Initial Mold Temperature Research Articles

Simulation of Glass Molding Process for Planar Type SOFC Sealing Devices

The glass sealant with pre-forming frame structure, used for joining dissimilar materials of planar type SOFC devices, was fabricated by molding process. The flow phenomena during glass molding were investigated by computational modeling. The physical properties of glass sealant fluid were constructed in numerical models. The process parameters, such as mold pressing velocity, initial glass fluid temperature (or viscosity of glass sealant), and initial mold temperature, were examined. As results, the sealants formability could be characterized by molten glass temperature, near the gap between upper and lower molds. If the temperature is greater than its glass transformation temperature Tg, the formability become better, and vice versa. Keywords: solid oxide fuel cells (SOFCs), computational modeling, glass sealant.

Induction heating with the ring effect for injection molding plates

Induction heating in injection molding has the advantages of rapid heating, reduced cycle time, and improved product quality. In this research, using both experiment and simulation, externally wrapped coil induction heating was applied to verify the heating capacity of a pair of mold plates. By applying different coil designs and mold gap, the effect of the externally wrapped coil induction heating was evaluated. Results showed that when a serial coil was used as an inductor, the heating rate reached 8.0°C/s. From an initial mold temperature of 40°C, after 15s heating, the mold surface temperature reached 159.9°C with the serial coil. The parallel coil shows a better heating uniformity but its heating rate is far lower than the serial coil. For the serial coil, the temperature distribution between the core and cavity plate are almost the same. The heating rate increases from 4.9°C/s to 10.6°C/s when the inductor design is changed from 5 turns to 7 turns. After 15s heating, the temperature at point T2 increases from 40°C to 166.7°C and 106.1°C with a mold gap of 1mm, and 6mm, respectively.

Influence of composition on hot tearing in binary Mg–Zn alloys

Mg–Zn alloys have a large freezing zone, and their susceptibility to hot tearing is high. Investigations on their hot tearing are necessary for both materials science and practical applications. The present work evaluates the susceptibility of hot tearing of Mg–Zn alloy using Clyne and Davies’s modelling combined with thermodynamic calculations. In order to compare with the calculated results, the susceptibility of hot tearing was measured using previously developed quantitative experimental method. It is found that the simulation results are in agreement with the experimental results. Both of them show that the curves of the susceptibility of hot tearing versus the content of Zn has a typical ‘Λ’ shape. With increasing content of Zn, the susceptibility of hot tearing first increases, reaches the maximum at 2–4%Zn and then decreases again. Experimental investigations also demonstrate that the hot tearing susceptibility decreases with increasing initial mould temperature.

Gas-assisted mold temperature control for improving the quality of injection molded parts with fiber additives

A rapid heating cycle has the advantage of improving product quality in injection molding. In this study, gas-assisted mold temperature control (GMTC) was combined with cool water to achieve dynamic mold surface temperature control. By applying the GMTC system on the mold of a rectangular plate, the advantages of using GMTC for injection molding were evaluated and compared with the traditional injection molding process using different gas gap sizes and gas flow capacities. The effect of GMTC on the quality of the part was also studied. Results showed that when GMTC was used, the heating rate can reach 28 °C/s. For an initial mold temperature of 60 °C, and an air gap size of 8 mm, after 6 s heating, the mold surface temperature can reach 147.8 °C, 167.2 °C, and 229 °C with gas flow capacities of 100, 200, and 300 l/min, respectively. When the gas gap size is changed from 4 mm to 8 mm, the uniformity of temperature distribution shows a clear improvement. When GMTC was used for injection molding of parts with fiber additives, the part surface was clearly improved.

Process Development in Precision Injection Molding by Cooling Rate Control Part I Control of Shrinkage Characteristics in Cylindrical PPS Parts

The dimensional accuracy of a molded product is an important element that determines qualities of parts and the development for high accuracy work has been researched. The new process "Precision injection molding by the cooling rate control" has been proposed to decrease the mold shrinkage ratio and to improve the dimension accuracy of molded products in this study. This method improved the crystallization of a resin while keeping pressure and holding the mold temperature after injection at a given mold temperature (i. e. initial mold temperature). Afterwards, leave a part of the molded product that requires high accuracy in the mold and cool it locally and rapidly. In this report, the shrinkage characteristics and the crystallinity were investigated when cylindrical parts were molded with polyphenylene sulfide (PPS). The results showed that the mold shrinkage ratio at rapid cooling is smaller compared to the ratio at normal cooling, and the rapid cooling method showed the improvement in the circularity of molded products, however the lower crystallinity and the water-pressure strength reduction were not caused. Therefore, this molding method was effective to improve the accuracy of molded products without the reduction in physical properties of PPS. On the other hand, the effect of the rapid cooling was limited in the case where the initial mold temperature is higher than the glass transition temperature (Tg), that is, Tg seems to have influence on the shrinkage characteristics of the product. The clarification of the mechanism should be solved in the future.

