Integrated numerical analysis to evaluate replication characteristics of micro channels in a locally heated mold by selective induction

High-frequency induction heating is an efficient way to heat mold surfaces by electromagnetic induction using a non-contact procedure. Due to its ability to rapidly heat and cool mold surfaces, this method has been applied recently to the injection molding of micro/nano structures. The present study investigates a localized heating method involving the selective use of mold materials to enhance the heating efficiency of high-frequency induction heating. A composite injection mold consisting of ferromagnetic material and paramagnetic material was used for localized induction heating. The feasibility of this localized heating method was investigated through numerical analyses in terms of its heating efficiency for localized mold surfaces and the resulting flow characteristics in micro channels. To take into account the effects of thermal boundary conditions of localized induction heating, a fully integrated numerical analysis effectively connecting electromagnetic field calculation, heat transfer analysis, and injection molding simulation was carried out. The proposed integrated simulation was applied to the injection molding of a rectangular strip containing micro channels, and the resulting mold heating capacity and replication characteristics of the micro channels were compared with experimental findings in order to verify the validity of the proposed simulation.     

Reducing the effects of weldlines on appearance of plastic products by Taguchi experimental method

Weldlines influence not only strength of injection products but also the appearance of the products. This paper studies the effects of processing parameters on the appearance of weldlines by Taguchi experimental design method. Weldlines are obtained by the right door of copy machine which is modeled with three gates. The pictures of molding products are taken by digital camera. The samples of products and weldlines are extracted by software photoshop. The hue values of the samples of products and weldlines are calculated by software matlab. The visibility of weldlines is defined with the difference of the hue values of products and weldlines. By analysis, it turns out melt temperature, injection velocity, and injection pressure are the main factors which influence the appearance of weldlines.     

Mold design and forming process parameters optimization for passenger vehicle front wing plate

The main objective of the present article is to solve the problems of poor molding quality, large warpage, inadequate cooling effect and unsuitable selection of process parameters, in the injection molding process for passenger vehicle front-end plastic wing plate. The thickness and parting surface of the vehicle front-end fender were determined, the injection mold and its cooling system were designed. The relevant process parameters, affecting the product molding quality, were tested, according to orthogonal experimental approach, while their influence on the warpage was obtained, by analyzing the data. Finally, the BP neural network of warpage model was established and globally optimized using genetic algorithm. The optimal parameter combination of the injection molding process was derived as: melt temperature 236 °C, mold temperature 51 °C, cooling time 32 s, packing pressure 97 MPa and packing time 16 s.

     

Optimal design of medium channels for water-assisted rapid thermal cycle mold using multi-objective evolutionary algorithm and multi-attribute decision-making method

Rapid heat cycle molding technology developed recently is a novel polymer injection molding process. In this study, a new water-assisted rapid heat cycle molding (WRHCM) mold used for producing a large-size air-conditioning plastic panel was investigated. Aiming at improving heating efficiency and temperature distribution uniformity of the mold cavity surface, a two-stage optimization approach was proposed to determine the optimal design parameters of medium channels for the WRHCM mold. First of all, the non-dominated sorting genetic algorithm-II (NSGA-II) combined with surrogate models was employed to search the Pareto-optimal solutions. Subsequently, the Technique for Order Preference by Similarity to Ideal Solution was adopted as a multi-attribute decision-making method to determine the best compromise solution from the Pareto set. Then, the layout of the medium channels for this air-conditioning panel WRHCM mold was optimized based on the developed optimization method. It was indicated that the heating efficiency and temperature distribution uniformity on the mold cavity surface were greatly improved by using the optimal design results. Furthermore, the effectiveness of the optimization method proposed in this study was validated by an industrial application.     

Three-dimensional numerical modeling of an induction heated injection molding tool with flow visualization

Using elevated mold temperature is known to have a positive influence of final injection molded parts. Induction heating is a method that allow obtaining a rapid thermal cycle, so the overall molding cycle time is not increased. In the present research work, an integrated multi-turn induction heating coil has been developed and assembled into an injection molding tool provided with a glass window, so the effect of induction heating can directly be captured by a high speed camera. In addition, thermocouples and pressure sensors are also installed, and together with the high speed videos, comparison of the induction heating and filling of the cavity is compared and validated with simulations. Two polymer materials ABS and HVPC were utilized during the injection molding experiments carried out in this work. A nonlinear electromagnetic model was employed to establish an effective linear magnetic permeability. The three-dimensional transient thermal field of the mold cavity was then calculated and compared with the experiments. This thermal field was transferred to an injection molding flow solver to compare simulations and experimental results from the high speed video, both with and without the effect of induction heating. A rapid thermal cycle was proved to be feasible in a mold with an integrated induction coil. Furthermore, it was shown that the process can be modeled with good accuracy, both in terms of the thermal field and of the flow pattern.     

