While the bulk of the welding equipment remains stationary during a weld, the weld head constantly moves small distances along at least two axes, both along and across the seam.Wind turbine technology, with its massive arrays of streamlined windmills blanketing hillsides, is an established sustainable, green technology. Many consider it a technology that will help define the energy future. However, wind energy also depends on the more traditional manufacturing techniques, such as welding, which is vitally important for creating the massive towers.

One of the leaders in creating welding solutions for the energy industry – as well as many other applications – is Rexburg, ID-based machine builder AMET Inc.

Since 1989, AMET has been an innovator in developing and integrating advanced welding solutions to meet a wide range of demanding needs. Recently, AMET called upon the Linear Motion and Assembly Technology specialists of Bosch Rexroth to help them create a new generation of custom welding systems for the increasingly important wind energy industry.

The design of AMET welding equipment – and the role of linear motion technologies – is largely dictated by the techniques required to create massive wind turbine towers that can be around 90m high (close to 300ft). Typically, a flat metal plate is rolled into a cylindrical shape called a can. The can (the most common size is approximately 9ft long by 8ft to 15ft in diameter), is then rotated while the welding machine, staying more or less stationary, performs circumferential welding across the entire diameter. Longitudinal welds are also required. Wind tower welding systems generally operate both inside and outside of the can at different times; the welding equipment is usually suspended from a guide rail for outside welding. In each case, while the bulk of the welding equipment remains stationary during a weld, the weld head constantly moves small distances along at least two (sometimes three) axes, both along and across the seam. A linear control actuator mounted at the end of a horizontal arm determines the motion of the weld head.

AMET’s goal was to create a cost effective, dependable welding system that could perform accurate longitudinal and circumferential submerged arc welding. The design, including the linear motion for weld head control, would ideally be straightforward and simple, so the welding system could enter an increasingly competitive market as quickly as possible.

One of the most important challenges, however, was to assure smooth and precise (within 0.001") control of the weld head, to avoid improper welds that would need to be redone, ultimately resulting in wasted time and materials. Additionally, this precise control had to be maintained within a very demanding environment. “The tremendous amount of particulates, especially flux dust, generated by this form of welding can really cause problems for this machine’s finer controls, particularly with systems such as linear actuators,” says Craig Dees, AMET engineering manager. “We needed to be sure that the linear motion components would stand up to this harsh welding environment, especially inside the can.”

In addition to good protection against flux particulates – which can cut into uptime – AMET also wanted linear motion elements that offered good strength (dynamic loads in excess of 20,000N), with light weight and compact size. Yet another challenge was to support smooth weld head acceleration of up to 3 meters per second squared (3m/s2), for a travel speed of 1.5 meters per minute.

The tremendous amount of particulates, especially flux dust, generated by welding can cause problems for the machine’s finer controls, particularly with systems such as linear actuators.Source for Solutions
To meet these needs, AMET turned to a familiar source for linear motion: Northwest Motion Inc., a distributor of Rexroth linear motion products. AMET had already used CKK Compact Modules, along with other Rexroth products, in a number of other custom welding applications. Northwest Motion had been supplying Rexroth linear motion technologies to AMET for several years, so they were able to recommend the CKK line for the desired strength-to-weight ratio. In fact, Rexroth products had become AMET’s standard platform for welding systems, and Rexroth precision-ground, hardened steel guide rails were to be specified for the guide rail that carries the suspended weld head for outside welding. With the CKK Compact Modules, however, AMET put Rexroth linear motion systems in a particularly crucial role.

AMET generally specifies two (occasionally three, for even more precision) CKK 20-145 linear actuators for their custom welding systems, in 490mm and 590mm standard lengths; some systems use CKK 15-110 actuators.

As Craig Dees points out, “One of the features that we noticed right away as a potential advantage for Rexroth actuators over other types is that their compact dual-rail system features a sealed rolling strip.”

That is important because many non-Rexroth linear systems use fabric or rubberized bellows to keep the rolling strip clean. The CKK’s seal keeps the module protected from the pitting that is caused in other actuators by the particulates welding generates. The compact CKK design, light in weight but durable and strong, makes machine assembly smoother and easier.

“We knew that other linear motion solutions couldn’t give us the reliability and protection against contamination and pitting that the CKK modules could,” Dees says.

But, there is more. Between the dual carriage option and the dual rail design integrated into the rigid aluminum frame, this CKK module gives AMET’s welding system a guideway with a dynamic load capacity of up to 61,000N with excellent stability. The CKK resists impact and stress as well as sparks and contaminants, further increasing uptime.

Making Tasks Easier
Another important feature leading to better and faster machine production is the fact that CKK 20 to145 modules are complete, prepackaged systems, with dual ballrails and a ballscrew drive integrated into the module. This simplifies design, saves space, and removes the costs and effort of machining, assembly, bearing alignment, and other application engineering tasks.

“The CKK modules are precision-machined at the factory by Bosch Rexroth, so we do not need to do any extra work ourselves,” Dees says. “They are ready to run as soon we get them – we can just add them to the system.”

Dees also notes that Rexroth can be counted on to meet their delivery dates consistently. For AMET, all this means a savings of up to two weeks in building time for this system, which presently is about 12 weeks per machine. Controlled by proprietary AMET systems, the CKK modules are helping AMET welding systems ensure dependable performance in many wind tower applications.

AMET, of course, gets considerable benefit from distributor Northwest Motion as well, including rapid delivery, superior parts availability and competitive pricing. “Getting quality linear motion for less cost allows us to pass the cost savings along to the customer, and give them the welding solution they want at an attractive price,” Dees states. The combination of superior performance and affordability of AMET systems is helping wind tower manufacturers make sustainable wind energy a reality – and Rexroth CKK 20-145 modules are playing a small but significant part in that.

Endusers get many other advantages from AMET welding systems using Rexroth’s linear modules. The modules contribute to a more compact system, with a high load rating and an overall strength, which is especially valuable if the weld head strikes the side of the can. By keeping out particulates, the sealed rolling strip maximizes reliability and uptime, while reducing maintenance. Wind turbine manufacturers also benefit from a welding system design that has ideally suited to the most common tower section sizes, including the larger sizes needed to create wind turbine support towers more than 75m high. Finally, AMET custom welding systems make a good appearance – they look as reliable and dependable as they are. Moreover, their economical cost has proven to be attractive, too.

Bosch Rexroth
Buchanan, MI
boschrexroth-us.com

AMET Inc.
Rexburg, ID
ametinc.com