Mold Cavity Surface Research Articles

Evaluation of High Pressure Die Casting Mold Temperature Relations Depending on the Location of the Tempering Channels

During the casting cycle, the relatively cold material of the mold comes into contact with the significantly higher temperature melt, which causes high temperature fluctuations on the face of the mold and in its volume, which cause cyclic temperature stress. The submitted article is based on conclusions of the article “Evaluation of the temperature distribution of a die casting mold of X38CrMoV5_1 steel”, in which the modification of temperature relations of the mold in the direction from the mold face to its volume was investigated. In current article, the influence of the tempering channel distance on the temperature modification in the volume of high pressure die casting mold is investigated. Three variants of the tempering channels placements with different location respecting the mold cavity were investigated. The temperature was monitored in two selected locations, with distribution of 1mm, 2mm, 5mm, 10mm and 20mm in the direction from the mold cavity surface to the volume of fixed and movable part of the mold. As a comparative parameter, the temperature of the melt in the center of the runner above the measuring point and the temperature of the melt close to the face of the mold were monitored. The measurement was performed using Magmasoft simulation software. It was discovered that up to a distance of 5mm from the face of the mold, a zone with complete heat transit without its accumulation occurs. Above this limit, the mold begins to accumulate heat, and from distance of 20mm from the face of the mold, the heat gradually passes into the entire mass of the mold without significant temperature fluctuations. The propositions derived from the results of the experiments presented at the end of the article will subsequently be experimentally verified in further research works.

Influence of Processing Conditions on the Generation of Surface Defects in a Heat-and-Cool Hybrid Injection Molding Technique for Carbon Fiber-Reinforced Thermoplastic Sheets and Development of a Suitable Mold Heated by Far-Infrared Radiation.

Recently, hybrid injection molding-a type of overmolding technology in which a short carbon fiber-reinforced thermoplastic is injection molded over a compression-molded carbon fiber-reinforced thermoplastic (CFRTP) sheet-has been introduced. A heat-and-cool hybrid injection molding technique has also been introduced for practical use. The technique yields high-quality molded products. This is achieved through the heating of the mold cavity surface to a temperature higher than the melting point of the base polymer impregnated into the carbon fiber fabric. However, few experimental analyses of the molding phenomena in heat-and-cool hybrid injection molding have been reported. In particular, the effect of the processing conditions on the transfer of the mold cavity surface shape to the CFRTP sheet has not been clarified in detail. Therefore, it has been impossible to take extensive measures when defects are generated in molded products. In this study, a mold is designed and fabricated for use with far-infrared radiation heating, a variotherm technology that is suitable for the experimental analysis of the heat-and-cool hybrid injection molding phenomenon. In particular, a mold is designed and fabricated to continuously perform the following three processes using only an injection molding machine: (1) the radiation heating of both the CFRTP sheet and the mold cavity surface using a far-infrared radiation heater, (2) the compression molding of the CFRTP sheet, and (3) the injection molding of the melt. The effects of the heating conditions of the mold and the injection molding process conditions on the appearance characteristics of the molded products are clarified using this mold and a far-infrared radiation heater.

The generation mechanism of demolding force based on themold‐partinterface contact mode in micro‐injection molding

AbstractDemolding is the key step of micro‐injection molding (μIM), which influences the molding quality of polymer parts to a great extent. The essence of demolding is to overcome interface interactions between the mold cavity surface and the part surface, which is closely related to factors such as the cavity surface topography and process parameters. However, a theoretical model predicting the demolding force of μIM is still lacking, resulting in the difficulty of improving the quality of demolding in μIM. Therefore, a comprehensive demolding force model is proposed to clarify the demolding mechanism of μIM. The model focuses on the adhesion behavior and friction behavior in the special contact mode formed by the replication effect of μIM. The theory proof and computation results indicate that the cavity surface topography determines the contact mode of the mold‐part interface (MPI), which in turn changes the real interface contact area, the composition mode of adhesion stress, and the friction forms, thereby affecting the adhesion and friction force during demolding. In addition, the process parameters can also change the contact mode of MPI as the process parameters have a great effect on the filling capacity and the degree of replication, thereby influencing the demolding process.

