基于神经网络遗传算法的磁粒研磨TC4材料工艺参数优化

目的利用磁粒研磨光整加工技术提高TC4材料的表面质量,使用BP神经网络建立加工工艺参数和表面粗糙度之间的关系,使用遗传算法寻找最优工艺参数组合。方法使用双级雾化快凝法制备的金刚石磁性磨料对TC4材料工件进行L9(34)正交试验,借助Matlab软件建立结构为4-12-1的BP神经网络,根据正交试验结果训练BP神经网络,探究工艺参数主轴转速n、加工间隙δ、进给速率v、磨料粒径D和表面粗糙度Ra之间的关系。使用决定系数R2评判BP神经网络训练结果,基于训练好的BP神经网络使用遗传算法对工艺参数进行全局寻优。使用计算得到的优化工艺参数进行试验,并测量工件表面粗糙度,与计算得到的表面粗糙度做对比。结果BP神经网络的预测误差在1.5%以下,通过决定系数R2优化的模型可在训练样本较少的情况下进行有效可靠的预测。遗传算法优化的结果,在主轴转速为1021.26 r/min、加工间隙为1.52 mm、进给速率为1.04 mm/min、磨料粒径为197.91μm下,获得最佳表面粗糙度,为0.0951μm。使用调整后的工艺参数,在主轴转速为1020 r/min、加工间隙为1.50 mm、进给速率为1.0 mm/min、磨料粒径为196μm下,试验得到的表面粗糙度为0.093μm,与计算得到的最佳表面粗糙度误差为2.21%。结论采用磁粒研磨光整加工技术与寻优参数结合,可以有效提高TC4材料加工后的表面质量。     

双磁极式磁粒研磨机理分析及试验研究

目的解决平面磁粒研磨中压力不均匀和需要反复调整研磨间隙的问题,设计双磁极式研磨方法。方法首先对双磁极式研磨方法机理进行分析,并对研磨区域单颗磨粒进行受力分析,寻找影响研磨压力的主要因素;其次利用Ansoft Maxwell软件对两种研磨方法进行磁场仿真,分析两种研磨方法的研磨区域磁场梯度变化,通过面积积分法对比磁感应强度的影响程度;最后设计试验装置,通过试验对理论分析及有限元分析的结果进行验证,对比研磨前后工件表面粗糙度及微观形貌变化。结果双磁极式研磨方法中磨粒的研磨压力完全由磁场力提供,与研磨区域磁感应强度成正比,研磨区域磁感应强度比"铣削式"研磨方法提高约34.56%。两种方法在相同试验条件下对SUS304不锈钢板研磨40 min,双磁极式研磨方法研磨后,工件表面原始纹理基本被去除,表面粗糙度值由原始的0.25μm下降至0.16μm,下降率为36%,比"铣削式"研磨方法提高约80%,粗糙度曲线波动平缓,波峰波谷高度差变化均匀且表面形貌光滑平整。结论双磁极式研磨方法研磨区域磁场梯度变化明显,利于磨粒流动更新,研磨压力相对稳定,表面粗糙度下降率高,研磨后工件表面形貌光整,与"铣削式"研磨方法相比具有较明显的优势。     

4320H钢风电机齿轮的渗碳淬火

4320H风电机齿轮需进行渗碳、淬火,达到表面硬度58~62HRC、心部硬度33~44HRC、有效硬化层(至515HV0.5)深度2.0~3.0mm,有非马氏体组织的深度≤0.05mm,马氏体1~4级,心部铁素体1~3级,但无连续网状碳化物。采用UBE密封箱式炉对4320H钢齿轮进行了渗碳、淬火。通过热处理工艺的调整,最终达到了上述质量要求。     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

GSH-responsive polyglutamic acid nanocarriers for dual targeted cancer therapy

In order to reduce the toxic side effects of chemotherapeutic drugs and improve the targeting and efficiency of cancer treatment, the development of drug delivery system has received great attention. In this study, second generation polyglutamic acid dendrimers (G₂) are used as basic materials to produce porous nanoparticles through cross link by crosslinkers containing disulfide bonds. The crosslinked products (G₂)_n have negative electricity and abundant voids, which enable them to adsorb the electronegative anticancer drug DOX. At the same time, in order to transport DOX to the tumor site, we modified FA on DOX and encapsulated it in magnetic mesoporous silica (FA-DOX-MSNs). Therefore, the final nanoparticles (FA-DOX-MSNs/(G₂)_n) not only have dual targeting ability to transport DOX to the tumor site, but also have reductive responsiveness that can release drugs responsively in the tumor cells. In addition, it has good biocompatibility and endocytosis ability.     

