![]() The first step of lamination is to apply a release agent on the mould, fundamental to avoid adhesion between the resin and the mould itself. Furthermore, the mould must be stable at the lamination temperature, bear the operative pressure, be resistant to wear, be compatible with the other tools used, be resistant to washing solvents and it must be easy to apply release agents. It can be made of different materials, depending on the shrinkage and the thermal expansion coefficient of the composite material, the stiffness required, the surface finish needed, the draft angles and the bending angle. The most important tool is the mould, which can be male or female depending on the application. Ĭleanroom used for the production of microsystems. Lamination is usually performed in a clean-room to avoid particle inclusions within the layers, which would interfere with the characteristics of the final product. In the case of Wet Lay-Up, the preparation of the resin is included in this operation, as the fabrics are not already impregnated. It is the procedure of overlapping all the layers in the correct order and with the correct orientation. Lamination of the fabrics is the second stage of the Lay-Up process. The patterns are generally created digitally and, when possible, given to a CNC machine or, otherwise, replicated by hand. ĭuring the cutting process, a fundamental parameter to be considered is the nesting layout, which is the arrangement of the different shapes to be cut from the fabric in order to reduce the scraps. Both these methods share a common disadvantage which needs to be considered before choosing the cutting methods: the beams create high-temperature areas along the cut axes, in which the physical characteristics of the material can be altered significantly. The latter is based on a high-pressure liquid beam which reaches a velocity of 2.5 times the speed of sound, creating a pressure on the fabric which is higher than the compression resistance of the material and resulting in a net cut. The former is obtained through a convergent radiation beam which vaporizes the material underneath and uses pressurized gas to remove the volatile particles and the melted material. There are also completely contact-free cutting techniques, such as laser cutting and water jet cutting, both usually embedded on CNC machines. An alternative process with less friction is the ultrasound method, which consists of cutting the fabrics with a blade actuated by high-frequency mechanical vibrations, produced by an internal source integrated into the system. These methods require different skills from the operator and provide different finish precisions, but they all are mechanical procedures and have one major disadvantage in common: the physical contact between the cutting tool and the fibres. More automatized alternatives are die-cutting systems, which allow higher production rates to be reached while limiting overall costs, as they allow more layers of fabric to be cut simultaneously. #7: cut materialĪs far as cutting tools are concerned, the most common are scissors, cutters, knives and saws. This process can be manual, semi-automatic or completely automatic. Even though the fibres, in general, have high tensile strength, the shear strength is usually quite low, so they are fairly easy to cut. Cutting Ĭutting fabrics is the first stage of the Lay-Up process. Hence, nowadays, it is mainly suitable for small series production runs of 10 to 1000 parts. Even though some of the production steps can be automated, this process is mainly manual (hence often referred to as the Hand Lay-Up process), leading to laminates with high production costs and low production rates with respect to other techniques. The main stages of the Lay-Up process are cutting, lamination and polymerization. On the contrary, as Wet Lay-Up does not allow uni-directional fabrics, which have better mechanical properties, it is mainly adopted for all other areas, which in general have lower requirements in terms of performance. It can be divided into Dry Lay-up and Wet Lay-Up, depending on whether the layers are pre-impregnated or not.ĭry Lay-up is a common process in the aerospace industry, due to the possibility of obtaining complex shapes with good mechanical properties, characteristics required in this field. A Lay-Up process is a moulding process for composite materials, in which the final product is obtained by overlapping a specific number of different layers, usually made of continuous polymeric or ceramic fibres and a thermoset polymeric liquid matrix.
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