Thermal effects when turning Al-MMC - experiments and simulations

铝-金属基复合材料（Al-MMC）是两相高性能材料。因此，由于其优异的性能，预计这些材料的使用将越来越多。车削过程中产生的热量会引起工件和刀具的热膨胀，从而降低加工精度。为了确定和补偿这种变形，目前需要进行时间和成本密集的实验研究。由于Al-MMC是高成本材料，因此减少这类材料的实验努力是特别有趣的。在项目的第一阶段和第二阶段，开发了计算铝和铝- mmc车削时工件和刀具变形的有限元模型。在项目的第三阶段，将补偿车削复杂工件几何形状时的热效应。Al-MMC的非均匀细观尺度已经在材料模型中表示，以便确定切屑形成的局部模型和工件的全局模型所需的材料特性。利用切屑形成的局部模型，分别计算了进入工件和刀具的热流密度以及加工力。这些结果作为工件和刀具整体模型的边界条件。全球模式计算了各自的温度分布、相关的热膨胀和由过程力引起的变形。开发的有限元模型将用于项目的第三阶段，以确定复杂工件几何形状车削时热效应的补偿策略。然后，对这些策略进行实验验证。降低热效应对加工精度的第一个一般方法是确定工艺参数和单个操作的顺序，以减少工件和工具的热负荷。因此，加工精度得到了显著提高。由工件和刀具的热效应引起的与标称工件几何形状的剩余偏差，可以通过相应的切削深度进行补偿。为了保证最小的公称直径偏差和适当的表面完整性，将考虑粗车削和精车削。利用CAD-CAM技术生成用于实验研究的刀具轨迹，这些轨迹是适应切削深度的结果。通过多个实验结果，如温度分布和加工力，分析计算精度和实验测量精度之间的潜在差异。该项目的结果是，首次通过实验验证了有限元模型，从而可以在加工铝和Al-MMC时进行工艺规划。这样可以显著提高加工精度。

Aluminum-Metal-Matrix-Composites (Al-MMC) are two-phase high-performance materials. Hence, an increasing usage is predicted for these materials due to their excellent properties. The generated heat during turning causes thermal expansions of the workpiece and the tool, which decrease the accuracy of machining. In order to determine and compensate such deformations, time and cost-intensive experimental investigations need to be carried out at present. Since Al-MMC are high cost materials, it is of particular interest to reduce the experimental effort for this class of materials. In the first and second period of the project, finite element models to calculate the deformations of the workpiece and the tool when turning aluminum and Al-MMC were developed. In the third period of the project thermal effects during turning complex workpiece geometries will be compensated. The heterogeneous meso-scale of the Al-MMC has been represented in a material model in order to determine the required material properties for a local model of chip formation and a global model of the workpiece. The heat flux into the workpiece and the tool respectively as well as the process forces are calculated using the local model of chip formation. These results serve as boundary conditions for the global model of the workpiece and the tool. The global models calculate the respective temperature distribution, the associated thermal expansion and the deformation due to the process forces. The developed finite element models will be used in the third period of the project to determine strategies for the compensation of thermal effects in turning of complex workpiece geometries. Afterwards, these strategies are to be verified experimentally. A first general reduction of thermal effects on the accuracy of machining is performed by determining process parameters and sequences of individual operations that reduce the thermal loads on the workpiece and the tool. The accuracy of machining is thus remarkably enhanced. The remaining deviation from the nominal workpiece geometry, caused by thermal effects in the workpiece and the tool, can then be compensated through accordingly adapted depths of cut. To ensure both a minimized deviation from the nominal diameter and an appropriate surface integrity, rough turning and finish turning will be considered. The tool paths, which are the result of the adapted depths of cut, for the experimental investigations are generated using CAD-CAM technology. Potential differences in terms of the calculated and experimentally measured accuracy of machining will be analyzed by multiple experimental results, such as the temperature distribution and the process forces. As a result of the project, for the first time experimentally validated finite element models allowing for process planning when turning aluminum and Al-MMC will be available. The accuracy of machining can thus be remarkably enhanced.