Hybrid Fabrication of Cold Metal Transfer Additive Manufacturing and Laser Metal Deposition for Ti6Al4V: The Microstructure and Dynamic/Static Mechanical Properties.

The titanium alloy components utilized in the aviation field are typically large in size and possess complex structures. By utilizing multiple additive manufacturing processes, the precision and efficiency requirements of production can be met. We investigated the hybrid additive manufacturing of Ti-6Al-4V using a combination of cold metal transfer additive manufacturing (CMTAM) and laser metal deposition (LMD), as well as the feasibility of using the CMT-LMD hybrid additive manufacturing process for fabricating Ti-6Al-4V components. Microstructural examinations, tensile testing coupled with digital image correlation and dynamic compressive experiments (by the split Hopkinson pressure bar (SHPB) system) were employed to assess the parts. The results indicate that the interface of the LMD and CMTAM zone formed a compact metallurgical bonding. In the CMTAM and LMD zone, the prior-ß grains exhibit epitaxial growth, forming columnar prior-ß grains. Due to laser remelting, the CMT-LMD hybrid additive zone experiences grain refinement, resulting in equiaxed prior-ß grains at the interface with an average grain size smaller than that of the CMTAM and LMD regions. The microstructures reveal significant differences in grain orientation and morphology among the zones, with distinct textures forming in each zone. In the CMT-LMD hybrid zone, due to interfacial strengthening, strain concentration occurs in the arc additive zone during tensile testing, leading to fracture on the CMTAM zone. Under high-strain-rate dynamic impact conditions, the LMD region exhibits ductile fracture, while the CMTAM zone demonstrates brittle fracture. The hybrid zone combines ductile and brittle fracture modes, and the CMT-LMD hybrid material exhibits superior dynamic impact performance compared to the single deposition zone.

Static and Dynamic Mechanical Behaviour of Hybrid-PBF-LB/M-Built and Hot Isostatic Pressed Lattice Structures.

We report on a comprehensive study of the mechanical properties of maraging steel body-centred cubic lattice structures fabricated by a hybrid additive manufacturing technology that combines laser powder bed fusion with in situ high-speed milling. As the mechanical properties of additive manufactured components are inferior to, e.g., cast components, surface modifications can improve the mechanical behaviour. Different hybrid additive manufacturing technologies have been designed using additive and subtractive processes, improving process quality. Following this, mechanical testing is performed with respect to static tensile properties and dynamic stress, hardness, and porosity, comparing specimens manufactured by laser powder bed fusion only to those manufactured by the hybrid approach. In addition, the influence of different heat-treatment techniques on the mechanical behaviour of the lattice structures is investigated, namely solution and aging treatment as well as hot isostatic pressing. Thus, the influence of the superior surface quality due to the hybrid approach is evaluated, leading to, e.g., an offset of about 14-16% for the static testing of HIP lattice structures. Furthermore, the dynamic load behaviour can be improved with a finished surface, heading to a shift of the different zones of fatigue behaviour in the testing of hybrid-built specimens.

Hybrid Additive Manufacturing of Fused Filament Fabrication and Ultrasonic Consolidation.

Fused filament fabrication (FFF) additive manufacturing technology has the advantages of being low cost, having a simple operation, using wide types of molding materials, and producing less pollution during the printing process. However, the mechanical properties of the molded sample are unsatisfactory due to the limited bonding force between the filaments during the forming process, which limits its further development and application in the engineering field. Herein, the hybrid additive manufacturing technology for heterogeneous materials based on the ultrasonic-assisted enhanced fused filament fabrication technology was proposed. The mechanism of ultrasonic vibration on the strengthening of FFF samples was explored. The influence mechanisms of bonding time and ultrasonic strengthening times, ultrasonic strengthening and static load compression on the strengthening of mechanical properties of the sample were investigated. The effects of the thickness and printing angle of the FFF samples on the ultrasonic-enhanced mechanical properties were explored. The tensile strength of the one-time ultrasonic-strengthened sample is up to 43.43 MPa, which is 16.12% higher than that of the original. The maximum bending strength of the four-time ultrasonic-strengthened sample is 73.38 MPa, which is 78.98% higher than that of the original. Ultrasonic strengthening not only re-fused the pores inside the sample, but also improved the bond strength between the rasters. With the increase in the thickness of the sample, the increase rate of ultrasonic to the strength of the sample decreased significantly. The effects of ultrasound on the interlayer adhesion of samples with various printing angles were different. Based on the systematic research on the influence mechanism of ultrasonic process parameters and molding process parameters on the strengthening of FFF, a molding method for additively manufacturing heterogeneous material parts while strengthening the mechanical properties of FFF samples was proposed, and the influence mechanisms of the molding process on the mechanical properties and shape memory properties of the sample were explored, which can broaden the application of FFF technology in the engineering field.

