Better Bending
Material quality, modern tooling, and advanced programming can all led to more efficient press brake operation
February 1, 2011
Examining best practices in press brake bending
Computer programmers and technicians will be familiar with the phrase Garbage in, garbage out, which essentially means that if you enter junk, you will produce junk.
The same theory can be applied to press brake bending, in which variables in material, human-machine interaction, and program creation can affect the outcome of the process in a negative fashion.
“Edge and surface quality and material flatness and straightness play a big part in getting dimensional correctness on your part,” explained Rick McLean, VP at Empire Machinery & Tools, Winnipeg.
Edge quality varies depending on how the blank has been prepared for the press brake. If the blank has been cut on a traditional plasma cutting system, then the edges must first be cleaned up before bending due to the slag left behind from the plasma flame.
Also, thicker material coming directly from the mill is very rarely straight enough to sit tightly against a backgauge finger, an extra step may be necessary to get a part within correct tolerance.
“The mill edge of the material will always have some variance. Usually it is as simple as making a trim cut on a shear to make sure that the material can be used,” said McLean. “If the blank has been laser-cut, there is usually no edge preparation needed. This has been for some time now the preferred choice of many manufacturers who want excellent edge quality and dimensional tolerances.”
Lasers are not the only way of ensuring excellent edge quality though. High-definition plasma, and waterjet cutting can also ensure that a proper edge is created.
Material thickness from one sheet to the next, even from the same batch, can have small variances, and this can create a error in the bend angle.
“If you are dealing with thicker materials and you are using some sort of flame cutting then you may have to look for heat distortion that could affect the flatness of your material,” said McLean.
While no manufacturer wants to perform unnecessary, secondary operations, processes such as surface finishing are sometimes required to ensure an excellent finished product.
“You really need to look at the material before it is bent,” advised McLean. “If you don’t have excellent edge and surface quality, the finished part will reflect that.”
Tooling Affects Quality
Tooling plays a large part in the bending process. More and more manufacturers are using precision-ground and hardened press brake tooling today instead of the conventional pressbrake tooling that wears quicker and is not near as accurate.
While more expensive, this type of tooling eliminates the variance that can be found along the length of tooling that is not hardened and ground thereby ensuring a perfect bend along the length of the part.
It’s just not enough to buy high-quality tooling, either, said McLean. Tooling maintenance is also very important. Operators sometimes tend to simply pile up unused tooling on a nearby bench or on the floor beside the brake. When this occurs, a tool can get nicked or dented, and the mar will transfer into a part, especially if you are bending aluminum or stainless steel.
“Companies are recognizing that the quality and accuracy of their tooling can make a big difference, not just during bending, but while the tooling is being stored as well, said McLean. It is not just tooling that is an accessory purchase anymore but storage systems as well.”
It also is important to make sure that the surface the tooling is being pressed against is clean and free of detritus like metal shavings or grit. A small amount of time and care during setup can save much time and a lot of money later.
Hydraulic or quick release clamping also reduces setup time.
“If a manufacturer is performing more than two or three tool changeovers in a day, then they are a very good candidate for quick-release clamping,” said McLean. “Gone are the days of an operator walking down the bed of a press brake with an Allen key loosening bolts to remove tooling. Now it’s simply the case of pushing a button or moving a lever to remove the tools.”
Production times can also be reduced through the use of technology like multiaxis backgauging, which eliminates the need to perform tooling changes during the creation of a single part.
“If a manufacturer has a programmable backgauge with Z1, Z2 fingers, for example, the fingers will automatically position themselves behind the proper tools according to the program during each step of the bend process,” explained McLean.
A control with 3-D visuals allows the operator to see in real time how the part should be manipulated during the bending process.
Press Brake Programming
When programming a part, whether at the machine or with offline software, the programmer must draw the tooling identical to the tooling that is actually being used. If the radii are off even slightly, the part will be out of tolerance.
“Programming is becoming more relevant in the industry today especially because of 3-D visuals on the control’s screen and bend simulation software,” said McLean. “The operator can see exactly what’s going to happen. You can tell before you even go to the press brake if a bend will cause the part to crash into the ram or the bed and eliminate these errors. That is why I always recommend offline programming.”
While a programmer works in the office programming parts, the machine can still be working bending other parts.
The programmer becomes even more important to the operation when a robot is added to the bending system.
“Turnkey-style bending operations are becoming increasingly popular,” said McLean. “Customers will give us a drawing of their parts and ask us to develop a bending solution for them. For many fabricators, the use of a robot is just the solution they need. Robots allow the manufacturer to use the press brake up to 24 hours per day, and, provided the setup is done correctly, it’s a great way to produce consistent parts time after time.”
Increasing Throughput, Reducing Scrap
“Bending has traditionally been a more labor-intensive process than other fabricating operations, and the press brake operator generally had to be a highly paid, skilled worker,” explained Amada America’s General Manager of Marketing Nick Ostrowski.
This situation, in the past, could create problems because all the knowledge that a company needed to bend a part, or a series of parts, was with that operator.
“What Amada has done is create software systems that enable press brake programming to move into the engineering office,” said Ostrowski. “We can now program offline and download the program to the machine as needed.”
Then the operator only needs to look at the screen in order to see where the tooling needs to be set up and how the bend is to proceed.
However, if a manufacturer wants to take the next step by incorporating these process changes, it needs customers that can supply appropriate data and drawings in a format that can be folded seamlessly into the process. Time is not wasted re-creating the part unnecessarily if the correct style of data is obtained.
“This is like any other new technology that comes along in manufacturing,” explained Ostrowski. “It will take a certain amount of time for the industry to become standardized because it requires a commitment from all parties. But, the payoff at the end of the day is substantial.”
Progressive manufacturers will embrace this technology, added Ostrowski.
“The press brakes that are being sold today have these capabilities, so you better know how to implement them,” he said.
Another advantage of implementing offline programming is the ability to reallocate people to other value-added processes. New technology also gives manufacturers the ability to be more flexible in the types of parts that are produced, how they are produced, and how many are produced at one time.
Lot size isn’t as important in a truly integrated, automated manufacturing setup.
“The days of having a manufacturing print stuck to the upper bed of the press brake while the operator tries to figure out how to correctly set up the tooling are gone,” said Ostrowski.
Before the advent of offline programming and its ability to bend the part virtually, press brake operators had to go through several test pieces before getting to the correct setup. Today any obstacle to the creation of a correct part in the first bend is overcome in the engineering office, rather than on the shop floor.
“In a traditional press brake setup, the operator has to repeatedly adjust the program and setup until a correct part is made. The first several parts could all be scrap. Today, with virtual bending, the objective is the elimination of any test pieces and the ability to run from the first part,” said Ostrowski.
For more information, visit www.amada.com and www.empire-machinery.com.
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