【作者】 欧栋生；

【导师】 汤勇；

【作者基本信息】 华南理工大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 随着电子芯片发热量的增加以及散热空间的大幅度减小，导致了高热流密度问题，严重影响着产品的性能及使用寿命。微型热管已为各种极端狭小空间、高热流密度元器件的散热难题提供一条行之有效的解决途径。而所要求的高导热率、高可靠性、热响应快、无需额外动力等特点的热管尺寸也越来越小，小尺寸热管将广泛应用于狭小空间内的电子元件及其应用系统如医疗科学手术设备等。微型热管的传统制造方法有挤压-犁切法和钢球高速充液旋压法，但采用该两种制造方法难以加工出直径Ф6mm特别是直径Ф4mm以下的微型沟槽式热管。本文结合钢球高速充液旋压技术和管材拉拔成形技术，提出了高速充液旋压-多级拉拔复合成形制造方法，用于加工直径在Ф2~6mm范围内的微型直齿沟槽式热管。首先采用钢球高速充液旋压技术加工出直径为Ф6mm与齿数适当的微型直齿沟槽管，然后再采用多级拉拔成形方法逐级加工出直径Ф2~6mm范围内的微型直齿沟槽管。通过对多级拉拔成形过程合理简化，建立了微型直齿沟槽管拉拔力学模型、沟槽拱起力学模型以及拉拔加工运动速度场理论计算模型，并进行了理论求解。得到了拉拔成形力、沟槽拱起高度以及拉拔变形加工功率计算公式。而且对微型直齿沟槽管在多级拉拔成形过程中沟槽拱形现象的产生机理进行了系统研究，把沟槽拱形现象形成过程分为沟槽堆积挤压、沟槽根裂、沟槽拱起以及沟槽饱满四个阶段。以MSC.MARC为分析平台，建立了微型直齿沟槽管多级拉拔成形有限元三维模型。获得了微型直齿沟槽管多级拉拔成形演变特征、三向主应力应变及等效应力分布规律以及金属流动规律。结果发现：当加工进行到四级拉拔即从直径Ф3mm成形到直径Ф2.5mm，沟槽发生拱形现象和燕尾槽结构特征。同时发现，拉拔力随着拉拔压缩率的增大先减小后增大，五级拉拔从直径Ф2mm拉拔到直径Ф1.8mm（拉拔压缩率为13.1%）拉拔力达到最小，而三级拉拔即从直径Ф4mm拉拔到直径Ф3mm（拉拔压缩率为21.9%），拉拔压缩率最大，拉拔力也达到最大。另外，微型直齿沟槽管进入了入口锥区沟槽拱起高度达到0.5mm，在定径区拱起高度继续增大，最大可达到0.62mm。采用扫描电镜、超景深显微镜、以及金相显微镜等微观检测手段，观察和分析了微沟槽几何参数、表面形貌和金相组织特性的变化规律。实验结果表明：当拉拔成形进行到三级拉拔时，微型直齿沟槽管沟槽发生了拱形现象；当拉拔成形进行到四级拉拔时，沟槽产生明显的燕尾槽结构，而且轴向沟槽产生了扭曲断裂现象。拉拔压缩率在0~16%范围内，拱形系数逐渐升高；而拉拔压缩率在16%以上的区域，拱形系数慢慢减小。拉拔力变化的过程一般分为三个阶段：初始接触阶段、稳定拉拔变形阶段、脱离拉拔模具阶段。拉拔力随着拉拔模具角的增大先减小后增大，当拉拔模具角为16°时，拉拔力最小。还总结了微型直齿沟槽管多级拉拔成形中表面成形质量及影响原因，发现微型直齿沟槽管多级拉拔成形工艺会产生表面刮伤、金属压入、褶皱或小裂块、裂纹（螺旋、纵向或横向裂纹）和弯曲等各种表面缺陷。采用红外热成像技术，对直径大小分别为Ф6mm、Ф5mm、Ф4mm、Ф3mm、Ф2.5mm、Ф2mm的微型直齿沟槽管毛细性能进行了测试，结果表明，拉拔成形直径大小在Ф3~6mm范围内，毛细高度随着拉拔成形直径的的缩小逐步增加；而拉拔成形直径大小在Ф2~2.5mm范围内，毛细高度急剧下降。接着，建立了微型直齿沟槽管的强化沸腾实验装置，对传热特性进行了测试分析，结果发现，随着拉拔成形直径的减小，努塞尔数也减小，两者呈线性关系。最后，对封装好的微型直齿沟槽式热管进行了启动及轴向等温性能测试：启动时间约为10s；输入功率为25W时，微型热管两端温差约为3℃。更多还原

