Drawing upon over 60 years’ heritage in high performance adhesives, Huntsman Advanced Materials announced at JEC World 2016 that it has developed a new epoxy resin system and a novel and cost efficient process to give an entirely new compression moulding concept.
By combining a new fast-cure Araldite epoxy chemistry with this new compression moulding process, Huntsman says it is not only facilitating the simple production of structural composite parts, but is also enabling cycle times as low as one minute without any further post-curing. For high-volume applications such as automotive, this process makes cost-efficient manufacture of high-performance structural parts using thermoset technology a reality.
The current, commercial epoxy solution for high-volume manufacture of composite parts is the Araldite system that’s used to manufacture the BMW i-Series of cars. With a cure time of two minutes at 130°C, this system gives a total cycle time of around two minutes 30 seconds. However, the latest rapid-cure Araldite epoxy system is not only quicker, but it also displays a higher Tg, thus enabling robust processing up to 150°C.
Bringing these factors together provides a cure time of just 30 seconds at 140°C, meaning that a press cycle time of only one minute is possible, without any further post-curing of the part. Following curing, the epoxy system displays a tensile elongation in excess of 5% with a Tg of 120°C.
To complement this new, rapid-cure epoxy system, an innovative Dynamic Fluid Compression Moulding (DFCM) process has also been developed by Huntsman. The simplicity of the new process removes the need for high-pressure injection and in many cases, even the need for a bonded fibre preform, thus eliminating a complex and costly step in production. Furthermore, resin impregnation of the fibres through-thickness virtually eradicates fibre-wash; a common problem with high-volume Resin Transfer Moulding (RTM) production parts.
In tests carried out by Huntsman, it was established that one of the main advantages of the new process is that it reduces void content of laminates in comparison to conventional Wet-Compression Moulding (WCM) process. It allows typical porosity content of less than 1%, making it comparable to High Pressure-RTM (HP-RTM) or autoclave prepress.
Significantly, fibre wet-out is so effective that fibre volume contents of 66% can be easily achieved with no special processing conditions. Heavy-tow industrial fabrics proved similarly easy to impregnate, with virtually void-free parts, even when parts were made with a 960 gsm plain weave fabric.
With the new DFCM process, equipment investment costs are reduced in comparison to HP-RTM or Compression-RTM, since lower mould pressures mean a lighter press is required, plus the need for a high-pressure injection machine is also eliminated.
The combination of high-fibre volume content and low-void content ensures exceptional mechanical properties for high-performance, structural applications, exceeding levels currently possible with HP-RTM processing and yet offering a faster and lower-cost process.
Compared to conventional compression moulding, where part geometry is limited to essentially flat parts, the new process easily achieves full-fibre impregnation, even with deep draw parts.
Traditional compression moulding commonly employs a surplus of resin and fibre during moulding in order to eliminate air bubbles, which are pushed to the outside of the part by the surplus resin. Using the new compression moulding process, wastage is largely eliminated since no surplus of resin or fibre is required in order to remove air from the part.
By creating a new range of opportunities in the mass-production of composites parts, Huntsman’s innovative compression moulding concept takes the industry another step forward from HP-RTM in the journey of composites to replace metals.
In the space of just a few years, the minimum part cycle-time for high-performance composites has reduced from 20-30 minutes, to a part-to-part cycle-time of 5-7 minutes. The recent developments with HP-RTM, using new resin systems and new automation methods play a major part in this remarkable improvement.
With Huntman’s latest innovation making the one-minute cycle time an actuality, epoxy thermosets are becoming very appealing to OEMs for new, mass-production applications.
Whilst thermosetting prepregs are an effective replacement for metals in high performance applications, their high cost or long processing times are often a barrier to usage. This new advancement from Huntsman also creates the anticipated opportunities to replace metal for structural applications.
High-performance thermoplastic composites or recent fast-curing prepregs overcome the long process time of prepregs, but raw material expenditure remains high. In addition, processing costs are also higher due to processing temperatures in the range of 250-300°C, thus creating high energy expenses.
In comparison, the high fibre-volume content, high quality and part consistency together with the reduced cost of a direct process ensures that this innovation leads the way for new composite applications.