Laser Energy Input Research Articles

Exploiting Laser‐Induced Oxidation Phase Diagrams for Multifunctional Titania Thin Films

AbstractLocal laser‐induced oxidation is an extremely valuable technique to perform high‐throughput optimization across multidimensional parameter sets. In this work, a versatile method is presented for the synthesis of titanium dioxide (TiO2) thin‐films with varying crystalline structures through the use of localized, visible, continuous‐wave laser‐processing. By controlling the laser intensity and the exposure time, the conversion of amorphous titanium disulfide (a‐TiS2) precursor films into distinct phases of TiO2 is achieved and a laser‐induced oxidation phase diagram is constructed with the resulting material phases, including anatase, rutile, and black TiO2. By utilizing the dependence of phase formation on the rate and duration of laser energy input, mixtures of anatase and rutile phases are fabricated with controlled spatial arrangements. Photocatalytic properties of the synthesized films are evaluated using the degradation of nitrogen oxide (NOx) gas under UV illumination and an organic dye under white‐light illumination, revealing that mixtures of anatase and rutile phases demonstrate superior photocatalytic activity. The laser‐induced oxidation method highlighted showcases a strategy for precisely tailored phase composition for directly tunable properties, paving the way for in‐depth studies into structure‐property relationships in photocatalysis and other applications of metal oxide films.

Residual regression on laser welding of CFRP-metal hybrid structures

The laser welding between high strength steel and carbon fiber reinforced polymer (CFRP) was explored in order to improve the mechanical properties and capacity to reflect physical relationships. The influence of process parameters on the mechanical properties of the joint was analyzed by RSM based on the experimental results. A residual regression method was proposed, using the residual block as the core structure and combined it with the fundamental concept and structure of the residual network. The residual regression model with two-layer residual block structure was compared with the RSM model at the same time, and the feasibility of this method was validated by experiments. The results show that the mechanical properties of the hybrid joint increase with the increase of the input laser energy per unit time. The proposed residual regression model can directly characterize the relationship between process parameters, intermediate physical quantities, and shear force and has better prediction accuracy and more physical relationships than RSM. The optimized parameters are laser power 1100 W, welding speed 9 mm/s and defocus distance 15 mm.

Numerical and experimental investigation on the heat transfer and mass transport in LPBF in-situ alloying of Al/Cu alloy

PurposeLaser powder bed fusion (LPBF) in-situ alloying is a recently developed technology that provides a facile approach to optimizing the microstructural and compositional characteristics of the components for high performance goals. However, the complex mass and heat transfer behavior of the molten pool results in an inhomogeneous composition distribution within the samples fabricated by LPBF in-situ alloying. The study aims to investigate the heat and mass transfer behavior of an in-situ alloyed molten pool by developing a three-dimensional transient thermal-flow model that couples the metallurgical behavior of the alloy, thereby revealing the formation mechanism of composition inhomogeneity.Design/methodology/approachA multispecies multiphase computational fluid dynamic model was developed with thermodynamic factors derived from the phase diagram of the selected alloy system. The characteristics of the Al/Cu powder bed in-situ alloying process were investigated as a benchmark. The metallurgical behaviors including powder melting, thermal-flow, element transfer and solidification were investigated.FindingsThe Peclet number indicates that the mass transfer in the molten pool is dominated by convection. The large variation in material properties and temperature results in the presence of partially melted Cu-powder and pre-solidified particles in the molten pool, which further hinder the convection mixing. The study of simulation and experiment indicates that optimizing the laser energy input is beneficial for element homogenization. The effective time and driving force of the convection stirring can be improved by increasing the volume energy density.Originality/valueThis study provides an in-depth understanding of the formation mechanism of composition inhomogeneity in alloy fabricated by LPBF in-situ alloying.

Microstructure and mechanical property of Ti/Cu ultra-thin foil lapped joints with different weld depths by nanosecond laser welding

In present study, 50 μm thick Ti/Cu pure metal ultra-thin foils are successfully lap-welded by a nanosecond fiber laser. The joints with adjustable depths are obtained by controlling the laser energy input precisely. The microstructure and mechanical properties of Ti/Cu joints with different depths are well analyzed, respectively. In the joint with smaller penetration depth of 10 μm, thin band-like Ti/Cu intermetallic compounds (IMCs) are formed, while in the joint with a larger penetration depth of 40 μm, thicker band-like Ti/Cu IMCs and sizable bright dendritic Ti2Cu phases are formed, since more Cu element are involved in the chemical reaction in the joint with penetration depth increasing. The tensile test results show that the weld with 10 μm penetration depth has the best tensile strength up to 240 MPa, which is mainly due to less IMCs and low heat input in the weld. In addition, the fracture mode of the joint is classified into two models, including brittle quasi-cleavage fracture on the Ti side fusion zone (FZ) and ductile fracture on the Cu heat affected zone (HAZ), respectively, depending on the penetration depth above or below 30 μm.

