i have a question based on real experience. I did an analysis on an existing piece.
During the real process I tried to use different cooling time and the result was that long cooling time reduce the deflection of the piece,as expected. Obviously, all others parameters were kept unchanged (packing phase and filling phase).
The deflection measured was about 0,9 mm for the short cooling time (9 sec) and about 0,5 for the long cooling time (50 sec).
But, when i try to simulate this on MoldFlow i found different result. I realized two different analysis with the same parameters except cooling time, like reality. The analisyses results show me about 0,8 mm for the short cooling time and about 0.75 mm for the long cooling time.
This is very strange for me.... There is an explanation for this difference?
Thanks in advance and excuse me for my broken english!!!
do you have the mold and waterlines in your model? if so, how are you setting up your water? are you matching the flow rate you are seeing in your process? do you have a way to correlate the temperature on the part at ejection, with yours? (thermal imager)
i would also focus on refine your mesh, are you dealing with a 3D mesh? fusion? midplane?
you are though seeing the same warpage trend, the little details like the packing pressures, fill time, melt temperature, mesh quality, water inlet temperatures, i think will get you on the right track.
FYI, also check if your material has CRIMS data...as these materials tend to have a more closer approach of the warpage 'numbers' than the rest...
thank you very much for your reply.
In my study i use a very fine 3d mesh, so i think this is not the possible reason to the fault results.
I also modeled the cooling channels and I think to use correct temperature.
The material that i used is crims caracterized.
I tried also a different material but with the same result... The analysis with long cycle time has similar deflection to analysis with short cycle time. I used 9 sec and 50 sec.
I modeled the mold by "geometry - mold surface" and now i have a doubt: in this case the cooling time considers the piece into the mold (forced into the shape cavity) or this time is only a cooling time without considering the mold?
ok it seems that your 3D mesh and your material are fine (just out of curiosity, what material is? amorphous, semi-crystalline?
what I would do in your case, is to keep a practical mind, after all, you are matching the warpage trend.
i would focus ONLY on the process settings of the cooling phase:
1. mold surface TARGET temperature, is the temperature you want your cavity to be, not your water temperature.
2. set your cavity water ~10C below this target temp. and the core water at ~15C below the same target.
3. find out the real pressure or gpm flow rate on your waterlines.
4. make some runs with AUTOMATIC cycle, to find out what the optimal coolling time is.
5. evaluate with 9s and 50s the temperature and time to reach ejection temperature through the thickness of the part (making some cut sections). this to see if the part is indeed below the ejection temperature on all cases.
if these steps doesn't work, i think the part is probably experiencing some other stresses from ejection that may not be captured by the injection molding simulation. you can evaluate the way the part is ejected from the mold...
Hi and thank you again,
the material that i used is a PP reinforced by 25% glass fiber plus 15% mineral fiber.
I also tried to all your suggestions without good results....
Probably You are right......the ejection of the piece amplify the deflection... and in the case with short time cycle (in the real process) the ejector is more aggressive... I must check the ejectors system and validate this hypothesis.
Thank You very much.