bend parts to an accuracy of ±1/3 degree, even on parts as long as 10 feet (3 meters) or more.
The technology only began to gain widespread use in North America in 1990. Since then, approximately 2,900 machines have been put into service, mostly for the roofing and building construction industries. Reasons for folding technology’s use for these applications include the following:
- Most roofing and building materials are prepainted or surface-sensitive, and folders do not mark the parts.
- Many parts have open and closed hems and multiple angles. These parts are more suitable for folders because they can be formed without multiple handlings.
- Setups and tool changes are not required.
- Construction and roofing fabricators often are required to fabricate sheet as large as 20 to 40 ft. (6 to 12 m) long, in 24-gauge (0.6-millimeter) thicknesses. Most press brakes are not well-suited to bend steel that size and thickness, because long press brakes generally are produced with heavy tonnage.
The Long and Short of Folder Sizes
Two types of folders generally are used in architectural and construction industries: short and long.Short folders are constructed using side frames with upper and lower clamping beams suspended in between. They usually measure 10 ft. (3 m) long, with a 16- to 14-ga. (0.5- to 2.0-mm) capacity (see Figure 1). This construction style is suitable for 3 or 4 m machines but not for machines that process longer sheet metal, because the suspended beams would have to become too large and difficult to move.
Long folders are designed for larger sheet metal fabrication. They are constructed using a series of C-frames (see introductory photo) to support the clamping jaws and folding beam and built in varying lengths including 21, 26, 32, and 40 ft. (6.4, 8, 10, and 12.2 m) and thickness capacities, including 18, 16, 14, and 11 ga. (1.25, 1.5, 2, and 3 mm). As the capacities and lengths increase, the mass and number of the C-frames increases, and the distances between them decreases. For example, a 6.4-m by 1.25-mm machine is built with five C-frames, and a 12.2-m by 3-mm folder has 15.
Control Software Brought Bending Improvements
In the last several years, control software has improved so that programming can be as simple as drawing a picture. The operator draws the part on the screen, assigns flange dimensions and bend angles, and is ready to produce the part. The positioning of the part—push in, pull out, flip over, and rotate—is shown in real time on-screen. A part can be made by manipulating it exactly as it is shown, which reduces the need for highly skilled operators.
This programming is helpful for parts with multiple bend angles and multiple radii (see Figure 3). These parts can be produced in a single handling without tool changes.
Handling Thicker Material
For architectural and construction industry metal fabricators, automatic folders are becoming more widely used in North America. While architectural folders often are used in applications other than roofing and construction, there are many applications for which they are not suitable, such as those that require bending thicker material or that have ultra-high precision requirements.
For thick material and ultra-high precision applications, manufacturers have produced a different class of machines. The machine shown is a seven-axis, CNC servo hydraulic folder capable of bending 0.020- to 0.250-in.-thick (0.5 to 6.4-mm) cold-rolled steel. The seven axes under control are:
- Upper clamping beam up and down motion.
- Positioning of the left and right clamping beam cylinders to ensure parallelism.
- Positioning of the folding beam swing for bend cycle (controllable to ±0.1 degree.)
- Linear movement of the folding beam relative to the bend moment and material thickness to affect the bend radius.
- CNC crowning of the folding beam tools to overcome deflection of the clamping and folding beams.
- Linear positioning of the lower clamping jaw and backgauge relative to the bending moment and material thickness. This combination of axes 4 and 6 allows the use of universal tools (see Figure 5).
- Backgauge position.
Electromechanical machines now are capable of bending up to 0.250-in. (6-mm) sheet thicknesses. In fact, most of the current new product development in Europe is related to switching from hydraulic to electric power, when possible, because electromechanical equipment offers reduced manufacturing costs and maintenance requirements. It also increases process speeds because electrically driven folding beams can be moved faster than hydraulically driven beams.
One of the most important aspects of this recent development is a new way to adjust material thickness changes without having to move the massive lower beams (see Figure 6). In this method, the folding beam adjusts in two ways: the pivot point moves, and the folding beam tooling is moved in relation to the pivot point. Perhaps, eventually this will lead to a 180-degree pivoting capability, consequently making positive/negative bending possible.
Another development has been the introduction of folding machines that can bend up and down, eliminating the need to turn the part over (see Figure 7). These machines can be used either with or without automatic grippers to provide different levels of automation. As with any new technology, the initial capital costs for this equipment are quite high, but are likely to lower.
Although folders are suitable for many applications, they are not as applicable for others. While folders are quick to set up, need few tool changes, and offer fast large-part material handling capabilities, generally, the actual bending cycle time for the folding beam is slow. Therefore, they are slower than press brakes in larger lot sizes of 100 or more.
In addition, folders are not well-suited for highly complex parts, such as a chassis with flanges being bent in many directions. This is because these parts will run into interference from the clamping jaw tools and back gauge.
Finally, they are not well-suited for making parts narrower than 5-in. because the gauging systems do not work well for parts that small.
The success of folding technology in North America has not yet equaled its success in Europe. However, each year more of these machines are being used for applications in which small lot production, varying material thicknesses, and high precision bending results are key factors.