Study On Optimization Of Surface Laser Cladding Layer Morphology And Evaluation Of Cladding Quality Of 45 Steel

45 steel is often used to manufacture critical components under high intensity motion conditions such as alternating loads,such as pistons,shafts,gears,connecting rods,bolts,etc.in compressors.These critical parts usually fail in practice due to surface wear,corrosion,oxidation,fracture,and other conditions.The failure of the parts not only increases the cost,but even causes serious safety accidents.To alleviate part failures,additive manufacturing is often used to repair surfaces,with laser cladding being the most common technique.Although laser cladding has evolved over the decades,there are still many problems that people face when using it for processing.For example,the laser cladding process is highly nonlinear,and different process parameters or different materials have a large impact on the coating morphology,so the selection of materials and process parameters can generally only rely on subjective experience;secondly,for the quality of laser clad coatings,people tend to study only from a few aspects,which is one-sided on the one hand,and does not break this abstract and vague concept on the other.In this paper,the coaxial powder feeding laser cladding technique was used to clad 316 L stainless steel coating on 45 steel.The response surface method combined with mathematical planning was used to explore the forming law of the clad morphology and optimize the morphology.At the same time,a fuzzy comprehensive evaluation model was used for the first time to evaluate the quality of the cladding layer in all aspects,breaking the inherent fuzzy concept.The main research contents and conclusions are as follows:By designing a full factorial experimental scheme and conducting experiments,four indexes of average cladding layer height,average melt pool depth,average dilution rate,and average surface height difference were used and a large number of experimental sample data were measured.The response surface analysis method was used to analyze the experimental data at 95% confidence level to find out the hidden mathematical expressions between the four indexes and the process parameters.From the standardized effect diagram,it can be seen that: the scanning speed has the most significant effect on the average height of the molten layer,the laser power has the most significant effect on the average depth of the melt pool,the distance from the melt head to the substrate has the most significant effect on the average dilution rate of the substrate,and the scanning speed has the most significant effect on the average height difference of the surface.The mathematical planning method is used to take into account all combinations of process parameters in the selection range,and the four mathematical expressions derived from the above steps are used as the objective functions in mathematical planning.The 4 objective functions are transformed into 1 new objective function with the help of Monte Carlo method and hierarchical analysis.The optimal values of the above four indicators were set as 0.7mm,0.15 mm,0.075,0mm,and the objective function was subjected to the constraint to find the optimum.The results showed that the process parameters for the optimum coating morphology were laser power equal to880.5W,scanning speed equal to 5.5692mm/s,lap rate equal to 21.28%,and distance from the coating head to the substrate equal to 1.509 mm.The experimental verification of the theoretical analysis shows that the coating layer is bright and flat,and the coating morphology meets the expected requirements.The fuzzy comprehensive evaluation model is used to establish the first-level evaluation indexes from macroscopic morphology,microstructure and mechanical properties.The first-level indicators of macroscopic morphology include four second-level indicators of average height of clad layer,average depth of melt pool,average dilution rate and average height difference of surface;the first-level indicators of microstructure include three second-level evaluation indicators of dendrite size,porosity and crack density;three second-level indicators of hardness ratio are included by the mechanical properties between substrate and clad layer,friction coefficient and wear amount.Different levels’ evaluation indexes are assigned weights to by using hierarchical analysis.Based on the existing experience,we set values’ range for each index that is corresponding to different quality levels and establish the affiliation function between them.The fuzzy comprehensive evaluation model was used to evaluate the quality of the experimental samples,which changed the original fuzzy qualitative analysis into quantitative expression,and thus ranked all workpieces’ coating quality.This paper presents a comprehensive study on the morphology prediction,optimization,and quality evaluation of laser clad coatings on 45 steel surfaces,achieving the expected results while giving assistance in the application of multi-pass laser cladding technology.