Mold Packing Research Articles

Study on Centrifugal Powder Molding for Microstructure Fabrication

Carbon or Ceramic particles are randomly arranged in conventional functional devices such as fuel cells or Li batteries because they are mainly produced by screen printing or spray coating. Carbon-aligned structures with low tortuosity and larger interface area can possibly improve the performance of such devices because it smoothens mass or proton transfer through membranes and increases active chemical reaction area. The biggest challenge faced while producing a carbon-aligned microstructure is the aggregation of particles, which prevents mold packing. We demonstrated a powder molding method with a centrifugal acceleration varying from 9.8−9.9×104 m/s2. Greater centrifugal force increased the ratio of fulfilled particles. Discrete element method simulation was also performed to clarify the interaction between particles. The simulation results are similar to the experimental results, and they indicate that centrifugal acceleration does contribute to mold packing in this method. This study investigated mold packing, which is the first stage of powder molding.

Void content analysis and processing issues to minimize defects in liquid composite molding

This investigation aims to study the impact of key process parameters dealing with the resin impregnation of fibrous reinforcements used in Liquid Composite Molding (LCM). The process parameters are the flow front velocity, the inlet mold pressure and the bleeding flow rate. The experimental setup consists of a computer‐assisted injection system and a Resin Transfer Molding (RTM) mold that allows monitoring the progression of the flow front and study the effects of resin bleeding and applying post‐fill resin pressure during cure (also known as “mold packing”). Three sets of RTM injections were carried out with a vinyl ester resin and a bidirectional 0°/90° E‐glass noncrimp fabrics under (1) constant injection pressure, (2) constant injection flow rate, and (3) bleeding as well as mold packing after filling. The quality of injected parts was evaluated by standard void content analysis based on ASTM burn‐off (D2734) tests. The experimental results are consistent with published data and with predictions of the optimal impregnation velocity obtained from capillary rise tests. This study also shows that the impregnation of fibrous reinforcements in LCM can be improved through various injection strategies, namely monitoring of the flow front velocity and specific post‐filling procedures. POLYM. COMPOS., 40:109–120, 2019. © 2017 Society of Plastics Engineers

Experimental study of saturation by visible light transmission in dual-scale fibrous reinforcements during composite manufacturing

A new in situ monitoring strategy is proposed to study void formation during real-time impregnation of dual-scale fibrous reinforcements in liquid composite molding. Void content data from burn-off tests are used to calibrate a refractive index matching approach based on two optical principles: Beer–Lambert and Fresnel laws. Once calibrated, this approach based on visible light transmission is used to study the impact of key process parameters on the saturation footprint of dual-scale fibrous reinforcements during and after mold filling. The injection parameters investigated are the flow front velocity, the pressure distribution inside the mold cavity, the bleeding flow rate, and the mold packing pressure. The experimental setup is a computer-assisted injection system and a transparent resin transfer molding mold is used to perform unidirectional injections. A vinyl ester resin is injected through E-glass bidirectional non-crimp fabrics under various manufacturing conditions. This investigation not only confirms the decreasing trend in void formation by mechanical entrapment of air with the decrease in impregnation velocity, as it converges toward the optimal impregnation conditions for this fibrous reinforcement reported in previous studies, but it also brings insights on void dissolution and transport in liquid composite molding.

Adhesion improvement of EMC–leadframe interface using brown oxide promoters

Moisture ingression in plastic packages essentially occurs through delaminated interfaces. Hence, package reliability depends on the interfacial integrity between the various materials. In the present work, the adhesion of epoxy-based molding compound and the copper leadframe is discussed. Results show that by the growth of a copper oxide layer, the surface roughness improves which promotes interlocking between the molding compound and leadframe during mold packing stage. Also by controlling the oxide thickness with pore-free structure, the adhesion strength can be significantly improved.