Tool Wear and Milling Characteristics for Hybrid Additive Manufacturing Combining Laser Powder Bed Fusion and In Situ High-Speed Milling.

We report on milling and tool wear characteristics of hybrid additive manufacturing comprising laser powder bed fusion and in situ high-speed milling, a particular process in which the cutter mills inside the powder bed without any cooling lubricant being applicable. Flank wear is found to be the dominant wear characteristic with its temporal evolution over utilization period revealing the typical s-shaped dependence. The flank wear land width is measured by microscopy and correlated to the achievable surface roughness of milled 3D-printed parts, showing that for flank wear levels up to 100 µm a superior surface roughness below 3 µm is accessible for hybrid additive manufacturing. Further, based on this correlation recommended tool, life scenarios can be deduced. In addition, by optimizing the finishing tool start position and the number of afore-built layers, the milling process is improved with respect to the maximum millable angle for undercut surfaces of 3D-printed parts to 30° for the roughing process and to 40° for the entire machining process including finishing.

Selectively Metalizable Low-Temperature Cofired Ceramic for Three-Dimensional Electronics via Hybrid Additive Manufacturing.

With increasing interest in the rapid development of customized ceramic electronics, hybrid additive manufacturing (HAM) technology has become a competent alternative to traditional solutions such as printed circuit boards and cofired ceramic technology. Herein, the novel HAM technology is proposed by combining a dispensing three-dimensional (3D) printing process and selectively laser-activated electroless plating for fabricating 3D fully functional ceramic electronic products. An appropriative 3D-printable and metalizable low-temperature cofired ceramic slurry is developed to build the green body of ceramic electronics. After the debinding and sintering process, the 3D ceramic structure can be selectively laser-activated and then electrolessly plated to achieve electronic functionality. The thickness of the plated copper layer approaches 10 µm after 4 h of plating, and the electrical conductivity is 5.5 × 107 S m-1, which is close to pure copper (5.8 × 107 S m-1). To reduce the surface roughness of the laser-activated ceramic surface and thereby enhance the conductivity of the copper layer, the laser parameters are optimized as a 1250 mm s-1 scan speed, a 0.4 W laser power, and a 20 kHz laser-spot frequency. A high-power 3D light-emitting diode circuit board with an internal cooling channel is successfully developed to prove the feasibility of this HAM technology for customizing fully functional 3D conformal ceramic electronics.

Friction Stir Welding Optimization of 3D-Printed Acrylonitrile Butadiene Styrene in Hybrid Additive Manufacturing.

The feasibility of joining material extrusion (MEX) 3D-printed acrylonitrile butadiene styrene (ABS) plates with the friction stir welding (FSW) process was investigated herein as a promising topic of hybrid additive manufacturing (HAM). The influence of three process parameters on the mechanical strength of the joints was thoroughly examined and analyzed with a full factorial experimental design and statistical modeling. Hereto, the welding tool pin geometry, travel speed, and rotational speed were investigated. The joint's efficiency and quality are evaluated through tensile tests and morphological characterization. More specifically, specimens' areas of particular interest were investigated with stereoscopic, optical, and scanning electron microscopy. Throughout the FSW experimental course, the welding temperature was monitored to evaluate the state of the ABS material during the process. The majority of the welded specimens exhibited increased mechanical strength compared with the respective ones of non-welded 3D printed specimens of the same geometry. Statistical modeling proved that all processing parameters were significant. The feasibility of the FSW process in 3D printed ABS workpieces was confirmed, making the FSW a cost-effective process for joining 3D printing parts, further expanding the industrial merit of the approach.

A review on spacers and membranes: Conventional or hybrid additive manufacturing?

Over the past decade, 3D printing or additive manufacturing (AM) technology has seen great advancement in many aspects such as printing resolution, speed and cost. Membranes for water treatment experienced significant breakthroughs owing to the unique benefits of additive manufacturing. In particular, 3D printing's high degree of freedom in various aspects such as material and prototype design has helped to fabricate innovative spacers and membranes. However, there were conflicting reports on the feasibility of 3D printing, especially for membranes. Some research groups stated that technology limitations today made it impossible to 3D print membranes, but others showed that it was possible by successfully fabricating prototypes. This paper will provide a critical and comprehensive discussion on 3D printing specifically for spacers and membranes. Various 3D printing techniques will be introduced, and their suitability for membrane and spacer fabrication will be discussed. It will be followed by a review of past studies associated with 3D-printed spacers and membranes. A new category of additive manufacturing in the membrane water industry will be introduced here, known as hybrid additive manufacturing, to address the controversies of 3D printing for membrane. As AM technology continues to advance, its possibilities in the water treatment is limitless. Some insightful future trends will be provided at the end of the paper.

