- Slides: 13
Simulation of Microcellular Injection Molding Process MPI/Mu. Cell®
Mu. Cell® Injection Molding Process § Mu. Cell is a variation of foam molding § This process is marketed by Trexel Inc. § In this process a Super Critical Fluid (SCF) of Nitrogen (N 2) or Carbon Dioxide (CO 2) is mixed with polymer melt to create a single phase solution which is then injected into the cavity DESIGN SOLUTIONS
Advantages of Mu. Cell § Lighter parts (due to material reduction) § Thin and difficult-to-fill sections can now be filled (due to reduction in material viscosity) § Reduced cycle times § Reduced clamp tonnage § Reduced part warpage DESIGN SOLUTIONS
Basic Mu. Cell Molding Machine Shut-off nozzle Optional air cooled heater bands SCF ports Trexel designed screw and barrel Super Critical Fluid (SCF) Delivery System Minor software and hydraulic changes DESIGN SOLUTIONS Mu. Cell Interface Kit Melt pressure transducer Image courtesy of Trexel Inc.
The Mu. Cell Process 1. Creation of a single phase solution 2. Homogeneous Nucleation 3. Cell Growth 4. Part Formation DESIGN SOLUTIONS Image courtesy of Trexel Inc.
Creation of a Single Phase Solution § The Super Critical Fluid (SCF) or Gas (N 2/CO 2) is injected into the polymer melt during screw rotation thus creating a 2 -phase solution § The SCF bubbles are broken down such that the volume of each bubble is minimized § SCF diffuses into the polymer melt creating a single phase solution DESIGN SOLUTIONS
MPI/Mu. Cell Simulation Features § Evaluate flow front pattern before and after the foaming (nucleation) begins § Establish the volume of plastic and gas mixture (shot size) required to prevent short shot and achieve desired part weight reduction § Determine the initial concentration of supercritical fluid (SCF) in the polymer to prevent short shot and achieve desired cell size DESIGN SOLUTIONS
MPI/Mu. Cell Simulation Features (contd. ) § Predict the cell size variation through the thickness and as a function of time to achieve desired cell size § Predict the cell pressure to ensure it is not too high to cause part warpage § Link to MPI/Cool to evaluate mold cooling with the influence of microcellular foam and minimize cycle time DESIGN SOLUTIONS
MPI/Mu. Cell Simulation Features (contd. ) § Link to MPI/Warp to estimate part shrinkage and warpage due to the influence of cell distribution and cell size § Supported with Midplane & Fusion models § Can be used with any material in the MPI/Synergy material database DESIGN SOLUTIONS
MPI/Mu. Cell Simulation Short shot comparison for gas concentration of 0. 5% (by weight) and shot size of 70% DESIGN SOLUTIONS
Simulation Results Bubble Radius at the end of cycle DESIGN SOLUTIONS
Simulation Results Bubble Radius as a function of time DESIGN SOLUTIONS
Simulation Results Predicted Shape & Magnitude of part deflection DESIGN SOLUTIONS