Injection Molding?

[glycerine]

Any of you do or ever done injection molding? I saw some old molds for sale on a web site that were for nib feeds. That would be one step closer to those of you who want to truly make your own pen "from scratch". Just wondering how difficult it would be and what other equipment is needed for injection molding other than the molds themselves...

 

[Constant Laubscher]

This would be like having the rims and tires for a car and you would need the rest to start driving around in your car.

The mold needs to be inspected to see if they are not damaged or warn out.
If they are fine you can actually take them to a company with injection molding machines. I assume those would be for a 50 to 100 ton machine.

Some molds can be changed to fit a different machine that is was made for.
They are normally pretty complicated and it might cost more than just the molds to get going and that would be for only one type of nib feed.

Hope this help?

 

[glycerine]

Yes, that helps. I skimmed the internet years ago about injection molding and thought I came across some stuff that talked about injection molding that you could do yourself at home. I did just find some "benchtop" injection molders online. What determines how much pressure you need in a machine? Is it the size of the mold? The type of plastic you are using? I know if this particular mold I saw on the internet was made for a particular type of machine, that's one thing, but do you think a feed could be made on one of these "home molders" if someone were to machine a mold for it?

 

[BRobbins629]

This is not something for the home shop. Like Constant said, the molds are useless without an injection molder and even the small lab size ones are pretty pricey. Additionally you would have to be lucky that they are the right size for the nibs you can buy. You would have to make huge quantities for it to pay off. If you needed to make new molds, they too are very expensive with the simplest small ones coating a least a few thousand dollars and they go up from there.

 

[glycerine]

This is not something for the home shop. Like Constant said, the molds are useless without an injection molder and even the small lab size ones are pretty pricey. Additionally you would have to be lucky that they are the right size for the nibs you can buy. You would have to make huge quantities for it to pay off. If you needed to make new molds, they too are very expensive with the simplest small ones coating a least a few thousand dollars and they go up from there.

How about starting with blank molds for a "benchtop" injection molder and having someone with a good CNC mill cut the molds. Do you know what determines that amount of pressure needed for injection molding?

 

[alphageek]

I can tell you that the pressure needed for injection molding is a very complicated process.... There are many factors:
- Type of plastic
- Size of the mold
- Size of the sprues/runners
- Number of cavities
- Temperature run at
- and other things

My FIL does injection mold design/creation for a living and I can tell you from having seen what they can do that it is NOT a trivial thing.

It is pretty fun watching the CNC machines cut out molds though

 

[Timebandit]

Check this out http://www.injectionmolder.net/index.htm

 

[glycerine]

Check this out http://www.injectionmolder.net/index.htm

Now THAT'S what I'm talkin' about!!

 

[glycerine]

I can tell you that the pressure needed for injection molding is a very complicated process.... There are many factors:
- Type of plastic
- Size of the mold
- Size of the sprues/runners
- Number of cavities
- Temperature run at
- and other things

My FIL does injection mold design/creation for a living and I can tell you from having seen what they can do that it is NOT a trivial thing.

It is pretty fun watching the CNC machines cut out molds though

Well, that sounds like a fun job!
Do you know the answer to this question: in an industrial injection molding machine, are the parts made one at a time, or are many molds "strung" together? I thought maybe the tons and tons of pressure were required if the plastic had to travel a longer distance or for very large molds (ie, if the plastic needed to be injected super fast so it fills the molds before hardening). I just looked at the site that Justin posted and some of those items look to be the same size or larger than a feed. Also, I wonder what type of plastic most feeds are made from...

 

[alphageek]

Well, that sounds like a fun job!
Do you know the answer to this question: in an industrial injection molding machine, are the parts made one at a time, or are many molds "strung" together? I thought maybe the tons and tons of pressure were required if the plastic had to travel a longer distance or for very large molds (ie, if the plastic needed to be injected super fast so it fills the molds before hardening). I just looked at the site that Justin posted and some of those items look to be the same size or larger than a feed. Also, I wonder what type of plastic most feeds are made from...

Next time I talk to my FIL, I'll ask him, but I think feeds are probably polypropylene.

As for the multi tons - most production molds that I've seen him work with have mutiple stringers and cavities for smaller parts (picture a model car... you cut the pieces from the stringers). So something like a feed holder would be N-up mold (where N is some number like 16) so that every cycle of the mold produces multiple parts. This is necessary to keep the run cost down. Each cycle of the mold (close, fill, cool, open, eject) takes a similar amount of time no matter if its 1 part or 20.

