April 25, 2013
The conventional production of wheels is an extremely cumbersome, labour-intensive and expensive process because it requires the manual production of several sand core segments and complicated undercuts. A defective turbine wheel meant that a small hospital in Ethiopia was no longer able to warrant the supply of its electricity. And it did not have enough money to replace the wheel.
"Once we heard about the problem, we immediately decided to help. Our 3D print technology is virtually predestined for cases such as these. says Dr. Ingo Ederer, CEO of voxeljet technology GmbH.
Precise sand mould after a five-hour printing period
Once the required CAD data for the wheel was available, voxeljet started with the process of producing the flow-carrying interior for the Francis wheel. In this context, the monoblock sand core, which is created on a fully automated basis using 3D printing, replaces many manually produced core segments that are strung together. In contrast to the conventional manufacture of moulds, in which the production of model plates or core boxes alone can take several weeks, 3D printing makes it possible to print smaller sand moulds in as little as a few hours.
The 250 millimetre mould for the wheel was built in layers over a period of almost five hours. Precision is considered a factor in this process - an accuracy of 0.2 millimetres in the x and y direction is setting new trends. In principle, voxeljet's large-format printers can produce moulds of particle material in dimensions of 4 x 2 x 1 metres.
The moulds are created without cumbersome and expensive mould set-ups, and are produced in a fully automated process purely based on CAD data using the layer building method, which consists of the repeated application of 300 micrometre thick quartz sand layers that are selectively glued together with a binder using the print head of the system. This method offers enormous production-related advantages that affect quality, production targets and profitability equally. In this case, 3D printing resulted in higher component accuracy, a significant reduction in subsequent machining as well as an excellent surface quality and contour precision.
High strength - easy handling
After the printing process is complete, the mould only has to be unpacked and cleaned of excess sand - and it is finished. The simple and easy handling of the moulds means that they can be easily transported to the foundry. Due to their low binder content of 1.2 percent and a pressure of 220N/cm², the sand cores are comparable to those derived from conventional series production. The moulds can be used immediately for further processing and are ready for casting.
"In this case, we decided on a combination of a 3D-printed sand core for the complicated turbine geometry and a conventionally produced exterior mould. This means that we use the advantage of 3D printing where it pays off the most - for the production of the complicated interior. Instead of many individual core segments which are strung together, the mono sand core impresses with higher component accuracy, smaller tolerances and fewer cleaning requirements, and does away with the need for many core separation devices", says Dr. Ederer. In most cases, it pays to produce both the interior as well as the exterior mould using the 3D printing method. In the final analysis, it is a question of unit numbers and individual circumstances that will determine how the exterior mould should be produced.
Turbal AG, the company led the project for the production of a new wheel and steel foundry Wolfensberger AG from Bauma were very impressed by the quality of the 3D prints. This 'help for self-help' project by the participating companies has restored the production of electricity at the clinic in Ethiopia.
Watch the video below the production of the wheel:
Source: voxeljet
Posted in 3D Printing Applications
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Something tells me that laser sintering or electron beam melting will soon scale to these sizes and eliminate the need for a mould step altogether, as well as the expensive and time-consuming subsequent steps. This could mean parts with otherwise impossible complexity, reduced energy requirements, drastically reduced costs, and a far quicker iterative cycles. Still, incremental progress is very good!
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