| Abstract Scope |
Introduction:
Wobble laser welding is a highly effective welding technique that utilizes a combination of rotational and linear motion of the laser beam to produce high-quality welds. This technique is becoming increasingly popular in industrial applications due to its ability to bridge gaps and control weld attributes superior to that attainable in traditional welding. Welding speed, amplitude and frequency of the wobble, laser beam radius, laser power, and alloy composition are important variables in the outcome of wobble welding. Since the roles of these variables are not well understood, we examine the heat transfer mechanism, power density distribution, fusion zone geometry, and fluid flow in the molten pool as a function of important process variables. The resulting quantitative understanding from the experimentally validated model would allow the selection of optimum process variables based on scientific principles.
Technical Approach:
One of the most important factors in wobble laser welding is the power density distribution during welding. The power density distribution determines the amount of heat input at different points on the surface of the workpiece. This distribution is examined numerically since it plays a crucial role in determining the weld attributes such as the depth of penetration. By understanding the power density distribution, we can optimize the welding parameters to achieve the desired fusion zone geometry and other attributes that are affected by heat transfer. The distribution of heat flux serves as an input into a computer program that solves the energy equation to obtain fusion zone geometry, cooling rates, temperature gradients, and other important parameters that cannot be obtained by experiments alone. The solution of the energy equation and the Navier-Stokes equations provide insight into the complexities of wobble welding by providing important information such as the temperature and velocity fields, cooling rates, and temperature gradients. This approach enables the evaluation of the roles of important variables of the wobble welds such as the fusion zone geometry, temperature fields, and cooling rates. Experiments are conducted to evaluate the fusion zone geometry as a function of important wobble parameters such as laser power, wobble amplitude, and frequency for a nickel base precipitation hardening alloy Inconel 740H.
Results and discussions:
Our experimental and theoretical results indicate that important wobble variables such as the wobble amplitude, beam radius, frequency, scanning speed, and laser power significantly affect the power density distribution, temperature distribution and fusion zone geometry. Convective heat transfer plays an important role in the distribution of heat in the fusion zone. Experimental results with alloy Inconel 740H show that higher power always resulted in a higher depth of penetration in keyhole mode wobble welding. Higher amplitude resulted in wider and shallower fusion zone geometry. The variation of wobble frequency in the range 150 to 411 Hz did not significantly affect fusion zone geometry in alloy Inconel 740H.
Summary and conclusions:
Depending on the position of the heat source at any given time, the laser beam travels along the same or the opposite direction to the welding direction. Locally asynchronous motion, i.e., the movement of the laser beam in the opposite directions to the welding direction is the origin of several special features of wobble welding. This wobbling motion helps to distribute heat input more evenly. The time average power density distribution is not radially symmetrical. This asymmetry originates from the location-dependent direction of motion of the heat source. As a result, the transverse cross-section of the fusion zone often exhibits geometric asymmetry between the left and right halves. The selection of the process parameter combinations, particularly the wobble amplitude, beam radius, wobble frequency, scanning speed, and laser power provides unprecedented flexibility in tailoring fusion zone attributes. The shape of the fusion zone may change from flat bottom to the traditional hemispherical shape depending on the selection of process variables. The temperature and velocity fields and fusion zone geometry vary significantly depending on the wobble welding variables providing unprecedented process flexibility. |