Temperature control | processing
The simulations showed that practically all of the hotspot areas could be improved through conformal cooling, with the wall temperatures reduced by up to 70°C.
Finally, in one area where there was insufficient
space in the mould to incorporate conformal cooling, Kärcher made clever improvements to the product design in order to alleviate the problem. Based on the results of the simulations, Renishaw
presented a comprehensive improvement plan to Kärcher. This showed that conformal cooling could be used to improve the temperature control of the mould hotspots, thereby achieving a more uniform cooling rate and a reduced cooling time. A modified mould design was proposed that would incorporate two additively manufactured cores to provide conformal cooling at the identified hotspots.
This revealed that, within the 52s cycle time, cooling accounted for 22s, with melting at 220°C and de-mould- ing at 100°C. The mould tool temperature was con- trolled with water at a temperature of 35°C and a throughput of 10 litres/minute. Hotspots, detected by the thermography, were also modelled, as these areas were responsible for the extended cycle time and needed to be analysed in more detail. With this data, a simulation of 20 cycles was completed, including an analysis of the wall temperature. Based on a suggestion from Hüsken, the tempera-
ture control on the nozzle side was improved for the second simulation run. The beryllium copper, threaded fitting dome, for the body cover was provided with additional cooling by inserting two conventional cooling channels into the mould plate on the nozzle side. Two simulations were then run to assess potential
improvements through the use of conformal cooling. Conventional mould cooling is made up of a network of drilled channels. Drilling the channels limits the geometries that can be produced so, while this is adequate for simpler moulds, it cannot provide the most efficient cooling in more complex examples. Conformal cooling is based on the use of metal
additive manufacturing to produce the core of the mould. Additive manufacturing builds the cores in a series of thin layers. The flexibility of this approach means that cooling channels of almost unlimited complexity can be incorporated. Typically, conformal cooling is used to keep the channels at a more equal distance from the moulding, giving more even cooling, or to focus on areas where hot spots are known to exist to give more rapid cooling in those areas.
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Faster cooling The results from the modified mould design were checked by Renishaw, using thermographic images supplied. These confirmed that the wall temperatures could be reduced by 40°C to 70°C. The cooling time was reduced from 22s to 10s, a 55% reduction. Volker Neu, technology and plastics group leader at
Kärcher, produced figures confirming that the new mould design, combined with the re-alignment of some peripheral components (material feed, handling systems, etc.), made it possible to reduce the cycle time from 52s to 37s. As a result, the daily capacity on one machine could be increased from 1,496 to 2,101 castings. Kärcher then implemented the design changes for the other moulds. The additively manufactured hybrid inserts for these moulds were produced and supplied by Renishaw, with Carlo Hüsken actively support- ing the mould-maker during the manufacture of the tooling. ❙
www.renishaw.com ❙
www.kaercher.com
Left: Kärcher’s distinctive yellow pressure washers are a familiar feature of German homes
Original design of tool for K2 rear yellow case (left) and new design of tool for the case including conformal cooling channels (above)
July/August 2017 | INJECTION WORLD 27
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