Cushion monitoring

[jnewmanco1]

Again with the old Van Dorn HT series questions, right? I'm new here, remember that, and I am seeing more and more things that just don't sit right with me and they are starting to become my recurring nightmares even when I am not at work.
We have to set 6 or 7 process parameter monitors on each job that we run. They use the same generic tolerences for all jobs no matter what the part looks like, no matter machine size, no matter what material we are running, etc. They are just the same for all jobs.
My biggest headache and source of most of my torment lately is the silly cushion monitor.
I am expected to hold a cushion with a tolerence of only .030" from shot to shot. In our brand new machines and with a properly developed process, I might hit that for a little while. On these old VD's, no way. Just so you have a little more info to gauge your response on, we are also running 25% regrind in most jobs, coming from press-side grinders that have old proportional valve loaders sucking up the regrind and the virgin from the dryers in "proportional amounts". I think you know how well those things work. One shot might be 85% regrind with the next only 2% and I'm going to hold a .030" cushion?

I'm new and I need to work so I don't want to start screaming this early in a new employment setting so I bite my tongue, work for hours and hours trying to achieve what I see as unachievable and it is making me ill. Have any of you been in a situation like this before? Do you think these kinds of tolerences are achievable under the mentioned conditions that we run under? I think maybe after I have been here awhile longer I will feel more comfortable challenging my manager over these things. For now however I guess I keep trying to reach those impossible goals and pulling my hair out and feeling horrible about my abilities when I simply cannot do it. TGIF.
James

[Suhas]

Hello James,
Good Post, thanks.
Holding a +/- 0.03 is not east on the older machines, agreed. But you have to think in terms of volume and not only just diameter. It is easy to hold a +/- 0.03" on 25mm screw but on a 75 mm screw, that will be tough. With regrind it is a nightmare.
My suggestion is: If possible, that track the cushion for about a shift and see what the variation is (without any process changes if possible). On purpose vary the cushion and see if you still make good parts. Show that to your boss and tell him the required tolerance is too tight for the parts you mold.
Having said that, it is not uncommon for parts with tight tolerances to have a +/- 0.03" cushion requirement.
Hope this helps.
Thanks,
Suhas

[rickbatey]

Let me turn on one more light in this dark room. If your trying to hold .3" on a press older than about 18 months old, using the last .3-1" of barrel, you're gonna be in a bell tower with a rifle in about 20 more days! That section sees like 95% of the wear because EVERY job stops in that area!!
Try to take a deep breath, then start proving that the tolerances are too tight for appropriate parts. Then you can keep your hair on your head! BTW- it WILL start showing up in your nose and ears! I guess our Dad's doomed us as well!!
Rick.

[jnewmanco1]

Thanks Suhas and Rick. I'm of the opinion that it is true, you could hold to a .03" cushion on the smaller machines IF they are capable of doing that in the first place. Some of mine are not, I'm afraid, and that is the main source of most of my frustration right now.
I'm starting a new thread next to see if there are some Van Dorn experts that can help me understand the tuning of one of these machines.
James