Sharif Digital Repository

During solidification and casting in metallic molds, the heat flow is controlled by the thermal resistance at the casting-mold interface. Thus heat transfer coefficient at the metal-mold interface has a predominant effect on the rate of heat transfer. In some processes such as low pressure and die-casting, the effect of pressure on molten metal will affect the rate of heat transfer at least at initial steps of solidification. In this study interfacial heat transfer coefficient at the interface between A356 alloy casting and metallic mold during the solidification of casting under pressure were obtained using the IHCP (Inverse Heat Conduction Problem) method. Temperature measurements are then... 

In the present investigation, mold filling process of resin injection/compression molding (RI/CM) is compared with resin transfer molding (RTM) for simple mold geometry. To do this, analytical solutions are obtained for RI/CM in unidirectional flow. Based on the analytical solutions, flow front progression and pressure distribution are compared with RTM at different fiber content. The results indicate that the RI/CM reduces the mold filling time significantly, particularly for composite parts with higher fiber content  

In compression resin transfer moulding (CRTM), resin flows inside a mould filled with fibrous reinforcement as a result of resin injection and mould compression. This process facilitates the resin flow through the fibrous reinforcement particularly for high fiber content parts. This paper presents the numerical simulation of filling process of CRTM in full three-dimensional domain. A mathematical model of three-dimensional resin flow inside the CRTM mould is presented. An effective elastic modulus is introduced for multi-layer preforms connecting the mould closing speed to deformation rate of individual layers. Control volume/finite element method (CV/FEM) is used and the numerical algorithm... 

In the casting process, as a mould is filled with molten metal, air escapes through the vents. Air pressure in the mould cavity has serious effects upon the filling behaviour such as surface profile of the molten metal and filling time. In this project a computational model was developed for calculation of air pressure during the mould filling. A 3D single phase code based on the SOLA-VOF algorithm was used for the prediction of the fluid flow. The ideal gas assumption, conservation of mass equation and Bernoulli law were used for the calculation of air pressure. A new algorithm was developed to interpolate air pressure on the surface cells. The creation of air pressure was correlated with... 

Several metals and alloys can be used to enhance the mechanical and physical properties of micro parts and components for micromechanical, micro-chemical or sensor applications. Such parts can be produced in series by the powder metallurgical process of micro metal injection moulding (μ-MIM). This paper describes a novel manufacturing route for metallic multi-material micro components, two-component micro metal injection moulding (2C-μ-MIM). Similar to "two-colour" injection moulding of plastics, the process allows the integration of multiple functions in a micro part by simultaneously injecting and joining two materials in one mould. Net-shape parts with solid material interfaces are... 

The role of initiators with different reactivities on the process cycle of nonisothermal resin transfer molding (RTM) was examined using the numerical simulation. A new process model was developed based on flow, heat and mass transfer equations combined with an appropriate mechanistic kinetics model which elucidates the functions of the initiators in the system. The process cycle of RTM with both single initiator and dual-initiator (combination of two initiators) was analyzed. The numerical simulations revealed that the single initiator with high reactivity reduces the cycle time, but there is a risk of incomplete mold filling and nonuniform temperature distribution. For dual-initiator... 

In resin injection/compression molding (RI/CM), a preform often comprises layers of different fiber reinforcements. Each fiber reinforcement has unique through thickness and in-plane permeabilities as well as compressibility, creating a heterogeneous porous medium in the mold cavity. In the present article, numerical simulation is utilized to investigate the filling process of RI/CM in such a heterogeneous porous medium. The filling stage is simulated in a full three-dimensional space by using control volume/finite element method and based upon an appropriate filling algorithm. The flow in the open gap which may be present in the mold cavity is modeled by Darcy's law using an equivalent... 

An experimental rheological study has been performed to evaluate the influence of TiC addition on the rheological behavior and stability of 316L stainless steel powder injection molding (PIM) feedstock. The effects of TiC concentration, solid loading, shear rate and temperature were investigated via capillary rheometer method. The stability of feedstocks was evaluated quantitatively using "instability index", which describes the threshold beyond which the variation of viscosity becomes unacceptable for PIM purposes. The results show that the rheological behavior of PIM feedstocks highly depends on the blend composition. The addition of TiC particles to the stainless steel powder increases... 

Abstract Sintering response and phase formation during sintering of WC-Co/316L stainless steel composites produced by assembling of powder injection molding (PIM) parts were studied. It is shown that during cosintering a significant mismatch strain (> 4 pct) is developed in the temperature range of 1080° C to 1350° C. This mismatch strain induces biaxial stresses at the interface, leading to interface delamination. Experimental results revealed that sintering at a heating rate of 20 K/min could be used to decrease the  

Purpose - Dimensional accuracy analysis of wax model created by room temperature vulcanization (RTV) silicone rubber molding to be used in investment casting is presented. The purpose of this paper is to discuss the effective parameters of dimensional accuracy in RTV tooling technique. Design/methodology/approach - After producing a pattern by stereolithography (SLA) and then creating the RTV silicone rubber mold by the SLA pattern, dimensional accuracy of wax models produced by RTV tool are analyzed. Design of experiments (DOE) using the Taguchi approach is used for analysis and determination of optimum condition. Findings - Experiments show that the dimensional accuracy in RTV technique is... 

