Standard laser welding heads are designed to focus a collimated laser beam to a required spot size, keeping the beam path static through the beam delivery and a static spot at the focal plane.
This standard configuration limits each setup to a specific application.
Wobble heads, on the other hand, incorporate scanning (oscilation or wobbling) mirror and lenses technology inside a standard laser weld head.
By moving the beam with internal mirrors, the focal spot is no longer static, and can be dynamically adjusted by changing the shape, amplitude, and frequency.
Laser wobble welding or Laser beam stir welding is increasingly being utilized to improve weld quality, properties, and reliability for a wide range of industries, and improvements in laser beam quality and delivery capabilities are helping to spur this growth. The process has wide application in the automotive, aerospace, and fabrication industries, to name a few.
The term "laser stir welding" or laser wobble welding was coined to describe a process in which the laser keyhole or vapor cavity was manipulated or oscillated at a relatively high rate to cause a stirring action within a larger pool. It has also been referred to as laser beam welding with wobbling. The phenomena is centered upon proper selection of the energy density of the laser and relative rate and motion of beam oscillation based on the thermal properties of the material being processed.
The ultimate effect when the correct parameters are chosen is the integration of energy distributed over the beam oscillation area, allowing the keyhole to cause a hydrodynamic stirring action at the rapidly moving beam. The total energy integrated over the oscillation region is responsible for maintaining the large molten pool, while the local intensity of the beam sustains the vapor cavity during oscillation and stirring within the molten pool. The rapid motion of the oscillated beam establishes a self-healing nature of the keyhole.
Research conducted during the development of the process had shown that laser beam welds produced on alloys using the laser stir welding process displayed less weld defects when compared to traditional laser beam welding, along with concomitant benefits of increased size of the weld to accommodate gaps and improve shear strength of lap joints, and enhanced ability to feed filler material. It was also established that by proper selection of parameters that govern the input and distribution of energy in relation to the thermal diffusivity and fluidity of the base metal, the process is easily applied to other alloy systems.
Recent research and applications of laser stir welding have increased significantly since its inception, based on the underlying principle that rapid oscillation of the vapor cavity within the molten pool provides a hydrodynamic stirring action that may reduce defects related to gas absorption and keyhole instability, while also providing simultaneous benefits associated with the formation of a larger weld pool.
The principle of the laser stir welding process remains the same, but laser sources providing improved beam quality and galvanometer-based systems for beam manipulation enable the process to be effectively adopted and utilized for a broad range of industrial applications.
A factor of 2-3 increase in both process parameters can be achieved compared to conventional laser welding without Wobbling!
Larger Wobbling Spot Size helps bridging bigger gaps
The required tolerance for fit-up is reeduced
The lower tolerances needed reduce the machining costs
Non tolerance parts can still be used : less scrap, less losses = big savings
Maximum yield and quality of welded part
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. As shown below, the top and bottom surfaces of an overlap weld of 0.6 mm thick 304 stainless steel and 0.5 mm thick zinc coated steel exhibit no cracking, porosity, or blowholes.
- left : Bottom bead (back side) of lap weld of 304 stainless steel and zinc coated steel. Shown is the zinc coated steel surface.
- right: Top bead of lap weld of 304 stainless steel and zinc coated steel. Shown is the stainless steel surface.
A material’s weldability is a factor. Most common materials a fab shop will process—be it carbon steel, stainless, or aluminum—have been successfully laser welded for years, using both continuous wave and pulsed modes. Lasers have performed dissimilar-metal welding ( Sample picture is copper joined with stainless steel by fiber laser welder), and specialized weld joint designs in galvanized material have even accounted for zinc outgassing. Moreover, a multikilowatt fiber laser has been shown to successfully weld even the most challenging of materials, including copper
To achieve the wobble method, a fixed laser is optically manipulated with attachments, such as our wobble head, that allow the laser to wobble to a programmed pattern down the seam of the weld. The wobble method produces a superior weld by greatly reducing imperfections, increasing consistency, reducing material cost and providing more tolerance for process variables.