Optimize a bending machine

Getting the most out of a humble press brake

Many of the press brakes that were installed 30 to 40 years ago are still in operation. Besides regular maintenance and replacing the tooling, there is not much that can go wrong with a good press brake.

For long part runs the introduction of a robotic arm to load and unload a machine is the modern solution to speed up production. “Press brake automation has evolved from just integrating a robot to a press brake,” says Scott Ottens, bending product manager for Amada. In the earliest forms of automation, operators had to manually move a robot through each step of the bending operation, record each move and ultimately build a program by teach mode. “As you can imagine, there are a lot of movements in the bending program so it could take hours to do a setup,” says Ottens.

Recently many press brake manufacturers have introduced much more flexible automated robotic bending cells, where they have been able to program off-line and the integrated system takes care of not only loading and unloading workpieces, but it can also change the bending tools and the robotic grippers automatically to move from job to job without human interference.

“The robot in front of a machine has been tried for 20 years and it can only go so far,” says Casey Schlachter national sales manager at MC Machinery Systems (Mitsubishi Corp.). “You can have a five- or six-axis robot which can mimic the movement of your hand from the elbow to the wrist, but it is costly and generally setup time takes a long time—up to three hours.” And traditionally, unless a company is processing several thousand identical parts, it would be difficult to justify upgrading an older press brake.

“There are integrators that will do that, but the problem is that you are putting an automated system with a machine that was never intended to be used for bending with a robot,” says Ottens. “A lot of press brakes that are in automated bending cells have a larger stroke and open height. They make a wider bending envelope, because a robot, even though it might have six- or seven-axis of freedom, it is still difficult to get into places like a human can or to turn a part and remove it from the bending area, especially after the last form. You need a bender with a large envelope so that the robot can get parts in and out of the machine easier."

Instead of spending a great deal of money integrating a robot to an older press brake, a wiser investment might be to acquire a modern turnkey solution consisting of a robot and press brake that are meant to work together.

“It is a more seamless integration for the end user,” says Tom Bailey, product manager for TRUMPF Inc. “That combined with offline programming software improvements have really got the setup into a manageable time frame.

“If you take a standard robot and a standard press brake and integrate them through a third-party integrator, it works all right if you have a very long run production requirements with piece counts that run into the thousands. We don’t see that too often in manufacturing in North America anymore. We see 50 parts or less. You really need a system that you can set up and run in an hour or less to justify the short runs.”

There is more to press brake automation than just a robot arm in front of a press brake. “A typical automated press brake consists of the following other components,” explains Paul LeTang, product manager of press brake/tooling at Bystronic Inc.:

Robots are useful
when manipulating
very large and heavy
parts in a bender
sequence.
PHOTO COURTESY
OF AMADA INC.

Robots are useful when manipulating very large and heavy parts in a bender sequence. PHOTO COURTESY OF AMADA INC.

  • Buffer/storage–typically flat blanks are produced at a different rate than the press brake can consume them. In many cases, the problem is compounded by nesting different-shaped blanks in a single sheet to improve material utilization.
  • Input station–blanks coming to the press brake need to be queued, located and oriented so the robot picks up the correct blank, the correct way and at the correct time.
  • Gripper changing station–it’s not likely that one gripper will fit all the bend part shapes. This is mainly due to the fact that the part shape changes during processing.
  • Referencing station–location of the blank in the gripper (end effector) must be verified to ensure consistency.
  • Turnover station–when there are up and down bends in a single part, the gripper location usually needs to be relocated from one side of the blank to the other. Suction tables or even rotation suction tables are often used to aid in this task.
  • Output station–bent part shapes exiting a system need to be either dropped in a basket, placed on a conveyor, nested in a single stack, or nested in multiple stacks depending on the application. Usually some sort of receiver is designed according to the parts addressed.

