What's new
What's new

Advice For First Mold Job

Joined
Nov 2, 2018
One man garage job shop here. I'm currently bidding on my first mold job. If I get it, I'll be doing it on my Mini-Mill. Customer is providing pre-ground PX5 stock. I've picked up a trick or two just reading around (e.g. tap runout out of finishing tools before hand) but I wanted to see what advice you guys with more experience might have.
 
One man garage job shop here. I'm currently bidding on my first mold job. If I get it, I'll be doing it on my Mini-Mill. Customer is providing pre-ground PX5 stock. I've picked up a trick or two just reading around (e.g. tap runout out of finishing tools before hand) but I wanted to see what advice you guys with more experience might have.


If he's designing the tool then you've just avoided a ton of work and responsibility.

Find out the part detail tolerances and finish requirements. A #1 finish will cost a lot more than 600 paper.


If you're designing the tool then find out the his spec requirements. If he is small he may not have even have any any. They typically cover things like how they like their shutoffs, pin clearances, even where they like their eye bolts placed. We build medium tooling (up to 20K pounds) and have very specific specs for each customer. Very anal customers might reject a tool for what seems very minor to you and me.

Does he have component brand preferences such as DME, National, etc-? If you buy a mold set complete from whoever then a lot of that work is done for. Now that I think of it, most builders use those sets anyway. Our customers require custom mold configurations so we rarely have the luxury of buying a mold set already complete.

We could write a book on this so simply post back here as you have more questions. ;)
 
What kind of mold? There are all kinds from plastic injection to hand injected bait, with far different issues to be aware of.
 
Partner with someone that has mold building experience.

Tom

What if I don't know anyone? (I don't.) :dunce:


If he's designing the tool then you've just avoided a ton of work and responsibility.

Find out the part detail tolerances and finish requirements. A #1 finish will cost a lot more than 600 paper.


If you're designing the tool then find out the his spec requirements. If he is small he may not have even have any any. They typically cover things like how they like their shutoffs, pin clearances, even where they like their eye bolts placed. We build medium tooling (up to 20K pounds) and have very specific specs for each customer. Very anal customers might reject a tool for what seems very minor to you and me.

Does he have component brand preferences such as DME, National, etc-? If you buy a mold set complete from whoever then a lot of that work is done for. Now that I think of it, most builders use those sets anyway. Our customers require custom mold configurations so we rarely have the luxury of buying a mold set already complete.

We could write a book on this so simply post back here as you have more questions. ;)

Luckily, and a huge reason I even had the confidence to bid it when he approached me, he is/has provided the blanks,tool design, drawings, etc... Even offered to provide tooling lol. The tightest tolerance is a +/-.002" counter-bore on what I believe is the watercooling port so that should be cake. Two of these counter-bores per half of the mold, UNC hole concentric to counter-bore and 3x holes on the periphery of the UNC hole- if that helps identify it for anyone. Sorry for being so broad- I guess my main intent with this post was getting any advice conducive to a good finish and any other gotchas I might be missing. You don't know what you don't know and all that :)


What kind of mold? There are all kinds from plastic injection to hand injected bait, with far different issues to be aware of.

My bad. Should have specified. It's an injection mold that will be going in a 20T hydraulic- I'm under the impression it's for plastic.
 
Hi TheWolfOfWalmart:
At the risk of sounding negative about this, do you have any idea what you're getting into here?
As others have pointed out, there is much to know and the "what to know" varies quite a bit depending on what the tool is supposed to make.
The best advice I've seen so far is to have experienced mold makers looking over your shoulder and an experienced and talented mold designer making your design for you if there is any complexity to your build.

If you are convinced your tightest tolerance is going to be +/- 0.002" you will have a nasty surprise.
You will need to do way way better than that in some areas and you can be much much sloppier in others without compromising the quality of the tool, but if you don't know where it matters and where it does not, you'll have a very hard time indeed.

Mold designers commonly do not make toleranced drawings; they assume the moldmaker knows what to care about and what not to care about, so they make a CAD mold model with no clearances and no interferences and the toolmaker is expected to make a workable tool from that primitive design.

It's true that some of the more sophisticated shops will design and build to print, but not with a Minimill and a couple of mikes in the garage.
These are heavily capitalized operations with millions invested in equipment and metrology.
Those of us who don't have the benefit of that technology need to fit the mold as they build it, and there is a workflow you need to know about to do that successfully, even for quite simple molds.
None of it is rocket science, but....

So there will definitely be handholding in your future in one form or another.

