Servo technology upgrades tube end forming equipment

Servo technology isn’t an end, but a means to achieve greater precision and control of metalworking processes like tube end forming. Image provided

Technology is anything but static, and nowhere is this more evident than in the electronics field. In 1965 Gordon Moore, an engineer working for Fairchild Semiconductor, noticed that the number of transistors on a typical integrated circuit (IC) chip doubled about every year, and this trend continues. The features and capacities of computers, digital cameras, mobile phones, and automobiles just a decade ago don’t compare with those of today, and connectivity now makes nearly everything more useful and convenient than ever before.

The electronics revolution made its way into the metal fabricating industry decades ago when CNC arrived. Before computer controls, a machine’s actuator or carriage simply ran in one direction until it encountered a limit switch, and then it retracted until it hit another limit switch. The machines were capable, but not versatile.

CNC changed all that, relying on programmed instructions to dictate the distance an actuator or carriage would travel. It took a rethinking of how machines worked, and the hiring of programmers to make them work, but suddenly the outcome was a sweeping change. Programmers exerted control over a carriage’s travel speed and the distance it moved, which was more versatile, reliable, and precise than using limit switches. It ushered in a new era of control and precision in manufacturing.

The same technology has updated electric motors. The simplest of motors, such as the motor in a power drill or the starter in an automobile, are designed to run at a certain speed or deliver a specified amount of torque without much of a control system. A servomotor within a sophisticated system allows programming so the motor runs at a variety of tightly regulated speeds or turns a specified number of revolutions and comes to a stop, providing much more control than a common electric motor. Typical is a closed-loop feedback system. The controller provides a command, or commands, for the motor; sensors measure the motor’s speed or track its revolutions and feed this information back to the controller; and the controller compares the intended output to the actual output. The controller then makes any necessary adjustments, providing an extreme level of precision.

These and related technologies have enabled equipment builders to develop machines that are more accurate in what they do, more versatile in how they do it, and consume power more efficiently than conventional machines.

Fluid Power and Servo Power

On many machine types, implementing servomotors means dispensing with something else—usually a hydraulic system. This doesn’t mean that hydraulic power is on the way out; it simply means that equipment builders have a choice.

“Four years ago, all of our tube end forming machines and presses were hydraulic,” said Joe Eramo, president and owner of Innovative Engineered Solutions (iES, formerly R&B Machining), Wilmington, Ohio. “Today we have six models that use servo technology.” It’s not necessarily a simple matter to replace a hydraulic system, well known for providing reliable “cheap power,” but iES has used its expertise to develop servo-powered end formers, presses, and a saw.

Merely replacing one power source with another would be a missed opportunity, so iES works to understand exactly what the customers need to do and find the most efficient way to do it.

“Servo technology is a source of innovation in that it’s an opportunity to take a fresh look at our machines and their functions,” Eramo said.

Advantages of a servo system over a hydraulic system include cleanness, quieter operation, and potentially reduced operating costs depending upon the end user’s duty cycle. It also provides more capabilities than hydraulic technology.

Nobody questions whether a hydraulic power system will leak; it’s a matter of when. Leaking systems aren’t clean, and they create slipping hazards. In terms of noise level, servo sizers have been measured at 70 dBa versus a similar hydraulic sizer at 80 dBa (recorded with time-weighted average measurements). Finally, while hydraulic systems generally run continuously, ready to provide power at any moment, a servo system shuts down when not in use, providing power only on demand. The energy savings help to offset the capital investment, Eramo said.

“In a test conducted by iES, when a duty cycle made fewer than six parts per minute, the servo sizer consumed less power,” Eramo said. “For higher duty cycles, this advantage diminished.”

Eramo acknowledges that developing such a system isn’t easy. The engineering work must be more thorough when developing a process that uses servo technology.

“The forces that are generated in metal forming operations are substantial,” he said. “A well-designed system has to take into account the required forces for both correct and incorrect setups, because a poor setup can cause the machine to crash and potentially damage a key machine component.” Nobody wants downtime, especially when it’s a ball screw, gear box, or some other component associated with a long lead time and a high cost.

The programming and process control also have to be robust enough to capture all of a servo system’s capabilities. Programmers take into account the many types of sensors and pneumatic clamps typically found in multistage press dies while controlling the three main forming factors: press velocity, position, and tonnage. The result is a part recipe that is errorproof, providing a poka-yoke concept that facilitates the forming of difficult-to-form parts.

Not the Beginning of the End

Fluid power is a time-tested and capable technology, and nobody claims that a servo-powered machine is a direct replacement. Two considerations are cost and speed. A servo system, with its actuators, drives, and gearboxes, costs more than a hydraulic system of similar capacity in terms of upfront capital expense. As far as speed, the difference is noticeable, favoring hydraulics. Still, these differences don’t stop some manufacturers from converting to servo technology, even for traditionally high-speed processes like stamping.

“One large manufacturer of outdoor equipment has started to convert some of their conventional stamping hydraulic presses to servo units,” Eramo said. “The company used to run their mechanical presses about five hours a day, and even though they now need to run their presses longer to accomplish the same amount of work, they realized advantages of the servo system to be beneficial in terms of lower acoustic emissions, improved process control, and a cleaner manufacturing process with no hydraulic leaks.”

System Design Freedom. Whether the power choice is hydraulic or electric, OEMs are in search of creative ways to handle conventional forming applications. A case in point is a tube sizer used to coin the ID and OD of material in a set of custom engineered tools. A conventional sizing machine is built into a steel frame, fixed or on casters, often in a cabinet. The power unit is located in the lower half, with a machine head or forming system in the upper half. Most of the machine is guarded for safe operation and limits access to the tube insertion area. Typically, an operator inserts the tube end into the forming head and initiates the cycle with a foot switch to make the desired end form. As such, the operator brings the tube to the machine.

An iES concept turns that that notion inside out. A customer needed a way to expand a series of tubes in a complex assembly inside a housing. Because the tubes are recessed, located inside the assembly, they could not be fed into the end former because of clearance issues with the housing. The iES engineering team developed a modular system that fixtures the assembly and uses several mobile sizing heads on slides. After securing the assembly, the operator slides each sizing head into each port and activates all of them simultaneously. The cycle time is just a few seconds.

Automation, Automation, Automation. “We’re down 80 people,” Eramo mentioned, noting that this seems to be a consistent theme heard throughout the industry. “I can’t tell you how many times I’ve heard that a manufacturer is down a significant number of people.”

Some have retired, and more of that is on the way. Certainly, some are absent from manufacturing jobs because of the pandemic, but it’s too soon to tell how many of those displacements are temporary and how many are permanent. Regardless of the reason or the specific number of absent employees, this is an opportunity for increased automation. An opportunity for a closely controlled process to be carried out by an employee who’s never absent. An opportunity for a robot or a cobot.

The engineering staff at iES is preparing for a future more reliant on robots and cobots. Eramo cited an article in the Wall Street Journal that reported record sales for robots for nonautomotive use in the U.S. in Q3 2021 as just further evidence supporting this point.

In a recent integration project, iES converted one of the more routine tasks in the tube and pipe industry, one involving boiler construction, to a robotic process. It involves fastening a large number of tubes to a metal sheet. Like the previous example, it relies on inserting a die set into the tube end and expanding it to fasten it in place.

Unlike the previous manual operation used by the customer, the new process is automated. To do so, iES relied extensively on mathematics, specifically quaternion values. This application, as it pertains to a vision system, enables a robot to locate every target in a vast array of bores. The end result is a successfully assembled boiler that doesn’t tax an equipment operator with an extremely mundane task.