Southern California has many charms, but as a manufacturing center it can be highly demanding. For decades, the area around San Diego has been a center for the U.S. aerospace industry, with highly qualified engineers and workers, and large network of suppliers. But the state’s regulations are notably rigorous with regard to sustainability and resource conservation.

In 2024 GKN Aerospace a opened a second manufacturing center in El Cajon, to specialize in MRO (Maintenance, Repair and Overhaul) services for all types of aircraft components. Fortunately, California’s high environmental protection standards are in alignment with GKN Aerospace’s sustainability targets. But for suppliers those standards present a real challenge.

All manufacturing machinery must comply with the state’s environmental regulations, but also must perform with precision, reliability, and high productivity. For the relatively complex reconditioning of turbine blades for aircraft engines GKN chose Rösler high-performance surface-finishing systems, not only for stripping of used turbine blades but also for the final mass-finishing operation.

The choice of Rösler finishing equipment was influenced by GKN Aerospace’s positive experience with the systems at a comparable operation in Malaysia.

MRO in demand

Aircraft engine blades - investment cast fan blades, pressure blades, and turbine blades - are exposed to tremendous stress, including high temperatures, strong centrifugal forces, and constant vibration. Over time, those loads can cause material fatigue, micro cracks and unwanted deposits. To ensure the safety, performance, and efficiency of aircraft engines, the blades must be periodically checked, cleaned, and overhauled, as needed. The MRO technical procedures required are spelled out in the repair manuals that engine manufacturers like GE Aerospace or Pratt & Whitney prepare for respective engine components. Such procedures stipulate that, prior to visual and x-ray inspection the components must be stripped of all coatings, respectively, deposits.

For these stripping operations GKN Aerospace is using a Rösler high-pressure water-jet system that produces ideal results. Because it does not require any processing media or chemicals, the stripping process with pure water is extremely eco-friendly.

A further advantage of this water-jet system is the automatic process-water cleaning and recycling system that significantly reduces the overall water consumption.

The final step of the overhaul operation, surface finishing of the reconditioned components, is also handled by Rösler equipment, namely 12 tub vibrators. Two process-water cleaning and recycling systems, each equipped with two centrifuges, are cleaning the process water contaminated with solids and sending the cleaned water back to the mass-finishing machines for reuse.

A digital monitoring tool supplied by Rösler Smart Solutions is continuously checking the quality of the process water. And in case of deviations from the set values it recommends corrective actions.

High-pressure water-jet system

As a first step, in order to gain an objective evaluation of blades’ surface conditions, coatings/deposits on must be removed. Until now, this was done using chemical stripping, which involved substances that had to be disposed of in a complex and costly process.

The GKN Aerospace plant in Malaysia has been using a Rösler high-pressure water jet stripping system for several years, and that positive experience recommended the same approach for the new plant in California.

“For GKN Aerospace we supplied a so-called ALS system, a robotic blast system equipped with a rotary table. Up to six turbine blades can be clamped on the table and are then processed, one after another,” explained Tobias Maaser, sales and project engineer, Shot Blasting, who works exclusively with aerospace industry customers.

The ALS system involves one stationary and one rotary nozzle, together ensuring effective, all-around treatment of titanium components.

“The high-pressure water-jet technology uses high energy in combination with a liquid medium, namely water,” Maaser reported. “This penetrates the surface and chips away the surface coatings. Water jetting is much faster than the previously used chemical stripping method.”

In fact, the system is twice as fast than the chemical stripping process, and highly “eco-friendly” too because it has eliminated the disposal of numerous batches of chemical waste and coating residues.

The highly regulated aerospace industry requires effective and sustainable equipment technologies, but complete documentation of all manufacturing processes is just as necessary. The robotic stripping of the turbine blades is fully automated, and the entire process (including the computer managing the robot movements) is controlled by a PC supervisory system.

The supervisor monitors all process parameters in real time, including all valves, maintenance components, and processes. The entire process status is digitally displayed. Based on their serial numbers, a barcode scanner assigns the respective processing program to the components, thus allowing complete documentation of every single process step.

Because the PC supervisor monitors all process parameters and makes sure that their values remain within set limits, guaranteeing complete traceability of the entire process - and therefore, absolute process safety. This is particularly critical for shotblasting, because one faulty operational parameter can damage or destroy a component.

Precision vibratory finishing

For another stage of the reconditioning operation, the surface refinement of overhauled turbine blades, GKN Aerospace is also using a Rösler system. In this operation, the savings in processing time and use of processing media are even more impressive.

Until recently surface finishing of the reconditioned components, was done in somewhat obsolete machines, and with comparatively low-quality processing media. “The finishing process as such is clearly prescribed, and we were not permitted to make any changes,” according to Rösler global sales expert Michael Striebe, who is responsible for managing aerospace mass-finishing projects.

“However, we completely replaced the old finishing equipment and are using our own high-quality processing media, with astonishing success: Through the higher efficiency of our tub vibrators and grinding media perfectly matched to the finishing task, we could reduce the media consumption by 30%. And processing times are 50% shorter than before.”

The new mass-finishing vibrators are designed for high efficiency but also offer optimized ergonomics. Pairs of two tub vibrators share a single pedestal. This shortens the distance a machine operator has to walk. For noise protection (an important consideration for the project), the mass-finishing machines were completely enclosed with noise-absorbing cabins. In each tub, equipped with dividers, two workpieces can be processed at the same time without touching each other.

With a suitable supervisor system the entire finishing process is monitored and all process stages documented. The specified finishing goal is a surface roughness value of Ra = 0.6 µm (24 micro inches).

A big step toward improving the sustainability of the mass-finishing operation is the switch from using fresh water for each finishing cycle to cleaning and recycling the process water. For this purpose four fully automatic centrifuges were installed to clean the process water and pump it back to the mass-finishing system for reuse.

Recycling process water

Depending on the actual water demand, one or two of these centrifuges can be turned on or off, operating on a master/servant principle.

“Recycling the process water had a real positive impact on the CO2 footprint of the entire mass-finishing operation,” according to Rösler’s Michael Striebe. “With the 12 finishing vibrators the customer lowers his consumption of fresh water by roughly 1,500 liters every hour. The cleaned and recycled process water has a usable life of about three months, before it must be replaced. This is a real breakthrough for sustainability at GKN Aerospace, and we at Rösler are proud for having played a key role in this project.“

The process water cleaning and recycling system is controlled by the advanced version of the Rösler Smart Solutions (RSS) software. This digital tool checks the condition of the process water and recommends corrective action, whenever predefined values of certain water parameters are out of the acceptable range.

Comprehensive monitoring of the process water conditions resulted in additional savings in consumables consumption, especially the compound usage. Compared to the exclusive use of fresh water the process water recycling system helped reduce the overall compound consumption by around 90%.

One supplier, two technologies

“Rösler was chosen for the vibro and HP projects, because the company worked closely with our engineering team to develop solutions that are perfectly adapted to our requirements,” according to Salvador Jaimez-Meneses, senior manufacturing engineer at GKN Aerospace in El Cajon. “While other suppliers only offered standard equipment without consideration of our specific technical needs, Rösler provided professional support during the entire planning and validation phase.”

He continued: “The Rösler engineering team was actively involved in adapting the blast and mass-finishing machinery to our requirements, including optimization of the ergonomics of the vibratory tubs. The ergonomic improvements are based on a recommendation by our sister plant in Malaysia, especially, the people who are operating the machines. This active participation of GKN Aerospace personnel helped to ensure that the Rösler equipment fully meets our production requirements and quality standards.”