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Keeping cars trim

From leather seats and velour carpets, to plastic cup holders and dashboards – in contrast to the exterior of a car, the materials found inside can vary considerably. And, new materials, such as carbon fibre, are finding their way into vehicles in order to reduce weight and improve fuel efficiency. Last month, BMW presented its i8 hybrid car made from carbon fibre, at a manufacturing plant in Washington DC solely focused on this new material, which has traditionally been difficult to process. So, what qualities do laser systems have that allow them to process such a variety of materials, and how is the technology being developed to cut new ones?

As opposed to the fibre lasers used to cut the metal components for the car body, CO₂ lasers are best suited to processing the variety of materials found inside the vehicle, according to Robin Urbach, manager of technical sales support at Eurolaser: ‘This [CO2] is a type of laser system which is used for plastics, textiles, foils and so on − a very wide range of materials.’

A large manufacturing sector in the automotive industry involves processing textiles, which traditionally was carried out with knife cutting machines. However, manufacturers are starting to move towards laser technology to take advantage of its speed and accuracy, according to Urbach: ‘A laser cutter is three to four times faster than a knife cutter. It is also more precise − we do not have all of the mechanical problems on the table.’ Using a laser also produces a cleaner cut than a knife-cutter, Urbach pointed out. ‘Normally, if you cut a textile with a knife, then after the cutting, the cut will unravel – this would not happen with a laser cutter.’

But, there are occasions when mechanical tools like knives are more efficient at processing certain fabrics. To accommodate different tools, Eurolaser’s laser systems have two additional instruments − a knife and a router − on the laser head, so that different processing techniques can be carried out on the same piece of fabric, one after the other. ‘We have a laser head which has two extra slots available for a knife tool or, for example, a routing tool,’ explained Urbach. ‘This is useful, for example, if you have acrylic sheets on the machine and you want to make a v-groove into the material − normally, we use a routing tool for this. A laser is also capable of doing this, but it takes a very long time and is not very economical,’ Urbach continued.

As fabrics normally come in large rolls, it is not as simple as just placing a part into the fixture of the laser system, as would be the case with a plastic cup holder. Spacer fabric, for example, is a popular choice of material for car seats as it is good for removing moisture, thermal regulation and providing pressure relief. However, this material, which consists of two textiles that are kept apart by spacer threads, can be crushed or distorted when it is cut. To overcome this problem, lasers are often equipped with a conveyor belt system to automate the textile cutting process, and to minimise placement errors and handling of the fabric. ‘Textiles are an interesting special case because you sometimes have a textile feeding system  such as a roll or conveyor belt system,’ said Frank Gaebler, product marketing manager for CO2 lasers at Coherent.

As part of Eurolaser’s conveyor system, a feeding unit forwards the raw material from the roll of fabric to the laser system. To ensure the material is consistently aligned, Edge Control Technology is used at this stage. ‘We have edge-control technology, based on light sensors, which checks the edge of the material and, if necessary, will correct the misalignment of the material.’ Once the material is on the laser bed, it is immediately processed by the laser. ‘Then the conveyor belt advances and transports the material to a table extension. On the table extension, you can unload the material manually or automatically,’ explained Urbach. A winding unit is integrated into the end of the system, to unwind the processed fabric evenly at the end.

The laser systems used to cut plastics work in a different way. Because plastic components tend to be three dimensional, the part stays still while the laser orientates around it, as opposed to the two dimensional process used with fabrics. ‘The part is put into the fixture of the machine, and is brought to the processing system itself − so either a 3D robot system or a gantry system with a cutting head − and the positioning system will run the cutting programme [pre-loaded onto the system] over the part by turning the laser on and off,’ explained Dr Torsten Scheller, head of product management, technology and applications at Jenoptik.

But, with all materials processed with a laser, there is a risk that the heat can affect the quality of the cut. ‘Laser cutting is a thermal process, so when processing different materials with a laser, there is always the risk that the heat affects the quality of the end-product,’ said Scheller. This is particularly the case for textile materials, according to Coherent’s Gaebler. ‘When you are cutting inflammable materials like leather, if you put too much heat into it you get a heat affected zone,’ he said. ‘It’s a matter of developing a proper process. You also have to make sure you are extracting fumes, adjusting the laser power accurately.’

