Metal Laser Sintering Additive Manufacturing Research Articles

Microstructural characterization on reused Ti6Al4V powder in direct metal laser sintering additive manufacturing

One of the biggest advantages in metal additive manufacturing using laser powder bed fusion is low powder usage compared to traditional manufacturing methods. The process can be made more efficient by enabling metal powder to be reused. Recycling promotes environmental sustainability by minimizing material wastage and decreasing the demand for raw materials, making the metal additive manufacturing process more resource efficient.In this study, Ti6Al4V powder was recycled and reused up to 50 times. In order to understand the effects of reusing powder, the study included a detailed examination of both the powder and the processing method. The microstructure and characteristics of the recycled powder were examined in extensive detail.

Heat Transfer Enhancement of Single-Phase Internal Flows using Shape Optimization and Additively Manufactured Flow Structures

• We optimize the shape of internal fins using generative design. • The optimized fins are additively manufactured from alsi10 mg. • Rigorous measurements and simulations characterize heat transfer performance. • The optimized fins have 65–77% lower thermal resistance than conventional designs. This paper reports heat transfer enhancement of forced internal single-phase flow enabled by additively manufactured internally finned channels. We consider internal liquid coolant flow through a tube with constant heat flux applied to the exterior surface. A genetic algorithm was developed and used to optimize the fin geometry in order to minimize total thermal resistance for laminar flow or convection thermal resistance for turbulent flow. The genetic algorithm sampled more than 500 fin geometries, evaluated thermal resistance, and selected the optimum fin geometry. We selected three designs for experimental testing: a complex fin structure suggested by the genetic algorithm; a straight fin design; and a smooth circular channel as a reference. The devices were made from aluminum silica (AlSi10Mg) using direct metal laser sintering additive manufacturing. The devices were tested using a water ethylene glycol mixture (80:20) over the hydraulic diameter based Reynolds number range of 400 – 18,000, covering both laminar and turbulent flow regimes. Finite element simulations of heat transfer and pressure drop helped to understand and interpret the measurements. Compared to the smooth pipe reference design, the total thermal resistance of the genetically optimized fin design was 77% lower for laminar flow at Re h = 2,000 and 65% lower for turbulent flow at Re h = 10,000. Compared to the straight fin design that is commonly used for enhancing convection heat transfer in internal flows, the total thermal resistance of the genetically optimized fin design was 55% lower for laminar flow at Re h = 2,000 and 29% lower for turbulent flow at Re h = 10,000. We explore the potential design space for different types of heat exchangers by investigating how total heat transfer varies with exterior heat transfer coefficient and channel wall thermal conductivity. This research shows how shape optimization and additive manufacturing can result in devices with improved internal convection heat transfer.

An assessment of biomedical CoCrMo alloy fabricated by direct metal laser sintering technique for implant applications.

CoCrMo alloys have been used for several decades in implantable devices due to their favourable mechanical properties, low wear rate in addition to good biocompatibility and high corrosion resistance. These alloys are conventionally produced via casting and/or forging route, however additive manufacturing techniques being recently employed in their fabrication. In this work, CoCrMo samples were produced by direct metal laser sintering additive manufacturing process. The microstructure and surface composition were examined employing scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The corrosion resistance was measured in 0.14 M sodium chloride solution and in phosphate buffered solution (PBS) both with and without addition of albumin at pH 7.4 and 37 °C. For this, potentiodynamic tests in addition to electrochemical impedance spectroscopy were employed. The studied CoCrMo alloy exhibits a good corrosion resistance in solutions tested being the highest in PBS solution without albumin addition. The XPS analysis showed that the passive film composition and its thickness are not modified by the adsorbed layer. Microstructural analysis revealed occurrence of strain-induced martensitic transformation.

Effect of phase transformation on ductility of additively manufactured Co–28Cr–6Mo alloy: An in situ synchrotron X-ray diffraction study during mechanical testing

The influence of strain-induced martensitic transformation on the mechanical properties of a Co–28Cr–6Mo alloy produced using the direct metal laser sintering additive manufacturing technique was analyzed. Both the as-built and solution heat-treated (ST) specimens were subjected to conventional tensile tests. Furthermore, X-ray diffraction spectra were simultaneously acquired using a synchrotron light source. In addition, electron backscatter diffraction analysis was performed on the specimens before and after tensile testing. Both techniques revealed the occurrence of the strain-induced γ-face-centered cubic → ε-hexagonal close-packed phase transformation. The higher microstrain and preferential grain orientation of the as-built specimen favored the onset of the phase transformation. Moreover, the ductility of the ST specimen was significantly higher than that of the as-built specimen. This behavior was attributed to the isotropic properties of the randomly-oriented and equiaxed grains, increase in resistance to necking, and reduction in internal stresses caused by the solution heat treatment.

Thermo-mechanical modeling and validation of stress field during laser powder bed fusion of AlSi10Mg built part

Abstract Direct metal laser sintering process is a layer based laser powder bed fusion additive manufacturing process used to fabricate near net shape metallic components directly from the metal powders. A high energy moving heat source is utilized to melt and fuse the powders in subsequent layers. During the direct metal laser sintering additive manufacturing process, rapid heating and cooling take place which results in an unexpected change in temperature in the scanned layers. This change in temperature induces thermal stresses in the build part after the accomplishment of the process and it can be destructive to the quality and performance of the build parts which hinders its end-user applications. In the present study, a comprehensive thermo-mechanical model has been developed for the purpose of investigating thermal residual stress in the AlSi10Mg single layer build part during the direct metal laser sintering process using finite element method. Further, the model has validated analytically by measuring the thermal strain. In addition, the effects of scan speed and laser power on the development of thermal residual stresses were investigated. It is found that repeated thermal expansion and contraction in the powder bed leads to the development of thermal residual stress and thermal stain in the build part. The finding of this study will help to optimize the processing conditions for minimizing the thermal residual stress in the build part to enhance its end user application.