Ajeet Kumar

Selective laser sintering (SLS) is one of the prominent methods of polymer additive manufacturing (AM). A low-power laser source is used to directly melt and sinter polymer material into the desired shape. This study focuses on the utilization of the low-power laser SLS system to successfully manufacture metallic components through the development of a metal–polymer composite material. In this study, 17-4 PH stainless powders are used and mixed with polyoxymethylene (POM) and high-density polyethylene (HDPE) to prepare the composite powder material. The polymeric mixture is removed during the thermal degreasing process and subsequent sintering results in a solid metallic component. Sinterit Lisa with a 5 W, 808 nm laser source is used to fabricate the green part. For the printing parameters of 140 °C, laser power of 35.87 mJ/mm², and layer thickness of 100 μm, the printed samples achieved a maximum density of 3.61 g/cm³ and a complete shape. After sintering at 1310 °C for 180 min, the tensile strength of the shrunk sample is 605.64 MPa, the hardness is HRC 14.8, the average shrinkage rate is 22%, and the density is 7.57 g/cm³, which can reach 97% of the theoretical density. This process allows the use of a wide range of particle sizes that the usual AM technologies have, making it a low-cost, low-energy-consumption, high-speed AM technology.

The properties of each lattice structure are a function of four basic lattice factors, namely the morphology of the unit cell, its tessellation, relative density, and the material properties. The recent advancements in additive manufacturing (AM) have facilitated the easy manipulation of these factors to obtain desired functionalities. This review attempts to expound on several such strategies to manipulate these lattice factors. Several design-based grading strategies, such as functional grading, with respect to size and density manipulation, multi-morphology, and spatial arrangement strategies, have been discussed and their link to the natural occurrences are highlighted. Furthermore, special emphasis is given to the recently designed tessellation strategies to deliver multi-functional lattice responses. Each tessellation on its own acts as a novel material, thereby tuning the required properties. The subsequent section explores various material processing techniques with respect to multi-material AM to achieve multi-functional properties. The sequential combination of multiple materials generates novel properties that a single material cannot achieve. The last section explores the scope for combining the design and process strategies to obtain unique lattice structures capable of catering to advanced requirements. In addition, the future role of artificial intelligence and machine learning in developing function-specific lattice properties is highlighted.

Increased usage of selective laser sintering (SLS) for the production of end-use functional components has generated a requirement of developing new materials and process improvements to improve the applicability of this technique. This article discusses a novel process wherein carbon black was applied to the surface of TPU powder to reduce the laser reflectivity during the SLS process. The printing was carried out with a preheating temperature of 75 °C, laser energy density of 0.028 J/mm², incorporating a 0.4 wt % addition of carbon black to the TPU powder, and controlling the powder layer thickness at 125 μm. The mixed powder, after printing, shows a reflectivity of 13.81%, accompanied by the highest average density of 1.09 g/cm³, hardness of 78 A, tensile strength of 7.9 MPa, and elongation at break was 364.9%. Compared to commercial TPU powder, which lacks the carbon black coating, the reflectance decreased by 1.78%, mechanical properties improved by 33.9%, and there was a notable reduction in the porosity of the sintered product.

This study proposes an innovative design solution based on the design for additive manufacturing (DfAM) and post-process for manufacturing industrial-grade products by reducing additive manufacturing (AM) time and improving production agility. The design of the supportless open cell Sea Urchin lattice structure is analyzed using DfAM for material extrusion (MEX) process to print support free in any direction. The open cell is converted into a global closed cell to entrap secondary foam material. The lattice structure is 3D printed with Polyethylene terephthalate glycol (PETG) material and is filled with foam using the Hybrid MEX process. Foam-filling improves the lattice structure’s energy absorption and crash force efficiency when tested at different strain rates. An industrial case study demonstrates the importance and application of this lightweight and tough design to meet the challenging current and future mass customization market. A consumer-based industrial scenario is chosen wherein an innovative 3D-printed universal puck accommodates different shapes of products across the supply line. The pucks are prone to collisions on the supply line, generating shock loads and hazardous noise. The results show that support-free global closed-cell lattice structures filled with foam improve energy absorption at a high strain rate and enhance the functional requirement of noise reduction during the collision.

This study analyses the energy absorption and stiffness behaviour of 3D-printed supportless, closed-cell lattice structures. The unit cell design is bioinspired by the sea urchin morphology having organism-level biomimicry. This gives rise to an open-cell lattice structure that can be used to produce two different closed-cell structures by closing the openings with thin or thick walls, respectively. In the design phase, the focus is placed on obtaining the same relative density with all structures. The present study demonstrates that closure of the open-cell lattice structure enhances the mechanical properties without affecting the functional requirements. Thermoplastic polyurethane (TPU) is used to produce the structures via additive manufacturing (AM) using fused filament fabrication (FFF). Uniaxial compression tests are performed to understand the mechanical and functional properties of the structures. Numerical models are developed adopting an advanced material model aimed at studying the hysteretic behaviour of the hyperelastic polymer. The study strengthens design principles for closed-cell lattice structures, highlighting the fact that a thin membrane is the best morphology to enhance structural properties. The results of this study can be generalised and easily applied to applications where functional requirements are of key importance, such as in the production of lightweight midsole shoes.

This study evaluates the challenges of powder removal inside surface-based lattice structures that have been fabricated by the polymer-powder-based additive manufacturing (AM) process. The natural flow adaptations of plant cells’ morphology and perforation that allow water and minerals easy transport have been bio-mimicked for ease of powder flow during post-processing powder removal. Vessel-shaped and supportless lattice structures with ventilations have been designed, followed by a Computational fluid dynamics (CFD) simulation. This is to study the fluid flow pattern and turbulence inside the lattice structures. The designed lattice structures were 3d printed with polyamide 12 (PA-12) material by HP-MJF 4200 powder bed technology. They were followed by powder removal using a pressurised air gun and computerised tomography (CT-scan) to observe the regions of trapped powder inside the lattice structures. The uni-axial compression tests were conducted to observe the effect of ventilation on the mechanical properties of the lattice structures.

This paper analyzes the effect of thin and thick walls on functional properties of 3D printed cell structures, designed from open cell structures inspired by the natural world. Different types of unit cells with the same density are introduced. The cells are studied in morphology and mechanical performance, in particular effective density, compressive stiffness, and energy absorption under cyclic loading. Material extrusion process with thermoplastic polyurethane filament is used as additive manufacturing technique, without any support structure. The designed printed cellular structures are studied numerically, using an advanced hyperelastic material model with hysteretic capacity, and experimentally by uniaxial compression testing for characterization of stiffness and energy absorption. The benefits and limitations of the method are highlighted.