Solution of the problem

Given the demanding requirements on technology, the boundary conditions (constraints) for the use of the casting mould had to be clearly defined. These conditions included connecting points for cooling and casting media, construction space in the casting machine, fixation, acting forces, and properties of the casting material. 

The key part of the design was to optimize the cooling element. Instead of the existing straight-drilled channels, the possibility of their replacement with round channels now arose. The combination of the additive manufacturing of the mould model and the casting of the final component required a close cooperation of additive manufacturing technologists and casting experts. Other issues to be solved included, for example, the distance of the cooling channels from the cast, channel geometry for media flow, and how to 3D print self-supporting channels.

As for the technology to be used, priority was given to DMLS (Direct Metal Laser Sintering), the material was set to be tool steel 1.2709. For reasons of cost-effectiveness, 3D printing must consider the surface area of the cast relative to the printing platform (which is 250×250 mm in the case of EOS M290), and the total volume of the cast. Topological optimization applies all boundary conditions and forces, and iteratively eliminates any superfluous material.  This helped save a lot of printing powder which the company can now use for other printing assignments.

In a specific design example, additive manufacturing was combined with conventional machining of a part of the mould. The resulting geometry was verified in a structural analysis, using the method of final elements. The design’s merit for die casting was also evaluated by the casting simulations software called MAGMA. The model was then complemented with machining add-ons and with any structures needed to ensure that the additive manufacturing process is in compliance with all technological principles.

Merits

The printing of a half of the mould took approximately 21 hours. Topology optimization helped reduce the printing time by 30 % and material waste by 64 %. The project fully benefited from conformal cooling and the production price compared well with a conventionally produced mould. Practical casting tests demonstrated that the bearing capacity of the casting is by 30 % higher, which is a result of improving the quality of technological principles of high-pressure casting, primarily by decreasing the number of casting defects. This also led to reducing the wasteage rate in parts manufacture. You can read more about the project here.