Another factor that can affect the quality of the cut is not having adequate suction, which is required to evacuate all of the fumes and smoke directly from the material. ‘If you do not have a good suction on the machine, then you will have residue or smoke on the surface or on the rear side of the material,’ Urbach pointed out. ‘This influences the complete quality of the material, and all of the OEMs in the industry are very strict on the quality − if there is even a small amount of residue on the material, they do not accept it.’

Changing the material support to fit the type of material being cut can improve the suction, according to Urbach. For example, an acrylic sheet needs a raster plate, which is an aluminium plate with holes evenly spaced to accelerate the air movement. Other types of materials, such as textiles, benefit from honeycomb-shaped grids to facilitate an adequate generation of vacuum underneath.

As OEMs are becoming stricter on quality requirements, vision analysis tools are being integrated into laser systems to improve accuracy. For example, when cutting a textile, the accuracy of the cut could be affected if there is any shrinkage, stretching or twists in the material. In Eurolaser’s optical recognition system, which consists of a CCD camera and analysis software, the camera is used ‘to recognise fiducial marks, which are normally printed or embroidered onto textiles’, explained Urbach. ‘The camera compares the marks in the [software] with the marks on the material, and then [the laser] starts cutting the outline precisely,’ Urbach continued. ‘This ensures quality and precision.’

New materials, new processes

As highlighted by BMW’s new i8 hybrid car, carbon fibre material is starting to appear in cars in order to improve fuel efficiency. The increasing government pressure to reduce emissions, such as the EU directive to reduce car emissions by 18 per cent − to 95 grams of CO2 per kilometre − by 2021, makes this material very attractive to car manufacturers.

The use of carbon fibre, although more popular in high-end cars, is still in the early stages for most car manufacturers, according to Coherent’s Gaebler: ‘Carbon fibre materials are used inside cars for fasteners and so on; they are not necessarily visible to the user. The volumes are very low; it is at a very early stage.’ This is because the methods of processing the material have not been perfected, he explained: ‘Because of the fibre materials in the carbon fibre structures, if you have higher carbon content inside, you have a higher melting point for the carbon fibre than the surrounding matrix. So when you cut this material, the matrix will melt at a lower temperature, or will melt faster than the fibre itself, so you have a higher danger of delamination and other effects. That is why this process is not 100 per cent developed or in production yet.’

Laser manufacturers are researching new methods of carbon fibre material, ready for when it goes into large-scale production. ‘For welding, adhesive bonding, cleaning and cutting processes for carbon fibre materials, more research and development is necessary,’ Gaebler said. ‘We have to develop processes for these new materials for when they go into volume; we have to give industry tools to process these materials.’

It is often a case of trial-and-error when processing new materials. In comparison to standard materials with longterm proven laser applications, for new ones it can be a time consuming process to find the most efficient laser source with regards to wavelength, power levels and pulse duration. ‘All of these factors will influence the quality of the laser cut and have to be optimised to use the powerful tool “laser” in a proper way,’ said Scheller from Jenoptik.

One method that has been effective for processing carbon fibre is adhesive bonding. However, when the carbon fibre parts are taken out of a mould after their manufacture, the release agent on the surface of the components prohibits a good adhesive bond, according to Gaebler. ‘[Manufacturers] have to take this release agent off without, of course, touching or destroying the carbon fibre piece,’ he explained. ‘Therefore, you typically use a UV laser to clean off the release agents from the carbon fibre components. Then you can adhesively bond or paint the materials afterwards,’ Gaebler continued. ‘We are working with customers to integrate this process into production lines.’

When asked when he thinks carbon fibre will start to be used in high volumes in the automotive industry, Gaebler said: ‘When you listen to analysts they talk about a 2018-2020 timeframe that you will see high volumes of carbon fibre. It’s an industry decision. The aerospace industry is using it in new airplanes in larger volumes. But it is a lengthy process to qualify a new manufacturing technology; the automotive industry has its own regulations which are also a barrier here.’

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