Can an ejector pin sit against a shutoff surface.

[DomB]

Hi Guys,
My investigations into the art of mould ejection continues.

Imagine a part like a drinking glass, the wall thickness is perhaps 3mm. Lets say for arguments sake that you are going to push the part off of the core by pushing against the 3mm rim of the glass at 12, 3,6 and 9 o'clock positions (4 pins).

Due to the rim being only 3mm I assume I would use a 2.5mm pin so there is no clearance issues.

When the part is ejected there would be 4 small complete circle marks from the ejection pins on the rim.


Now rather than using tiny 2.5mm pins that are awkward to drill ream etc (drill wandering etc), you choose to use say 8mm diameter pins. Rather than pressing all of the pins against the rim, only a crescent of each pin would contact the part rim, but will probably have a much larger surface area than the small pins in complete contact.

Now the problem is that the pins when the mould is clamped together, rather than being in free space, are now against the cavity shutoff surface with only a crescent poking over the edge into the cavity.

Is this an accepted practice?
Are there pin length accuracy problems?
Will there be leaking flashing problems if the pin is not the correct length and perfectly square on its end?
Does the ejector plate/assembly have to be different to allow for the cavity (A side) plate pushing the pins back?

Could the pins be sprung loaded to allow for a small error to ensure a good seal? or would spring loaded pins be pushed back by the plastic injection pressure?

Sorry for the bombardment of questions.

many thanks for any replies.

Dom

[MrMold]

Hi Guys,
My investigations into the art of mould ejection continues.

Imagine a part like a drinking glass, the wall thickness is perhaps 3mm. Lets say for arguments sake that you are going to push the part off of the core by pushing against the 3mm rim of the glass at 12, 3,6 and 9 o'clock positions (4 pins).

Due to the rim being only 3mm I assume I would use a 2.5mm pin so there is no clearance issues.

When the part is ejected there would be 4 small complete circle marks from the ejection pins on the rim.


Now rather than using tiny 2.5mm pins that are awkward to drill ream etc (drill wandering etc), you choose to use say 8mm diameter pins. Rather than pressing all of the pins against the rim, only a crescent of each pin would contact the part rim, but will probably have a much larger surface area than the small pins in complete contact.


Now the problem is that the pins when the mould is clamped together, rather than being in free space, are now against the cavity shutoff surface with only a crescent poking over the edge into the cavity.

Is this an accepted practice?

I've seen it done many times. I never do it though.
Are there pin length accuracy problems?
Yes, but it is not out of the range of a skilled moldmaker.
Will there be leaking flashing problems if the pin is not the correct length and perfectly square on its end?
Yes, but it depends on the material.
Does the ejector plate/assembly have to be different to allow for the cavity (A side) plate pushing the pins back?
No, but the return pins have to be more acurate. I would also spring load the ejector system.

Could the pins be sprung loaded to allow for a small error to ensure a good seal? or would spring loaded pins be pushed back by the plastic injection pressure?

Yes, and No.

Sorry for the bombardment of questions.

many thanks for any replies.

OK first off, If you cannot drill an ejector pin hole and hit a 3 mm wall you probably don't have any rights to attempt it, and I question your ability as a mold maker. That being said, I suppose use of ejector pins on this application would not be ideal way of ejection. The larger pin idea.. not much better. I call this the "Toe nail" method. It's probably OK for a prototype or other small run application., but if thats the case I'd probably run the pins into the bottom of the cup shape. It might not be automatic (without opperator) and there's a chance of the part not falling off the pins when ejecting even with spring loading. I would use an air popett valve or ejector connectors to the ejector plate and maybe use mutiple knock out strokes if your press allows this. You may be able to run it automatic. The best way is to design a three plate mold using a stripper plate rather than ejector pins. Also, might try a stripper ring bolted to ejection. I call this the "poor man's 3-plate" system.

Dom

[DomB]

Hi,
Well many thnaks for the reply, I think.

Firstly the nice bit,

Many thanks for the reply. I thankyou for the helpful parts of your answer.

Now the other bit.

Don't tell me, you are also a member of a well known 'practical machining' forum? Yes the very reason I do not use that forum anymore is because up until now the responses at cnczone have been helpful and informative, whilst the replies at certain other practical machining forums just tell you about how wonderful and skilled a person is and how they "question your abilities as a mould maker" (mould is spelt with a U where I live). Then they proceed to tell you how rubbish your idea is and that would never do it that way etc etc.

