Live: gwk close-to-cavity, segmented and cyclic mould temperature control
Professionals Meet Customers’ Exacting Quality Requirements for Surfaces
gwk creates a complex moulded part in collaboration with notable partners
It has already stirred great interest amongst customers, partners and suppliers alike at the technology day, and now gwk Gesellschaft Wärme Kältetechnik mbH, Meinerzhagen is making it accessible to the wider expert audience. At Fakuma 2015, the company is demonstrating live the production of a plastic moulded part with very high quality and surface specifications using cyclic temperature control. gwk is working in co-operation with numerous partners who have been involved with the project from the beginning.
“The product is a bowl with our logo on it”, explains gwk’s head of development, Guido Peters. “The aim of the product design was not to demonstrate technology, but to design a moulded part with practical uses that exhibits the typical problems of surfaces of plastic parts. This includes the high gloss surface around the edge and around the gwk lettering, the precise and even moulding of the laser-structured surface structure in the mould, and avoiding weld-lines behind the recess on the edge. In addition, it was effective in preventing flow lines in the gwk logo.”
Iserlohner Kunststoff-Technologie GmbH (ISK) was responsible for the product design and the proper shaping of the plastic. “A prototype in 3D print was created to evaluate the component concept and to prepare for the realisation of the mould”, Peters explained. The partner for material selection was Covestro, Leverkusen. “Together we selected the material Bayblend T65Hg. The material properties enable the desired specifications to be achieved during the variothermal process control”, explains the head of development.
Then partner ISK came back into play, reports Peters. The experts created a fill simulation using the software Sigmasoft. “This served to check the rheology, the fill behaviour and the formation of the moulded shape. The problems uncovered were then remedied by changes to the design, in particular to the wall-thickness”, he added, explaining the procedure.
gwk was then able to contribute its extensive know-how on temperature control. “It was planned that temperature control of the mould surface would use cyclic water-water temperature control, which heats up the mould wall temperature to around 140 °C at the beginning of the injection process and cools it to around 75 °C for demoulding”, explains Carsten Schmidt, head of injection moulding process engineering. He further explained that it was planned that temperature control of the outside of the mould would use continuous temperature control with water, and a wall temperature of 80 °C.
“The design of the channel layout is decisive for the successful use of a cyclic temperature control procedure. A temperature control system capable of following the contours of a large-scale channel system can realise the desired quick temperature change”, explains the expert. Together with ISK, thermal simulation was carried out, and using Sigmasoft, the channel layout was analysed and iteratively optimised.
The mould concept was implemented in close collaboration with Grote + Brocksieper GmbH + Co. KG, Kierspe, and Hasco Hasenclever GmbH + Co KG, Lüdenscheid. On the nozzle side of the needle valve gate, Hasco integrated a hot channel nozzle as well as the ejector in order to avoid marks on the mould surface. The required pressure and temperature sensors for quality monitoring and process optimisation were included in the planning. A competent partner for the selection and integration of two pressure sensors came on board in the shape of Kistler Instrumente GmbH, Ostfildern. The sensors were integrated on the nozzle side of the tool close to the injection and on the end of the flow path.
The next step was to realise the mould. As well as Grote + Brocksieper and Hasco, Werkzeugbau-Institut Südwestfalen GmbH, Lüdenscheid was responsible for this. “Thanks to the detailed project planning, implementation was possible within a very short time”, Peters explained with a smile. “The mould was created by Grote + Brocksieper and the partially pre-made mould templates, the hot channel nozzle and the hydraulic cylinder were provided by Hasco. The laser-structured surface of the mould was contributed by Werkzeugbau-Institut Südwestfalen”, he reflects. “We manufactured the mould using integrated close-to-cavity temperature control channels here in our vacuum joining process and delivered it to the mould builder who undertook the final processing and integration into the mould.”
After manufacturing, the mould was incorporated into an injection moulding machine of the type Allrounder 630 S 2500 – 1300, made available by partner Arburg GmbH + Co KG, Loßburg. “Temperature control of the mould flow occurs via a gwk cyclic temperature control system. The teco vario generates heat output of 36 kW. It supplies the mould via a ESR-switch unit with an alternating hot and cold medium”, explains process engineer, Schmidt.
The temperature control system is controlled via the interface of the Arburg injection-moulding machine. “For temperature control of the fixed mould-side, an integrat 40 multi-circuit temperature control system from our company is used”, he reports. Colleague Peters expands: “The process monitoring and quality monitoring were realised using a Kistler Como System, which monitors the pressure flow in the mould.” In addition, a thermo control system from partner GTT Willi Steinko GmbH, Nassau was used that employs a thermal camera to analyse the surface temperature of the part to be moulded shortly before demoulding and detects deviations.
“Close collaboration of the right partners is essential to the planning and successful implementation of such a project to manufacture a variotherm temperature-controlled plastic mould with high specifications in terms of quality and surface-finish”, observes Peters. “Even the development of moulds for dynamic temperature-controlled applications requires extensive analysis of the integration of the temperature control channels in the moulds in order to quickly and effectively realise the temperature change. The integration of sensor technology allows an optimised process. Fakuma visitors will soon be able to see for themselves the success of these endeavours.”