Mold flow analysis

PTA and the customer engaged early in the project to determine material selection. The decision must be based on chemical resistance, material strength, and weight. To ensure all critical conditions are met, PTA performed a complete Design for Manufacturability review on every part, which included draft angle, wall thickness, gate location, and mold flow analysis. 

Bird RB, Curtiss CF, Armstrong RC, Hassager O (1987b) Dynamics of polymeric liquids. Volume 2 Kinetic Theory. Volume 2 John Wiley and Sons, New York Bogaerds ACB, Hulsen MA, Peters GWM, Baaijens FPT (2004) Stability analysis of injection molding flows. J Rheol 48 765-785... 

The entire mold design is created using CAD data. Here, the optimization of the plastic part is done based on the plastic design, which includes a mold flow analysis. 

There are available CAD software programs that model the mold filling process. Many of the commercial finite-element analysis programs contain mold flow modules as well as programs that are specifically developed to perform mold flow analysis. 

To aid in the initial processing of the part, a computer aided mold-flow analysis was completed to identify processing windows. The mold-flow analysis allowed for the evaluation of dimensional stability, mold fill times, weld line identification, as well as many other outputs. The analysis also served... 

In this study, a commercial mold-flow analysis program, Moldex3D copyrighted by CoreTech System at Hsinchu, Taiwan, has been chosen for toe analysis tool on simulating toe conditions of polymeric melt inside toe mold cavity throughout the process. The main features of toe program are simulation of thermo-mechanical history of molded lenses during toe process, typically... 

The % filled (by volnme) and the corresponding predicted injeetion pressure were then reeorded Ifom the mold flow analysis log file and are shown in Table 4. Figme 1 also shows the predieted injection pressure versus the % filled (by volume) plotted in a graph. 

The pressure drop to fill a part fi om 23.5% to a part 94.2% filled part (26.39 MPa - 16.79 MPa) was 9.6 MPa. The predieted pressure drop from the mold flow analysis over a similar range (24.6% to 98.0%) was 7.31 MPa. This is a difference of 2.31 MPa between the actual molded part and the mold flow study predicted pressures. 

The results of this study showed that the mold flow simulation fill pattern compared favorably to the fill pattern of the actual molded part. In this particnlar study, the fusion type mesh proved the most accurate. This, however, will not always be the case. The 3D type mesh inaccurately predicted that the flow fi ont would freeze in the very n sections of the part. For future studies the 3D mesh and solver may prove to be the more accurate of the different analysis types. 

Suspension Polymers. Methacrylate suspension polymers are characterized by thek composition and particle-size distribution. Screen analysis is the most common method for determining particle size. Melt-flow characteristics under various conditions of heat and pressure are important for polymers intended for extmsion or injection molding appHcations. Suspension polymers prepared as ion-exchange resins are characterized by thek ion-exchange capacity, density (apparent and wet), solvent sweUing, moisture holding capacity, porosity, and salt-spHtting characteristics (105). 

To constitute the We number, characteristic values such as the drop diameter, d, and particularly the interfacial tension, w, must be experimentally determined. However, the We number can also be obtained by deduction from mathematical analysis of droplet deforma-tional properties assuming a realistic model of the system. For a shear flow that is still dominant in the case of injection molding, Cox [25] derived an expression that for Newtonian fluids at not too high deformation has been proven to be valid ... 

Regarding this relationship, when designing the mold it is necessary to know the flow direction. To obtain this information, a simple flow pattern construction can be used (Fig. 3-28) via computer analysis. However, the flow direction is not constant. In some cases the flow direction in the filling phase differs from that in the holding phase. Here the question arises of whether this must be considered using superposition. 

It would be desirable to make sample prototype tooling and analyze the flow effects on a product that is likely to present a flow problem. In addition to the usual physical testing of the product, the use of photo-stress analysis techniques plus the exposure to selected solvents to check for stress crack characteristics would lead to changes in the product to minimize the effects of the molding on the product performance. As an example there have been cases in the past where piano keys with frozen-in stresses have been released from perspiration, leaving open flow lines (Chapter 5, STRESS ANALYSIS). 

Computer-aided flow-simulation programs are also available for dies. All the programs can successfully predict a certain amount of shrinkage under specific conditions that can be applied to experience. The actual shrinkage is finally determined after molding or extruding the products. When not in spec process control changes can meet the requirements unless some drastic error had been included in the analysis. 

PCs all have one thing in common. They monitor the process variables, compare them to values known to be acceptable, and make appropriate corrections without operator intervention. The acceptable range of values can be determined by using melt flow analysis software and/or trial and error when the machine is first starting its production. Using the software approach, the acceptable process values are known before the mold or die is ever built. It should be noted that none of the PC solutions address the problem of the lack of skilled setup people. Most of the PC systems available today are rather complex and require skilled people to use them efficiently or at least start up the line. 

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