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Content archived on 2024-04-15

ADAPTIVE CONTROL OF LASER PROCESSING

Objective


A comprehensive database was established of near-field and far-field intensity distributions for 3 representative types of DC excited carbon dioxide lasers, together with their characteristic fluctuation amplitudes and frequencies. Beams were monitored from typical examples of each of these lasers, ie 400 Watt slow axial gas flow; 1.2 kW fast axial gas flow; 5 and 10 kW transverse gas flow. Measurements of significant increases in laser-polarization fluctuation levels, from 2 to 20 percent, in a typical 10 kW carbon dioxide laser beam were made during blind and full penetration welding in mild steel plate. Means for suppressing these fluctuations were demonstrated successfully and their effects on weld root porosity were investigated.

Laser hardening with a continuous wave carbon dioxide laser and surface texturing with a pulsed Nd:YAG laser were demonstrated successfully on selected materials suitable for moulds used in the manufacture of plastic components. A technique was developed to produce homogeneous hardening in overlapping laser tracks and an experimental mould was constructed to compare laser surface treatments with conventional processes. The influence of gas impurities on laser cutting performance was also examined in detail in 0.5 to 2.0 mm mild steel using an 800 W carbon dioxide laser. With a newly-developed shaping technique - 'Laser Micro Machining' - simple 3 dimensional shapes were machined in mould quality steels. Using this technique a surface roughness of better than 2 um and dimensional tolerances of better than 5 um were achieved.

A prototype beam control system was developed which is capable of correcting a carbon dioxide laser beam to within an angular pointing error of less than 0.1 mrad, at a slew rate of 1 mrad per second, and at frequencies oup to 5Hz. This system also provides automatic coalignment of beams from a 5 mW visible helium neon laser and a 10 kW infra-red carbon dioxide laser. A commercial scanning detector was also mo dified to enhance the safety and beam quality monitoring of carbon dioxide laser. A commercial scanning detector was also modified to enhance the safety and beam quality monitoring of carbon dioxide laser processing cells by sensing the beam alignment without breaking the integrity of any safety enclosures.

An Oldelft Seampilot vision system was assessed under representative welding conditions on a 5 kW carbon dioxide laser and commissioned for use with the high speeds encountered in laser welding. Plate edge preparations were quantified for several industrial cutting techniques, in steel up to 20 mm thick, to define the operating range that would be encountered by the vision system in high power laser welding. Dynamic trials showed that the Seampilot's response was adequate for estimating weld gap areas for plates cut by standard industrial methods such as oxypropane or plasma torches.

Observations of the porosity levels in laser welds by means of off-line and on-line rediography were made during a systematic variation of laser welding parameters to study their effects on keyhole stability. On-line radiography was used to study blind and fully penetrating welds made with a 5 kW carbon dioxide laser in mild steel. Keyhold fluctuations and consequent formation of porosity were recorded in realtime with normal and high speed videos.

A 6 metre long 3 axis welding gantry was constructed for use with a 10 kW carbon dioxide laser. This equipment incorporates the Seampilot vision system and a dual-capstan wire feed unit.

The main objectives of the project were to investigate beam quality and stability in different types of high power carbon dioxide lasers; to determine the influence of operational factors on selected manufacturing processes with carbon dioxide lasers and neodymium yttrium aluminium garnet lasers; to investigate the micromachining of machine tools and the surface treatment of tooling; to develop a semicontrolled beam alignment system for use with multikilowatt laser beams; to select an online weld penetration monitor and to demonstrate its reliability when used with a 10 kW carbon dioxide laser; to adopt a seam following vision system for controlling laser welding processes; to study the effects on keyhole stability of varying laser welding parameters and to optimize weld quality; and to design and construct a large scale gantry to demonstrate adaptive control of welding with a 10 k W carbon dioxide laser.
The main practical objective was to weld steel plates 10 to 20 mm thick and to develop a commercial vision system capable of guiding the laser along the weld line. The main problems encountered related to the movement of the sheets being welded together during the welding process. A series of tack welds were put in place prior to welding and the vision system ensured that as the laser moved along the gantry to complete the weld that the laser beam was correctly aligned. A wire feed was also developed that fed wire between the plates prior to laser welding. The use of wire increased the strength of the weld. In addition to the successful demonstration of the welding of 20 mm steel sheets a safe area was constructed in which the laser and gantry could be operated with out risk. The micromachining of machine tools with the use of lasers and the texturing of moulds using laser techniques were also successfully achieved. It was found that the creation of cavities in a machine tool by use of a laser beam could be satisfactorily substituted for traditional techniques.
A PRIMARY OBJECTIVE IS THE DEMONSTRATION OF REPEATABLE WELDING CAPABILITY FOR THE JOINING OF PLATES UP TO 6 METERS LONG USING SINGLE SIDED FILLET WELDING IN T-BUTT GEOMETRY IN ONE LINEAR DIMENSION WITH A 10 KW CO2 LASER.
THE GOALS TO BE REACHED ARE COVER BEAM STRUCTURE CHARACTERISATION THROUGH TO DEMONSTRATOR, VIA :

- OPERATIONAL FACTORS,
- PROCESS MONITORING INCLUDING WIRE FEED AND A WELDING VISION SYSTEM, - CONTROL OF THE WELD-KEYHOLE PHENOMENA,

THE FINAL STAGE WILL BE THE OPERATION OF A FULL SCALE PROTOTYPE 6 METRE GANTRY PLATE-WELDER. THE EQUIPMENT WILL BE ABLE TO DEMONSTRATE WELDING ON 12MM THICK STEEL PLATE (SINGLE PASS) OR 25MM PLATE (MULTIPASS).

IN ADDITION, LOWER POWER CO2 AND YAG LASERS WILL BE USED TO INVESTIGATE FACTORS AFFECTING PRODUCT QUALITY FOR CUTTING AND SURFACE TREATMENTS : PRODUCTS INVESTIGATED WILL INCLUDE DIES AND MOULDS.

Topic(s)

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Call for proposal

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Coordinator

United Kingdom Atomic Energy Authority (UKAEA)
EU contribution
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Address
Culham Laboratory
OX14 3DB Abingdon
United Kingdom

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