Energy-efficient scheduling for a flexible flow shop using an improved genetic-simulated annealing algorithm

The traditional production scheduling problem considers performance indicators such as processing time, cost, and quality as optimization objectives in manufacturing systems; however, it does not take energy consumption or environmental impacts completely into account. Therefore, this paper proposes an energy-efficient model for flexible flow shop scheduling (FFS). First, a mathematical model for a FFS problem, which is based on an energy-efficient mechanism, is described to solve multi-objective optimization. Since FFS is well known as a NP-hard problem, an improved, genetic-simulated annealing algorithm is adopted to make a significant trade-off between the makespan and the total energy consumption to implement a feasible scheduling. Finally, a case study of a production scheduling problem for a metalworking workshop in a plant is simulated. The experimental results show that the relationship between the makespan and the energy consumption may be apparently conflicting. In addition, an energy-saving decision is performed in a feasible scheduling. Using the decision method, there could be significant potential for minimizing energy consumption.     

Effects of pulsating electrolyte flow in electrochemical machining

Electrochemical machining (ECM) is a promising and low-cost process for yielding various components of difficult-to-machine materials, and has been well established in diverse applications. Distributions of gas and temperature affect the electrolyte electrical conductivity and determine the machining accuracy in ECM. Attempts have been made to generate the pulsating flow via a servo-valve in the electrolytic supply pipe, which is introduced to improve the heat transfer, material removal rate and surface profile in ECM. A multi-physics model coupling of electric, heat, transport of diluted species and fluid flow is presented. Simulation results indicate that pulsating flow has a significant impact on the distributions of velocity, gas fraction, and temperature near the workpiece surface along the flow direction. Experiments are conducted to verify the feasibility of the proposed process and study the effects of pulsating flow on material removal rate. The experimental results agree well with the simulations. Using optimal pulsating parameters, the material removal rate and surface profile are enhanced.     

Modeling of material removal rate in electric discharge grinding process

The mechanism of material removal in electric discharge grinding (EDG) is very complex due to interdependence of mechanical and thermal energies responsible for material removal. Therefore, on the basis of conceived process physics for material removal, an attempt has been made to predict the material removal rate (MRR). The proposed mathematical model is based on the fundamental principles of material removal in electric discharge machining (EDM) and conventional grinding processes. The inter-dependence of the thermal and mechanical phenomena has been realized by scanning electron microscopy (SEM) characterization of the samples machined at different processing conditions. The key input process parameters like pulse on time, pulse current, gap voltage, duty cycle, pulse off time, frequency, depth of cut, wheel speed and table speed are co-related with MRR for three distinct idealized processing conditions. The constant showing the extent of interdependence of two phenomena were evaluated by experimental data. The obtained expressions of MRR have been validated for processing conditions other than those used for obtaining constants. It was found that the discharge energy plays prominent role in material removal. The percentage difference in experimental findings and theoretical predictions was found to be less than 3%.     

Improving hole exit quality in rotary ultrasonic machining of ceramic matrix composites using a compound step-taper drill

Mechanical-machining-induced tearing defects at hole exits restrict the application of C/SiC composites. Rotary ultrasonic machining (RUM) is suitable for hole manufacture in brittle composites, providing reduced tearing size as compared with conventional grinding. Even so, substantial tearing defects at the hole exit remain with RUM. In this study, a novel compound step-taper diamond core drill for RUM of C/SiC was developed to further improve the hole exit quality. Contrastive machining tests were conducted to evaluate the effectiveness of the new type drill. Experimental results show that the compound drill can help reduce the tearing size by 30% on average. Results of variance analysis indicate that there is little dependency of tearing size on processing variables with the compound drill, whereas the common drill shows substantial dependence. Detailed observation of the thrust force reveals that the tearing size reduction using the compound drill is due to the reprocessing effects of its taper face. In the reprocessing process of the taper face, the thrust force gradually decreases at the hole exit. Increasing the ultrasonic amplitude can help further improve the hole exit quality when using our compound drill.     