Effect of inhomogeneous mold cavity surface temperature rapid self-cooling on β phase contents and mechanical properties of injection-molded polypropylene

A dynamic self-cooling inhomogeneous temperature gradient field was applied instead of steady-state temperature at the mold cavity surface to study the effect of different cooling rates on the crystallization progress after the melt flow. The results showed that both the crystallinity and the β phase content increased with the gradient of the inhomogeneous mold temperature. When the mold temperature gradient of the high-temperature and the low-temperature sides increased from 0 to 40 °C, the size of the shish-kebab in the shear layer and the amount of small β phase spherulites in the transition layer increased. During the melt flows, a cavity temperature gradient higher than 30 °C was required to increase the stability of β phase in the transition layer. The yield stress and the elongation at break increased with the temperature gradient, but decreased at the temperature gradient of 45 °C.

Regional temperature control in ceramic injection moulding: An approach based on cooling rate optimisation

The injection moulding of ceramic components with uneven wall thickness presents challenges due to differential cooling rates developing in the injected parts, which cause premature solidification of the feedstock at thin features and lead to detrimental defects, worsening in components from green to sintered states. To cope with this, suitable mould thermal control approaches have to be selected and validated, as current control methods are based on the achievement of a uniform cavity surface temperature, which is not tailored to such complex geometries. In this work, a novel thermal control system is proposed, based on regional mould temperatures, implemented with the use of Peltier modules, which locally and independently heat and cool different cavity features according to their thickness. The regional temperature profiles are optimised over time with the use of a coupled Finite Element - Particle Swarm Optimisation (FE-PSO), to achieve uniform cooling rates throughout the moulded components. The performance of this approach is compared to both constant ambient mould temperature and Rapid Heat Cycle Moulding (RHCM) techniques, which instead aim at achieving uniform temperatures throughout the mould cavity surface. Results show that the novel proposed method, based on regional temperature control and uniform cooling rates, promotes the simultaneous solidification of features with a 10-times difference in surface-to-volume ratio. Due to this, in terms of components quality, the novel method brings the advantages of higher dimensional control and reduction of differential shrinkage compared to the other analysed approaches, thus increasing the capability to use injection moulding to manufacture ceramic components characterised by non-uniform wall thickness.

Thermodynamic and shear effects of ultrasonic vibration on the flow‐induced crystallization of polypropylene

AbstractIn order to achieve optimal mechanical properties in injection‐molded parts, continuous ultrasonic vibration is applied to a mold cavity during the filling and solidification stages of injection molding. In this work, the effect of ultrasonic thermodynamics and ultrasonic shear on the condensed structure of the parts are studied. Thermocouple measurement results show that the increase in the temperature of the mold cavity surface caused by ultrasonic thermodynamics can reach up to 15°C; Molecular dynamics simulation results show that the molecular chain morphology under ultrasonic shear is more stretched during the melt flow process. Microscopic results show that with increasing ultrasonic power and ultrasonic time, the ultrasonic thermodynamic effect causes the thickness of the shear layer to increase. With increaseing ultrasonic power, the lamella thickness of the core layer increases, while the crystal size in the transition layer shows a trend of first decreasing and then increasing. The ultrasonic shear causes the overall crystallinity and β crystal content of the parts to increase with increaseing the ultrasonic power. The crystallinity starts to decrease when the ultrasonic vibration is still applied at a melt temperature below 67°C during cooling. When the ultrasonic power is increased to 1000 W and the ultrasonic vibration time is applied for 30 s, β spherulites transform to β‐transcrystalline. The yield stress results show that when the ultrasonic vibration time is 0–20 s, the yield stress of the parts increases with the ultrasonic power; while when the ultrasonic time is increased to 30 s, the yield stress decreases.

Multi-objective optimization of heating system for rapid thermal cycling molding mold with internal induction heating

A rapid thermal cycling molding (RTCM) with novel internal induction heating mode is proposed in this work. The induction coils are directly inserted in the corresponding mounting holes of mold with an annular gap in between. During mold heating, eddy current losses confined at the walls of the mounting holes act as thermal sources to rapidly heat the mold cavity surface. Water passed through the annular gaps can be utilized to cool the mold in the cooling stage. Moreover, a design framework of the internal induction heating system in the RTCM mold is also developed. Firstly, a unit cell model of the mold was established to evaluate mold thermal response via numerical simulations, in which the effect of frequency and magnitude of coil current, the layout of induction coils and the annular gap size were examined. Then, a hybrid multi-objective optimization method was applied to optimize the induction heating system for the unit cell model. Finally, based on the obtained optimal parameters, a novel design strategy was adopted to conformally arrange the induction coils for the industrial RTCM molds. The blow mold of automotive spoiler was taken as an example to validate the effectiveness of the proposed approach. The results show that the present approach cannot only improve the mold thermal response performance, but also facilitate the mold heating system design process. This work may provide an effective method to realize RTCM of industrial plastics parts with free-form shape.

