压铸模具表面激光仿生强化的仿生耦合模型研究

With the growing demands for lightweight, energy-saving and green products, the aluminum and magnesium alloy die-casting dies are used more extensively. Die wear and failure is a significant issue in die-casting industry, owing to the high cost of dies. Nevertheless, as the service condition of the die-casting dies is harsh and thermal fatigue process is complex, die wear and failure has been a technical difficult problem and die service life improvement is an important issue in high pressure die-casting industry. Experiment results on die steel shows that biomimetic laser-remelting process provides a promising method to improve the service life of die-casting dies, which processes the die surface by mimicking the natural wear-resistance surface using low-power laser. This project concentrates on the biomimetic coupling model, which includes two key problems for adopting biomimetic laser-remelting process, the prediction of the die-failure area and the design method of biomimetic model. The study includes three aspects. 1) Based on the temperature field, velocity field and pressure field of the die-casting mold by die-casting CAE analysis, the equivalent stress field of the mold can be established. 2) The correlation model is constructed and analyzed between equivalent stress field and the failure area of the mold. The geometric characteristics of failure area of the mold can be classified. The method to predict the location and the possibility of failure on the mold surface are studied. 3) According to the mold surface of the stress field for different geometric characteristics of the failure area, the biomimetic model design method is studied, including the size of the hardening units, the various shapes and the distributions of the units, and the corresponding influence to the service life of die-casting dies. The biomimetic model design method can provide a theoretical basis and decision support for adopting biomimetic laser-remelting process for the die-casting dies. Hence, the work of this project will promote the application of biomimetic laser-remelting process, which has important theoretical and practical significance to improve the service life of die-casting die.

在产品轻量化、节能化、绿色化发展趋势的推动下，铝、镁合金压铸模需求量不断增大，压铸模面临的主要问题是寿命低。激光仿生强化是模仿生物耐磨损、抗疲劳结构，将其在模具型面上予以"复制"，以提高模具寿命。本项目针对压铸模具激光仿生强化关键问题- - 仿生耦合模型进行研究，1）通过压铸CAE进行压铸模具温度场、速度场以及压力场的综合分析，进行信息融合获得模具表面等效应力场；2）建立模具表面等效应力场与失效区域之间的关联，归类失效区域的不同几何特征，对模具表面产生失效的部位及可能性进行预测；3）根据模具表面的等效应力场，针对不同几何特征的失效区域，研究仿生耦合模型的设计方法，包括强化单元体的尺寸、网格的疏密、形态及空间分布等对模具寿命的影响，提出仿生耦合模型设计准则，为压铸模具实施激光仿生强化提供理论依据和决策支持。本项目的研究将有助于激光仿生强化技术的应用，对提高压铸模具寿命具有重要的理论和现实意义。

压铸模作为模具的重要组成部分，是铝镁合金成型的重要工艺装备，在汽车、电子和通讯等领域具有广泛的应用。在各种模具中，压铸模的工作条件最为恶劣，压铸模面临的主要问题是寿命低，压铸模具寿命直接影响到压铸件的成本。在压铸生产中，高温金属溶液以高速、高压喷射充型，充型完成后又要对压铸模具进行冷却，开模时模具表面喷脱模剂，引起模具表面产生周期性的热膨胀和收缩，并最终导致压铸模具的热疲劳失效，由热疲劳引起的模具表面龟裂是压铸模具破坏的最主要形式。本项目以提高压铸模寿命为目标，重点研究了基于CAE分析的复杂压铸模具表面失效区域预测和激光仿生强化技术的仿生模型设计方法、激光仿生强化的机理，主要内容包括：1）通过正交实验和单因素法研究了激光工艺参数对熔凝单元体尺寸和形态的影响规律；2）分析了激光熔凝单元体的显微硬度、微观组织；3）设计制备了不同仿生模型试样，进行热疲劳实验，分析了裂纹生长机理；4）研究了激光仿生强化处理后不同仿生模型试样的热摩擦磨损性能；5）基于CAE分析对压铸模具失效区域进行预测分析，建立了模具表面应力场与失效区域之间的关联，为压铸模具表面实施强化提供了指导；6）针对压铸模具龟裂失效，采用激光仿生强化进行了修复实验。研究结果表明，经过激光熔凝仿生强化后的试样由于晶粒细化，单元体显微硬度提高，形成了软硬结合仿生结构，其热疲劳性能和热摩擦磨损性能都有显著提高。根据本项目的研究结果，针对多副实际生产用压铸模具进行了仿生强化处理，应用结果表明，在CAE分析的基础上，预测的压铸模具表面的易失效区域与实际破坏区域吻合，对该区域实施激光仿生强化处理后显著提高了压铸模具寿命，本研究具有重要的理论和实际应用价值。