So let me spell it out.

Quote "If you cannot drill an ejector pin hole and hit a 3 mm wall you probably don't have any rights to attempt it, and I question your ability as a mold maker."

Well as it is going to be my machining centre that will be drilling the holes, perhaps you should question its abilities as a VMC. The pins need to be drilled through 120mm with a 2.45mm drill and then reamed with a 2.5mm reamer. The most skilled person in the world cant skill a wandering drill straight. Hence why many mould makers send all their moulds off to special gun drilling companies for deep ejector holes.

Who is trying to proclaim their ability as a mould maker? So who are you to question any ability about anything.

The fact is that you have missed the entire point of this question. It is a hypothetical question, therefore a situation is described for no reason other than to illustrate to the reader a what is trying to be asked.

There is possibly no mould, no pins it's just a posed question. I have given out parameters and asked fairly specific questions, and therefore if you can respond to the situation posed within the parameters of my question that I asked then do so. But don't start banging on about how you would never do it this way and how great and "skilled" you are.. Well guess what, maybe I would never do it this way either, however that's not the point of this question. the point was to address a specific situation set out in the question.

One of the questions and responses:
Are there pin length accuracy problems?
"Yes, but it is not out of the range of a skilled moldmaker."

Well how wonderful for the skilled mould maker, how about actually answering the question with perhaps some possible problems and tricks for getting around them. I don't want to hear about this skilled mould maker, I want to hear about what he actually does with his skills to solve a problem.

Skills are 'skills' i.e. a wood carver or an artist. But information is information, just because one person posseses it doen not make them skilled. If you hand carved a complex mould cavity with a chisel to 0.001mm tolerance than you would be skilled.

Lets look at another question:

Could the pins be sprung loaded to allow for a small error to ensure a good seal? or would spring loaded pins be pushed back by the plastic injection pressure?

"Yes, and No."

Well thats me filled right in then, off I go to be a skilled mould maker.

And one parting note, if anyone suggested " I'd probably run the pins into the bottom of the cup shape." to any of the mould shops that I know, they would tell you to go back to mould school, and learn about pushing cup shapes off of cores from the top, not the bottom, which actually pulls the cup shape onto the core even harder.

So I'm sure that they would question your abilities as a mould maker as well.

I'm sure you run a very sucessful mould company, but perhaps you can see now that nobody likes being talked to like that.

You may be a skilled mold maker, but you seem to not have picked up any people skills along the way.

By the way in the UK mold is the stuff that grows on wet things.



Best of luck to you

Goodnight

[slucas_clmach]

I would most likely use a different ejection technique. Ejector pin marks on a surface that you are going to put against your mouth would be questionable. I have built this type of tool with an ejector plate instead, this works very well and is durable and quick. Implementing it in the tool is a little more difficult and much more time consuming.

[MrMold]

WOW...?,
Sorry didn't mean to set you off there. Perhaps I could use some more people skills. You spend 20+ years in the shop working 60-80 hours a week and the one thing that suffers is your people skills. Sorry if I offended you, it was not my intention. There was alot of good free information there if you open up your mind some of it. Now don't take that wrong either.
I never attempt to drill extremely small ejector pin on my VMC. I only do them manually and you have to have a feel for it.
The Yes and NO answer came off wrong. You actually asked two questions. The first was Yes the second was NO. I explained later on more in depth.
You've taken every thing I said wrong. Must be lost in translation or something. I suggested that you shouldn't attempt drilling these holes unless you are skilled at that. Then a gave you several ways around this. There is no Right and wrong way of doing something as long as the outcome is acceptable to you or your customer. I've worked at over a dozen shops and owned my own for 10 years. Every one has their own way of doing things and I found that arguing about it accomplishes nothing. I tried to talk in laymans terms when I can, but there are alot of buzz words. People from different parts of the country call things differently i.e. "A half, cavity, stationary side, B half, ejector side, core, movable side, Cams, Slides, lifters"
You folks on that side of the pond sure are touchy?

[bryon]

Hi Guys,
My investigations into the art of mould ejection continues.

