1.How can I check if the internal structure is "uniform"?
The microstructure of a material has a significant impact on its bending properties. If the grain size in the matrix is uneven (with abnormally large grains), or if there is a large amount of carbide precipitation at the grain boundaries, the material's plasticity will be greatly reduced, leading to cracking along the grain boundaries during bending. This situation usually needs to be resolved by optimizing the steel mill's heat treatment process (such as annealing temperature and time).
2.How can I verify whether the material composition meets the standards?
If the material strength is too high, its plasticity will naturally be poor. For some special applications, such as hard-rolled coils that require 90° right-angle bending, steel mills will use low-carbon and low-manganese compositions to ensure that the material has sufficient softness and ductility to meet the requirements of direct bending.
3.How to check for "hard damage" on the surface?
Surface defects in materials are the starting point for stress concentration during bending, easily leading to cracks. Careful inspection is essential:
Scratches and abrasions: Any surface scratches can become a source of cracks during bending.
Edge cracks: Tiny cracks at the edges of the strip can propagate rapidly under bending tension.
Bubbles and folds: These internal or surface discontinuities can directly cause cracking under stress.
4.How to optimize the bending process?
Adjusting the bending radius: This is one of the most critical factors. If the bending radius is too small, the tensile stress on the outer side of the material will increase sharply, easily leading to cracking. A general principle is that the inner bending radius should be at least equal to or greater than the material thickness. For materials with higher hardness (such as stainless steel), it is recommended to use 1.5 times the plate thickness or greater.
Controlling bending speed: Excessive speed will prevent the material from deforming evenly, resulting in excessive localized stress. Using low-speed, smooth bending allows the internal stress of the material to be fully released, effectively reducing the risk of cracking.
Consider step-by-step forming: For workpieces with complex shapes or large bending angles, do not attempt to complete the bending in one step. Use step-by-step bending or add a pre-bending process to allow the material to gradually take shape, avoiding excessive deformation at once.
5.How to inspect and lubricate the mold?
Optimize mold design: Check if the mold edges are sharp or have burrs. Designing the edges of the punch and die with rounded corners can effectively distribute stress and prevent scratching or cutting the material surface during bending.
Ensure adequate lubrication: During bending, the material and mold experience intense friction. Using a suitable lubricant not only reduces friction but also helps dissipate heat, preventing micro-cracks from forming on the material surface due to overheating.