Mold Cavity Surface Research Articles

The Increase in Effectivity of Material Processing with Employment of Liquid CO2 during Aluminium Die Casting

The article is focused on monitoring the cooling effect of the liquid CO2. This unconventional cooling system was used as a supplement method added to the standard tempering system of the die casting mould particularly intended for aluminium alloy castings. Standard tempering system of die casting moulds enables preheating the mould to operating temperature before the particular production starts and then the tempering system regulates the temperature balance between the mould and the casting during individu al production cycles. Conventional cooling system is based on drilled or milled interconnected channels with predominantly parallel orientation to the parting line, through which a tempering medium (oil, water etc.) flows. This system has some limitations that can be overcame with utilizing of special approaches. One of these approach is employment of liquid CO2.This study revealed the positive impact of this additive cooling on homogeneity of temperature field distribution on the mould cavity surface, which assures first of all the uniform coating the cavity surface by separating agent and sticking the melt on the cores. The products were analysed using the metallographic and CT analyses and the leak tightness was tested.

A sub-space artificial neural network for mold cooling in injection molding

The applications of artificial intelligence (AI) have considerably expanded over recent years. A new class of industrial systems is beginning to evolve that incorporates using high volume data and advanced analytics to better optimize product quality while reducing energy consumption. Artificial neural networks (ANN) when combined with advanced modeling and control, begins to form an AI platform that can be further enhanced for factories of the future. This paper provides a demonstration of such initial work that can be further developed for future systems in a generic way. When considering polymer processing such as plastic injection molding, the mold cavity temperature (MCT) profile directly relates to part quality and part reject rates. Therefore, it is desirable to optimize the mold cooling process using real time control of MCT as it directly affect part quality. However, MCT is affected by a number of interacting nonlinear dynamic parameters that are often neglected due to the challenge of quantifying such parameters. Advanced model based control algorithms are often used for providing improved control of complex systems. However, they depend on good model formulations that are analytically insufficient. An online intelligent system identification approach for the mold cooling process is developed and tested. An ANN is designed to adjust online sub-space parameters that govern a mold cooling model. Results demonstrate that this online ANN approach can be used to accurately predict the dynamic behavior of mold cavity surface temperature. This is key to many industrial systems where their states are not directly observable and uncertainties are unknown. The methodology can be readily adapted for different operating conditions as in this case of polymer processing and has good potential for its integration with advanced model based control schemes and cloud computing approaches for the next generation of machines.

Study of the NURBS Geometric Description Method on the Mold Cavity Surface

The mold cavity is usually linked by various curved surfaces smoothly and gradually. At present descriptive methods for mold cavity surface are grid method, algebraic method and NURBS (Non-Uniform Rational B-Spline) method. This paper analyzes the characteristics of NURBS surface and presents the calculating method of the NURBS description of the mold cavity. Research shows that it is the most effective to describe the mold cavities surface when free-form surfaces and analytical surfaces coexist on the surface of mold cavities.

Application of surface treatments on releasing adhesion force during thermoplastic polyurethane injection molding process

With injection molding process, thermoplastic polyurethane is generally used to fabricate shoes, boots, rollers and golf balls, etc. However, serious adhesion causes molded part difficult to be released from tool surface. To alleviate adhesion force during ejection stage, chromium‐nitride (CrN) based and diamond like carbon (DLC) coatings prepared by physical vapor deposition were coated on mold cavity surface. Single layer CrN and modifying CrN coatings were found to be beneficial to alleviate adhesion force whereas multilayer CrN and DLC surface treatments were ineffective during continuous experiments. Further investigation found that single layer CrN and modifying CrN both had excellent water‐repellency properties with low surface energy and exhibited the distinctive conical structure with uniform grain size. Although multilayer CrN coating exhibited similar morphology as that of single layer CrN coating, it showed significant variations in grain size and height. In contrary, although DLC coating adequately showed uniform topography, its larger grain size and wider valley between grains both lead to larger adhesion force due to mechanical anchoring. POLYM. ENG. SCI., 57:299–305, 2017. © 2016 Society of Plastics Engineers

Study on reducing sink mark depth of a microcellular injection molded part with many reinforcing ribs

