1.What is the core logic of elongation determining "plastic deformation capacity"?
Elongation is essentially the maximum degree of plastic deformation a material can withstand before breaking (i.e., its "ductility"). The higher the elongation, the more the material can be stretched and bent without breaking, while a lower elongation makes it more susceptible to "brittle cracking" during processing.
For example, a galvanized coil with a 25% elongation can be stretched to 1.25 times its original length before breaking; whereas a material with a 15% elongation will break after being stretched to only 1.15 times its original length. The former has a much greater processing margin than the latter.
2.What is the influence of the growth rate on stamping?
Simple shallow punching (such as punching holes in flat sheets and shallow drawing):
Only minor plastic deformation is required, and the elongation requirement is relatively low (typically ≥18%). For example, for file cabinet side panels and air conditioner outdoor unit back panels, DX51D with an elongation of 20%-22% is sufficient. If the elongation is too low (e.g., <15%), "micro-cracks" may form at the hole edges or in the stretched areas during punching, leading to increased scrap rates.
Complex deep drawing (such as automotive fuel tanks, thermos flask liners, and washing machine drums):
The material needs to be significantly stretched in the die (up to 5-10 times its thickness). Elongation is a critical threshold here-typically ≥28% is required (e.g., DX54D and DC06 galvanized coil). Insufficient elongation (e.g., DX51D with only 20%) can lead to insufficient plastic reserve during deep drawing, resulting in fracture at the most stretched areas (e.g., bottom fillets) and failure to form.
3.What is the effect of elongation on bending?
Small radius/large angle bends (e.g., 180° fold, r=0.5t bend, where t is thickness):
The material requires high elongation (typically ≥22%). For example, to achieve a 180° fold (bend radius r=1mm) on a 2mm thick galvanized coil, the elongation must be ≥25%. If the elongation is only 18%, the inner material will crack due to "unable to withstand compression deformation" during bending, and the outer zinc layer will also fall off due to excessive stretching.
Large radius/small angle bends (e.g., 90° bend, r=2t bend):
The elongation requirement is lower (≥15%). Even high-strength galvanized coil with slightly lower elongation (e.g., S350GD, elongation 18%-22%) can be successfully completed.
4.What is the effect of elongation on roll forming?
Roll forming involves using multiple sets of rollers to gradually press a flat sheet into a specific cross-section (such as a C-shaped steel or U-shaped channel). During this process, the material undergoes repeated tensile and compressive deformation. The role of elongation is to prevent cracking caused by localized stress concentration.
If the elongation is insufficient (e.g., <18%), the material is prone to edge cracking or uneven cross-sectional deformation at the "corners" (where stress is most concentrated) during rolling, leading to frequent production line downtime and adjustments.
If the elongation meets the required standards (e.g., ≥20%), the material can release localized stress through plastic deformation, ensuring the stability of continuous forming. This high elongation can significantly reduce scrap rates, especially for thin-walled, complex-cross-section roll-formed parts (such as photovoltaic brackets).
5.What are the common processing problems of insufficient elongation?
Cracking: Cracking at the bottom during deep drawing and cracking at the corners during bending are the most direct forms of failure.
Zinc peeling: When the material's plasticity is insufficient, the deformation of the zinc layer and the base material does not match. After bending or stretching, the zinc layer peels and falls off, losing its corrosion protection.
Excessive springback: After bending, the product cannot maintain the specified angle (for example, a required 90° may actually spring back to 95°), requiring secondary correction and reducing production efficiency.
Poor dimensional accuracy: During stretching or rolling, uneven plasticity can cause inconsistent local deformation, resulting in dimensional deviations and failure to meet assembly requirements.