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Small-tube Benders: Green And Versatile

February 2012

In tube bending, there is much more going on besides mechanical developments in the machines themselves. They’re doing more and doing it faster, such as implementing automatic loading and unloading, integrating control data with upstream and downstream operations and simplifying user interfaces.

These trends are changing the way operators interact with the machines, boosting productivity and improving accuracy and repeatability.

They’re also offering enhanced versatility, including performing rotary-draw and push-bending on one machine, while the march to all-electric benders is driving the development of new small-tube CNC benders.

The switch from hydraulics has been going on for over a decade, but it’s accelerating, with demand growing to avoid the use of hydraulic oil and for better energy efficiency. Several machine builders say they’re “going green” with electrics. Prices for electric benders have been higher in the past, and still are, but they’re getting closer to the price of hydraulics.

AddisonMcKee

“There’s a reduced price differential between electric and hydraulic machines now,” says Jim Sabine, engineer at AddisonMcKee. “Electrics are more expensive to purchase but less expensive to operate. We’ve been driving component prices down, particularly for motors and controls by partnering with vendors.”

Whether in production or jobbing applications, the demand is for machines that will handle a bigger variety of work. AddisonMcKee’s all-electric bender will do rotary-draw bending around a die and push-bending, making a gentler bend by running the part through a series of two or three rollers, both on the same machine. Tooling for one operation is stacked on top of the other. Under CNC control, working on the same part, the machine can make a draw bend, switch to push-bending and then switch back to a draw bend or any other combination.

Streamlining programming, and reducing errors by avoiding manual data entry is a goal of most builders of CNC benders. AddisonMcKee’s Windows-based controller accepts CAD data in IGES, STEP and other common data-exchange formats. Operating interfaces for the controllers on the current generation of machines is based on the expectation that the operator has no CNC or programming experience. The AddisonMcKee CNC drives up to 11 different axes of motion, but the integration and much of the decision-making is built into the software with graphic interfaces and fill-in-the-blank commands to prompt the user.

BLM Group

The major builders are echoing the same themes regarding electric benders. BLM Group’s SMART all-electric bender focuses on “flexibility, precision, quick changeover, and ease of programming and operation.” Energy use is reduced 50 percent over hydraulic benders, the company claims.

“All our products are moving toward electric,” says BLM’s Lindley Searles. The ability to make both left-hand and right-hand bends in a part is common on many of the new generation, including the SMART. BLM uses Siemens brushless servo motors driving a variety of actuators – primarily rack-and-pinion and ballscrews – on different axes of motion, as required. Most of the electric benders from other builders use similar components.

Electric drives are producing more accuracy in finished parts partly because of the high resolution of servo motors and the ability of “hard” drive components to transmit motion accurately, and partly because the thermal stability of electric drives is much greater. Hydraulic oil expands more as it heats and limits the accuracy of an actuator. The SMART bender, which handles tubes up to 1.12 in. diameter, claims accuracy of ± 0.002in. in the X-axis and ± 0.05 degrees in Y and Z axes. Overall, the major builders claim on the order of 50 percent improvements in accuracy with electric drives.

Eaton Leonard

Automation through robotics is carried to an extreme in Eaton Leonard’s RoboFlex that incorporates a six-axis robot for automatic loading of tubes, a Y-axis feed, B-axis tube rotation and off loading. The robot replaces other loading schemes and the carriage-type part progression commonly used with CNC benders.

The company claims greater flexibility and exceptionally fast throughput. It will bend hybrid tubes with accessories already attached to the tube, or with end-forming performed in a previous operation, and it performs clockwise and counterclockwise bending on the same part. The ability to handle partially-assembled tube devices lends the RoboFlex to applications such as assembled air conditioning tubes, power steering tubes, brake lines and gas tubes. Only one handling device – the robot – is required for full automation.

Winton Machine Company

“A key development in CNC-tube benders is the use of STEP to automatically transfer CAD data to the bender’s controller,” says Winton Machine’s George Winton. Using standardized data-exchange formats to automatically load CAD data into a bender’s CNC is becoming a popular way to streamline programming and improve accuracy of data entry. “The original data could be in Pro-E, Solid Works, Inventor or other CAD formats. In the old days, you had to type in the coordinates. Downloading it automatically saves a lot of time,” he remarks.

“You can extract a lot of things from the STEP file if you want to: wall thickness, centerline, bend radius, tube diameter, plane rotation, distance between bends and material properties. Complete STEP files have a boatload of data we don’t use, but they have everything we need.” The CAD files containing the original design data typically are 3-D solid models.

Employing STEP and other exchange formats is just one part of the data integration. Tube benders are going through some of the same centralized data handling as metal-cutting machine tools went through in recent decades. Third-party inspection systems, including multi-axis ROMER and FARO arms and similar dimensional-data acquisition devices, can be – and are – integrated with a bender on the downstream end for quality-control data acquisition and for feedback to the control programs on the machines.

But much programming is still manual, and the simplified interfaces, almost always Windows-based, continue to develop and will continue to play a major role in tube bending. Menu-driven graphical interfaces are the norm; flexibility to accept X, Y and Z data or bend data is nearly universal on new bending systems.

As always, and particularly in automotive applications, margins in tube bending are slim; downtime is serious; and longevity is important in production. The cost-per-part is crucial and all of these technical advances have to justify themselves in terms of that cost.

So purchase price-points and operating costs are an especially delicate balancing act. It’s clear that this has raised the cost-performance bar for high-tech tube benders, probably delaying their adoption of some of the control and automation features that are common in chip-cutting and other machine tools.

Their per-part costs had to come down, and now they are doing so. Where the volume and changeover times result in lower part costs, the level of automation, accuracy, versatility and speed afforded by programmable systems is reaching a high plane.

AddisonMcKee
BLM Group
Eaton Leonard
Winton Machine Company