Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Additive manufacturing of metals

Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

Laser additive manufacturing of metallic components: materials, processes and mechanisms

A study of the microstructural evolution during selective laser melting of Ti–6Al–4V

We have determined the phase composition and microhardness of coatings produced by the laser melting of silicon powder on the surface of steel substrates. Laser exposure leads to the formation of iron silicides on the substrate surface. The iron content of the silicides depends on the effective laser power and increases from that of FeSi2 to Fe0.9Si0.1. The coatings have the highest microhardness at an effective power of ≏ 400 W s/m, which corresponds to the highest FeSi content.

Laser-induced reaction of Si powder with a steel substrate

The type of material used in biomedical applications depends on specific implant applications; different types of the implant need different mechanical properties. Since the architectures of bone tissues in the human body are not completely dense and solid, it is desirable to produce biomimic structures as a replacement for damaged bone tissues. Learning from nature, it can be understood that cellular structures would be more preferable for biomedical implants than dense solid structures. Ti6Al4V alloy is well known to have a superior track record as leading material for bone replacement since it is a light weight and biocompatible material, but the density of human cortical bone is 2 times lower than that of solid Ti6Al4V implants. The mismatch of the elastic modulus between such implants and bone tissue is one of the major causes of stress shielding, bone resorption and implant loosening. FEA has proven to be a very effective tool for predicting the biomechanical behavior of various implant designs as well as clinical factors on implant success. The elastic modulus of lattice structures would be used to stimulate a complex mandible to obtain foreknowledge of manufacturing advanced light-weight implants with suitable biomechanical properties.

Evaluation of the compressive mechanical properties of cellular dmls structures for biomedical applications

The kinetics of interparticle contacts formation during the liquid-phase sintering of unlike materials under the action of laser irradiation was investigated. Trios of particles arranged in a row according to the schemes glass—polymer glass, metal—polymer—metal, and metal—glass—metal were sintered. The processes of particle approach and liquid neck formation between particles were studied. Possibilities for the manufacture of powder components with polymer and glass binders by the use of selective laser sintering followed by heat treatment are considered].

Kinetics of interparticle contact formation during the laser sintering of two-component powders

Selective laser melting (SLM) is an additive manufacturing technique that produces functional parts from metal powders. SLM is a powerful technology for automotive, medical, chemical, aerospace and other hi-tech industries. SLM is a well-suited technology for the mould industry: it can considerably reduce the time for engineering and fabrication of moulds. SLM provides extraordinary freedom to validate design of moulds and to develop new materials. The extension of applications requires different materials with specific properties. To show the potential and features of SLM for mould manufacturing applications, fully-dense samples from AISI 420 stainless steel powder were fabricated. AISI 420 stainless steel is a material widely used in the plastics-moulding industry where high hardness and wear resistance is required. The study discusses the influence of laser power, scanning speed, layer thickness and hatch distance on the formation of single tracks and layers. Algorithm for finding optimal process parameters is indicated with respect to features of single tracks, layers and 3D objects. Width of the single track determines the hatch-distance to form a single layer. Height of the tracks and scanning strategy define the morphology of the synthesized layer. Morphology of the layer has a significant impact on the variation of the thickness of the next delivered powder layer. This should be considered when choosing the optimal process parameters. An energy input should be adequate to melt powder layer and to achieve remelted depth providing good cohesion between the layers. The pore analysis (shapes and sizes) can also contribute to the identification of optimal process parameters. To produce non-porous objects from AISI 420 (–32 µm) stainless steel powder, 60 W laser power, 70 µm spot diameter, 0.12 m/s scanning speed, 120 µm hatch-distance and 40 µm thickness of powder layer and two-zone scanning strategy with following 90 turning for each next layer were applied. Microhardness of the SLM samples was 513±19.5 HV0.3 for inner regions; upper layers had 700-750 HV0.3.

Strategy toward the manufacturing of fully dense parts from aisi 420 stainless steel by selective laser melting

Selective Laser Melting (SLM) is a powder bed fusion process which is an additive manufacturing (AM) process, whereby a laser beam selectively fuses regions of a powder bed to form complex objects. Growth in the SLM field has revealed the need for parts containing multiple materials for applications in the medical, tool making, aerospace and other hi-tech industries. By applying multiple materials, regions with different mechanical properties, thermal conductivity zones or corrosion-resistant coatings can be achieved in a single manufacturing cycle utilizing the SLM process. With the SLM process physical bonds can be formed between different materials by creating an interlocking interface due to the rapid solidification of the molten materials. With the current SLM equipment, multi material objects are possible but only with material differences between the layers. New approaches are needed to develop a method that allows multi material parts not only in the Z axis, but also allow material differences on a single layer (X-Y axis). Approaches such as powder feeding through a capillary tube, auger feed system, electrostatic charge or masks have all been proposed as solutions to multi material deposition. Multi material objects produced in a single cycle with complex geometry and prescribed properties has the opportunity of further growing the AM market.

Igor Yadroitsev

Papers

Laser-induced reaction of Si powder with a steel substrate

Evaluation of the compressive mechanical properties of cellular dmls structures for biomedical applications

Kinetics of interparticle contact formation during the laser sintering of two-component powders

Strategy toward the manufacturing of fully dense parts from aisi 420 stainless steel by selective laser melting

Multi material powder delivering systems for selective laser melting