Purpose:　This　paper　aims　to　study　numerically　the　influence　of　the　applied　laser　energy　density　and　the　porosity　of　the　powder　bed　on　the　thermal　behavior　of　the　melt　and　the　resultant　instability　of　the　liquid　track.　Design/methodology/approach:　A　three-dimensional　model　was　proposed　to　predict　local　powder　melting　process.　The　model　accounts　for　heat　transfer,　melting,　solidification　and　evaporation　in　granular　system　at　particle　scale.　The　proposed　model　has　been　proved　to　be　a　good　approach　for　the　simulation　of　the　laser　melting　process.　Findings:　The　results　shows　that　the　applied　laser　energy　density　has　a　significantly　influence　on　the　shape　of　the　molten　pool　and　the　local　thermal　properties.　The　relative　low　or　high　input　laser　energy　density　has　the　main　negative　impact　on　the　stability　of　the　scan　track.　Decreasing　the　porosity　of　the　powder　bed　lowers　the　heat　dissipation　in　the　downward　direction,　resulting　in　a　shallower　melt　pool,　whereas　pushing　results　in　improvement　in　liquid　track　quality.　Originality/value:　The　randomly　packed　powder　bed　is　calculated　using　discrete　element　method.　The　powder　particle　information　including　particle　size　distribution　and　packing　density　is　taken　into　account　in　placement　of　individual　particles.　The　effect　of　volumetric　shrinkage　and　evaporation　is　considered　in　numerical　model.　©　2018,　Emerald　Publishing　Limited.