When SPH275 cracks during deep drawing, frustration sets in fast. The material should form well—it's designed for it. But when parts split at the punch radius or thin excessively at sidewalls, something's off. Here's how to diagnose and fix the problem.
Not all SPH275 behaves the same. Verify your mill test certificate shows elongation values meeting requirements—typically 25% or higher for formability grades. If the coil came from a mill known for tighter mechanical ranges, swapping to a different heat often resolves mysterious cracking issues.
Edge condition matters tremendously for deep drawing. Sheared blanks develop work-hardened zones that become stress risers during forming. If cracks initiate at blank edges, consider laser cutting instead of shearing, or add an edge conditioning step to remove the work-hardened layer.
Die radius and punch profile dictate how material flows. A punch radius too small for the drawing depth creates localized thinning that leads to cracking. For SPH275, maintain punch radii at least 4 to 6 times material thickness for deeper draws. Draw beads or pressure pad adjustments that grip the blank too tightly can also restrict material flow into the cavity.
Deep drawing SPH275 demands proper film strength. Light-duty oils fail as pressure builds. Switch to heavy-duty stamping lubricants formulated for hot-rolled steel, and ensure consistent application across the entire blank face. Inadequate lubrication shows up as galling marks near fracture points.
When single-stage drawing pushes SPH275 beyond its limits, annealing between stages restores ductility. If your part geometry demands reduction ratios exceeding 40% in one hit, redesigning as a multi-stage operation with intermediate annealing eliminates cracking issues.
Remember that SPH275 shows directional properties from rolling. Cracking often follows the rolling direction. If your deep draws crack consistently along one axis, rotate blank orientation 90 degrees in your nest layout.
