A press brake is an indispensable machine in the sheet metal industry, used for bending metal sheets into desired shapes. Depending on the working method, press brakes can be classified into manual, hydraulic, and CNC (computer numerical control) types. This article explores the principles, maintenance, and key considerations for choosing a hydraulic press brake.
Types of Hydraulic Press Brakes
Hydraulic press brakes are versatile and powerful, offering different synchronization methods and movement types:
1. Synchronization Methods:
- Torsion Bar Synchronization: Uses a torsion bar to synchronize the movement of the hydraulic cylinders.
- Hydraulic-Mechanical Synchronization: Combines hydraulic power with mechanical synchronization elements.
- Electro-Hydraulic Synchronization: Utilizes electro-hydraulic servo valves and CNC systems for precise control.
2. Movement Types:
- Top-Moving: The ram moves downward to bend the metal sheet.
- Bottom-Moving: The bed moves upward to bend the metal sheet against a stationary ram.
Features of CNC Hydraulic Press Brakes
Key Features of Juquan CNC Press Brakes
- Hydraulic Crown Automatic Compensation System: Automatically adjusts the compensation amount to correct any deformation of the ram during bending, ensuring high-quality workpieces.
- Comprehensive Back Gauge Mechanism: Controls multiple back gauge axes, with precision components like imported guide rails, ball screws, and bearings for high accuracy.
- Integrated Welded Structure: The machine body is welded as a whole, ensuring easy transportation, processing, and overall machine precision.
- Finite Element Analysis: Critical components like the machine body and ram are analyzed using ANSYS software to ensure reliability.
- German Imported Hydraulic System: An integrated control system reduces piping installation and enhances operational stability and aesthetics.
Working Principle of a Press Brake
Components and Mechanism
A press brake consists of a frame, workbench, and clamping plate. The workbench, placed on the frame, includes a base and a pressure plate. The base is connected to the clamping plate via hinges and comprises a housing, coil, and cover. The coil sits within a recess in the housing, covered by a top plate.
Operation
- Electromagnetic Clamping: When the coil is energized, it generates a magnetic force that clamps the thin sheet between the pressure plate and base, allowing for various bending operations.
- Versatility: This mechanism allows the pressure plate to accommodate various workpiece requirements, including those with side walls.
Selecting a Press Brake
Key Considerations
1. Machine Purpose:
- Assess the intended use of the machine and the maximum expected deflection.
2. Part Bending Radius:
- Determine the required bending force and workbench length based on the shape and size of the parts.
3. Material Type:
- Different materials require different tonnages. For example, stainless steel typically requires 50% more load than low-carbon steel, while soft aluminum requires 50% less.
4. Maximum Processing Thickness and Length:
- Choose a press brake with the appropriate tonnage and workbench length based on the maximum thickness and length of the parts to be processed.
Importance of Part Length
The length of the part is crucial in determining the specifications of the press brake. Under the same load, a longer workbench and ram will deflect more than a shorter one. Shorter machines require fewer shim adjustments, reducing preparation time and improving efficiency.
Material Grades
Different materials require different loads. For instance, stainless steel needs about 50% more load compared to low-carbon steel, while soft aluminum needs about 50% less. Press brake manufacturers often provide tonnage charts to estimate the required tonnage per foot length for different materials and thicknesses.
Bending Radius
- Free Bending: The bending radius is typically 0.156 times the V-die opening width. The V-die opening should be eight times the material thickness for free bending.
- Bottoming and Coining: These methods require higher pressure compared to free bending.
Die Angle
- Free Bending Dies: Dies are typically machined to 85° or less.
- Bottoming Dies: These dies usually have angles between 86° and 90°.
Key Parameters
| Parameter | Description |
|---------------------|--------------------------------------------------|
| Workbench Length | The length of the press brake's workbench. |
| Bending Force | The maximum bending force the press brake can achieve. |
| Back Gauge Travel | The distance the back gauge can move. |
| Stroke Speed | The speed at which the ram descends and ascends. |
| Control System | The type of control system, such as CNC or hydraulic-mechanical synchronization. |
Maintaining a Hydraulic Press Brake
Hydraulic Oil System Maintenance
1. Regular Oil Level Checks:
- Frequency: Weekly.
- Procedure: Check the oil level in the tank. Add hydraulic oil if the level is below the observation window.
2. Oil Specifications:
- Recommended Oils: Use ISO HM46 or Mobil DTE 25 hydraulic oil.
3. Oil Change Schedule:
- Initial Change: After the first 2000 hours of operation.
- Subsequent Changes: Every 4000-6000 hours.
4. Oil Temperature Control:
- Optimal Range: Maintain between 35℃ and 60℃.
- Maximum Limit: Do not exceed 70℃.
Filter Maintenance
1. Regular Replacement:
- Frequency: With each oil change.
- Procedure: Replace or clean the filter thoroughly.
2. Air Filter Maintenance:
- Frequency: Every three months, and replace annually.
Hydraulic Component Maintenance
1. Monthly Cleaning:
- Components: Clean the base plate, valves, motors, pumps, and oil pipes.
- Precautions: Avoid using cleaning agents that might damage the components.
2. Oil Pipe Inspection:
- Initial Check: Inspect all oil pipes for deformation after the first month.
3. Tightening Connections:
- Frequency: After two months of operation.
- Procedure: Tighten all fittings and connections with the machine off and system depressurized.
Electrical and Servo System Maintenance
1. Electrical Interface Checks:
- Regularly inspect all electrical interfaces to ensure they are secure.
2. Position Switch Inspection:
- Check position switches for looseness or malfunction.
3. Calibration:
- Verify and calibrate reference values upon startup to ensure accuracy.
Troubleshooting Common Issues
1. Inconsistent Feeding Motion:
- Cause: Loose lead screw or excessive lead screw clearance.
- Solution: Tighten the lead screw.
2. Unstable Pressure:
- Cause: Faulty pump, valves, or oil pipes.
- Solution: Inspect and repair or replace the affected components.
3. Short Stroke:
- Cause: Faulty stroke limit switch or servo motor.
- Solution: Inspect and repair or replace the switch or motor.
Conclusion
Choosing the right press brake and maintaining it properly are crucial for efficient and precise metal bending. By considering key factors such as machine purpose, part length, material type, and bending radius, and following the maintenance steps outlined in this guide, you can ensure your hydraulic press brake operates at its best. Regular maintenance not only extends the machine's lifespan but also ensures high-quality output.
FAQs
What are the types of hydraulic press brakes?
- Hydraulic press brakes include torsion bar synchronization, hydraulic-mechanical synchronization, and electro-hydraulic synchronization, with top-moving and bottom-moving variations.
How do you choose the right press brake?
- Consider the machine's purpose, part bending radius, material type, maximum processing thickness, and length.
What are the key maintenance steps for a hydraulic press brake?
- Regularly check the hydraulic oil level, replace filters, clean hydraulic components, inspect oil pipes, tighten connections, and calibrate electrical and servo systems.
What causes inconsistent feeding motion in a press brake?
- Loose lead screws or excessive lead screw clearance, which can be fixed by tightening the screws.
How can you ensure stable pressure in a press brake?
- Inspect and repair or replace faulty pumps, valves, or oil pipes.
