【作者】 邱诚；

【导师】 夏伟；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2014， 博士

【摘要】 在粉末冶金生产实践中，装备水平是制约产品密度和精度的重要因素。针对目前国内粉末成形装备中存在的结构复杂、体积较大，设备成本较高等不足之处；本文提出的研究目标是：研制一种粉末精密成形专用设备，集成上二下三模架，通过集成的油缸驱动，结合闭环控制，能成形高精度、高密度且密度分布均匀的复杂粉末冶金零件。本文为研制出新型粉末精密成形设备提出了集成模架设计方案，它实现压机与模架集成化设计，使得设备结构简单，调试方便，能最大限度发挥粉末成形专用设备的特点，提高成形精度，降低设备价格。针对模架集成式粉末成形设备设计，首先对粉末压制过程中粉末的本构模型进行力学建模，提出一种更符合实验结果的的粉末材料流动应力模型，获得压制过程的载荷；并以此为基础，通过数值模拟方法，研究在典型粉末冶金零件的压制成形过程中,压制载荷对粉末精密成形设备的影响，实现对设备结构设计方案校核；并针对模架集成式粉末精密成形设备的特点设计制造液压系统，综合压机本体和液压系统设计制造配套的控制系统，编制控制软件，并实现了样机研制，并取得以下研究成果：首先要取得压制过程设备的载荷，通过对粉末压制过程中粉末力学模型进行研究，推导出椭球形粉末屈服准则，以实现粉末压制过程的数值模拟，分别模拟计算粉末压制过程的载荷－行程曲线，通过实验和模拟的载荷－行程曲线的对比，分析粉末压制过程中流动应力的变化。结合粉末进行压制实验，对结果进行分析、整理，考虑了Doraivelu的流动应力模型对δ(ρ)的量纲分析，提出用于模架集成式粉末成形设备设计的流动应力模型。采用该模型模拟圆柱试样的压制过程，计算粉末压制的载荷-行程曲线,实验结果表明，该模型更贴近粉末力学行为。采用该模型计算粉末压坯的相对密度分布,与实验值比较,表明该模型模拟的结果较为可靠。采用上述流动应力模型，模拟了典型零件的粉末压制过程，为下一步模架集成式粉末成形设备成形加载提供基础数据。基于多体动力学数值模拟方法，建立了模架集成式粉末成形设备整机接触分析的有限元计算模型，进行了粉末成形设备整机结构强度与刚度分析，得出了整机及其各子结构的变形和应力分布云图，从变形云图中可以得出，各个模板的最大变形挠度均在安全范围之内。将各子结构的最大应力值与其材料的屈服极限进行比较后，可知各零件仍处于弹性变形范围之内，没有发生屈服；计算结果对于结构优化设计具有理论指导作用。对模架集成式粉末成形设备进行模态分析，得到各阶固有频率及对应的固有振型。提取前10阶固有频率及对应的固有振型。设备模态分析计算结果表明，设备的各阶模态频率之间没有重叠，不会产生共振，各阶模态的变形趋势小；从计算结果来看，可以看出整机的固有频率对整机振动的影响，显示出了整机各部分结构振动的强弱分布以及抗振薄弱区，为减少模架集成式粉末成形设备振动和噪声提供了可靠的依据，为成形设备结构动力学优化设计提供了必要的依据。对模架集成式粉末成形设备的液压及控制系统进行研究，液压传动回路中使用插装阀回路、电液比例阀，与光栅尺、压力传感器构成控制回路，实现每个冲头都能独立进行精确的连续轨迹控制，在压制各台面之间高度差别大的多台面零件时，能够使各冲头在压制过程中保持近乎一致的高度变化速率，以较高的工作效率和较高的成形精度压制出密度均匀的粉末零件。成功研制了模架集成式粉末成形设备样机，并成功实现典型零件加工试制，设备满足设计要求，所提出的用于模架与粉末成形设备相集成的设计方案改变传统设备的结构，能最大限度发挥粉末成形专用设备的特点，并形成自主知识产权。该设备的模架由对称分布的集成油缸驱动，独立控制多个模冲实现上二、下三多台面复杂零件的压制。采用光栅尺、传感器和液压系统组合，检测模冲位置和压力，能进行精确闭环控制，设备精度达到±0.03mm。更多还原

