Fixing mistakes in secondary operations with laser scanning.

The metalcasting process isn't the only place where miscalculation can result in an undeliverable part. Subsequent finishing and treating operations sometimes can do damage, as well. This damage late in the line can be expensive for the metalcaster to fix and cause delays in delivering the part to the customer.

This was the case for an aluminum aerospace casting that was left too long in a heat treating operation. The oven distorted its geometry to the point where machining operators felt they would be unable to produce a good part. They could not determine a part orientation that would eliminate the need to add material to achieve required dimensions. The part could have been recast, but that would have cost $5,000 and taken two months.

The solution turned out to be the use of a laser scanner from NVision Inc., Southlake, Texas. The scanner produces a point cloud with 10 million points to accurately describe the geometry of a casting. It took two hours to scan the distorted part, which was so big that an engineer had to split it up into sections to scan each separately.

The point cloud was imported into software that allows the actual geometry of the casting to be compared to the design intent of the original solid model. A best-fit analysis oriented the as-built model to match the design geometry as closely as possible. At this point, a difference analysis showed the areas on the as-built part that were larger or smaller than the final design. The goal was to find an orientation in which every area on the as-built part was larger than the design intent. Larger areas can be removed easily during machining, but adding metal back to the part is much more expensive and might affect its physical properties.

The best-fit analysis moved the part into an orientation that was close to solving the problem. Only one area remained where stock was insufficient to meet the design intent. The engineer manually adjusted the orientation of the part on the screen until the small undersized area was eliminated. Next, reference dimensions to fixture the part were generated using the model. CNC programmers checked the as-built model with their CNC program used to drive the machine tool that cuts the part to its final dimensions. Once it was determined the fixture would work without any modifications, the CNC programmers designed a new fixture to hold the distorted casting in the proper orientation. When the casting was run on a machining center with the new fixture and existing program, the result was a part that met all dimensional and structural requirements. The aerospace company got its part on time, and the metalcaster avoided recasting it.

Visit www.nvisions3d.com for more information.

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