Originally Posted by
bryon
DOM,
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. Of course not, but who is trying to be skilled? all I am asking for is a little knowledge so I can go and practice to find out more about something from my own experimentation.
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.
It's CV time again.
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 think we have different opinions of what constitutes a skill. A skill is a physical thing that a person learns, like Mr Mold using the feel in a manual drill press to drill a hole, or a mould polisher having a feel for the surface of the part. What most people are talking about is knowledge and experience, for example whan a part comes in and you decide how to make a mould for it, where to the put the pins etc, that is not skill being used, that is previous experience, and generally accepted knowledge of how certain mould problems are solved, which generally comes from other peoples collective experience through nothing more than trial and error over many years. And to be honest it is quite normal for a mould to be modified several times before it will work properly as almost every job is slighlty different and experimental.
When I use my cam system to mill out a mould I am not using skill I am using cam. I also use knowledge and experience to choose what tools to use and how to hold/mount the workpiece in the mill, but this is not skill.
Tig Welding is a skill.
Even a mould polisher is only using a tiny part of his skill to do the polishing, but it is such a difficult thing to learn the feel for, that is the longest thing to learn how to get the feel for it. The tools/compounds he uses to polish and the direction he polishes in, is not a skill this is defined information that once again comes from collective knowledge from many years of trial and error. He uses this knowledge and his skill to polish the mould.
But that does not mean that somebody who is not a skilled mould polisher can not be told how to technically polish a mould.
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. Again it's not a glass that is just a way of describing the shape so people can imagine what I am talking about. the finish is unimportant, as it is held with large gaps all around it within a large assembly.
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. Actually I totally agree with the poppet valve, my quote was for the earlier metion of use of pins in the bottom
Quote:"I'd probably run the pins into the bottom of the cup shape."
which was talked about before the poppet valve.
Pin length accuracy problems? Flashing problems? You may not like hearing it, but again, this depends on the skill of the mold maker.
Well in that case I better go sit in a box for the rest of my life and never try to make a mould. How about any tips about setting pin lengths or other problems that you may have come across building your Knowledge and Experience.
Spring loaded to allow for small errors? No. If you build the mold accurately, this is totally unnecessary.
What do you think to the idea of leaving a 0.02mm gap between the shutoff surface and the end of the pin?
bryon