The increased application for lithium batteries in electric cars and many electronic devices now utilize fiber laser welding in the product design. Components carrying electric current produced from copper or aluminum alloys join terminals using fiber laser welding to connect a series of cells in the battery.
Aluminum alloys, typically 3000 series, and pure copper are laser welded to create electrical contact to positive and negative battery terminals. The full range of materials and material combinations used in batteries which are candidates for the new fiber laser welding processes include those shown below.
Overlap, butt and fillet-welded joints make the various connections within the battery. Welding of tab material to negative and positive terminals creates the pack’s electrical contact. The final cell assembly welding step, seam sealing of the aluminum cans, creates a barrier for the internal electrolyte.
Since the battery is expected to operate reliably for 10 or more years, these laser welds are consistently high quality. The bottom line: with the correct fiber laser welding equipment and process, laser welding is proven to consistently produce high quality welds in 3000 series aluminum alloys that have connections within dissimilar metal joints.
Seals used in ships and chemical refineries and for pharmaceutical manufacturing were originally TIG welded. Because of their use in sensitive environments, these components are precision machined and ground from high temperature and chemical resistant nickel-based alloy material. Lot sizes are usually small and the number of setups are many.
The assembly of these components has been improved using fiber laser welding.
Justification to replace the earlier robotic arc welding process with fiber laser welding using a four axis cartesian coordinate machine tool were:
- consistently higher quality of the laser welds,
- ease of changeover from one component configuration to another that reduced setup time,
- automating the laser welding process using a four-axis CNC laser machine improved throughput while decreasing assembly costs.
Laser welding nickel and titanium-based aerospace alloys requires control of the weld geometry and weld microstructure, including minimizing porosity and controlling grain size. In many aerospace applications, the fatigue properties of the weld are a critical design criteria. For this reason, designers nearly always specify that the weld surfaces be convex, or slightly crowned, to create a reinforcement of the weld.
To achieve this, a 1.2 mm diameter filler wire is used in the automated process. Addition of the filler wire to a butt joint leads to a consistent crown on both the top and bottom weld bead. The selection of the alloy of the wire also contributes to the weld’s mechanical properties by ensuring a sound microstructure of the weld.
Hermetic sealing electronics in medical devices, such as pacemakers, and other electronic products has made fiber laser welding the process of choice for applications requiring the highest reliability. A recent advance in the hermetic welding process has addressed concerns about laser welding and the end point of the weld, a critical location point in completing the hermetic seal. Previous laser welding techniques resulted in a depression at the end point when the laser beam is turned off, even when ramping down the laser power. Advanced control of the laser beam eliminates the depression in both thin and deep penetration welds. The result is consistent geometry and lack of porosity at the end point with improved cosmetic appearance and more reliable hermeticity.
The ability to create products using different metals and alloys greatly increases both design and production flexibility. Optimizing properties such as corrosion, wear and heat resistance of the finished product while managing its cost, is a common motivation for dissimilar metal welding.
Joining stainless steel and zinc coated (galvanized) steel is a one example. Because of their excellent corrosion resistance, both 304 stainless steel and zinc coated carbon steel have found widespread use in applications as diverse as kitchen appliances and aeronautical components.
The process presents some special challenges, particularly since the zinc coating can present serious problems with weld porosity. During the welding process, the energy that melts steel and stainless steel will vaporize the zinc at approximately 900⁰C, which is significantly lower than the melting point of the stainless steel.
The low boiling (vaporization) point of zinc causes a vapor to form during the keyhole welding process. In seeking to escape the molten metal, the zinc vapor may become trapped in the solidifying weld pool resulting in excessive weld porosity. In some cases, the zinc vapor will escape as the metal is solidifying creating blowholes or roughness of the weld surface.
With proper joint design and selection of laser process parameters, cosmetic and mechanically sound welds are readily produced.
Laser welding shouldn’t be considered ‘nontraditional’ given the many applications over many years. Now with fiber laser welding, new product applications are everywhere – in electronic packages, medical devices, the vehicles we drive, the aircraft in which we fly, in process equipment and sensors. The list is almost endless. Most of the earlier limitations of laser welding no longer exist or are easily overcome.
While fiber laser welding may at first be intimidating, it has been repeatedly demonstrated to enable new product designs with significant improvements in cost, quality and performance. Laser system suppliers, with available applications engineering staff, now provide turnkey solutions. That includes not only the machine but also fixturing and easily learned processing techniques.
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