TL;DR
Wrinkling or collapse during bending indicates insufficient mandrel support or wrong wiper die position. Check mandrel position and mandrel lubrication before adjusting bend parameters.
What you might see
- visible wrinkles on the inside radius of the bend
- tube wall collapses at the bend area
- mandrel ball shows scuffing or galling marks
- final part angle correct but wall integrity fails inspection
Likely causes
Mandrel retracted too far from the tangent point, leaving the tube wall unsupported
Insufficient or failed mandrel lubrication causing friction-induced collapse
Wiper die not flush with the bend die tangent point or worn wiper tip
Boost pressure too low not providing enough longitudinal push to fill the bend
Required tools
- Digital calipers for tube wall measurement
- Mandrel lubrication per machine specification
- Replacement wiper die tip (if worn)
- Scrap tube of production specification
Safety first
- Keep hands clear of the bending die and clamp zone during any test bend. The tube and tooling move rapidly.
- Lock out the machine before making any mechanical adjustments to the wiper die or mandrel rod connections.
Procedure
- 1
Stop the bending cycle and measure the mandrel nose position relative to the bend die tangent point using the machine's mandrel position display.[1]
- 2
Advance the mandrel nose forward by 0.5 mm increments toward the tangent point until wrinkling reduces, testing each increment on scrap tube.
- 3
Verify the mandrel lubrication system is flowing. Check the lubricant level in the mandrel lube reservoir and confirm the lube is reaching the mandrel balls.[1]
- 4
Inspect the wiper die tip for wear or rounding. Replace the wiper die if the tip is worn back from the nominal profile.
- 5
Confirm the wiper die is positioned with zero gap at the tangent point. Adjust the wiper die mounting screw to achieve flush contact.
- 6
Check the boost assist pressure in the machine control. Increase boost by small increments and test on scrap until wall integrity improves.
- 7
Once wrinkling is eliminated on scrap, run a production part and inspect the inside radius, outside radius, and cross-section ovality against the part specification.
Sources
Schwarze-Robitec BLM Group e-TURN / Smart Tube / Pipe Bender general technical documentation, Schwarze-Robitec
BLM Group e-TURN / Smart tube bender operator and tooling setup documentation (general)
More guides for Schwarze-Robitec BLM Group e-TURN / Smart
How to diagnose a carriage drive fault on a BLM Group e-TURN / Smart tube bender
Carriage drive faults on CNC tube benders typically come from servo drive alarms, encoder errors, or lubrication starvation on the carriage linear guides. Check the servo drive alarm code first.
How to correct springback variation on a BLM Group e-TURN / Smart tube bender
Inconsistent springback between parts typically means the material yield strength has shifted between coils. Re-measure springback on each new coil and update the overbend compensation value in the CNC.
Stop fixing the same fault twice.
Dovient turns guides like this into your team's shared playbook, with AI that catches recurring issues before they break the line.