topic Volumetric shrinkage result has negative value in Moldflow Insight Forum

Volumetric shrinkage result has negative value

Sanjay_paul — Thu, 02 Feb 2017 05:46:23 GMT

Hello everyone,

In the below picture there showing negative volumetric shrinkage on some areas. What does this mean?

Regards

Sanjay Paul

Re: Volumetric shrinkage result has negative value

bernor_mf — Thu, 02 Feb 2017 07:19:14 GMT

Hi Sanjay,

Negative volumetric values indicate expansion rather than shrinkage.

Negative volumetric shrinkage means expansion : the material does not shrink, rather expand.

If you see this,area of the part is overpacked - in filling phase and/or in packing phase.

Negative volumetric shrinkage in features like ribs, bosses etc means higher risk of getting stuck in mold, and cause ejection problems.

Regards,

Berndt

Re: Volumetric shrinkage result has negative value

Sanjay_paul — Thu, 02 Feb 2017 07:56:22 GMT

Hello,

That means the packing pressure is greater than required. I have set 60% of fill pressure as packing pressure. How much packing pressure do you recommend for running an analysis? How much should I reduce?

Regards

Sanjay Paul

Re: Volumetric shrinkage result has negative value

mppkumar — Thu, 02 Feb 2017 08:41:31 GMT

Hi @Sanjay_paul

It's not only packing pressure ... packing time also matters

generally on the thinner regions like ribs it may be there (it's best practice to avoid it)

in your case, the negative volumetric shrinkage values is very close to zero, this can be neglected

Re: Volumetric shrinkage result has negative value

madhukeshwart — Mon, 06 Feb 2017 04:56:27 GMT

@Sanjay_paul

Negative volumetric shrinkages means the part will actually expand on removal from the mold.

This effect occurs if there is residual pressure inside the part at the end of the molding cycle.

Typically negative volumetric shrinkages are associated with excessive packing pressure.

Refer

1. http://forums.autodesk.com/t5/moldflow-insight-forum/negative-volumetric-shrinkage/td-p/4754459

2. http://forums.autodesk.com/t5/moldflow-insight-forum/negative-value-for-volumetric-shrinkage/td-p/3432819

Re: Volumetric shrinkage result has negative value

Anonymous — Thu, 09 Feb 2017 22:00:44 GMT

@Sanjay_paul normally negative volumetric shrinkage indicates that you are over packing the part. this negative Volumetric will help you understand that you are giving excessive packing pressure or over packing the part. with that you can easily optimize the required packing pressure which this part actually needs.

Re: Volumetric shrinkage result has negative value

Sanjay_paul — Sat, 11 Feb 2017 03:17:53 GMT

Thanks everyone for your comments. It was really helpful.

Regards

Paul

Re: Volumetric shrinkage result has negative value

ktr.mech — Wed, 06 Mar 2019 07:01:21 GMT

Could you please tell me the solution of negative volumetric shrinkage ,

what we are going to do ?

Re: Volumetric shrinkage result has negative value

bernor_mf — Wed, 06 Mar 2019 08:16:40 GMT

Hi,

negative volumetric shrinkage means significant over packing.

Review your packing pressure level and time.

Adjust and profile the packing in time and pressure level for a more uniform volumetric shrinkage.

Hope this helps.

Regards,

Berndt

Re: Volumetric shrinkage result has negative value

Anonymous — Fri, 23 Jul 2021 13:13:29 GMT

Good Morning, I am currently having an issue with 3mm of Negative Volumetric Shrinkage in the X direction and 1.8mm of Positive Volumetric Shrinkage in the Y direction on the actual parts. Mold flow indicates the Negative shrinkage almost spot on and indicates only .5mm of Positive shrinkage. Any help or advice with correcting this would be greatly appreciated.