STRESS ANALYSIS OF INJECTION MOLDED PARTS IN POST-FILLING STAGE

0 INTRODUCTIONThe wmpage of injection molded parts is a difficult problem to the mold designers. There are manyfactors that cause Warpage, such as the technics of injection molding, the designing of mold and thematerial Of mold, etc. Inappropriate parameters of those factors can cause differential shrinkage of theparts during POst-filling and cooling stage, which may be the reason of the differential distribution of theresidual thermal stress. Then the residual stress will lead to waIPa…     

分层实体制造中层间应力和翘曲变形的研究

分层实体制造(LOM)是一种典型的快速成形(RP)技术,该文对分层实体制造中的层间应力和翘曲变形进行了深入研究。建立了一种LOM工艺的简化模型,通过对模型的分析,给出了零件层间正应力和切应力的计算公式。通过试验现象,对翘曲变形的两种主要形式进行了说明。首次建立了翘曲变形过程描述模型,深入分析了翘曲变形的机理,认为内应力产生的等效弯矩是使零件翘曲变形的原因。最后从材料和成形工艺两个方面对减小内应力和翘曲变形的措施进行了论述。     

CRITERIA FOR THE QUALITY ASSESSMENT OF CONSTITUTIVE EQUATIONS DEDICATED TO CUTTING MODELS

Determination of the flow stress under metal cutting conditions is difficult because high values of strains, strain rates and temperature exist in practical machining operations. Conventional tests for determining flow stress data cannot duplicate these deformation conditions and therefore, extrapolation will be required. In this study we have investigated critical issues regarding the constitutive equation determination by direct methods such as split Hopkinson's pressure bar bench (SHPB) tests. Quantitative analysis about the suitability of an experimentally determined constitutive equation for different purpose modeling is provided, leading to guidelines for the quality improvement of constitutive law dedicated to cutting, from the points of view of formulation and identification sequence.     

CRITERIA FOR THE QUALITY ASSESSMENT OF CONSTITUTIVE EQUATIONS DEDICATED TO CUTTING MODELS

Determination of the flow stress under metal cutting conditions is difficult because high values of strains, strain rates and temperature exist in practical machining operations. Conventional tests for determining flow stress data cannot duplicate these deformation conditions and therefore, extrapolation will be required. In this study we have investigated critical issues regarding the constitutive equation determination by direct methods such as split Hopkinson's pressure bar bench (SHPB) tests. Quantitative analysis about the suitability of an experimentally determined constitutive equation for different purpose modeling is provided, leading to guidelines for the quality improvement of constitutive law dedicated to cutting, from the points of view of formulation and identification sequence.     

An effective warpage optimization method in injection molding based on the Kriging model

In this paper, an effective optimization method using the Kriging model is proposed to minimize the warpage in injection molding. The warpage deformations are nonlinear, implicit functions of the process conditions, which are typically evaluated by the solution of finite element (FE) equations, a complicated task which often involves huge computational effort. The Kriging model can build an approximate function relationship between warpage and the process conditions, replacing the expensive FE reanalysis of warpage in the optimization. In addition, a “space-filing” sampling strategy for the Kriging model, named rectangular grid, is modified. Moldflow Corporation’s Plastics Insight software is used to analyze the warpage deformations of the injection-molded parts. As an example, the warpage of a cellular phone cover is investigated, where the mold temperature, melt temperature, injection time, and packing pressure are regarded as the design variables. The result shows that the proposed optimization method can effectively decrease the warpage deformations of the cellular phone cover and that the injection time has the most important influence on warpage in the chosen range.     

