Question

6b2. Discuss two laser characteristics that are important for evaluating use in materials processing (laser cleaning, cutting, or welding).

Answer 1

LASER CUTTING:---

Laser cutting, the most established laser materials processing technology, is a method for shaping and separating a workpiece into segments of desired geometry. The cutting process is executed by moving a focused laser beam along the surface of the workpiece with constant distance, thereby generating a narrow typically some tenths of a millimeter cut kerf. This kerf fully penetrates the material along the desired cut contour. Laser cutting is a thermal cutting process. During the process, part of the laser radiation is absorbed at the end of the kerf, called the cutting front. Fig.2.1 shows the cutting front of the Laser Beam and co-axial nozzle orifice with gas flow. The absorbed energy heats up and transforms the prospective kerf volume into a state (molten, vaporized, or chemically changed) which is volatile or which can be removed easily. Normally, the material removal is supported by a gas jet, impinging coaxially to the laser beam. This cutting gas accelerates the transformed material and ejects it from the kerf. Various types of laser cutting processes such as fusion cutting, oxidation cutting, and vaporization cutting, mixed process, new cutting processes with specialities, single and multi-dimensional cutting are described here in after.

LASER MARKING OR ENGRAVING 68 Laser marking often takes the form of an alphanumeric code imprinted on the label or on the surface of the product to describe date of manufacture, best-before date, serial number or part number, etc. but the mark can also be a machine-readable bar code or 2D symbol (ID matrix). As well as coding, laser marking sometimes takes the form of functional marking such as gradation lines on a syringe or decorative marking such as a logo or graphic image on an integrated circuit. Laser marking is often one of the final processes in the assembly of a product, taking place during the final filling cycle on a finished product before it is boxed for shipment. Compared to other on-line marking techniques, such as inject, hot stamping, or mechanical scribing, laser marking offers many advantages such as indelibility, reliability, no consumables, cleanliness and high speed. Laser marking is usually the best marking solution with one proviso. All materials can not be marked with every Laser.

THE BASICS OF LASER MARKING Laser marking can take a number of forms as follows: (i) Black carbonisation, (ii) Bleaching or changing the colour of the material, (iii) modification of the surface finish, (iv) Scribing a shallow groove into the material by vaporization, (v)Highly controlled modification of the surface by melting, or A combination of any of the above.