Abstract: The sheet metal forming of magnesium alloy is studied. A novel hydro-mechanical deep drawing for magnesium alloy sheets at gradient temperature is proposed on the basis of the study in this domain, the properties of magnesium alloy and the forming characteristics of workpiece in deep drawing. It is indicated that the deep drawing operation should be done in the warm condition and the temperature gradient of workpiece is necessary. The essence why the limited drawing ratio can be improved by means of the new process is demonstrated. The proper temperature gradient can be obtained by the control of the hydraulic during deep drawing operation. Thus the feasibility of the new technology is verified. It plays a solid foundation for solving the forming problem of magnesium alloy sheets and designing the novel setup of hydro-mechanical deep drawing with gradient temperature.
Abstract: Cross wedge rolling (CWR) technology, which is a new metal forming process to produce stepped shaft in forging industry, has developed rapidly in the last decades. Tool wear is a key factor to influence products’ quality during CWR process in practice. Basing on the analysis of characteristic of the tool wear, the similar outline dimension of the worn tool in service is obtained by blocking up the end of the tool. A series of experiments are completed to research the influence of the tool wear on the center defects of the workpiece, and the available method to repair the worn tools is brought forward.
Abstract: With JC2000A Contact Angle Measuring Apparatus and established model of rice straw surface wetting, to improve the surface wetting properties of Rice Straw, effects of four kinds of alkali spray on Rice Straw at room temperature on contact angle was studied. The result shows that after alkali treatment the surface wettability of Rice Straw obtained significant improvement, contact angle decreases with the treatment time extended. The contact angle change rate reached the largest within 10min with the decreasing gradient of 20.64% when rice straw was dealt with NaNH2 at the mass fraction of 1%. Under the same conditions, rice straw processing with CaH2 has the minimum gradient contact angle change rate of 3.6%, A large number of Ca(OH)2 formation made The contact angle did not change significantly with time extended. Effect of NaOH treatment changed significantly over time, the optimum conditions of processing technology were obtained through orthogonal test: concentration of NaOH is 0.6%,solvent ratio 1:3.5 and reaction time 12h.
Abstract: A Ni-based alloy NiCrSiB laser cladding layer was made on the surface of CrNiMo stainless steel specimens using NiCrSiB powder. Cavitation erosion behavior of the laser cladding layer and the CrNiMo stainless steel was investigated by ultrasonic vibration cavitation erosion equipment The results shown that laser cladding layer has dense microstructure and has metallurgical combination with CrNiMo stainless steel substrate. Because of impact effect of cavities collapse, micro-cracks caused material broke off from samples. NiCrSiB laser cladding layer have better micro-crack propagate resistance property than CrNiMo stainless steel.Laser cladding layer has better cavitation resistance properties because of strengthening effect by precipitated phases such as M23[CB]6、CrB、CrSi、Fe2B、B4C and work hardening effect during cavitation erosion process.
Abstract: This study introduces an Abrasive Jet Polishing (AJP) technique using wax-coated abrasive SiC particle to improve the polishing quality of mold surface. The experimental results showed that the surface roughness of EDM machined mold cavity improved by 82% (from 4.23 μmRa to 0.76μmRa) within 90 minutes. Moreover, the parting surface roughness improved by 94.7% (from 1.14μmRa to 0.06μmRa). We show that employing the abrasive jet polishing technique with wax-coated SiC particles, not only the mold surface roughness got a good improvement, but also significantly shorten the polishing time.