Design Rules for Hybrid Additive Manufacturing Combining Selective Laser Melting and Micromilling.

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 < 2µm. 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.

Selectively Metalizable Stereolithography Resin for Three-Dimensional DC and High-Frequency Electronics via Hybrid Additive Manufacturing.

Direct manufacturing of customized end-use electronic products is becoming an emerging trend of additive manufacturing (AM). This highly demands the evolution of the conventional AM processes from simply building single-material parts to simultaneously delivering complex structures and end-use functionalities. In this work, we propose a novel hybrid additive manufacturing solution that combines stereolithography (SLA) three-dimensional (3D) printing and laser-activated electroless plating for the manufacture of 3D fully functional electronic products. With our newly developed functional SLA resin that can be 3D printed, laser-activated, and thereafter selectively metalized, high-resolution circuitry can be free-formly patterned on 3D structures. In virtue of high-performance electrical materials, this technology is capable of creating not only 3D direct-current (DC) electronics but also 3D high-frequency devices like microwave/millimeter-wave antennas, which cannot be fabricated via traditional printed circuit board (PCB) technology and not even by most AM processes. This study represents a significant advance in additive manufacturing technologies, and more importantly offers a unique opportunity for the mass customization of fully functional 3D electronic products, which shows great potentials in consumer electronics, communication engineering, and automobile and aerospace industries.

Drug delivery device for the inner ear: ultra-sharp fully metallic microneedles.

Drug delivery into the inner ear is a significant challenge due to its inaccessibility as a fluid-filled cavity within the temporal bone of the skull. The round window membrane (RWM) is the only delivery portal from the middle ear to the inner ear that does not require perforation of bone. Recent advances in microneedle fabrication enable the RWM to be perforated safely with polymeric microneedles as a means to enhance the rate of drug delivery from the middle ear to the inner ear. However, the polymeric material is not biocompatible and also lacks the strength of other materials. Herein we describe the design and development of gold-coated metallic microneedles suitable for RWM perforation. When developing microneedle technology for drug delivery, we considered three important general attributes: (1) high strength and ductility material, (2) high accuracy and precision of fabrication, and (3) broad design freedom. We developed a hybrid additive manufacturing method using two-photon lithography and electrochemical deposition to fabricate ultra-sharp gold-coated copper microneedles with these attributes. We refer to the microneedle fabrication methodology as two-photon templated electrodeposition (2PTE). We demonstrate the use of these microneedles by inducing a perforation with a minimal degree of trauma in a guinea pig RWM while the microneedle itself remains undamaged. Thus, this microneedle has the potential literally of opening the RWM for enhanced drug delivery into the inner ear. Finally, the 2PTE methodology can be applied to many different classes of microneedles for other drug delivery purposes as well the fabrication of small scale structures and devices for non-medical applications. Graphical Abstract Fully metallic ultra-sharp microneedle mounted at end of a 24-gauge stainless steel blunt syringe needle tip: (left) Size of microneedle shown relative to date stamp on U.S. one-cent coin; (right) Perforation through guinea pig round window membrane introduced with microneedle.

Hybrid Approaches for Selective Laser Sintering by Building on Dissimilar Materials.

We introduced a new approach in selective laser sintering for hybrid multicomponent systems by fabricating the sintered polyamide 12 (PA12) part directly onto a similar (PA12) or dissimilar (polyamide 6 (PA6) and tool steel 1.2709) joining partner. Thus, the need for adhesive substances or joining pressure was completely circumvented, leading to the possibility of pure hybrid lightweight bi-polymer or metal-polymer systems. By taking advantage of the heating capabilities of the sinter laser regarding the substrate surface, different exposure strategies circumvented the lack of overlapping melting temperatures of dissimilar polymers. Therefore, even sintering on non-PA12 polymers was made possible. Finally, the transfer on metallic substrates-made up by selective laser melting (SLM)-was successfully performed, closing the gap between two powder-based additive processes, selective laser sintering (SLS) and SLM.

3D Bioprinting in Tissue Engineering for Medical Applications: The Classic and the Hybrid.