半固态材料触变成形通用本构方程及其优化

采用半固态成形机理分析和试验研究相结合的方法,建立半固态触变成形的粘塑性本构方程,并提出本构方程的优化新方法。通过半固态Al-4Cu-Mg合金的等温压缩试验研究,分析试验数据,得到本构方程中的4个待定系数,并以此作为优化设计的初试值。结合本构方程的形式,对其进行特性分析和优化。将含优化变量的本构方程作为子程序引入到有限元数值模拟中,可以得到对照热模拟试验结果的若干工艺条件下半固态Al-4Cu-Mg合金的应力应变曲线。通过比较有限元数值模拟结果和热模拟试验结果可知,利用提出的本构方程优化新方法,不仅可以剔除热模拟试验数据中几何效应的影响,而且还能准确地描述半固态材料的触变成形规律,从而可以提高数值模拟的精度与可靠性。     

运用热模拟压缩试验确定精确的金属流动方程

研究分析在用压缩试验确定金属高温塑性流动方程时影响流动应力，应变值精度的主要因素即试样表面摩擦与变形温升，并提出了相应的的修正方法。     

管坯大变形自由推压缩径残余应力的研究

管坯大变形自由推压缩径时端部存在翘曲,即端部外径大于定径区外径.针对端部翘曲区进行变形分析,并基于平衡条件推导了周向残余应力与翘曲变形和剪应力的关系表达式,揭示了由内表面层到外表面层整体存在周向残余拉应力的事实.在三向液压机上进行?219 mm×7.5 mm无缝钢管的双侧大变形缩径,在缩径管件上截取包含端部翘曲区和定径...     

金属切削加工热弹塑性大变形有限元理论及关键技术研究

基于有限变形理论、虚功原理和更新的拉格朗日公式建立了热弹塑性本构方程，导出了热弹塑性大变形耦合控制方程。对切削加工有限元模拟中的关键技术，如材料模型，工件和切屑的分离、断裂准则，刀具、切屑间的接触摩擦模型以及切削热进行了探讨，针对这些关键技术建立了正交切削加工铝合金7050T7451有限元模型，对切屑形态、切削力、切削温度以及应力场和应变场等物理量的分布进行了有效预测。     

基于双弹簧双活塞本构模型的聚合物密封材料黏弹特性表征

提出一种新型的双弹簧、双活塞黏弹性本构模型来表征聚合物密封材料黏弹特性,并推导相应的蠕变方程和应力松驰方程。以聚四氟乙烯和聚醚型聚氨酯,在CETR UMT-2型试验机及LKDM-2000轮廓摩擦磨损仪上考察其蠕变、松驰特性,并与本构模型计算结果进行比较。该本构模型计算得到的聚四氟乙烯和聚醚型聚氨酯的蠕变、松驰特性与实验结果基本一致,表明该本构模型能较好地反映这2种聚合物材料的黏弹性质。     

Constitutive relations for compressible granular materials using non-Newtonian fluid mechanics

This paper is about constitutive relations which can model the flow of granular materials with cohesion, friction, and collisions between particles. The constitutive model represents compressible viscoplastic fluids with second-order effects, in which the Cauchy stress tensor depends on the velocity components and on the rate of volume distribution. An alternative model employs the maximum volume distribution to take second-order effects into account. It is shown that the simplification of the model in which compressibility and second-order effects are neglected leads to the constitutive model of Diez and Godoy. The formulation is employed to solve the flow through an inclined channel, for which the problem reducesto a one-dimensional situation. Explicit solutions are obtained for this case, and are presented in some detail for different degrees of approximation. The results are compared with theoretical values by other authors and with experimental data available in the literature, by Drake and Walton and by Savage, with excellent agreement. The constitutive equation in which second-order terms are a function of the volume distribution is the most general of the constitutive relations presented.     

