Lazarchuk K. Improving the process of joining wood-working band saws by laser welding

The dissertation deals with the solution of an urgent scientific and technical problem - improving the join of wood-working band saws. Sawing with a band saw is a simple, cheap and cost-effective sawing method, which provides quite satisfactory results when cutting wood. At present, the most common methods for joining band saws into an endless belt are soldering or welding. Laser welding is the most effective method for joining together the ends of band saw blades in the presence of high requirements for reliable joining and it can be used to obtain a high-quality weld seam without deformation and distortion. A physical model of laser welding of band saws has been developed, which includes definition of weldability, the sequence of formation of a welded joint and methods for forming its structure, which is the basis for developing a computer model of laser welding. On the basis of the physical model, an electronic model of laser welding has been developed which is based on four main parameters of welding process: temperature, time, heating rate and cooling rate. To determine the effect on the strength of the saw after laser welding, experiments were performed on the basis of mathematical planning and two variables were chosen: the angle of the weld, the second factor is the feed speed of the laser welding head. The output parameter is the tensile strength of the samples. The coefficients of the regression equation for two variable factors are established in the form of an incomplete quadratic equation, both in normalized and explicit form. By comparing welding at different angles, it was found that, in terms of absolute value, the tensile strength of a seam welded at angles of 15–25 degrees approaches the tensile strength of the base material, which means that such values of the indicated angles are optimal for welding. It has been experimentally established that the use of laser butt welding at an angle to the line of action of maximum bending stresses for band saw blades can reduce the noise level of the band saw machine by 10-15 dB compared to the use of 6 saws with traditional welding. A new design of the damping device on the upper branch of the band saw is proposed, which will reduce the noise level of the band saw machine by another 5-10 dB and bring it closer to the level of sanitary norms. To improve the joint, it is proposed to equalize the hardness of the area of the welded joint of the band saw after welding, and a utility model patent was obtained for this.