This study examines the possibility of applying lasers for the formation of laser-affected bands in hardenable steel sheets, with a specific focus on how the formation of these hardened bands can improve the accuracy of the single point incremental forming process (SPIF). For this purpose, the process parameters for the hardening process have been chosen using finite-element (FE) modeling. The results of the modeling have been validated by temperature field measurements obtained from IR camera observations. The microstructural analysis of the laser-affected zones has been performed using optical microscopy (OM) and scanning electron microscopy (SEM). These investigations confirm a phase transformation to a martensitic structure during laser scanning, and microhardness (HV0·1) results show a hardness increase by a factor of about three in the laser-affected region in comparison to that of the base metal (BM). Finally, using a laser assisted single point incremental forming (LASPIF) setup, hardened bands have been generated for preprocessing and intermediate processing during the different phases of a SPIF procedure. Geometric accuracy studies show that appropriate use of hard martensitic bands can increase the process accuracy through significantly reduction of an unwanted sheet deformation, and has the potential to eliminate the need for a backing plate.

Incremental Sheet Forming processes suffer from stringent forming limits, restricting the range of producible geometries. Through in-process cooling of the sheet to cryogenic level, this paper explores the potential of altering material properties benefiting the formability and residual hardness of different aluminium alloys. Global cooling of aluminium sheets with liquid nitrogen and dry ice allows to reach temperatures of 78K and 193K respectively. Extended with experiments at room temperature (293K), these tests form a base for comparison of surface quality, formability and residual hardness. As an aluminium alloy commonly used for its high strength to weight ratio, but suffering from limited formability compared to draw-quality steels, AA5083-H111 is of interest for cryogenic treatment. AA1050-H24 is included in the test campaign as a base for commercially pure aluminium.

Recent advances towards patient specific titanium sheet based medical implants introduce a new challenge for the fixation of these implants to bones. Mainly, the use of locking screws requires an implant thickness of approximately 2 mm for screw thread formation. Friction drilling is a hole-making process that displaces material to create a bushing below the sheet rather than extracting material. This experimental study explores the influence of axial force, rotational speed, and workpiece pre-heating temperature on the bushing height and thickness during friction drilling of titanium grade 2 sheets. The drilling parameters are optimized for both drilling at room temperature and at elevated temperatures for maximum bushing thickness with at least a bushing height of 1 mm. Subsequently, the samples are characterized for their microstructure and hardness, revealing preserved strength with a larger thermomechanical affected zone (TMAZ), a more gradual hardness gradient around the drill zone, and a significant reduction in microdefects in the bushing structure of the pre-heated sheets.

The effect of localized laser hardening on the dimensional accuracy of incrementally formed steel sheets has been studied. By dynamically heating by means of laser beam scanning (500W Nd:YAG) the temperature of the sheet reaches the austenization temperature and by subsequent self-quenching a hard martensitic structure will form. Using FE modeling, a laser power setting of 202 W, scanning velocity of 600 mm/min and beam diameter of 6 mm were selected as optimum processing parameters for transformation hardening. Hardness tests were performed in order to investigate the hardness profile along the depth and width of the laser hardened zone. Experimental results reveal that generation of a selectively hardened martensitic band, formed by transformation hardening, can increase the accuracy of the incrementally formed part.

Local reinforcement of titanium sheet by means of GTAW droplet deposition for threaded connections VANHOVE Hans, KURTOV Oleksandr, DEJANS Arnout, OZDEN Ecem