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Plastic part and casted part
Plastic part and casted part.
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The casting process.
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3D-printed Francis wheel using voxeljet technology.
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The raw cast part.
Leading 3D printing industry company voxeljet's additive manufacturing expertise has set the benchmark for ensuring efficiency, accuracy, complexity and rapidity in producing investment patterns.
The Schmolz + Bickenbach Guss Gruppe favours 3D printing technology, transforming the landscape of long lead times and high cost traditionally associated with the low volume production of complex parts using investment casting to a different animal entirely.
Whether for the automotive industry or machine building, the production of precision parts such as powertrain components for development or small series production, gearboxes, FEAD brackets, should be much more expedient using additive manufacturing technology.
There are weaknesses, says Schmolz + Bickenbach Guss Investment Casting Manager Thomas Peipp, regarding the creation of investment patterns for industrial applications.
"The problem is the immediate production of the required wax patterns that result in expensive injection moulding tools and wax presses," he said. "These tool costs can become prohibitively expensive and time consuming when used with small series or development, as they ultimately result in very high unit prices."
3D printing to replace wax models?
This is where voxeljet's 3D printing technology comes into play. Modern 3D printers from voxeljet can produce precise investment patterns rapidly and cost-effectively. These PMMA models could, in effect, completely replace wax models. The production of plastic models using additive technology is simple, accurate and swift with no tooling required, as the digital printing process is based on a CAD model of the component, which is then built up layer by layer, allowing designs to be developed beyond what would be capable using traditional manufacturing techniques, while designs are simple to change using a CAD system.
voxeljet's newest 3D printing machines can produce a plastic model of a Francis wheel with a 500 mm diameter in less than 24 hours using PMMA material, which softens at 73 degrees centigrade and burns without residue at temperature exceeding 700 degrees centigrade. This means the parts are ideally suited for use as smelt models for investment casting purposes.
Schmolz + Bickenbach has extensive experience with the 3D printing of plastic models. Peipp added: "In the past, we had the models printed at the voxeljet service centre. The advantages of the 3D print technology, along with continuously rising order volumes, prompted us to invest in our own voxeljet printer in 2013. With the VX1000 printer, our investment casting plant can print parts up to a size of 1060 x 600 x 500 mm and a maximum unit weight of 70 kg. Now we can offer our customers even more rapid and efficient support."
The 3D printing process involves spreading plastic powder onto the build plate then selectively printing the shape of the model into the powder using a solvent. This ensures the particles glue together over a restricted area. The finished object is then built up and unused powder supports the product, so even complicated free-form surfaces with undercuts can be made without a supporting structure that would need to be filed off in post-processing. After the 3D printing process, the residual particle material is removed from the finished model, which is then infiltrated with wax providing the plastic models with a closed and clean surface perfect for investment cast parts.
The subsequent handling process is the same regardless of how the model has been produced, be with using conventional wax techniques or on a 3D printer. The first ceramic coatings are than applied following inspection and mounting the deadhead system and after, the models are put in the kiln. The plastic models soften at 73 degrees C and so there are no tears in the ceramic shell. The moulds burn out completely without residue when the kiln reaches 700 degrees centigrade, giving these one-time usage models the name 'lost models'.
Next, the casting dies are blown out before the glowing hot steel or aluminium alloys are poured into the dies. The casting dies must be removed after the cooling period, along with the casting and feeding systems and sharp corners must be debured and any unwanted surface defects are removed. This process is then followed by non-destructive inspections and dimension controls according to the customer's specification.
Peipp stated: "Whether prototype, individual part or small series - 3D printing technology makes it possible to produce highly complex design and investment casting models quickly, easily and cost-effectively. An enormous advantage for investment casting specialists, and especially our customers."