Optimal injection molding conditions considering the core shift for a plastic battery case with thin and deep walls

The objective of this paper is to examine the influence of injection molding parameters on the core shift to obtain the optimal injection molding conditions of a plastic battery case with thin and deep walls using numerical analyses and experiments. Unlike conventional injection molding analysis, the flexible parts of the mold were represented by 3-D tetrahedron meshes to consider the core shift in the numerical analysis. The design of experiments (DOE) was used to estimate the proper molding conditions that minimize the core shift and a dominant parameter. The results of the DOE showed that the dominant parameter is the injection pressure, and the core shift decreases when the injection pressure decreases. In addition, it was shown that the initial mold temperature and the injection time hardly affect the core shift. The results of the experiments showed that products without warpage are manufactured when the injection pressure is nearly 32 MPa. Comparing the results of the analyses with those of the experiments, optimal injection molding conditions were determined. In addition, it was shown that the core shift should be considered to simulate the injection molding process of a plastic battery case with thin and deep walls.

Modeling of eutectic macrosegregation in centrifugal casting of thin walled ZA8 zinc alloy

The maximum segregation zone and microstructure formation during the solidification of thin walled ZA8 zinc–aluminum alloy produced by centrifugal casting are investigated. From the results obtained, it is seen that the maximum segregation zone of the eutectic through the part section corresponds to the zone of final solidification point. The concentration of eutectic through the section changes depending on the initial mold temperature, pouring temperature, and cooling rate. A high cooling rate reduces the rate of change in eutectic concentration across the section. The distance separating the maximum segregation zone from the inner and outer faces of the casting can be controlled by controlling the ratio between the speeds of the solidification fronts advancing from opposite sides. The microstructure obtained becomes finer as the cooling rate increases. The structure of eutectic changes according to the cooling rate, and may be granular or lamellar.

Prediction of Hot Tear Formation in a Magnesium Alloy Permanent Mold Casting

A viscoplastic deformation model considering material damage is used to predict hot tear evolution in AZ91D magnesium alloy castings. The simulation model calculates the solid deformation and ductile damage. The viscoplastic constitutive theory accounts for temperature dependent properties and includes creep and isotropic hardening. The mechanical properties are estimated from data found in the literature. Ductile damage theory is used to find mechanically induced voiding, and hot tears are expected in regions of extensive damage. Simulations are performed for a test casting consisting of a 260 mm (10.2 in) long horizontal bar connected to a vertical sprue on one side and an anchoring flange on the other. The contraction of the horizontal bar is restrained during solidification and hot tears nucleate at the junction between the horizontal bar and the vertical sprue. The hot tearing severity is manipulated by adjusting the initial mold temperature from 140°C (284°F) to 380°C (716°F). For the simulation, a trial-and-error method is used to determine the mold-metal interfacial heat transfer coefficient from experimental thermocouple results. The simulation results suggest that the predicted damage is in agreement with the hot tears observed in the experimental castings, both in terms of location and severity. The simulation results also confirm the observed decrease in hot tear susceptibility with increasing mold temperature. These results suggest that the proposed viscoplastic model with damage shows promise for predicting hot tearing.

Vertical Centrifugal Casting of Aluminum Matrix Particle Reinforced Composites

Centrifugal casting of composites gives rise to a certain distribution of reinforcement particles due to the natural liquid flow and solidification pattern. The particle rich regions are strongly influenced by rotational speed of the mold, particle size, relative density difference between particles and melt, initial pouring temperature, initial mold temperature, and by the nature of the particles added [1—3]. In the present work zirconia, silicon carbide, and ilmenite particles have been added to an aluminum—magnesium alloy and cast using a vertical centrifugal casting machine. The particle distribution and the resultant hardness variation have been analyzed. The particles are invariably associated with porosity. In the case of ilmenite particles, there is extensive reaction with the liquid metal. The combined effect of vol % of particles, porosity, and extent of reaction gives rise to a complex hardness variation. There is a substantial increase in hardness with particle addition. The particles tend to concentrate at the middle of the casting.