In the present work, co-sintering of various powder injection molding (PIM) feedstocks including iron, low-alloy steels, high-alloy steels, and hardmetals was investigated. Dilatometric analysis was used to evaluate the sintering behaviour of co-injection moulded feedstocks after debinding. An approach based on the data of dimensional change versus time and temperature was proposed to determine the compatibility of two materials system for the two component powder injection molding (2C-PIM) process. The similarity of sintering behaviour of the twobody parts produced by 2C-PIM was quantified trough definition of a parameter termed as Apparent Co-Sintering Index (ACSI). The results determined... 

The effects of the mold preheating and the silicon content of ductile iron on the percentage of carbides, graphite nodule counts and shrinkage volume were investigated. The results showed that the percentage of carbides and the shrinkage volume decreased when the mold preheating increased. The ductile iron with the carbon equivalent of 4.45% and the silicon content of 2.5% without any porosity defects was achieved when the mold preheating was 450 °C. Increasing the silicon content in the range of 2.1%-3.3% led to the increase in graphite nodule count and graphite size and the decrease in percentage of carbides. It is due to the increase in induced expansion pressure during the graphite... 

Experiments are being conduced in a photography technique to examine flow of aluminum, cast iron and steel into the molds. The purpose is to observe some parameters such as gas gap length, foam decomposition products, metal front and mold filling time in lost foam casting of aluminum, cast iron and steel. Foam-metal interface reactions and gas evolution have been observed during mold filling. The results indicate that the metal pouring temperature and foam density and coating layer thickness affect mold filling time. In the steel lost foam casting, the gas gap length and gaseous products volume and the mold filling time are significantly larger than the cast iron. In both the cast iron and... 

In the investigations presented here, the feasibility of producing magnetic-nonmagnetic bimetals made of 316L/17-4PH and 316L/Fe powders by micro-metal injection moulding process (μ-MIM) was studied. In order to achieve sound replication of small specimens with dimensions less than 1 mm, very fine powders with mean particle sizes in the range of 3-7 μm were used. A wax-polymer binder system specially designed for micro-moulding was used to make up the feedstock. The isothermal and non-isothermal sintering behaviour of the moulded components was evaluated under hydrogen atmosphere. The effect of powder-binder-ratio of the feedstock, master alloy addition, and sintering conditions on the... 

Unidirectional experiments were carried out for the evaluation of the unsaturated permeability of the reinforcement during the injection and the saturated permeability. Saturated permeability was found to govern the permanent flow established after filling of the cavity. The unsaturated permeability was evaluated by a linear regression in function of the position of the resin front during transient flow experiments performed at constant injection pressure. The difference between these two permeability values is also related to the pore structure of the fiber bed  

Numerical simulation of resin transfer molding (RTM) is known as a useful method to analyze the process before the mold is actually built. In thick parts, the resin flow is no longer two-dimensional and must be simulated in a fully three-dimensional space. This article presents numerical simulations of three-dimensional non-isothermal mold filling of the RTM process. The control volume/finite element method (CV/FEM) is used in this study. Numerical formulation for resin flow is based on the concept of nodal partial saturation at the flow front. This approach permits to include a transient term in the working equation, removing the need for calculation of time step to track the flow front in... 

Injection molding is one of the most important manufacturing processes for mass production of complex plastic parts. In this study, mold filling is simulated by using the OpenFOAM software for Non- isothermal Newtonian fluid. The OpenFOAM is an open source software that is used in Computational Fluid Dynamics (CFD) tools. The studied mold shape has a rectangular structure with a gate for Newtonian fluid injection. The simulation carried out at non-isothermal conditions and two-dimensional flow is considered. The velocity, shear stress and temperature changes in different parts of the mold are critically studied. We show that vortex formation plays an important role on changes of shear stress... 

In this study, the effects of mold constraints and cooling rate on residual stress were analyzed during the shaped casting process. For this purpose, an H-shaped sample was designed in which the contraction of its middle portion is highly restricted by the mold during the cooling process. The effects of an increasing cooling rate combined with mold constraints were analyzed by reducing the thickness of the middle portion in the second sample. A three-dimensional coupled temperature-displacement analysis was performed in finite-element code ABAQUS to simulate residual stress distribution, and then numerical results were verified by the hole-drilling strain-gauge method. It was concluded that... 

In this investigation, a computational-model has been developed, including heat transfer and the effects of the resistance of a metal-mold interface and pressure, for simulation of the solidification process. Simulation of the interface resistance is based on the Zero Thickness Element (ZTE), utilizing the Finite Element Method (FEM). Solid boundary conditions, including contact resistances, have been modified by a pressure gradient in each of the ZTE. The pressure gradient has been modeled, based on experimental data. In order to verify the computational results, an Al-11.5 wt% Si alloy was poured into a permanent mold and the temperature of the interface was measured by a data acquisition...