1.What are the key determining factors?
Material Properties:
Thickness: The thicker the material, the greater the difference in tensile and compressive stress between the inner and outer sides during bending, making precision control more difficult.
Material and Strength: Different grades (e.g., Q235, SPCC, DC01, etc.) have different yield strengths and springback characteristics. Springback is the primary cause of angle deviation. High-strength steel exhibits greater springback, making control more difficult.
Rolling Direction: Bending along or perpendicular to the rolling direction results in slight differences in springback.
Machining Accuracy Grades:
Ordinary Accuracy: Suitable for appearance parts and general structural components.
Precision Accuracy: Suitable for parts requiring assembly and functional requirements (such as the tube sheet and slots in dust removal equipment mentioned earlier).
Equipment and Dies:
Bending Machine Accuracy: CNC bending machines offer significantly higher repeatability and slider parallelism than ordinary bending machines.
Die Condition: New dies, V-groove size matching, and die wear all directly affect the angle.
2.What are some common industry practices?
High precision requirements: within ±0.5°. This requires precision equipment, specialized molds, skilled operators, and strict process control (such as springback compensation).
General precision requirements: ±1° is a common and acceptable target. Most general-purpose equipment can achieve this in good condition.
Lower precision or large-size parts: tolerances may be between ±1.5° and ±2°.
3.How to determine specific tolerances?
Primary Basis: Product Drawings. Design engineers should clearly indicate angular tolerances on the drawings based on the assembly and functional requirements of the parts. This is the legally binding final basis.
Communicate with the Process Department. The production or process department will assess the economic feasibility of the tolerance based on equipment capabilities and material characteristics, and adjust it in consultation with the design department if necessary.
Conduct First-Piece Inspection and Springback Testing. For new products or materials, a trial bend must be performed to measure the actual angle. The bending depth of the bending machine is adjusted according to the deviation (i.e., springback compensation) until the target angle is achieved. This is a crucial step in ensuring batch consistency.
4.What are the common causes of deviations exceeding tolerance?
Inaccurate springback calculation/compensation: This is the primary cause.
Material property fluctuations: Yield strength varies between different batches of steel.
Wear or improper selection of molds (e.g., excessively large V-groove opening).
Decreased equipment precision or improper operation.
Bending sequence: An improper sequence can lead to changes in stress, affecting subsequent bending angles.
5.What specific suggestions are there?
As a designer: Clearly indicate tolerances on the drawings and select an appropriate grade based on GB/T 1804.
As a manufacturer/purchaser:
Prioritize the tolerances on the drawings.
If not indicated, clarify the accuracy requirements with the other party (e.g., agree to comply with GB/T 1804-m grade).
For critical components (such as the tube sheet of dust removal equipment), it is essential to require a higher accuracy grade (e.g., ±0.5° or f grade), and conduct random checks using a ruler or three-dimensional measurement during incoming material inspection.