【Abstract】 In the Powder Metallurgy (P/M) production, P/M equipments are vital important indetermining the formed P/M parts’ precision and density. Domestic produced P/Mequipment now is large, complex and expensive, so an advanced P/M precisionforming equipment is designed, the new equipment have two upper and three lowermulti-plate mold base, drived and closed-loop controlled by integrated cylinder, thehigh-precision, high-density, uniform density P/M complicated production can beproduced.The integrated mold base P/M precision forming equipment is developed. Due tothe integrated mold base structure, the equipment can be specialized in P/Mproduction, which makes it simpler, cheaper and easier to debug, furthermore theformed parts are more precise. To ground the design of integrated mold base in reality,the constitutive model accurately describing the specific deformation behavior of thepowder compacted in the equipment is established, in which the flow stress relationfits experimental results better is used, then numerical simulation m odels of the P/Mparts’ forming process and the whole equipment’s simultaneous activity areestablished, by which the influence of equipment structure, parts structure andforming process on equipment are analyzed, and the overall design plan is checkedthen. Electrohydraulic proportional control system of equipment is studied, thecontrol software is programmed considering the specific characteristics of the pressesand their hydraulic system used in the equipment, the prototype is successfullydeveloped, related research results achieved are listed as follows.By numerical simulation method based on the ellipsoidal yield criterion, thepowder’s mechanical behaviors in the compacting process are studied, through thecomparison of load-stroke curve of model with that of experiments, the change of thepowder’s flow stress in the whole compacting process is analyzed. The powdercompacting experiments with different apparent density are carried out, theexperimental results are analyzed and arranged, combining with the dimensionalanalysis of the Doraivelu’s flow stress model, the flow stress model δ(ρ)which canbetter apply to the integrated mold base P/M precision forming equipment.The compacting process of the powder cylindrical specimens is analyzed by themodel established, the load-stroke curves of model agrees with that of experiments quite well, which means that the model is better in describing the powder’smechanical behaviors in the compacting process. The relative density distribution ofmodel is compared with that of experiments and they agree with each other quite welltoo, which supports the conclusion that present model is better than the past models.Based on the model established, the numerical simulation of the compacting processof some classical parts are carried out systematically, which supply the design ofintegrated mold base P/M precision forming equipment with a theoretical basis.Using multibody dynamics numerical simulation method, finite element model ofthe entire equipment is established, which can be used to analyze the contact statusbetween every equipment’s composing parts, also the deformation, stress distributionof all composing parts can be seen from the nephograms given by the model, whichshows that the deflection of mold plates area are within the safe levels. Compare themaximum stress of each composing parts with its yield limit, it can be seen that allparts are in the elastic limits, no yield behaviors are exhibited. The simulated resultsprovide the optimization design of equipment with a scientific basis.The modal analysis of the equipment is performed, every natural frequencies andcorresponding vibration modes can then be predicted, and the first to the tenth ordernatural frequencies are derived. The modal analysis shows that all natural frequenciesof the equipment have no overlap with each other, no resonance occurs and thedeformation tendency is quite small. From the vibration shape in every naturalfrequency calculated by modal analysis, the vibration amplitude distribution and theanti-vibration weak area are displayed, the study provides a reliable basis onsuppressing the vibration and noise of the entire equipment, and also providesnecessary a theoretical basis for the structure dynamic optimization of the entireequipment.The key technologies being proposed and implemented in the equipment includesthe cartridge valve circuit, electrical and hydraulic proportional valve and the gratingscale used in the hydraulic transmission system, accurate and independe nt continuouspath control to every punch through combination control by different sensors,assurance of height change rate’s uniformity of the mould’s pressing plane whencompacting multi-plane P/M parts with big height differences, and then compactinghigh-precision, high-uniformity density P/M parts with higher level of productivityand quality.The equipment successfully developed and the integration of the mold base structure with the P/M forming equipment, with independent intellectual propertyrights, utterly change the traditional P/M equipment’s structure, which makes itsimple, easy to debug and can make best of the characteristics of integrated equipment.The mold base is driven by symmetric integrated hydro-cylinder with theindependently control of all the presses, then the compacting of P/M part with twoupper step faces and three lower step faces are achieved. Using the grating scale,sensors and the hydraulic system, the location and pressure of the presses can beaccurately closed-loop controlled, the attainable precision of the equipment is±0.03mm.更多还原