Analysis of the main factors affecting mass production in the plastic molding process by using the finite element method

Plastic injection molding is widely used in many industrial applications. Plastic products are mostly used as disposable parts or as portable parts for fast replacements in many devices and machines. However, mass production is always adopted as an ideal method to cover the huge demands and customers’ needs. The problems of warpage due to thermal stresses, non-uniform pressure distribution around cavities, shrinkage, sticking and overall products quality are some of the important challenges. The main objective of this work is to analyze the stress distribution around the cavities during the molding and demolding to avoid their effects on the product quality. Moreover, diagnosing the critical pressure points around and overall the cavity projection area, which is subjected to high pressure will help to determine the optimum pressure distribution and ensure filling all cavities at the same time, which is another significant objective. Computer-aided design (CAD) and CATIA V5R20 are adopted for design and modeling procedures. The computer-aided engineering (CAE) commercial software ABAQUS 6141 has been dedicated as finite element simulation packages for the analysis of this process. Simulation results show that stress distribution over the cavities depends on both pressure and temperature gradient over the contact surfaces and can be considered as the main affecting factor. The acceptable ranges of the cavity stresses were determined according to the following values: the cavity and core region temperature of 55–65 °C, filling time of 10–20 s, ejection pressure 0.85 % of injection pressure, and holding time of 10–15 s. Also, theoretical results reveal that the uniform pressure and temperature distribution can be controlled by adjusting the cavities layout, runner, and gate size. Moreover, the simulation process shows that it is possible to facilitate and identify many difficulties during the process and modify the prototype to evaluate the overall manufacturability before further investing in tooling. Furthermore, it is also concluded that tooling iterations will be minimized according to the design of the selected process

Coating flow on a rotating cylinder in the presence of an irrotational airflow with circulation

A detailed analysis of steady coating flow of a thin film of a viscous fluid on the outside of a uniformly rotating horizontal circular cylinder in the absence of surface-tension effects but in the presence of a non-uniform pressure distribution due to an irrotational airflow with circulation shows that the presence of the airflow can result in qualitatively different behaviour of the fluid film from that in classical coating flow. Full-film solutions corresponding to a continuous film of fluid covering the entire cylinder are possible only when the flux and mass of fluid do not exceed critical values, which are determined in terms of the non-dimensional parameters $F$ and $K$ representing the speed of the far-field airflow and the circulation of the airflow, respectively. The qualitative changes in the behaviour of the film thickness as $F$ and $K$ are varied are described. In particular, the film thickness can have as many as four stationary points and, in general, has neither top-to-bottom nor right-to-left symmetry. In addition, when the circulation of the airflow is in the same direction as the rotation of the cylinder the maximum mass of fluid that can be supported on the cylinder is always less than that in classical coating flow, whereas when the circulation is in the opposite direction the maximum mass of fluid can be greater than that in classical coating flow.

Pressure fluctuation study in the stages of a multistage pump at best efficiency points under various operating speeds

The interaction between the rotor and stator is a major source of high amplitude pressure fluctuation and flow-induced vibration in multistage centrifugal pumps. The pressure fluctuation is detrimental to the reliable operation of pumps. The sensitivity of vibration is severe if the number of stages is more. In the present experimental study, a vertical multistage centrifugal submersible pump is used to measure the pressure fluctuation level at Best Efficiency Points (BEP) and to determine the influence of stage and operating speed on pressure fluctuation. For this purpose, pressure fluctuation signals were captured at the delivery side of the pump at BEP at various speed settings. The characteristics of pressure fluctuation at BEP at various operating speeds were studied with the help of spectra, i.e., in the frequency domain. The amplitude variation of pressure fluctuation with harmonics of vane passing frequency at stages were studied. Results have indicated that variation of pressure fluctuation with stage and speed exhibited a non-linear variation. In addition, such a pressure fluctuation study will be helpful to modify the design to obtain a uniform pressure distribution in the stages of a multistage pump.