New Laser applications for light weight material in automotive manufacturing

Coherent DIAMOND E-400

Coherent DIAMOND E-400





February 04, 2013

Coherent Inc, Frank Gaebler, Director of Marketing, frank.gaebler@coherent.com, www.coherent.com

Historically the automotive industry has been an important segment for the laser industry. It demands for a variety of laser technologies and processes. Most famous are BIW and power train welding, cutting of 3D components but also brazing of metal e.g. for car roofs and trunks. Most of the components used in a car are laser marked. But there are more applications coming up in car manufacturing, which are not known as well yet. Coherent is engaged in new developments as it offers the broadest product portfolio in terms of wavelength (From UV to far IR), pulse width (from fs to CW) and power levels (from mW to kW). The optimal laser source can be chosen offering an ideal tool for new unsolved application requests.

One major trend in automotive industry is to become more environments friendly. Reduction of weight is one way to reach this goal; therefore the automotive industry is evaluating use of carbon fiber reinforced plastic. New manufacturing processes have to be developed enabling CFRP joints within the body structure. In Automotive manufacturing Thermoset CFRP holds the lion share in material use. A suitable joining technology of CFRP components is adhesive bonding as traditional technologies like welding, bolting or riveting do not apply or have unfavorable side effects. During the manufacturing process of a CFRP component, the part will be cured in mold tools. These tools are covered with release agents allowing an easy removal of the part. But these agents remain on the surface of the CFRP component. It has been proven that the remaining release agent on the surface of a part leads to reduced bonding performance of adhesives and paint. In order to allow maximum bonding strength, the release agent has to be removed from the surface together with a certain amount of resin. Traditionally this has been achieved by manual grinding. Industry is looking into automatic procedures which allow for a repeatable process including possibilities of monitoring.

Coherent Excimer LEAP 130C
Coherent Excimer LEAP 130C

One innovative method for the pre-treatment of CFRP is the application of laser radiation to achieve a selective removal of resin without impairing the fibers. When using a laser the most important parameter is the absorption of the radiation, which defines the portion of energy deposit within the material and the penetration depth. The laser should achieve a surface ablation only without damaging the CFRP matrix. Another important factor is the ablation rate, as maximum speed and best cost of ownership are required. Research has proven that either UV radiation (300-360nm) or far infrared radiation (10µm) offer ideal absorption values for an ablative process. Lap-shear specimens were laser ablated and bonded with a one component epoxy film adhesive. For the trials a Coherent Excimer Leap 130C and a CO2 DIAMOND E-400 lasers were used to ablate the surface layer of the specimen. In both cases the laser was used in pulsed operation. The beam of the Excimer laser was homogenized and directed unfocussed to the part. The laser beam was fixed while the specimen was moved. With the CO2 laser the beam was directed to the part by using a scanner head. In order to achieve a good cleaning rate an optimal pulse overlap was chosen. Both laser cleaned samples, treated with CO2 and Excimer laser, have demonstrated equal or better shear strength than the manual grinded, untreated or samples which were covered with a peel ply. Ablation rates of >10m2/hour were achieved, which is within customers expectations.

Source: TU Braunschweig
Source: TU Braunschweig

As a result it could be demonstrated that Lasers are an ideal tool for cleaning of CFRP components in preparation for adhesive bonding. Lasers offer a repeatable process which can easily be automated. Coherent lasers offer diagnostic tools which enable process monitoring. In future work both laser processes will be optimized so that customers can choose the best laser technology for their application. Furthermore automated production machines for the automotive industry need to be developed together with laser integration partners.

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