Cutting, or to cut, in the context of fabrication, may be considered as 'to divide' or 'to sever'. This is an important operation in producing sheets to size, removing waste material, making weld joint preparations and in removing defects. Cutting can be carried out using a number of techniques such as:
- Mechanical (as in machining, sawing, shearing, punching, drilling)
- Thermal (as in oxygen cutting, spark erosion, laser cutting, plasma)
- Hydraulic (as in water and abrasive water jet cutting)
The process selected to make a cut will result from considering a number of interrelated factors, such as:
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Material
Some materials cannot be easily cut using thermal techniques (e.g. oxy-gas cutting of stainless steel or grey cast iron) or would give off noxious fumes (e.g. plastics). Others (e.g. hardened steels) may be difficult to cut using mechanical methods, while most carbon and low alloy steels can be readily cut by most techniques.
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Thickness
The thicker the material, the more difficult it is to produce high quality and fast cuts.
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Type/shape of cut
If a shaped cut is required (as in a weld preparation) this may severely limit the available cutting techniques. For example, none of the thermal cutting processes is capable of producing a 'J' preparation.
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Quality required
Mechanical techniques are normally used when the finish of the cut must be of very high quality. With thermal cutting techniques, cut quality varies with factors such as thickness, speed and process. Of the thermal cutting processes, laser cutting is capable of giving very accurate, high quality edges, but the thickness that can be cut is limited.
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Cutting speed and number required
These factors influence costs as well as process selection and the degree of automation employed in the cutting operation.
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Available equipment
Manufactures will frequently try to use their existing cutting equipment, rather than purchase new equipment. If it is necessary to purchase new equipment, manual oxy-gas or air-arc equipment is the cheapest (approximately ?1k/unit) whereas laser cutting systems can require considerable capital expenditure (e.g. 100k to 500k).
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Environment
The approach taken to cutting on site will be different to that taken in a factory. Also important will be aspects such as the presence of flammable or heat-sensitive materials in the cutting environment. Cutting may be carried out 'on the bench' or on a dedicated machine. If waterbeds are used, there are benefits in terms of noise and fume level reduction.
Cutting operations present health & safety risks from hazards such as materials handling, heat, fume and noise. Risk assessments should be made of the process and its operation.
Choosing a cutting process that will do the task is often relatively straightforward but to achieve optimum cutting performance at lowest cost can require considerable analysis and evaluation.
Further information
What are the advantages and disadvantages of the principal cutting process?
Profile cutting - guide to process selection