The NNSY Mechanical Group (Code 930) Cold Spray Team performed another first for Norfolk Naval Shipyard (NNSY) – completing a complex cold spray procedure on two seawater check valve disks onboard the USS George H.W. Bush (CVN 77).
“It was decided a year ago that there would be weld repairs on the seawater check valve disks for the Bush project,” said Code 930 Trades Manager Nicholas Allen. “The Inside Machine Shop (Shop 31) and Welding Shop (Shop 26) did the prep work and got the repair done. However, in the process of it, the flapper actually bowed. This prompted some hesitation to correct the bow with welding and the shipyard was looking for solutions for how to make this repair as quickly and as durable as possible.”
The shipyard has been working to establish its cold spray program since 2016, so the team members threw their hats into the ring as a possible solution for the bowed part. Once approved, the team hit the ground running, preparing for this new endeavor.
“Cold spray is an additive repair process where powdered metal is mechanically bonded to a base material after passing through a nozzle at supersonic speed via a heated carrier gas,” said Code 265 Submarine Mechanical/Piping Branch Head Daniel Stanley. “The cold spray process occurs at significantly lower temperatures than traditional repair methods such as welding and thermal spray. In respect to shipyard applications, cold spray has the potential to repair components previously deemed beyond capable repair as well as provide more durable repairs for those items previously epoxy/electroplate repaired. With our Cold Spray Booth now established in Bldg. 163, we were ready to move forward with what repair efforts we could offer.”
“When we began to plan out our procedures for the job, it looked like a straightforward operation; however, we quickly learned that this was a far more complex job than we had ever done at NNSY,” said Allen. “There were complex angles and low areas we had to maneuver to ensure an even and consistent cold spray application to the part.”
The team, including Machinists Sean Schuffert and Sterling Slaughter, had to take a step back from their original planning when they noted that the equipment they had on-hand was not set up to handle such a complex job. They would need a special cutter and fixtures to perform the task and they also needed to develop a new procedure from scratch to accommodate the amount of angles for the part.
“We originally had a small mockup made to test for the part but quickly found that it wasn’t going to work for how many angles we would need to spray. So I 3-D modeled the full mockup of the part and CNC Work Leader Patrick Felts machined it for us to use for testing and planning,” said Schuffert. “We then moved forward with our Qualified Spray Procedure (QSP) to determine the job, what we have to program, and if it was feasible to perform cold spray for the desired repair. We had 6,200 lines of code established for the part that needed to be entered manually for the job. From there, we ended up with 275 individual datapoints to connect everything together. I wrote a formula for plotting these points so we could get the consistent spray pattern from the robots performing the cold spray.”
The team went through a lot of testing to ensure its approach provided full cold spray coverage of the part and met the technical requirements established by the Uniform Industrial Process Instruction (UIPI). The team also reached out to Penn State Applied Research Laboratory (ARL), one of the shipyard’s academic partners in cold spray, to coordinate some of the required material testing. From start to finish, the qualified repair procedure and execution of the first repair was completed in approximately six weeks. Following suit, the NNSY Cold Spray team cold spray repaired the second valve disk in about a week and a half considering the repair procedure was developed.
“This was the most complex cold spray job performed at the shipyard to date but also the first time that an existing QSP was used to repair multiple parts at NNSY,” said Stanley. “A lot of times when we do cold spray repairs it’s a pretty straightforward operation in respect to part geometry. For the check valve disks, however, it was a fairly complex part and there were no spares on a shelf if the team ran into issues. By doing these repairs we were able to return two components to CVN-77 in support of their undocking milestone but also allowed NNSY to demonstrate the cold spray repair time differences when you have a QSP already developed.”
“One of the challenges we had was that there was a lot of interest and visibility on us getting the part taken care of so that we could meet the undocking,” said Allen. “It was a big win for us to be able to overcome the roadblocks and meet the needs of the Bush. It also helped us showcase what is still a relatively new technology at the shipyard. We’ve been working hard for years to bring cold spray to NNSY. For many of us, we have spent a majority of our careers using relatively established and older industrial instructions. Now we’re flipping the script, taking on something brand new and documenting every feasible piece of information we can to establish it as a set process. The mindset of our team has changed from dealing with those older instructions to developing something more complex that we are building from the ground up, requiring us to shift our mentalities from what we’ve been used to. We’re invested in servicing America’s Shipyard and the fleet and we’ve had support from various shops and codes to make it happen.”
Stanley added, “It’s a big win for the shipyard. It took some trial and error but with hammering out everything we were able to get the job done and also establish that process for future jobs at the shipyard. Tackling complex work while also expanding our knowledge so we can utilize those processes for the future is huge. In addition, we have the ability to share what we learned with the other shipyards who are working to get their cold spray programs up and running. It would be less legwork going forward for everyone involved and we can all be aligned.”
“This was a long voyage of discovery,” said Schuffert. “We were sailing into uncharted territory and though it looked like clear, calm waters – it was actually a path full of obstacles. But we persevered to get the job done for NNSY and the Bush!”
For more information regarding Cold Spray at NNSY, contact Stanley at email@example.com