Optimierung Entwicklungsschleifen dank Vakuumguss
4. März 2019
Die Prototech FL AG stellte der Hoval AG mehrere Sätze von Vakuumgussteilen für die Feldprüfung zur Verfügung. So konnte Hoval seine Wohnungslüftungsanlage in kurzen Entwicklungsschleifen optimieren - weshalb dieser Showcase für den Swiss AM Guide 2019 ausgewählt wurde.
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Fresh air awakens the spirit of life and activates the immune system. Disease inducing particles such as viruses, bacteria or mould have to be minimized - a challenge for today's new buildings, which are more or less "airtight". Hoval AG has developed a home ventilation system, which guides and distributes filtered outside air optimally and completely without draught to the inside. Noise, dust and dirt particles remain outside, while odours and moisture are discharged to the outside in a controlled manner. The newest iteration of the air outlet has been thoroughly re-engineered to improve assembly and installation. The joint development with Prototech FL AG heavily relied on field testing with vacuum casted parts. Therefore, this showcase discusses their approach of combining Additive Manufacturing with vacuum casting for the early validation of series parts.
Description of the Showcase
While re-engineering the air outlet of the home ventilation system for improved assembly and installation, Hoval faced several uncertainties. These included the functional design of the break-outs (especially for the nails), the adjustability of the two-component grid supports, as well as the behavior of the frictional locking. To ensure that the product requirements of the individual components were met, it was necessary to validate the design solutions envisaged by Hoval in practical field tests. These were performed in close cooperation with Prototech FL AG. In an initial requirements evaluation, the vacuum casting process was chosen, as it is suitable for such pilot series. Strengths of this process include high repeatability, short implementation times, high flexibility and a broad range of materials including multi material solutions. In comparison to "linear" price scaling of AM, output ratios of 40-80 components per silicone mould enable a high cost-benefit factor for prototype series, especially for complex or voluminous components with an edge length of up to 1.20m.
Vacuum casting is a proven reproduction technology starting from a so-called master pattern which is additively manufactured (stereolithography) based on a CAD data set. Compared to conventional AM process chains, the final surface structure is already applied to the 3D-printed master pattern. Therefore, it will be reproduced during the casting process instead of being “finished” onto the later vacuum casted parts.
The prepared master pattern is casted in silicone and de-gassed in the vacuum chamber. The cured silicone mould is appropriately cut off the master pattern. Additional insert components like threads or other prefabricated parts can be easily integrated with interlocking connections. For complex parts the silicone mould is divided into several components. Furthermore, multiple cavities can be integrated to improve both cycle time per part and application rate per silicone mould.
The reassembled silicone mould is then placed in the bottom compartment of the vacuum casting machine. The casting machine is closed, and the two components of polyurethane based casting resins are mixed in the top compartment semi-automatically under vacuum conditions. Once the pre-defined mixing time has elapsed, the resin is casted into the silicone mould. After completing the casting, the mould is placed in an oven to cure. Post curing the vacuum cast parts are removed from the mould, which then can be re-used for the next production cycle. Runner and risers are then removed from the cast parts (finishing) followed by an outgoing inspection and packaging.
In cooperation with the Hoval development team, Prototech first discussed the initial design, pre-optimized it and manufactured it using the vacuum casting process described above. In the course of the field tests, various design details were further adapted on the basis of empirical findings. The revised components were then cast by Prototech FL AG within a few days and re-tested by Hoval.
These revised components include for example the friction-locked fasteners. The optimum thickness, number of fins and Shore hardness were quickly determined through the means of vacuum casting. The same procedure has proven effective for optimizing the snap-in hook of the clamping strip. The geometries of the snap-fit and the clamping band fastener were adapted and simplified on the basis of the practical tests.
The functional validation of the breakable housing cover was unproblematic, unlike the nail breakouts. The challenge was that these must be able to withstand the impact of the nails during installation, but when the casing is removed they must break out reliably. In the course of the field tests, it was revealed that the original design did not sufficiently meet the requirements. With the subsequent design modification, the functionality could be proven without significant loss of time.
To sum up, thanks to the close collaboration between the Hoval development team and Prototech, the new product has been significantly improved within a few optimization loops. The process merely spanned a few weeks, ranging from the first concept drafts to series readiness through pre-tests on an actual construction site. This showcase strikingly demonstrates, how AM in combination with other processes as vacuum casting can substantially minimize risks and therefore time and costs during the late phases of a product development project.
Indirekte Prozesse (Vakuumguss, Sandguss, Feinguss etc.)