Schichtbau² | Mold generation for the castings of tomorrow

Unconventional, cleanable mold division with indirect additive manufacturing

Indirect additive manufacturing offers some great advantages with the printing of molds and cores, such as the possibility to produce very complex geometries at moderate costs. In this context, the following should be noted: The more complex the mold, the more complex is the subsequent cleaning process to remove sand build-up. Here, the layer construction method offers a possible solution, which additionally offers the prospect of a fully automated process.

In the project Schichtbau², individual, load-bearing layers with easier to clean geometries are created by means of a mathematically topology-optimized division of the mold. This creates favorable conditions for the subsequent processes up to casting. The layers are produced in a binder jetting process and can be cleaned automatically after the printing process and then stacked.

Analysis of mold generation to identify suitable component types for stack casting

The focus is first of all on the disassembly of the components in terms of data technology. The separation into layers must be carried out in such a way that no areas are created where individual mold structures are not connected or are only connected by thin-walled webs. The layer thickness and the angles with which the molds are cut are considered as central parameters. The theoretical considerations are followed by practical experiments.

For this purpose, common methods of component cleaning and their quantitative effects are then analyzed and described. The investigations on cleaning are combined with mathematical algorithms for undercut-free division. From the results, the range of application of the proposed methodology can be assessed.

In the next step of the investigations the stacking of the layers and their connection to the complete casting mold is in the foreground. Structural features are examined for their suitability to connect the layer elements in the layer. This applies to the area of the casting cavity.

Subsequently, the burr formation on the casting is analyzed. Due to the stacked mold, burr formation at the layer boundaries is inevitable. The analysis includes a geometry determination of the molds before casting and an analysis of the casting after casting. This is followed by an evaluation as to which added value (improved cleaning) of the proposed mold division is offset by which disadvantage (burr formation).

Finally, a tabular comparison of the advantages and disadvantages can be used to assess which component types can be better produced in stack casting in the future.

Wheel carrier produced by stack casting for the TU Munich

The illustration shows a wheel carrier produced by stack casting, which was manufactured as part of a project for the Formula Student racing team of the TU Munich:

a) CAD model

b) Virtual layers

(c) Layer stacks

(d) Finished casting

Wheel carrier of the Formula Student racing team of the TU Munich produced by stack casting
© Fraunhofer IGCV
Wheel carrier of the Formula Student racing team of the TU Munich produced by stack casting

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