Abstract

The uncertainty in the prediction of machining stability increases with the increasing flexibility of the workpiece. The past research showed that the process cannot be stabilized even using the largest pockets in the stability diagrams due to high flexibility of the parts. Therefore, the present research emphasizes extensive experimental analysis where the uncertainty of the stability lobe diagrams was brought into the light, especially in the case of machining of flexible parts. This led to the introduction of a new term “Stability Region Diagram (SRD)” in the present research. The three generalized machining scenarios for chatter-free machining of thin-walled features on low rigidity Ti-6Al-V4 were experimentally analyzed. These include Scenario-I, where workpieces have identical pre-machining stiffness and natural frequency that varies during and after machining. In Scenario-II, workpiece stiffness and natural frequencies vary initially but are identical after machining. In Scenario-III, workpieces have identical pre-machining stiffness and natural frequency but vary during and after machining over central 1/3 part, straddled between bosses. Various machining strategies with an optimum combination of cutting speed-feed-radial depth of cut were developed using stability region diagrams (SRD) to achieve stable machining throughout the length of the cut along the flexible workpiece surface. For Scenario-I and II, stable machining is possible at widths of cut lesser than or equal to the final thickness of workpiece and at a constant spindle speed of 4,000 rpm throughout the length of the workpiece. However, while machining at widths of cut more than the post-machining thickness of the workpiece, the stable machining is possible using a spindle speed ramp-up technique. In the Scenario-III, the surrounding uncut material is found to make machining unstable which can be improved by spindle speed ramp-down technique.

摘要

加工稳定性预测的不确定性随着工件柔性的增加而增加。过去的研究表明，由于零件的高度灵活性，即使在稳定性图中使用最大的口袋也无法稳定过程。因此，目前的研究强调广泛的实验分析，其中稳定瓣图的不确定性被揭示出来，特别是在柔性零件的加工情况下。这导致在本研究中引入了一个新术语“稳定区域图（SRD）”。实验分析了在低刚度 Ti-6Al-V4 上对薄壁特征进行无颤振加工的三种通用加工方案。其中包括场景一、其中工件具有相同的预加工刚度和在加工过程中和加工后变化的固有频率。在场景 II 中，工件刚度和固有频率最初不同，但在加工后相同。在场景 III 中，工件具有相同的预加工刚度和固有频率，但在加工过程中和加工后的中央 1/3 零件上有所不同，横跨凸台之间。使用稳定区域图 (SRD) 开发了具有切削速度-进给-径向切削深度的最佳组合的各种加工策略，以在沿柔性工件表面的整个切削长度上实现稳定加工。对于场景 I 和场景 II，在小于或等于工件最终厚度的切削宽度和 4 的恒定主轴速度下，可以稳定加工，整个工件长度为 000 rpm。然而，当以大于工件加工后厚度的切削宽度进行加工时，使用主轴速度斜坡技术可以实现稳定的加工。在场景 III 中，发现周围的未切削材料使加工不稳定，这可以通过主轴速度斜坡下降技术来改善。