某加工中心刀塔芯轴在使用过程中发生断裂。通过宏观观查、化学成分分析、冶金质量分析、金相检验、断口分析、硬度测试、芯轴尺寸及表面加工质量分析等方法对芯轴断裂的原因进行了分析。结果表明： 该刀塔芯轴硬度未达到技术要求且A类夹杂物含量较高，降低了芯轴的抗疲劳性能，同时由于未设计砂轮越程槽导致退刀槽过渡圆角在砂轮打磨时被破坏，应力集中加剧，在交变载荷作用下芯轴发生了疲劳断裂。

The cutter tower mandrel of a machining center fractured during use. The causes of mandrel fracture were analyzed by means of macroscopic observation, chemical composition analysis, metallurgical quality analysis, metallographic examination, fracture analysis, hardness test, mandrel size and surface processing quality analysis. The results show that the hardness of the cutter tower mandrel was not up to the technical requirements and the content of A-type inclusions was high, which reduced the fatigue resistance of the cutter tower mandrel. At the same time, the transition fillet of the undercut groove was damaged during grinding, and the stress concentration was intensified when the grinding wheel groove was not designed, and the cutter tower mandrel had fatigue fracture under the action of alternating load.