Development of high gloss plastic for injection molding by utilizing wollastonite(CaSiO<Subscript>3</Subscript>) and talc fillers

The gloss of plastic products is an important factor with which customers rapidly and directly decide the value of product. In general, these high-gloss plastic molded parts are produced through the injection molding of glass fiber-added plastic resin using a high temperature mold with the fine surfaces like glass. However, making the mold temperature higher causes the cooling time of injection molding longer, and the prolongation of cooling time leads to the extension of whole cycle of injection molding process. In order to resolve this problem, we developed a resin which makes the high-gloss injection modeling possible at low mold temperature by replacing conventional glass fiber filler with wollastonite filler. The tensile strength, flexural strain, impact strength, flow rate, gloss level and so on of the developed resin were tested with respect to the content of wollastonite. The results show that most of the properties except for the flow rate and gloss level are reduced in the newly developed resin. However, the decline in these properties was not enough to limit the use of new resins. In the gloss level test, as for the equal gloss of injection molded parts, the mold temperature for the developed resin was 30 °C lower than the mold temperature for the conventional resin. The difference of gloss between two injection molded parts using two different resins has been confirmed from the surface inspection of injection molded parts by SEM (scanning electron microscope).     

Research on thermal stress, deformation, and fatigue lifetime of the rapid heating cycle injection mold

Rapid heating cycle molding (RHCM) is a novel plastic injection molding process. It can be used effectively to prevent many defects of products produced in conventional injection molding process. In this paper, the panel of large-size liquid crystal display TV was taken as an example. Thermal, deformation, and fatigue analysis models for RHCM injection mold were established. Firstly, by analyzing the heat transfer process of the RHCM mold, the temperature distributions on the mold cavity surface were studied. Secondly, through numerical simulation, the tendency of the stress and deformation of the RHCM mold was obtained. It showed that the fixing mode between the stationary mold insert and the stationary mold plate had a great influence on the thermal stress and deformation of the mold. As a result, a new fixing mode for the stationary mold insert was proposed which could effectively decrease the deformation caused by the temperature changing. Lastly, the lifetime of the mold under different fixing modes was evaluated, and reasonable suggestions which could improve the lifetime of RHCM mold were also proposed. Application in engineering proved that it was a very effective way to improve the lifetime of RHCM mold by using the suggested fixing mode.     

Mold surface roughness effects on cavity filling of polymer melt in micro injection molding

Micro injection molding presents many challenges in the injection-molding community. When the dimensions of the part (and thus the cavity of the mold) are small, micro-scale factors such as mold surface roughness may play an important role in the filling of polymer melt. This paper investigates the effects of mold surface roughness on cavity filling of polymer melt in micro injection molding. A disk insert, which has two halves with different surface roughness but with the same roughness mean lines, was used in the investigations. The ratio of flow area of the rougher half with the total flow area of the molded part is used to evaluate the significance of surface roughness effect. The experimental results revealed that mold surface roughness does resist the cavity filling of polymer melt in micro injection molding. For the limited range of injection rate investigated, it is not significant on the surface roughness effects. The increase of mold temperature will decrease surface roughness effects. The change of melt temperature within the range allowed by the process is insignificant for surface roughness effects.     

An experimental work on the effect of injection molding parameters on the cavity pressure and product weight

The injection molding process is one of the most efficient processes where mass production through automation is feasible and products with complex geometry at low cost are easily attained. In this study, an experimental work is performed on the effect of injection molding parameters on the polymer pressure inside the mold cavity. Also, the effect of these parameters on the final products' weight is studied. Different process parameters of the injection molding are considered during the experimental work (packing pressure, packing time, injection pressure, injection time, and injection temperature). Two polymer materials are used during the experimental work (polystyrene (PS) and low-density polyethylene (LDPE)). The mold cavity has a cuboidal form with two different thicknesses. The cavity pressure is measured with time by using pressure Kistler sensor at different injection molding cycles. The results indicate that the cavity pressure and product weight increase with an increase in the packing pressure, packing time, and injection pressure for all the analyzed polymers. They also show that the increase of the filling time decreases the cavity pressure and decreases the product weight in case of PS and LDPE. The results show that the increase of packing pressure by 100 % increases the cavity pressure 50 % in the case of PS and 70 % in the case of LDPE. They also show that the increase of injection pressure by 60 % increases the cavity pressure 36 % in case of PS and 90 % in case of LDPE at an injection temperature of 220 °C. The results indicate that process parameters have an effect on the product weight for LDPE greater than PS. The results obtained specify well the developing of the cavity pressure inside the mold cavity during the injection molding cycles.     

