1. About the main causes and measures of cracking at the ends of sheet metal bending:
1) Burrs and defects on the outer surface of the material
Burrs and defects from shearing or punching can lead to stress concentration, causing cracking at the sheared or punched edges and defects during bending. Measures:
1) For aluminum sheets with thickness ≥4mm, carbon steel with thickness ≥6mm, and bending angle ≤90°, for bent products after shearing or punching, before bending, grind the ends of the bend within the range of L>5t to chamfer >C1.5 or >R1.5. When creating process flow charts or process cards, pay attention to adding a grinding step before bending, to be completed by the bending team.
2) For aluminum sheets with thickness ≥4mm, carbon steel with thickness ≥6mm, and bending angle ≤90°, for bent products after shearing or punching, bend with the sheared or punched edge facing the inside of the bend radius. When creating process cards, please include this instruction.
3) Select the correct bending tool and die.
4) If defects persist after implementing the above measures, consider using oxy-acetylene flame heating or baking. Control the temperature of aluminum at around 200°C and steel within the range of 500-600°C.
2) Small bending radius (R)
Measure: For aluminum sheets with thickness ≥4mm, carbon steel with thickness ≥6mm; when the bending radius is ≤t and the bending angle is ≤90°, it is advisable to suggest a design change to increase the bending radius to R>t or follow the measures in point 1.
2. About the main causes and measures of cracking at the bending line of sheet metal bending:
1) Material reasons
Measure: Some materials are not suitable for forming. Communicate with the customer during the process of technical drawing review, or if feasible but requiring a change in its heat treatment state, such as annealing.
2) Minimum bending radius smaller than its limit value
Measure: During the technical drawing review, check if the product's minimum bending radius Rmin is smaller than its limit value. If it is, request a design change to increase the bending radius, referring to standards EN485-2, EN10025-2.
3) Bending direction consistent with the material's fiber direction?
Measure: When nesting material, consider that the material's fiber direction should not be parallel to the bending line, preferably at 90 degrees. For products prone to cracking during bending, include this in the process documents when preparing them.
4) Heat treatment state
Measure: When reviewing drawings, pay attention to the material's heat treatment requirements. Some products may require a surface treatment state of quenching or tempering. When processing bending products, consider bending first before performing the heat treatment process.
