Papers by Author: Jian Hua Yao

Abstract: This article discusses the influence factors of bilingual teaching effect by bilingual teaching practice of the Advanced Manufacturing Technology, and proposes solutions. Practice shows that the reform of teaching idea is the prerequisite for the effective bilingual teaching, and PBL teaching model is the effect ways to improve the effects of bilingual teaching.

Abstract: This paper was focus on the technical parameters matching model of laser direct metal deposition（DMD）forming. Based on a series of DMD forming experiments, the energy balance equation of laser power, beam radius, powder feeding velocity and scanning velocity was established which could provide a theoretical principle for parameter selection and optimizing.

Abstract: High power continuous wave (CW) CO2 laser cladding was performed on H13 steel, pre-coated by superfine WC. After laser cladding, the materials were tempered for 6 hours. Scanning electronic microscopy (SEM) was used to observe the morphologies of the cladding layer. X-ray diffraction (XRD) was employed to analyze the microstructure of the cladding layer. The changes of microhardness, temper resistance and wear resistance were tested. The microhardness of cladding layer before tempering was 1.4 times of that of base metal and 1.9 times after tempering at 500°C. The wear resistance and tempering resistance were improved.

Abstract: In order to monitor the process of laser remanufacturing and control the quality of remanufacturing, a monitoring and control system for laser remanufacturing was constructed with its hardware and software. The schedule of the system including signal condition, software interface, sampling and control method, was introduced. Infra-red thermometer with dynamic aiming device was designed to track the molten pool location. Photoelectric sensor was developed to measure the flow of powder. The contrast test results show that the fuzzy PID control system for powder feeding could achieve stable flow.

Abstract: The stability of powder feeding is important to guarantee the quality of the laser remanufacturing. In order to detect and control the powder flow, a new powder feeding device is designed for laser remanufacturing. Scraper-type conveyer and capacitance sensor are used into the device which is tested by 2Cr13 and H13 powder. The results show that: Using H13 metal powder as medium will get a better effect，and when the changes of powder density are more than 10-1g/min, the device acts better distinguish-ability. The experimental results demonstrate that the system can be used to control the steel base powder feeding.

Abstract: The technological parameters of laser direct metal deposition (DMD) were researched by DMD forming experiments using 2Cr13 powder. Fixing other parameters, the lower of laser power, the smaller the characteristic sizes of cladding layer are. Increasing of laser power, cladding height would firstly increase and then decrease, cladding width would firstly increase and then almost maintain constant, while cladding depth would gradually increase. When other parameters are invariable, with increasing of powder feeding speed, cladding height would increase, cladding width and cladding depth would decrease. When other parameters are invariable, cladding width, cladding height and cladding depth would decrease with the adding of scanning speed. The microstructure of single track cladding had three typical patterns, cellular dendritic, column dendritic and equiaxed crystal. The patterns depended on the temperature gradient and the solidification velocity. Under different technical parameters, the average hardness of specimens would change from 300HV0.2 to 550HV0.2.

Abstract: Featured by cheap equipment, easy operation, nice controllability and low consumption, compound electroless deposit becomes an effective method to avoid failures such as high-temperature corrosion, fatigue and abrasion. Combined with the merits of nanometer material and laser treatment technology, the Ni-P nanometer Al2O3 electroless deposit after laser strengthening can get finer grains with high performances. This paper researched the technique of laser strengthening on 3Cr13 stainless steel after Ni-P-nano Al2O3 electroless plating. The experiments with low laser power and high laser power were performed. The crystallinity, phases and element distribution of coating were analyzed by X-ray Diffraction (XRD) and energy spectrometer (EDS). The microhardness and wear resistance of coating were measured as well. The results showed that composite coating heated by low laser power leads to transformation from non-crystal to crystal with high hardness. When heated by high laser power, the electroless deposit layer melted, and most of amorphous transformed to crystal. Combined with high laser power and high scanning velocity, the electroless deposit with finer grains and excellent properties was obtained. The strengthening mechanism was analyzed, and the properties including hardening and wear resistance were investigated as well.