螺纹塑件的注射模设计

分析了螺纹塑件的工艺结构及品质要求,详细阐述了该螺纹塑件注射模的结构设计要点与工作过程,通过使用齿条、齿轮组合的脱模机构,使得模具的使用寿命和可靠性大大提高,重点阐述了齿务、齿轮脱模机构的设计要点。     

保压时间和保压压力对注塑制品厚度分布的影响

通过实验研究了保压压力和保压时间对制品厚度分布的影响,所得的结论可以指导塑件和模具的设计。     

退火对注射成型PC制品力学性能的影响

注射成型的塑料光学制品应用日益广泛,但注射成型加工的聚碳酸酯制品通常有较大的残余应力,会对制品的光学性能、力学性能有负面的影响,而退火可减少/消除制品的残余应力。本文考察了退火对不同工艺条件下注射制品残余应力和力学性能的影响。研究的工艺条件包括三水平的变化的模具温度、熔体温度、保压压力、冷却时间等;残余应力的变化通过光弹实验的应力干涉条纹表示,力学性能的变化以拉伸强度、延伸率的变化表示。实验发现,退火前后,不同工艺条件下注塑PC制品拉伸强度平均提高4.5%,最大达9.0%;同时,断裂延伸率平均降低3%,最多减少14%。     

扭蛋机里面板注射模具设计

本文主要介绍了扭蛋机里面板的改造,同时详细的介绍了里面板注射模具的设计过程与制造方法。     

Dimensional study of thermoplastic parts made using sequential injection molding

As a result of new aesthetical and economical requirements in injection molding, several processes have been developed during last years. In spite of conventional process, sequential injection molding is a versatile technique based on independent control for each gate opening. This procedure allows part filling without weld lines or, at least, these defects can be relocated in suitable positions. A short discussion about sequential principles is made introducing computer simulations. Pressure required for part filling and molding shrinkage were evaluated using experimental procedures with a prototype mold and using conventional and sequential methods. Several setting up parameters were also used to analyze the effect on injection process. Final results show that shrinkage in sequential injection is similar to conventional process but some new effects could be induced by the process asymmetry and should be investigated further. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Morphology evolution during injection molding: Effect of packing pressure

Injection molding is one of the most widely employed methods for manufacturing polymeric products. The final properties and then the quality of an injection molded part are to a great extent affected by morphology. Thus, the prediction of microstructure formation is of technological importance, also for optimizing processing variables. In this work, some injection molding tests were performed with the aim of studying the effects of packing pressure on morphology distribution. The resulting morphology of the moldings was characterized and it was compared with previous results gathered on samples obtained by applying a lower holding pressure. Furthermore, the molding tests were simulated by means of a code developed at University of Salerno. The results obtained show that on increasing holding pressure the molecular orientation inside the samples increases, and simulations show that this is due mainly to the increase of relaxation time caused by the higher pressures. On discussing the simulation results, some considerations are made on the effects of pressure on crystallization kinetics and on rheology.     

Tensile stresses in the edges of injection moldings: Roles of packing pressure,machine compliance,and resin compression

The slow spontaneous development of cracks in the edges of injection moldings under “field” conditions has been observed for 30 years or more. While environmental stress cracking agents have long been implicated, the magnitude and distribution of the stresses associated with cracking have been obscure. The current study of these stresses involved polycarbonate as a model test material that was molded under systematically varied molding conditions. Surface tensile stresses, though rarely great enough alone to cause “dry” crazing or cracking were revealed through exposure to environmental stress crazing and cracking (ESC) agents. Using an old technique involving a set of calibrated ESC liquids, edge tensile stresses as great as 18 MPa were found in the edges of the moldings. Other, independent methods of stress assessment gave results in semiquantitative agreement with those of the ESC tests. Packing force, machine compliance, injection hold time, and mold flashing emerged as major variables either raising or mitigating stress levels. The root cause of the edge tensions is the mismatch in the times and pressures at which the skins and cores of moldings solidify. In short, skins quench at low pressure first, while cores solidify later during the packing stage. Upon release from the mold, elastic recovery of the core stretches the skin. More importantly, machine and mold compliances allow expansion of the part in the packing stage, during which certain areas of the skin are stretched. Solidifying the core during the packing preserves part of the skin extension as elastic strain. These effects are capable of outweighing the classical tendency of quenching to generate skin compression and core tension. A number of other effects, including release from the mold before the core has solidified, and flashing of the mold, have been found to limit the rise of skin tension.     