So I gotta ask: how did you even quote the tool knowing so little about molds and molding?
Do you expect to make money on this project or are you willing to eat it in order to learn something new?
Who designed the part?
Who (if anyone) designed the mold?
Do you know the plastic it will run, do you know the shrinkage factor you need to work to, do you know if it even matters?

Is it a simple core-cavity mold in your opinion or is it a mechanical mold with special features to release and eject the part?

It sounds as though your customer can support you to some extent, but why is he offering you this project when there are specialist mold shops out the wazoo in Utah and everywhere else in the USA?
Does he hope to get it for cheap?
Does he have expectations about the required performance of the mold before he pays you?
Is he perhaps a buddy, and will he still remain a buddy if you fuck it up?

My gut tells me this is probably a simple core-cavity or cavity-cavity mold...if that is so, are you sure at this point that you can mill all the features?
What will you do if you can't?
I know you specifically asked about milled finishes, and they are important, but that is such a trivial concern next to everything else that it's not the thing to get too focused on.
Polishing stones and elbow grease have solved many sins for a very long time in the moldmaking world.

So I encourage you to post as much as you can...there are lots of very knowledgeable people on this forum.
Once we see what you're up against, we can give more useful advice.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
and any other gotchas I might be missing. You don't know what you don't know and all that :)
I'm under the impression it's for plastic.

You are under the impression it's for plastic? Wow.

Implmex spelled it out pretty well. Making a plastic injection mold is WAY harder than it looks. There is a reason even simple molds can cost $50k.

I'm not being negative here, but your first couple of molds will probably be unusable even after reworking them several times which means taking them in and out of the molding press each time and that cost adds up.

Very important to NOT break any corners on the parting line. They must be dead sharp to avoid any flash. Even something tiny like a .005" edge break makes the part look like shit. I worked in a mold shop a long time ago and I learned the hard way to not break any edges.

You will need to add venting to the mold cavity and in the correct places to remove the trapped air when the plastic is injected at very high pressure.

You got a setup to accurately grind ejector pins? Can't do that OP on a CNC Mill.
I'm in for the popcorn. :popcorn:

If you are serious about getting into injection molding, I would suggest buying a book on the subject vs trial and error. Something like this would be a good start:

https://www.amazon.com/Handbook-Shr...t+Shrinkage+and+Warpage&qid=1571530614&sr=8-1
 
That is only one of many factors in mold design. Gating, ejectors, methods of sticking part to one side, venting, cooling or heating, parting line. Type of molding compound, filled or unfilled, mold filling and flow. Controlling dieseling in deep pockets or ribs. Type A finish or textured.

Just some of the problems I have seen over the years. Lots of others I haven't

Tom
 
I really appreciate when the guys like implmex (Marcus) get into the details on stuff like this. No matter how long I've been in this trade, there's guys who know more and it's great to learn from them.

What I'd suggest is don't touch the customer's materials until you've proofed out some real programs on scrap steel or Al blocks. You might even quote to include this "Pre" work, especially if the customer has designed the mold but themselves aren't experts. This way you could both learn as you go, figure out what aspects need changing, then when you've got a true design commit to the mold blanks.

You can run plastic shots using Al, just keep in mind the cooling characteristics are different than steel, so what gives a good cycle in Al may not be optimal in the real parts.
 
Wish I didn't always have to justify myself for asking questions but...

do you have any idea what you're getting into here?

Enough to either make a mess or make some money and get my name out more. Doing my research and looking for smart advice is how I've gotten through any other thing people say I shouldn't do up to now so idk.

The best advice I've seen so far is to have experienced mold makers looking over your shoulder and an experienced and talented mold designer making your design for you if there is any complexity to your build.

That would be a fantastic resource if I had it. But to be honest I don't even really know any machinists. I started my business about a year ago on the side (I work in semiconductor manufacturing full time) because I enjoy this. This forum is probably the closest thing I have to what you're suggesting.

If you are convinced your tightest tolerance is going to be +/- 0.002" you will have a nasty surprise.
...
Mold designers commonly do not make toleranced drawings; they assume the moldmaker knows what to care about and what not to care about, so they make a CAD mold model with no clearances and no interferences and the toolmaker is expected to make a workable tool from that primitive design.

Yeah not sure what to say. This one did. Perhaps I could have been more specific but this isn't a high volume production mold. It's for a guy that converted the machine to run in his garage. He designed the part and the tool. I think it's something I can do. The CAD assembly has a core and so I guess It's a core cavity mold. Most of my jobs have been pretty prismatic so far. It's a pretty simple design, it's just more 3D finishing toolpaths than I'm used to. I don't know if you're referring to stacked tolerances or what but like I said it's all pre-ground and all datum/features are based off those surfaces. So in my uneducated eyes, my main concerns would be TIR, rigidity, minimizing tram error on faced surfaces, etc...I don't think it's assembly level GD&T.