Predictable thermoelectric performance of directly synthesized Bi0.5Sb1.5Te3 using laser powder bed fusion additive manufacturing

Laser powder bed fusion (LPBF) additive manufacturing, as a novel technique provides broad benefits in thermoelectric materials synthesis, such as enhanced printing speed, reduced waste materials, and customized dimension design. The high energy density of laser could potentially balance the synthesis rate and thermoelectric figure-of-merit zT, but the correlations between laser energy and material performance are still vague. Herein, Bi0.5Sb1.5Te3 bulks are directly synthesized by LPBF with a recorded synthesis rate of 254 g h−1. The maximum zT, without any post-processing, reaches 1.1 at 75 °C. Induced nanoscale pores by high laser energy printing, obtain a comparable diameter to phonon mean free path, leading to reduced lattice thermal conductivity and enhanced TE performance. We found that input laser energy critically affected thermoelectric performance and concluded the correlation between volumetric energy density EV and power factor PF, PF = 9.05EV2 – 30.01EV + 48.84. It potentially predicts thermoelectric performance with inputted laser energy density.

Performance of electrochemically deposited hydroxyapatite on textured 316L SS for applications in biomedicine

ABSTRACT This study investigates the biocompatibility of laser-textured 316L stainless steel (SS) coated with hydroxyapatite (HA) for orthopaedic implants. Powdered HA was electrochemically deposited on the laser-textured surface of 316L SS, and various tests were conducted on its surface to assess its biocompatibility. A particle size analyser was used to determine the average HA particle size, and a 3D optical profilometer was employed to characterise the surface roughness of the laser-textured samples. Contact angle measurement results provide insights into the wettability of the substrate. Microscopy tests revealed that, compared to those without HA coating, HA coatings on spherical dimpled textures exhibited better cell adherence. Among the tested samples, a sample with 98% laser energy input, 40.45° contact angle, and 75.976 µm HA coating thickness was found to be the most suitable for bone implantation.

Unleashing multi-scale mechanical enhancement in NiTi shape memory alloy via annular intra-laser deposition with homogenized Ti2Ni nanoprecipitates

Additive manufacturing (AM) of composition-sensitive NiTi shape memory alloys (SMAs) is hindered by uncontrollable non-equilibrium microstructures, leading to functional performance degradation and limitations in high-throughput net-shaping applications. To address these challenges, we propose a novel approach combining annular intra-laser directed energy deposition (AIL-DED) with a tailored gradient post-treatment process. This enables the fabrication of nanocomposite microstructures in NiTi SMAs with precise control over the homogenization of Ti2Ni nanoprecipitates. In-situ monitoring and characterization of thermal history, microstrain, and constitutional phases, were utilized to uncover the relationship between multi-scale structural features and mechanical responses. The interplay between laser reflectivity, energy input, and lattice thermal vibrations affects forming quality in AIL-DED. Dynamic temperature variations were studied before reaching thermal equilibrium, revealing insights into thermal and mechanical interactions during the process. These findings contribute to understanding challenges in fabricating high-quality NiTi SMAs. Examining phase transformation behavior and its correlation with processing parameters deepens understanding of microstructural evolution and provides insights for tailoring material properties. The stress relaxation and dislocation evacuation at elevated temperatures caused the expansion of lattice and interplanar spacing in the age-treated SMA's B2 matrix phase, exhibiting a stable two-step phase transformation behavior (B19′↔R↔B2). AIL-DED combined with two-stage heat treatment strategy demonstrated enhanced homogeneity of non-equilibrium microstructures, resulting in the formation of high-density, well-dispersed Ti2Ni nanoprecipitates, with a semi-coherent interface to B2 matrix. The combination of load-bearing strengthening through well-dispersed Ti2Ni nanoprecipitates and Orowan strengthening at the semi-coherent interface yielded simultaneous enhancements in nanohardness, ultimate compressive strength, compressive fracture strain, and deformation recovery, following the AIL-DED combined with two-stage heat treatment process. The fracture mechanism transitioned from a mixture of brittle-ductile behavior to predominantly ductile characteristics. This study provides valuable insights that advance additive manufacturing and enhance the functional performance of SMAs in critical applications.

