| The metal structure additive manufacturing based on pulsed laser is the research hotspot and frontier problem of 3D printing technology.The technology mainly divides the 3D solids into several two-dimensional planes,which is called “dimension reduction processing” in the industry,and use laser as a heat source to melt powder which will be stacked to form the target entities layer by layer.Compared with the traditional processing methods,the technology has advantages of simple process,moderate accuracy and short production cycle which make it potential in the field of manufacture.In addition,the metal additive manufacturing technology using the pulsed laser is mainly based on the Selective Laser Melting process,and its theoretical and process research are becoming more and more consummate.Until now,the technology has been widely used in aviation,medical,automotive and other related fields.However,SLM usually requires high-specification,high-cost equipment and special molten powder,which restrict its wide use in the civil industry.For manufacturing metal structure,this paper proposes a low-cost method called quasi-SLM,which uses laser source of laser spot welder and domestic metal powder to achieve the direct formation of metal microstructure based on layered manufacturing principle.Under the premise of ensuring the forming quality,the process is able to greatly reduce the manufacturing cost.Firstly,the principle of pulsed laser forming technology was deeply analyzed.The physical model was established and used to simulate the temperature field by ANSYS software.Then the relationship between the experimental parameters,such as layer thickness,laser power,moving speed,and internal temperature field of alloy powder was analyzed.Secondly,the single factor analysis about single-layer single-melt morphology was carried out,and the optimal range of each parameter and the parameter combination were determined.Then,the appropriate line lap rate and scanning strategy were selected by analyzing the results of forming multi-channel and multi-layer.Thirdly,the micro-convex arrays with suitable size were formed on the smooth surface using the selected process parameters.The variation trend of the friction coefficient of the micro-convex arrays with different distribution densities under sufficient lubrication was studied to judge whether the texture has anti-friction properties.Fourthly,the feature structures were formed with optimal combination of parameters,and the forming quality was analyzed.Fifthly,the hardness,metallographic structure and density of the prepared samples were tested and analyzed,providing basic data for applied research.The research results show that the metal structure with good deposition quality can be obtained under certain conditions.The optimized experimental parameters are powder particle size of 15 μm to 50 μm,a layer thickness of 200 μm,a laser frequency of 12 Hz,a pulse width of 1.4 ms,a peak current of 100 A,and a scanning speed of 2.5 mm/s.With these parameters,different dip angle structures,variable density grid structures and honeycomb unit structures were successfully produced.These final parts have high accuracy,dense internal structure,no obvious defects,and a density of 95.75%.At the same time,the surface texture of micro-convex arrays created by using pulsed laser was observed,and the surface texture of different distribution densities was prepared.Finally,the antifriction properties of the textured surface were confirmed by experiments.Moreover,the coefficient of friction at the surface texture distribution density of 51.02% was reduced by 12.5% with respect to the smooth surface. |
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