【作者】 王德广；

【导师】 吴玉程； Philip Nash；

【作者基本信息】 合肥工业大学 ， 材料学， 2010， 博士

【摘要】 粉末冶金零部件已广泛用于机械、汽车、电子、自动化等领域,市场前景非常广阔。但孔隙的存在显著影响着粉末冶金制品性能,也增加了精密成形的难度,而传统的粉末压制制品相对密度一般小于90%,如何获得高密度高性能的粉末冶金制品成为目前粉末冶金行业的发展方向和研究重点。有限元数值模拟技术可以快捷、有效、详细的对粉末成型致密化过程进行研究。故此本文就粉末高致密化成型技术致密化机理、多孔材料力学性能与密度的关系以及粉末成型有限元数值模拟进行研究:(1)分析了粉末温压工艺关键要素—粉末模具控制温度和压制力对粉末温压致密化的影响,设计了电阻式加热控温的方法,验证了该加热控温方法的有效性。研究了铁基合金温压粉末在不同温度下流动性,获得温压过程中粉末控制温度范围。分析粉末和模具温度以及压制力变化对制品密度变化影响规律,得出了最佳温压工艺路线,分析了粉末温压成形致密化机理。(2)分析了电磁感应加热技术在粉末温压工艺中应用,设计了电磁感应温压加热控温系统,验证了电磁感应加热加热和控制温度的有效性。试验结果显示,电磁感应加热技术可以快速、精确、有效性的控制模具温度,成功地将电磁感应加热技术应用于金属粉末温压工艺,温压试验结果显示电磁感应加热温压加热系统可以获得了较高密度的粉末制品,磁化对致密化没有影响。(3)采用冲击锤法和分离式霍普金森高速撞击试验两种方法对铁基合金粉末(Distaloy4600A)和纯钛粉末(Ti-Dupont)高速成形变形过程进行了分析。利用National Instruments公司生产的数据采集模块(SCXI-1520和SCXI-1314)和采集软件Labview,编写了应变信息采集程序,研究了粉末高速成形过程模具变形特征。对于冲击锤法,研究了冲击锤高度和重量、粉末类型和质量、不同压制工艺等对高速成形制品密度的影响。对于分离式霍普金森高速撞击试验,分析了不同撞击压力下粉末致密化规律。分析了两种方法粉末致密化规律,研究了高速成形制品密度均匀性。试验结果显示冲击锤方法可以获得较高密度且均匀性较高粉末冶金制品,多次冲击对提高制品密度的作用是有限的。对于分离式霍普金森高速撞击试验,试验结果显示应力波对致密化没有影响。(4)研究了铁基合金粉末制品密度与力学性能的关系,成功的建立了相对密度与杨氏模量关,为了粉末成形有限元数值模拟建立了模型基础;分析了粉末压制过程中的摩擦行为,得到随着粉末制品密度的增加,摩擦先增加,达到一定程度后,几乎直线降低的规律。研究了铁基合金粉末、纯钛粉末、铝基合金粉末制品相对密度与维氏硬度之间的关系,成功的建立了相对密度与维氏硬度关系模型,通过此方法可以简单方便的研究制品局部密度分别规律,特别是复杂形状制品。(5)基于粉末温压成形致密化研究基础,建立了热力耦合的有限元模型,考虑温度、摩擦对压坯变形与性能的影响,采用更新的拉格朗日方法,对粉末温压成型过程进行了有限元数值模拟。分析了不同加热方式、不同摩擦状况、不同压坯高径比、不同压制方式、摩擦有利化和三轴向压制等多种不同的压制工艺形式对粉末温压工艺的致密化规律的影响,分析了压制过程的粉末颗粒变形,获得了粉末温压成形制品密度变化和应力分布规律。更多还原

【Abstract】 The powder metallurgic parts have wildy been applied in mechanics, automobiles, electronics, automation and so on, it is has wide market prospect in industry. But the inherent pores have an important influence on the properties of PM parts, and also add difficulties to high precise forming. The relative density of PM parts are generally lower than 90% by conventional powder compaction processes, therefore how to get high density and high properties of powder metallurgic parts becomes to the current development and research focus of powder metallurgic industry. Finite element simulation technology is a rapid, effective and detailed method to analyze densification of powder compaction process. In this article, high densification principle of powders compaction processes, relationship between mechanical properties and density, and finite element simulation of powder compaction are studied:(1) The key influences on densification of warm compaction process: powder and die temperature, pressing pressure, are analyzed. And the resistance heating method is designed for warm compaction process and the effectiveness of this method is verified. Research on fluidity of Fe-based alloy powder at different temperatures is done, and the controlling temperature range of powder is obtained for warm compaction process. The influence of powder and die temperature variation under different pressing pressures are analyzed on densification of powder compaction. The optimism of process parameters for warm compaction process is concluded. And the densification mechanism of warm compaction process is studied.(2) The application of electromagnetic induction heating technology in warm compaction process is researched. Electromagnetic induction heating system is designed for warm compaction process, and effectiveness of this system is verified. The experimental results of this system show that electromagnetic induction heating technology can rapidly, accurately and effectively control die temperature, and this heating technology is successfully applied in warm compaction process. Experimental results of compaction process show that electromagnetic induction heating system for warm compaction process can get high density of PM parts, and there is no influence of magnetism of powders and dies on densification of powder.(3) The dropping hammer and split Hopkinson bar test are applied for researching on high velocity compaction process. The deformation of two powder materials, Fe-based alloy powder (Distaloy4600A) and Pure Ti powder (Ti-Dupont), are analyzed for high velocity compaction process. The data collecting mode (SCXI-1520 and SCXI-1314) and data collecting software (Labview) made by National Instruments, In.. are applied for studying dies deformation during high velocity compaction process. The data collecting program is designed for this research in this article. For dropping hammer test method, height and weight of hammer, type and weight of powder and different compacting processes, and so on are researched on densification of powder. For split Hopkinson bar test, the influence of different impacting pressure on densification of powder is analyzed. The densification mechanism of powder is studied for these two methods, and uniformity of density distribution is researched for high velocity compaction process. The experimental results show that high density and good uniformity of density distribution can be obtained for PM parts by dropping hammer process, it is limited to improve density of PM parts for several hitting on powder.. And the experimental results also show that stress wave has no effect on densification of powder for split Hopkinson bar test.(4) The relationship between density and mechanical properties of Fe-based alloy powder metallurgic parts are studied, and the relationship between relative density and Young’s modulus is generalized, this mode can offer basic material information for powder compaction by finite element simulation. And the frictional behavior of powder compaction is also researched in this article, and the results express that at the initial stage of powder compaction, with the increasing of PM parts density, the friction parameter increases, and when the frictional parameter reaches some value, it will almost linearly decrease. The relationship between relative density and Vickers hardness is analyzed for Fe-based alloy powder, Pure Ti powder, and Al6061 powder. And the relationship between relative density and Vickers hardness are established, this mode can be easily applied for analyzing the distribution of local density of powder metallurgic parts, especially complex PM parts.(5) Based on the research of powde densification for warm compaction process, the couple thermal-mechanical finite element mode is obtained for simulating the warm compaction process. The influence of temperature and frictional behavior on the deformation and properties of green are considered. And the updated Lagrangian Method is applied for the simulation of warm compaction process. In this article the influence of different compaction processes on densification of warm compaction are researched, including different heating methods, different frictional status, different ratio of height and diameter, different compaction methods, favorable of conversion of friction, and three-axial compaction method. The deformation of powder particles are analyzed, variation of density and stress distribution are obtained for warm compaction process.更多还原