what's new

Moldflow Plastics Insight 4.0 - MPI/3D Enhancements

By Murali Anna-Reddy, Moldflow Corporation

There is a certain class of plastic injection molded parts that are best described geometrically as being thick and solid in nature. In other words, they do not exhibit the common characteristics of the majority of plastic injection molded parts, which tend to be of relatively uniform and nominal wall thickness. Because of their thick and solid nature and the difficulty associated with defining explicit part wall thickness, these parts are best analyzed using true three-dimensional (3D) analysis technology, where the part model is meshed with solid tetrahedral elements throughout the thickness. Moldflow Corporation has led the industry in the creation of true 3D analysis technology with the release of 3D mold filling and cooling analysis modules in recent years. With the recent release of Moldflow Plastics Insight® (MPI®) 4.0, the best true 3D product on the market today just got better with major new innovations to our existing 3D simulation technology.

3D Warpage Analysis

In MPI 4.0, new solver technology was introduced for predicting warpage in 3D-type geometry, that is, thick and solid parts that are not well represented as Midplane or Fusion analysis models. The 3D warpage analysis helps to identify the magnitude and source of part warpage, where the source can be either differential cooling or differential shrinkage. This insight can then be used to take corrective actions to reduce or eliminate part warpage. While thickness effects such as the “corner effect” can be simulated, the current analytical model used is isotropic in nature and does not utilize measured shrinkage data. Development is underway to incorporate fiber orientation and residual stress calculations in a future release of MPI.

3D Insert Overmolding Analysis

Insert overmolding is a process where some type of insert is placed into an injection mold between machine cycles and polymer melt is injected into the mold cavity and around the insert. The insert materials can vary and range from metals, plastics, textiles, or films. The insert material’s thermal and mechanical properties can have a significant effect on the flow of plastic around the insert. In general, metal inserts act as conductors and draw heat away from the polymer melt, resulting in flow hesitation at the cavity-to-insert interface. On the other hand, plastic inserts act as insulators, reducing the cooling effects on the plastic melt and potentially resulting in a flow “race-tracking” effect at the cavity-to-insert interface. MPI 4.0 supports insert overmolding analysis for both thermoplastic and thermoset applications to evaluate the effect of the insert on the polymer melt flow front. Inserts can be imported directly as solid models and meshed along with the cavity using 3D tetrahedral elements. The meshing process offers the flexibility to use an unmatched mesh along the interface of the cavity and inserts. The left image below shows an example of the differences in the mesh of the insert and cavity.

There is no limit to the number of inserts that can be analyzed for a given part model, and it is also possible to use plastic and metal inserts simultaneously, as shown in the image on the right above. For each insert, you can specify its material properties and an initial temperature. Then a flow analysis can be launched to obtain the temperature variation within the insert during the molding cycle. The analysis will help identify changes to polymer flow pattern due to the presence of inserts. In the example below, the left image shows a partially filled cavity and the right image shows the temperature distribution in the insert at the same time instance. It can be clearly seen that the temperature rises in the insert in areas where it is in contact with the plastic melt.

3D 2-Shot Sequential Overmolding Analysis

Typically, 2-shot sequential overmolding is the process where a rigid substrate is overmolded with a flexible material. This process is used for manufacturing multi-component applications such as toothbrushes, shaving systems, telephone keypads, automotive interior components, and medical devices. In 2-shot sequential overmolding, the substrate is first injected in a closed cavity. Soon after, some movement of the mold or cores positions the substrate as an insert for the overmolded material. However, the temperature of the substrate may not be uniform and is determined by its processing conditions.

The thermal interaction between the substrate and overmolding materials can be analyzed through the use of the new 3D 2-shot sequential overmolding analysis capability in MPI 4.0. Also, analysis results can be reviewed to determine the potential for thermal degradation of the substrate material. Degradation can occur in the substrate material from reheating as it comes in contact with the hot overmolding material. Additionally, users will be able to better determine gate locations and processing conditions for optimized bonding between the substrate and overmolding materials. The example below shows a common household screwdriver, which is molded using the 2-shot sequential overmolding process. The screwdriver (top left) is made up of two plastic components and a metal insert in the middle. Also shown are the filling patterns of the substrate (top right) and the overmolding material (bottom left). The bottom right image shows the temperature distribution of a cross-section of the part.