Imagine a part like a drinking glass, the wall thickness is perhaps 3mm. Lets say for arguments sake that you are going to push the part off of the core by pushing against the 3mm rim of the glass at 12, 3,6 and 9 o'clock positions (4 pins).

Due to the rim being only 3mm I assume I would use a 2.5mm pin so there is no clearance issues.

When the part is ejected there would be 4 small complete circle marks from the ejection pins on the rim.


Now rather than using tiny 2.5mm pins that are awkward to drill ream etc (drill wandering etc), you choose to use say 8mm diameter pins. Rather than pressing all of the pins against the rim, only a crescent of each pin would contact the part rim, but will probably have a much larger surface area than the small pins in complete contact.

Now the problem is that the pins when the mould is clamped together, rather than being in free space, are now against the cavity shutoff surface with only a crescent poking over the edge into the cavity.

Is this an accepted practice?
Are there pin length accuracy problems?
Will there be leaking flashing problems if the pin is not the correct length and perfectly square on its end?
Does the ejector plate/assembly have to be different to allow for the cavity (A side) plate pushing the pins back?

Could the pins be sprung loaded to allow for a small error to ensure a good seal? or would spring loaded pins be pushed back by the plastic injection pressure?

Sorry for the bombardment of questions.

many thanks for any replies.

Dom

DOM,
Although MrMold may have come off sounding a bit harsh to you, he did provide sound information.

Moldmaking does take skill whether you'd like to believe that or not. You said yourself that possessing information doesn't make you skilled. Do you think telling someone who is across an ocean how to design and build an ejector system will make that person "skilled"? I hope you do not.

I have been a moldmaker for nearly 25 years now and for the past 15 have been involved with the design, building and repairing of 30+ ton automotive injection molds. Some of the repair work doesn't have to be accurate, but some of it has to be very much so - like in the airbag areas etc. Sure, you can explain to a non-skilled person how to do the work, but that is most definitely not the same as having a skilled person do the work. The fact is, you learn by doing and that's why there are apprenticeships for these types of trades.

I have seen the ejection technique you've described done many times on the edges of dashboard retainers. Mind you these parts don't have to be pretty, they just have to work. If you were doing a drinking glass, then you wouldn't want ejector marks on the rim. MrMold was right in saying that you could eject from the bottom of the part and utilize a poppet valve. In spite of what you think, this is done often. It all depends on the part design and customer requirements.

Pin length accuracy problems? Flashing problems? You may not like hearing it, but again, this depends on the skill of the mold maker.

Spring loaded to allow for small errors? No. If you build the mold accurately, this is totally unnecessary.

bryon

[spider]

I've "toe-nailed" ejector pins many times. Recently i had a PolyPro. side airbag cover that was sticking. I added a 1/2 inch ejector pin underneath the wall (and with most of it on the sealoff....010 from vertical vall) and it worked fine.......don't forget to add those WASHER SPRINGS UNDER THE RETURN PINS Just to make sure the ejection is all the way back before closing.

If you do a good job spotting down the pins, you shouldn't have much problems with it......


oh and if your working in one of those shops that likes to have a .100 hard line around the part, and rest of 1" ground "close enough" GOOD LUCK.

if you lower the cavity down at 0 pressure on half of toalet paper, the entire 1" of sealloff SHOULD BE BLUE!!!!!!! (one of my pet peeves.)

[DavyD]

Dom
I would avoid using edge ejector pins as you described - it is done but is not good practice. In theory if you have a sprung ejection system then the pins should be back flush with the split line before the mould closes but in my experience the pins can stick slightly forward and upon mould closing end up hobbing into the opposing mould face and damaging the surface leading to flash etc. This problem would be worse with soft aluminium cavity plates.

Good alternative methods would be a stripper ring or plate. If you have enough draft and a good surface finish on the core then the poppet valve will also work well. We have succesfully used this method without using air. Make the top of the poppet ejector as big an area as possible.

Davy

[DomB]

I would most likely use a different ejection technique. Ejector pin marks on a surface that you are going to put against your mouth would be questionable. I have built this type of tool with an ejector plate instead, this works very well and is durable and quick. Implementing it in the tool is a little more difficult and much more time consuming.

Hi the shape is just called a glass so people can imaging the type of shape I am talking about. So it's nothing to do with peoples feel of the product etc.

