金属注射成形的数值模拟

论文摘要

金属注射成形（MIM）是一种制造复杂三维小零件的近净成形技术。与其它的加工艺相比,如压模成型、机加工和铸造等,MIM技术能够低成本地生产高机械性能的复杂零件,因此有着明显的优势。MIM工艺主要包括四个过程:1)填料的混合 2)注射 3)脱塑 4)烧结。 MIM作为一种新的制造技术,数值模拟在其高效率的应用上有着重要作用。在MIM各个工艺阶段的模拟中,注射阶段的模拟显得更为重要。因为在这个阶段出现的任何缺陷,在接下来的脱塑和烧结阶段都会被放大,以至于影响产品的最终质量。温度、压力等注射工艺参数的正确选取及合理的模具设计是保证产品质量的关键。金属注射成形的数值模拟软件提供了预测填充过程任意时刻填料的流动前沿面、速度场、压力场和温度场的强大功能。除了能够预测注塑成形过程的各种缺陷外,金属注射成形过程中的离析现象在双相流模型中也能够被预测。离析是脱塑过程中产生塌陷和烧结过程中导致翘曲、变形的根本原因。 为了预测金属注射成形过程中的粉末离析现象,引入混合理论是必要的,这样求解两个耦合的Navier-Stokes方程不可避免。如果应用传统的算法,计算量会异常的繁重以至于影响其实际应用。为了达到高效模拟的目的,专门用于模拟金属注射填充的矢量化显式算法首先得以实施。在此基础上,扩展为针对双相流的矢量化算法以模拟粉末离析现象。在新的双相流算法中,既没有全局求解也没有构筑任何全局矩阵,矩阵操作仅在单元一级进行。从整体来看,全局操作完全矢量化,因此计算效率非常高。新算法的另一显著特点,是采用等阶插值的普通单元代替MINI单元,不可压缩条件通过反馈修正的方法得到满足,通过系统化的光顺处理来避免由于采用等阶插值而导致的自锁。同时引入了另外一个光顺处理用来避免由于采用离散的有限元模型引起的初始填充阶段的计算不稳定。新算法在求解大规模工业问题上显示出其明显的计算速度优

论文目录

• Introduction
• Chapter 1: Experiment and Simulation Technology in Metal Injection Moulding
• 1.1 Introduction of MIM process
• 1.1.1 Notable features of MIM manufacturing
• 1.1.2 Limitations of the MIM technology
• 1.1.3 The advantages of MIM technology
• 1.2 Challenging problems of MIM simulations
• 1.2.1 Prediction of possible defects in process design
• 1.2.2 Processing parameters determination
• 1.2.3 Determination of the mould configuration
• 1.3 Conclusions
• Chapter 2: Development of New Vectorial Software and its Application in MIM
• 2.1 Introduction
• 2.2 Mechanical modeling
• 2.2.1 General Definition
• 2.2.2 Governing Equations
• 2.3 New explicit vectorial algorithm for simulation
• 2.3.1 Determination of the filling states
• 2.3.2 Solution of momentum conservation
• 2.3.3 Calculation of Heat transfer and temperature field
• 2.3.4 Calculation of the pressure field
• 2.3.5 Time step determination
• 2.4 Comparison of new algorithm with previous explicit algorithm
• 2.4.1 Elements used in both algorithms
• 2.4.2 Fractional steps in both algorithms
• Chapter 3 Validation of the Vectorial Algorithm for Mould Filling Process
• 3.1 Filling process in a straight channel for 2D and 3D case
• 3.1.1 Comparison of the filling fronts
• 3.1.2 Comparison of the volume conservation
• 3.1.3 Comparison on computational cost
• 3.2 Influence of the advection term in momentum conservation
• 3.3 Filling flow in the increasing section
• 3.3.1 Comparison of the filling fronts
• 3.3.2 Comparison of the velocity fields
• 3.4 Filling flow in elbow cavities
• 3.4.1 Comparison of the velocity fields in 2D model
• 3.4.2 Comparison of velocity fields in 3D model
• 3.5 Filling pattern and temperature fields in a branching-joining cavity
• 3.5.1 Comparison of the filling fronts with the results of the previous algorithm and experiment
• 3.5.2 Comparison of the temperature fields in 3D model
• 3.6 Comparison with experimental results
• 3.7 Comparison with the previous algorithm and experiment
• 3.8 Conclusions
• Chapter 4: New Method for Bi-phasic Simulation - Prediction of the Powder Segregation
• 4.1 Introduction
• 4.2 Bi-phasic modeling of the MEM injection
• 4.2.1 Definition of the effective velocity in the mixture flow
• 4.2.2 Advection equation for filling state
• 4.2.3 Volume saturation and mass conservation
• 4.2.4 Momentum conservations and their exchange
• 4.2.5 Energy conservation
• 4.3 The vectorial algorithm for bi-phasic model
• 4.3.1 Determination of the filling state
• 4.3.2 Solution of the momentum conservation
• 4.3.3 Determination of the volume fractions
• 4.3.4 Heat transfer and temperature field calculation
• 4.3.5 Evaluation of the pressure field
• 4.3.6 Time step determination
• 4.4 Comparison of new algorithm with previous explicit algorithm
• Chapter 5 Bi-phasic Simulation with New Algorithm: Mould Filling and Phase Segregation
• 5.1 Simulation of the mixture flow filling in a straight channel
• 5.1.1 Comparison of the filling fronts
• 5.1.2 Comparison on the computational cost
• 5.2 The filling flow of mixture in an increased section
• 5.2.1 Comparison of the filling fronts
• 5.2.2 Velocity fields Comparison
• 5.3 The example of bi-phasic filling in a 3D mould
• 5.4 Bi-phasic Simulation of the filling flow in an elbow cavity
• 5.4.1 Comparison of the filling fronts
• 5.4.2 Comparison of the velocity fields
• 5.4.3 Comparison of phase segregation effects
• 5.4.4 The influence of elbow radius and interaction coefficient on phase segregation
• 5.5 Velocity fields and segregation for the filling in a trapezoidal passage
• 5.5.1 Comparison of the velocity fields
• 5.5.2 Comparison of the results in phase segregation
• 5.6 Validation by comparison with experiments
• 5.6.1 Comparison of the filling fronts
• 5.6.2 Comparison of the solid volume fractions
• 5.7 Conclusions
• Conclusions and perspectives
• Acknowledgement
• References
• Publications