【作者】 毛锋；

【导师】 莫健华；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2005， 博士

【摘要】 传统的板材零件通常通过模具的凸、凹模作用获得所需形状。因为制造模具的成本很高,这种制造方法仅仅适合于大批量生产。为了满足用户产品多样化的要求,需要开发适合于小批量产品生产的新工艺。在过去几年开发的多种方法中,应用简单工具的板材数控渐进成形工艺的研究受到极大的关注。板材数控渐进成形工艺不需要专用的模具,是一种柔性的成形工艺,它根据板材零件的成形要求设计数控程序,然后通过数控机床的进给系统,成形工具按照一定的轨迹逐步地成形板材,直到得到需要的零件。可以通过修改产品的数字模型来调节成形工具的运动轨迹,达到改变成形零件形状的目的。因此,它的成形周期短,产品更新快。这种工艺非常适合于小批量、多品种和复杂的板料产品。本文紧紧围绕该成形工艺的柔性特点,对开放式控制系统以及与其相适应的开放式软件系统进行了深入研究,并针对不同成形问题深入研究了各种工艺规划策略,在提高加工效率、改进加工工艺、改善系统的可靠性和提高制件精度等方面取得了大量的研究成果,而且这些研究成果已被应用于HRPB系列快速成形系统中,对该系统快速制造出质优价廉的零件起到了重要的作用。本课题所开发的金属板材数控渐进成形机,其机身为框架式结构,具有结构简单、惯量小的优点。由于设备X方向行程较长、转矩较大,本系统采用了X轴双电机驱动方案,保证了动横梁的运动平稳。作者对不同的控制策略进行了分析对比之后,使用全坐标控制方式有效地解决了双电机驱动的同步问题。另外,在成形过程中,成形力将随着材料堆积和硬化而不断发生变化,从而诱使系统发生机械振荡,经过试验证明,在PID控制基础上加入加速度负反馈和陷波滤波功能的控制方案能够较好地抑制振荡的发生。考虑到金属板材数控渐进成形工艺对于系统快速扩展功能、多操作平台可移植性等方面的要求,以具有高度开放能力的PMAC2-PC多轴运动控制器作为控制下位机,以PC机作为控制上位机,将实时控制任务和设备管理任务分开,两者之间采用高速双端口RAM作为数据传送接口,通过中断通讯的方式保证数据通路畅通。组件化的程序设计方法被引入到数控软件系统的开发中,通过构建二进制一级可重用组件库,采用多层式系统模型,实现了软件系统的开放性和体系结构可复用性的目的。在基于组件的系统平台上,本系统采用了先进的结构化存储方法对加工数据进行存储,实现了加工数据内部的文件系统管理,对分层制造中的加工数据进行结构明晰、存取方便、高效可靠的存储管理。通过对轨迹段进行拼接整合,压缩简化了加工数据,为轨迹的工艺规划奠定基础。人机交互轨迹修改功能允许操作者使用计算机鼠标器对加工轨迹进行拖动修改,从而绕过由实际加工返回CAD模型的步骤,达到了现场快速响应的目的。从防止压痕累积、加工效率两个方面考虑,设计实现了轨迹环起止点匀布算法,为防止材料堆积和形状扭转,对轨迹环进行逆向处理,实现了正逆相间的加工工艺。为了消除底支撑模型的局限性,论文提出了点支撑无模渐进成形的新方法,通过工艺试验验证了点支撑无模渐进成形的工艺可行性,总结了成形缺陷和解决对策,并通过有限元数值模拟,对其成形过程和机理进行了分析研究。更多还原

【Abstract】 Conventionally, a sheet metal component is manufactured with dies and punches. However, the high cost of dies and punches limits the traditional manufacturing method only to mass production. Recently, customer’s demand in product diversification in this field calls for new manufacturing processes appropriate for small-lot production. Among various kinds of processes developed over the past few years, the research of the NC incremental sheet forming process which utilizes a simple tool has been paid great attention to.The NC incremental sheet metal forming process is a flexible forming process without dedicated forming dies, in which the NC program is designed according to the forming requirement of sheet metal components. The sheet metal is formed step by step with a forming tool according to a certain trace prescribed by the feed system of the NC forming machine until the required shape is obtained. The forming trace of the forming tool can be adjusted by correcting the numerical model of the product. Thus, its forming period is short and products can be quickly renovated. This process is very suitable for small-lot, varied and complex sheet metal products. Based on the programmable multi axis controller PMAC, an open architecture CNC system is built to suit with the flexibility of the sheet metal incremental forming. Being separately realized on different hardware --- the upper PC and the lower PMAC, the real-time control and the equipment management cooperate with each other through the high speed dual port RAM.Full coordination method of gantry motors is applied to provide the tightest and smoothest possible link. Meanwhile, acceleration negative feedback and notch filter are added to the servo loop to restrain the mechanical oscillation. Because the X axis has long travel range, the equipment drives the Y axis gantry by the use of double motors in the direction of X to balance the torque in the Z plane. After theoretical analysis of different control projects, full coordination method is adopted and practically verified that it can keep well synchronization between the two motors. The unstable forming force, which comes from the material stacking and hardening, will induce the mechanical oscillation. Experiments testify that the acceleration negative feedback and notch filter based on the conventional PID control algorithm can effectively attenuate this oscillation. System software HrpDSF is designed and realized by the component program method.The component program method is applied to the development of CNC software system which has multi-layer multi-module structure constructed by the binary reusable components. The System software HrpDSF has open architecture which accords with CNC hardware platform.NC data is stored and managed by structured storage method. On the basis of component program method, HrpDSF organizes the NC data into compound document format to realize the file system in the NC data following the forming logic. The NC component document has advantages of legible structure and fast access.The integration of trajectories and man-machine interactive modification algorithm are realized. The integration of trajectories not only compresses and simplifies the NC data but prepares for the further trajectory layout. To response to the flexibility of the technology varieties, the Man-machine interactive modification permits the operator to rapidly modify the local trajectories by the mouse instead of returning to the CAD model.The engage/retract points dispersing algorithm and loop reversing algorithm are realized. The engage/retract points dispersing algorithm is used for avoiding the accumulation of impacting pits, and loop reversing algorithm for wrinkling and buckling. The system and algorithm are all testified to be effectivity and reliability.The point bolster incremental forming, which adopts point rod as bolster instead of the conventional model bolster, eliminates the constraint of the mould and realizes the real incremental forming. The feasibility of this new forming method is verified by plenty of experiments on the axisymmetric part and FEM simulation. The forming instability flaws and these solutions are studied.更多还原