Investigation Of Laser Precise Repairing Technologies Of Plastic Moulds

The pulsed laser cladding is one of the most promising technologies of the plasticmoulds repairing. In order to industrialize it, the choice of repairing materials, theoryof repairing technology and properties assessing need to be solved. With theexperiment of pulsed Nd:YAG laser repairing plastic mould, the paper is carried onsystematic analysis on the optimization of parameters, the analysis of cladding defectsand the repairing properties. The main topics and achievements of the thesis are asfollows:1. The optimization of processing parametersIn order to fully consider the effect of these processing parameters and simply theadjustment course of parameters, single pulse energy is quoted and spot overlap ratedefinition is referred. With the help of theoretic analysis, the relationship between spotoverlap and there parameters (the pulse frequency, scanning speed and beam diameterof the Nd:YAG laser) is formulated. The experiment based on lower carbon steel iscarried out with pre-coated layer by laser cladding Ni-base alloy power. The perfectprocessing parameters are available, with single pulse energy and spot overlapseparately 6.7J and 97.4% or 21J and 69.4%. The investigations demonstrate thatchanging the six processing parameters (the voltage, electric current, pulse length,pulse frequency, scanning speed and beam diameter of the Nd:YAG laser) can't effectthe quality of pulsed Nd:YAG laser cladding.2. The layers' defects analysis of laser claddingThrough a lot of experiments, it found that the usual defects in laser claddinglayers are cracks, porosities, inclusions, segregation and fringe concavity. The reasonsand precautionary measures of defects are analyzed.3. The measure of repairing layers' mechanical propertiesOn the basis of the theory investigations, the lower carbon steel plastic mould isrepaired by pulsed Nd:YAG laser cladding used Ni-base alloy powers. Microstructure, hardness and wear characteristic of laser repairing coatings was respectivelysystematically studied by using optics microscope, scanning electron microscope,micro-hardness machine and wear testing machine. The results demonstrate that thecompleted repaired layers without pores and cracks can be obtained. An excellentbonding between the cladding layer and the substrate was ensured by a strongmetallurgical interface. The micro-hardness of repairing plastic mould is 230 HV,which is better than the lower carbon steel plastic mould. And compared with theprimitive low carbon steel mould, the friction coefficient of repairing plastic mould isdescended 40%. This is useful to increase the lifespan of plastic mould.