Structural Mold Designs

The main considerations in mold design effecting product shrinkage are to provide, for instance, with IM of RTPs, adequate cooling, proper gate size and location, and structural rigidity. Of these three, cooling conditions is the most critical, especially for crystalline TPs. 

Opportunities and Risks of Structural Component Design and Mold Engineering. 337... 

The risks involved in plastics processing, as in other material technologies, frequently involve poorly planned structural component designs leading to high-cost mold manufacturing and alterations. The choice of the wrong material usually means the molds have to be remade from scratch. In addition to the direct costs involved, there is the risk that a considerable amount of - costly - time will also be lost. 

Compression molding is a relatively simple and inexpensive procedure for the manufacture of moderate piece counts. For the production of bipolar plates compression molds with surface structured inserts were designed and manufactured. For the molding, the granulate can directly be molded in a heated mold under high pressure. Another way is the direct extmsion of a profile (semifinished material) into the structured mold, forming the plates from this plasticized polymer. In this variant the tool temperature is kept constant. With a multicavity-mold the cycle time can accordingly be shortened, and the output quantity of plates per cycle increased (Fig. 12). 

The principles that apply to material selection and process engineering, i.e., those of simultaneous engineering, apply most particularly to structural component design and mold engineering. 

In this section as well, examples provide insights into the opportunities and risks involved in structural component design and mold engineering. 

EXTREN Fiberglass structural shapes, Design Manual, Morrison Molded Glass... 

EXTREN fiberglass structural shapes—Design Manual, Morrison Molded... 

Gating for reaction injection molding requires laminar flow and a built in after mixer as part of the gate design. Structural foam and RIM molds require nonconventional gating and venting considerations and the mold designer and the molder should be consulted. 

Once a geometric model of data base is created it may be shared for many of the product development steps described earlier. The data base may be copied and scaled for shrink factors to enable a mold designer to do preliminary mold design, or an engineer can use the same data base to perform structural analysis. Numerical control tool paths may be developed concurrently with the final mold design. Such modeling tools as finite element analysis, mold fill, and mold thermal... 

In order to work efficiently, the mechanical properties of the layer should be tailored. A thin residual layer reduces the shear stress needed to induce failure, while the use of a brittle polymer allows for a cleaner failure of the layer and, consequently, smoother surface and sidewalls of the final transferred structures than if a ductile polymer is used. The quality of the process depends as well on mold design molds with sharp edges induce failure of the residual layer in a specific location, while molds where protrusions edges are not sharp lead to nonspecific layer failure and, consequently, patterned features with rough edges [31]. 

In thermo set tape laying, the manual laying process of the prepreg is automated. This can be done directly inside the mold or through an intermediate step of a flat textile structure (prepreg laminate). The aforementioned conditions apply for the mold design and the mold requirements. 

In certain cases it will be necessary to provide for preliminary experiments. Programs for the computer-aided simulation of the micro-injection molding can be helpful in the early stages of part development and mold design. Under certain circumstances, such programs are overwhelmed by the size of the parts or structures. The programs available on the market should therefore be subjected to a detailed evaluation and testing phase. 

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