Investigating the effect of laser modulation and input energy on bending mechanism and bending angle in the multi-pass laser forming process through real-time monitoring

Laser forming is a non-contact type process used for bending, spatial forming, and alignment of metallic components through a controlled application of laser energy. The process involves localized rapid heating and cooling, inducing thermal strains exceeding the elastic strain of the material resulting in plastic deformation. The process is broadly governed by the temperature gradient mechanism (TGM), buckling mechanism (BM), and upsetting mechanism (UM). However, in the case of multi-pass laser forming process, heat accumulation and variation in the flow stress because of consecutive thermal cycles and strain hardening due to multiple bending cycles makes the process highly complicated. While operating laser in modulated mode may be a wise choice to handle the heat accumulation, inter-pulse cooling cycles along with variation in peak and average power with change in duty cycle affects the bending mechanism and angle significantly. Therefore, in the present study, a real-time monitoring system was developed to investigate the bending mechanism for a multi-pass laser forming process carried out in laser modulated mode. Also, the effect of average power, peak power, heat accumulation, strain hardening on bending mechanism and bending angle were investigated. Keeping the peak power constant, variation in duty cycle from 100% to 40% resulted in reduced average energy and strain hardening was found to be dominant, decreasing bending angle per pass. On contrast, variation in duty cycle by keeping the average power constant resulted in heat accumulation dominating the bending mechanism.

Finite Element Simulation and Experimental Assessment of Laser Cutting Unidirectional CFRP at Cutting Angles of 45° and 90°.

Laser cutting of carbon fibre-reinforced plastics (CFRP) is a promising alternative to traditional manufacturing methods due to its non-contact nature and high automation potential. To establish the process for an industrial application, it is necessary to predict the temperature fields arising as a result of the laser energy input. Elevated temperatures during the cutting process can lead to damage in the composite's matrix material, resulting in local changes in the structural properties and reduced material strength. To address this, a three-dimensional finite element model is developed to predict the temporal and spatial temperature evolution during laser cutting. Experimental values are compared with simulated temperatures, and the cutting kerf geometry is examined. Experiments are conducted at 45° and 90° cutting angles relative to the main fibre orientation using a 1.1 mm thick epoxy-based laminate. The simulation accurately captures the overall temperature field expansion caused by multiple laser beam passes over the workpiece. The influence of fibre orientation is evident, with deviations in specific temperature data indicating differences between the estimated and real material properties. The model tends to overestimate the ablation rate in the kerf geometry, attributed to mesh resolution limitations. Within the parameters investigated, hardly any expansion of a heat affected zone (HAZ) is visible, which is confirmed by the simulation results.

Joining of Aluminum and CFRP via Laser Powder Bed Fusion: Influence of Experimental Set-Up and Laser Processing on Microstructure and Mechanical Properties.

Additive-manufacturing-based joining methods enable tailored or even functionalized joints and allow for hybridization at small scales. The current study explored an innovative joining method for aluminum cast alloys (AlSi12) with thermoset carbon-fiber-reinforced polymers (CFRPs) via laser powder bed fusion (LPBF). The direct build-up of AlSi12 on a CFRP substrate proved to be challenging due to the dissimilar thermal properties of the considered materials, which led to substrate damage and low joint adhesion. These effects could be overcome by introducing an AlSi12 foil as an interlayer between the two joining partners, acting as a thermal barrier and further improving the AlSi12 melt wettability of the substrate. Within LPBF, the energy input in the form of volumetric laser energy density influenced both the porosity of the fused layers and the formation of thermally induced stresses due to the high cooling rates and different thermal expansion properties of the materials. While the AlSi12 volume density increased with a higher laser energy input, simultaneously increasing thermal stresses caused the debonding and deformation of the AlSi12 foil. However, within a narrow processing window of laser parameters, the samples achieved remarkably high shear strengths of τ > 20 MPa, comparable to those of conventional joining methods.