Bigger parts means less pieces per cycle, due to the physical limits of the molds (and some of them are HUGE).

But in either case, the pressure helps get the parts filled correctly, and sometimes they heat the mold in the process as well to change the flow rates.

 

[glycerine]

Well, that sounds like a fun job!
Do you know the answer to this question: in an industrial injection molding machine, are the parts made one at a time, or are many molds "strung" together? I thought maybe the tons and tons of pressure were required if the plastic had to travel a longer distance or for very large molds (ie, if the plastic needed to be injected super fast so it fills the molds before hardening). I just looked at the site that Justin posted and some of those items look to be the same size or larger than a feed. Also, I wonder what type of plastic most feeds are made from...

Next time I talk to my FIL, I'll ask him, but I think feeds are probably polypropylene.

As for the multi tons - most production molds that I've seen him work with have mutiple stringers and cavities for smaller parts (picture a model car... you cut the pieces from the stringers). So something like a feed holder would be N-up mold (where N is some number like 16) so that every cycle of the mold produces multiple parts. This is necessary to keep the run cost down. Each cycle of the mold (close, fill, cool, open, eject) takes a similar amount of time no matter if its 1 part or 20.

Bigger parts means less pieces per cycle, due to the physical limits of the molds (and some of them are HUGE).

But in either case, the pressure helps get the parts filled correctly, and sometimes they heat the mold in the process as well to change the flow rates.

Ok, now things make a little more sense. The model car is a good example. I used to build them alot when I was younger. The mold that I saw was just a single feed mold, so that's why I was thinking it couldn't be that hard to melt some plastic and get it into that mold. But that one also could have been just a piece of a larger mold where they are all bolted together or something, who knows.

 

[BRobbins629]

Check this out http://www.injectionmolder.net/index.htm

Now THAT'S what I'm talkin' about!!

While a cute litle machine that may be good to make a few sample prototypes, it has many limitations. Most injection molding macines have a little plastic extruder attached which continuously heats, melts and delivers the plastic to the mold. with this one, you need to scoop in a few pellets and wait a few minutes for them to melt. Okay for a few quick prototypes, but impossible for production. Its also nice in a production setup where the molds pneumatically open and close. Try opeing one by hand when the plastic gets sticks to the mold. Also it says to use a low viscosity resin which although available, may not be the best one for a feed. As for the molds, yes - many are made by CNC but usually require a significant post polishing step to get the desired finish on the part.

 

[Russianwolf]

I can tell you that the pressure needed for injection molding is a very complicated process.... There are many factors:
- Type of plastic
- Size of the mold
- Size of the sprues/runners
- Number of cavities
- Temperature run at
- and other things

My FIL does injection mold design/creation for a living and I can tell you from having seen what they can do that it is NOT a trivial thing.

It is pretty fun watching the CNC machines cut out molds though

Well, that sounds like a fun job!
Do you know the answer to this question: in an industrial injection molding machine, are the parts made one at a time, or are many molds "strung" together? I thought maybe the tons and tons of pressure were required if the plastic had to travel a longer distance or for very large molds (ie, if the plastic needed to be injected super fast so it fills the molds before hardening). I just looked at the site that Justin posted and some of those items look to be the same size or larger than a feed. Also, I wonder what type of plastic most feeds are made from...

Check out 2:13

http://www.youtube.com/watch?v=eMQ6oDoFE3w

 

[glycerine]

Check out 2:13

http://www.youtube.com/watch?v=eMQ6oDoFE3w

Ebonite, that's interesting. After seeing that mold, I assumed all feeds were injection molded, never thought about them being machined from a solid piece, much less ebonite!
I guess with the right CNC equipment and bits, it would probably be easier to make one from a thin rod of ebonite than to do it by injection molding anyway...

 

[Russianwolf]

Check out 2:13

http://www.youtube.com/watch?v=eMQ6oDoFE3w

Ebonite, that's interesting. After seeing that mold, I assumed all feeds were injection molded, never thought about them being machined from a solid piece, much less ebonite!
I guess with the right CNC equipment and bits, it would probably be easier to make one from a thin rod of ebonite than to do it by injection molding anyway...

Now that being said, obviously the ones in our kits are injection molded. The ebonites are more of an upgrade, and aren't we all shooting for quality (perceived value) over quantity? I think other materials are a possibility also as long as the shape is right.