电热式变模温注塑模具热响应辅助分析程序开发

针对快速变模温注塑成型模具热响应分析复杂问题,对电热式变模温注塑模具热响应作了研究,采用随形加热系统设计方法,将复杂的电热式变模温注塑模具简化为单个加热细胞单元,以电热元件的规格和布局为设计变量,以加热时间和型腔表面温差为热响应指标,结合Matlab图形界面开发模块和ANSYS有限元分析软件,开发了基于加热细胞单元的电热式变模温注塑模具热响应辅助分析程序,并对其准确性做了验证分析。研究结果表明,该辅助分析程序可以较好地预测模具的加热效率和型腔表面温度均匀性,可为电热式变模温注塑模具的设计、分析一体化提供一条快捷和高效的途径。     

高温快速成形工艺对制品复原性影响试验研究

以自主开发的车用蓝牙高光模具和温控辅助装备为基础，利用高温快速成形工艺对制品型腔复原性的影响进行试验研究。结果表明：高温快速成形与普通成形主要区别在于当模温升高至塑料热变形温度附近时，制品复制率明显提高，在低于或超出塑料热变形温度区域，模温变化影响甚微，而其他参数的影响与普通成形类似；各参数对浇道凝料的影响与普通成形区别不大，且浇道凝料对模温的变化并不敏感，故可通过提高模温在不增加废料的前提下提高制品复制率。     

注射模具调温系统设计

模具温度(模温)指模具型腔和型芯的表面温度。不论是热塑性塑料还是热固性塑料成型,模具温度对塑料熔体的充模流动、固化定型、生产率及塑件的形状和尺寸精度都有重要的影响。主要介绍一防护罩制件注射模具调温系统设计方法,通过有效的对模具温度进行调节,对模具进行冷却或加热,必要时两者兼有,从而达到控制模温的目的。     

Effect of mold temperature on motion behavior of short glass fibers in injection molding process

In injection molding process, the mold temperature can strongly affect the fiber orientation and distribution state in plastic parts. The fiber orientation behavior is discussed, and a model is used to describe the layered structure in injection parts. By studying the injected specimens, the fiber distribution and the layered structure in the part are illustrated and a variation of the fiber distribution along with the increasing of the mold temperatures is also demonstrated. The surface morphologies of the fiber-reinforced specimens at different mold temperatures are analyzed which are used to study the effect of the mold temperature on the fiber motion process of the resultant parts. Results show that in proper mold temperature, the fibers can be completely covered in polymer matrix and the mold temperature can greatly affect the part surface quality.     

Heat transfer in injection molding for reproduction of sub-micron-sized features

Heat transfer in injection molding was quantitatively measured with micro heat-flux sensors. The 0.1–10 micron-wide micro-grooves with aspect ratios of 0.5–1.0 were etched by focus ion beam on a Ni-plated mold. During the short time just after injecting, heat-flux in the mold was maximized to 10–50 W/cm², and heat transfer coefficient between plastic and mold was 0.27 W/(cm²K) with PMMA and 0.085 W/(cm²K) with PS. The maximum mold surface temperature just after injecting should be above the glass transition temperature of plastic, then reproducing sub-micron-wide micro-ridges.     

Surface microstructure replication in injection molding

In recent years, polymer components with surface microstructures have been in rising demand for applications such as lab-on-a-chip and optical components. Injection molding has proven to be a feasible and efficient way to manufacture such components. In injection molding, the mold surface topography is transcribed onto the plastic part through complex mechanisms. This replication, however, is not perfect, and the replication quality depends on the plastic material properties, the topography itself, and the process conditions. This paper describes and discusses an investigation of injection molding of surface microstructures. The fundamental problem of surface microstructure replication has been studied. The research is based on specific microstructures as found in lab-on-a-chip products and on rough surfaces generated from EDM (electro discharge machining) mold cavities. Emphasis is put on the ability to replicate surface microstructures under normal injection-molding conditions, i.e., with commodity materials within typical process windows. It was found that within typical process windows the replication quality depends significantly on several process parameters, and especially the mold temperature. For the specific microstructures, evidence suggests that step-height replication quality depends linearly on structure width in a certain range.     