Simulation of the aluminum alloy A356 solidification cast in cylindrical permanent molds

A mathematical model based on the control volume method with fixed mesh was selected in order to simulate the solidification of cylindrical castings poured in permanent steel mold. The latent heat was incorporated using the effective specific heat. The application of the model allowed us to obtain the solidification front and the temperature fields at any time from the pouring. The mold was made of the SAE 1010 steel. Two mold temperatures were evaluated: 25°C and 300°C. The mathematical model showed sensitivity to changes in mold temperatures. For the casting poured with an initial mold temperature of 300°C, the solidification time was greater than that of the casting poured in the mold at 25°C. When the perfect contact condition between the mold and the metal was considered, the theoretical solidification times were shorter than the experimental results. When the imperfect contact supposition was assumed, this resulted in longer times of solidification very close to the experimental data. A reasonable fitting was reached when the heat transfer coefficient between mold and casting surfaces in the range of 100 to 500 W/m 2 °K was used for the experiments with the mold at 25°C.

Numerical Study of Functionally Graded Materials

One-dimensional comprehensive mathematical model coupling particle movement and thermal conduction in the casting mould system is developed. A formula for pressure in liquid metal during the centrifuge process is derived. The model takes into consideration the propagation of solidification front and movement of particles due to centrifugal acceleration which takes place either in the same or in opposite direction to that of the solidification front depending on the relative density difference between the particles and melts. In the force balance expression, repulsive force term is incorporated for the particles that are at the vicinity of the solid/liquid interface to calculate the particle segregation pattern in the casting region The effects of various process parameters such as, rotational speed of the mold, size of the reinforcing material, relative density difference between the particle and melt, initial pouring temperature of the liquid melt, mold pre-heating temperature, heat transfer coefficient between the casting/mold interface are studied. It is noted that for a given set of operating conditions, the thickness of the particle rich region in the composite decreases with increase in rotational speed, particle size, relative density difference between the particle and melt, initial pouring temperature and initial mold temperature. With decrease in the heat transfer coefficient between the casting/mold interface, the solidification time increases which, in turn, results in more intense segregation of solid particulates. Again, with increase in the initial volume fraction of the solid particulates, both the solidification time as well as the final thickness of the particulate rich region increase.

Vacuum Induction Melting and Investment Casting Technologies Tailored to Near-Gamma TiAl Alloys

The present study focuses on vacuum induction melting and investment casting of neargamma TiAl intermetallic alloys. The attention is mainly given to a cost-effective melting process in which a primary alloy ingot is re-melted in a ceramic crucible and cast into a ceramic shell mould. Two types of crucibles (based on Al2O3 and Y2O3) are considered. The most detrimental reactions that govern the contamination of the molten alloy with ceramic particles were determined. Results suggest that the crucible wall attack can be considerably limited by using either the Y2O3 (with no SiO2-type binder) or Al2O3 crucibles with a suitable coating. After pouring, a mechanical interaction associated with different thermal expansions of TiAl casts and ceramic shell moulds can result in serious product damage. A simple 1D-1D model of the cooling process was formulated and the heat flow as well as stress states in the cast-mould system were numerically solved. Process parameters (melt superheat, initial mould temperature, cooling kinetics and mould composition) were optimized in order to reduce the stress in the casts. The optimized parameters delimited a processing window in which complex-shaped TiAl castings like turbocharger wheels can be fabricated.

A Study of Integration of LIGA and M-EDM Technology on the Micro Injection Molding of Super Thin Plates with Micro Through Holes

Abstract There are still some difficulties in injection molding a super thin plate with micro through holes. Nozzle or filter plates are some examples of typical products. Conventional processes to manufacture nozzle plates of ink jet printer heads are electroplating or laser machining. In order to reduce the production cost and improve the performance of nozzle plates, a new approach, micro injection molding, is introduced to manufacture nozzle plates in this study. The micro mold was made by integration of the LIGA and M-EDM technology to improve the positioning and alignment accuracy. After assembling the micro mold, micro injection molding technique was applied to produce four nozzle plates in one shot. There are sixty micro through-holes on each plate and their diameters have been inspected and met the specification, 101 ± 1 microns, under a proposed vario-thermal molding process. The flow hesitation problem for molding a thin film of 50 microns was then solved. Experimental and simulation results indicated that the most significant factor for molding these nozzle plates is the initial mold temperature. This work recommends that the best initial mold temperature for molding such a thin film with the nozzle array is about 150°C for PP. The manufacturing procedures proposed here are believed to be more accurate and economical, and can be applied to mold similar micro parts.

