Mechanical behavior analysis on the compression molding process of NdFeB by different molding technology
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摘要: 为了优化钕铁硼粉末模压成型工艺, 通过离散元软件EDEM建立模压成型过程的离散元模型, 分析不同成型工艺条件(压制速度和摩擦系数)对压坯力学特征(压制力和压坯内应力)的影响, 为优化钕铁硼成型工艺提供理论参考。结果表明: 在成型过程中, 钕铁硼粉末位置状态基本保持与布粉时一致, 只有靠近模冲区域的粉末发生较大位移; 压坯成型时会出现应力松弛现象, 不同速度压制成型对压制力峰值影响不同, 但压制力最终均会收敛至相近的平衡值; 添加润滑剂能改善压坯内部受力状态, 减小压制力, 但是也会减小压坯相对密度; 对于大尺寸压坯成型宜采用双向压制方式。Abstract: The discrete element model of the compression molding process was established by the EDEM discrete element software to optimize the process of NdFeB powders compression molding. The effects of the different molding conditions (pressing speed and friction coefficient) on the mechanical characteristics of the green pressing (compression force and pressing internal stress) were analyzed to provide the reference for the optimizing of the molding parameters. The results show that, the position of NdFeB powders is the same as that at the time of powder distraction during the molding process, but the powders near the die-stamping area displace greatly. The stress relaxation phenomenon occurs at the molding of green pressing. It is worthy noticing that the pressing speed has the different effects on the peak force of compression, but eventually it will converge to a similar stable value. The addition of lubricant can improve the internal stress state of the green pressing, reduce the compression force, and decrease the relative density of the green pressing. For the large-scale green pressing, the two-directional pressing should be adopted.
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Key words:
- NdFeB /
- compression molding /
- mechanical behavior /
- molding technology
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图 1 软球模型对颗粒间接触力的简化处理：（a）法向力；（b）切向力
Figure 1. Simplified treatment of the contact force between the particles in soft ball model: (a)normal force; (b)tangential force
图 4 压制过程颗粒流动状态：（a）压制前；（b）压制后
Figure 4. Flow state of particles during pressing: (a)before suppression; (b)after suppression
图 5 100 mm/s压制速度下的钕铁硼粉末压制力变化曲线
Figure 5. Compression forces of Nd FeB powder particles at the pressing speed of 100 mm/s
图 6 不同压制速度下钕铁硼粉末压制力变化曲线
Figure 6. Compression forces of Nd FeB powder particles at the different pressing speeds
图 8 不同压制速度下的钕铁硼粉末压坯沿中轴线的内应力变化
Figure 8. Pressing internal stress of NdFeB in the axle wire at the different pressing speeds
图 9 减小摩擦系数对压制力的影响
Figure 9. Effect of reducing friction coefficient on the compression force
图 10 减小摩擦系数对压坯内应力的影响
Figure 10. Effect of reducing the friction coefficient on the pressing internal stress
表 1 EDEM软件中钕铁硼粉末颗粒参数
Table 1. NdFeB powder particle parameters in EDEM discrete element software
密度/(kg·m-3) 维氏硬度 泊松比，μ 弹性模量，E/MPa 抗压强度/MPa 7500 950 0.24 158 × 103 1100 
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表 2 304不锈钢材料参数
Table 2. Material parameters of 304 stainless steel
密度/ (kg·m-3) 维氏硬度 泊松比，μ 弹性模量，E/MPa 抗压强度/MPa 7930 — 0.3 194 × 103 —
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表 3 材料间接触参数
Table 3. Contact parameters between the materials
接触材料 恢复系数 静摩擦系数 滚动摩擦系数 颗粒-颗粒 0.2 0.545 0.01 颗粒-模具 0.2 0.300 0.01
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