AUTOMOTIVE | UNDER THE HOOD
Right: A car battery cover made with Cell- mould
technology from Wittmann Battenfeld
pressure of up to 330 bar, the nitrogen is supplied in a kind of liquid form and subsequently dissolves in the plastic melt as a supercriti- cal fluid. When injected into the vented cavity of the mould, the pressure is released into the melt. The plastic/ nitrogen blend separates again. Simultaneously, the supercritical fluid returns to its gaseous state, forming a fine bubble structure based on its homogeneous distribution. Its actual structure depends on the conditions in the injection moulding process. These include the melt viscosity of the plastic material, injection speed – the higher the speed, the finer the foam structure – and finally the quantity of material – the less plastic, the more space is available for the formation of a foam structure with material reduction. The material quantity is achieved by either an appropriately lower dosing for a fixed cavity or completely filling the cavity and subsequently opening it by a pre-determined high-precision opening stroke. The company says that as well as weight
reduction, other advantages include elimination of sink marks, reduced warpage and part costs, and lower tolerances. The process also provides higher rigidity with the same weight, longer flow paths through reduced viscosity, new design options, and lower internal mould pressure and clamping force requirements.
Airmould is the internal gas pressure technology
that is used in several different process variants, depending on the part geometry, plastic material used and the specific requirements for the product. A distinction is made between the partial filling process, and the spill-over cavity process for the production of hollow parts, and the shrinkage compensation process. These differ from each other by their specific mould technologies and the equipment and control system of the injection moulding machine. All three process variants can be achieved with the modular Airmould gas supply system. According to Wittmann Battenfeld, advantages include an improvement in quality and the elimina- tion of sink marks and warpage due to shrinkage. There is also a reduction of the required clamping force, cycle time and weight, as well as additional scope for design. For exhausted engine vehicles, noise reduction,
efficiency and weight reduction remain major trends, reports injection moulding machinery manufacturer Sumitomo (SHI) Demag. “Addition- ally, for hybrid vehicles there is a focus on improving and regulating the thermal management of the temperature to ensure the system can adapt to the
26 INJECTION WORLD | May 2021
ambient temperature and maintain comfort for passen- gers,” says Nigel Flowers, UK Managing Director. “In all-electric vehicles, current trends are focused on improving the protection of the current. Materials like Duroplastics are experiencing a renais- sance. Additionally, the vibration and resonance behaviour are totally different and consequently need a new selection of materials and part design.” He says: “As more complexity is added into vehicle electronics, demand for connectors, micro-gears and micro-switches is rising. In the fibre optics market, this particular technology is adopted for moulding gears such as micro connectors, ceramic holders and optics housings. Other applications comprise micro engines, micro drive control systems and micromechanics rotators.”
Materials selection Polyamide-based engineering plastics are widely preferred in under-the-hood applications across the automotive industry for their high heat, hydrolysis and oil resistance properties, according to Eurotec of Turkey. The properties of these materials should be enhanced and improved for resistance through special formulations so that they meet the required automotive specifications. With its recently developed ‘A’ series codes, the company says that it offers a material portfolio consistent with OEM specifications due the right-application-right-material selection principle. Eurotec adds that superior mechanical proper-
ties, stipulated by OEM specifications for under- the-hood applications – such as motor cooling systems and drivetrains in conventional internal combustion vehicles – require the use of materials that are highly heat- and hydrolysis-resistant. These applications are functional components requiring consideration of their mechanical and thermal properties. For this reason, materials appropriate for long-term strength tests are preferred. The company says that it offers a wide range of technical polyamide engineering plastics with advanced mechanical and thermal properties intended for the automotive industry.
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IMAGE: WITTMANN BATTENFELD
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