As a novel injection molding process, microcellular injection molding process has the characteristics of saving material, decreasing warpage and surface sink mark, improving dimensional accuracy, etc. But for the plastic part with thick reinforcing ribs, if selection of process parameters are not reasonable, foaming quality of melt will be affected and obvious sink mark defects will appear on the surface of plastic part. This paper selected a medical appliance shell with many reinforcing ribs as research object. Simulation experiments of microcellular injection molding process were performed by using orthogonal experiment method. The influence of different process parameters, such as mold cavity surface temperature, melt temperature, injection rate, cooling time, weight reduction ratio and supercritical fluid level, on the surface sink mark of microcellular injection molding part was studied by using signal-to-noise ratio analysis and analysis of variance . The results showed that mold cavity surface temperature was the most important influence factor on surface sink mark depth of microcellular injection molding part, followed by weight reduction ratio, cooling time, supercritical fluid level, injection rate and melt temperature. Meanwhile, the optimal combination of process parameters was obtained for minimizing sink mark depth of microcellular injection molding part. The average surface sink mark depth of microcellular injection molding part molded by using the optimized process parameters was only 2.62 µm, compared to 4.87 µm of average surface sink mark depth of microcellular injection molding part molded by using the process parameters before optimization, the average sink mark depth of microcellular injection molding part was reduced by 46.2%. Finally, the forming mechanism of sink mark of microcellular injection molding part at locations of reinforcing ribs was discussed, and the influence mechanism of different process parameters on surface sink mark defects of microcellular injection molding part was also analyzed.

Numerical simulation of melt filling process in complex mold cavity with insets using IB-CLSVOF method

A coupled level-set and volume-of-fluid (CLSVOF) method is proposed for tracking interface of incompressible two-phase flows, where the VOF advection is carried out only, and a zero level-set (LS) formula and LS reinitialization equation are employed to reestablish the signed distanced field near the interface, which can program easily. Meanwhile, a mass-correction scheme based on the interface curvature is used to conserve the liquid mass correctly. Firstly, the performance of the CLSVOF method is evaluated through two- and three-dimensional deformation field tests. Then, the CLSVOF method is adopted to simulate the rising bubble and droplet falling problems. Finally, a shape LS function is used to describe and treat the irregular surface (immersed boundary) of mold cavity. With the aid of the shape function, the coupled immersed boundary (IB) and CLSVOF (IB-CLSVOF) method is applied to the melt filling process in the complex mold cavity with insets. The numerical results show that the proposed IB-CLSVOF method has the capability to cope with complex interface variations accurately. And also, the numerical results demonstrate that IB-CLSVOF method is able to successfully depict the phenomena of race-tracking, air entrapment and weldline development, which are very helpful for determining processing conditions and designing mold cavities.

Al6063, Pure Aluminium and Brass Casting Solidification using Explicit Scheme

Finite difference modeling of solidification of pure aluminum, Al 6063 and brass casting in green sand mould has been simulated. Unsteady heat conduction eq. in twodimensional form governs the physical problem. Convective boundary conditions have been considered at the interface where molten metal meets the mould cavity surface. Heat conduction eq. in unsteady state and transient state have been solved by using Two dimensional finite analyses difference method using MATLAB to study thermal flow and cooling rate. The properties of materials utilized are green sand and pure Al, Al6063 and brass. The results obtained are: cooling rate of pure Aluminum, Al6063 and brass in green sand mould for 2D casting for unsteady problem and temperature distribution in steady case.

Development and application of rapid thermal cycling molding with electric heating for improving surface quality of microcellular injection molded parts

A rapid thermal cycling molding (RTCM) technology with electric heating and water cooling was developed to eliminate the surface defects of microcellular injection molded parts. To verify its effectiveness, an RTCM mold for producing microcellular cover plates was constructed. Experiments and simulations were conducted to evaluate the mold thermal response. The results show that the mold cavity surface temperature (TM) can be rapidly adjusted in a large range. Moreover, empirical correlations for predicting the TMs were proposed and validated, and then can be used as an effective tool to accurately control the TMs in actual molding. Finally, microcellular polyformaldehyde (POM) cover plates were molded. The effect of the TM on their surface roughness was investigated and relevant mechanism was analyzed. It is found that the part surface roughness can be effectively reduced by increasing the TM. When raising the TM close to or above 150 °C, the microcellular POM cover plates with glossy appearance comparable to the solid counterpart can be molded within an accepted molding cycle time, demonstrating the effectiveness of the developed molding technology.

Mold Surface Analysis after Injection Molding of Highly Filled Polymeric Compounds

This work deals with an impact of abrasive particles used in powder injection molding (PIM) on a surface roughness of the tool. For this purpose, the surface of new mold cavity was compared with the same mold cavity after 2 000 injection molding cycles. Processed PIM compounds contained polymeric binder with around 60 vol. % of metal or ceramic particles (0.1 up to 20 μm). Surface analysis was performed on cavity impressions prepared from a special silicone imprinting substance in two directions by a 3D surface scanner. Investigated parameters were surface roughness (Ra) and roughness depth (Rz) which have an influence on flow instabilities of highly filled compounds such as wall slip affecting the final product quality. Obtained results showed a significant wear of the mold cavity which was statistically confirmed by t-test and F-test parametric methods. A greater part of the mold cavity was smoothed during injection of PIM compounds, while the surface roughness increased near the point gate (runner system) probably due to a high injection pressure in this part of the mold.

