The CNC Press Brake described in this article is an electro-hydraulic, synchronous, double-cylinder, up-moving machine.
The principle of CNC Press Brake
The principle of bending is essentially identical to the angle forming principle of a traditional press brake machine (as depicted in Figure 1). The formation of the bend angle (air bending method) is regulated by the depth (bend depth) of the punch pressing the sheet in the lower die opening.
Alternatively, the workpiece is pressed to match the angle (shape) of the die (bottoming bending method).
Related reading: Bending Depth Calculator
So what is CNC Press Brake?
The CNC system controls the electro-hydraulic proportional directional valve, creating a fully closed-loop digital control mode for the bend depth via feedback from the grating ruler.
The numerical control system also controls the ball screw, driven by an AC digital servo system, and utilizes a disk-type photoelectric encoder to establish a semi-closed loop digital control mode for the positioning of the rear stopper.
Related reading: Open Loop vs Closed Loop
Therefore, a CNC Press Brake can be succinctly defined as: a bending machine controlled by a CNC system, allowing for automatic adjustment of the rear stopper positioning, bend depth of the ram, and worktable deformation.
Fig. 1: Angle forming process of press brake machine
Currently, there is a more advanced type of CNC Press Brake available. The primary difference between it and the previously described CNC Press Brake is that the most advanced model employs an angle closed-loop control mode, whereas the earlier version uses a bend depth closed-loop control mode.
Related reading: Top 10 Press Brake Manufacturers
Advantages of CNC Press Brake
Then, what are the advantages of a CNC Press Brake compared to a conventional press brake machine?
These advantages are easily observable from the following basic features.
- Ram Synchronization on Both Sides
The CNC press brake has stable and flexible synchronization performance and features a slide tilt detection and correction function in its CNC system.
- Bend Angle (Depth) Calculation
The CNC system can automatically calculate the bending depth based on the selected die angle, opening, R size, and sheet thickness.
- Bending Depth Feedback
The imported grating ruler directly measures the positions of both sides of the ram and has a throat deformation compensation mechanism to ensure consistent angles.
- Worktable Torsion Compensation
The CNC system can calculate the pressure of the compensation cylinder required to compensate for worktable deformation during the bending process, ensuring uniform full-length bending angles and improving workpiece straightness.
- Angle Correction
If there is a discrepancy between the programmed angle and the actual molding angle, the user can simply enter the error value and the system will automatically compensate and correct.
- Retaining Position Calculation
The system can automatically calculate the stopper’s axis position for each bend height and can change steps automatically, making correction convenient and fast.
- Programming Mode
With both graphic and data programming functions, the program is easily modified and edited.
- Unfold Length Calculation
The CNC system can calculate the unfold length based on the graphic programming of external dimensions (or internal dimensions).
- Interference Calculation
The CNC system can automatically determine the optimal bending process based on the programming graphics, mold, and machine tool profile, and can alert the user to bending interference. The bending process can also be manually modified.
Axis configuration of CNC Press Brake
What are CNC Press Brake Axes?
CNC Press Brake Axes refer to the movements and functional components that are controlled by the CNC system in a CNC Press Brake machine.
Typically, the axes are named based on their position within the machine tool and the coordinate system. Meanwhile, other motions and functional parts may have names that are based on conventional usage or international standards.
Related reading: Explanation of CNC press brake axis
A CNC Press Brake is equipped with multiple axes, which are usually configured based on the processing requirements of the user for the workpiece.
Figure 2 illustrates the typical configuration of the CNC axes in a CNC Press Brake.
Table: CNC Axis Setting and Configuration Selection
The table below outlines the functions defined for each axis:
|Axis||Axis function description|
|Y1||Left cylinder electro-hydraulic synchronous full closed loop control shaft|
|Y2||Right cylinder electro-hydraulic synchronous full closed loop control shaft|
|X||Rear stopper semi-closed loop mechanical movement shaft. If equipped with X1 axle, this is the left-finger stop control axle.|
|X1||The right rear stopper finger control shaft.|
|R||Rear stop finger refers to the vertical lifting control axis.|
|Z1||The left side stopper refers to the mechanical shaft moving left and right on the stopper beam.|
|Z2||The right stopper refers to the mechanical shaft moving left and right on the stopper beam.|
CNC Press Brake Troubleshooting
1. The NC system cannot be started
- The oil pump has not been activated.
- The input signal light for DM02 module 14 is not functioning. Please examine the DC24V control circuit by referring to the electrical schematic diagrams in Appendices C and D.
2. No downward movement of the ram
- Verify that the input signal lamp of DM02 module 15 is illuminated after stepping on the foot switch.
- After the foot switch has been verified, check the DC24V power supply. WS should check Line 200, while PB should check Line 214.
- For the WS model, ensure that the enabling signal (represented by a green light) of the BOSCH proportional valve magnifying plate 7KA3 is activated.
- Verify the status of the quick release relay 7KA1, i.e., confirm that the quick release electromagnet is energized for both the WS and PB models.
- Confirm that the proportional valve is open by checking the feedback voltage.
3. No slow down bending of ram
- Verify if the programming pressure is insufficient.
- If the upper die does not reach the programmed speed conversion point when it makes contact with the sheet metal.
- If the hydraulic system pressure cannot be established, inspect the electrical signal and clean the pressure valve block.
- If the hydraulic system’s flushing valve is not shut, clean valves 100 (PB) and 3 (WS).
- Determine if 7KA2 is damaged.
4. The ram slides at the top dead center
The ram oscillates after the transition point
- Clean Valve 8 of the WS model.
- Clean Valve 50 of the PB model.
