Process And Device Of Laser Alloying On Piston Pin Working Face

The piston pin working face was strengthened by the laser alloying technology with Nd:YAG laser, its surface hardness and wear resistance was improved effectively. Optimizing process parameters and improving the quality of the alloy by the experiment research and theoretical analysis. Details are as follows:（1） The process of laser alloying on piston pin working face was formulated from laser processing method, alloying material selection, alloying material adding, material surface pretreatment and scanning path planning.（2） According to the size and the structure characteristics of piston pin, special fixture and power coating equipment were designed to get a better surface quality for easily laser alloying on piston pin working face, which improved the processing efficiency.（3） Through the single factor experiment, the influences of pulse current, scanning speed, pulse width and frequency,defocusing amount to the quality of alloying layer were obtained. The pulse current, scanning speed and defocusing amount were selected for orthogonal test, the optimal process parameters combination for: pulse current I=150A, scanning speed V=160mm/min, defocusing amount L=12mm, pulse width ti =0.8ms and pulse frequency f =100Hz, establishing the mathematical model on the piston pin surface hardness and the thickness of the alloy layer.（4） Under the optimal process parameters combination, the X-ray diffraction analyzing that the main phases of the alloy layer are martensite, Fe-Ni solid solution,Ni-Cr-Fe solid solution, Cr₂₃C₆, CrB₂, Ni₂ Si, etc, which plays an important role in the surface hardening of alloy layer.（5） Under the optimal process parameters combination, using pin type wear test machine to test the piston pin laser alloying processing part, the result shows that the wear resistance of laser alloying on 20 Cr steel piston pin enhanced 4.3 times than before treatment. The wear surface of the piston pin by alloying is smooth, not obvious spalling and furrow phenomenon, which was observed by scanning electron microscopy. These results show that the wear resistance of the piston pin laser alloying processing part is greatly improved.