橡胶注射成型机合模导柱力学性能分析

以橡胶注射成型机合模机构为分析对象,研究其导柱的静态力学性能。采用三维有限元分析方法,计算出导柱的应力值。研究结果表明,模具的大小对导柱的影响较大。     

Nature of contact between polymer and mold in injection molding. Part II: Influence of mold deflection on pressure history and shrinkage

In injection molding of thermoplastic parts, high hold pressures are set during the packing phase to generate a post‐filling, which compensates the shrinkage of polymer due to its cooling. The polymer pressure in mold cavity leads to a cavity deformation due to mold and machine compliance. Then, the increase in cavity thickness can modify the post‐filling and consequently the pressure history, the volumetric shrinkage and the part mass. The first goal of this paper is to present a simple method to locally determine mold rigidities: over‐packed slabs are injected and local deflections are determined from measurements of the local residual pressure, the local in‐plane shrinkages and the plate thickness. In the studied plate mold, which can be considered as stiff compared to some industrial molds, a rigidity of more than 1 μm/MPa has been measured close to the center of the plate. The second goal of this paper is to show the influence of mold deflection on dimensional properties. If the cavity thickness is small as for our 1‐mm‐thick plate mold, considering an infinitely rigid mold cannot do realistic predictions of polymer pressure history, volumetric shrinkages and part mass. Nevertheless, in‐plane shrinkage seems to be less affected by mold deflection. It means that the additional polymer mass due to mold deflection is mainly distributed in the part thickness.     

Estimation of injection pressure during mold filling

Dimensionless diagrams for estimating the bulk temperature of the flow front and injection pressure in the limit of small viscous generation are obtained. Also, a criterion for neglecting viscous generation is identified, The diagrams, based on the Lord and Williams model, refer to rectangular geometry and amorphous materials. A satisfactory comparison is obtained with literature data taken on polystyrene. A reasonable estimate of polyethylene injection pressure was obtained by roughly accounting for latent heat of crystallization through modified thermal diffusivity.     

Estimation of injection pressure during mold filling

Dimensionless diagrams for estimating the bulk temperature of the flow front and injection pressure in the limit of small viscous generation are obtained. Also, a criterion for neglecting viscous generation is identified. The diagrams, based on the Lord and Williams model, refer to rectangular geometry and amorphous materials. A satisfactory comparison is obtained with literature data taken on polystyrene. A reasonable estimate of polyethylene injection pressure was obtained by roughly accounting for latent heat of crystallization through modified thermal diffusivity.     

基于Moldflow的汽车仪表板大型塑件注塑模工艺优化

以大型汽车仪表板塑件为例,采用模流分析软件Moldflow分析了多浇口的最佳浇口位置.以翘曲变形量为主要分析指标建立了正交实验方案,通过分析比对获得了最佳的工艺组合.通过模拟分析,发现翘曲变形量过大和表面有熔接痕是主要缺陷.不均匀收缩、取向效应和冷却不均是导致翘曲变形量过大的主要原因.通过采用顺序阀浇口技术、优化相关注...     

