Linear VS volume shot size

[Lonewolf]

I've been doing this for (only) about 5 years and all of our processes are set up in linear shot size, i.e, how far the screw moves for the shot. We move molds between various machines (we have 32 machines ranging from a 55T to 750T) and may not put the mold in a machine of the same size which requires reprocessing (unless we've done it before and have a setup for it). I've asked about using volume as shot size since that would be consistent across machine sizes, meaning 2 cubic inches is 2 cubic inches regardless of barrel size as opposed to 3" linear movement is NOT the same with a different barrel size. Volume would seem to make transitioning to a different size machine easier, plus when a new mold comes out of our tool room, the guys could give us the volume of the cavities and we'd have a better starting point than guessing linear movement (of course we could do all the math to convert but I'm lazy... :cool: ). This makes more sense in my mind.... am I wrong?
Answers I've gotten are:
1: "We've always done it that way". A company mindset that doesn't seem open to much change.
2: Volume is too imprecise and difficult to process.
3: It's stupid to do it that way, more or less referring to 1 & 2

So what are the opinions of those in other shops and more experience?
Thanks

[iautry1973]

Makes sense to use volume, but a lot of old school techs aren't used to it. It's like converting to metric...not what they are used to. I have run into it a lot. When you use volume it helps, but it doesn't always translate perfectly. Slight differences from machine to machine will make you change it slightly. It will give a very good starting point however. Also it will give you a point of reference between machines as volumetric rate is the same no matter what size screw/barrel you are using. As far as volume being imprecise it is still measured using the same linear encoder on the machine. So it is as accurate as the linear speed would be. It would only be inaccurate if the screw size was set incorrectly in the machine.

[Suhas]

(Agreed with the post above by inautry1973)

Absolutely! Volume is the way to go! You now ALWAYS have apples to apples right? In regards to their comments:

1: "We've always done it that way". A company mindset that doesn't seem open to much change.
"If you do what you have done, you will get what you have got' - So make things easier by calculating volume.

2: Volume is too imprecise and difficult to process.
Absolutely not. We all know it is a simple linear formula.

3: It's stupid to do it that way, more or less referring to 1 & 2
Lot of people thought Steve Jobs was stupid :) - By the way, I am not an Apple guy, but love the guys thinking.

Get a copy of my free software. I have something called as 'Process Transfer' It will do all the calculations for you. Please request it from my website at www.fimmtech.com.

Thanks,
Suhas

[rickbatey]

I've never been a fan of volumetric settings. I'm not to lazy to do the math plus I always end up doing it anyway due to tool shops never use the same brand press, screw size, or an injection unit with the same intensification ratio. Besides you'll be shocked at how far off theoretical shot volume/weight of a cavity or tool is when compared to your actual end results. Unless you're running plastic pressure settings on your machines, you'll still end up doing the math to find the correct hold pressure and fill rate (volumetric). If you feel that strongly get someone to help you create an Xcel spreadsheet to do the math for you! I did several over the years for drier hopper capacities, color dosing, residence time, drier throughput and for runner and gate sizing.
Rick.

[Lonewolf]

Ian, I'll give you a hint where I am. My initials are BW. :) That will tell you a lot.

[Lonewolf]

Thanks guys. I know that volume isn't exactly transferable between machines but it's a lot closer using a volume than 3" in a 55T and (WTF??) in a 175T.

Suhas, thanks for the process link.

[iautry1973]

BW, well if you flash it just toss it in that 730 ton you guys have and create some new shutoffs LOL.