 

[BRobbins629]

Just did a test using infrared spectorscopy on a few different feeds I had. Tested a Berea feed, one I got from Brian Gray probably from Germany and one very small custom one someone sent me to fit a real small vintage Conway Stewart nib.

The Berea and one from Brian are polystyrene and I suspect most kit and commercially produced feeds are the same. The custom one matched a piece of ebonite I also tested as a control.

 

[pianomanpj]

I just remembered I have a book at home on how to make your own injection molding machine - Secrets of Building A Plastic Injection Molding Machine, by Vince Gingery.

Here's a link to where I bought the book: http://www.lindsaybks.com/dgjp/djgbk/inject/index.html

This link is a set of mods for the same machine: http://rick.sparber.org/Articles/gpi.pdf

The book is a good read, and you could have a machine running for about $100 or so. I haven't fully read the mods, so I can't say anything about them.

NOTE: I have not made this machine, so I can't verify the accuracy of this information!

 

[glycerine]

Just did a test using infrared spectorscopy on a few different feeds I had. Tested a Berea feed, one I got from Brian Gray probably from Germany and one very small custom one someone sent me to fit a real small vintage Conway Stewart nib.

The Berea and one from Brian are polystyrene and I suspect most kit and commercially produced feeds are the same. The custom one matched a piece of ebonite I also tested as a control.

you lost me at "infrared"... no, I'm kidding. That's interesting. Do you know who made the custom feed? Can you tell a difference in the "performance" of the ebonite vs. the polystyrene feeds?

 

[glycerine]

I just remembered I have a book at home on how to make your own injection molding machine - Secrets of Building A Plastic Injection Molding Machine, by Vince Gingery.

Here's a link to where I bought the book: http://www.lindsaybks.com/dgjp/djgbk/inject/index.html

This link is a set of mods for the same machine: http://rick.sparber.org/Articles/gpi.pdf

The book is a good read, and you could have a machine running for about $100 or so. I haven't fully read the mods, so I can't say anything about them.

NOTE: I have not made this machine, so I can't verify the accuracy of this information!

That's cool, I have some of Dave Gingery's books!

 

[Curly]

There is a Yahoo group dedicated to home injection molding.

 

[BRobbins629]

Just did a test using infrared spectorscopy on a few different feeds I had. Tested a Berea feed, one I got from Brian Gray probably from Germany and one very small custom one someone sent me to fit a real small vintage Conway Stewart nib.

The Berea and one from Brian are polystyrene and I suspect most kit and commercially produced feeds are the same. The custom one matched a piece of ebonite I also tested as a control.

you lost me at "infrared"... no, I'm kidding. That's interesting. Do you know who made the custom feed? Can you tell a difference in the "performance" of the ebonite vs. the polystyrene feeds?

Actually have yet to make a pen with the ebonite but I suspect the nib and how it's tuned has a greater influence on the writing than the feed. I guess to really tell you would have to make one for a regular size nib and try to compare. I probably wouldn't know how to tell. Perhaps its a good question for the fountain pen network gurus. As fo who made the one I have, TerryF picked up the feed for me so probably somewhere in SA. If you're really interested in getting a size 5 or 6 he'd be the one I'd ask but you'd have to be sure it would fit in the section.

 

[glycerine]

Just did a test using infrared spectorscopy on a few different feeds I had. Tested a Berea feed, one I got from Brian Gray probably from Germany and one very small custom one someone sent me to fit a real small vintage Conway Stewart nib.

The Berea and one from Brian are polystyrene and I suspect most kit and commercially produced feeds are the same. The custom one matched a piece of ebonite I also tested as a control.

you lost me at "infrared"... no, I'm kidding. That's interesting. Do you know who made the custom feed? Can you tell a difference in the "performance" of the ebonite vs. the polystyrene feeds?

Actually have yet to make a pen with the ebonite but I suspect the nib and how it's tuned has a greater influence on the writing than the feed. I guess to really tell you would have to make one for a regular size nib and try to compare. I probably wouldn't know how to tell. Perhaps its a good question for the fountain pen network gurus. As fo who made the one I have, TerryF picked up the feed for me so probably somewhere in SA. If you're really interested in getting a size 5 or 6 he'd be the one I'd ask but you'd have to be sure it would fit in the section.

Ok, thanks.