Performance evaluation of a bubble generator and a bubble separator designed for the gas removal system of a small thorium molten salt reactor

In the present study, a bubble generator and a bubble separator were designed and evaluated for an independent off-gas removal system of a small thorium molten salt reactor(TMSR) with reference to the design of the Oak Ridge National Laboratory(ONRL). The bubble generator employed a Venturi tube as its main body owing to its simplicity and highly reliable structure. A centrifugal separator was used as the bubble separator, taking advantage of the kinetic energy of fluid to create a centrifugal force to separate gas bubbles from the mixture flow. Both the bubble generator and the separator were demonstrated to have good potential to meet the performance requirements of an off-gas removal system for a small TMSR. With water and air as the working fluids, for the final designs of the two key pieces of equipment, a liquid flow rate exceeding 15 m~3·h~(-1) can essentially make their performance meet the requirements of the off-gas removal system in terms of the average size of the generated bubbles and gas separation efficiency.     

Enhanced heat transfer in rectangular duct with punched winglets

Thermal performance of a heat exchanger duct with punched winglets(PWs) mounted on the upper duct wall has been examined for Reynolds number(Re) ranging from 4100 to 25,500. In the present experiment, two types of PWs: punched delta-and elliptical-winglets(P-DW and P-EW) with four punched-hole sizes were tested at a fixed attack angle, optimal relative pitch and height. Also, data of solid delta-and elliptical-winglets(DW and EW) were included for comparison. The investigation has shown that the P-DW yields higher thermal-performance enhancement factor(η) than the P-EW. Although the solid DW and EW with no punch have the highest heat transfer and friction loss, the PWs yield better η than the solid ones. For PWs, the P-DW with smaller hole size has the peak heat transfer and friction loss around 5.7 and 40 times over the smooth duct, respectively but the optimum η of 2.17 is seen for the one with a certain hole size. The PWs provide η at about 5%–8% above the solid winglets.     

双机器人系统运动协调仿真与实验研究

针对具有重量大、形状不规则特征的物品,采用双机器人协同作业是该技术领域的研究热点问题之一。运用ADAMS软件对双机器人虚拟样机进行运动学仿真分析,模拟空间搬运轨迹,对DREE末端点的运动轨迹曲线进行同步误差分析。搭建了实验平台,对双机器人同步搬运箱体进行实验验证。实验结果表明:双机器人协作搬运箱体时,在水平方向和垂直方向的轨迹误差均小于±2.8mm,较好地满足同步搬运作业工艺要求。     

25Cr2Ni4MoV锻轴制造工艺研究

对25Cr2Ni4MoV钢锻轴的冶炼、锻造、热处理工艺进行研究,并通过超声检测和力学性能检验,充分证明了其冶炼、锻造、热处理工艺的可行性。在生产实践中,成功地制造出了4支该材质的60 MW空冷发电机转子。     

Reduction in Microsegregation in Al-Cu Alloy by Alternating Magnetic Field

The microsegregation behavior of the Al-4.5 wt%Cu alloy solidified at different cooling rates under the alternating magnetic field(AMF) was investigated.The experimental results showed that the amount of non-equilibrium eutectics in the interdendritic region decreased upon applying the AMF at the same cooling rate.The change in microsegregation could be explained quantificationally by the modifications of dendritic coarsening,solid-state back diffusion and convection in the AMF.The enhanced diffusivity in the solid owing to the AMF was beneficial for the improvement in microsegregation compared to the cases without an AMF.In contrast,the enhanced dendritic coarsening and forced convection in the AMF were found to aggravate the microsegregation level.Considering the contributions of the changes in above factors,an increase in solid diffusivity was found to be primarily responsible for the reduced microsegregation in the AMF.In addition,the microsegregation in the AMF was modeled using the analytical model developed by Voller.The calculated and experimental results were in reasonable agreement.