Tube Bender Troubleshooting: Causes & Fixes

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Problems on this page:

Wrinkles on the inside of the bend Flattening or ovality at the bend Cracks on the outside of the bend Bend angle varies Tube slipping in the clamp Scoring or tool marks on the tube Mandrel breaking or sticking Bends in the wrong plane

Wrinkles on the inside of the bend

Hits OEE: Quality

Symptoms: Waves or wrinkles form on the inside radius of the bend.

Wiper die not set close to the tangent

Set the wiper die tip close to the tangent point with the right rake.

Mandrel too far back

Move the mandrel forward to support the tube through the bend.

Pressure die pressure too low

Increase the pressure die force.

Thin wall for the bend radius

Use a closer fitting mandrel or a larger radius where the design allows.

Prevention: Tool setup sheets with wiper and mandrel positions for each part.

Flattening or ovality at the bend

Hits OEE: Quality

Symptoms: The tube section goes oval through the bend.

No mandrel or mandrel too small

Use the mandrel size matched to the tube bore.

Mandrel extracted too early

Set the mandrel extraction to follow the end of the bend.

Bend die groove worn

Check and replace the bend die.

Prevention: Ovality measured on first parts.

Cracks on the outside of the bend

Hits OEE: Quality

Symptoms: The outer wall splits or thins too much at the bend.

Material elongation too low for the radius

Check the material certificate and the bend radius.

Pressure die boost too low or too high

Adjust the boost so the wall is pushed into the bend without tearing.

Tube weld seam on the outside of the bend

Orient the seam to the neutral axis.

Mandrel set too far forward

Move the mandrel back slightly.

Prevention: Material certificates checked for each tube lot.

Bend angle varies

Hits OEE: Quality

Symptoms: Springback changes from part to part and the angle is out of tolerance.

Material properties vary between lots

Check springback on the first parts of each lot and adjust.

Springback compensation not updated

Update the compensation in the program.

Tube slipping in the clamp

Check the clamp die and pressure.

Bend arm encoder or servo fault

Check the axis position against a reference.

Prevention: Angle checked on first-off parts of every lot.

Tube slipping in the clamp

Hits OEE: Quality

Symptoms: The tube moves in the clamp die and bends end up in the wrong place.

Clamp die worn or wrong size

Replace the clamp die with the right size and grip.

Clamp pressure too low

Increase the clamp pressure.

Lubricant on the clamp area

Keep lubricant off the clamp section of the tube.

Prevention: Clamp dies inspected at each tool change.

Scoring or tool marks on the tube

Hits OEE: Quality

Symptoms: Scratches or marks appear along the bend.

Lubrication wrong or missing

Use the bending lubricant specified and apply it evenly.

Dies damaged or galled

Polish or replace the dies.

Pressure die dragging

Check the pressure die assist speed.

Prevention: Die surfaces inspected weekly.

Mandrel breaking or sticking

Hits OEE: Availability

Symptoms: The mandrel balls break off or the mandrel will not extract.

Mandrel extracted at the wrong time

Reset the extraction timing.

Galling between mandrel and tube

Use the right lubricant and mandrel material.

Mandrel worn

Replace the mandrel on a schedule.

Prevention: Mandrel condition checked at each tool change.

Bends in the wrong plane

Hits OEE: Quality

Symptoms: The rotation between bends is wrong and the part does not fit the gauge.

Collet slipping

Check the collet and its pressure.

Rotation axis error

Check the axis against a reference.

Program data wrong

Check the bend data against the drawing.

Prevention: Each new program proved with a gauge check.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: press brake · hydraulic system · CNC machine · laser cutter · servo drive

Stop the same fault coming back

Recurring tube bender stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover