Prediction of Geometrical Error Due to Gas and Plasma Cuttings and Its Control

为了实现船舶结构装配线的自动化或机械化，与依赖工人技能的系统相比，需要在每个制造阶段保持更高的精度，例如切割和焊接。由于火焰切割是装配的第一阶段，它决定了很大一部分的精度问题，因此火焰切割的精度受到越来越多的关注。长期以来，人们一直认为残余塑性应变和切削过程中由于瞬态热变形引起的板的运动是切削误差的主要原因，但很少有研究从理论上和定量地探讨这些因素。本文提出了一种基于热弹塑性有限元法的切削过程模拟方法。通过与等离子体切割实验结果的比较，验证了所提方法的正确性。利用有限元模型，计算了板的残余塑性应变和瞬态热膨胀引起的板的运动。定量讨论了它们对切削误差的影响。结果表明，这些因素对单面切削影响较大，对双面同时切削影响较小。研究了切削前板料中残余应力的影响。

To achieve automation or mechanization of a ship structure assembling line, it is necessary to maintain much higher precision in each manufacturing stage, such as cutting and welding, compared to that required for a system which depends on skills of workers. Since flame cutting is the first stage of assembly and it determines a large part of the accuracy problems, the precision of flame cutting is the receiving more attention. Although it has long been considered that residual plastic strain and the motion of the plate due to the transient thermal deformation during cutting are the main causes of cutting error, hardly any studies have been conducted to investigate these factors theoretically and quantitatively. In this research, a computational method, based on thermal-elastic-plastic FEM,has been developed to simulate the cutting process. The proposed method is verified by comparing the computations with the experimental results obtained for plasma cutting.Using the FEM model, the residual plastic strain and the motion of the plate due to the transient thermal expansion are computed. Their effects on cutting error are quantitatively discussed. The results show that these factors have great influences on one-side cutting and small effects on two-side simultaneous cutting. The influences of the residual stress existing in the plate before cutting are also investigated.