In keeping with the Christmas season and its traditions,
Open Mind Technologies AG has made an exact replica of a famous nutcracker from the Erzgebirge, a region in East Germany. Milled from aluminium, the example demonstrates an end-to-end digital process chain and efficient five-axis machining with hyperMILL. Together with
Emuge-Franken, Open Mind set itself a task — to digitally reproduce a 400mm tall nutcracker as accurately as possible and mill it from aluminium in the most efficient way possible. The traditional Seiffener Volkskunst provided the wooden figure, which was handcrafted in around 150 steps and consists of around 30 individual components.
Open Mind turned to
WestCAM Datentechnik GmbH for the 3-D scan of the nutcracker. The Austrian partner is not only characterised by its hyperMILL expertise, but it also has extensive know-how in 3-D measurement technology. The result of the scan was a high-resolution mesh model consisting of 1.2 million triangles. At Open Mind, a surface-based 3-D model was created using the hyperMILL CAD/CAM solution and designed completely parametrically. The advantage of the latter is that production-related changes to the model can be made very easily afterwards. For production, the nutcracker model was divided into the upper part, legs, arms and lever, which were pinned and glued together after completion.
Production was carried out at Franken’s Rückersdorf application centre on a Hermle C32 machining centre in a single clamping operation using five-axis simultaneous machining. This allowed the surfaces to be machined continuously without segmentation. The opening cut for the large central pocket of the upper body was efficiently achieved using five-axis helical drilling, which enables a particularly high level of material removal and is also gentle on the tool when compared to a helical plunging movement.
Strategies from the hyperMILL MAXX Machining high-performance package were used to optimise roughing operations. The 5-axis rest machining function then ensured that the roughing was completed safely and efficiently. The new EvoGrip centric clamp from Emuge was used for workpiece clamping. With its modular and slim system design, reliable clamping was guaranteed.
High-quality surfacesThe ‘high-precision surface’ mode was used for finishing, whereby hyperMILL generates tool paths on the actual CAD surfaces and not on a calculation model. The large surfaces of the nutcracker that are curved in two directions, lent themselves to the use of Franken’s circle segment end mill in various shapes. For this application, taper and teardrop shape tools with cutting radii from 200mm to 1,000mm were used. These tools, also known as barrel cutters, enable particularly efficient production of high-quality surfaces despite the large in-feeds or large step-over line increments. hyperMILL offers optimum control of the cutting edge area of circle segment cutters.
Michael Förster, senior product marketing manager at Open Mind Technologies AG, said: “In the nutcracker machining example, we had the problem that the dimensions of the part were actually too large for the work area of the machine - a challenge that many manufacturers have already faced. What would normally require many manual adjustments and individual simulations in order to avoid travel limitations and find safe tilt positions can now be implemented quickly and reliably thanks to the virtual machine and NC code-based simulation.”
The hyperMILL ‘VIRTUAL Machining’ package includes an optimiser that perfectly adapts the connecting movements between the individual milling operations to the kinematics of the machine and can therefore solve limit switch problems. Communication between the milling center and the software, which contains a digital twin of the machine, allows precise machining-based simulation of the actual NC code.
Mr Förster concluded: “We would like to thank Emuge-Franken, WestCAM and Seiffener Volkskunst for their cooperation. We are delighted that we were able to impress the artisans from the Erzgebirge with the detailed execution of this adaptation of their original design.”