This guest contribution on Innovation Intelligence is written by Chao-Tsai Huang, Director of Technical Research at CoreTech System, developers of Moldex3D. CoreTech is a member of the Altair Partner Alliance.
MCM Product Development
Multi-component molding (MCM) is a process that involves injecting multiple types of materials into the mold to manufacture products. MCM has been widely applied to diversify product design for not only combining different colors, but also different functions (e.g., soft skin with hard core). However, there are a variety of cavity interchangeable mechanism molding rules in addition to conventional injection molding with a single material, causing complexity during design and manufacturing.
Due to the complicated nature of the MCM process during injection, conventional trial-and-error methods have their limitations to effectively catch crucial factors that compromise product quality, and can largely increase development expenses [1-8]. Therefore, MCM process development currently still faces many challenges. To get a clearer idea on how the MCM process works, general MCM processes can be categorized into inset molding and over molding, as shown in Figure 1. Insert molding has a plastic or non-plastic insert plug in during injection molding, while over molding applies sequential multiple shots.
Benefit by CAE Tool to MCM Issues
CAE mold filling simulation is a very powerful tool to deal with the unclear physical mechanism of the MCM processes and provides problem diagnosis and design validation. For example, Figure 2 shows the geometrical models for an over molding process, containing two shots through mold rotation. For this case, residual temperature, strain and stress occurs, induced by filling, cooling or even fiber orientation during each of the shots. Because of the consequent molding procedures, those process induced factors will be brought from the previous shot into the next, and can significantly impact the final product performance. Moldex3D provides professional simulation for designers and molders to quickly evaluate those molding induced factors in MCM process. In Figure 3, it is clear that the residual effect from the first shot can affect the warpage by about 40% to the final product.
On the other hand, under the assistance of insert molding, the electronic plug has been made by integration of metal and plastics materials, as Figure 4 shows. The original design and process conditions in single piece injection molding cannot directly apply to the MCM, but a new process is required [1-4]. One of the critical factors in MCM process is insert deflection, or the so called core-shift problem [9-10]. Core-shift is the result of melt flow interaction with the insert solid, such as the metal insert in an ear phone plug, as an example in Figure 5a. Similar defect can also happen during the warpage stage, such as the case in Figure 5b. During the fabrication using injection molding, the insert core will be deformed due to the core-shift effect and can cause defects such as shortage for electronics devices. This kind of interaction is pretty complicated and very difficult to catch by human guess and trial-and-error.
To overcome the challenge, the simulation technology has been developed and utilized frequently, and a CAE tool can help the designer during the revision process to be much faster with less expense. For example, to solve the core-shift problem in Figure 5a, one of the solutions is to redesign a more suitable gating location to minimize the core deformation. In Figure 6, using a CAE tool (Moldex3D), the optimized gating design with minimum deflect to the insert can be obtained in the earlier prior mold tooling. The improvement with design revision of gating can be demonstrated in real time through Moldex3D.
MCM is widely used in modern product development. However, due to its complex nature and physical mechanism, it is difficult to control critical process factors using traditional trial-and-error approach. Today, no matter what kind of over molding or insert molding system it is, a CAE tool has proven to be very useful for optimizing gate locations, estimating warpage concerning the material interaction, and many advanced issues. Professional simulation can drive the study, validation and optimization of not only part and mold design, but also engineering specialist solution.
Want to learn more? Register now for the upcoming Injection Molding webinar with HyperWorks and Moldex3D.
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