The additive manufacturing contractor making Delcam’s parts did not want to produce all four parts in the same build, even if those parts did all fit on the plate. The reason: AM involves considerable uncertainty related to residual stress and other effects as the part is forming. Better to build just one part first, see how it forms, see if there are lessons to be learned, and then build the other three.

And there was indeed an unexpected effect observed in the first build. Residual stress affecting the formation of the “trees” apparently caused one of these trees to poke up just high enough that it marred the machine’s recoater bar that passes over each layer of material. This defect of the bar affected every layer thereafter, and it could still be seen as a corresponding defect in the final surface of the part that the machine produced. The defect was concerning, because it meant that material from the blade had been lost somewhere, and might be embedded in the part. In a component as critical as a turbine blade, for example, that possibility would have to be addressed. But with the trial manifold, the team decided to continue. The surface showing evidence of the defect had been meant to be milled flat anyway.

A more directly meaningful lesson of the first build came too late to apply it. That is, a discovery about removing the part from the plate that would have affected the part’s sizing (see the next point) did not come until the 80-hour second build was already underway. Then also came a discovery that—frustratingly—affected only the second build. One of the three pieces in this second build formed with a minor but noticeable geometric defect. The reason why just this one piece was affected is still unknown.

Ultimately, says Gunnink, the choice to run a single part first—even though that choice was prudent and correct—did not help with the build of the remaining parts in any meaningful way.

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