【作者】 黄小毛；

【导师】 莫健华； 叶春生；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2009， 博士

【摘要】 熔丝沉积成形(Fused Deposition Modeling,FDM)技术具有设备、材料和运行成本低,操作简单,适合办公室环境,制件强度好等一系列优点,非常适合产品设计阶段的外观验证、装配及功能测试,一直备受中小企业及教育机构的青睐。扫描填充的速度低和出丝的精度差是FDM与其他激光快速成形工艺最大的不同,FDM对工艺支撑及路径的好坏体现得更加敏感。这使得工艺支撑及路径的优化工作变得尤为重要。本文是在作者参与研发HRPF熔丝沉积成形设备的基础上成文的,针对研发过程中出现的关键性技术难题,从设备稳定性、成形效率和精度等角度入手,重点研究了挤出机构、工艺支撑生成、扫描填充路径生成、扫描填充路径优化、控制系统及工艺过程控制等五个方面的关键问题。材料挤出机构是FDM的核心使能技术。作者首先对挤出机构进行设计攻关,解决了出现的丝材失稳、摩擦轮打滑、加热方式、送丝入口溢流、起停响应滞后(包括流涎)、挤出头堵塞等关键问题,实现了挤出机构稳定可靠工作,为后续工艺试验及设备商品化创造了条件。研究熔丝沉积成形设备所需要的工艺支撑结构,提出斜壁结构工艺支撑的概念及自动生成算法。基于STL文件数据,实现斜壁结构支撑的自动添加。这种支撑结构由于充分利用了支撑自身的自支撑能力,极大的减少了支撑的体积,从而节省了支撑材料,同时也提高了制件的成形效率。在熔丝沉积成形工艺的路径规划方面,提出一种并行栅格扫描填充路径及其规划算法。这种路径使得层面的成形过程趋于近似并行,从而均匀了温度场,减少了制件的翘曲变形量。同时这种路径还减少了路径中小线段的数目,最大限度的降低了高速运行时机械振动对设备产生的影响。以提高制件表面成形质量为目的,研究熔丝沉积成形工艺的路径优化算法,提出基于潜在起点和添加节点的路径排序优化算法、基于两种不同合并原则的路径合并优化算法和针对栅格及轮廓偏置混合路径的起终点内置优化算法。研究熔丝沉积成形设备所需要的控制系统,实现基于PC+PLC模式的快速成形控制方案,完成了加工所需海量数据的PLC自由口通讯动态传输、三轴实时连续加工轨迹运动控制、送丝电机的开关量控制和温度的模拟量控制。针对挤出机构起停响应滞后的问题,提出一种新的控制策略——迂回起停控制策略,将原来不可控的“点”问题平均的分摊到一条“线段”上,与路径起终点内置优化算法和空行程快速抬刀运动方法配合起来使用,基本上消除了由于挤出头起停响应滞后性而引起的制件外观填充缺陷。通过本论文的系统研究,解决了熔丝沉积成形设备研发过程中所碰到的挤出机构不能稳定可靠工作、工艺支撑及扫描填充路径生成和优化、工艺过程控制等关键问题,为该熔丝沉积成形技术深入发展奠定了一定的理论和实践基础。更多还原

【Abstract】 Fused Deposition Modeling(FDM) with a number of advantages of its relatively inexpensive equipment and materials, low running costs, operation-friendly, pollution-free, suitable for the office environment, encompasses a wide range of applications including 3D printing of design and concept models, assembly and functional testing for small and medium enterprises and educational institutions. Low-speed scanning and filling and bad-accuracy filament are the biggest differences of FDM to other laser-enabling rapid prototyping processes. FDM is more sensitive to the quality of the support and toolpath. This makes the optimization of support and toolpath especially important.This article is involved in research and development in HRPF fused deposition modeling equipment. The key technical problems are including the extrusion head, control systems and some software key algorithms such as support generation, toolpath planning and optimization.First of all, as the core enabling technology of the system, the extrusion head is discussed and practical solutions are proposed to address some key problems including the filament instability, the spinning of the friction wheels, the overflow of the delivering material entrance, on-off response lag (including salivation), temperature controling and the plugging of the nozzle. The reliable and stable work of the extrusion device creates the conditions for the follow-up process test.Support structure for fused deposition three-dimensional printing equipment is discussed and a novel support structure of sloping wall structure with its automatic generation algorithm is proposed based on STL file data. This new structure reducing the volume of the support helps saving a lot of materials and improving the modeling efficiency.Many types of tool paths for fused deposition three-dimensional printing device are analysed. A novel tool path - parallel raster - with its planning algorithm is proposed. This tool path makes the forming process tended to parallel approximation, a uniform temperature field in order to reduce the amount of warpage. At the same time, this path also reduces the number of the path of small-sized segments, and then improves the vibration characteristics of the equipment while in high-speed running.To improve the forming quality of parts surface, serval path optimization methods are proposed and realised for the fused deposition three-dimensional printing. They are path sequencing optimization algorithm based on potential starting point and adding node method, combined optimization algorithm based on two different merger principles, and end node ensconcing optimization algorithm for the path hybridized by raster and courtour offset paths.A control system based on model of personal general PC + PLC is designed and carried out for Fused deposition three-dimensional printing device, in which massive data rapid prototyping is required to be processed by dynamic transmission through PLC Freeport communications, and a real-time three-axis motion control must be achieved too.For the on-off response lagging phnomenon, a new control strategy -detouring on-off control strategy is forwarded, which transforms the non-controllable filling bug in "point" to in a "line" segment on average. Cooperated with end node ensconcing optimization algorithm and high-speed jumping, it helps reducing the filling defects of parts.In conclusion, the problems such as on-off response lagging, distortion, support and toolpath generation and unreliability of extrution head, have been solved in the fused deposition modeling processing, which has laid a certain amount of theoretical and practical basis for its further development.更多还原