5. No automatic return of ram
- The programmed angle is too low, causing the ram to not reach the bend endpoint as programmed.
- For the WS model, verify that the enabling signal of the BOSCH proportional valve (enlarged plate) 7KA3 is active (the green light should be lit). Refer to Appendices C and D for more information.
- The return pressure is too low, resulting in a lack of system pressure. Clean the pressure valve.
- The proportional valve is not functioning in reverse and requires cleaning. Clean the left side by returning it and clean the proportional valve on the right valve stack on the right side.
6. The rear stopper cannot move
- Verify if the IRT and Panasonic drives have any alarms.
- Inspect the limit switch for each axis.
- Evaluate the dependability of the connectors.
Related reading: 56 Press Brake Bending Problems: Proved Troubleshooting & Repair Solutions
CNC Press Brake Application and Development Analysis
1. Discussion on numerical control technology
CNC press brakes typically have more than two axes, one of which are the control shafts.
The two crucial axes are the X-axis, also known as the rear stop axis, with an accuracy requirement of less than 0.1mm, and the Y-axis, referred to as the ram axis, with a tighter accuracy requirement of below 0.01mm.
Following the explanation of the axes of a CNC press brake, we will delve further into the development of the NC (Numerical Control) system.
1. Multi axis control technology
In a numerical control system, the addition of a motion axis is often used to enhance control accuracy and make the operating process more efficient and convenient.
Although there may be various reasons for incorporating multiple axes, the ultimate goal is always the same: to improve both the quality of the product and the efficiency of the operating process.
2. Replacing DC servo motor with AC servo motor
The AC motor is known for its dependable performance, high torque at high frequencies, powerful output, dynamic servo capabilities, and low moment of inertia.
In summary, the AC servo motor offers superior advantages compared to the DC servo motor, making it the preferred choice for replacing DC servo motors.
3. Adoption and application of advanced CPU
The CNC system has seen significant advancements since its inception. Initially, the system was 8-bit, but it has since evolved into a 16-bit and then a 32-bit system. Over time, the system has improved greatly in many aspects, including control, programming, and management.
The graphical programming process and bending process have also been advanced to the point where they can display images and bending processes with high resolution, making it easier for people to observe the bending operations of the NC system.
In addition, the use of a high-level CPU processing system has resulted in the control system having increased storage space on both hard disk and floppy disk, allowing the system to store more information.
4. Carry out research on rich software and good operation adaptability
We can write programs using software disks or keyboards engraved with standard characters and letters, making the programming process simpler and clearer and easier to master and understand by individuals.
For instance, LVD, a company in Belgium, is well-known globally for its plate processing equipment.
The press brake owned by LVD has a highly advanced CNC system.
The company offers various systems to meet the diverse needs of different jobs.
2. Application of CAD and CAPP
Once NC programming is finished, it is typically carried out by human operators.
This process imposes high demands on personnel, as they must not only describe and comprehend each stage of the programming process but also be aware of the precise position of each press brake axis and how to adjust auxiliary functions.
The step is a highly complex task.
In addition to these complexities, we must also tackle a range of challenges, such as enhancing productivity and reducing the time required for programming.
In our NC bending technology, we are currently focusing on incorporating CAD and CAPP into our automatic programming system.
In the following sections, we will delve into the functions of the automatic scheduling processing process in detail.
1. Determine the optimal scheme of the workpiece in the bending process
The definition of “best” here is not in the conventional sense.
The optimization mentioned here is a more suitable approach considering the desired precision of the workpiece and the production standards.
It is an optimally relative concept.
When making automatic arrangements, we should make intelligent modifications based on actual circumstances and not rigidly adhere to rules.
For instance, if the written program does not fulfill the user’s needs for the work, they can freely modify it. The user can adjust the program content to meet their specific requirements for the program.
2. Simulated bending process
During the bending process, we can illustrate the proper operation of this part at a specific position using images. This allows us to visually inspect and analyze the operation process and see the details of the bending operation in a qualitative manner.
Additionally, we can demonstrate the bending process dynamically through videos, giving people a more direct observation of the process. This enhances the authenticity of the operation and reduces the sense of distance, allowing people to better understand and express the bending process.
Through the use of videos, we can also display the bending parameters and alert people of any issues or faults, providing them with valuable information.
3. Generate NC program
NC (Numerical Control) programs are automated programs that control machine tools to bend parts efficiently, reducing the need for manual labor and conserving both manpower and material resources. One such program associated with NC is the DNC (Distributed Numerical Control) program.
The NC program is inputted into the control device of the press brake through the system. After the system sends the command to input the NC program, the program is inputted after receiving consent. In some cases, the contents of the instructions can be modified, and the updated information is returned to the computer.
The calculation of springback compensation is a critical aspect in the process calculation. When processing a part, it’s essential to choose the correct angle. If there’s any deviation, the angle must be adjusted accordingly and transferred to the control device. When the system knows the correct angle, it will perform the operations efficiently.
When making process arrangements, it’s crucial to establish the purpose of the arrangement. The process arrangement involves determining the motion sequence and speed between each axis, while adhering to established principles, such as avoiding interference between the workpiece and the machine tool and die, and processing the workpiece in different ways based on the accuracy requirements.
The recent advancements and applications of the CNC press brake have made it faster and more efficient in operation, thanks to the integration of intelligent and automation technology. This significantly simplifies the bending processing and enhances work efficiency and quality.
Additionally, the press brake machine provides optimal conditions for observing the bending process, allowing for clear and detailed observation of the operation. This allows for a more intuitive understanding of the bending process.
In conclusion, the development of the press brake has a promising future, and there is still ample room for growth and development in CNC bending.