There is often a need to join billets being extruded in the forward extrusion processes in order to preserve the continuity of manufacturing of products. The primary problem connected with joining while extruding is to ensure the required state of stress, deformation and temperature assuring a good weld quality. The paper contains numerical analyses of the transverse joining processes of billets in the course of forward extruding. The impact of the friction between welded objects on the material flow in vicinity of the joints is analyzed. A numerical method for determination of the weld length at the longitudinal section, by assuming the homogeneity of the strain rate at both sides of the joined elements contact line, is proposed. Three cases of the forward extruding are analyzed. Two friction shear factors equal to $ m=0.4$ and $ m=0.9$ at the billets interface are modelled for each case and weld the lengths at the longitudinal sections are presented. In addition; distributions of the flowing material velocities and effective strains in the weld vicinity are added for all tested processes.