Experimental Research On The Dimensional Accuracy And Surface Quality Of Selective Laser Melting Forming With Gap

Selective Laser Melting(SLM)technology can directly form parts with complex structure,high density and excellent mechanical properties.It is also an ideal technology for direct manufacturing of"assembly-free mechanisms".However,there are problems that the dimensional accuracy of the molded part is too low and the surface quality is too poor.If the dimensional accuracy or surface quality at the gap of the movement pair in the assembly-free mechanism is too low,it may cause the formed mechanism to fail to meet its movement requirements.Aiming at the above problems,this paper takes the assembly mechanism as the background,and focuses on the structure with gaps formed by SLM,and mainly uses experimental methods to study the influence of various process parameters on the dimensional accuracy and surface quality of the structure with gaps in order to find the optimal combination of parameters.The main content and results of the full text are as follows:(1)Analyzed the forming conditions of SLM forming structures with gaps under different placement methods.The placement methods are mainly divided into horizontal placement,vertical placement and inclined placement,The horizontal placement mode is easy to cause a large amount of support inside the gap of the movement pair,and it is difficult to remove the support,The vertical placement of molding reduces the processing efficiency,and when the length of the molded part exceeds the maximum range of the molding chamber,the processing will fail,When the quality requirements of the molded parts are not too high,the inclined placement method is preferred.(2)The gap size between the inclined gap and the curved surface gap is analyzed by forming experiments,which provides an experimental basis for the selection of the gap size of the molded part in the subsequent process parameter experiments.By using SLM,the inclined gap and curved gap of different gap sizes are formed,Through analysis,it is known that regardless of the inclined gap and the curved surface gap,when the gap size is 0.4mm,the gap is well formed at this time,And the relative error is below 20%,so the gap size of the molded part in the subsequent process experiment is chosen to be 0.4mm.(3)The influence of the step effect on the dimensional accuracy and surface quality of the gap of the moving pair in the SLM forming process is analyzed separately,The biggest influencing factors are the tilt angle and the thickness of the powder layer.Theoretical analysis of the reasons for the formation of surface defects(powder sticking phenomenon,slagging phenomenon,spheroidization phenomenon,warping deformation phenomenon,etc.)during the molding process and the influence on the dimensional accuracy and surface quality of the molded part,The main reason for the formation is the unreasonable setting of process parameters.Among them,the slagging phenomenon has the greatest impact on the dimensional accuracy and surface quality.(4)The influence of process parameters on the dimensional accuracy of SLM forming mechanism with clearance is studied.The dimensional accuracy gradually increases with the increase of laser power,and shows a trend of first increasing and then decreasing as the scanning distance and scanning speed increase,The highest dimensional accuracy when the scanning distance is 0.08mm and the scanning speed is600mm/s,As the tilt angle increases,the dimensional accuracy becomes higher,and the dimensional accuracy is highest when the body energy density is 80J/mm~3 to 110J/mm~3.(5)The influence of process parameters on the surface quality of SLM forming structure with clearance is studied.The surface quality of the mechanism with clearance is divided into overhanging surface part and non-overhanging surface part.Each process parameter has an impact on the surface quality.The surface roughness of the molded part gradually decreases with the increase of the laser power,and it first decreases and then increases with the increase of the scanning distance and scanning speed.The optimal parameter combination is 0.08mm scanning distance,200w laser power,and 600mm/s scanning speed.The surface roughness gradually increases with the increase of the inclination angle,and the inclination angle has a greater influence on the surface roughness of the overhanging structure.When the volume energy density is 80J/mm~3 to110J/mm~3,the upper and lower surface quality of the molded parts are both For the best.