Talk with a buyer about their concerns on a hydraulic press brake and tonnage will likely be the initial thing that comes up.
When you ask an operator, you’re likely to get a different answer.
They are interested in: Is the ram in the position required? Are they in sync on both sides? Does the bend get bigger when the machine gets hotter? Does yesterday’s program still make the same part today?
This is how to better comprehend a hydraulic metal bending press brake.
The force is generated by hydraulics, but good metal bending requires that this force be applied to the press in a manner that is generated, synchronized and controlled during the stroke. So, a modern press brake is more than about pressure; it’s about a rigid frame, controlled ram motion and accurate positioning. APEX is a software that describes the press brake‘s platform around rigid structures, synced hydraulic systems and CNC control for repeatable bending.
More than One Job for the Hydraulic System
The cylinders push NOT just the ram down.
The movements of the machine in a bending cycle are: Approach, Controlled Working Movement and Return. When there is increased resistance of the material, the system must be able to supply the force to the ram, but also the ram must be able to move in a predictable manner for accurate penetration depth.
This balance is important because the bend angle with air bending can vary significantly depending on the distance that the punch penetrates the opening of the die. Actual changes in ram position can, therefore, show up as changes in the finished angle, albeit small changes.
APEX’s hydraulic press brake machine uses hydraulic control unit in conjunction with double cylinder synchronizing. It also present Y1 and Y2 as the stroke axes of the left and right cylinder of its product specification that enables the control of the two sides of the ram as part of the bending system.
How much pressure the machine can create isn’t the only practical question.
It’s “How is that pressure regularized as ram movement?”
There are two Cylinders that must behave like one Ram.
For wide press brake, left-right synchronisation should be considered.
One side may be oriented differently than the other and this can produce a different bend at different points on the workpiece. This is more apparent with longer bends as there is more over the distance that the small difference will be observed.
Two cylinder axes can be controlled by electro-hydraulic systems, which provide position feedback as part of the motion-control process. The hydraulic platform on the APEX is provided with dual-cylinder synchronization and Y1/Y2 control and programmable crowning on qualifying configurations.
For buyers this means that a demonstration should comprise of more than a couple of short samples in the middle of the bed.
Take a typical long part.
Determine the size of the angle close to the left side, close to the center and close to the right side. That provides a far more valuable indication of the combined operations of the hydraulics and mechanics.
| Shop-Floor Symptom | First Item to Check | Useful Observation |
| Left and right angles differ | Y1 / Y2 synchronization | Compare both ends of the same bend |
| Angle changes unexpectedly | Ram position and material | Record actual angle by cycle |
| Ram movement becomes irregular | Hydraulic system condition | Observe motion and unusual noise |
| Machine runs unusually hot | Oil temperature / cooling | Compare with normal operating condition |
| Correction keeps increasing | Process stability | Check whether the change is gradual or sudden |
| Oil leakage appears | Seals / hoses / fittings | Locate leak before continued production |
The hydraulic motion is transformed into a repeatable process by CNC Control.
While traditional hydraulic power is good, CNC control makes the power easier to reproduce.
Unlike with a conventional CNC press brake, this modern CNC press brake will manage the ram depth in co-ordination with backgauge positions and a programmed bend sequence, instead of having to manually set the ram up again and again. APEX’s WC67K uses a hybrid system of hydraulic force and controlled axes, servo backgauges and programmable CNC systems.
This can be particularly helpful when dealing with parts that have multiple bends.
The operator is not required to memorise the individual gauge position, sequence and depth of the bends. After validation of the setup the machine can be used to repeat the programmed movements while the operator can focus on correct loading of materials, material orientation and inspection.
The forming is done with hydraulic power.
The forming process is facilitated by CNC control so that it can be repeated easily.
There are still more tonnages that need to be matched up to the tooling.
But, not all tooling setups are safe or correct with a large hydraulic cylinder.
The bending force is dependent on the strength of the material, thickness of the material, length of the bend and the opening of the V-die. The smaller the V opening the more force will be required and vice versa, however, a larger V opening will decrease the required force but will also affect the natural bend radius and minimum flange conditions.
