3D scan and CAD comparisons of large castings

The core business of Duisburger Modellfabrik GmbH is the production of large foundry patterns made of wood, plastic block materials and foam for the manufacture of steam and gas turbines, engine beds, diesel engines and components for wind turbines in steel, grey or nodular iron castings.

More and more frequently, customers are requesting a comparison of the manufactured model equipment with the original CAD data. A model equipment consists of the model and core boxes. These later serve in the foundry as tools for creating a mould (individual parts, see picture). The digital surveying service was initially purchased externally by Duisburger Modellfabrik for their first few years of operation.

Production hall for model equipment. 3D measurements are made directly on the component

The decision was soon made to purchase their own measuring system in order to reduce costs and avoid frictional losses between model builder and surveyor. Since the company manufactures components of several metres in length, width and height, it was important to find a 3D measuring system that could scan large surfaces quickly and easily. Of course, not at the expense of accuracy. Since the company did not have a dedicated measuring room, the measuring system had to be portable and able to withstand adverse environmental influences (dust, dirt, vibration). In other words, the company would be able to use it virtually anywhere.

Implementation of 3D scanner into the workflow
They settled on Creaform’s MetraSCAN 3D Scanner, an optical CMM scanner specifically designed for high-precision and repeatable metrology-quality measurements and 3D geometric surface inspection in manufacturing. The decisive factors were the flexibility of the scanner, the ability to digitise undercuts, and the possibility of virtual assembly.

3D scanning

Not all of the model fixtures need to be measured visually. But where necessary, these are scanned after completion of the individual components. When Duisburger Modellfabrik was still dependent on service providers, this was not possible. To make it worthwhile to travel to the site and hire a metrology service provider, a larger quantity of components had to be completed first to justify about three days of 3D scanning. But now, finished components are measured and shipped directly with the 3D scanner.

Colour matching against customer’s finished part data with PolyWorks Inspector

Herbert Schild, Managing Director of Duisburger Modellfabrik GmbH, notes: “Implementing the MetraSCAN 3D into our workflow, as well as training our staff, was very easy for us because our staff already had experience in CAD/CAM, so they already had an affinity for computer work. By scanning the unfinished parts, an optimal milling path can be programmed and many empty runs of the cutter can be avoided.”

Which processes does the 3D scanner support?

Quality control
When creating the blanks, the MetraSCAN 3D is used for accurate digitisation and subsequent geometric inspection by means of colour comparison in InnovMetric’s PolyWorks software. Thanks to its portability, the measuring system can be brought to the component, and scan the latter quickly and accurately, regardless of its size. Even hard-to-reach areas such as pockets or shiny surfaces can be easily detected. It is not necessary to use a chalk spray.

Virtual Assembly
In addition, components can also be measured in the actual assembled state after they have been disassembled. This works through the intelligent use of the target model. This makes the comparison to the actual data much easier.

Some prototypes need to be adjusted using CAD. The scan data enables easy adjustment and design in CAD, even for complex free-form surfaces. The .stl data makes this possible, even for more complex free-form surfaces in terms of reverse engineering.

CNC programming
Of course, the final product is also digitised and checked for dimensional accuracy. However, the 3D data can also be easily used to program the milling machine. Thus, milling is not done blindly, which significantly reduces costs.