MPI/3D Extended to Microchip Encapsulation

Microchip encapsulation is the process by which semiconductor chips are encapsulated with epoxy (thermoset) materials. The complexity of the molding process is mainly due to the intricate nature of the components, which include wires, leads, and a paddle. Paddle shift and wire sweep are two problems that are unique to this process. Simulation provides quantitative estimates for these two problems. Previously, simulation of microchip encapsulation was supported with Midplane and Fusion models. MPI 4.0 extends this to true 3D applications. Areas filled with epoxy can be meshed with 3D tetrahedral elements. Using the true 3D approach has several advantages including accurate pressure and flow front predictions for complex lead-frame geometries. Also, it eliminates the need for special modeling of the lead frame to simulate the flow of polymer between the leads (cross-flow). The example here shows the encapsulation of a series of microchips.

MPI/3D Extended to Underfill Encapsulation

Underfill encapsulation is the process used in the manufacture of flip-chip semiconductor devices. These flip chips are instrumental in the semiconductor industry’s trend towards miniaturization. There are two variations to the encapsulation process. The first process, dispensing encapsulation, involves the dispensing of a low-viscosity material near the flip chip, which then flows under the chip driven by capillary action. The second process, injection encapsulation, uses a solid molding compound, which is injected at high pressures to fill the gap below the chip. With MPI 4.0 it is now possible to simulate these two processes using analysis models meshed with 3D tetrahedral elements. Benefits of using a true 3D analysis include improved accuracy in calculating the effects of solders on the flow of the encapsulant and easier modeling of the chip geometry. The example to the left shows the simulation of a standard IBM flip chip where the encapsulant is dispensed along the entire bottom edge.

3D Mesh Optimization

A new mesh optimization scheme was introduced in MPI 4.0, which is aimed at creating an optimized 3D tetrahedral mesh with elements of relatively uniform aspect ratio and mesh density, resulting in reduced analysis times while maintaining analysis accuracy. Prior to the release of MPI 4.0, certain types of parts with predominantly 3D geometry combined with some thin wall sections required a larger number of tetrahedral elements to mesh, resulting in unnecessarily long analysis times. The new MPI 4.0 mesh optimization routine focuses specifically on these thin sections to create an optimized mesh with elements of relatively uniform aspect ratio and mesh density throughout the thickness. The example below displays 3D meshes created in both MPI 3.1 and MPI 4.0 to illustrate the benefits of the mesh optimization.

MPI 3.1: 56,000 elements

MPI 4.0: Optimized mesh with 27,000 elements

The mesh optimization scheme uses surface mesh matching information to create internal layers with fewer nodes and refrains from splitting surface facets to reduce dense patches of mesh. As a result, the number of elements and nodes in the mesh should decrease significantly, resulting in faster analysis times.

Additional MPI/3D Enhancements

Based on user enhancement requests, two new analysis results, Temperature at the Flow Front and Beam Flow Rate, were added in MPI 4.0.

Temperature at the Flow Front

Beam Flow Rate

Further, velocity vectors can now be plotted as darts (arrows). The color of the dart represents the magnitude of the vector, and its length may either be fixed as a constant, or change according to the magnitude of the velocity. By default, the dart length is fixed at the average mesh element size.

With the release of MPI 4.0, Moldflow has demonstrated a commitment to true 3D analysis with significant new capabilities in 3D warpage, 2-shot sequential overmolding, and insert overmolding. We have also demonstrated our commitment to extend 3D simulation technology to existing MPI modules with new 3D capability for MPI/Microchip Encapsulation and MPI/Underfill Encapsulation. Finally, our ongoing commitment to reduce 3D analysis times while maintaining analysis accuracy has resulted in a new 3D mesh optimization utility in MPI 4.0.

For more information about Moldflow Plastics Insight 4.0, visit www.moldflow.com or contact your local Moldflow representative.