Microsecond and nanosecond lasers have been studied in the past for laser cleaning applications and, today, femtosecond lasers are also being used successfully for removing paint, rust, and surface contamination. For diamond segmented drill bits, it may be also necessary to improve the mechanical properties of the laser-welded joint, i.e., to increase the tensile strength and toughness. Therefore, in this study, we investigated the possibility of using femtosecond lasers to clean the surface before laser welding to see what effect it has on the mechanical properties of the joint. The end surface of the thin-walled tube was pretreated to remove grease and oil before laser-beam welding a powder metallurgical segment onto it and the results are compared to an untreated sample. The laser-welded seams were investigated by micro-computer tomography, break-out test, and optical microscopy. Any defects in the seams were analyzed and, according to the results obtained in this study, no cracks were found by computer tomography, a shade of grey diagram shows, and all the pre-treated samples had a higher absorption than the untreated sample. Four of the six treating parameters had a significant effect, +30% on average, and two treating parameters had a positive effect, +13.5% on average, compared to the untreated sample. In addition, the break-out values showed that only one treating parameter had a significantly, +19%, higher effect than the other treating parameters. This test showed different results from the micro-CT scan. The optimal process parameters for oil and grease removal are discussed in the conclusion. [ABSTRACT FROM AUTHOR]