How laser texturing can improve injection-moulded car parts
While the electrification of vehicles has big business potential for laser suppliers – the laser is a particularly adept tool for making the electrical contacts in batteries – other areas of car manufacturing are turning to laser technology just as readily for benefits in terms of quality, reproducibility and speed of production.
Reichle Technologiezentrum, based near Stuttgart, Germany, has built a large part of its business on laser texturing injection moulds for making car components such as dashboards, headlamp bezels, door trim, engine covers and many other moulded parts. According to Marco Reichle, the firm laser grains more than 3,000 injection tools a year, 85 per cent of which are for the automotive sector. ‘That’s a huge amount,’ he said. ‘Our competitors believe that laser graining is a small niche, but for us it’s not a niche … this is the biggest part of our business.’
The company started laser texturing in 2012 and it’s now the largest service supplier for laser texturing in Europe. It also operates in Asia through its Chinese partner. It currently has 26 GF Machining Solutions laser graining systems spread across its sites.
What is laser graining?
Laser graining or texturing is a technique for patterning injection moulds to give decorative surface finish to the plastic parts produced by the moulds. Textures can be designed to mimic the look of leather, wood and geometric patterns. These kinds of surface finish have traditionally been applied to mould tools using chemical etching, but now the laser is starting to take over to imprint the pattern digitally by ablation. The GF laser texturing machines contain a fibre laser operating at nanosecond pulse durations, which ablates the material.
Marco Reichle explained that applying acid films to a mould to produce a leather grain for a car interior, for example, might need to be masked for 20 or 30 hours. ‘It’s a very complex job doing this 100 per cent by hand,’ he said.
The same job on a laser machine is fully digital. The first step is to map the pattern as a greyscale bitmap, with the darker sections representing deeper ablation. The greyscale bitmap is then layered on top of 3D data of the mould. The injection tool is positioned inside the laser machine and the grain applied according to the program.
‘There are a lot of standard automotive grains,’ Reichle commented. One automotive OEM, for example, uses a fine grain of 27µm depth, and the laser machine is able to apply the approved grain in one or 10 tools with the same quality.
Laser machining injection moulds is taking over from chemical etching. (Image: Reichle Technologiezentrum)
Production time depends on the shape of the tool. A small tool, like that to produce a headlamp bezel or a part for the interior, would have a curing time using traditional chemical etching of around 2.5 to 3.5 weeks, according to Reichle. ‘When you do it by laser, you can do the same job in a few days,’ he said. An engine cover would have a lead time of three to four weeks using acid graining; with a laser grain, it’s one week.
Why laser texturing is not always faster
However, the larger the grain surface is, the smaller the difference in the lead time between acid graining and laser graining. For example, laser graining an entire dashboard would require between four to seven weeks, about the same time as acid graining, according to Reichle. ‘But with a lot of jobs, lasers are faster than using traditional acid graining,’ he added.
The main advantage, besides the short lead time is the reproducibility of the process. There is no variance between one tool and another. Moulds for dashboards and the b-pillar around the door are normally both grained with the same pattern at 80µm, and there won’t be any difference between the two moulds when they are laser grained. With traditional manual graining methods, however, there is inevitably going to be some variability in the graining depth and gloss level.
‘We’ve developed our special low gloss and ultra-low gloss concept, which means we can achieve any gloss level in any plastic material,’ Reichle said. Traditional etching methods are not able to achieve low gloss levels of 2.0 or 3.0 gloss units when working with PC-ABS or PC plastics, but a laser can achieve a gloss level of 0.5 for head-up displays, for example.
The laser graining method is not going to replace acid grain completely, Reichle said, and the production time gains depend a lot on size of the surface area. When an injection tool is put in an acid bath, the grain is applied over the entire surface, whereas a laser machine running time will double when the surface area doubles. ‘Graining over large surfaces is quite difficult to achieve the same price level as acid graining,’ Reichle said, adding ‘but you get a better quality.’
A textured engine cover produced from a mould that has been laser grained. (Image: Reichle Technologiezentrum)
The price depends on the grain pattern and the shape of the surface. Producing deeper grains of around 200 to 300µm will cost more using a laser than traditional etching, but a traditional fine grain or leather grain would be around the same cost, whether it’s laser machined or etched with chemicals. However, when a graining surface is directly next to a high gloss surface – in a headlamp bezel for example – then the cost will be much lower using a laser than with chemical etching, because the high-gloss surface doesn’t need to be protected in the laser machine, as it does in a chemical bath.
‘For surfaces in car dashboards, door trims and exterior bumpers, the graining market is moving from traditional leather and fine grain to geometrical grains,’ explained Reichle. Geometrical patterns tend to incorporate a gradient in the grain. A more traditional bezel or door trim will have one grain from the left to the right side, but now new designs will start with a grain depth of 10µm and very glossy on the left of the part, and then the gloss level will change, moving to the right of the bezel and the pattern becomes more 3D. ‘In these new designs, it is only possible to do it by laser graining,’ Reichle said, ‘and that’s the reason why the laser business is growing. We started in 2012 and we’ve doubled our laser graining department every year.’
Trumpf e-mobility sales double in 2018
Sales of lasers for electromobility from system supplier Trumpf have doubled in 2018 compared to 2017, according to the company. ‘Twenty per cent of our order intake from the auto industry is now coming from e-mobility – that’s twice as much as last year,’ Christian Schmitz, head of the laser technology division at Trumpf, commented during an Automotive Photonics technology conference organised at its Ditzingen, Germany, head office on 14 February.
‘The transition toward e-mobility offers some major opportunities for industry,’ Schmitz said.
Lasers have a key role to play in battery production. The batteries consist of multiple layers of copper and aluminium foils that are cut to size using lasers. After adding liquid electrolyte, the battery is welded shut with a cap. A lot of the welding, including joining the copper foils, is carried out using a laser.
Left: Trumpf laser technology for welding hairpins in electric motors. Right: Laser welding of a battery tray for electric vehicles in the laser laboratory of Trumpf (Images: Trumpf)
Trumpf’s laser systems feature sensors that help control the welding process. ‘One problem for battery manufacturers is that they can’t test whether a battery actually works until the very end of the manufacturing process. They need the process to be monitored continuously to ensure that the battery comes out the other end working properly,’ said Schmitz.
In addition, a series of laser techniques have been shown to weld all the seams on an electric motor in just one minute. Instead of winding thick copper wire around the coils of electric motors, a technique called the hairpin method uses a compressed-air pistol to fire a rectangular copper wire, similar to a hairpin, into a slot on the side of the motor. The protruding parts of the wire are then twisted together and welded using a laser.
Trumpf has now sold more than 500 lasers worldwide for use in battery manufacturing.