Effects of Heating and Cooling of Injection Mold Cavity Surface and Melt Flow Control on Properties of Carbon Fiber Reinforced Semi-Aromatic Polyamide Molded Products.

Fiber reinforced thermoplastics (FRTP), reinforced with glass or carbon fibers, are used to improve the mechanical strength of injection-molded products. However, FRTP has problems such as the formation of weld lines, the deterioration of appearance due to the exposure of fibers on the molded product surface, and the deterioration of the strength of molded products due to the fiber orientation in the molded products. We have designed and fabricated an injection mold capable of melt flow control and induction heating and cooling. This mold can both heat and cool the injection mold. It can also control the melt flow direction using a movable core pin. In this study, the above-mentioned mold was used for the molding of carbon fiber reinforced semi-aromatic polyamide. As a result, we found that increasing the heating temperature of the mold and increasing melt flow control volume contribute to the prevention of the generation of a weld line and the exposure of fibers on the molded product surface, as well as to the formation of a flat surface and increased bending strength. The relationships of these results with the carbon fiber orientation in the molded products and the crystallization of semi-aromatic polyamide were also examined in this study.

Effects of physical foaming of PA66 + 30%GF thick-walled parts

The paper presents the effect of gas dosing parameters on the microporous structure of physically foamed polyamide 66 reinforced with 30 wt% of glass fibers (PA66 + 30% GF). The thick-walled molding was used as the research object. To realize the research aim, simulation software was applied. The variable parameter in a research program was a dose of supercritical fluid, in this case, nitrogen. The tested properties of a cellular structure were: cell size, cell density and local density of a material. All the parameters were considered based on 30 measurement points evenly distributed in the central zone of the sample’s cross-sectional area. The largest size of pores was observed in the core region of molding for every amount of supercritical (SCF) fluid used. It was shown that regardless of the amount of gas, the pore size increases as a function of the distance from the mold cavity surface until it achieves a constant value. However, the most rapid increase was observed in the case of the smallest amount of gas dosed (0.25 wt%) which also resulted in the largest pore size in the core zone of a molding. The lowest value of cell density was noticed for 0.25 wt% of gas used. In the case of 0.5 wt%, 0.75 wt% and 1 wt% of gas dosed, results of cell size, as well as cell density, were comparable. However, dosing 1 wt% of gas resulted in obtaining the finest structure, characterized by the smallest pore size and highest cell density. As a parameter resulting from a cell size and cell density, the local density of material was analyzed. The lowest value of local density in the core area was noticed for 0.25 wt% of SCF dosed.

An Analysis of the Casting Polymer Mold Wear Manufactured Using PolyJet Method Based on the Measurement of the Surface Topography.

An important factor having an impact on the condition of machine parts is their surface topography. For instance, in the production of a molded element in casting or injection molding processes, the surface topography of the molding cavity has a significant impact on the surface condition of the product. An analysis of the wear of a mold made with the PolyJet technique was performed in this work, and we examined the surface topography using the stylus method after casting a wax model of the turbine blade. The surface topographies showed a gradual degradation of the mold cavity surface. After the manufacture of 40 castings, there was a significant deformation of the microstructure of the mold cavity. The maximum height value (Sz) parameter had the most dynamic change from 18.980 to 27.920 μm. Its growth dynamics are mainly influenced by maximum peak height (Sp) rather than the maximum pit height (Sv) parameter. In the case of the root mean square height (Sq) and arithmetic mean height (Sa), their gradual increases can be seen from 2.578 to 3.599 μm and from 2.038 to 2.746 μm. In the case of the value of the skewness (Ssk) parameter, a small positive skew was observed. As for the kurtosis (Sku) values, the distributions are clearly leptokurtic.

