Creative Manufacturing: Breaking Down a Complex Weldment Assembly Into Smaller, More Manageable Pieces

A maritime industry project called for a capture spine, which is a lifting beam used for launching and retrieving vehicles from the ocean. Since the weldment assembly was required to be very strong, light and resistant to the corrosion associated with seawater, the lead design team decided to use titanium.

The Challenge

The challenge was twofold.

First, the required raw materials were in short supply. Since stronger-grade titanium was hard to come by, the ENI team helped the customer design the project based on material sizes we knew were routinely available, such as plate titanium in common thicknesses.

The second, and more pressing challenge was the complex shape of the capture spine. The customer partnered with us early in the process to design the part for optimal structural strength and weight. The goal was a square beam of shifting size, weight and wall thickness to allow extra strength to be added where it was needed.

We had to contend with changing cross sections, variable wall thicknesses, a difficult box size and intersecting arms with all of the welds being full-penetration. Since the capture spine was a critical-use lifting device, it came with stringent weld quality requirements.

The Journey

The customer knew the desired end result, but it was up to our team to figure out how to get there.

We had to design the weld joints in a way that gave us access for full-penetration welds, which was a complex challenge given the unusual configuration of the plates. We had to place all the weld joints and plan for weld distortion and shrinkage.

The Discovery

There were simply too many joint considerations, and the project was too complex to manufacture as a single assembly.

Another variable was the tricky nature of welding titanium, which comes with its own set of quality control. Titanium work requires the use of inert gasses to shield the metal from oxygen during welding.

The Solution

In order to meet their manufacturing goals, we needed to break the capture spine weldment into a series of smaller sub-assemblies. This would allow us to address the distortion and shrinkage in each small assembly, merge the assemblies, and address the distortion in the larger combined assembly. We would have to manufacture the assembly one piece at a time, yet always work with the end goal in mind.

The most pressing priority was accessibility. Since our teams had to reach every weld, we couldn't put too much together and then wind up facing an obstacle, such as a part enclosed inside of a box that couldn't be welded because it was out of reach. Size and weight were also concerns. The goal was to build a few smaller pieces and then combine them to avoid working with a single, heavy weldment.

A critical ingredient to success was experimenting and learning along the way. By putting together easier subassemblies first, we could measure and learn from shrinkage or distortion before moving to critical portions, where shrinkage tolerances were as tight as a 1000th of an inch.

The Results

To date, ENI is the only manufacturer that has been able to solve the riddle of this welded assembly. The end customer hired a total of four other intermediate subcontractors to provide a solution — in every case, all four subcontractors chose ENI as the lower-tier manufacturer. Altogether, we have completed nine of these assemblies for four different contractors working under the same end client.

Success can be traced to the level of manufacturing planning, forethought, detail and design that went into the project. A single drawing for the customer was 15 pages long, but our team made over 100 of their own intermediate-levels drawing to identify each component, the component's associated tolerances and each sub-assembly step along the way.

We now use the project as an internal reference for the high level of manufacturing thought that goes into breaking down a weldment of this size and complexity into smaller sub-assemblies.

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