Press brakes are essential machines in the metalworking industry, used to bend metal sheets into specific shapes. This article delves into the working principles of press brake dies, the types of press brake machines, and key considerations for selecting the right machine and dies.
Working Principles of Press Brake Dies
Components and Mechanism
Press brake dies consist of several critical components that work together to bend metal sheets:
1. Bracket, Workbench, and Clamping Plate: The workbench sits on the bracket, and the clamping plate secures the metal sheet.
2. Base and Pressure Plate: The base connects to the clamping plate via hinges and consists of a housing, coil, and cover. The coil generates electromagnetic force to hold the metal sheet in place.
3. Electromagnetic Clamping: When the coil is energized, it creates a magnetic force that clamps the metal sheet between the pressure plate and the base, allowing for various bending operations.
Operation Process
1. Power Connection: Connect the power and activate the oil pump to initiate the machine.
2. Stroke Adjustment: Adjust the stroke to ensure a gap equal to the sheet thickness when the upper die reaches its lowest point.
3. Die Selection: Choose a V-groove width approximately eight times the thickness of the sheet.
4. Back Gauge Adjustment: Set the back gauge position using electric or manual controls.
5. Bending Process: Press the foot switch to start bending and release it to stop.
Types of Press Brakes
Electro-Hydraulic Servo Press Brake
- Mechanism: Uses a proportional electro-hydraulic servo valve and a grating ruler for closed-loop control, managed independently by a CNC system.
- Features: Provides precise feedback and high accuracy in ram positioning, ensuring consistent bending angles.
Torsion Bar Sync Press Brake
- Mechanism: Utilizes a torsion bar to connect the left and right swing arms, forming a forced synchronization system that ensures both hydraulic cylinders move in unison.
- Features: Guarantees synchronized movement, improving bending precision.
Electro-Hydraulic Proportional CNC Press Brake
- Mechanism: Employs an electro-hydraulic proportional servo valve to control the flow of hydraulic oil, achieving proportional control for better accuracy and efficiency.
- Features: Offers high precision and is suitable for complex bending tasks.
Torsion Bar Sync CNC Press Brake
- Mechanism: Uses a torsion bar to connect the left and right swing arms and integrates a servo motor or stepper motor with a ball screw for CNC operation.
- Features: Ensures accurate synchronization and allows for computerized control, enhancing precision.
Fully Servo-Driven CNC Press Brake
- Mechanism: Driven entirely by servo motors for both the ram and back gauge movements.
- Features: Provides higher precision and efficiency, ideal for forming complex shapes.
Pneumatic Press Brake
- Mechanism: Uses compressed air as the power source, driving the ram up and down through an air cylinder.
- Features: Suitable for bending small and thin metal sheets due to its lower power.
Pure Electric Press Brake
- Mechanism: Driven by electric motors, it offers low noise and no pollution.
- Features: Typically less powerful, making it suitable for small and lightweight metal sheets.
Choosing the Right Press Brake
Key Considerations
1. Workpiece Requirements: Determine the size, thickness, and material of the sheets you will be bending. For example, low-carbon steel with a thickness of 16 gauge and a maximum length of 10 feet may require a press brake with a minimum bending force of 50 tons.
2. Machine Deflection: Understand that deflection increases with the length of the machine. A 10-foot machine will deflect more under the same load than a 5-foot machine, affecting the accuracy of the bends.
3. Material Type: Different materials require different bending forces. Stainless steel typically requires 50% more force than low-carbon steel, while soft aluminum requires about 50% less.
4. Bending Radius: The bending radius is approximately 0.156 times the V-die opening in free bending. If the radius needs to be smaller than the material thickness, bottom bending or coining may be required.
5. Precision Requirements: High precision requirements may necessitate a CNC press brake, which offers higher repeatability and accuracy compared to manual press brakes.
6. Tooling Compatibility: Ensure that existing dies and tools are compatible with the new machine, considering factors like wear and precision.
Using Hydraulic Press Brakes
Typical Operation Process
1. Power Connection: Turn on the power and start the oil pump.
2. Stroke Adjustment: Adjust the stroke to ensure a gap equal to the sheet thickness when the upper die is at its lowest point.
3. Die Selection: Choose a V-die with a width approximately eight times the sheet thickness.
4. Back Gauge Adjustment: Use electric or manual controls to set the back gauge position.
5. Bending Operation: Press the foot switch to start the bending process, releasing it to stop and pressing again to continue.
Hydraulic System Function
1. Power Supply: The oil pump provides the hydraulic power needed for the bending process.
2. Valve Control: Hydraulic valves direct the flow and pressure of the hydraulic oil, controlling the movement of the ram.
3. Bending Force: The hydraulic cylinder converts hydraulic pressure into mechanical force, driving the ram to bend the metal sheet.
Conclusion
Understanding the working principles of press brake dies and the types of press brake machines is crucial for achieving high-quality and efficient metal bending. By considering key factors such as workpiece requirements, machine deflection, material type, bending radius, precision needs, and tooling compatibility, operators can select the right press brake and dies for their specific applications.
FAQs
How do press brake dies work?
- Press brake dies consist of a clamping plate and base that use electromagnetic force to hold and bend metal sheets between a matching top and bottom die.
What are the different types of press brakes?
- Types include electro-hydraulic servo, torsion bar sync, electro-hydraulic proportional CNC, torsion bar sync CNC, fully servo-driven CNC, pneumatic, and pure electric press brakes.
How do you choose the right press brake?
- Consider workpiece requirements, machine deflection, material type, bending radius, precision needs, and tooling compatibility.
What is the typical operation process for a hydraulic press brake?
- Connect power, adjust stroke, select appropriate die, set back gauge, and start the bending operation.
What factors affect the bending force required for different materials?
- Material type, thickness, and length all influence the required bending force. For example, stainless steel requires more force than low-carbon steel, while soft aluminum requires less.
How do hydraulic systems in press brakes work?
- The oil pump provides hydraulic power, valves control the flow and pressure, and the hydraulic cylinder converts pressure into mechanical force to bend the metal sheet.
