【作者】 朱兆民；

【导师】 徐文骥；

【作者基本信息】 大连理工大学 ， 机械设计及理论， 2004， 硕士

【摘要】 等离子体弧切割因具备切割速度快、切割面光滑、容易设定切割条件、适合自动化、无人化作业等优点，正逐步在板材切割中占据主导地位。在实际生产中存在大量变厚度工件的切割，如果在此类工件的等离子体弧切割仍然沿用切割等厚度板的方式设定工艺参数，将造成切割质量的不稳定，增加了后续处理工作的难度。 等离子体弧切割是通过高温等离子体弧将工件弧柱部分的材料熔化并利用高速离子流将切渣吹除的物理过程，弧柱的功率和作用力将直接影响到切口质量。当工件的几何尺寸发生改变时，弧柱的功率和作用力应该随之而改变。弧柱功率的大小和作用力又与等离子体弧的切割电压、切割电流、压缩空气的压力和流量、电极与喷嘴的同心度、电极与喷嘴的距离、喷嘴直径的大小以及等离子体弧切割速度有关。分析和掌握上述工艺参数对等离子体弧切割质量的影响规律是合理调整等离子体弧切割工艺参数的前提和基础。 本文将从两方面来讨论对等离子体弧切割工艺参数的切割质量影响规律以及调整方法。一是根据工件厚度的变化来调整等离子体弧切割速度，即改变单位体积上工件所吸收的功率。二是调整等离子体弧的切割电压或者切割电流，即改变等离子体弧的输入功率。重点研究对切割速度的调整以及实现方法。 基于弧柱双区域理论，本文通过建立数学模型对等离子体弧柱特性进行了研究，讨论了在一定条件下喷嘴出口处压力、弧半径、切割电压、弧柱功率、作用力与切割电流之间的关系，为合理的调整等离子体弧工艺参数从而调整等离子体弧柱的功率提供理论依据。 根据热传导的平衡方程，本文建立了等离子体弧切割热传导损失的数学模型，推导了等离子体弧切割过程中温度场分布的数学公式。将温度场公式进行变换，就可以根据工件材料的熔点求得将工件切透所需输入的功率。根据切割材料的相变，结合热传导平衡方程可以用来估算等离子体弧的最佳切割速度。 现代制造系统应该能在指定的时间内满足消费者对新产品的不同要求，同时也要适应迅速发展的计算机技术。在本文中，我们研究了一种针对基于个人计算机的开放式等离子体弧切割控制系统的模块化实现方法。针对等离子体弧切割的特殊性，讨论了等离子体弧切割系统的抗干扰措施。 本文的最后部分对等离子体弧切割变厚度板材进行实验研究。根据前面讨论的数控等离子体弧切割系统的技术方案组装了一套开环控制的简易切割装置。选择了几种不同厚度试件进行了大量的切割实验，分析了切割速度对各种厚度板材的切口宽度、挂渣情况、切割面割纹深度等切割质量的影响规律。实验验证，通过改变切割速度提高变厚度工件的切割质量是可行的。 上述研究工作为发展变厚度板材等离子体弧切割技术，扩展等离子体弧切割技术的应用范围，为最终形成三维零件的等离子体弧加工技术提供了参考依据。更多还原

【Abstract】 Plasma arc cutting plays a significant role for its traits such as the faster cutting velocity, the smooth cutting surface, the easily setting condition, the application fitting for automatic operation. In actual production there are lot of variable thickness panels cutting, the cutting quality will be unstable if process parameters are set according to the way cutting ordinary plates, which will increase difficulty of follow-up procedure.Plasma arc cutting is a physical process which utilize high temperature to heat materials and high speed flow to blow melted metal, cutting quality is directly influenced by arc power and arc force. When the change takes pace in the size of geometry of work piece, the arc power and arc force should change with it. There are a lot of factors that influence the arc power and arc force. These factors include cutting voltage, cutting current, pressure and runoff of air, tungsten setback, nozzle diameter and cutting speed. To analyze and know the rules above-mentioned process parameters influence the quality of plasma arc cutting is the foundation and premise to adjust the optimum process parameters of plasma arc cutting.This article will proceed discuss the influence of mechanical properties on cutting quality from two aspects. The first step is to change cutting speed according to the thickness of work piece, which means to change the absorbed heat of unit. The second step is to change the arc current or the arc voltage, which means to change inputting power. It will be the focus of this article to discuss the adjustment of cutting speed and its implementation method.In accordance with a two-zone approximation of the arc column, a model has been developed to study the properties of plasma arc cutting process. The results of the pressure at the nozzle, arc radius, arc voltage, arc power, arc force exit as a function of arc current have been obtained for a range of operating conditions. It provides the theoretical foundation to adjust the arc process parameters of plasma arc cutting rationally in order to adjust the arc power.According to the equation of the heat conduction a plasma arc cutting mathematics model is founded, this article deduces a temperature distribution by solving the model. By switching temperature field formula arc power absorbed for cutting can be obtained with melting point of material. Contacting the phase transformation enthalpy of material with heat-conduction equation, an appropriate cutting speed can be then predicted in plasma arc cutting.A modern manufacturing system should have the capability to meet consumer’s various demands to new products within a certain designated time. Also, it should be able to accommodate the rapid development of computer technologies. In this paper, a modular and object-oriented approach for the PC-based open plasma arc cutting control system is investigated. In addition, the corresponding methods of anti-interference are described according to property of plasma arc cutting.In the finality of this article an experiment study about plasma arc cutting variable-thickness plate is introduced. According to the above-mentioned technique projectabout simple NC system for plasma arc cutting, an experimental equipment based on open-loop control is made. In the experiment different samples were cut using plasma, and the rules of cutting dap, cutting residue and height of chamfer affected by cutting speed is analyzed. The result demonstrated that the way of adjusting cutting speed is obtained.Acted as a reference, the research above- involved will promote the development of the technology of plasma arc cutting variable-thickness plate, extend the applications of plasma arc cutting, and development three-dimensional plasma arc cutting finally.更多还原