【作者】 何伟；

【导师】 万里；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2009， 硕士

【摘要】 高真空压铸法是将模具型腔中的气体抽出,金属液在高真空状态下(型腔内真空度达到90KPa以上或绝对压力小于10KPa)充填型腔,减少压铸件内部气孔,提升压铸件力学性能的一种先进成形方法。高真空压铸技术的首要瓶颈是真空截止阀的结构设计及真空方法的控制。目前国内对高真空压铸技术的开发处于空白状态,因此本文基于高真空压铸的Minimum Fill Time法(MFT法),改进了现有真空阀的结构设计,研制出结构更合理、更可靠的新型高真空压铸用真空截止阀以及基于PLC技术和触摸屏技术的高真空控制系统装置,对促进高真空压铸技术在我国压铸业中的应用具有重要意义。本文设计的真空截止阀沿用了已有真空截止阀的一主动一从动两类活塞的结构,利用杠杠原理实现主动活塞带动从动活塞动作。为保证从动活塞关闭气道的可靠性和快速响应性,设计了伺服驱动机构。同时,改进了复位机构,以空气弹簧代替普通弹簧,避免普通弹簧在高温下易失效,可靠性降低的缺点。改进后的新型真空截止阀具有灵活、快捷、可靠的优点,能够适应不同的压铸工艺模式。真空控制系统包括硬件和软件两部分,硬件系统采用PLC作为上位机控制单元,结合嵌入式触摸屏和A/D转换模块组成整个系统的核心,完成对真空泵、电磁阀和传感器的输出逻辑控制,提高系统的稳定性并实现不同的压铸工作模式。基于PLC技术和触摸屏技术的软件系统包含PLC微机控制程序和触摸屏组态系统,具有参数输入及显示方便,界面直观、简洁的优点。开发的真空控制技术能自动和压铸机匹配,设有普通压铸、低真空压铸、高真空压铸三种工作模式,以适应压铸机的不同工作状态。系统具有自动检测模具型腔中的真空度及其变化;自动检测真空管路的堵塞状态;自动清洗管路;自动监视及报警等功能。更多还原

【Abstract】 High vacuum pressure casting is an advanced materials shaping method since the air is pumped from the mould cavity so the liquid metal can be filled in the mould under high vacuum (the degree of vacuum in mould reaches 90KPa or the absolute pressure is less than 10KPa). In this way, the porosity of products can be restrained and the mechanical property is enhanced. However, the bottleneck including structure designing and vacuum controlling limits the application of this technology. Because the research in this field is nearly hitherto blank, in this paper, Minimum Fill Time(MFT)based on high vacuum pressure casting is adopted to improve the design of vacuum valve. Due to its great rationality and reliability, the meliorated stop valve and its matching control system which is based on PLC technique will have significant impacts on the technology of high vacuum pressure casting and die casting industry in China.The prepared vacuum stop valve follows the existing structure comprised initiative and driven piston where the transmission is conducted according to the lever principle. To ensure the reliability and fast response of closure airway in driven piston, the servo drive is devised. Meanwhile, the common spring in reposition mechanism is replaced by the air one, and this amendment assures to avoid the failure and unreliability during the move. This brand new design can be applied in various technology modes of die casting for its flexibility, celerity and reliability.The vacuum control system contains hardware and software. The former one employs PLC as the host compute control unit, embedded touch screen combined A/D conversion module as the kernel of whole system. The logic control of vacuum pump, electromagnetic valve and sensor output is operated by the system above; the latter one is based on the technology of PLC and the touch screen is composed of PLC microcomputer control program and configuration system. The advantages include convenience for display, visualized, simple interface and so on. The developed vacuum control system can automatically match the corresponding die casting machine since it contains three operation modes: regular, low and high vacuum pressure, all of which can be adapted to different working states. Additionally, this system can automatically detect the vacuum degree of the mould cavity, blocks in vacuum line; moreover, it is also able to clean the line and monitor/alert the operation status itself.更多还原