TWI Industrial Member Report Summary 740/2002
D W Taylor
Cutting is an important application for materials processing with lasers, dominated by the use of CO 2 lasers for the cutting of steels. Laser users have four basic requirements for laser cutting: cut quality, cutting speed, cutting reproducibility and material cost. There is evidence that some types and grades of steel have improved quality, cutting speed and reproducibility over others.
Currently the evidence for factors that affect cuttability comes from anecdotal evidence from end users and from steel suppliers who have launched 'laser grade' steels. As described in this report, laser grade steels are those which are marketed as providing improved cutting speed, quality and reproducibility. The compositions and manufacturing processes used by other steel makers may also provide benefits for laser cutting, but these are not always promoted on this basis. The issue of laser cutting quality is complex with a variety of parameters that can affect the process such as:
- Variable laser related parameters - including power, speed, assist gas pressure, lens focal length.
- Fixed laser parameters - for example laser beam quality or pulsing capabilities.
- Machine performance - such as focus position control or stability of motion.
- Operator influence - both at an individual level and a company level.
- Material composition - such as levels of carbon, manganese, silicon, phosphorus, sulphur.
- Surface condition - mill scale condition and surface preparation methods.
- Material dimensional effects - flatness and material thickness control.
Greater understanding of the influence of the above factors should allow steel makers to supply steel plates with improved cuttability, leading to greater consistency and reproducibility of the laser cutting process. To provide some of this understanding a study of how the material composition and surface condition of carbon and C-Mn steels can affect the quality of CO 2 laser cut edges has been carried out.
The objectives of the work performed were:-
- To determine current market views and establish the level of current understanding of factors that affect laser cut quality of carbon and C-Mn steels through an industry survey.
- To determine the influence of different operators and laser cutting systems on laser cut quality of carbon and C-Mn steels up to 12mm thickness.
- To determine the influence of the plate composition effects and plate surface condition effects on laser cut edge quality and propose guidelines for the selection of carbon and C-Mn steels, up to 12mm thickness, for laser cutting.