Decoding all the tube bender options

Today’s tube bending machines offer shops a rich range of control and system options. RbSA Industria

The very first tube bender I ever saw, I had to fix. It was my first day as maintenance manager at an exhaust manufacturer, and I was feeling more than a bit overwhelmed.

The plant was huge, with more than 600,000 sq. ft. under a single roof. About half was dedicated to manufacturing; the other half warehouse and shipping. My work history included plant engineer at a chemical manufacturer, lead electrician at a rock quarry, and field technician/service manager for a company that worked on electronic scales. I had rarely had to think about more than one machine at a time, and I had never had more than four employees as direct reports.

This company had more than 1,000 pieces of equipment, including welding machines, presses, flangers, and two tube mills with Floop vertical strip accumulators, none of which I had heard of, much less worked on before. On the list of machinery that I was suddenly responsible for were 22 CNC tube benders from various manufacturers, four NC tube benders, several press benders, and dozens of end forming machines. Along with all that equipment came a maintenance staff of 12 highly skilled technicians. Because virtually everything in the building was new to me, they may as well have been speaking Latin with all of the names and acronyms and abbreviations they threw around.

As in any industry, we sometimes use shorthand that does not always translate very well. I was recently asked to explain the difference between a hydraulic and an all-electric tube bender. This was someone I had been speaking with for some time about his existing and potentially new machines, and I was embarrassed to discover we had effectively been speaking different languages.

Knowing the lingo of this business is key, though, if you want to make informed purchasing and maintenance decisions. Here are some basics.

NC or CNC?

NC and CNC are abbreviations for the type of control system a tube bender uses. NC stands for numerical control; CNC stands for computer numerical control. These are very broad definitions when related to tube benders, but you can think of them in terms of control system decision-making and the requirement for operator input.

NC. On an NC tube bender, there is feedback that helps the control system make decisions, but the machine is mostly manually operated. For example, an older single-axis bender like a Pines model 2 may have a series of switches that tell the control system when the clamp die is open or closed, the pressure die is open or closed, or the bend arm has returned to its zero or target position.

During the fabrication process, a series of relays determine if the machine is able to move on to the next step of its bending sequence, but the operator still must push the correct buttons to move through the sequence of bending a part.

A new or upgraded NC bender may have a more sophisticated control system, such as a Control-A-Bend from Current Tech or Comptrol from Sierra Corp., in which the mechanical relays have been replaced with a microchip-based control system and solid-state relays to control movement and receive feedback from switches mounted on the machine. Instead of switches determining when the bend arm is at home or at its target, an encoder provides precision feedback to the control system, which makes decisions based on that feedback. The machine may operate semiautomatically with fewer required inputs from the operator, but it still requires significant operator input.

CNC. A CNC tube bender is computer controlled. Most modern benders are truly controlled by what we think of today as a computer, but this could mean a programmable logic controller, human machine interface, or some other control system. These systems interface with the machine to get feedback and make decisions with minimal operator input, usually controlling multiple axes that provide continuous position feedback.

For example, BendPro CNC bender controls from Current Tech use an actual industrial computer with a Windows operating system, almost exactly the same as your PC. That system interfaces with the machine through an I/O system connected to the various switches, sensors, encoders, motors, and drive systems on the machine.

Once the part and the required parameters are set and the control system is placed in automatic mode, the only operator input required is to start the process. The control system decides when it is OK to move to the next step and produces a complete part without any further input from a human. The control system gathers feedback from one to more than 16 axes that move and manipulate a straight tube into a bent shape.

Hydraulic, Hybrid, or All-Electric?

Beyond the controls lie the actual mechanics of the machine. Most CNC tubing benders have a minimum of three servo-controlled axes: bend, feed, and rotate. An axis is servo-controlled when the position, velocity, and direction of movement are continuously monitored and adjusted by the control system. These axes can have a hydraulic/hybrid or all-electric configuration.

Hydraulic/Hybrid. I don’t know of any manufacturers that are making fully hydraulic CNC rotary draw tubing benders today. Because of this, the terms hydraulic and hybrid have essentially become interchangeable when talking about CNC tubing benders.

A hybrid CNC bender’s movement is controlled both by electric motors and hydraulic pressure.

In this kind of system, it is not uncommon for the bending axis to be hydraulic servo and the feeding and rotation axes to be electric servo. More commonly today, on a hybrid machine, the three main axes are electric servo, driven by an electric motor, while all of the other movements, such as clamping and unclamping, are hydraulically driven through a series of directional valves.

Most CNC tubing benders have a minimum of three servo-driven axis. A hybrid machine could have any number of servo-controlled axes but still use directional hydraulics for some movements.

For instance, a FlectePRO 453HSI bender is a hybrid, 45-mm bender with three electric servo axes that uses directional valves for hydraulic clamping, to control the mandrel and pressure die assist (PDA), and to return an independent bend die. Another FlectePRO model, the 456HMI, is still a hybrid 45-mm bender, but it has six servo axes—the standard bend, feed, and rotate axes, as well as electric servo for horizontal shift, vertical shift, and PDA. This allows the machine to move the tube between multiple stacks of tooling (vertical) at the correct bending radius (horizontal), with precise control of the speed and force applied to the PDA. Clamping, movement of the mandrel, and return of the independent bend die are all accomplished with hydraulics through directional valves.

All-Electric. On an all-electric CNC bender, the entire hydraulic system is ditched and every axis of movement uses electric servo control, with the possible exception of the collet, which may be pneumatic.

Because every axis is completely controlled, the machine can make very precise moves that are not possible on a hybrid machine. For example, the clamp die and pressure die may be only partially opened after bending to save production time, or the mandrel can be placed at different positions for different bends.

With some control systems, the position feedback of the clamp or pressure die can be used to set up bend tooling accurately and repeatably without the need for as much (if any) mechanical adjustment or trial and error to get to a good part. As an example, the FlectePro 259AEMI is a 25-mm, all-electric tube bender with nine electric servo axes (bend, feed, rotate, horizontal, vertical, clamp die, pressure die, PDA, mandrel). The BendPro control system on this machine allows the electric servo clamp and pressure dies to set their own close positions against the tube, with virtually no mechanical setup required by the operator.

While an all-electric bender may be more expensive than its hybrid counterpart, it is generally less expensive to run. It consumes less electricity without the need for a hydraulic pump and motor to run continuously. It produces fewer scrap parts and requires much shorter setup times. Part cycle times can be reduced as more axes can move simultaneously, often for shorter distances.

With no hydraulics, all-electric machines stay cleaner and are quieter than hybrids, improving the work environment substantially. With some control systems, almost all troubleshooting can be accomplished remotely with the cabinet doors closed.