Selective laser melting is gaining importance to manufacture reliable and highly complex parts. However, the surfaces of the selective laser melted parts exhibit for many applications an insufficient high roughness, thus require subsequent post processing steps. A relatively new way to reduce the surface roughness is the laser polishing technique. In the present paper, additively manufactured AlSi10Mg samples were polished with different laser intensities and laser modes. The investigations contain the potential of roughness reduction and enhancement of the surface appearances, which can be achieved by laser polishing of the as‐built surfaces. An initial arithmetic mean roughness of 8.43 μm was remarkably reduced up to 98 %. The compositions of the polished surfaces were detected and the surface appearances were examined. Reasons and mechanisms were explained and depicted for the occurred shade formations on the polished surfaces. High laser intensity led to segregation of silicon and magnesium on the surface. A higher laser intensity enabled an increased melt depth within the conture layer of the selective laser melting structure. Through increasing melt depth, a porosity of max. 1.7 % was detected in the remolten area. Hardness investigations of the initial and laser remolten cross section revealed no significant reduction in hardness.

Laser powder bed fusion is a well‐established 3D printing technique for metal alloys, but exhibits a poor surface quality. Laser polishing provides the possibility of a fast contact‐free and fully‐automatable surface treatment. This paper deals with the experimental investigation of laser polishing of laser powder bed fusion parts made of aluminium AlSi10Mg. Laser polishing is done with a 4 kW solid state disc laser in combination with a multi‐axis system and a one dimensional scanner optic. The laser is operated at continuous and pulsed operation mode. The parameter study reveals a high dependency of the achievable roughness on the laser beam intensity, the track and pulse overlap, the energy density and the number of polishing passes and polishing directions. Pulsed laser polishing mode with up to four passes from different directions revealed the lowest surface roughness of 0.14 μm Ra. With respect to the initial average surface roughness of Ra = 8.03 μm a reduction of the surface roughness of greater than 98 % could be achieved. Polishing with continuous laser radiation at one polishing pass resulted in Ra = 0.23 μm at an area rate of 20 cm2/min. Laser polishing using four passes achieved a further improvement up to Ra = 0.14 μm.

No abstract

Conventional polishing of components is a time-and labor-intensive process. Moreover, manual polishing mostly depends on the processor's abilities. In accordance with these and additional difficulties, there is a strong need for automatable and efficient variants. For this purpose, polishing by means of laser beam, which enables a contact free and automatable processing of surfaces, provides a promising alternative. This paper investigates the laser polishing of the aluminum alloy AlSi9MnMg. Aluminum poses a particular challenge for laser polishing, due to high level of reflection, high thermal conductivity, and high coefficient of thermal expansion. For the investigations, a disk laser with a maximum power of 4000 W was used. The processing took place with pulsed wave laser beam at a pulse frequency of 1000 Hz and a minimal pulse duration of 0.3 ms as well as a continuous wave laser beam. The beam guidance was done by 1D-scanner optics in a highly pure inert gas atmosphere. The samples were first generated by vacural pressure and gravity die casting and afterward (belt) ground with a grain size of mesh 180 resulting in a roughness of the initial surfaces from Ra ¼ 1 lm to Ra ¼ 4 lm. A cleaning of the surfaces by means of short pulsed wave laser beam with ns pulse duration followed. The samples were analyzed quantitatively by perthometer for determining surface characteristics Ra, Rz, and Rt according to EN ISO 4288 as well as qualitatively using a white light interferometer and a microscope. First of all, the influence of the manufacturing process of the components on the laser polishing was investigated. A dependence is detected on laser polishing with pulsed and continuous wave laser beam, resulting in more favorable pressure die casted samples compared with gravity die casted samples. Both laser processing variants lead to a reduction of roughness of the initial surfaces in the range of Ra ¼ 2.17 lm to Ra ¼ 2.34 lm to a minimum roughness reached by laser polishing with pulsed wave laser beams of Ra ¼ 0.19 lm and with continuous wave to a minimum of Ra ¼ 0.15 lm. The achieved area rates at a continuous wave mode ranged between 20 and 60 cm 2 /min, whereas pulsed wave laser beams achieved only 5.5 cm 2 /min due to hardware-specific limits of the used system.