1.What are the mechanisms and phenomena of yield strength fluctuation?
Mechanism: The higher the yield strength of a material, the greater the springback after forming. If the properties of the head, middle, and tail sections of the same batch of cold-rolled coils are inconsistent, or if the yield strength of different batches of incoming materials deviates significantly (e.g., ±30MPa or more), the amount of springback will vary considerably.
Phenomenon: Unpredictable changes in the flange angle and sidewall deflection.
2.What are the mechanisms and consequences of fluctuations in the work hardening index (n value) and the plastic strain ratio (r value)?
Mechanism: The n-value determines the hardening rate and strain distribution capability of a material under tension; the r-value (thickness anisotropy coefficient) determines the thinning resistance of the material in the thickness direction.
Consequences: Fluctuations in these two parameters can lead to inconsistent thinning of parts under the same die clearance, thus affecting the stiffness (dent resistance) and final dimensions after forming.
3.What are the mechanisms and phenomena of plate thickness tolerance (thickness fluctuation)?
Mechanism: For fine blanking or ordinary drawing, the die clearance is fixed. When the incoming material is too thin (negative tolerance), the fit between the material and the die deteriorates, easily causing warping; when the incoming material is too thick (positive tolerance), the extrusion pressure increases, die wear intensifies, and temperature rises, leading to thermal expansion and further altering the clearance.
Phenomenon: The depth of the blanking marks on the parts varies, or the parts become stuck on the die, causing deformation.
4.What are the effects of changes in mold temperature?
Key point: During continuous production, the mold temperature will rise from room temperature (approximately 20°C) to thermal equilibrium (potentially reaching 50-80°C or even higher).
Consequences: The punch and die expand due to heat, reducing the clearance and increasing friction. Without temperature control measures (such as a mold temperature controller), there will be a significant dimensional difference between the first part produced in the morning (cold mold) and the part produced in the afternoon (hot mold) (generally, springback is less in the hot mold state).
5.What are the consequences of mold wear and scratching?
When the radius (R) of the mold wears significantly, or when wear on the working belt causes increased clearance, the constraint force on the material weakens, the flow rate increases, and the part size gradually increases or springback increases.
If the mold surface develops roughening (material sticking), the local friction increases dramatically, causing the material in that area to be "stuck," resulting in abnormal local deformation.