LaserSnake Residual Beam Effects on Concrete TWI

Transcription

1 o LaserSnake Residual Beam Effects on Concrete TWI

2 Contents 1 Introduction 1 2 Experimental Arrangements Laser cutting equipment Samples 1 3 Experimental Method 1 4 Results and Discussion 1 5 Conclusions 2 6 Acknowledgements 2 Figures / Copyright TWI Ltd 2016

3 1 Introduction This report details the results of an experiment to determine the effects, after cutting steel plate, of the energy in the residual laser beam on concrete positioned behind the material being cut. This is relevant to the cutting of active parts in-situ, where it is highly likely that the walls, roof and floor of the building in which the size reduction is taking place, will be made of concrete. To perform the work, plates of 15mm thickness steel were positioned at distances from 250 to 1000mm in front of the concrete. Horizontal lines were then cut in these plates, using laser powers of 5 and 10kW, at two cutting speeds. The first close to the maximum achievable for 15mm plate and the second, at half this speed. In addition two different cutting gas pressures were used. 2 Experimental Arrangements 2.1 Laser cutting equipment The 10kW laser was used for the trials and the cutting was performed using the ULO water cooled head. The head was moved using a Kawasaki articulated arm robot. The stand-off distance between plate and nozzle tip was kept at 15mm throughout. 2.2 Samples The samples used for cutting were plates of S355 CMn steel, 300mm wide and 15mm thickness. Two such plates were used in the trials. The concrete was in the form of a pre-fabricated L shaped wall section about 1.5m high. In the trials both sides of the concrete were used. 3 Experimental Method Figure 1 shows how the experiments were performed. The steel plates were positioned at distances D of 250, 500, 750 and 1000mm from the concrete surface. Cutting was performed at the speeds, powers and gas pressures shown in the table below. The cutting gas used was compressed air. The cutting head was moved horizontally. The laser beam was first released on the concrete, travelling at the chosen cutting speed, for about 75mm before it hit the plate. The cutting took place for 250mm and at the end of the cutting, the robot was stopped and the laser beam and gas left on for 3 seconds. In this way the effects of three different conditions could be seen on the concrete, for each traverse of the cutting head. Gas pressure Cutting speed used 5kW power 10kW power 6bar 350mm/min 700mm/min 2bar 175mm/min 350mm/min 4 Results and Discussion Figures 2 and 3 show the sides of the concrete used for trials at 5 and 10kW respectively. The gas pressure used was 6bar, on the right hand side and 2bar on the left hand side, of each image. Results for full speed (FS) and half speed (HS) can be seen for each distance D. Some damage to the concrete can be seen in all cases where the beam was either missing the steel plate (at the start) or when the cut had finished and the beam was stationary. The damage was not particularly deep (a few mm) for these cases apart from when D was equal to 250mm, where up to 10mm penetration was visible. See Figure / Copyright TWI Ltd 2016

4 However, for the length of track adjacent to where the steel was being cut, different effects on the concrete surface could be seen. Most obvious is that a larger effect could be seen when cutting at half speed, which is entirely reasonable, as under these conditions more energy is available to pass through the cut. It is also clear that when cutting near to the maximum available for any particular thickness, then for distances D equal to or greater than 500mm, very little damage is recorded on the concrete surface. However, even at D equal to 1000mm, significant damage can be seen at half cutting speed. Generally, little difference could be seen between the two different assist gas pressures, other than perhaps at D equal to 250mm. Similar trends were observed when the power was increased to 10kW, although at this power, more damage is evident for the higher assist gas pressure. More damage can also be seen on the full speed results at 10kW but this is perhaps because the speed was not quite the maximum for cutting 15mm steel at the higher power. 5 Conclusions This work, using laser powers of 5 and 10kW, has shown the effects of the residual laser beam on a concrete slab, when cutting 15mm thickness steel plate. It is clear that if the cutting is performed near to the maximum for that thickness, then the residual beam has minimum effect on the surface of the concrete. However, when cutting at half the maximum speed possible, the residual beam has a greater effect on the concrete. At 5kW power, a change in the cutting assist gas pressure had little effect on the results for any distance D. At 10kW power, a higher assist gas pressure generally produced more effect on the concrete surface than observed at the lower assist gas pressure. 6 Acknowledgements The author would like to thank Frank Nolan who conducted the trials. This work was carried out as part of the LaserSnake2 collaborative research project. LaserSnake2 is co-funded by Innovate UK, the Department of Energy and Climate Change, and the Nuclear Decommissioning Authority, under grant number The LaserSnake2 project includes OC Robotics, TWI, Laser Optical Engineering, ULO Ltd and the UK s national Nuclear Laboratory / Copyright TWI Ltd 2016

5 Figure 1 Steel plate positioned 1m in front of the concrete wall / Copyright TWI Ltd 2016

6 a) b) Figure 2 Effects on concrete when cutting 15mm thickness steel at 5kW laser power using: b) 2bar assist gas pressure and two different cutting speeds, for four distances between the concrete and the plate being cut; c) 6bar / Copyright TWI Ltd 2016

7 a) b) Figure 3 Effects on concrete when cutting 15mm thickness steel at 10kW laser power, using: a) 2bar assist gas pressure and two different cutting speeds, for four distances between the concrete and the plate being cut; b) 6bar / Copyright TWI Ltd 2016

8 Figure 4 Shows maximum effect of 10kW beam on concrete. (Travelling at 350mm/min with no cutting). Maximum penetration 10mm / Copyright TWI Ltd 2016

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