What metal fabricators can do when a tube bender breaks

CNC tube benders are going to break—the forces involved encourage entropy all too well. What to do about it requires a long list of considerations. Images: Lincoln Brunner

How long should a CNC tubing bender last? At what point in the machine's life do you start to look at a complete rebuild or replacement? What is the difference between rebuild and re-control?

Eventually, all tube benders will need to be repaired, rebuilt, re-controlled, or replaced. But why?

Well, they use the force: CNC tube benders produce amazing amounts of force to form a straight tube into a bent shape. I often use the example of a 4-in. hydraulic cylinder that operates the pressure die on a typical 3-in. hybrid tube bender. The hydraulic systems on most of these machines can generate 2,000 lbs. per square inch of pressure.

To calculate the total amount of force that potentially can be applied, multiply hydraulic pressure in psi by the total surface area of the cylinder's piston. A 4-in. piston has just more than 12.5 sq. in. of surface area. At 2,000 psi, that cylinder can produce more than 25,000 lbs. of force.

A typical pressure die setup may only use 1,000 psi to make a good part, but that means that 12,500 lbs. of force is still being applied to the tube and machine mechanics over and over while the machine runs.

So, with tube bending, it is not a question of if the machine is going to break but when.

In addition to mechanics, all CNC tube benders have some form of control system. The first PC-based control systems used DOS-based operating systems. Some recently made machines may have a Windows-based computer for data entry but use a PLC for actual integration and control of the devices on the machine. Over time, these components start to fail, support for software becomes scarce, and finding replacements becomes more and more difficult.

Inside the cabinet and on the control console, buttons, switches, motor contactors, overloads, relays, power supplies, I/O, and other components all have a finite number of cycles they can go through before they start to fail.

Most of the time, when you get a quote to rebuild a machine, it will include the cost of installing a new control system. All of the mechanics will either be replaced or repaired to like-new condition. However, a machine can be re-controlled without necessarily performing a mechanical rebuild.

If your machine is mechanically sound, replacing or upgrading the control system may be less than half the cost of a complete rebuild. Also consider that outdated motors and hydraulic and drive systems can be replaced without the expense of replacing gear reducers, ballscrews, or other mechanics.

With tube bending, it is not a question of if the machine is going to break but when.

Here are a few things to consider.

Machine Size. Smaller machines (less than 2-in.-OD capacity) typically do not take the same abuse as machines 2 in. and larger. While the mechanics required for a rebuild may be less expensive than larger machines, the amount of labor that goes into a rebuild is about the same. The cost of a complete rebuild may start to approach the cost of buying new.

Part Complexity. One factor you should consider heavily when deciding to rebuild or re-control an existing machine is the complexity of the parts you produce. Most manufacturers of new machines can simulate parts for you, but this may not be practical if you run hundreds of different parts. Parts you are currently able to produce on an existing machine can definitely continue to be produced after a rebuild or re-control.

Available Tooling. Some benders by themselves may not be worth the investment of a rebuild or re-control, but they may also have tons of bend tooling that is used often and fits the machine. Some new machines can be ordered with specific tool mounts or adapters so the existing bend tools can be used, but this is not always as easy as it sounds. The cost of replacing all of the available tooling in a shop may far outweigh the cost of rebuild or re-control.

Parts Availability. Some great tube benders still in use were built by manufacturers that either went out of business or were bought by companies that are no longer making parts for them. Most of the companies that offer complete rebuild services will produce new parts or find an adequate cross reference, but even a complete rebuild will re-use a large amount of what is on the machine. This may make it difficult to just pick up the phone and order parts when something breaks.

Power Consumption. When considering a new machine versus rebuilding or re-controlling an existing one, consider closely the amount of power it takes to run it. Most newer machines use electric bending, while a lot of older machines have hydraulic bend arms. Electric machines tend to consume less electricity, so the day-to-day cost of operation can be considerably lower. Even hybrid machines that use electric bending with hydraulic clamping don't require the big energy-consuming hydraulic pumps and motors that some hydraulic bending machines have.

Machine Capacity. When considering a new machine in comparison to an existing bender, be sure the new machine's capacity is the same (or greater). When moving from a machine with hydraulic bending and clamping to a new all-electric machine, or even a hybrid with electric bending, be sure the machine's ability to bend your parts is the same.

It is not unusual for an electric machine to be rated for the same size tube OD but at a much smaller wall thickness. Use the 80/20 rule of thumb: No more than 20% of your production parts should exceed 80% of the capacity of the machine. If you will be regularly bending parts that are more than 90% of the new machine's capacity, you should really consider moving up a size. The cost difference may make rebuilding an older machine that has a higher capacity much more attractive.

There are many more things to consider when deciding whether to invest in existing bending equipment or replace it with new, and the companies that sell this equipment can help you work through the advantages and disadvantages of each option. Be sure to ask plenty of questions, carefully consider the information given, and make the best decision for your production!

There are many more things to consider when deciding whether to invest in existing bending equipment or replace it with new.