高速精密磨削9CrWMn冷作模具钢的磨削力和比磨削能

分析了高速精密磨削9CrWMn冷作模具钢的机理,采用DEFORM软件对高速磨削模具钢9CrWMn过程进行了磨削力仿真。使用高精密高速平面磨床对模具钢9CrWMn进行了高速精密磨削试验,并在线测量了多种工况下的磨削力。结果表明:在其他两组工艺参数不变时,随着工件进给速度增加,磨削力特别是法向磨削力会增大近45%;法向磨削力和切向磨削力随着砂轮的线速度上升而下降,法向磨削力下降近33%;磨削深度对磨削力影响较大,大的磨削深度对法向磨削力的影响尤其显著,可使法向磨削力增大近100%。分析了磨削工艺参数对比磨削能的影响规律,结果显示:随着磨削深度和工件进给速度的增大,比磨削能呈比较明显的下降趋势,符合磨削加工中的尺寸效应;随着砂轮线速度的增大,比磨削能呈上升趋势。最后,对高速磨削前后工件表面的微观形貌进行了对比分析,磨削力试验结果和仿真理论分析相一致。     

机器人负载惯性参数的快速辨识

机器人的惯性参数辨识是基于动力学模型控制器设计的基础,除了需要辨识机器人自身的惯性参数外,还需要快速准确地辨识负载的惯性参数。针对需要更换负载的工作场景,提出了一种快速辨识负载的激励轨迹,该轨迹不需要经过优化,即可在短时间内覆盖更多的机器人运动状态,从而获得更为全面的采样参数集,提高了辨识效率的同时增强了辨识模型的泛化能力。实验表明,辨识的结果与负载模型的CAD参数符合,机器人关节理论力矩能较好地拟合实际驱动力矩,验证了负载参数的正确性。     

Processing of high-performance Co doped Y2O3 as a single-phase electrolyte for low temperature solid oxide fuel cell (LT-SOFC)

The high-performance single-phase semiconductor materials with higher ionic conductivity have drawn substantial attention in fuel cell applications. Semiconductor materials play a key role to enhance ionic conductivity subsequently promoting low temperature solid oxide fuel cell (LT-SOFC) research. Herein, we proposed a semiconductor Co doped Y₂O₃ (YCO) samples with different molar ratios, which may easily access the high ionic conductivity and electrochemical performances at low operating temperatures. The resulting fabricated fuel cell 10% Co doped Y₂O₃ (YCO-10) device exhibits high ionic conductivity of ∼0.16 S cm⁻¹ and a feasible peak power density of 856 mW cm⁻² along with 1.09 OCV at 530 °C under H₂/air conditions. The electrochemical impedance spectroscopy (EIS) reveals that YCO-10 electrolyte based SOFC device delivers the least ohmic resistance of 0.11–0.16 Ω cm² at 530-450 °C. Electrode polarization resistance of the constructed fuel cell device noticed from 0.59 Ω cm² to 0.28 Ω cm² in H₂/air environment at different elevated temperatures (450 °C to 530 °C). This work suggests that YCO-10 can be a promising alternative electrolyte, owing to its high fuel cell performance and enhanced ionic conductivity for LT-SOFC.     

Wetting and interfacial reactions in liquid Au-Ti alloys / ZrO2 system

This study investigates wetting of zirconia by Au-Ti alloys containing 0.6–4 wt% Ti in view of brazing zirconia to titanium with pure gold for biomedical applications. Experiments were carried out using sessile and dispensed drop methods under high vacuum at 1040–1250 °C. Bulk drops and Au-Ti / ZrO₂ interfaces were characterized by SEM and FEG-SEM with EDXS analysis. While Au does not wet zirconia, the contact angle θ being ∼ 120°, the addition of Ti in Au leads to a significant improvement of wetting due to the formation of a wettable oxide layer at Au-Ti / ZrO₂ interface. The nature of this oxide was determined by X-ray diffraction of the reaction layer after the detachment of the droplet from the substrate or after the dissolution of the droplet. The mechanism of formation and growth of the oxide layer and its growth kinetics were determined based on fine analysis of the Au-Ti / oxide layer / ZrO₂ interfacial system.     

Investigation of a heat pipe cooling system in high-efficiency grinding

The high grinding temperature is one of the problems restricting on the further development of high-efficiency grinding due to the workpiece burnout and excessive wheel wear. An original method about enhancing heat transfer in the contact zone based on heat pipe technology is put forward to reduce the grinding temperature in this paper. Drawing on the structure of rotation heat pipe, one heat pipe cooling system, heat pipe grinding wheel (HPGW) applied to high-efficiency grinding, is developed and its heat transfer principle is illustrated. Besides, the cooling effect in the contact zone using HPGW is simulated through a three-dimensional heat transfer model in grinding, and the influence of different parameters of the wheel speed, cooling condition, and heat flux input on the grinding temperature is analyzed. Eventually, preliminary grinding experiments with HPGW were carried out to verify the cooling effect by comparing with non-HPGW in grinding of 0.45 wt.% C steel and titanium alloy Ti-6A1-6V. Results show that using HPGW can significantly reduce the grinding temperature and prevent the burnout.