Injection mold design of reverse engineering using injection molding analysis and machine learning

Plastic composites are used in vehicle components to improve fuel efficiency. Thus, the warpage of injection-molded plastic parts has become a quality issue. Factors, such as product shape and thickness, resin, and other injection molding conditions, can be modified to improve the warpage problem. However, if these factors are set with no possible adjustments, reverse engineering may be required. Reverse engineering is a difficult process that requires many trials and errors; thus, it is only used as a last resort. With respect to the warpage issue, reverse engineering considers the following: (1) Predicting and (2) modeling the warpage in opposite directions. Autodesk Moldflow Insight accommodates these key considerations, but many researchers are reluctant to use it. Although existing injectionmolding analysis programs are mainly used to predict qualitative results, computer-aided engineering (CAE) for reverse engineering requires quantitative analysis. Hence, the considerations are different from the existing analyses. An error in warpage prediction may lead to a costly mold modification because of the molds' complex structures. Quantitative warpage prediction for reverse engineering depends on process variables; thus, understanding how warpages are affected by uncertain process variables is important to improve the reliability of reverse engineering. Moreover, even if appropriate process variables are set, they cannot be applied due to tolerance in lengths. For this reason, mold shrinkage must be identified before designing a mold. This study conducted injection molding analysis for a radiator tank that uses glass fiber-reinforced plastic using Autodesk Moldflow Insight 2018.2. Data for warpage prediction were generated in accordance with five process variables to identify the relationship between the level of warpage and process variables. CAE also showed the level of mold shrinkage that can reduce warpage. In addition, a predictive model was created using the multilayer perceptron (MLP)- supervised learning technique, which is a deep learning method for artificial neural networks. The predictive model was compared with typical regression models, such as polynomial regression (also known as response surface model), EDT and RBF, to determine the optimal approximation model. The real modeling time for a radiator tank product is 1 h, but the MLP approximation model required only 1 min and 8 s to perform 8530 iterations with a similar reliability.

     

An elastic-plastic constitutive equation for transversely isotropic materials and its application to the bending of perforated circular plates

Extending Hencky's interpretation for Mises' yield condition to anisotropic materials, it is first assumed that the plastic deformation occurs when the elastic distortion energy attains to a certain constant value. Then, the shearing stress and the shearing strain intensities are defined in terms of the elastic and the plastic distortion energy. By assuming the deformation theory of plasticity along with the hydrostatic pressure insensitivity of material response, trigonometric representations of stress and strain are derived in order to formulate an elastic-plastic constitutive equation for transversely isotropic materials. Yield conditions and the corresponding yield loci for the relevant materials are also discussed. As an application of the resulting constitutive equation, elastic-plastic bending of perforated circular plates is analysed by modelling them by equivalent homogeneous transversely isotropic plates.     

振动拉伸的弹粘塑性模型

基于弹粘塑性本构关系 ,讨论了附加振动时单轴拉伸的应变及应力变化过程。分析结果表明 ,本文所给出的力学模型 ,再现了振动拉伸过程中的应力超调及平均应力降低等现象     

A mathematical model for smart functionally graded beam integrated with shape memory alloy actuators

This paper presents a theoretical study of the thermally driven behavior of a shape memory alloy (SMA)/FGM actuator under arbitrary loading and boundary conditions by developing an integrated mathematical model. The model studied is established on the geometric parameters of the three-dimensional laminated composite box beam as an actuator that consists of a functionally graded core integrated with SMA actuator layers with a uniform rectangular cross section. The constitutive equation and linear phase transformation kinetics relations of SMA layers based on Tanaka and Nagaki model are coupled with the governing equation of the actuator to predict the stress history and to model the thermo-mechanical behavior of the smart shape memory alloy/FGM beam. Based on the classical laminated beam theory, the explicit solution to the structural response of the structure, including axial and lateral deflections of the structure, is investigated. As an example, a cantilever box beam subjected to a transverse concentrated load is solved numerically. It is found that the changes in the actuator’s responses during the phase transformation due to the strain recovery are significant.     