Modeling and Control of an Electro-hydraulic Injection Molding Machine With Smoothed Fill-to-Pack Transition*

In this paper the modeling of a typical injection cycle for an injection-molding machine (IMM) is examined. Both the mold filling and mold packing phases of the cycle are examined along with a critical fill-to-pack transition. The novelty in this modeling work is that the nonlinear model considers both the machine hydraulic actuator and polymer flow characteristics in extensive detail. The simulation model is validated against experimental data and demonstrates the availability of a relatively accurate system model for full cycle control design of this electro-hydraulic system. The accurate process model is used in the design of a controller for the injection cycle including the fill-to-pack transition. The overall algorithm includes two Iterative Learning Controllers connected by a bumpless transfer scheme between them. The algorithm is successfully tested through model simulations and machine experiments. The simulation and experimental results presented demonstrate a significantly smoother control signal and pressure transient between the two learning controlled phases as well as overall tracking convergence for each phase.

Nonlinear control of an electrohydraulic injection molding machine via iterative adaptive learning

Examines the control of an industrial injection molding machine (IMM) for both mold filling and mold packing. The machine is a Boy 50 Ton system operated by hydraulics with electronically controlled valves. A nonlinear model of the system is determined for the filling and packing stages, then verified against experimental data. The model includes several key aspects of the actual machine dynamics including stick-slip friction, time delays, nonlinear valve flow characteristics, and deadzones. A feedforward control input is determined via an iterative learning control scheme. This input is combined with either a feedback strategy or an open-loop strategy for the filling and packing control phases, respectively. The time delay, which exists in both stages, is accounted for by time shifting the learning feedforward signal relative to the feedback control signal. Simulation and experimental investigations indicate the benefits of the proposed strategy for control of electrohydraulic IMMs. Subsequent to demonstrating the benefits for fill-stage and pack-stage learning control, a complete cycle, including fill-to-pack transfer, is demonstrated.

Computer modelling of the origin of defects in ceramic injection moulding

A finite difference method for the calculation of sprue closure time is described and compared with measured cavity pressure fall for a zirconia-polystyrene suspension. The disparity between measured and calculated values is explained by the balance of volume shrinkage rate in the cavity and flow rate in the sprue during the final stage of mould packing and cooling. © 1991 Chapman and Hall Ltd.

Computer modelling of the origin of defects in ceramic injection moulding

Using the thermal properties previously acquired for a polystyrene-zirconia suspension, the solidification and shrinkage of injection-moulded rectangular bars was computed by a finite difference numerical method. By considering the final stage of mould packing, upper and lower bounds for the moulding conditions needed to avoid internal shrinkage defects and sink marks were successfully predicted. The resulting computer method allows the influence of a wide range of material and machine parameters to be explored.

AN UNDERSTANDING OF THE FLUID MOTION AND PRESSURE BUILD-UP IN A NON-ISOTHERMAL INJECTION MOLD PACKING STAGE

Article AN UNDERSTANDING OF THE FLUID MOTION AND PRESSURE BUILD-UP IN A NON-ISOTHERMAL INJECTION MOLD PACKING STAGE was published on July 1, 1988 in the journal Journal of Polymer Engineering (volume 8, issue 3-4).

Non-destructive examination of short carbon fibre-reinforced injection moulded thermoplastics

An injection moulded lever, made from 40% by weight short carbon fibre-reinforced nylon, has been non-destructively examined. Visual inspection and low power magnification revealed surface fibre flow in a skin at least 1 mm thick. Red-dye penetrant revealed open surface defects, while fluorescent penetrant accented only visible fibre flow. Low kV X-rays revealed internal shrinkage cracking and voids in flanges and bosses. Internal defects were examined by sectioning and found to be below the skin. Fibre orientation appeared to be a major cause of flange defects initiated by poor mould packing.

Using ram velocity to control IMM part quality

AbstractOne of the primary factors to consider during an injection molding cycle is the judicious switch‐over from HIGH to HOLD injection pressure setting. Historically, this switchover was effected either as a function of time or ram position. Unfortunately, neither of those parameters correlated satisfactorily to the processing event that was supposed to be detected, i.e., the “packing” of molten polymer in the mold. There are several IMM Process Controllers that directly sense rate of change of cavity pressure, but these require special transducers to be inserted in the mold. This paper describes a scheme that uses the feedback of injection ram velocity to determine mold packing and the resulting optimum point at which pressure switchover should be initiated.