Analysis and modeling of effective parameters for dimension shrinkage variation of injection molded part with thin shell feature using response surface methodology

The injection molded housing part with thin shell feature could be produced to increase the internal space for packing more components. In this study, injection velocity, packing pressure, mold temperature, and melt temperature were selected as effective parameters for injection molding process. For the purpose of reducing dimension shrinkage variation of thin shell molded part, the response surface methodology was utilized to determine the relationship between input parameters and responses. Then the optimization condition was obtained according to the desirability function. Results show that melt temperature is the most significant factor on dimension shrinkage variation in transverse direction, followed by packing pressure, mold temperature, and injection velocity. However, in the longitudinal direction, packing pressure has the greatest influence on the dimension shrinkage variation, followed by injection velocity, melt temperature, and mold temperature. In accordance with verification experiments, the difference between the experimental data and predicted values ranges from ?9.8% to 1.8%. To obtain the optimal condition, the overall desirability must be larger than 0.9. Based on analysis of variance, the proposed models look reasonably accurate.     

Powder injection molding 440C stainless steel

In this work, the processing steps for producing 440C stainless steel parts by means of powder injection molding technique were investigated. The molded specimens were debinded by solvent debinding followed by thermal debinding methods and were sintered under vacuum atmosphere. Effective densification took place in the temperature range 1,230–1,240°C in the sintering. After heat treatment, specimens sintered at 1,240°C for 30 min had the tensile strength of 876.3 MPa, the hardness of 57.7 HRC. Pitting mainly occurred in injection molding 440C stainless steel specimens in NaCl solution. The content of carbon has serious effect on the shape retention. Some methods, such as preventing from oxidation, are presented to avoid the as-sintered specimens from deformation.     

Small-hole arrays of ceramic material manufactured by micro powder injection molding

Ceramic substrate with three kinds of small-hole arrays (the minimum diameter is 400?μm) was manufactured by micro powder injection molding. The homogeneity, thermal, and rheological properties of the feedstock was characterized by means of SEM, Archimedes method, TGA, DSC, and capillary rheometer, respectively. The feedstock has good uniformity and the viscosity of feedstock accords with the pseudo-plastic behavior which is suitable for micro powder injection molding. The test results also show that the linear shrinkage of small holes is lower than the substrate which is important to mold design and size contraction of the sample. Moreover, the porosity of the sintered substrate is lower than that of the thin wall between two neighborhood small holes. Good surface roughness of the sintered samples is obtained by using sub-micron ZrO₂ powder which is even lower than molded surface. The relative density and hardness of the ceramic substrate with small-hole arrays sintered under 1,500°C for 2?h is 98.3% and 13.68?GPa, respectively.     

Optimization of conformal cooling channels with array of baffles for plastic injection mold

Cooling system has an important role in the injection molding process in terms of not only productivity and quality, but also mold-making cost. In this paper, a conformal cooling channel with an array of baffles is proposed for obtaining uniform cooling over the entire free-form surface of molded parts. A new algorithm for calculating temperature distribution through molding thickness, mold surface temperature and cooling time was presented. The relation among cooling channels’ configuration, process parameters, mold material, molding thickness and temperature distribution in the mold for a given polymer is expressed by a system of approximate equations. This relation was established by the design of experiment and response surface methodology based on an adequate physical-mathematical model, finite difference method and numerical simulation. By applying this approximate mathematical relation, the optimization process for obtaining target mold temperature, uniform temperature distribution and minimizing the cooling time becomes more effective. Two case studies were carried out to test and validate the proposed method. The results show that present approach improves the cooling performance and facilitates the mold design process in comparison to the trial-and-error simulation-based method.     

多型腔注射模充填不平衡试验

多型腔注射模在实际生产中有着广泛应用,充填平衡是保证多型腔模塑制品质量均匀一致的关键。自然平衡流道中也会发生充填不平衡现象,其原因可能是熔体流动产生的剪切热所致,但一直没有试验结果予以证明。基于此,利用可视化注射模具和红外温度传感器,通过直接观测熔体在流道和型腔中的动态流动行为并测量型腔入口处熔体的温度变化,对不同注射速率下不同材料在自然平衡多型腔注射模的充填不平衡进行研究。结果表明,由于剪切热的作用,主流道中不均匀但对称的熔体温度分布在分流道中失去对称性是产生充填不平衡的根本原因;充填不平衡程度不但取决于主流道中熔体的温度分布,还取决于分流道中凝固层的分布及熔体粘度对温度变化的敏感性。解决自然平衡多型腔注射模充填不平衡问题的根本,在于改善或消除分流道中熔体温度分布在流动平面的不对称性。