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Hand-lay or Contact-Moulding is the simple but effective process on which the composites industry was founded nearly 60 years ago. It continues to be very extensively employed. Its main points of interest are:
• It is highly labour-intensive
• It is ideal for prototypes
• It is suited to short runs and the larger one-piece component or assembly.
The Process
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Figure 1. Schematic of the hand lay up or contact moulding process.
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Moulds and Tooling
‘Open’ tooling - most frequently also fabricated in composites - is employed, to which a release agent is applied as a first stage in the moulding process.
Materials Application
The application of a resin-rich, typically pigmented gel coat follows and when this has cured, a thin layer of the requisite type and quantity of matrix resin is applied to the tool surface prior to carefully positioning the cut-to-shape reinforcement. The latter is normally chopped strand mat (CSM), although the entire or partial use of fabrics such as woven roving can apply.
Using additional resin, perhaps further reinforcement and also other ‘mats and fabrics’, this composite laminate is consolidated by hand in to an air and void-free homogeneous moulding using either a brush or a roller. For very large mouldings the resin may be dispensed to the reinforcement through a mechanical roller system.
Trimming
Just before full-cure has been developed, the component may be roughly trimmed to shape, after which it is stripped (or released) from the mould-tool, which is then cleaned, re-released and returned to use.
Design Parameters
Laminate thickness is in principle controlled by the weight (and type) of reinforcement employed, with the mechanical and physical properties similarly governed, but in addition by for example, the actual resin matrix employed as well as the resin:reinforcement ratio (the optimum for chopped strand mat is 2 to 2.5:1 by weight), and the degree of cure - or polymerisation - achieved.
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