【Abstract】 Recently,with the trend of electronics processors towards higher performance andsmaller packaging, the heat dissipation from these devices is growing and the heat flux isgreater than ever, and the size of micro heat pipe,with high thermal conductivity,goodisotherm performance, rapid heat response and no extra power, is becoming smaller andsmaller. Micro heat pipe provide an effective solution for a variety of extremely small spaceand the cooling problem of high heat flux components. And will be wildly used inultra-samllelectronic compents and application systems, special in surgical thermalmanagement. However, it has proven hard tomanufacture micro heat pipe having an outerdiameter less than6mm (especially less than Ф4mm) by the traditional manufacturing methodsuch as extrusion-ploughing or high speed Ball-spinning.The compound spinning anddrawing manufacture technique is developed for the efficient and economical manufacture ofthe micro-grooved copper pipe.then, micro straight groove of copper tube with outer diameterabout Ф2~6mm was obtained using a compound technology of high-speed oil-filledspinning and multi-pass drawing in this paper.Micro straight groove of copper tube which had an outer diameter of Ф6mm wasobtained by high-speed oil-filled spinning method first.After that,multi-pass drawingprocessing method was designed to manufacture micro straight groove of copper tube withouter diameter about Ф2~6mm.In this paper, the optimal design theory is presented tosimplified the forming process of multi-pass drawing,and then,the drawing force of microstraight groove of copper tube and the model of admissible velocity field、the deformationpower and the arch effect have been established. Use the analytical method to derived thedrawing force、the height of the arch effect and the deformation power. The mechanism ofarch effect of the grooves in the drawing process were investigated. And devided to foursteps,and they are:grooves accumulation extrusion, grooves cracking, arch effect formationand grooves saturation.On the basis of elastic-plastic finite element analysis of large deformationtheory,three-dimensional finite analysis model are established by MSC.MARC for muti-passdrawing.The metal flow rule,distribution rule of stress and strain, the influence of formingprocess parameters on drawing quality and the corresponding forming mechanism by themuti-pass drawing has been simulated. Results indicate that the grooves generated the arch effect andswallow tailed during the fourth passes drawing with the outer diameter reduces from3mm to 2.5mm. Moreover,the drawing force decreases firstly and then increases with the increases ofreduction. And when the value of reduction is13.1%, the drawing force is smallest. when thevalue of reduction is21.9%, the drawing become maximum. The value of the height of thearch effect is0.5mm on the reducing area,while the value is0.62mm on the calibrating area.To reveal the mechanism of high-speed oil-filled spinning and multi-pass drawingcomposite forming technique, scanning electron microscopy, ultra-deep microscope andmetallurgical microscop methods are performed. The structure evolution of micro straightgroove of copper tube by composite forming was concluded.Results show that the groovesgenerated the arch effect during the third passes drawing and swallow tailed at the fourthpasses. However,arch coefficient increases firstly at0~16%and then decreases above16%asthe increase of drawing reduction. The process of drawing force are generally classified intothree stages: the initial contact, stable drawing deformation, and leaving the drawing die. Thedrawing force decreases firstly and then increases with the increases of die angle. And whendie angle is16°,the drawing force is smallest.Furthermore,There are many kinds of flawseasily generated during multi-pass tube drawing,such as surface scratches,metal pressed into,bonding or segmental teeth, Spiral, vertical or horizontal crack,bending and so on.The capillary performance of the micro straight groove with outer diameter of Ф6mm,Ф5mm, Ф4mm, Ф3mm, Ф2.5mm and Ф2mm are done by infrared thermal imagingtechnology.The results show that the capillary force increases firstly with outer diameter about3~6mm and then decreases with outer diameter about2~2.5mm as the decrease of drawingdiameter.Moreover,boiling experimental apparatus of the micro straight groove are alsoestablished,and the heat transfer charateristics were analyzed.Results indicated that the valueof N_u decreases as the decrease of drawing diameter.At last,the start-up and isothermalperformance of micro copper heat pipe with straight grooves are tested. The results show thatthe startup time of micro-heat pipe is about10s,and the value of temperature difference isabout3℃.更多还原