RUNNER BALANCE

[edytaskiba]

HELLO EVERYONE

I ' VE A PROBLEM WITH RUNNERS. THE RESULTS OF ANALYZE SHOW ME VOLUME CHANGE ABOUT -90%. HOW TO INTERPETATE THIS RESULT BECAUSE I THINK THAT CAHNGE IS NOT POSSIBLE - RUNNERS ARE TOO SMALL. COULD YOU ALSO EXPALIN ME WHAT EXECLY IS A TARGET PRESSURE - IS IT PRESSURE IN THE CAVITY OR AT INJECTION LOCATION.
THANKS FOR HELP.

[igalabroad]

target pressure at the gate location is the pressure that will allow you to fill your part's cavity (considering it's unique voleume, geometry, injected material etc.)

you should also take into consideration that you need enough pressure so the part won't warp at cooling, but not too much pressure - so you won't "overpack" your part.

there are some engineering equations you can use in order to estimate the needed pressure, if you having any disagreements with the moldflow's results.

[Jay.Shoemaker]

Good Day Edytaskiba,

The target pressure for a runner balancing analysis is the pressure that the runner balance analysis is trying to achieve by changing the diameters of the runners. To determine a target pressure (it is an educated guess), is to start with the pressure required to fill for a fill analysis with the original runner sizes. Look at the Pressure at the injection location XY graph. If there is a big spike in pressure near the end of fill, this may suggest the fill pressure of the original analysis might be too high. If there is not a huge pressure spike, the target pressure could be a bit higher than the pressure to fill.

For example, if the pressure to fill was 70 MPa with a 20 MPa pressure spike, you may find that you need to lower the target pressure to prevent your runners from getting too small. This also assumes the runners are not too big to begin with.

There are several things you can look at to determine if your runners are about the right size.

1. Compare the time to ejection of the smallest runner to that of the part. If the cooling time is less than 80% of the part cooling time, the runner is too small. You can be a bit more conservative and say the runner can't have a cooling time less than 100% of the part. You can also try to make the largest runner to have a cooling time no more than 200%-300% of the part cooling time. Most of the time, you can't satisfy both requirements.

2. Run a packing analysis. The shrinkage distribution bettween the different parts should be very similar. If the part being fed by the smaller runners has a significantly higher shrinkage, then the runners are too small.

3. Run a warpage analysis. Look at the shrinkage between two nodes in a cavity (examine results tool), and compare that to the same location in other cavities. Also look at the deflection plots and ensure the warpage for all the cavities is similar.

Regards,
Jay Shoemaker

[Jay.Shoemaker]

Good Day Edytaskiba,

The target pressure for a runner balancing analysis is the pressure that the runner balance analysis is trying to achieve by changing the diameters of the runners. To determine a target pressure (it is an educated guess), is to start with the pressure required to fill for a fill analysis with the original runner sizes. Look at the Pressure at the injection location XY graph. If there is a big spike in pressure near the end of fill, this may suggest the fill pressure of the original analysis might be too high. If there is not a huge pressure spike, the target pressure could be a bit higher than the pressure to fill.

For example, if the pressure to fill was 70 MPa with a 20 MPa pressure spike, you may find that you need to lower the target pressure to prevent your runners from getting too small. This also assumes the runners are not too big to begin with.

There are several things you can look at to determine if your runners are about the right size.

1. Compare the time to ejection of the smallest runner to that of the part. If the cooling time is less than 80% of the part cooling time, the runner is too small. You can be a bit more conservative and say the runner can't have a cooling time less than 100% of the part. You can also try to make the largest runner to have a cooling time no more than 200%-300% of the part cooling time. Most of the time, you can't satisfy both requirements.

2. Run a packing analysis. The shrinkage distribution bettween the different parts should be very similar. If the part being fed by the smaller runners has a significantly higher shrinkage, then the runners are too small.

3. Run a warpage analysis. Look at the shrinkage between two nodes in a cavity (examine results tool), and compare that to the same location in other cavities. Also look at the deflection plots and ensure the warpage for all the cavities is similar.

Regards,
Jay Shoemaker