Liquid Crystal Polymers such as Vectra LCP are some of the most intriguing super engineering resins of our time. With this blog, I hope to begin to alleviate some issues with designing parts with LCP.
When designing a part with this resin, one must understand shrink rates in the flow vs. transverse directions and molecular structure. The molecular structure of this resin is much like a dry box of spaghetti. These molecules are long rigid rods that can be tricky when designing parts. This material flows very easily as the rods tend to slide off each other under shear.
Take for instance, the gate position and dimensions. In order to avoid any processing issues, the gate design must be 75%-85% of the wall thickness to ensure no jetting will occur. If one cannot design such a thick gate for their part, then one must design the flow coming through the gate to bounce off a sidewall or a boss to avoid the jetting. Jetting occurs when a resin has little to no die swell (expansion) entering a gate.
In addition, you must avoid any butt weld lines throughout the part. The reason behind this is again that long rigid rod structure. As it flows around bosses, those rigid rods tend to butt up against each other and not blend/flow causing a butt weld line. In order to gain weld line strength, you can install an over flow tab for the flow fronts to meet and then flow into, to gain strength.
Warpage can be another issue when designing a part with LCP. Remember, LCP has more shrinkage in the flow vs. transverse direction. If you design a gate in the middle of the part, expect the shrinkage rates to work against each other and cause warpage. You will be better off when designing the gate to be at one end of the part and allow the flow front to flow the length of the part.
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