By: Anna Unt, Heidi Piili, Marika Hirvimäki, Matti Manninen, Antti Salminen

Lappeenranta University of Technology, Laser Processing Technology Research Group, Finland
Machine Technology Centre Turku Ltd, Finland

Improving control and decreasing energy needs have been the most addressed problems of chemical industry in recent years. One of the thoroughly researched options has been bringing down the scale of production units. Productivity comparable with large-scale industrial mechanisms can be reached by grouping simultaneously working milli-scale production units with volumes of few ml/min having reaction channels with length of 1-100 mm, width of 0.5-2 mm and depth of 0.25-2 mm. The use of milliscale devices has been limited due to the lack of cost-efficient production method, manufacturing such channels by laser can give savings on cost and simplify the production cycle.

Laser machining is very flexible production technique, since same laser can be used for several operations (like scribing, drilling and subsequent cleaning of surface) on variety of materials. Processing of fine geometries with strict tolerances has been previously done using conventional micromachining techniques such as EDM, micromilling, LIGA or by pulsed lasers. All mentioned technologies have certain limitations in technological aspects or cost of equipment.

It is known, that pulsed lasers are suitable for making microscale grooves with dimensions of 30-100 µm. But when it comes to dimensions close to millimeter, machining becomes too time-and energy consuming due to small material removal capacity. CW (continuous wave) fiber lasers, the other hand, are unable to produce features close to micrometer scale, but according to preliminary study, they can be used for obtaining grooves with dimensions of 0.5 – 2 mm.

When laser scribing of SS 316L was performed with IPG Photonics YLR-5000 S 5kW multimode CW fiber laser and focal position was decreased gradually during processing cycle, it was possible to attain ~ 400 µm wide and ~ 150 µm deep grooves with smooth inner surface. It is also worth mentioning, that CW fiber laser equipment is generally cheaper compared to other laser or workstation types.

Results gained during preliminary study indicate that scribing is possible, and current approach should be investigated further to understand the effect of parameters on the outcome and for process optimization. To the knowledge of authors, CW fiber lasers have not been used for scribing stainless steel before.

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