Mathematical modeling of particle segregation during centrifugal casting of metal matrix composites

A one-dimensional transient heat-transfer model coupled with an equation for force balance on particles is developed to predict the particle segregation pattern in a centrifugally cast product, temperature distribution in the casting and the mold, and time for complete solidification. The force balance equation contains a repulsive force term for the particles that are in the vicinity of the solid/liquid interface. The solution of the model equations has been obtained by the pure implicit finite volume technique with modified variable time-step approach. It is seen that for a given set of operating conditions, the thickness of the particle-rich region in the composite decreases with an increase in rotational speed, particle size, relative density difference between particles and melt, initial pouring temperature, and initial mold temperature. With reduced heat-transfer coefficient at the casting/mold interface, the solidification time increases, which, in turn, results in more intense segregation of solid particulates. Again, with increased initial volume fraction of the solid particulates in the melt, both the solidification time and the final thickness of the particulate-rich region increase. It is noted that for Al-Al2O3 and Al-SiC systems, in castings produced using finer particles, lower rotational speeds, and an enhanced heat-transfer coefficient at the casting/mold interface, the volume fraction of particles in the outer layer of the casting remains more or less the same as in the initial melt. However, for castings produced with coarser particles at higher rotational speeds and reduced heat-transfer coefficients at the casting/mold interface, intense segregation is predicted even at the outer periphery of the casting. In the case of the Al-Gr system, however, intense segregation is predicted at the innermost layers.

Computer Simulation of Casting Process of Aluminium Wheels - A Case Study

Aluminium disc wheels intended for normal use in passenger cars are commonly produced by gravity casting. If the cooling process and the initial temperature of the mould are not well controlled, shrinkage cavity will occur after solidification, causing leakage in the disc wheel. In this research, a casting simulation software is used to simulate the casting process of aluminium wheels. The casting simulation is done iteratively until the mould temperature converges to a stable temperature. A ‘shrinkage index’ (SI) is defined to provide a quantified index of casting quality of aluminium wheels, based on the phenomenon of liquid entrapped at the joints of rim and spokes of the wheel where shrinkage cavity usually happens. This shrinkage index shows good correlation with the aluminium wheel leakage test results. This paper also discusses the influence of cooling process parameters on SI, including initial mould temperature, and geometry of the wheel, which verifies engineers' empirical data. This iterative simulation process and SI can be used to predict the casting quality of aluminium wheels and to find the optimal parameters of the casting process.

Caprolactam-Laurolactam (Nylon 6/12) Copolymers: Synthesis and Characterization

The paper present the synthesis of a series of nylons as constituent polymers of parts obtained by rotational molding via activated anionic copolymerization of caprolactam with laurolactam. The initial mold temperature (initial polymerization temperature) was kept constant at 160° for all experiments. The initial laurolactamn content influence was investigated in terms of nylon yield, viscosity, density, melting temperature, degree of crystallinity, water absorption, impact strength and flexural modulus. The characteristics of copolymers were compared with those of the polyamide 6. From X-ray diffraction patterns and FT JR spectra it was found that the obtained polyamides are predominantly in the α-form.

Analysis of Gap Formation at Mold-Shell Interface during Solidification of Aluminum Alloy Plate

Thermal contraction of the casting and the thermal expansion of the mold result in gap formation at the mold-casting interface, which affects greatly the heat transfer between the mold and casting. Information on the movements of the mold and casting during solidification and cooling is also the basis for the investigation of the casting deformation.Movements of the casting and mold were analyzed simultaneously using coupled thermo-mechanical contact boundary model for the plate casting of aluminum alloy. The calculated displacement and temperature distributions of the casting and mold were compared with the previous measured data. It was confirmed that the mold and the casting moved together until the air gap formed by the calculation. Comparing the air gap curve with the displacement curve of the casting just before and after air gap formation made it apparent that the growth of the air gap was mainly due to contraction of the casting because the change in the mold displacement was not significant. Gap formation time increased with increase in initial mold temperature.

Pilot Calculation Of The Temperature Field Of The Ceramic Material EUCOR

Pilot Calculation Of The Temperature Field Of The Ceramic Material EUCOR

Prediction and measurement of residual stresses in injection molded parts

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait’s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching and the constrained quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.

Polyamides from lactams by centrifugal molding via anionic ring-opening polymerization

This paper deals with a study of some properties of the polymers obtained by centrifugal molding via activated anionic ring-opening polymerization of ϵ-caprolactam and copolymerization of ϵ-caprolactam with laurolactam. Ethyl magnesium bromide, as initiator and N-benzoyl ϵ-caprolactam and N,N′-isophthaloyl-bis-ϵ-caprolactam, as activators were used. The initial mold temperature (initial polymerization temperature) was kept constant at 160°C. Our experimental data demonstrated that the degree of crystallinity depends on the activator type and concentration. The incorporation of laurolactam into nylon 6 chain depresses both in the degree of crystallinity and the melting temperature of nylon 6/12 copolymers. The notched Izod impact strength of the copolymers increased as the laurolactam content was increased, while the flexural modulus and the water absorption decreased.