Three-dimensional (3D) printing, as one of the most popular recent additive manufacturing processes, has shown strong potential for the fabrication of biostructures in the field of tissue engineering, most notably for bones, orthopedic tissues, and associated organs. Desirable biological, structural, and mechanical properties can be achieved for 3D-printed constructs with a proper selection of biomaterials and compatible bioprinting methods, possibly even while combining additive and conventional manufacturing (AM and CM) procedures. However, challenges remain in the need for improved printing resolution (especially at the nanometer level), speed, and biomaterial compatibilities, and a broader range of suitable 3D-printed materials. This review provides an overview of recent advances in the development of 3D bioprinting techniques, particularly new hybrid 3D bioprinting technologies for combining the strengths of both AM and CM, along with a comprehensive set of material selection principles, promising medical applications, and limitations and future prospects.

Areal Surface Roughness Optimization of Maraging Steel Parts Produced by Hybrid Additive Manufacturing.

We report on an experimental study and statistical optimization of the surface roughness using design of experiments and the Taguchi method for parts made of 1.2709 maraging steel. We employ a hybrid additive manufacturing approach that combines additive manufacturing by selective laser melting with subtractive manufacturing using milling in an automated process within a single machine. Input parameters such as laser power, scan speed, and hatching distance have been varied in order to improve surface quality of unmachined surfaces. Cutting speed, feed per tooth, and radial depth of cut have been varied to optimize surface roughness of the milled surfaces. The surfaces of the samples were characterized using 3D profilometry. Scan speed was determined as the most important parameter for non-machined surfaces; radial depth of cut was found to be the most significant parameter for milled surfaces. Areal surface roughness S a could be reduced by up to 40% for unmachined samples and by 23% for milled samples as compared to the prior state of the art.

Numerical Modeling Design for the Hybrid Additive Manufacturing of Laser Directed Energy Deposition and Shot Peening Forming Fe-Cr-Ni-B-Si Alloy.

Hybrid additive manufacturing is of great significance to make up for the deficiency of the metal forming process; it has been one of the main trends of additive manufacturing in recent years. The hybrid process of laser directed energy deposition (laser DED) and shot peening is a new technology combining the principles of surface strengthening and additive manufacturing, whose difficulty is to reduce the interaction between the two processes. In this paper, a new model with a discrete phase and fluid-solid interaction method is established, and the location of the shot peening point in the hybrid process is optimized. The distributions of the temperature field and powder trajectory were researched and experiments were carried out with the optimized parameters to verify simulation results. It was found that the temperature field and the powder trajectory partly change, and the optimized injection point is located in the stress relaxation zone of the material. The densities and surface residual stresses of samples were improved, and the density increased by 8.83%. The surface stress changed from tensile stress to compressive stress, and the introduced compressive stress by shot peening was 2.26 times the tensile stress produced by laser directed energy deposition.

Electrical and Thermal Characterization of 3D Printed Thermoplastic Parts with Embedded Wires for High Current-Carrying Applications.

Fabrication of parts exhibiting multi-functionality has recently been complemented by hybrid polymer extrusion additive manufacturing in combination with wire embedding technology. While much mechanical characterization has been performed on parts produced with fused deposition modeling, limited characterization has been performed when combined electrical and thermal loads are applied to 3D printed multi-material parts. As such, this work describes the design, fabrication, and testing of 3D printed thermoplastic coupons containing embedded copper wires that carried current. An automated fabrication process was used employing a hybrid additive manufacturing machine that dispensed polycarbonate thermoplastic and embedded bare copper wires. Testing included AC and DC hipot testing as well as thermal testing on as-fabricated and heat treated coupons to determine the effect of porosity in the substrate. The heat-treated parts contained reduced amounts of porosity, as corroborated through scanning electron microscopy, which led to 50 % increased breakdown strength and 30 to 40 % increased heat dissipation capabilities. The results of this research are describing a set of design protocol that can be used as a guideline for 3D printed embedded electronics to predict the electrical and thermal behavior.

A Novel Hybrid Additive Manufacturing Process for Drug Delivery Systems with Locally Incorporated Drug Depots.

Here, we present a new hybrid additive manufacturing (AM) process to create drug delivery systems (DDSs) with selectively incorporated drug depots. The matrix of a DDS was generated by stereolithography (SLA), whereas the drug depots were loaded using inkjet printing. The novel AM process combining SLA with inkjet printing was successfully implemented in an existing SLA test setup. In the first studies, poly(ethylene glycol) diacrylate-based specimens with integrated depots were generated. As test liquids, blue and pink ink solutions were used. Furthermore, bovine serum albumin labeled with Coomassie blue dye as a model drug was successfully placed in a depot inside a DDS. The new hybrid AM process makes it possible to place several drugs independently of each other within the matrix. This allows adjustment of the release profiles of the drugs depending on the size as well as the position of the depots in the DDS.