What I mean is that if this method of ejection is used for whatever reason are there any difficulties with an ejector pin sitting up against a shutoff surface?

Normally pins obviously sit just in open space before the plastic is injected.

Thanks
Dom

[DavyD]

Dom
I think in my last post I described why I think its not good practice to have edge ejectors on the shut off face as you described i.e. over time they can hob into the opposing half and damage its surface leading to flash.

Another alternative if you have a plate too thick to drill & ream 2.5mm through may be to cut a circular slot type pocket around the base of the core and fit a ring type insert. This need only be 10mm thick and then you can drill and ream the 2.5mm ejector holes in this. You might want to use the stepped type ejector pins for extra pin strength. They are the 'CN' type in the DMS catalogue.

Regards
Davy

[DomB]

Hi Davy,

many thanks for you usual, useful and straight to the point replies.

I have been recently been learning about a new method of mold making that leaves a gap between the core and the inner shutoff surfaces of a part (i.e. not the complete perimeter, just the individual peaks of a complex core that normally sit against the shutoff surface of the opposite plate.)

Its nothing more complicated than leaving a 0.02mm gap between the two, which is a pretty average vent sized gap. But it is supposed to avoid wear of the shutoff surface as it does not touch (depending on the flexing of the mould under high clamp pressure).

This is supposed to help the venting of the mould as obviously the air can move between the cavitys to get to a vent, so less vents are needed.

Perhaps this could stop wear problems.

Dom

[DomB]

WOW...?,
Sorry didn't mean to set you off there. Perhaps I could use some more people skills. You spend 20+ years in the shop working 60-80 hours a week and the one thing that suffers is your people skills. Sorry if I offended you, it was not my intention. There was alot of good free information there if you open up your mind some of it. Now don't take that wrong either.
I never attempt to drill extremely small ejector pin on my VMC. I only do them manually and you have to have a feel for it.
The Yes and NO answer came off wrong. You actually asked two questions. The first was Yes the second was NO. I explained later on more in depth.
You've taken every thing I said wrong. Must be lost in translation or something. I suggested that you shouldn't attempt drilling these holes unless you are skilled at that. Then a gave you several ways around this. There is no Right and wrong way of doing something as long as the outcome is acceptable to you or your customer. I've worked at over a dozen shops and owned my own for 10 years. Every one has their own way of doing things and I found that arguing about it accomplishes nothing. I tried to talk in laymans terms when I can, but there are alot of buzz words. People from different parts of the country call things differently i.e. "A half, cavity, stationary side, B half, ejector side, core, movable side, Cams, Slides, lifters"
You folks on that side of the pond sure are touchy?

Mr Mold

Don't take things personally, i had just seen one too many replies that day from people saying, oh you shouldn't try that, ah that depends on skill, etc and not answering the questions with any useful info.

Don't worry about laymans terms, I am quite educated and anybody coming specificially to the mould area of the forum, probably has a pretty good grasp of the terms, and if not they can ask a question to clear it up. The way I test official world recognised terms for processes or mould parts for instance, is to google it. If you get no useful returns on the subject then thats probably not the recognised way of naming something, thats my method anyway. If you stay away from those americanisms like "the poor mans....." or the "Homebrew blah blah....." or anything that soulds like it is a book title from the palidin press catalogue, then we should all be able to keep up with what is being described.

PS
As i am also feeling generous today I will offer some people skills training for you free of charge.

Tip 1: Nobody, particularly the British likes people blasting in tooting their own horn, in this case by repeatedly starting their posts with either a life story or CV of their whole working life. i.e. "You spend 20+ years in the shop working 60-80 hours a week and the one thing that suffers is your people skills. " subtle as that one may have been.

Now I appreciate experience as much as the next person but, numbers don't impress me, I personally work over 90 hours a week have no social life as a consequencs and have black ringed, panda like eyes to show for it. But I wouldn't listen to someone with 20 years experience any more than I might listen to an 18 year old who has come up with a good idea.

And I certainly wouldn't just follow some advice from a forum about drilling or not drilling etc. I would always collect as much useful information as possible, then make my own judgement and develop my own method based on all the info, which might be completely different than anyones idea anyway.

This should be useful reference. http://www.worldcitizensguide.org/fi...izensGuide.pdf

Many Thanks

Dom