低频振动塑性成形粘弹塑性模型的体积效应分析

采用Kirchner对应变时间历程的基本假设,针对振动拉伸建立一个一维粘弹塑性模型;利用MATLAB中的符号计算,推导粘弹塑性本构方程的显式表达式.通过确立粘弹塑性边界并对本构方程进行数值求解,可以确定金属在振动加工过程中,其应力应变在粘弹性与粘塑性之间的变化情况.通过计算瞬时应变的大小与屈服限建立粘弹性变形和粘塑性变形的判断准则.在考虑粘弹塑性本构关系中的后继屈服情况、应变历程、应变率历程及弹性应变等因素后,可以确定单轴振动拉伸时材料变形的动态应力和平均应力.根据所给定的振型参数和材料力学性能参数,结合特定的振动拉伸实例,分别得出金属在准静态拉伸和振动拉伸时的动态应力-时间、动态应力-应变和平均应力-应变率的变化趋势等,实现基于粘弹塑性本构关系的低频振动塑性成形的体积效应机理分析.     

A new hardening rule for metallic foam plasticity

Metallic foams are a class of porous materials widely used in the industry because of their advantages. In recent years, extensive studies on the behavior of these materials have been conducted. Several constitutive equations have also been presented and applied. This study proposes a new constitutive equation that predicts metallic foam behavior using the stress–strain curve in uniaxial compression. The proposed model offers a new functionality for work hardening and is evaluated for both isotropic and combined hardening. The constitutive equations are implemented in MATLAB and integrated using return mapping algorithm. The material parameters are identified using genetic algorithm and through a comparison of the experimental and numerical results. The aluminum foams discussed in this paper are the commercially available types, Foaminal and Alporas. The comparison of numerical and experimental results indicate that this new constitutive equation predicts foam behavior in a reasonable manner. Moreover, a good agreement is observed between the experimental and computational curves.     

Efficient warpage optimization of thin shell plastic parts using response surface methodology and genetic algorithm

During the production of thin shell plastic parts by injection molding, warpage depending on the process conditions is often encountered. In this study, efficient minimization of warpage on thin shell plastic parts by integrating finite element (FE) analysis, statistical design of experiment method, response surface methodology (RSM), and genetic algorithm (GA) is investigated. A bus ceiling lamp base is considered as a thin shell plastic part example. To achieve the minimum warpage, optimum process condition parameters are determined. Mold temperature, melt temperature, packing pressure, packing time, and cooling time are considered as process condition parameters. FE analyses are conducted for a combination of process parameters organized using statistical three-level full factorial experimental design. The most important process parameters influencing warpage are determined using FE analysis results based on analysis of variance (ANOVA) method. A predictive response surface model for warpage data is created using RSM. The response surface (RS) model is interfaced with an effective GA to find the optimum process parameter values.     

含增粘剂润滑油粘弹性的实验研究

本文将系统分析原理引入到对润滑剂本构方程的研究中来,进而提出了一种对本构方程研究的新的实验方法。通过实验得到了含增粘剂润滑油的本构方程的频谱特征图,从而证实了该方法的可行性。将四种增粘剂润滑油在不同增粘剂含量不同温度下的实验数据按照Maxwell流变模型进行回归,得到流变参数(剪切弹性模量)与增粘剂含量、温度之间的关系,给出了回归公式。该公式在一定范围内反映了流变参数的变化规律。     

Analysis of frictional phenomena in friction welding of mild steel

A dynamical analysis of the “equilibrium phase” of friction welding is presented. The fundamental idea is that the observed phenomena are controlled by the behaviour of a viscous layer of plasticised metal at the rubbing surfaces. This layer is postulated to obey a constitutive equation relating shear stress to rate of strain which is similar to the well-known “Bingham plastic” model. Formulae are thus obtained which predict the external driving torque, as well as the thickness and temperature distribution of the plasticised layer. A comparison is made between the theoretical results and a number of experiments which have been carried out on mild steel tubular specimens, over a range of conditions. Good agreement is found in all cases. Preliminary results are presented for the apparent viscosity of plasticised mild steel.