For this reason, press brake tonnage calculation should occur before deciding on press capacity and/or tooling.
The calculation also should account for the actual bend made.
When a machine is rated for a total tonnage, this does not necessarily mean that all punches, dies or short lengths of tooling should be subjected to the total tonnage. Machines capacities need to be taken in hand along with the tooling.
The Bending System includes Hydraulic Oil.
Since the hydraulic oil is concealed within the machine, it’s easy to overlook.
Until something changes.
Oil condition, contamination and temperature affects the behavior of the hydraulic-system and the life of the components. Filters, seals, valves, hoses and cooling are part of regular maintenance and not just something that has to be decided upon when a fault occurs.
In particular, APEX maintenance advice identifies hydraulic contamination and oil temperature as parts that should be controlled when maintaining the performance of a press brake.
Simple habit for production shop is to document abnormal heat, leaks, unusual motion, changes in bend behavior as early as possible.
Don’t wait until the press brake comes to a halt before determining that hydraulic system needs attention.
The Decision Making Process that Tooling Carries out with the Hydraulic Force is What it Does to the Metal.
The hydraulic system may precisely provide the requested load and the part still could be wrong.
This can be due to the die.
The V-die opening affects the amount of force needed to open it, the inside radius, the minimum flange support and the surface marking. Hence, it cannot be assumed that the same opening would work for different materials or part geometries. APEX’s guide to press brake tooling and V-die selection also states that die opening should be considered in conjunction with the material, thickness, radius, flange length and machine capacity.
This is a crucial difference.
The force and the load are created by hydraulic force. How that load gets into that material is determined by tooling.
Both must be right for good bending to be accomplished.
Use Your Parts to test the Hydraulic Press Brake, Don’t Use a “Easy Demonstration” piece.
A test coupon provided by the supplier may demonstrate that the machine is in motion.
Does not necessarily imply that it is compatible with your production.
Take parts that fall on the challenging side of your production: a bend that is harder to make, a thicker material, a short flange, a multi-bend part or a tighter tolerance.
Then look at more than the last angle.
Observe the ram movement, left-right uniformity, positioning, appropriateness of the tooling and if the machine needs to be corrected repeatedly to keep it on target.
The bending operation of a hydraulic metal bending press brake should be a controlled and repeatable bending process that uses hydraulic force.
That is a better guideline for what to buy than tonnage alone.
| Production Input | Information to Prepare |
| Material Range | Grade and tensile strength |
| Thickness Range | Minimum / typical / maximum |
| Bend Length | Longest regular bend |
| Part Geometry | Radius, flange and bend sequence |
| Tooling | Existing or required punch / die |
| Production Pattern | Batch size and job frequency |
| Quality Target | Critical angle and dimensional tolerance |
FAQ
Q1. What is a metal bending press brake that is hydraulic?
It is a hydraulic ram type press brake which uses hydraulic cylinders to lift the ram and impart forming force via a punch and die. The modern machines are often combined with CNC positioning and synchronization with hydraulic power.
Q2. Why is there a pair of synchronised cylinders in a hydraulic press brake?
Two sides of the ram are operated by the cylinders. The synchronization allows for maintaining the same ram position throughout the working length, especially for longer bends.
Q3. In what way to choose the tonnage of hydraulic press brake?
Material strength, sheet thickness, bend length, V-die opening and bending method are the factors which influence tonnage. Production should be checked prior to production for the machine and tooling capacities.
Q4. Is there any difference in bending performance due to the condition of the hydraulic oil?
It can. In addition, the reliability of the system can be affected by oil contamination, condition of the hydraulic components and temperature, and should be dealt with during maintenance through filtration, checking for leaks and testing for oil condition.
Q5. What are the tests to do before purchasing a hydraulic press brake?
Test the strip with representative production parts (not only a test strip that is easy to test). See if the angle is consistent, flange size, ram synchronization and tooling compatibility and repeatability for multiple bends.