page_title: Lay-Up process
section_title: Cutting
hierarchical_section_title: Lay-Up process / Cutting
caption_attribution_description: English: Diagram of a laser cutter
context_page_description: 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. It can be divided into Dry Lay-up and Wet Lay-Up, depending on whether the layers are pre-impregnated or not.
  Dry 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. On the contrary, as Wet Lay-Up does not allow uni-directional fabrics, which have better mechanical properties, it is mainly adopted for all the other areas, which in general have lower requirements in terms of performances.
  The main stages of the Lay-Up process are the cutting, the lamination and the polymerization. Even if some of the production steps can be automatised, this process is mainly manual, leading to laminates with high production costs and low production rates with respect to the other techniques. Hence, nowadays, it is mainly suitable for small series productions of 10 to 1000 parts.
context_section_description: Cutting fabrics is the first stage of the Lay-Up process. Even though the fibres, in general, have high tensile strength, the shear strength is usually quite low, so it is fairly easy to cut. This process can be manual, semi-automatic or completely automatic.
  For what concerns the tools, the most common are scissors, cutters, knives and saws. More automatized alternatives are the die-cutting systems, which allow reaching higher production rates and maintaining contained costs, as they allow to cut more layers of fabric at the same time. These methods require different skills from the operator and provide different finish precisions, but they all are mechanical procedures and have a major disadvantage in common: the physical contact between the cutting tool and the fibres. An alternative with less friction is the ultrasound method, which consists of cutting the fabrics with a blade solicited with high-frequency mechanical vibrations, produced by an internal source integrated into the system. There are also completely contact-free cutting techniques, like laser cutting and water jet cutting, both usually embedded on CNC machines. The first is obtained through a convergent radiation beam which vaporizes the material underneath and pressurized gas to remove the volatile particles and the melted material. The second 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. Both these methods have a 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.
  
  During the cutting process, a fundamental parameter to be considered is the nesting layout, as to say the arrangement of the different shapes to be cut in the fabric in order to reduce the scraps. The patterns are generally created digitally and, when possible, given to a CNC machine or, otherwise, replicated by hand.
caption: Laser cutter.
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