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Up and Down Folding

Continuing a discussion of CNC folding machines from our April issue, details of the machine operation and dynamics illuminate their distinction from press brakes.

The press brake has been a valuable and useful machine for the North American manufacturer. It has been the one machine that is absolutely needed to form a punched or laser cut blank into its final shape. However, many press brake users are taking a closer look at this bending application.

A press brake operator is normally the most skilled operator in the fab shop. A really good one can read a drawing, pull the correct tools for the process, set up the machine, bend the part, check for quality assurance and generally maintain the machine. The problem has become the simple fact that one operator does not do all of these tasks any longer. It could take as many as three or four different people to do what one good operator used to.

What has helped improve this process has been the introduction of the CNC folding machine. Even more importantly, the folding machine that folds flanges up and down. No more supporting the overall of the blank and just turning the flange like a press brake, a folding machine holds the part on the sheet support/backgauge system. Gauging the overall of the part and just folding the flange like it is done on the folder is much easier than gauging the flange on a press brake and manually supporting the overall.

Most bending systems have been limited to folding only up, just like a press brake. To achieve an up and down bend without flipping the blank required a fully-automatic bending system or a double-beam folding machine. Recent advancements have allowed a folding machine to perform compound, bidirectional bends up and down without flipping the blank, and all with a single beam.
 
As mentioned, press brakes and folding machines handle the work piece differently. The press brake gauges the flange and the operator supports the part. The folding machine gauges and supports the blank on the sheet support system. The flange to be folded (up or down) is the only thing that is moved on the blank.


The folding beam can swing to position with high accuracy — within 0.1 degree. Accuracy in positioning reduces the number of tools required; usually, to one universal set of tools
 
On a folder, the blank is positioned on the sheet support backgauging system, clamped between the upper and lower beams and then the single folding beam rotates to the pre-programmed degree of angle. The system is servo-electric and clamps to a positive position rather than to pressure; this ensures that Y1 and Y2 axes are always parallel to the folding beam. If the operator has programmed the control to have the machine clamp .050”, it will move to exactly .050”, no more, no less. This eliminates, among other things, positioning issues when folding geometries such as open hems.

The folding beam can swing to position within 0.1 degree — very accurate positioning. Due to this accuracy in positioning, the vast majority of folding applications can be completed with one universal set of tools.

Unlike a press brake, the folding machine does not bend with tonnage. Bending force comes from the folding beam, not from tonnage exerted by the press brake’s hydraulic cylinders. A folding machine that will fold up and down can fold material as thick as 9-gauge (.1495”) mild steel using an 8-in.-tall tool. You can produce nine gauge, 8 in. deep, four-sided boxes with one operator and no struggle.
 
The process is pretty simple. The blank rests on the backgauge/sheet support system. The gauging system moves the part forward and positions it for each fold. The operator checks to make sure the blank edge is against the gauging fingers and then steps on the foot pedal to start the folding sequence. The blank is supported through the complete process, large part or small.
A press brake can bend in only one direction because the geometry is based solely on the tooling. In most cases, unless specialized punch and die sets like offset tools are used, most press brakes make one bend per hit and it is in the upward direction.
 
Conventional single beam folders bend only up as well. The UpDownBend folder can fold in both directions because the leading edge of the bend changes with the direction of the bend; the top of the folding beam blade for positive bends and the bottom of the blade for negative bends. This requires the beam to pivot around a slightly different point to maintain the proper bend line position throughout the bending operation.


Advanced folding machines use a ‘beam-in-beam’design, with one beam inside of another, to handle deflection. The dynamics are different from those of a press brake.

To make up and down bending work with a single beam, two things must happen. One, the beam pivot point must change. Two, the beam must extend outward, away from the machine, in order to get around any flanges that have already been folded. An example would be, we have just bent a 5-in. up flange and now we need a 2-in. down flange. To get into position, the folding beam must move away from the machine 5 in. to get around the first flange.

When using a bidirectional folding system, the operator stands behind the backgauge/sheet support system. The support system adjusts to the size of the part and the surface area decreases for narrow or smaller parts, and increases for better support of larger parts. This feature is done automatically in the part program.
 
There is also an UpDownBend machine available with an automatic tool changer and a backgauge support system that will pneumatically hold the part in place during the folding process of side one. The operator would only have to rotate the part to side 2 and step on the foot pedal to complete side 2. This process is repeated for all four sides of the part. Tools can automatically be changed during the folding process if needed. 


The operator stands behind the backgauge/sheet support system when using a bidirectional folding system.

An additional feature of this machine with a tool changer and pneumatic support table is its ability to accept a DXF, STEP or GEO file directly. No programming at all. The file is sent to the machine and the CNC takes it from there. Folding sequence and tool set up all complete in the blink of an eye.
 
Bidirectional, single-beam folding systems handle deflection in a very unique way. Modern folding machines like press brakes have crowning systems to calculate and compensate for deflection during the bending cycle. These systems are very good at ensuring every bend is an accurate bend.

However, there is another approach that eliminates the need for this type of crowning system. In a conventional bending beam, the center – the farthest distance from the end supports makes the connection to the machine frame – experiences the most deflection. The most state-of-the-art folding machines today are engineered to eliminate deflection effects and increase rigidity with a beam-in-beam design. The beam has a smaller beam welded and gusseted inside of it.

Single beam, bidirectional folding is a proven concept and represents a fact that will evolve into commonplace technology, with greater potential in an industry starved for skilled labor. As mentioned earlier, the common skills of a press brake operator have diminished over the years. The modern day folder replaces the skills that an operator had to have. Tool set up, folding sequence, bend compensation and many other functions have been taken out of the operator’s hands and are now applied
automatically, resulting in less material handling, more accurate parts, less scrap and a more profitable bottom line.
 
If you already use a press brake, a folding machine should make your existing press brakes more productive at what they do best. Let a folder do your large panel work and complicated parts, a folder is a niche machine but together with the press brake, they make a great team.