For a typical square tube draw, large-scale cracking can occur near the center of the straight side wall.
Root Cause Analysis
Geometry
① Draw height too large:
Before reducing draw depth to prevent cracking, verify all other conditions first. If the issue persists after checking everything else, then reduce the draw height and add a separate draw-and-restrike operation to hit final dimensions.
② Die fillet radius too small:
In square tube deep drawing, the usual fix for springback sag on the straight side wall is to use draw beads, but that leaves bead marks on the part. So when running without draw beads, set the die gap slightly tighter than the material thickness and use a small corner radius. If cracks appear beyond the material's tensile limit, increase the radius slightly and run a trial draw.
Stamping Conditions
① Excessive blank holder force:
A fully polished flange surface indicates the blank holder force is too high. Reduce it until the material flows in freely without wrinkling.
② Poor lubrication on die surfaces:
To promote material flow, check both the lubricant type and the application rate.
Methanol Injection System Solenoid Valve Housing Body
Methanol Injection System Solenoid Valve Housing Body
Tooling Issues
① Poor die surface finish or fit:
If the product cracks and the flange shows scratches, polish the die surfaces with a grinding wheel to get a smooth finish that lets material flow easily.
② Die gap too tight:
②the gap is too small:
When the side wall shows a shiny, cracked surface, that's typically a sign the wall is too thin for the draw. You'll want to open up the die clearance to reduce the thinning and prevent fracture.
③ Poor draw bead location or geometry:
Excessive draw bead force is a common cause of rupture. Reduce the bead pressure or adjust the bead profile to let material flow more freely without tearing.
④ Poor die accuracy:
If the tooling isn't precise, the core can shift, and the punch-to-die alignment—parallelism and perpendicularity—will be off. A thorough pre-run die inspection will catch these issues before you ever pull a trial part.
⑤ Insufficient blank holder rigidity:
When the blank holder flexes under load, only a few buffer pins end up carrying the force, which leads to localized stretching and cracking. Stiffen the holder or redistribute the pin layout to even out the pressure.
⑥ Poor press accuracy:
A press that's out of tolerance will produce the same defects as misaligned tooling. Before any trial draw, verify the machine is holding its specified precision—check ram parallelism, gib clearance, and cushion performance—then run your test parts.
Material
① If the defect traces back to insufficient tensile strength or oversized grain structure in the blank, you need to switch to a higher-grade material that can handle the draw.
② If the failure is due to the sheet being too thin for the application, spec a thicker gauge to provide enough material for the draw without necking or splitting.