天然大理石成形铣削加工硬质合金刀具失效机理研究

Stone products are widely used in modern decoration and urban construction. However, the traditional machining process for stone products is low efficiency, high labor costs and poor machining conditions. Therefore, it is necessary to introduce automated equipment to promote the transformation and upgrade for stone machining industry. The cutting tool is the key factor to realize the automatic and intelligent machining of stone products. However, the lack of research on tool failure mechanism for stone machining restrict the fabrication of high-performance cutting tools and formulation of efficient machining process. The aim of this proposal is to investigate the multi-scale failure modes and failure mechanisms of carbide cutting tools in milling of marble by means of finite element analysis (FEA) and experimental methods. Firstly, the tool life of carbide tools and determined factors under different cutting conditions were analyzed by milling test. Then, the dynamic thermo-mechanical loadings were extracted, and the competition and coupling mechanisms between thermal and mechanical loadings at multi-time scales were analyzed based on thermo-mechanical impact tests. Finally, a coupled thermo-mechanical-microstructural finite element model was developed to reveal the time-dependent damage mechanisms of cutting tool at spatial scales, and the relationship between the stress orientation and the crack propagation direction was established. This proposal is of great practical significance for the design and manufacture of stone machining tools.

石材制品在现代装饰行业及城市建设中的应用十分广泛，但传统的石材加工工艺，加工效率低，人工成本高，加工环境差。因此引入自动化加工设备和加工工艺，对于推动石材加工行业的转型和升级至关重要。石材加工刀具是实现石材自动化加工和智能加工的关键载体，但目前缺乏对石材成形刀具磨损、破损失效机理的系统研究，制约着高性能刀具的制备和高效加工工艺规程的制定。本项目针对大理石成形铣削加工过程中硬质合金刀具宏微观失效形式和失效机理进行研究。首先，通过铣削试验研究不同切削条件下刀具寿命影响规律及刀具失效形式；然后，通过提取石材切削过程中热机械动态载荷，研究多时间尺度下高低频热机械冲击载荷对刀具材料破坏的竞争、耦合机制；最后，针对大理石切削构建热-力-微观组织耦合切削仿真模型，建立刀具空间应力取向与裂纹扩展方向之间映射关系，揭示空间尺度下刀具时变损伤机理。研究成果对于石材切削刀具的设计及制备具有重要意义。

石材为典型的微观非均质硬脆材料，同时石材成形铣削为典型的断续切削过程。石材加工刀具是实现石材自动化加工关键载体，但目前缺乏对石材成形刀具磨损、破损失效机理的系统研究。本项目围绕大理石成形铣削加工，采用有限元仿真与实验分析相结合的方法，分析了大理石切削过程切削参数及刀具几何参数对切削力、切屑形成及加工表面质量的影响规律。揭示了大理石切削加工过程中，非连续切削形成对切削过程的影响，特别是切屑演化与刀具宏观破坏形式之间的并联机制，相关结果可以为石材加工切削参数优化以及刀具几何结构设计提供理论依据。主要结论：.大理石加工过程中，初期阶段，硬质合金刀具主要以后刀面的磨粒磨损为主，同时有部分程度的岩屑粘结，中期阶段，岩屑在刀具前刀面粘结加剧，部分刃口出现微崩刃，主要原因是石材加工过程的不稳定，特别是非连续切屑的形成造成加工过程的不稳定，对刀具局部产生高频的机械冲击，最终导致刀具内在微观裂纹萌生扩展最后出现崩刃。.大理石切削过程中，不同加工参数下岩屑粒度存在较大差异，随着进给量增加，大粒径岩屑增多，同时随主轴转速提高，岩屑出现明显细化，且粒径分布更加均匀、集中。通过对比切削力和切屑粒径分布，发现大理石切削过程切削力的演变与岩屑粒度分布具有明显的正相关性，当切屑中大颗粒岩屑增多，对应各向切削力升高，当切屑中大颗粒岩屑数量减少，各向切削力明显降低。.基于数值仿真结果，发现岩石的材料失效过程主要由剪切破坏主导，高速、大切深下刀具前刀面应力更大、岩石内部应力分布范围更广泛，低速、小切深、较小的刃口圆弧和正前角切削均能降低大理石表面的材料损伤层厚度。.

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