[Paper Review] Magneto-active composites with locally tailored stiffness produced by laser powder bed fusion

Kilian Schäfer, Matthias Lutzi+12 more|TUbilio (Technical University of Darmstadt)|May 4, 2023

Advanced Materials and Mechanics64 references5 citations

TL;DR

This study presents a single-step laser powder bed fusion (LPBF) method to fabricate magneto-active composites with locally tailored stiffness by adjusting laser parameters in specific regions. The approach enables precise stiffness control from 2 to 22 MPa within a thermoplastic polyurethane and Nd-Fe-B magnetic powder composite, significantly enhancing actuator performance and enabling patient-specific stent designs with customized mechanical properties.

ABSTRACT

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.

Motivation & Objective

• To develop a single-step additive manufacturing process for magneto-active composites with spatially controlled mechanical stiffness.
• To overcome the complexity of multi-material printing by enabling stiffness gradients through laser parameter modulation alone.
• To demonstrate improved magnetic actuation performance in composites with tailored local stiffness compared to homogeneous counterparts.
• To enable patient-specific biomedical devices, such as stents, with customized geometry and localized mechanical properties.

Proposed method

• Laser powder bed fusion (LPBF) was used to process a composite of thermoplastic polyurethane and atomized Nd-Fe-B magnetic powder.
• Laser parameters (e.g., power, scan speed) were locally varied to induce controlled variations in melt pool dynamics and solidification, altering the local density and microstructure.
• The resulting changes in material density and interfacial bonding led to stiffness gradients ranging from 2 to 22 MPa across different regions of the part.
• Finite element modeling and mechanical testing were used to validate the stiffness distribution and correlate it with laser processing parameters.
• Functional actuators and a magnetically responsive stent were fabricated to demonstrate performance and biocompatibility potential.
• Magnetic actuation response was measured and compared between locally tailored and homogeneous versions of the same geometry.

Experimental results

Research questions

• RQ1 Can laser powder bed fusion be used to produce magneto-active composites with spatially varying stiffness using only single-material processing and laser parameter tuning?
• RQ2 How does local variation in laser parameters influence the mechanical stiffness of LPBF-fabricated magnetic composites?
• RQ3 To what extent does locally tailored stiffness improve the magnetic actuation performance of soft robotic devices compared to homogeneous counterparts?
• RQ4 Can this method enable patient-specific biomedical implants with customized mechanical properties based on anatomical and pathological conditions?
• RQ5 What is the achievable range and precision of stiffness control in such composites using this single-step LPBF approach?

Key findings

• The LPBF process enabled precise local stiffness tuning within the composite, achieving a range of 2 to 22 MPa by adjusting laser parameters.
• Actuators with locally tailored stiffness exhibited a significantly enhanced magnetic response compared to their homogeneous counterparts with identical geometry.
• The stiffness gradient was achieved without multi-material printing, relying solely on process parameter modulation in a single material system.
• A functional, magnetically responsive stent with localized stiffness adjustment was fabricated, demonstrating potential for personalized medical devices.
• The method enables the creation of functionally graded materials in a single manufacturing step, with implications beyond magneto-active systems.
• The results confirm that microstructural and density variations induced by laser processing can be harnessed to tailor mechanical properties effectively.