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，由于这些材料具有优异的性能，预计它们的用途将会越来越多。车削过程中产生的热量会导致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，目前需要进行耗时和成本较高的实验研究。由于Al-MMC是高成本材料，因此减少这类材料的实验工作量是特别有意义的。在项目的第一阶段和第二阶段，建立了有限元模型，计算了车削铝材和铝基复合材料时工件和刀具的变形。在项目的第三阶段，复杂零件几何形状的车削过程中的热效应将得到补偿。为了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，Al-MMC的非均质细观尺度被表示在材料模型中。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过程作用力。这些结果用作工件和刀具的全局模型的边界条件。全局模型计算各自的温度分布、相关的热膨胀和由过程作用力引起的变形。开发的有限元模型将用于该项目的第三阶段，以确定复杂零件几何形状车削中的热效应补偿策略。之后，这些策略将得到实验验证。首先，通过确定工艺参数和单个操作的顺序来降低对加工精度的热影响，以降低对工件和刀具的热负荷。从而显著提高了加工精度。由工件和刀具中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调整的切割深度进行补偿。为了确保与公称直径的偏差最小化和表面的完整性，将考虑粗车削和精车削。用于实验研究的刀具轨迹是使用CAD-CAM技术生成的，它是适应切割深度的结果。计算和实验测量的加工精度之间的潜在差异将通过多个实验结果进行分析，例如温度分布和加工力。作为该项目的结果，将首次提供经过实验验证的有限元模型，以便在车削铝和铝复合材料时进行工艺规划。因此，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.