Characterization of mold fouling during elastomer injection molding

Consideration is given to the characterization and origins of mold fouling occurring during the injection molding of elastomers. Results for nitrile rubber and fluoroelastomer compounds are presented with a range of techniques, including light microscopy, scanning electron microscopy, elemental analysis by energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy, and surface‐energy measurements with the sessile drop approach. A specially designed mold tool combined with interchangeable cavity inserts has also enabled the exploration of the effects of different metal surface treatments on the onset and extent of mold fouling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3186–3194, 2006     

Dynamic modeling of the mold filling process in an injection molding machine

This paper presents the development of a nonlinear mathematical model for the study of the mold filling process in an injection molding machine. The model is formulated by the Reynolds transport theorem which is applied to describe the polymer flow dynamics. The mold filling process can be approximated by the transient phenomenon of the non-Newtonian fluids flowing through a closed conduit. The comparison between the experimental results and the theoretical simulation indicate that the nonlinear model is a reasonable representation of the mold filling dynamics when the acrylonitrile-butadiene-styrene (ABS) is injected into a disk shape mold. The actuation system dynamics of an injection molding machine are also investigated. The results indicate that the nonlinear model can also adequately predict the transient behavior of the actuation system.     

Polymer flow length simulation during injection mold filling

The maximum flow length of a polymer for a given set of processing conditions is important in injection molding to avoid incomplete mold filling. Experimental analysis, using various processing conditions, can generate the actual influence of processing conditions on the maximum flow length. However, the experimental determination of the flow length for all known industrial polymers would be time consuming and expensive. A non-Newtonian, nonisothermal model of mold filling was developed to evaluate the flow length without requiring large amounts of computation time. The model implements the use of both a temperature and shear rate–dependent viscosity as well as viscous heating. This paper presents the model and its numerical implementation, followed by simulation results. The model is compared with other simulation programs and experimental results using both an amorphous Styron 484-27 polystyrene and a semicrystalline 640I polyethylene in a spiral mold geometry. Good agreement between the three is observed.     

Improving appearance quality of injection molded microcellular parts through mold coating of PTFE and zirconia

The application of microcellular parts in the field of high appearance quality is limited due to its appearance defects. In order to improve the appearance quality of microcellular parts, low heat transfer coefficient mold coating with PTFE and zirconia was employed in this study. The appearance quality of microcellular was evaluated by the surface roughness of microcellular parts. The numerical and experimental results show that delayed heat transfer between the melt and the mold can be achieved through both mold coatings, which improve the melt fluidity and reduce the shear force of the mold on the melt effectively. It is demonstrated that the PTFE has a better effect of delay heat transfer under thinner coating. The polished zirconia coating shows more conducive to the melt wall slip due to its stable molecular structure and smooth surface, resulting in microcellular parts with better appearance quality.     

Rheology studies of foam flow during injection mold filling

This work studies the flow behavior of a developing two‐phase gas‐polymer suspension during injection into the instrumented mold cavity of an injection molding machine. In the experiments, blowing agent type and concentration were varied along with processing conditions, to generate controlled cell structures in two different polymers, low density polyethylene and thermoplastic polyolefin. Experimental results indicate that the rheological properties of two phase gas‐polymer suspensions were sensitive to shear rate, blowing agent concentration, melt temperature, and mold temperature. The viscosity of all gas‐polymer suspensions revealed a reduction compared with neat polymer melt in the presence of gas bubbles, because of the reduced volume fraction of polymer matrix. A two‐phase rheological model has been used for fitting with our experimental results for estimating the shear viscosity of two‐phase flow in the mold cavity of the injection molding machine. POLYM. ENG. SCI., 47:522–529, 2007. © 2007 Society of Plastics Engineers.     

Pressure build-up during the packing stage of injection molding

A thorough study of an isothermal fluid motion within the mold cavity during the packing stage is presented. The fluid is considered Newtonian, and its compressible behavior is assumed to obey the Spencer-Gilmore equation of state. Mathematical results indicate that the pressure built up during the packing stage is strongly dependent on the melt viscosity and the boundary of the cavity. The effects of pressure gradient and distribution, during this stage, on the shrinkage of the final products are also discussed.