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Diamond-like carbon coating offers ‘relief’ to plastic injection moulds

A new low-friction, high-hardness coating is poised to expand the range of surface treatments to help tooling stand up to tough moulding challenges. The new diamond-like coating can increase the mould service life by up to 10 times compared to the state of the art.

Industrial Technologies

Telephones, PC parts, toys, electrical plugs, and other everyday products like shoes and pens are made with plastics using a process called injection moulding. The technology can produce identical parts at high volumes at a low cost per part. However, its start-up cost is relatively high, mainly because custom tooling is needed. An injection mould can cost anywhere between EUR 100 000 and EUR 300 000, depending on its complexity, material and accuracy.

Keeping moulds running longer

Prolonging tooling service life is of paramount importance for any moulding project since downtime for repairs jeopardises profit margins. According to estimates, around EUR 10 billion are spent each year for maintenance operations worldwide. During the moulding process, the friction forces developed between the closing surface and those contacting the injected plastic largely account for the damage caused to the surfaces. Ultimately, the mould needs to be scrapped. Put together, these significantly affect the mould’s service life. The EU-funded cleanMOULD project demonstrated novel coatings based on a multilayer diamond-like carbon formulation that prolong the life of injection moulding tools, offering corrosion protection, reduced wear and resistance to friction. “Importantly, our novel coating solutions increase mould performance and extend its operation before the need to take it out of service for preventive maintenance,” reports project coordinator Michael Hvam.

cleanMOULD – a mould’s best friend

A key attribute of the diamond-like carbon coatings is the ability to resist wear by lowering the friction between sliding surfaces. This largely eliminates the need for surface lubrication and post-finishing, which are deemed primary sources of pollutant releases to the atmosphere for certain industries such as pharmaceutical and food. The coatings are applied using a physical vapour deposition process called magnetron sputtering at temperatures as low as 180 °C. Due to this advanced deposition process, the diamond-like carbon coatings can maintain a very thin, uniform finish (1-5 μm) over the entire mould independently of its geometry. “cleanMOULD’s novel coatings optimise both surface hardness and lubricity to minimise the impact of fretting,” notes Hvam. The high hardness of the newly demonstrated diamond-like carbon coatings, which are 8 times harder compared to other coatings, allows the surfaces to become more resistant to scratches that occur during operation. It goes without saying that the absence of oil lubricants makes mould cleaning much easier: it only requires applying ethanol to a cloth for less than 10 minutes. cleanMOULD’s ‘mould breaking’ has the potential to become a key enabling technology for the entire plastics industry. Overall, the return on investment for cleanMOULD users is expected to be over 20 times the expected coating costs, thus providing a compelling value proposition. Pilot-test results demonstrated a sixfold decrease in the maintenance interval compared to state-of-the-art coatings. No fretting corrosion has been observed on any coated moulds. What’s more, “cleanMOULD’s coating demonstrated a decrease in the moulding cycle time of screw lids from 40 to 36 seconds, which is equivalent to an 11 % increase in productivity,” concludes Hvam.

Keywords

cleanMOULD, mould, coating, friction, diamond-like carbon coating, tooling, maintenance, plastic injection mould

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