1.What are the core challenges?
Material Properties: Higher yield strength results in greater springback (e.g., high-strength steel has greater springback than low-carbon steel).
Material Thickness: Greater thickness leads to a relatively increased tendency for springback.
Bending Angle: Smaller angles (e.g., 90° vs. 135°) result in more pronounced springback.
Bending Radius: A larger ratio of inner radius (R-angle) to material thickness (R/T) results in greater springback.
Die Parameters: Lower die V-groove width.
2.What preparations are needed before calibration?
Equipment Inspection:
Ensure the bending machine (electro-hydraulic servo or hydraulic) is in good working order, and that the slider parallelism and repeatability accuracy have been calibrated.
Clean the worktable, slider, and lower die, ensuring they are free of debris.
Die Selection:
Lower die V-groove width (V): Typically, V = sheet thickness (T) × 6–8 times. A wider V-groove requires less bending force, but may slightly increase springback.
Ensure the upper die (blade tip) radius matches or closely approximates the inner radius required by the drawing.
Obtain Material Parameters:
Confirm the accurate thickness and material grade of the sheet metal (e.g., SPCC, Q235, DC01, etc.). Springback may vary slightly between different batches of material.
3.What is the calibration procedure using trial bending and compensation methods?
Programming and Initial Design:
Input the material thickness, length, and target angle (e.g., 90°) into the bending machine controller.
Select the die; the machine will automatically calculate a bottom dead center position (Y-axis depth) as the initial value.
Initial Trial Bending:
Take a sample piece of material with the same thickness as the production part (recommended width ≥ 2 times the V-groove width).
Perform the bend and measure the actual angle using an angle gauge (or digital angle measuring instrument). Assume the angle is 92°.
Calculation and Compensation:
Springback = Measured Angle - Target Angle (92° - 90° = 2°).
On the controller, perform angle compensation: Set the target angle to 90° - 2° = 88°. Alternatively, directly input a "springback compensation" value (+2° compensation). The machine will automatically calculate a new, deeper bottom dead center to "over-bend" and offset the springback.
Verification and Fine-tuning:
Trial bend again with the new parameters and measure the angle. Repeat step 3 until the angle is within tolerance (typically ±0.5° or higher).
Record parameters:
Record the final bottom dead center position, pressure, compensation angle, etc., for mass production.
4.How to calibrate based on deflection compensation?
Problem: When bending long plates, a slight elastic deformation (deflection) occurs between the slide block and the bed, causing the angle in the middle of the workpiece to be greater than that at the ends.
Calibration:
Modern CNC bending machines have deflection compensation systems (such as hydraulic or mechanical compensation).
After bending a long workpiece, measure the angles at three points: left, center, and right.
Input the angle deviation at the center point into the controller, and the system will automatically adjust the support height in the middle of the worktable to ensure a consistent angle along the entire bending line.
5.What are the key points to note?
Consistency is Key:
During mass production, material consistency must be guaranteed. Different batches of material must be recalibrated and trial-bent.
Maintain a stable bending speed. Speed variations affect springback.
Springback Formulas and Software Assistance:
For complex or multi-bending operations, the springback compensation software built into the bending machine can be used. By inputting material parameters and die information, the software can provide more accurate predictions.
Empirical Formula: For a 90° bend of low-carbon steel, the compensation angle can be roughly estimated (this needs to be verified and corrected in practice).
Impact of Die Combination:
Using an acute-angle upper die or a bending bottom die with raised ribs (correction die) can change the material's stress point, effectively reducing springback.
Measuring Tools:
Precise measuring tools must be used. Digital protractors are more reliable than ordinary protractors. For high-requirement products, a 3D coordinate measuring machine can be used for spot checks.