Our September 2008 newsletter briefly touched on the effects of polymer orientation on warpage/deflection. In this newsletter we will discuss, more specifically, how the orientation of the fiber affects deflection.
When using a fiber filled material, it is very important to understand the characteristics and behaviors of that material. The only way to have a good understanding is to either have the material tested or acquire the test data.
A typical shrinkage test will reveal a lot about a material.
For example, a sample of 25% glass filled Nylon was tested and the observed nominal shrinkage in the direction parallel to flow was 0.1192% and 1.002% in the direction perpendicular to the direction of flow. That's 8.4 times more shrinkage in the direction perpendicular to flow.
This is extremely important information.
When optimizing the injection molding process, it is typical to ensure a part is filled and packed with sufficient pressure and cooled adequately so it can be ejected.
But what happens when the part warps more than expected?
The first aspect typically checked is 2nd stage pack. Most professionals ask
"Has the part been packed enough"? So the 2nd stage pack time and the pack pressure are both increased....
But to no avail, nothing changes.
Why not? It may have a lot to do with
fiber orientation.
It is very important to understand the path the polymer will take as it fills the part so that orientation of the molecules and fiber can be understood.
The best way to accomplish this is through FEA.
Once the orientation is understood, we can then have some idea of how much shrinkage will occur in the parallel and in the perpendicular directions. Unfortunately, just knowing the orientation and the amount of shrinkage isn't enough. The geometry of the part and the amount of orientation through the thickness of the part also come into play.
When factoring in all of these components, it's not very easy to determine how much a part will deflect by simply looking at it. This is why FEA is so important. Cutting steel without this information has been proven difficult, if not disastrous and costly.
In conclusion, it's very important to understand the behavior and characteristics of the material being used so that the process can be optimized. However, even knowing the material and part information may not be enough to determine the overall part deflection without the utilization of FEA.
Contact Bozilla Corporation for your FEA and injection molding troubleshooting needs and please visit our website at www.BozillaCorporation.com.