Comparative Study on Thermal and Laser Sintering of Silver Nanocubes and Silver Nanoplates

Compared with silver nanowires and silver nanospheres, silver nanocubes and silver nanoplates with larger curvature structures like sharp vertices and edges have great potential in optical applications. In general, the controllable joining of silver nanomaterials has become an effective way to change the electrical and optical properties of silver nanomaterials in recent years. However, urgent research on the controllable joining of silver nanocubes or silver nanocubes is still rarely reported. After being thermal treated at 250 °C for 8 min, a good joining among silver nanocubes can be obtained without significant damage to the cubic structure. For laser sintering, with the increase of laser energy input, silver nanocubes gradually transform to spherical particles. Joining among few particles can be observed when silver nanocubes are scanned by 5 W of laser at 1.0 mm s−1. Obvious joining among silver nanocubes can be obtained by thermal treating at 300 °C for 5 min and laser scanning at 7 W at 0.2 mm s−1. Thermal heating is more suitable for forming different degrees of connection between silver nanocubes or between silver nanocubes, while laser treatment is suitable for changing the shape of silver nanocubes or silver nanocubes without obvious connection.

Direct joining of quartz glass and copper by nanosecond laser

In present study, quartz glass and copper, which are with a large difference of coefficient of thermal expansion by 38 times, were successfully welded without any interlayer by nanosecond (ns) laser under non-optical contact for the first time. By reasonably tuning the welding parameters, well-formed quartz glass/copper joints without any defects such as microcracks or voids can be achieved. The welded seam includes laser-unirradiated smooth region and laser-irradiated spindle melted region and both the region are composed of “Cu2O″-SiO2 system (Cu–O–Si system) and CuO. The formation of such a particular microstructure feature is attributed to the recoil pressure from ns laser ablation and the Marangoni convection at the interface. The parameters of ns laser welding including laser power, scanning velocity and the number of scans influence the laser energy input and thermal accumulation greatly during welding, thus affecting the interfacial feature and the mechanical property of the resultant joints. The shear strength of the joint can reach 33.4 MPa, which is about 80% of quartz glass shear strength. The metallurgical bonding from interfacial reaction and mechanical interlocking from physical spindle structures are the main reasons for achieving a high shear strength of the joint. We expect this study could provide a new idea for joining materials with large differences in thermophysical properties.

A study on cracks and IMCs in laser welding of Al and Cu

Aluminum-copper laser welding has become a crucial joining technology for battery manufacturing. However, dissimilar material mixing in welding often causes the formation of intermetallic compounds (IMCs) and cracks, which reduce weld quality. In this study, the effects of laser power and welding speed on material mixing, IMCs formations, and crack formation were investigated by 3D micro-X-ray computed tomography imaging, computational fluid dynamics, and chemical/elemental analyses. Of crack formation during Al-Cu laser welding, transverse cracking was found to be the major type. The crack formation is associated with the IMC distributions generated throughout the weld fusion zone when high laser energy input caused more extensive Al/Cu material mixing.

Toughening additive manufactured Zr-based bulk metallic glass composites by martensite phase transformation

Additive manufacturing technology based on laser powder bed fusion (LPBF) offers a novel approach for fabricating bulk metallic glass (BMG) products without restriction in size and geometry. Nevertheless, the BMGs prepared by LPBF usually suffered from less plasticity and poorer fracture toughness as compared to their cast counterparts due to partial crystallization in heat-affected zones (HAZs). Since crystallization in HAZs is hard to avoid completely in LPBF BMGs, it is desirable to design a suitable alloy system, in which only ductile crystalline phase, instead of brittle intermetallics, is formed in HAZs. This unique structure could effectively increase the toughness/plasticity of the LPBF BMGs. To achieve this goal, a quaternary BMG system with a composition of Zr47.5Cu45.5Al5Co2 is adopted and subjected to LPBF. It is found that nearly a single phase of B2-ZrCu is precipitated in HAZs, while a fully amorphous phase is formed in molten pools (MPs). This B2 phase reinforced BMG composite exhibits excellent mechanical properties with enhanced plasticity and toughness. Furthermore, it is easy to modulate the mechanical properties by altering the amount of the B2 phase via adjusting the laser energy input. Finally, the best combination of strength, plasticity, and notch toughness is obtained in the BMG composite containing 27.4% B2 phase and 72.6% amorphous phase, which exhibits yield strength (σs) of 1423 MPa, plastic strain (εp) of 4.65%, and notch toughness (Kq) of 53.9 MPa m1/2. Furthermore, a notable strain-hardening is also observed. The improvement of plasticity/toughness and appearance of strain-hardening behavior are mainly due to the martensite phase transformation from the B2 phase to the Cm phase during plastic deformation (i.e., the phase transformation-induced plasticity effect). The current work provides a guide for making advanced BMGs and BMG composites by additive manufacturing.

