This work is the first to address the problem of dynamic deviation of tool geometric parameters from the kinematic model of a multi-axis manipulator in the additive manufacturing technology based on Gas Metal Arc Welding, better known as Wire and Arc Additive Manufacturing or WAAM.
It was found that a constant increase in the deviation of the filler wire from the tool center point negatively affects the stability of the deposition process and the surface quality of the printed objects. The deterioration in the quality and accuracy of the geometry reduces the mechanical properties of the parts, as well as the efficiency of material use and the environmental friendliness of production.
As a result of the work, the important scientific and applied problem of improving the controllability of the formation process of deposited metal layers and normalizing the irregularities of the side surfaces of WAAM parts, as well as reducing the shape deviations, was solved, which in combination improved the efficiency of material use, reduced the need for excessive post-processing, and improved the operational properties of as-deposited parts.
The scientific novelty of the work is to establish the dependence of the surface irregularities of the printed objects on the stress-strain state of the filler wire, the contact tip wear, and the dynamic processes in the molten pool, which comprehensively affect the process of bead formation from heat-resistant alloys during WAAM.
At the same time, the relationship between the magnitude of contact tip wear and the magnitude of filler wire deviation from the tool center point with the formation of irregularities of WAAM surfaces was first established and proved. The dependence of the nonlinear change of the contact tip wear rate in WAAM on the stress-strain state of the filler wire was first established by experimental and computational means. Its dynamic variation determines the contact interaction conditions between tip and wire. A tendency for the contact tip wear rate to decrease with an increase in filler wire radius of curvature or an increase in the magnitude of contact tip wear was found, which is explained by a decrease in contact force with a decrease in elastic deformation. A significant relationship was established and the functional dependence of the contact tip wear on the normal contact force, the length of the wire used, its radius of curvature, and the stiffness and hardness of the material was determined. The functional relationship between the value of the filler wire deviation from the tool center point and the contact tip wear was determined. The developed mathematical models describe the complex effect of the stress-strain state of the wire on its deflection and allow to predict the value of the deflection during the deposition process.
For the first time, theoretical and applied problems of improving the controllability of bead formation have been solved, ensuring a reduction of the shape deviation of the side surfaces in WAAM by limiting the life of the molten pool, which made it possible to establish rational deposition modes and ensure a reduction of the deviation in the deposited side surfaces by up to 60% and improve the stability of the deposited geometry by three times.
For the first time, the equivalent wall width parameter was introduced and calculated, which justifies the need to compensate for the decrease in strength of the deposited wall due to the influence of the defect caused by contact tip wear, and establishes the relationship between the strength of as-deposited and machined walls without considering the influence of microstructure.
For the first time, a method of compensating for the deviation of the filler wire from the tool center point for GMAW-based WAAM has been developed and implemented in software, according to which the coordinates of the tool center point in the kinematic model of the robot acquire a variable character, which is controlled by neural models based on experimental and statistical data. This ensures a constant positional accuracy of the filler wire with a deviation of up to ±0.2 mm in the X coordinate and ±0.12 mm in the Y coordinate.
The practical significance of the results obtained is a major improvement in the accuracy and repeatability of the deposited geometry, which can significantly increase the efficiency of material use, shorten the production time, and reduce the need for post-processing. The developed computational and experimental models allow to predict the working cycle of welding torch contact tips. The algorithm for compensation of the filler wire deviation from the tool center point was developed with the possibility of implementation not only in additive manufacturing, but also in robotic or automated welding and surfacing.
