The tools and processes required to realize a part can be a as complex and challenging as the part itself. Here are some recommendations and practices that should be considered to achieve the best results possible.
The perfect part design, tool design and molding process creates conditions that produce a void-free, fully crosslinked Engineering Thermosets (ETS) polymer network, in which fillers and reinforcing fibers are isotropically oriented and uniformly distributed throughout the material matrix.
True perfection is not attainable. Molded ETS test specimens used to measure material properties come close. But they are small parts with simple geometry that are easy to mold. Real parts are complex.
To achieve optimal performance in a real ETS part, design, tooling and processing should create conditions as close to ideal as practically possible. Following a few basic best practice design principles will ensure the best outcome.
Best practice design principles for engineering thermosets:
> Uniform wall thicknesses — avoid creating areas of material accumulation
> Radius on all corners — inside corners especially critical
> Draft on all features with depth (walls, ribs, gussets, bosses, stand-offs)
> Adequate venting in tool (and process if practical)
> Isolated tall features supported by gussets or ribs (bosses, stand-offs)
> Material flow that allows even filling of features – fill from thick to thin
> Minimal weld/knitlines located in non-critical areas
> Gate type and size to minimize shear and avoid jetting
> Balanced runners sized for minimal pressure drop
> Uniform temperature control throughout tool
Mold flow analysis, in conjunction with CAD modeling, should be employed during the design of all parts. It is especially critical for complex tooling and large format parts. Together, the two techniques enable optimization of the material flow and management of heat transfer by allowing simulations of different part and tool configurations. Features, such as the number, type, size and location of gates as well as ribs, bosses, and flow leaders can be tested and refined before steel is cut. Likewise, modeling also makes it possible to predict heat flow in the cavity and tool during process cycles allowing for optimization of heat transfer systems.
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