Phthalocyanine covalent frameworks doped in PMMA matrix as high performance nonlinear optical limiter

Phthalocyanine compounds are a class of macrocyclic conjugated structures with 18 π-electrons. And have better photophysical properties. However, the π-π electron interactions lead to aggregation between phthalocyanine molecules, which affects optical limiting properties. In this work, the conjugated organic small molecule antiphenylenediamine (PDA) is grafted onto the phthalocyanine conjugate system through the azo condensation reaction, and the covalent organic framework polymer (PDA-InPc) was obtained. Then it is doped into the polymethyl methylmethacrylate (PMMA) matrix to produce a phthalocyanine solid device with different thickness (PMMA-PDA-InPc). The aggregation-free phthalocyanine covalent organic frameworks avoids intramolecular aggregation of the phthalocyanine units, and dispersing it in PMMA solid devices can also reduce intermolecular π-π stacking. As a result, the fluorescence lifetime of PMMA-PDA-InPc is τ1 = 0.52 ns (A1 = 95.71%) and τ2 = 11.5 ns (A2 = 4.29%), indicating that the phthalocyanine conjugated unit exists mainly as monomers (95.71%), while the proportion as aggregates is very small (4.29%). At the input laser energy of 9 μJ, the nonlinear absorption coefficient of PMMA-PDA-InPc device is (2.2 × 10−9 m/W), which is significantly better than PMMA-InPc device (1.0 × 10−9 m/W), indicating that PMMA-PDA-InPc has improved nonlinear absorption and reverse saturation absorption. This design idea of non-aggregated phthalocyanine covalent organic frameworks and its solid device expands a new idea for the development of useable phthalocyanine optical limiters.

Numerical simulation of the thermal behaviors for two typical damping alloys during selective laser melting

In this work, the three-dimensional transient temperature field model of two typical damping alloys (i.e., AZ31 Mg alloy and Mn-Cu alloy) were developed during selective laser melting (SLM) using ANSYS finite element analysis software, considering thermophysical properties and phase transformation latent heat of the materials. The simulated molten pool width values of the Mn-Cu alloy show a 6 % error with the experimental SLMed Mn-Cu sample, verifying that the developed model agrees well with the experimental results. Based on the developed numerical model, the temperature distribution, temperature gradients, and cooling rates of the two alloys were investigated during horizontal deposition and vertical deposition of SLM at different scanning speeds (300–700 mm/s). The results showed that the simulated peak temperatures of the AZ31 Mg alloy during the SLM process show a small fluctuation and are well below its boiling point (1107 °C) at the scanning speed of 500–700 mm/s. The temperature gradient increases from 8.5 × 106 °C/m to 20.2 × 106 °C/m with the laser scanning speed. The cooling rate increases from 1.7 × 106 °C/s to 4.1 × 106 °C/s, then reaches stable at 500–600 mm/s. As for Mn-Cu alloy, the cooling rate fluctuates between 7.5 and 8.8 × 106 °C/s during the SLM process at a scanning speed of 300–700 mm/s. By comparing the thermal behavior of the two alloys, the peak temperatures, temperature gradients, and cooling rate of both alloys are closely associated with their thermophysical properties and the laser energy input.

Modeling for evaluating the effect of powder flow during laser cladding process: From thermal and flow fields to microstructure of the molten pool

During the laser cladding process, the mass, energy and momentum inputs of the powder flow play a significant role in the evolution of the molten pool and microstructure. Considering the mass, energy and momentum inputs of the powder flow can significantly improve the accuracy of the simulation. In this study, an integrated modeling framework containing a computational fluid dynamics (CFD) model with the powder source described by ray tracing method and a cellular automata (CA) model was established to investigate the effects of powder flow on the evolution of the molten pool and microstructure during the laser cladding process. The accuracy of the modeling framework was verified by experiments with different powder particles velocities. The results indicated that the powder flow impact changed the vortices of the molten pool, resulting in less high–temperature molten metal flowing into the tail but more high–temperature metal accumulating at the bottom of the molten pool, thus decreasing the height but increasing the depth of the cladding layer. And the tail of the molten pool is more easily to be nucleated than other zones for the same reason. Increasing the powder particles velocity increases the percentage of equiaxed grains in the cladding layer from 46.21 % to 52.64 % and the aspect ratio of the grains at the top of the cladding layer decreases by 16.92 %. This study helps to optimize the laser cladding process and provides a basis for regulating the microstructure by controlling powder flow.

