Laser scanning closes the digital gap in 3D printing and high-end milling workflow

GF Machining Solutions is one of the world’s leading providers of machine tools and diverse solutions for manufacturers of precision parts and the mould-making industry. Its portfolio includes machines for milling, Electrical Discharge Machining (EDM), 3D laser texturing, laser micromachining and additive manufacturing.

Based in Switzerland, the company is a globally acting division of the Georg Fischer Group with its own sales companies in over 50 countries. In addition, the division operates production facilities and research and development centres in Switzerland, the USA, Sweden  and China. 

In response to a customer request to produce a turbocharger for use in a Formula 1 car, GF was asked to develop the best possible manufacturing workflow, from design, simulation and production through to qualification.

The part is a double-walled F1 turbocharger, made from a nickel-based heat resistant superalloy (Inconel LaserForm^® Ni718 A) and manufactured using additive and subtractive processes. 

In Formula 1, double-walled turbochargers are needed to bypass turbo lag and increase efficiency, and thermal insulation is necessary for their effective operation. However, creating an air gap using a double-wall construction that prevents the heat within the core from reaching the outer shell can be tough to manage with casting, which falters with thin wall thicknesses.  

In short, for double-walled applications, metal casting is not an option for producing the basic shape, which is why GF Casting Solutions turned to its sister company, GF Machining Solutions, to make the part using an additive process.

After printing, critical part features were checked for dimensional accuracy on a Hexagon Leitz Reference CMM, including individual points, angles, inside and outside diameters, and widths of the turbocharger. These measurements identified deviations from the nominal condition of up to 1 mm, which can occur naturally due to the thermal process of powder melting and are considered normal for functional surfaces in 3D printing. 

The turbocharger has various functional surfaces and complex internal features (connecting elements) that needed to be precisely milled in post-build machining with a dimensional accuracy of maximum ± 0.01 mm compared to the CAD file. Machining could only occur after accurate reference points on the part had first been established.

The clamping of parts on a machine tool is typically aligned to ensure the surfaces to be milled can be reached as easily as possible. On a 3D printer, however, the part’s orientation can be entirely different to ensure each element can be printed efficiently. In addition, there are distortions in the part due to the printing process itself. As mentioned, this was a factor with the turbocharger as well.

GF prepared and performed the 3D printing using the CAD file of the raw part as a basis. But this was done without knowing the exact future clamping position and orientation in the machine tool to be used for subsequent milling. 

In addition, to achieve the best printing results, the original CAD file had to be adjusted using specialised software. This included modifying the reference of the workpiece zero point and allowances for functional surfaces and contour supports. However, these modifications meant that even if this data could be reissued as STL data, it would no longer be compatible with the original CAD data in terms of reference points and surfaces.

 

He wanted to close this gap by performing the alignment of the turbocharger on their milling machine much faster and, if possible, in the best case, to digitise the entire part as well. During his research, Hexagon introduced him to its complete machine tool laser scanning solution.

Another difficulty with 3D-printed parts is that, by their very nature, the functional surfaces cannot be used for precise alignment using a tactile probe. However, using 3D laser scanning, the complete surfaces can be used to determine if there is uniform oversize allowance across the entire part to achieve the best possible result before machining.