Fill Analysis Issues Help

[Anonymous]

Hello everyone

Im a student from a university in Portugal and im making a project on Moldflow.

After the Fill Analysis ive got 2 issues ( On attachments)

Can u explain me scientifically why the bulk temperatures are so diferent and why in the pressure on VP ive grey results?

Greetings

[Alex.Bakharev]

1. I guess the ribs in your molding are thinner than the main body, thus, A) they cool down faster; B) there is less flow of the hot melt through those ribs. Both results lead to the polymer in the ribs being colder than in the rest of the part

2. V/P transfer occurs below the end of fill (usually at 90..99% of fill). At that time some volume of the cavity is not yet filled. This empty volume does not have melt pressure at V/P and is shown as grey.

[Anonymous]

Thanks for your answer.

Ive heard that that grey space is filled with compression afterwards. is this true?

I know that there is less flow but how do i manage to get the whole piece even in terms of bulk temperature? How can i have orange all over the place?

Trough increasing the pressure? Decrease the flow??

[Anonymous · Accepted solution]

Hi srpinto,

1. Yes you are right regarding p/v switchover, after  switchover packing phase intiates. Moldflow's explanation for packing "The stage of the injection molding cycle when pressure is applied to the polymer melt to compress the polymer and to force more material into the mold. This compensates for the shrinkage that occurs as the polymer cools from the melt temperature to ambient temperature (hours or even days after the part has left the mold). From 5 percent to 25 percent more material is added to the mold during the packing stage. The gate should freeze during the packing time to prevent material from exiting the mold"
2. Rgarding bulk temperature, you can have uniform bulk temperature all over the part by having uniform wall thickness. In your case since the rib edges are thinner compared to the other regions, you can't have uniform bulk temperature as for as i know.

P.S: 

 please go through below mentioned link to know more:

http://help.autodesk.com/view/MFIA/2014/ENU/?guid=GUID-5F3A6D60-7140-4389-B35C-C03DE61B2041

http://help.autodesk.com/view/MFIA/2014/ENU/?guid=GUID-62332401-77B2-4C52-9051-E18BBD06EDB2

http://help.autodesk.com/view/MFIA/2014/ENU/?guid=GUID-927CDD74-5892-4FA5-85D3-E0354F8A5654

http://help.autodesk.com/view/MFIA/2014/ENU/?guid=GUID-6B47F6F8-9017-4AA0-9B1A-71701134A756

[Anonymous]

thank you so much.....one last question. why the thickness makes the distribution of the bulk temperatures so different?
kindest regards

[Anonymous]

Moldflow definition for buk temperature "The temperature of polymer melt changes not only with time and location, but also with thickness during the entire injection molding cycle. It is difficult to illustrate all these changes in a single display. The bulk temperature captures energy transmission within the polymer . When there is no flow, bulk temperature is simply an average temperature of cross section. When there is plastic flow higher the velocity , greater the weight that is given to that portion of cross section "

In simple words : The thicker regions of the part, requires more time to dissipate the heat build - up in your mold  because of their higher volume (compared to thinner regions) . 

If your doubt still persists, please let me know the material you had used for the analysis ( Image you had attached earlier) .

For more information on Moldflow results,  please go through document in below mentioned link :

http://www.pt.bme.hu/futotargyak/56_BMEGEPTMG11_2013oszi/AMI_theory.pdf

[Anonymous]

im using PBT. Im simulation the injection of an ashtray from Volvo Car