arXiv subjects

Kilian Schäfer

Publications and source records attributed to Kilian Schäfer.

4 recordsLinked to original sources

arXiv2026

Muscle-inspired magnetic actuators that push, pull, crawl, and grasp

Functional magnetic composites capable of large deformation, load bearing, and multifunctional motion are essential for next-generation adaptive soft robots. Here, we present muscle-inspired magnetic actuators (MMA), additively manufactured from a thermoplastic/permanent magnet polyurethane/Nd2Fe14B (TPU/MQP-S) composite using laser powder bed fusion (LPBF). By tuning the laser-energy scale between 1.0 and 3.0, both mechanical stiffness and magnetic response are precisely controlled: the tensile strength increases from 0.28 to 0.99 MPa while maintaining 30-45% elongation at break. This process enables the creation of 0.5 mm-thick flexural hinges, which reversibly bend and fold under moderate magnetic fields without damage. Two actuator types are reported showing the system versatility. The elongated actuator with self-weight of 1.57 g, magnetized in its contracted state, achieves linear contraction under a 500 mT field, lifting 50 g (32x its own weight) and sustaining performance over at least 50 cycles. Equipped with anisotropic frictional feet, it supports movement of a magnetic crawling robot that achieves up to 100% locomotion success on textured substrates. The expandable actuator exhibits reversible opening and closing under a 300 mT field, reliably grasping and releasing different objects, including soft berries and rigid 3D printed geometries. It can also anchor in a tube while holding suspended 50 g loads. This work demonstrates a LPBF-based strategy to program both stiffness and magnetization within a single material system, enabling remotely driven, reconfigurable, and fatigue-resistant soft actuators. The approach opens new possibilities for force controlled, multifunctional magnetic soft robots for adaptive gripping, locomotion, and minimally invasive manipulation of biomedical tools.

cs.RO↗

arXiv2023

Magneto-active composites with locally tailored stiffness produced by laser powder bed fusion

Additive manufacturing technologies enable the production of complex and bioinspired shapes using magneto-responsive materials, which find diverse applications in soft robotics. Particularly, the development of composites with controlled gradients in mechanical properties offers new prospects for advancements in magneto-active materials. However, achieving such composites with gradients typically involves complex multi-material printing procedures. In this study, a single-step laser powder bed fusion (LPBF) process is proposed that enables precise local adjustments of the mechanical stiffness within magneto-active composites. By utilizing distinct laser parameters in specific regions of a composite containing thermoplastic polyurethane and atomized magnetic powder derived from hard magnetic Nd-Fe-B, the stiffness of the composite can be modified within the range of 2 to 22 MPa. Various magneto-responsive actuators with locally tailored stiffness are fabricated and their magnetic performance is investigated. The enhanced response exhibited by actuators with locally adjusted mechanical properties in comparison to their homogeneous counterparts with identical geometries is shown. As a demonstration of a biomedical application, a magnetically responsive stent with localized adjustment is presented with the ability to meet specific requirements in terms of geometry and local stiffness based on an individual's anatomy and disease condition. The proposed method presents an approach for creating functionally graded materials using LPBF, not only for magneto-active materials but also for several other structural and functional materials.

physics.app-ph↗

arXiv2023

Laser Powder Bed Fusion of anisotropic Nd-Fe-B bonded magnets utilizing an in situ mechanical alignment approach

Nd-Fe-B bonded magnets are an important class of permanent magnets, employed in many technological sectors. The Additive Manufacturing (AM) processes enables the fabrication of net-shape bonded magnets with complex geometries, allowing to tailor their magnetic stray field specifically for a given application. A crucial challenge to be addressed concerning AM of bonded magnets is the production of magnetically anisotropic components. The common approaches presented in the literature up to now, required a post-printing procedure or the complex integration of a magnetic field source into the AM process. Here, we present a technique to fabricate anisotropic bonded magnets via Laser Powder Bed Fusion (LPBF) by utilizing the mechanical alignment of anisotropic particles in a single step, without the need for a magnetic field source. Anisotropic bonded magnets were fabricated using a mixture of anisotropic Nd-Fe-B powder (MQA-38-14) and polyamide-12 (PA12). This magnetic powder consists of ellipsoidal particles, where the easy magnetization axis is distributed perpendicular to their longest side, which can be exploited to generate magnetic texture. Depending on the particle size used as feedstock, the degree of alignment ( ) can be tailored to a maximum of = 0.78. The fabricated anisotropic bonded magnets exhibited a maximum remanence of Jr = 377 mT and an energy product of (BH)max = 28.6 kJ/m3, respectively.

physics.app-ph↗

arXiv2022

Polymer-bonded magnets produced by laser powder bed fusion: Influence of powder morphology, filler fraction and energy input on the magnetic and mechanical properties

Bonded permanent magnets are key components in many energy conversion, sensor and actuator devices. These applications require high magnetic performance and freedom of shape. With additive manufacturing processes, for example laser powder bed fusion (LPBF), it is possible to produce bonded magnets with customized stray field distribution. Up to now, most studies use spherical powders as magnetic fillers due to their good flowability. Here, the behavior of large SmFeN platelets with a high aspect ratio as filler material and its influence on the arrangement and the resulting magnetic properties are examined in comparison to a spherical magnetic filler. The 3D distribution and orientation of the magnetic filler was studied by computed tomography and digital image analysis. The platelet-shaped particles align themselves perpendicular to the buildup direction during the process, which offers a new and cost-effective way of producing composites by LPBF with anisotropic structural and functional properties. The influence of LPBF parameters on the properties of the composites is investigated. Highest filling fractions are required for high magnetic remanence, however the powder itself limits this maximum due to particle shape and required minimal polymer fraction to form mechanically stable magnets. The coercivity decreases for higher filling fractions, which is attributed to increased rotation of insufficiently embedded magnetic particles in the matrix. It is discussed how filler morphology influences the observed change in coercivity since the rotation of spherical particles in comparison to platelet-shaped particles requires less energy. Our work shows the challenges and opportunities of large platelet shaped fillers used in LPBF for the production of anisotropic functional and structural composites.

physics.app-ph↗