For the bulk manufacture of short-fibre reinforced thermoplastics, the most successful processes are extrusion and injection moulding.

The manufacture of continuous fibre reinforced composites has been reviewed by Åström [1], Gutowski [2], Davé and Loos [3], Akovali [4], Mazumdar [5], Campbell [6] and Strong [7].   For low performance components, spray and hand-lamination are often chosen because the raw materials are relatively inexpensive, they can use relatively unskilled labour and the mould tools do not need to be vacuum tight.   However, these open mould processes produce composites with low fibre volume fractions and high levels of voids (porosity).  For higher-performance composites, vacuum bagging of wet-lay-up or pre-impregnated (prepreg) materials can add one bar of pressure for consolidation.  For the highest performance autoclave consolidation can add further external pressure to the bag [8-11] or the component can be manufactured by compression moulding.

Resin Transfer Moulding (RTM) [12-19] is emerging as the most probable route to mass production for small-medium sized composite components of complex shape.   In RTM, a mould is loaded with dry fibres then resin flows into the fabric stack before the resin cures to produce a solid component.   While RTM is appropriate for relatively small components, the mould closure forces become excessive as component size increases.

One solution to this problem is to use only vacuum to drive long-range resin flow and enclose the laminate in a bag rather than in a matched pair of moulds.   This technique is known by various names including resin infusion under flexible tooling (RIFT) [20-25] and the Seeman Composites Resin Infusion Molding Process (SCRIMP^TM) [26] and Vacuum-Assisted Resin Transfer Moulding (VARTM).   Smith [27] has reviewed the current status of resin infusion in the context of its application for toughened aerospace structures.

An alternative route is the use of un-reinforced B-staged resin film stacked with the dry reinforcement fabrics.   This process is most commonly known as resin film infusion (RFI) or ‘semi-preg’ [28].   The process minimises the resin flow distance by utilising only through-thickness flow and uses the resin in a form where the base/hardener mix ratio is set by the materials supplier.   Commercial versions of this process are Carboform (Cytec), HexFIT^TM (Hexcel Composites), SPRINT^TM (SP Systems) and ZPREG (Umeco, formerly Advanced Composites Group).  When a thermoplastic matrix is used the process is known as film-stacking.

Automated processes include filament winding [29, 30], robot-assisted placement [31] and pultrusion [32, 33].   Machining of composites has been reviewed by various authors [34-38].   Methodologies for the care and repair of composites have been presented by Armstrong et al [34].

Process monitoring techniques have been reviewed by Summerscales [40] and process modelling has been reviewed by Advani and Sozer [41].  NPL have recently produced draft guides to the measurement of temperature [42] and humidity [43].  The data available from these techniques may be used as a record of the process. In combination with techniques such as Statistical Process Control (SPC), the information can provide a basis for action to improve the process, reduce scrap and/or prevent the production of items that do not meet the design intent or customer expectations [44]. Further information can be found in the literature [45-50].

Genichi Taguchi [51] explained the economic value of reducing variation and proposed that by reducing the variation about the nominal specification (rather than working with a tolerance range), it was possible to produce manufactured goods with better quality. Taguchi measured quality as “the variation from the target value of a design specification” and translated the variation into an economic “loss function” experiments. Taguchi built on the Latin Squares techniques in the context of Design of Experiments to develop orthogonal arrays in order to determine the critical factors while reducing the influence of interactions.

Six-Sigma is a Total Quality Management (TQM) technique pioneered by Motorola in an attempt to move to absolute perfection in product quality [51, 52]. They had observed that while their process shifted over time, the maximum shift was around 1.5 standard deviations. By allowing the process mean to shift by that amount and setting process limits at ±4.5 standard deviations, only 3.4 parts per million would be anticipated to be outside the specification limits. Six-Sigma represents this quality level in defects per million operations and has a systematic problem-solving approach: Define- Measure – Analyse – Improve – Control (DMIAC).

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