By means of precise laser-based paint removal, it is not only possible to spot-de-coat battery housings made of aluminum or galvanized sheet steel, but also to remove paint from enamelled copper wire residue-free. The blank copper wires are thus optimally prepared for the further soldering or welding process in the stator production of the electric motor.
Left: Laser paint stripping allows the cathodic dip coating of a battery tray to be removed gently.
Right: In addition to battery housings, copper wire can also be de-coated residue-free, which is needed above all in stator production for the electric motor.
Battery boxes for storing battery modules are usually composed of numerous individual parts to safely protect the sensitive batteries from damage and the accompanying risk of fire in the event of an accident. After installation, these battery modules are tightly sealed so that no moisture can ingress. Electromagnetic radiation may also no longer enter the battery. Effective protection and an improvement in electromagnetic compatibility (EMC) can be achieved by establishing electrical contact between the battery housing and the cover. In doing so, it is necessary to avoid corrosion of such “blank” contact surfaces and to ensure safe ground contacting for current conduction of the battery modules.
Clean-Lasersysteme GmbH (cleanLASER) from Herzogenrath has developed various solutions for electrical contacting. For the complete processing of large battery boxes, a modular all-in-one system is particularly suitable, which allows components made of galvanized steel or aluminum to be de-coated at up to 30 cm² per second, depending on the type of coating and the layer thickness.
In the case of aluminum, the paint removal is automatically restricted by the reflection on the “blank” metal. The challenge with sheet steel is to preserve the zinc layer underneath the cathodic dip-paint coating on the sheet steel, thus protecting it from corrosion. Using laser technology, it is possible to remove the paint from galvanized areas so gently that the zinc layer is not damaged. At the same time, punched areas such as screw holes can be left out, since often the inside of a drill hole must remain coated here in order not to offer any starting points for corrosion damage.
Since the processing of the battery housings and covers has to be accurate in terms of position and contour on the one hand, but on the other hand there should be as little programming effort as possible during the application. Due to the integrated CAD/CAM interface, the precise paint removal is achieved with only a few mouse clicks from the drawing data. The software can be used with standard automation systems. These highly accurate gantry systems allow the processing of large components and assemblies in a reproducible and quality-controlled manner.
Another application is the post-treatment of weld seams, e.g., for sealing with hot butyl or MS polymers, which can be carried out by means of laser cleaning in a contamination-tolerant and process-stable manner. Basically, the laser process is always a suitable option when a ” blank” metal surface free of organic materials and coatings is a requirement for the subsequent process, e.g., for the cathodic dip coating preparation of radiator components in the thermal management of the battery or also for the welding pre-treatment in general. The laser process has proven to achieve very good adhesion properties and bonding strength, to increase corrosion resistance and to ensure a permanently stable seal and crash resistance.
Residue-free processing also includes an efficient suction system by means of which the removed paint particles are captured. This allows 24/7 use of the systems with minimized maintenance interruptions. Additionally, process control solutions are available for the laser de-coating of battery components, which, in addition to the technology for securing the system technology, for example for measuring the laser power, also include monitoring systems for ensuring the results. These are, for example, comparative systems based on camera technology, which are able to compare the workpiece processing with corresponding reference parts inline at any time.
These and other process parameters as well as measurement data can be made available via corresponding interface standards, for example OPC UA, for data exchange with production data acquisition systems (PDA).
Efficient wire de-coating required
In the production of electric motors, enamelled copper wires with special insulation coatings made of plastics are used. Typically, these are temperature-resistant plastics such as polyamide (PA), polyamide-imide (PAI) or polyetheretherketone (PEEK). A combination of several plastics is also possible. The coatings serve to insulate and protect the copper cables. In order to achieve optimum welding and soldering results on the copper, the insulation coating must be partially removed. This paint removal can be carried out with mechanical methods or much more reproducibly and reliably with laser cleaning technology.
In the production of stators, especially in the field of e-mobility, enamelled copper wires are used that are protected against short circuits with a coating or insulation. During paint removal for welding pre-treatment, the raw material is supplied from the coil and the coated wire for the winding is cut into pieces typically 100 to 800 mm long, depending on the power and design of the motor, to produce pins.
These linear I-pins or hairpins bent into half loops are then inserted into the perforated stator plates. To create a closed winding, the half-loops must be soldered or welded together. For optimal welding, the ends of the pins are de-coated. Ideally, this takes place inline on the continuous wire, so that after the cut in the middle of the paint stripping point, two stripped paint-free wire ends are produced. The requirements demanded by the industry for wire de-coating are manifold: all-sided paint de-coating, complete absence of paint as well as high reproducibility in case of varying paint layer thickness. The paint removal process should also be contamination-free – and that with a high cycle time and minimized costs.
Increased ablation speed at reduced laser power
With a solid-state laser-based system solution, which allows processing over a large length of the running wire in the range of approx. 300 mm working area, the paint is removed verifiably residue-free with a residual fluorescence (RFU) < 5. The measurement correlates with an organic contamination and ensures that the paint is also completely removed. The wire cross-section is not measurably reduced by the reflection of the laser beam on the copper.
The new solution irradiates the wire directly with four optics and four laser systems. It is particularly suitable for changing wire types and offers high flexibility for different wire cross-sections. The cycle times are very short due to the relatively high total laser power which continuously acts on the wire (“on-the-fly”) during the feed movement: For a wire with an edge length of up to 4 mm and a 90 μm PA/PAI coating thickness, the cycle time is ~0.6 seconds.
The wire can thus be removed up to 40 % faster by means of the moving processing (also with variable speed) than with previous laser processes, which process the stationary wire. In this way, the laser power could be reduced by 70 % compared to conventional static processing and the corresponding energy consumption significantly reduced.
For the above example, at an assumed operating life of six years and a stator with approximately 150 hair pins, the paint removal costs would amount to only 0.50 euros per stator with an annual capacity of more than 150,000 stators. As in the case of the battery boxes, there are also suitable process monitoring solutions and suction techniques available for wire de-coating, which are adapted to the wire and coating requirements.