Thermoset compounding made easy

Materials World magazine
1 Jan 2010

A direct compounding process that makes the production of high volume and complex
thermoset-based composite parts production easier may soon be available.

German organisations DSM Composite Resins, Diefenbacher and Fraunhofer Institute for Chemical Technology (ICT) believe that their technology will open up opportunities for lightweight thermoset polymer-based composites.

Large composite parts are usually made using conventional sheet moulding compounds (SMC) that are compression moulded. However quality and rework issues occur due to the localised and temporarily separated nature of SMC manufacturing and part moulding. Furthermore, limited control over the formulation of raw materials, especially the type and amount of mineral fillers and the quality of glass fibre loading, causes problems.

The new process is said to offer an integrated continuous extrusion process chain from raw material to the ready made part, saving time and enabling control of key parameters with reproducible fibre impregnation. Furthermore alternative mineral fillers can be used so that it is possible to obtain higher filler and fibre loadings for increased stiffness.

Tobias Potyra of the Fraunhofer ICT in Pfinztal, Germany, explains, ‘A gravimetrically dosing unit is used so that all resins, additives and fillers are in container on a balance system that is controlled by loss of weight. The solid and liquid raw materials are mixed in the extruder then the next step is to add the fibres.

The compound is then cut into portions online and taken up with a robot and placed in the mould in a press. It cures for a couple of minutes, then is de-moulded, creating a continuous fully automated system removing the need for separate machinery’.

He adds, ‘Superset line control on a central computer controls all activities within the process. We can feed the compound into one to six moulds at the same time and design it to the customers’ needs’.

The process is said to allow for formulation flexibility, high series length, complex parts in a just-in-time process with consistent quality.

Potyra says, ‘With this new process we are targeting new applications where composite parts replace existing metallic parts or assemblies. We combine advantages of compression moulded composites with a continuous process chain. The key benefits are mainly added value as the material formulations can become more extreme. In terms of transportation, we are targeting truck and automotive business as well as public transportation’.

He claims that lower cycle time and only one step in moulding means that you do not need high investment in many machines. A commercial production line will be tested next year.

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