Due to its thermal and chemical resistance, borosilicate glass finds a wide range of applications in optics, chemical laboratories and in glass apparatus engineering. For the manufacturing of complex glass components, the welding of semi-finished glass products is essential. In the majority of industry, this is realized by operating gas burners in manual processes with low efficiencies. Here, laser-based processing offers the advantage of local heating with high efficiency, since borosilicate-glass has a high absorption for CO2-laser radiation. For this purpose, the welding partners are heated with the CO2-laser, while a borosilicate rod is fed under an angle into the welding zone. In this paper, the welding of borosilicate glasses in butt and 90°-angles using CO2-laser irradiation is demonstrated. Prior to the manufacturing of the weld seams with additional material and the examination via 3-point bending tests, parameter studies are performed for the welding of blind weld seams with regard to the weld seam geometry.