Research On LOM-Hybrid Waterjet-Guided Pulsed Nd:YAG Laser Thin Wood Micromachining Mechanism

Wood is a green,renewable,eco-friendly natural material widely accessible and applied in many fields worldwide.With the rapid growth of China’s economy and the continuous improvement of people’s living standards,processing molded products with specific shapes,sizes,and surface quality to meet the increasingly rich material and cultural life increases the social demand for wood products.Traditional wood product processing techniques are tiresome,time-consuming,inefficient,costly,and eco-pollutant,requiring specific tools that are not fully controllable with no accuracy or quality guarantee.Laser machining has been widely used in manufacturing,cutting,and engraving wood products as an efficient,flexible,and advanced subtractive process.However,high-powered laser ablation results in serious carbonization and wood burning,affecting the physical properties of the proceeded wood part and the machining quality.Even though gas or waterjet-assisted has been used to improve laser wood processing involving vaporization cutting,expelling excess or debris materials,cutting surface cooling,reducing heat accumulation and heat-affected zone expansion,and other conditions,the following problems remain unsolved.Traditional waterjet-assisted laser wood processing not only involves optical processing and multiphysics,the release of harmful,unsafe,and eco-pollutant gases but also favors the heat loss in water,the increase of wood water content affecting its thermophysical properties and machining performance,thus compromising the industrial application benefits of this technology.To mitigate the above problems comprehensively,a new laser wood products processing technique is developed considering laminated object manufacturing(LOM)pulsed neodymium-doped yttrium-aluminum-garnet(Nd: YAG)laser technology.The processing of thin wood products by LOM pulsed Nd: YAG laser and hybrid waterjet-guided Nd: YAG laser is studied deeply.The heat transfer,multiple physics,and interaction processes are analyzed through theoretical and thermonumerical modeling.The rationality and applicability of the developed models and predicted results are verified experimentally,providing the basis for efficient and eco-friendly thin wood product manufacturing.The main research contents are as follows:Thin wood products processing mechanism based on LOM pulsed Nd: YAG laser subtractive technology is studied.The theoretical basis of the heat transfer theory of laser micro-thin wood processing is constructed.Theoretical and thermonumerical models of pulsed Nd: YAG laser thin wood processing are established to study the mechanism of material processing,heat transfer,and heat interaction in laser wood micromachining.The cutting models of thin wood heating and evaporation processes were constructed according to wood workpiece thickness at temperature-independent thermophysical properties and laser operating parameters.Based on pulsed laser-wood interaction,heat transfer mechanism,and the established numerical relations,Black walnut and Korean pine wood are selected as wood workpieces for simulation using Engineering Equation Solver(EES)and Finite Element Analysis(FEA)COMSOL Multiphysics software.The temporal wood surface and gradient temperature profiles,heat penetration depth,melting and ignition time,wood thickness and laser power influence on the cut surface,and volume temperature were analyzed for thin wood parts under 1.064 μm pulsed Nd: YAG laser irradiation.Study on LOM pulsed Nd: YAG laser micro-thin wood processing.Pulsed Nd:YAG laser wood veneer micromachining is experimentally analyzed for efficient and eco-friendly wood product processing using LOM-based technology.An experimental case study is conducted for thermonumerical modeling validation and characterizing pulsed Nd: YAG laser micro-thin wood processing.Based on processing conditions and wood veneer characteristics,mathematical relationships are established between woodcut depth and influencing process parameters: laser power,cutting speed,and wood variables at temperature-independent properties.Considering the wood veneer worksheet used by LOM-based technology,a low-power pulsed Nd: YAG laser system is developed to machine black walnut veneer workpieces under different operational machining conditions.Based on the machining quality under the selected conditions,the influence of process parameters on cut kerf and surface quality was investigated via micro-morphology,experiment,and parametrical analysis.The feasibility study of hybrid waterjet-guided pulsed Nd: YAG laser thin wood processing is analyzed.The heat conduction and coupling mechanism of the hybrid waterjet-guided pulsed Nd: YAG laser for thin wood processing are studied.The heat transfer mechanism of the pulsed Nd: YAG laser,pressurized waterjet,multiphysics,laser-waterjet interaction,and the thin wood micromachining process were analyzed.Numerical and thermodynamic models of laser heating and water jet ejection are established to analyze the laser-waterjet interaction and its influence on the surface temperature field.Waterjet impingement and its thickness,laser absorption coefficient,laser-induced plasma,bubble formation,and beam refraction at the air-water interface were investigated through simulation using Engineering Equation Solver(EES),Finite Element Analysis(FEA)COMSOL Multiphysics,and experimental data.Based on initial and boundary conditions,the numerical model of the temperature field of the hybrid waterjet-guided pulsed Nd: YAG laser thin wood processing is established to solve the time-dependent temperature profiling problem.The analytical solutions of the time three-dimensional temperature field as a function of hybrid waterjet-guided pulsed Nd: YAG laser processing parameters and thermal physical properties of thin wood materials were obtained.Practical verification of the LOM-hybrid waterjet-guided pulsed Nd: YAG laser wood product processing is carried out.Hybrid waterjet-guided pulsed Nd: YAG laser thin wood processing is experimentally studied for eco-friendly LOM wood product manufacturing.Regarding traditional waterjet-guided laser processing,based on LOM-pulsed Nd: YAG laser thin wood processing technology and theoretical hybrid waterjet-guided pulsed Nd: YAG laser wood processing,hybrid waterjet-guided pulsed Nd: YAG laser system was established to complete thin wood processing under different machining conditions.Korean pine(Pinus Koraiensis)and Northeast China ash(Fraxinus mandshurica)are selected as thin wood workpieces characterizing the two leading wood groups: soft and hardwood.Based on machining conditions and parameters characterization,the influence of machining parameters,the cut kerf,heat affected zone,surface roughness,and micromorphology on machining efficiency and surface quality are studied via scanning electron microscopy(SEM)and experiment analysis,providing technical resources for efficient and eco-friendly LOM-hybrid waterjet-guided pulsed Nd: YAG laser thin wood product manufacturing.