Thermal stability of laser track microstructures in an Al-Cr-Co-Mn-Zr I-phase alloy

Laser glazing of solid metal surfaces is an efficient and cost-effective way to evaluate the potential of an alloy system for use in metal additive manufacturing (MAM), but there are concerns about the stability of the resulting microstructures. Here it is shown that in situ transmission electron microscopy heating experiments on specimens cut from laser glazing tracks using focused ion beam methods can provide a useful insight into the transformation phenomena that occur upon reheating. Examples of such experiments are presented for laser tracks in a powder-processed Al-Cr-Mn-Co-Zr alloy, which contains a complex distribution of icosahedral quasicrystal (I-phase) dispersoids in a polycrystalline FCC Al matrix. Initial ramped heating experiments were performed to identify suitable conditions for isothermal studies of transformation pathways. Tracks with the lowest laser energy input exhibited supersaturated solid solution microstructures. These were stable during ramped heating to around 375 °C. For isothermal exposures at 400 °C there was precipitation of Al4(Cr,Mn) both at grain boundaries and within the FCC Al matrix phase. In tracks with higher laser energy input, equiaxed I-phase dispersoids were formed in the matrix. These microstructures were stable during ramped heating to around 400 °C. In isothermal experiments at 425 °C, there was precipitation of Al4(Cr,Mn), followed by the onset of I-phase decomposition. The partially decomposed dispersoids exhibited an I-phase core surrounded by a shell of Al45(Cr,Mn)7. In isothermal experiments at 450 °C, the dispersoids decomposed completely to form Al4(Cr,Mn), indicating that Al45(Cr,Mn)7 is a metastable intermediate transformation product. These observations provide a useful guide to the transformations that might occur during MAM processing of this alloy system.

Enhanced heat source modeling in particle-based laser manufacturing simulations with ray tracing

Particle-based spatial discretization methods such as smoothed particle hydrodynamics (SPH) possess suitability for the high-fidelity simulation of laser manufacturing processes due to their capability in treating complex free-surface and multiphase problems. In such simulations, laser heat source modeling remains a central concern as the mechanisms governing the material deformations and phase changes strongly depend on the input laser energy and its distribution details. Ray tracing (RT) is a realistic and accurate approach for high-fidelity heat source modeling that can capture surface heterogeneity and multiple reflections. However, RT heat source modeling for particle-based numerical methods faces additional challenges rooted in the lack of explicit surface representation, intensive computational efforts, and implementation complexities. This work addresses these issues by proposing an enhanced and efficient RT heat source model for particle-based laser manufacturing simulations with negligible computational overhead and without requiring background nodes or surface mesh reconstruction. After validating the RT heat source model versus analytical and experimental results, we assess its computational performance through two test cases, showing that the computing workload imposed by our RT model is between 0.1% and 25% of the total runtime in different SPH-based laser manufacturing simulations. With the achieved efficiency and robustness, it becomes convenient yet advantageous to simulate processes like laser drilling and laser powder bed fusion with precision far beyond the conventional approaches using volumetric heat sources.

Quantification of supplied laser energy and its relationship with powder melting process in PBF-LB/P using near-infrared laser

This study discusses the quantitative understanding of the laser input energy considering the optical properties and its effect on the melting process of powder materials in PBF-LB/P using a near-infrared laser. With the increased use of near-infrared lasers for PBF-LB/P in recent years, the influence of the input energy loss due to transmission and reflection on the powder melting process must be considered. Therefore, the modified energy melt ratio (Modified EMR), which is the ratio of the input energy to the energy required to melt the powder material, was proposed as a new energy supply index in this study. The energy absorbed by the powder layer was estimated from the transmission and diffuse reflection properties obtained in a previous study and the specular reflection properties obtained in this study. The powder layer thickness was determined by considering the consolidation of the powder layer, which affected the optical properties. The parts were fabricated with various optical properties, powder bed temperatures, and input energies to evaluate part density, which is closely related to the melting process. Compared to conventional indices, such as the energy density or EMR, the relationship between the Modified EMR and part density was more consistent, regardless of the optical properties and powder bed temperature. This study also investigated the effect of the laser heating of the layer below the powder layer on the melting process of the powder layer. The optical properties of a thin plate simulating the underlying layer were obtained, and the temperature increase in the underlying layer was determined from the known transmittance of the powder layer. It was concluded that heating the underlying layer does not accelerate the melting of the powder layer even at low powder bed temperatures, which require the highest laser energy for melting the powder material.