How to Understand Technical Requirements on Process Drawings
When you receive a batch of hydraulic press stamped parts, besides visually inspecting for cracks, what other methods can you use to judge their manufacturing quality? Actually, a qualified process drawing is the “health check report” for these parts. Understanding the technical requirements allows you to immediately spot whether the supplier has cut corners.
1. Pay attention to the “springback angle” annotation. After metal sheets are formed on a hydraulic press, there will always be a certain amount of springback due to the release of internal stress. Excellent process drawings will indicate the springback compensation value next to the bending angle, such as “angle 90°, compensated die angle 88°”. If this annotation is missing, it indicates that the supplier may lack experience in precision forming, and the final part’s angular tolerances will be difficult to guarantee.
2. Pay attention to the “surface roughness” requirements. The surface roughness of hydraulic press-formed parts directly reflects the smoothness and lubrication level of the die. Generally, for external parts, Ra≤0.8μm is required, and for internal structural parts, Ra≤3.2μm is sufficient. If the drawing only states “smooth surface without burrs,” this vague description often leaves room for defective products.
3. Check “Flatness” and “Straightness”
For large cover parts, flatness is a crucial indicator of the hydraulic press’s clamping accuracy. Typically, the flatness error should not exceed 1.5mm per meter of length. If “wavy lines” appear on the parts after assembly, it’s most likely due to excessive flatness.
4. The Hidden Code of Material Flow
Advanced process drawings will also indicate the “rolling direction.” Because sheet metal exhibits anisotropic mechanical properties, stretching along the rolling direction reduces the likelihood of cracking. If suppliers ignore this marking and arrange materials arbitrarily, the fatigue life of the parts will be significantly reduced.