The Importance of Tooling

While the press brake itself provides the force to bend the sheet metal, it is the precision tools that will determine the quality of the finished part. “Initial tooling investment on these types of systems is quite expensive, especially if you are going into the tool changing system where there are special tools that have other operations needed for the automated tool changer to work,” says Ottens.

High quality press brake tools start with high quality steel. “Manufacturers should look for tools that are made from a CrMo steel with a core hardness near 30 HRC,” suggests Michael Sosnoski, Director of Operations for Wilson Tool. “If tools are made with lesser grades of steel, or with lower core hardness, the tools will deform over time. If tools have too high of a core hardness, they could pose a safety issue when they break if they are overloaded.

“Quality tools are heat treated on the working surfaces. The heat treatment allows the tools to perform like new for longer than non-heat-treated tools. Manufacturers should look for precision tools that will allow for interchangeability of tools, allowing different tools purchased at different times to match up.”

To cope with higher tolerances required from parts, the tools themselves must be made to extremely fine tolerances. “Generally what we are looking at is measuring tooling tolerances in 10,000’s of an inch, a pretty common tolerance would be plus or minus 4/10,000 of an inch or 2/10,000,” says Bailey.

No matter how hard the tool is, it will eventually wear out. “Yes, the tools do wear,” says  Sosnoski. “The life of the tool depends on the manufacturer’s applications. Difficult-to-bend materials, such as Domex will wear tools much faster than mild steel.”

He suggests that a great way to extend the life of tools is to keep the tools clean. “If material builds up on the surface of the tooling, it can damage the tool. This is very common when working with galvanized steel and aluminum.”

Material build up also causes cross contamination when switching materials, notes Sosnoski, such as bending mild steel and then switching to stainless steel. “Nitrex coating solution is a great way to reduce the rate of material build up on dies. Wilson Tool recommends cleaning the tools with a Scotch-Bright scouring pad and oil.”

The V-Series Black
press brake dies
incorporate
replaceable inserts
to decrease friction
and enable better
performance on
certain tough-tobend
applications.
PHOTO COURTESY
OF WILSON TOOL
INTERNATIONAL

The V-Series Black press brake dies incorporate replaceable inserts to decrease friction and enable better performance on certain tough-tobend applications. PHOTO COURTESY OF WILSON TOOL INTERNATIONAL

Depending on how the tool is used, uneven wear can also affect part quality. “If the tool is being used on a particular part repetitively, the area where the bend is made will get worn and the area where the tool is not being used will not get worn,” notes Frank Baeumler, vice president at Mate Precision Tooling. “So the tool itself might have a portion in the middle which is highly used and portions on the extreme ends which are rarely used, and therefore you get a change in the tool. In those cases, when you have a worn tool it will show up in the bent parts and the quality of the parts will go down.”

Visual inspection of tools can pick up any problems with the tooling. “In order to determine the condition of the tooling, most often, users will need to visually inspect the tools, looking for wear on the working surfaces. If the tools do not line up in the brake, it might be a sign that the tool is worn out or has been over loaded,” says  Sosnoski.

Where a worn tool will show up immediately will be in the bent part. “In reality it is the parts produced by the press brake that will determine whether the tooling is working or not,” says Baeumler. “If the bend is not achieving the 90-degree bend that I am hoping for, for example, you have to examine why the tool is not allowing the material to bend to 90 degrees. It will be a tool issue and you will have to replace the tool.”

Press brake operators have various methods of checking the health of their tools. “You could inspect the tools off-line and discover something about their current status,” says LeTang. “Calculating this back to part tolerance will be a challenge. The best way to verify tooling condition is to make a full-length bend, rotate just the punch end-to-end then make another bend. Repeat this process with just the die. If all parts are identical your tools are likely good to go.”

Quality tooling is manufactured from
premium tool steel with the business
end heat treated for extra durability
PHOTO COURTESY OF MATE PRECISION TOOLING

Quality tooling is manufactured from premium tool steel with the business end heat treated for extra durability PHOTO COURTESY OF MATE PRECISION TOOLING