Features

Cut Cost, Save Weight, and Speed up Production

Figure 2. VICTREX AE™ 250 composites: unidirectional tapes and laminate panels offer benefits in terms of speed of component manufacture and cost-efficient installation. (Credit: Victrex plc)

One of the outstanding thermoplastic polymers that has received a lot of attention over the three-plus decades since it was first created is polyetheretherketone (PEEK)*. This is a tough, high-temperature polymer that melts at 343°C/650°F. Other high performance polymers utilized within the aerospace industry include polyetherketoneketone (PEKK) and polyphenylene sulphide (PPS). A more recent addition to the fold is VICTREX AE™250 polymer which is related to PEEK except that the chemistry of this polymer has been modified to reduce the melting temperature somewhat below that of PEEK (305°C/581°F vs. 343°C/ 650°F) which widens the processing window, aiding parts manufacture (Figure 1). This polymer has been incorporated into composite tapes (Figure 2) and fabrics, being offered to the market, in effect, as easier processing PEEK.

Such materials lend themselves to modern prepreg layup processes, for example automated tape laying (ATL) and automated fiber placement (AFP) which, using robotic manipulation and heat, can lay down prepreg tapes onto tooling to build complex curved parts. Development work is progressing that aims to provide fully consolidated laminates ‘out of the box’ using these robotic layup machines. For now there has to be a secondary consolidation step, which might include hot stamping in a press, or consolidation under pressure in an autoclave.

Lower Temperature Processing

The newer material VICTREX AE 250 composites, can be easily consolidated under moderate pressure (1 bar/14.5 psi) in an out of autoclave (OoA) process, further simplifying the production of aerospace parts and saving the expense of an autoclave. The innovative low melt PAEK composites family enables a unique hybrid molding process, a development which incorporates pre-consolidated composite structural elements overmolded with short carbon fiber compounds to create yet further opportunities to save manufacturing cost and component mass compared with metallic counterparts. Parts manufactured via hybrid overmolding are largely used for structural brackets because they can be manufactured into complex geometries and offer the strength of continuously reinforced composite.

Figure 3. Aerospace grid stiffened demonstration panel – thermoplastic composite using VICTREX™ PAEK-based solutions. (Credit: ThermoPlastic Composite Research Center (TPRC))

As supply chain and capacity are important criteria for increasing the amount of thermoplastic composites in future aircraft programs, Victrex has teamed up with TriMack in the US to create TxV Aero Composites, a joint venture dedicated to further developing hybrid overmolding by offering design and manufacturing services to the aerospace supply chain. Together with a broader representation across the aerospace industry, Victrex is actively participating in a hybrid overmolding development project with the Thermoplastic Composite Research Center (TPRC), Enchede, Netherlands, creating parts that demonstrate the fundamental relationships between materials and processing ( Figure 3).

A Bright Future

Recently introduced innovative thermoplastic composites for aerospace offer multiple advantages, including very short production times and low overall costs, compared to their thermoset counterparts, which today are in frequent use.

A typical VICTREX AE 250 thermoplastic composite part such as a structural bracket,

  • can reduce manufacturing time by 20-30% compared to metals or other polymer materials;

  • can deliver weight savings of up to 60% over conventional metallic solutions, contributing to cuts in fuel consumption and thus emissions;

  • overall can reduce cost by 40% compared to machined metals;

  • offers continuous manufacturing processes and cycle times measured in minutes versus hours for thermoset alternatives.

Thermoset and thermoplastic composites will continue to compete as they vie for space as aerospace structural materials, but no doubt eventually there will be more of a balance between the use of these materials as engineers select the most appropriate materials for any particular application based on cost and fitness for purpose.

This article was written by Dr. Stuart Green, Market Technology Manager Aerospace, Victrex plc (Lancashire, UK). For more information, visit here.