Formation and Spreading of Cracks at Die due to Heat Fatigue

The moment of formation and spread of cracks on the surface of metal mould cavity is rather significant in the sphere of die casting due to durability of these costly tools and especially in case of casting of metals and alloys with higher melting temperature. The issue examination requires analysis of the thermal aspect of the process and of the mechanism of mechanical stress occurrence of material.For the purpose of verification of occurrence and spread of cracks the fragile materials were firstly tested in case of which inevitable number of cycles was possible to be considered acceptable for testing performance. The first tests were accompanied by the ring dipping with diameter of 60 mm with the central hole with diameter of 15 mm from alloy according STN 42 2420 standard, i.e. with dimensions reaching the used mould filler into molten salt at temperature of 1000°C for the period of 30 s with following dipping into water (20°C). The sample surface checking was performed visually after every 100 cycles.To make a comparison the dependence of length of cracks with circular samples with diameter of 12.7 mm made of material H11, H13, H21 and of steel Maraging.

Effect of rapid heating cycle injection mold temperature on crystal structures, morphology of polypropylene and surface quality of plastic parts

The present study mainly investigated the effect of mold cavity surface temperature in the filling process on the crystallization status of polypropylene (PP) in different thickness layers of injected plastic parts, and revealed the inner relationship between the surface quality of plastic parts, crystallinity and residual stress under rapid heating cycle molding (RHCM) process conditions. The morphology of PP was studied by using a transmission-polarized optical microscope (POM) and a scanning electron microscope (SEM). The crystal structures of PP on different thickness layers of plastic parts were examined by using a wide-angle X-ray diffraction (WAXD). The surface quality of plastic parts was characterized by using a glossiness tester. With the increase of mold cavity surface temperature, the thickness of frozen layer of plastic parts is drastically reduced, and the crystallinity of PP in the external surface first increases, then decreases, and finally tends to a constant, but the crystallization in the sub-surface layer first increases, then decreases, and finally increases again. When the temperature of mold cavity surface is close to the glass transition temperature of PP, the crystallinity in the external surface reaches the maximum and the crystallization status in the sub-surface and core layers is close to each other. Meanwhile, the surface glossiness of plastic parts also achieves its best. In addition, the high crystallinity and low residual stress in the external surface are both favorable conditions for obtaining a high surface glossiness of plastic parts.

Improving the Properties of Injection Molded Products with Induction Heating and Cooling Molds

An induction heating and cooling mold that can keep the surface temperature of the entire mold cavity uniform and has a new heating and cooling insert with a gas vent mechanism is designed and produced. The effects of the temperature of the mold cavity surface, of the cavity air during the melt filling process, and of the organic gas generated fromthe melt on the appearance andmechanical properties of an injectionmolded product made of high impact polystyrene are studied. It is found that the heating and coolingmold with a gas vent can suppress molding defects, such as a weld lines and gas burns, and can greatly increase the displacement ratio of molded products obtained in the tensile test. This means that the effects of the gas vent and the surface temperature of the cavity have been quantitatively clarified using this type of mold.

Three Dimensional Numerical Simulation of Melt Filling Process in Mold Cavity with Insets

This paper presents a level set function, named shape function, to describe and treat the irregular surface of mold cavity. With the aid of the shape function, the continuity, momentum and energy equations can be extended for solving two-phase flows with an immersed solid surface. The governing equations are solved by using the finite volume solver with the coupled level set and volume of fluid (CLSVOF) method to track the polymer melt front. As case studies, the melt filling processes are simulated in mold cavities with cylindrical insets. The numerical results show that the mathematical model can successfully depict the phenomenon of race-tracking and fountain, which are very helpful for determining processing conditions and designing mold cavities.

A rapid BEM-based method for cooling simulation of injection molding

Cooling simulation is significant for optimization of the cooling system of injection molds. The boundary element method (BEM) is thought to be one of the best approaches suiting the steady-state cooling simulation. In spite of the merits of the BEM, the long computational time and the exorbitant memory requirement are two bottleneck problems in the current BEM-based cooling simulation method for industrial applications. The problems are caused by two reasons. One is the coupled heat transfer between the mold and the part and another is attributed to the inherent drawback of the BEM. In this article, the outer iteration, which is traditionally used to achieve consistency of boundary conditions on the mold cavity surface, is eliminated by introducing analytical solutions of the part temperature into the BEM equations. Then the dense coefficient matrix is sparsified by a combination of coefficient items using geometric topology. Moreover, parallel computing has been employed to speed up the computation. The case study showed that the sparse ratio reaches 7% with a temperature error of ±1 oC and the total computational time is reduced by almost one order of magnitude simultaneously.

