Common Tube Bending Issues

Tube bending can present a complex set of challenges, transforming what seems like a straightforward process into a nuanced art form. Over the past 30 years here at Trick Tools, we've encountered, analyzed, and helped our customers overcome nearly every obstacle imaginable. These challenges can stem from a variety of sources, including the specific characteristics of the material being bent, the calibration and capabilities of the bending machine itself, the design and condition of the tooling, and sometimes even the experience and technique of the operator. Understanding these potential pitfalls is the first step toward achieving perfect, consistent bends. That's why we've created this article, designed to equip you with the insights and solutions you need to troubleshoot and conquer the most common tube bending issues you might encounter.

Note: These tips mostly apply to non-mandrel, rotary draw bending applications. If you have questions about mandrel bending or issues not included in this article, please feel free to drop us an email or give us a call.

• Wrinkling:
  The inside of the bend can develop wrinkles or buckles, particularly in thinner-walled tubes with tighter bends. This can be solved by using a larger radius former die or a thicker wall tube. If tooling is worn out, replace components of dies as necessary.
  
  
• Kinking:
  The tube can kink or collapse if the material isn't supported properly during the bend or it is being bent to a radius that is too tight for the wall thickness. This can also be a result of slippage of the tube in the die. The harder the material, the more likely it is to kink when bent to a tight radius. Try clamping the tube or gritting the die to prevent slippage.
  
• Flattening:
  The cross-section of the tube becomes flattened on the outside of the bend. Different bending styles will be worse than others, but this is typically due to slippage of the tube in the die or worn tooling. Mark the tube before bending to check if slippage is occurring. Replace worn components of dies as necessary.
  
  
• Cracking/Splitting:
  Cracks or splits can occur on the outer radius of the bend, especially with copper and aluminum tubing. Age and alloy of material are major factors. This can be caused by excessive pressure of the counter die, resulting in excessive wall thinning and stretching. Larger radius dies can resolve this if the material is not the problem. Consider annealing the tube or trying a different alloy.
  
  
• Ovality:
  Similar to flattening, ovality is a change in the roundness of the tube's cross-section, making it elliptical rather than circular. Open (non-mandrel) draw bending will always have a certain amount of ovality. Worn tooling or bending on tight radius dies will be worse. If the ovality is parallel with the bending plane, with new tooling, there can be too much pre-ovalization for the material. Opening up the pinch of the counter die can reduce this issue.
  
  
• Galling/Scoring:
  These surface defects can occur due to friction between the tube and the tooling, especially with improper lubrication. A quality high-pressure bending lube (not WD-40) is recommended on any sliding components. Deburr or blend any sharp edges on dies to reduce marking, or consider alternative counter die options such as Delrin or roller dies.
  
  
• Inconsistent Bend Angle:
  Tubing properties can vary from batch to batch, but inconsistency within a batch may be machine, operator, or tooling issues. Start by verifying that the machine is repeating with no tooling installed and the operator is doing all bending operations consistently. Slippage of the tube in the die will cause inconsistent results.
  
  
• Twisting Within Bend:
  Tubes can twist within a bend, usually only noticeable when bending greater than 90 degrees. This can be a machine issue or a tooling issue. If possible, place the tube weld seam in the same orientation each time, and contact your manufacturer if problems persist.