FEATURE: CUTTING
Amada’s Ventis machine was first
shown at Euroblech 2018; the official launch will be in May 2019 in Japan
greplaced by laser fusion cutting using nitrogen as an assist gas. Nitrogen is used to eject the molten material. In the past laser power was expensive, so the addition of oxygen was used alongside a lower power beam to create enough heat to make the cut. ‘Nowadays, because there is enough laser power available, even mild steel at thicknesses of 15mm can be cut by a fusion process using a 10kW laser, or higher power,’ Wetzig said. Oxygen cutting is still used for very thick
material of 50mm. But, compared to oxygen cutting, fusion cutting with nitrogen is faster and the cut edge has a better quality – it avoids oxidation of the cut edge. One big challenge for laser cutting is
gas consumption; nitrogen is delivered at a pressure of up to 20 bar in fusion cutting. ‘Gas consumption could account for up to 10 per cent of the running cost of the machine. It’s really significant,’ Wetzig said. ‘One goal for laser cutting machine manufacturers is to reduce the gas consumption, because you reduce costs.’ Machines for cutting thin metal sheets normally have enough laser power available. Machine manufacturers are therefore putting development efforts into automation, into ways of speeding up aspects like feeding the material into the machine or removing cut parts as fast as possible. Wood at Amada said: ‘Automation is still
very relevant to laser cutting in general. Because solid-state machines are cutting so much quicker compared to CO2
lasers
– especially thin materials – the machine is finished before the operator has managed to get the parts out of the skeleton and put a new sheet on. It’s important to consider automation, because you’ll get more out of the laser machine,’ he continued. ‘Whatever laser technology you decide to buy you need to match that with some kind of automation to get the benefit.’
14 LASER SYSTEMS EUROPE SUMMER 2019
Process control Fraunhofer IWS is working on new beam shaping optics, using one gimbal mirror instead of two galvo-driven mirrors, for instance, which is a more elegant way to manipulate the beam in a compact set-up. The scientists are also experimenting with a z-axis adaptable mirror to move the focal point of the laser from the top side to the bottom side of the material with a frequency of 2kHz – up and down like a saw. ‘We haven’t seen a positive effect on the speed and cutting quality yet, but we are expecting one,’ remarked Wetzig.
“The aim in the long run is to have a machine that works more or less autonomously overnight or over the weekend”
‘The focal position of the laser within
the material is a critical parameter for laser cutting. ‘Even if there isn’t a direct advantage of
moving the beam quickly in the z direction regarding the cut quality, we might have a tool for closed-loop control to change the focal position if it starts to shift over time. ‘In addition, a quick adaption of the
focal position will also help to optimise the so-called piercing process that is used to initiate the cutting process for thick plates.’ One of the parameters that should
remain constant over time is the kerf width, the width between the two cut edges. ‘It’s important to have a robust process,’
Wetzig said. ‘This means having no breaks in machining and maintaining a constant cutting quality.’ Fraunhofer IWS is working on process
monitoring for better cut quality, potentially with a view to have closed-loop control of the process at some point in the future. ‘If you have a way of detecting a decrease in cut quality then you can control the process – you can reduce or increase the power, adapt the position of the laser focus, adapt your feed rate, or change the laser beam parameters,’ Wetzig explained. ‘But first of all you need to monitor the process; you need correlation between what is observed and the cut quality.’ This might include information on whether
there is dross left on the backside of the plate or not; information about how smooth the cut edge is; and some information on the width of the cutting kerf. One monitoring method is to measure
the intensity of radiation emitted during the process – from UV to infrared wavelengths – and compare these readings to the cut quality. There is some correlation between these variables, according to Wetzig. More promising is to use a thermal camera to image the molten material, which will provide localised information about the temperature field within the kerf width. Fraunhofer IWS is working on this. There are other methods as well – a visible camera will provide some information about the kerf width, for instance. There are many reasons why the cutting
quality might degrade over time, such as dust on the optics or material restricting the gas flow. The aim is to have a machine that works more or less autonomously overnight or over the weekend. ‘One of our goals is to tie in process
monitoring with beam shaping,’ Wetzig said. ‘We haven’t done it yet, but we will do it. We are currently working separately on both issues and then we will combine them.’ l
@lasersystemsmag |
www.lasersystemseurope.com
Amada
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