Variable Distance Adjustment for Conformal Cooling Channel Design in Rapid Tool

During thermoplastic injection moulding process, the gradual increase of the coolant temperature along the conformal cooling channel (CCC) inside the rapid tool reduces the rate of heat transfer from the polymeric melt to the cooling channel surface at the outlet portion. Injection moulded defects such as irregular warpage of the part between the coolant inlet and outlet cannot be avoided. Rapid tooling (RT) technology offers a speedy and automatic method for rapid tool design and fabrication integrated with complex internal structure such as CCC. This paper presents a novel adjustment method for cooling distance modification between the CCC and its mould cavity (or core) surface along the cooling channel. The proposed method can compensate the gradual increase of the coolant temperature from the coolant inlet to the coolant outlet. More heat can be transferred from the mould surface near the coolant outlet to the proposed variable distance conformal cooling channel (VDCCC). In this study, the cooling channel distance modification relies on two adjustment attributes: (1) the adjustment direction and (2) the adjustment amount, between the mould cavity (or core) surface (terrain) and the cooling channel axis (polyline) after the linearized approximation. A computer-aided melt flow analysis tool of moldflow plastics insight is employed in the case study in order to demonstrate the feasibility of the proposed method. The cooling performance of the proposed VDCCC design can be verified.

Optimal design of heating system for rapid thermal cycling mold using particle swarm optimization and finite element method

Heating efficiency and cavity surface temperature distribution are two key factors for the design of heating system in rapid thermal cycling molding (RTCM) mold. Aiming at high heating efficiency and uniform cavity surface temperature distribution, an optimization method combining particle swarm optimization (PSO) with finite element method (FEM) is proposed to design the heating system for RTCM mold in this work. The proposed optimization design method is applied to design the electric-heating system for an RTCM blow mold of automotive spoiler to verify its effectiveness. The results demonstrate that the method can be used to effectively obtain the optimal design parameters compared with the simulation-based trial and error design method. Based on the optimal results, the RTCM spoiler blow mold with electric heating is constructed. Then, both infrared thermal imaging system and numerical simulation method are used to evaluate the mold thermal response and cavity surface temperature distribution. It is found that the simulated results are in good agreement with the measured ones. The blow molding experiments conducted using the constructed RTCM mold show that the surface quality of molded spoilers is dramatically improved.

Study on Induction Heating Coil for Uniform Mold Cavity Surface Heating

Recently, energy saving is one of the important issues for polymer processing industry. Electromagnetic induction heating has many advantages such as fast heating and low energy consumption. Previous studies using electromagnetic induction heating for rapid tool heating have indicated that the temperature uniformity on a cavity surface is not easy to be achieved. In this paper, two different coils were used for heating uniform 7 mm thick hot work tool steel (JIS SKD61) surface. One is a four-row coil with opposite current directions and the other is a two-row coil with identical current directions. Magnetic flux concentrators were used to control magnetic field and heat the workpiece uniformly. The heating experiment results showed that coil with opposite adjacent current directions had more uniform temperature distribution on tool surface. The temperature uniformity was about 94%∼95%. The coil with identical adjacent current directions had higher average temperature and the temperature rose from 50°C to 150°C in 15 seconds.

Grinding Affect the Service Life of Mould Research

In the process of modern mould manufacturing, grinding work still account for 25% ~ 45% of the total manufacturing time mould. Mould manufacturing quality of the finished product is closely related to the precision of mould manufacturing, particularly with the mould cavity surface accuracy and surface roughness has a close relationship. In the manufacturing of mould to make grinding micro cracks and residual stress is reduced to a minimum, full attention, grinding process in order to improve the service life of mould. So research to improve grinding processing quality, improve the service life of the mold, to extend the time of service, has the positive significance

Multiobjective optimization design of heating system in electric heating rapid thermal cycling mold for yielding high gloss parts

AbstractAn optimization design method is developed for the electric heating system in rapid thermal cycling molding (RTCM) mold. First, a multiobjective optimization model is established, in which the distance between the mold cavity surface and the center of heating elements and the number and power density of heating elements are the design variables, the required heating time th and the highest cavity surface temperature Tmax at time th are the objective functions. Then, an optimization strategy consisting of design of experiment, finite element analysis, artificial neural network (ANN) and response surface methodology (RSM) models, and Pareto‐based genetic algorithm is proposed to solve the multiobjective optimization model. Finally, the optimization strategy is applied for the design of the heating system for an automotive spoiler blow mold. The results show that the temperature distribution uniformity on the blow mold cavity surface is obviously improved and high heating efficiency is also ensured with the optimized design parameters. Moreover, the ANN model exhibits its superiority over the RSM model in terms of modeling and predictive abilities. A RTCM blow mold with the optimized electric heating system is constructed and successfully utilized to mold high gloss automotive spoiler. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39976.

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.