Common mandrel bending challenges and solutions

Key takeaways:

• Mandrel bending maintains internal diameter and shape in tight-radius or thin-wall tubing.
• Without a mandrel, tubes can wrinkle, ovalize, or collapse during bending.
• It is commonly required for high-purity, fluid handling, and cosmetic-critical applications.
• The tighter the bend radius relative to tube diameter, the more likely a mandrel is needed.
• Mandrel type, plug, ball, or multi-ball, directly affects bend quality and consistency.
• Tooling setup and process control are as critical as the mandrel itself.
• It increases upfront cost but reduces defects, scrap, and rework.
• For flow-sensitive or contamination-critical systems, mandrel bending is often the safer choice.

It’s often said that metal tube bending is both an art and a science. Finding success within art and science typically involves trial and error before accomplishment. Here are some common tube bending challenges – and tube bending solutions for success.

Springback 

Challenge: After being bent, metals such as stainless steel will attempt to return to their original, unbent shape. This is called springback. When stainless steel bends, the inner region of the bend compresses while the outer region stretches. The molecular density is greater on the inside of the bend than on the outer portion of the metal. Higher tensile forces try to force the metal back to a flat position versus lower compressive forces. Hand benders sometimes over bend the required bending angle to accommodate for springback. This tactic can result in imperfect bends.

Solution: This is not a concern for our in-house tube bending jobs, because they are performed on a Horn Metric CNC Tube Bender machine. We don’t need to overcompensate bends for springback, because there isn’t a risk of springback when properly bending on a CNC machine.

Damaged or weakened mandrel and/or tooling

Challenge: A mandrel provides stability for bend tooling and provides internal pressure for the bending. Accurate mandrel bending results in perfect, strong, repeatable bends.

Challenges with mandrel bending include:

• Humps at the end of a bend
• Humps from mandrel balls
• Tube collapse
• Tooling breakage from too much pressure

Any of these results in failed tube bending. Using improper or weakened tooling will also not produce perfect bends. Worn tools are a top foe for a piece of tube bending machinery. One common mistake is attempting to substitute the machine’s force for proper tooling setup. This can be damaging to both the machine and the tooling. Perfect tube bending is challenging enough. When you couple that with worn and/or inadequate tooling, faults are likely occurrences even with routine bending jobs.

Solution: Axenics ensures the mandrel tooling we use on our tube bender is properly functioning and free from faults, because even the most-experienced technician would struggle without proper tools. Our mandrel and tooling receive regular maintenance check-ups to ensure perfect performance. Our CNC tube bender provides fast, consistent, high-quality tube bends while eradicating many of the defaults that can arise from weld seams (such as humps).

Tube breaking isn’t a risk with our experienced team. We know which materials are best for each job. With tube bending, we choose to work most often with 300-series stainless steel. Not only does it result in perfect, faultless bends, but it’s a cleaner metal than most.

Lubrication 

Challenge: Lubricant is used to coat the inside of a tube, as well as the bending mandrels and the outside diameters of the tube and wiper die. Its main function is to reduce friction during the tube bending process. Lubrication is also key to successful tube bends. Not using proper and adequate tube bending lubricants, will cause some serious challenges within the bending process – including costly damages to the machine itself.

Solution: Not using proper and adequate tube bending lubricants can cause serious challenges during the bending process. Using lubricants on the machinery reduces friction during the bending process, decreases the build up of scrap material and offers a longer life for your tooling.

Keeping your machinery well lubricated is always a best practice when aiming for perfect tube bending results.

Axenics uses fluids that are free of sulfur and chlorine additives. It’s essential that the lubricants are water soluble to minimize wear and tear on the tooling and the bend dies. Using proper lubricants also provides minimum corrosion when bent parts are stored.

We currently use two types of fluids:

• Houghto-Draw 7000 series
• IRMCO Extreme

Cost 

Challenge: Speaking of cost, of course cost is a challenge if you’re going to set up a new tube bending production. Consider just the cost of basic equipment such as a quality tube bending machine and you’re looking at investing more than $10,000. Other costs include but aren’t limited to:

• Hardware and software
• Machine training
• Machine tooling
• Lubrication
• Repair parts
• Machine servicing and support

Solution: The costs we mention above are not necessary for your next mandrel bending job, as we’ve already absorbed them. Also, tube bending is one of Axenics’ longtime specialties, which is why we rarely encounter the challenges listed above when performing jobs for clients.

You may be surprised to learn that an automated tube bending machine provides efficiencies, and often erases the need for welds or multiple fittings. We have an impressive machine, updated software and hardware, fully-trained technicians, proper tooling and materials, and regularly-scheduled maintenance to keep it all in top form. 

All we require now are your job specifics and we’re ready to roll.

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