An imaging performance analysis method correlated with geometrical deviation for the injection molded high-precision aspheric negative plastic lens

High-precision aspheric negative plastic lenses are widely used in optical systems owing to their excellent performance and ease of high-efficiency manufacturing. The imaging performance of the lens is difficult to control, because it is unable to perform optical measurements directly and is sensitive to manufacturing processing meanwhile. Generally, the imaging performance is guaranteed by a strict control of geometrical deviation, such as Peak-to-Valley (PV) and Root-Mean-Square (RMS). In this study, an optical ray-tracing algorithm with the measured geometrical deviation data is proposed to perform an imaging performance analysis correlated with geometrical deviation for the injection molded high-precision aspheric negative plastic lens. Taguchi experiments are applied to investigating the effect of processing parameters. The geometrical deviation of the convex surface is found to be an order of magnitude greater than that of the concave surface. The geometrical dimension of the concave surface is mainly determined by the machining precision of the mold cavity surface, whereas the convex surface dimension is mainly affected by the lens shrinkage. However, the imaging performance has a nonlinear correlation with the geometrical deviation. Modulation Transfer Function (MTF) and Spot Diagram are equivalently affected by the concave and convex geometrical deviations, and depend on the object field height. The effect of processing parameters on geometrical deviation and imaging performance is uncorrelated. Thus, the imaging performance should be simultaneously considered as a criterion as well as the geometrical deviation in the optimization of aspheric negative lens injection molding processing. The imaging performance prediction using an optical ray-tracing algorithm with the measured geometrical deviation data is instrumental to optimize the manufacturing processing.

Relationship Between Forced Vibration Method and Residual Stress in Die Materials

During aluminum die-casting, tensile residual stress accumulates on the cavity surface of the die by repeated heating and cooling processes. Recently, to improve productivity, dies with high cycle and longer life have become necessary, and reduction or removal of tensile residual stress can be used to prevent heat cracks that cause mold fracture. Heat treatment is often used for residual stress reduction but a more efficient residual stress reduction method that can be carried out with simpler equipment is required. In this study, the relationship between the residual stress after forced vibration and the amplitude at the time of excitation is investigated by mechanical vibration of the SKD61 die materials and the die-casting mold through the application of forced vibration by an eccentric motor. Residual stress on the surface of each test plate treated by the heat treatment and the surface of mold cavity after excitation is evaluated by the X-ray residual stress measurement. It was found that the residual strain after excitation accumulated in compression as the amplitude of oscillation of the specimen became negative. Residual stress in the excitation direction of the specimens increased in the compression direction due to the excitation, demonstrating the effective stress reduction by the excitation method.

Microstructure, Tensile Property, and Surface Quality of Glass Fiber-Reinforced Polypropylene Parts Molded by Rapid Heat Cycle Molding

The microstructure of a molded product considerably influences its macroscopic properties. In this study, the influence of molding process on microstructure, tensile property, and surface quality was explored on the glass fiber-reinforced polypropylene (GFRPP) parts molded by rapid heat cycle molding (RHCM) and conversion injection molding (CIM). Tensile strength and surface gloss were chosen to measure macroscopic properties of the molded parts. The microstructure including multilayer, fiber orientation, crystallinity, and fiber-matrix bonding strength were analyzed by simulations, scanning electron microscopy, wide-angle X-ray diffraction, and dynamic mechanical analysis. The relationship between the macroscopic properties and microstructure of the RHCM samples was also discussed. The results indicate that as the mold cavity surface temperature increases, the tensile strength increases firstly and decreases thereafter. The tensile strength of RHCM parts reached the maximum at the mold heating temperature of 60°C. It is also observed that the surface gloss of the sample increases as the mold cavity surface temperature rises, and the increase of surface gloss decreases distinctly with the mold heating temperature higher than 90°C.

The Measurements of the Shear Stress Distribution at the Cavity Surface during Melt Filling in an Injection Mold

Measurement of shear stress distribution is important for examining phenomena occurring in the interface between the mold cavity surface and molten resin in injection molding. The authors developed a high precision measurement technique for shear stress distribution using a movable block and 3-component force transducer. In this study, we analyzed the influence of resins, cavity surface properties, and cavity thicknesses on shear stress distribution. The results are summarized below：

Heating properties of ERHCM molds based on heating cell units

A thermal analysis method was developed based on heating cell units to study the thermal response of electrical rapid heat cycle molding (ERHCM) molds. Heating efficiency, mold strength and uniformity of temperature distribution on the mold cavity surface were studied as a function of the distance from the center of heating rods to the mold cavity surface, which is one of the most important parameters for mold design. In this paper, the height/diameter (H/D) value was employed to describe the distance from the center of the heating rods to the mold cavity surface. Additionally, the maximum von Mises stress after heating was determined to describe the mold strength, and the temperature difference was applied to characterize the temperature distribution uniformity of the cavity surface. The results showed that electrical rapid heating cycle injection molds obtain reasonable heating efficiency, mold strength and cavity surface temperature uniformity when the distance from the center of heating rods to the mold cavity surface is approximately 1–1·5 times their diameter.

