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Laser turning with ultra-short laser pulses provides the possibility of manufacturing rotationally symmetric geometries, even of hard to machine materials as fused silica, down to a micrometer scale. In this laser micro machining approach, the laser beam is oriented perpendicularly to the rotational axis and tangentially to the material, whereas the target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. Due to the fric-tion-less laser ablation it is possible to realize a turning process in fused silica without the use of a contacting tool and therefore without causing mechanical tensions in the work piece. The processing head focuses the laser to a calculated spot size of 18 μm in diameter and the applied processing gas pressure assists in removing the ablated material. In this study, femto-second laser turning of fused silica with a diameter of 3.7 mm is investigated. The influence of the applied pulse energy is stated and the use of a trepanning optic during the turning process is characterized. Furthermore, compre-hensive parameter studies in order to optimize roughness and to find the maximum achievable abla-tion rate are shown. Limited by the mechanical speed of the rotational axis, the highest feasible abla-tion rate is 19.5 mm³/min. A roughness of Ra 0.65 μm are demonstrated.
We report on a comprehensive micromachining study of rotationally symmetric parts using femtosecond laser. A
laser turning process with tangential impingement of the laser radiation complemented by a trepanning optics is
implemented as to accomplish a true laser lathe micromachining approach. With the objective of optimized
ablation rate and reduced surface roughness, the influence of pulse energy, feed rate, trepanning diameter and
angular beam incidence, respectively, is investigated for processing stellite rods. We find the smallest feasible
feature sizes of 8.5 μm in diameter and smoothest surfaces with an arithmetic average of the roughness profile as
low as 0.18 μm. The surface roughness, however, appears to be limited by the occurrence of laser induced periodic
surface structures provoked by the femtosecond laser radiation. Furthermore, the variation of the fluence
in accordance to the incidence on a curved surface is discussed and the heat input into the material is examined
through a longitudinal cross section.
We report on the fabrication of rotationally symmetrical geometries with ultrashort laser pulses impinging the constant rotating workpiece tangentially. This particular micro machin-ing of geometry is referred to as laser turning, upon which the laser beam is, in general, orient-ed perpendicularly to the rotational axis and tangentially to the work piece. The target geome-try is realized by moving the constantly rotating specimen according to the specified geometry along the focused laser spot. In contrast to mechanical turning, laser turning induces a mini-mized amount of lateral forces through friction that might deteriorate the geometry. In this study, laser turning is examined for stellite as a function of pulse energy and pulse length in the range between 240 fs and 10 ps. Shorter pulse lengths and higher pulse energies increase the achievable ablation rate, while in the pulse length regime of below 1 ps lower roughness is achieved. With a maximum ablation rate of 1.27 mm³/min and a minimum roughness of 0.17 µm, laser turning combines both, fast processing and high surface quality.
This article discusses the process of the laser turning of rotational symmetric, cylindrical components using ultrashort laser pulses with respect to the geometrical conditions and the resulting energy distribution during the laser turning process. As a result, process predictions and potential process optimizations are feasible. Particular attention is drawn to the laser spot formation on the cylindrical surface of the work piece in conjunction with the positioning of the laser beam relative to the rotation axis of the specimen. Based on fundamental calculations and experimental results, an optimum processing strategy is discussed, whereat the use of a trepanning optic in the laser turning process and the forming of a particular surface structure is additionally being issued.
Design Rules for Hybrid Additive Manufacturing Combining Selective Laser Melting and Micromilling
(2021)
We report on a comprehensive study to evaluate fundamental properties of a hybrid
manufacturing approach, combining selective laser melting and high speed milling, and to characterize
typical geometrical features and conclude on a catalogue of design rules. As for any additive
manufacturing approach, the understanding of the machine properties and the process behaviour as
well as such a selection guide is of upmost importance to foster the implementation of new machining
concepts and support design engineers. Geometrical accuracy between digitally designed and
physically realized parts made of maraging steel and dimensional limits are analyzed by stripe line
projection. In particular, we identify design rules for numerous basic geometric elements like walls,
cylinders, angles, inclinations, overhangs, notches, inner and outer radii of spheres, chamfers in build
direction, and holes of different shape, respectively, as being manufactured by the hybrid approach
and compare them to sole selective laser melting. While the cutting tool defines the manufacturability
of, e.g., edges and corners, the milling itself improves the surface roughness to Ra < 2 µm. Thus,
the given advantages of this hybrid process, e.g., space-resolved and custom-designed roughness
and the superior geometrical accuracy are evaluated. Finally, we exemplify the potential of this
particular promising hybrid approach by demonstrating an injection mold with a conformal cooling
for a charge socket for an electro mobile