Contactless surface flattening of additive manufactured nickel-base alloy parts by ultra-short pulsed laser ablation

Nickel-base alloy samples produced by selective laser melting (SLM) exhibit high surface roughness of 14.2 μm ±4.8 μm standard deviation at the sidewalls. Ultra-short pulsed (USP) laser ablation at a pulse duration of 10 ps is applied to reduce the surface roughness. This flattening method does not require a melting phase. The influence of the tilt angle and the orientation of the SLM layers on the surface topography of the sample is investigated. Orthogonal laser ablation of Ni-base alloy samples leads to irregular surface topography and exposure of sharp spikes. Surface flattening by laser ablation is demonstrated applying a tilt angle of 80° in combination with a projected pulse fluence of 0.21 J/cm². A significant influence of the tilt angle and SLM layer orientation on the surface roughness is observed.ISSN:2212-827

300 fs pulsed laser ablation of Al2O3 ceramic and introduction of a predictive model

In this study a calculation routine for predicting the ablation topography considering the angle of incidence and the evolution of the ablated surface pulse by pulse is presented and applied. Laser processing of Al2O3 ceramic is studied by the ablation of single craters as well as by macroscopic ablation pockets for a pulse duration of 300 fs at a wavelength of 515 nm. The threshold fluence is determined and compared for different process configurations and it is demonstrated that lower scanspeed leads to a higher removal rate. The accuracy of this method is evaluated in an ablation experiment. The presented method is useful for predicting the surface topography in order to optimize the scanpath or to apply machine learning algorithms.ISSN:0264-1275ISSN:1873-419

Picosecond pulsed laser machining of hardened martensitic stainless steel drive shaft

A fundamental method for estimating the laser parameters and for predicting the achievable ablation rate is demonstrated for hardened martensitic stainless steel X46Cr13. The laser ablation rate is evaluated for a range of pulse energies. The effective threshold fluence for ablation and the effective penetration depth are determined for a low and a high energy regime applying the Neuenschwander model. These parameters are used for numerical prediction of the ablated geometry. A very time efficient processing strategy and parameter set is selected and applied for laser machining of micro channels into a high precision drive shaft to increase friction for torque transmission leading to a processing time of 30 s per part, which corresponds to a structuring rate of 0.88 mms-1 . The deviation between the simulation and the ablated depth in the experiment are measured to be below 7 % at a total ablation depth of 25 µm. This demonstrates that the Neuenschwander model is suitable to determine the parameters needed for the prediction of the geometry resulting from an ablation process on martensitic stainless steel.ISSN:2212-827

Pulsed laser ablation of cutting edge geometries in alumina and zirconia composites at 200 fs and 2 ps

In this study, the feasibility of lasermachining cutting edges into mixed oxide ceramics such as alumina toughened zirconia (ATZ) and zirconia toughened alumina (ZTA) is evaluated. A simplified standard wedge geometry is machined into cylindrical samples by combining orthogonal and quasi-tangential laser machining strategies. For the experiments a laser source emitting a wavelength of 515 nm is applied and the pulse duration is varied between 0.2 and 2 ps. As target parameters the cutting edge radius and Sa value of the rake face are analyzed. The heat affected zone is analyzed by FIB SEM. An edge radius of 6.7 ± 1.6 μm at an Sa value of 0.115 μm in the case of ZTA and an edge radius of 4.9 ± 0.3 μm at an Sa value of 0.125 μm in the case of ATZ can be achieved. The results are promising for the application of laser ablation towards the manufacturing of cutting edges in oxide ceramics such as ATZ and ZTA.ISSN:0272-8842ISSN:1873-395

Cold surface treatments on fiber-reinforced plastics by pulsed laser

When producing fiber-reinforced plastic (FRP) suitable for mass production, new technologies have to be developed to overcome existing challenges such as increased efficiency in resource consumption or higher process flexibility. In the past, laser processing has been shown to yield important advantages such as non-contact processing, no tool wear and high design flexibility.Pulsed laser ablation of FRP offers a promising alternative to state of the art mechanical blasting. The selective matrix removal enables a high potential to improve adhesive bonding, molding processes and coating deposition of lightweight materials, especially FRP-metal or FRP-ceramic hybrids. The resulting increase in surface area exhibits forms lock characteristics and simultaneously provides an expanded interface area. As a result, 40 % higher tensile strength can be reached in pull-off tests compared to a mechanically blasted organic sheet surface, joined by thermal spraying of aluminum on carbon fiber-reinforced epoxy (CFRP)

Laser Ablation Study of Cutting Ceramics with Consideration of the Beam Inclination Angle

Silicon alumina nitride (SiAlON) and alumina toughened zirconia (ATZ) ceramics are applied for ceramic cutting tools to machine, e.g., cast iron, nickel base alloys and other difficult-to-machine materials. The state of the art technology for manufacturing of the cutting tool geometry is grinding. Laser processing of ceramics is already studied in terms of ablation rate and roughness evaluation with the application of dental implant manufacturing. In the present study, laser machining of the mentioned ceramics is explored with a laser beam source of 1064 nm wavelength and 10 ps pulse duration (FWHM). The angle dependent energy specific removal rate is described in a model and the optimal pulse fluence for the different materials and the irradiation angles can be derived. For processing at irradiation angle of up to 75° no decrease of the relative absorption could be observed. For ATZ, lowest surface roughness is determined for both, orthogonal and quasi-tangential processing angle. For SiAlON, the roughness decreases constantly for higher tilt angles. A significant difference in the material answer with change of the sample composition can be detected and the results show the potential of further developing SiAlON ceramics towards machineability for laser ablation.ISSN:1996-194

Ultra-short pulsed laser processing of single crystalline diamonds for tooling applications

This study investigates the feasibility of using ultra-short pulsed (USP) lasers to fabricate single crystalline diamond (SCD) tools. SCD has exceptional mechanical, tribological, and thermal properties and offers excellent performance in the precision machining of hard and brittle materials over polycrystalline diamond and diamond-coated tools. However, the anisotropic nature of the SCD makes it difficult for laser machining because the material shows susceptibility to cracking, defect growth, and breakout depending on its crystallographic orientation. Anisotropy needs to be considered while optimizing the geometry of the tool to minimize wear and improve tool performance. An advanced four-axis laser machining approach with optimized laser parameters and temporal beam shaping is used to mitigate challenges related to defect growth and orientation dependence, leading to the production of high-quality single cutting-edge SCD tools. Cylindrical diamonds and diamond crystals with top surface planes { 100 } and { 111 } are used in the study. The occurrence of defects in the diamond when laser machined and their dependence on the crystallographic orientation along the circumference of the diamond is thoroughly investigated via SEM, electron backscatter diffraction, and light microscopy images. Finally, the laser-manufactured SCD tools are tested by turning fully sintered zirconia ceramics (3Y-TZP-A). USP laser machining of SCD is demonstrated to be a viable alternative to traditional manufacturing methods for producing high-quality SCD tools with unique properties and performance. The results further emphasize the importance of understanding the crystallographic orientation dependence when laser machining crystalline materials like diamonds.ISSN:1938-1387ISSN:1042-346