Custom cooling core ups cycle rate for Kärcher cleaner moulds

Renishaw cooling cores have boosted productivity for jet washer manufacturer Kärcher by cutting cooling time by 55 per cent.

Renishaw uses metal additive manufacturing technology for its cooling cores, which were added to Kärcher’s line of six moulding machines as it looked to reduce cycle times to fulfil higher orders for its pressure washers.

After contacting Renishaw’s subsidiary LBC Engineering, Kärcher’s moulding manager Leopold Hoffer used LBC’s cores to reduce cycles from 52 seconds to 40 seconds.

Global demand for the K2 Pressure Washer has increased, so current production rate of 1,496 casing moulds a day is to be increased to 12,000.

Carlo Hüsken, Renishaw project manager, said: “The first stage of the project was to obtain data for the existing moulds to determine whether Kärcher’s goal was feasible.”

The existing injection moulding process was mapped with thermographic images provided by Kärcher and simulated using Cadmould 3D-F simulation software.

This revealed that, within the 52 second cycle time, cooling accounted for 22 seconds, with melting at 220°C and de-moulding at 100°C. The mould tool temperature was controlled 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. 

Hüsken's suggestion was to improve the temperature control on the nozzle side 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 run to assess improvements using 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 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. 

The simulations showed that practically all the hotspot areas could be improved through conformal cooling, with the wall temperatures reduced by up to 70°C.

Based on 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 3D printed cores to provide conformal cooling at the identified hotspots.

The results’ thermographic images confirmed wall temperatures could be reduced by 40°C, to 70°C. The cooling time was reduced from 22 seconds to 10 seconds, a 55 per cent reduction. The daily capacity on one machine could be increased from 1,496 to 2,101 castings.

Leopold Hoffer said: “The results were better than expected. Renishaw sold us a complete improvement package, with a holistic consideration and analysis of the mould used to achieve the best results - In our case, this meant a mix of conventional cooling technology, project-specific cores produced using additive manufacturing, and vacuum-brazed cores."

Hoffer said he gained important experience: “In future, we will give more attention to cooling in the design phase. Cooling calculations will be an essential stage of each mould design at Kärcher. Using this information, we can then make the decision whether to work with conventional cooling or a conformal cooling solution.”