Tube bending is a critical process in industries ranging from automotive and aerospace to furniture and architecture. However, even experienced fabricators can encounter two common issues: wrinkling on the inner bend radius and flattening on the outer radius. These defects not only affect the appearance of the part but can also compromise structural integrity and dimensional accuracy.
In this post, we’ll explore the main causes of these issues and provide expert strategies to prevent wrinkles and flattening during the tube bending process.
1. Understand the Material and Wall Thickness
Material selection plays a major role in bend quality. Softer metals (like copper or aluminium) are more prone to wrinkling, while harder metals may be more susceptible to cracking or flattening if not properly supported.
- Use a thicker wall when possible — thin-walled tubing is more likely to deform.
- Know the D/t ratio (bend radius divided by tube wall thickness). Lower D/t ratios increase the risk of defects and may require advanced bending techniques.
2. Use the Right Bending Method
Choose the bending technique based on the application and part geometry:
- Rotary Draw Bending is ideal for precision and tight radii. It uses internal and external support tools to minimise deformation.
- Compression Bending is quicker but less precise, and more prone to flattening and wrinkling.
- Mandrel Bending incorporates a mandrel inserted inside the tube to support the wall during bending, which is highly effective at preventing collapse and wrinkles.
3. Tooling Matters: Use Mandrels and Wiper Dies
For tight bends or thin-walled tubing, internal support is essential.
- Mandrel: Supports the interior of the tube during bending and helps maintain shape.
- Wiper Die: Prevents the inside radius of the bend from wrinkling by smoothing and guiding the material as it compresses.
Tooling should be clean, precisely matched to the tube size, and made from appropriate materials (e.g., hardened steel for high-strength alloys).
4. Optimise Machine Settings
Incorrect bending speed, pressure, or alignment can lead to poor results.
- Bend speed: Too fast can cause wrinkles; too slow can cause material stress or cracking.
- Clamp pressure: Insufficient pressure may allow slippage and deformation.
- Lubrication: Proper lubrication reduces friction and wear, allowing smoother material flow.
Advanced CNC tube benders like those from the SOCO range allow precise control of these parameters, improving consistency and repeatability.
5. Consider the Bend Radius
A tighter bend radius increases the likelihood of defects. Where possible:
- Increase the bend radius relative to the tube diameter (1.5D or more is generally safer).
- For mandatory tight-radius applications, ensure you’re using mandrel support and optimised tooling.
6. Perform Regular Maintenance & Inspection
Even the best equipment can cause poor bends if the tooling is worn or misaligned.
- Inspect and replace worn dies, mandrels, or wiper dies.
- Regularly calibrate your CNC bender to ensure bending accuracy.
- Clean surfaces to prevent contamination or scratching during bending.
Precision Comes from Preparation
Preventing wrinkles and flattening in tube bending requires the right material selection, bending technique, support tooling, and machine settings. Whether you’re bending simple radii or producing complex exhaust systems, using the correct method and maintaining high standards ensures clean, repeatable, and structurally sound bends.
Need help improving your tube bending process?
Langbow offers expert advice, high-performance SOCO CNC tube benders, and a full range of tooling solutions to ensure perfect results every time.