Injection Molding Simulation
for Product/Process Design

Diskflow/Diskmold Flow Analysis

An injection molding simulation, DISKFLOW, was developed in 1991 using a simple one-dimensional creeping flow representation and purely viscous constitutive equation to model the radial flow behavior of polymer melts in the injection molding process. The analysis can predict the injection pressure required to fill an approximate mold geometry as well as the final flow length of a material given process conditions and machine/material limitations. DISKFLOW is entirely self-contained and allows for exact analysis of radial geometries and good engineering estimations of more complex geometries (see Figure at right for simulation of a John Deere tractor hood circa 1991). The ease of use and analysis speed allowed for the interactive use by the vast majority of the plastics community who do not have the time, resources, or understanding required for more complex injection molding simulation such as Moldflow.

Diskflow was originally derived from General Electric Corporate Research's Finite Element Mold Analysis Program (FEMAP) to run on Digital VMS9000 super computers with run times on the order of a few seconds. The short execution time allowed for design of experiments to be integrated within the user interface of GE's Engineering Design Database (EDD). Literally millions of analyses have been performed across thousands of plastic part design applications. It was subsequently re-written twice: first to run on Microsoft PCs and again to run on cloud computing architectures. It was extended to include melt compressibility as well as moving mold cores for simulation of injection compression molding. It was licensed to GE Plastics and Sabic as their web-based flow analysis engine, and remains in use today.

Melt Front Advancement in Multi Gated John Deere Tractor Hood (circa 1991)

Birefringence and Shrinkage/Warpage Predictions

The flow and thermally induced birefringence of injection-compression molded optical media such as compact discs and digital video discs is predicted by applying a stress-optical rule to the flow and thermally induced stresses, which are estimated with a viscoelastic material model integrated into a non-isothermal compressible flow simulation. The resulting model considers flow and cooling induced molecular orientation, and the transient effect of thermal stress and pressure. Contrary to previous research for polystyrene, the validated results indicate that, for polycarbonate, the magnitude of the thermally induced birefringence is comparable to the flow induced birefringence. Simulation results of the flow and thermally induced in-plane birefringence for compact-disc-recordable moldings with an optical grade of polycarbonate compared well with experimental observations at different mold and melt temperatures. Both injection molding simulation and experiments indicate that mold and melt temperatures have a significant effect on the level of birefringence; increasing mold or melt temperature significantly reduces the birefringence.

Viscoelastic material modeling was also conducted to simulate the warpage of injection–compression-molded optical media, such as compact discs and digital video discs, due to asymmetric cooling during production. Thermally induced stress is calculated with a nonisothermal compressible flow simulation with a viscoelastic constitutive model. A finite element analysis is formulated with axisymmetric plate elements based on Kirchhoff thin-plate theory to simulate the warpage of the disc due to the asymmetric thermal stress and gravity after demolding. Simulation results of warpage for compact-disc-recordable moldings are compared with experimental observations under different processing conditions, such as the melt temperature, mold temperature, and packing pressure, with an optical grade of polycarbonate. The comparison shows that the simulation well predicts the effects of various processing conditions. Both the simulation and experiment indicate that of the processing conditions, the mold temperature has the greatest effect on
warpage.

Birefringence Path Difference in Compact Disc Molding

Related Publications

Check the archive for all our publications. Specific related publications will be subsequently added once links to the publications are completed.