Innovative micro-tool manufacturing using ultra-short pulse laser ablation

The commonly used Gaussian intensity distribution during the laser-based processing of metals can negatively affect melt pool stability, which might lead to defects such as porosity, hot cracking, or poor surface quality. Hot cracking is a major factor in limiting production rates of high-strength aluminium alloys in laser-based processes such as welding or the powder bed fusion of metals (PBF-LB/M). Going away from a Gaussian intensity distribution to ring-shaped profiles allows for a more even heat distribution during processing, resulting in more stable melt pools and reduced defect formations. Therefore, the aim of this study is to investigate the influence of different laser beam profiles on the processing of high-strength aluminium alloys by using a multicore fiber laser, allowing for in-house beam shaping. Single weld tracks on the aluminium alloy EN AW-5083 are produced with varying laser powers and weld speeds, as well as different beam profiles, ranging from Gaussian intensity distribution to point/ring profiles. The molten cross sections are analyzed regarding their geometry and defects, and the surface roughness of the weld tracks is measured. By using point/ring beam profiles, the processing window can be significantly increased. Hot cracking is considerably reduced for weld speeds of up to 1000 mm/s compared to the Gaussian beam profile. Furthermore, the melt pool width and depth are more stable, with varying parameters for the point/ring profiles, while the Gaussian beam tends to keyhole formation at higher beam powers. Finally, a strong decrease in surface roughness for the point/ring profiles, accompanied by a significantly reduced humping effect, starting even at lower beam powers of 200 W, can be observed. Therefore, these results show the potential of beam shaping for further applications in laser-based processing of high-strength aluminium alloys.

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Influence of Novel Beam Shapes on Laser-Based Processing of High-Strength Aluminium Alloys on the Basis of EN AW-5083 Single Weld Tracks

The influence of thermophysical properties of materials on the porosity and microstructure of dissimilar lap joints between laser-welded Al-Si-Mg cast and Al-Mg-Si-Cu wrought aluminum alloys was investigated. The low thermal conductivity and viscosity of the weld would promote bubble escape, while the high electrical conductivity of the base material would increase the melt depth and reduce the convection intensity in the melt pool, thus increasing the difficulty of bubble escape. The variation in thermophysical properties did not significantly impact the distribution of elements, the type of precipitated phases, and the dislocation density, however, it did affect grain morphology. Differences in thermal diffusion coefficients between base materials created conditions for constitutional supercooling, increasing the likelihood of a columnar-to-equiaxed transition. Moreover, the temperature difference between the liquid phase lines of the weld and base materials facilitated the liquid base material flushed into the weld to solidify before mixing, resulting in an "island" formation. This "island" acted as a heterogeneous nucleation site, leading to equiaxed grain layer formation in the lowest zone of the weld. The variations in thermophysical properties exerted an influence on the tensile strength by impacting both the melt depth and the grain morphology of the weld but did not yield a significant impact on the average microhardness. 

Effect of thermophysical properties on porosity and microstructure of laser welded cast and wrought aluminum alloy dissimilar lap joints

FEM-Design & fabrication of a micro-milling tool by tangential laser machining

Exploring the application of laser thermal effect in the multilayer gradient coatings designed by electrochemical deposition: Parameters, advancements, and limitations

Analysis on the influence of vapor capillary aspect ratio on pore formation in laser beam welding of aluminum

The ongoing development of lasers with integrated beam-shaping features offers new opportunities for research in the field of laser beam welding. Main challenges for laser welding of aluminum alloys, such as AW-5083 or AW-6082, are pore formation and cracking. The locally adapted power distribution has a major influence on the keyhole required for deep penetration welding and therefore on occurring weld defects. To determine the reasons, the use of synchrotron radiation during the welding process enables the visibility of the keyhole shape. This investigation contains an analysis of the keyhole and melt pool shape based on the high-speed video images of the synchrotron radiation. The variation of the power ratio of center beam to ring allows a comparison of the influence of the beam shaping method. To stabilize the keyhole, a temporal power modulation is used for the ring. The results show an influence of the ring mode on the keyhole depth and the melt pool shape. The videos allow an analysis of different mechanisms for pore formation, such as the collapse of the keyhole.

Influence of ring-shaped laser beam during welding of AW-5083 and AW-6082

Pulsed laser ablation is increasingly being used for the manufacturing of cutting tools, both with undefined and defined cutting edges. The machining of cutting inserts made of ultra-hard material with pulsed lasers is an industrially established process, while the production of more complex geometries, such as fluted tools is being developed. Ultrashort-pulsed laser processes, contrary to conventional tool manufacturing processes, are not based on the mechanical removal of material and are thus free of wear or cutting forces. Especially for the production of micro tools are cutting forces detrimental: the resulting deformations need to be compensated and can lead to tool failure during production. The absence of forces make laser processing an interesting alternative to the grinding of micro tools. In this paper, processes for manufacturing carbide micro cutting tools with defined cutting edges using an ultra-shortpulsed laser are detailed. Processing strategies to machine a tool using a setup consisting of four mechanical and two optical axes are developed. Tungsten Carbide (WC) single-edge micro milling tools-with Ø 200 μm-are machined using a laser source (τp<12 ps, λ= 532 nm) with an average power of Pmax= 4 Watt. By using self-limiting laser ablation finishing processes, high surface quality and geometrical accuracy are achieved. No significant thermal damage of the material by the laser processes can be observed. Milling experiments in low alloyed copper with the laser produced tools demonstrate the applicability of such technology for the manufacturing of WC micro milling tools.

Laser manufacturing of carbide micro milling tools

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Papers

Analysis on the influence of vapor capillary aspect ratio on pore formation in laser beam welding of aluminum

Influence of ring-shaped laser beam during welding of AW-5083 and AW-6082

FEM-Design & fabrication of a micro-milling tool by tangential laser machining

Laser manufacturing of carbide micro milling tools