Effects of process conditions on the heat transfer coefficient at the polymer-mold interface and tensile strength of thin-wall injection molding parts

Abstract Generally, the strength at the weld line of the injection molded part is very weak. The heat transfer coefficient (HTC) between the polymer melt and the mold cavity surface was analyzed to solve this problem. The surface roughness of the mold cavity and the material of the mold insert were changed to adjust the interface environment between the polymer melt and the mold cavity surface. HTC was obtained by combing the experimental measurement with the theoretical calculation. In the current study, the influence of HTC on the tensile strength of the weld line of the molded specimen was investigated. The results show that the weld line strength of the molded specimen increases with the decrease in HTC between the polymer and the mold cavity surface. Meanwhile, the decrease in the surface roughness of the mold cavity or replacing the mold material with lower thermal conductivity can reduce the value of the HTC between the polymer and the mold effectively and can delay the cooling rate of the hot polymer melt. This provides a new idea to solve thin-wall injection molding weld line defects.

Fluidity of Rubber and TPE Influenced by Mold Surface Roughness

Injection molding is one of the most extended plastic processing technologies. Delivery of polymer melts into the mold cavity is the most important stage of the injection molding process. This paper shows the influence of mold cavity surface roughness and technological parameters on the flow length of thermoplastic elastomers and rubber into mold cavity. The fluidity of polymers is affected by many parameters (mold design, melt temperature, injection rate and pressures) and by the flow properties of polymers. Evaluation of the data obtained by experiments where the testing conditions were widely changed shows that quality of the cavity surface does not affect the length of flow.

Polymer Flow Influenced by Mold Cavity Surface Roughness

Polymer injection molding is the most used technology of polymer processing nowadays. It enables the manufacture of final products, which do not require any further operations. Working of shaping cavities is the major problem involving not only the cavity of the mold itself, giving the shape and dimensions of the future product, but also the flow pathway (runners) leading the polymer melt to the separate cavities. This paper shows the influence of cavity surface roughness, polymer material (with different flow properties) and technological parameters on the flow length of polymers into mold cavity. Application of the measured results may have significant influence on the production of shaping parts of the injection molds especially in changing the so far used processes and substituting them by less less expensive production processes which might increase the competitiveness of the tool producers and shorten the time between product plan and its implementation.

Micro-injection molding using a polymer coated mold

We applied an insulating polymer layer to the surface of mold cavity to injection-mold large plastic parts with a microsized thickness. Polyimide (PI) was coated on the mold wall using spray coating method. A thin light guide plate (LGP) was designed and fabricated via micro-injection molding. The polymeric coating layer could enhance the fluidity of polymer melt in the cavity during filling stage by minimizing the formation of the skin layer during injection molding. The surface roughness and pattern transfer rate of the LGPs were analyzed experimentally. In addition, numerical simulation was carried out to understand the insulation effect of the layer in the injection molding.

Optimal design of heating system for electrical rapid heat cycle mold based on multi-objective optimization, multiple-attribute decision-making, and conformal design theory

To improve the heating efficiency and cavity surface temperature uniformity, an optimal design method was developed for the heating system in electrical rapid heat cycle molding mold. First, an electrical rapid heat cycle molding mold was simplified as a single heating cell unit for thermal response analysis based on conformal design theory. Second, a response surface using back propagation neural network was constructed on the ground of initial finite element experiments. Then, a non-dominated sorting genetic algorithm-II combined with the polynomial back propagation neural network model was proposed to capture the Pareto-optimal solutions. Subsequently, the technique for order preference by similarity to ideal solution based on entropy-based weight was adopted as a multi-attribute decision-making method to choose the trade-off optimal design point from the Pareto-optimal set. To gain the optimal design of heating system, the optimized heating cell unit for electrical rapid heat cycle molding mold was calculated and finally mapped into the entire mold. Cavity surface temperature uniformity increased by 17.1%, and heating efficiency increased by 26%. The results show that the temperature distribution uniformity on the mold cavity surface was obviously improved and using this optimization strategy ensured high heating efficiency.