When building superconducting systems, coil winding is often treated as a technical afterthought, a simple fabrication step on the road to a functional magnet. But as we’ve seen at Re:Build DAPR, winding isn’t just about wrapping wire. It’s a delicate, high-stakes process that demands precision engineering, deep material understanding, and a proactive approach to process development.
In a recent project involving a superconducting magnet, our team encountered and solved complex winding challenges we’ve seen to date. Here’s what we learned.
At the core of the challenge was the need to produce superconducting coils with tightly controlled electromagnetic (EM) centers. Any deviation in the coil’s radial thickness, caused by winding tension, epoxy or adhesive shrinkage from curing, or demolding stress, could interfere with or affect performance, introduce risk during operation, and compromise integration with the rest of the system.
What complicated matters further was the cryogenic operating environment. Every design decision had to account for how materials would behave during cooldown to cryogenic temperatures. The extreme temperature changes required Re:Build DAPR to manage system shrinkage and stress, and build tolerance into every pocket, flange, and fixture involved in the winding process.
The first hurdle was determining the correct dimensions for the mandrel pockets where each coil would be wound and cured. The problem? Winding tension compresses the coil, while demolding releases that tension, causing radial shrinkage that can shift the EM center and reduce performance.
To understand and predict this behavior, we developed a custom calculator in Excel and validated our assumptions using a Coordinate Measuring Machine (CMM). We simulated barrel deflection using FEA and used these results to refine pocket dimensions across four unique coil sizes. The outcome was a set of mandrel pockets designed to handle shrinkage, stress, and dimensional variation without compromising repeatability.
Even when winding goes according to plan, small geometric inconsistencies can compound over multiple layers. One of the most difficult to manage is the “transition zone hump,” a raised area where wire transitions from one layer to the next.
In an orthocyclic winding pattern, each wire layer nests into the one beneath it, except in the transition zones. When stacked repeatedly at the same radial location, these areas can create non-uniformity in the coil’s outer diameter. This was especially problematic for our tight 2 mm TIR (Total Indicator Runout) requirement.
Our solution was to strategically divide the transition area into multiple locations around the coil and introduce filler wire where appropriate. The adjustment succeeded in reducing the hump and achieving geometric uniformity, which was essential for downstream machining and EM performance.
The tooling had to solve multiple problems simultaneously. It needed to be rigid under winding tension, collapsible after curing, and operator-safe during handling. Our team rejected early segmented barrel designs after finding they were too difficult to collapse without damaging the coil.
Instead, we designed a continuous aluminum barrel that could be cryogenically shrunk using liquid nitrogen. This allowed for safe and uniform demolding. We also standardized features across all four coil sizes to improve manufacturability and streamline setup.
Safety and usability also shaped our approach. From avoiding sharp edges on flange cutouts to managing lead routing for superconducting wires and heaters, every detail was optimized for both function and operator ergonomics.
We didn’t just engineer the coils. We engineered the process. Using a Broomfield 500C winding machine, we developed custom adapters and epoxy delivery systems to maintain control across all four coil sizes. From tangent point optimization to operator ergonomics, the entire platform was customized for precision, repeatability, and long-duration comfort.
Coil winding isn’t a commodity. It’s a core part of product performance and system reliability. Here’s what we’d recommend for any team tackling similar challenges:
At Re:Build DAPR, we don’t just build superconducting systems. We make sure systems are built robustly and enhance product repeatability. If your team is scaling physics-intensive hardware, you need an engineering partner that understands the hidden complexities of manufacturing. From coil winding to system integration, we help you go from prototype to production with confidence.
Need help engineering your winding process? Let’s talk.
Looking to connect with an experienced team?
Look no further than Re:Build Optimation! We are excited to connect with you.