So there will definitely be handholding in your future in one form or another.

Just trying to learn and upsklll like everyone else.

So I gotta ask: how did you even quote the tool knowing so little about molds and molding?
Do you expect to make money on this project or are you willing to eat it in order to learn something new?
Who designed the part?
Who (if anyone) designed the mold?
Do you know the plastic it will run, do you know the shrinkage factor you need to work to, do you know if it even matters?

Same way I usually do. I don't have to design anything. So handling, shop rate, spindle time, etc...

I expect to make money, to make something I'll be proud of, and will quote appropriately- but I'm sure no one is coming to me for aerospace parts. The guy designed everything so I wouldn't consider myself accountable for anything other than his tolerances and finish specifications. I'm willing to sacrifice a little on the job to learn and show what I can do. But it seems simple enough that I don't think it's appropriate I devalue what little time I have to grow my business.

My gut tells me this is probably a simple core-cavity or cavity-cavity mold...if that is so, are you sure at this point that you can mill all the features?

Yes, I'm sure. Simulations with the tooling look good.

What will you do if you can't?

Let him know I fucked it up and make it as right as I can.

So I encourage you to post as much as you can...there are lots of very knowledgeable people on this forum.
Once we see what you're up against, we can give more useful advice.

Thank you and thanks for your post. Hope I've provided enough detail to make it a question worth answering.
 
Hi again TheWolfOfWalmart:
OK, we have a bit more information, but we still don't have enough to help you.
Are you bound by an NDA or can you post freely online.
If you can, show us everything you have, and I'll happily put in my two cents' worth to help you out.

I'd need to see the part design and I'd need to see the mold design.
I'd also need to know if the designer of the mold knows his stuff or not; it's pretty easy to make some judgments from what the mold design looks like but it would also be useful to know something of his background.

If he has experience in the field, his design will likely cover all the basics pretty well, (they're not all that complicated) but if he has little prior experience, you might be building something that doesn't work properly or worse yet injures or even kills somebody.

It's not all that commonly known that these tools run under some pretty extreme conditions and need to be built with that in mind.
The clamping forces are measured in multiple tens of tons and the injection pressures are often in the tens of thousands of PSI, and the plastic is HOT and sticks like crazy to skin if a mold springs a leak and it happens to get on someone.
Burns from hot plastic are pretty much always third degree burns, so the danger is very real and not trivial.

Something as simple as too big a projected area for the clamp tonnage and too thin a part wall and you can force the mold open during the injection phase of a molding cycle with potentially really bad consequences to anyone nearby.
Also, some plastics flash like crazy even into gaps as small as 0.0005" and can end up in unexpected places.

So this is not stuff to screw around with...again it's not rocket science, but I've seen some pretty nasty ignorance related shit and many guys who've worked in molding plants can tell some stories.

Not to scare you into abandoning your ambition to learn some of this stuff, but just to advise you of the potential unforseen consequences of a misstep.

So the offer of design and build assistance is open if you care to take it up, so long as we can do it on the forum so others can learn too.
Talk to your customer and ask him if he's OK with a plan like that.
If he's open to it, I'll be happy to help as I can, and you'll likely get some great advice from others on this forum too.
There are some really smart dudes on here with tons of experience.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
 
Hmmmmm – potential truckload of worms here:)

A lifetime of designing, building, specifying, and running plastic mould tools serves to teach you that you only ever know 85-90% of how it might go. There is always something that will firmly bite you on the bum when you think you know it all.
How much does your client know about mould tool design? If he gives you a bad design to make and it doesn't work, whose fault is that – and who pays for the mistake and rectification/adjustment?

Often (on technical/critical parts) the first thing we would design into the tool would be the cooling circuits, and then the general tooling build and component layout around that. And leave the initial tooling in a metal-safe condition in areas where warp and critical geometry were placed. Then we could measure first-run parts on a CMM and then re-machine to correct geometry.
Any sharp corners? May need to use need an EDM or design for separate inserts.

What about payment terms? We always used a 1/3rd & 1/3rd & 1/3rd. First 1/3rd with order, second on delivery, and final on 30 days.

I won't try and put you off, I think this will be a great learning experience, and I wish you well with it. But if you're offered advice from people with experience here then grab it with both hands.
 
I'll also chip in any assistance I can, as a moldmaker with 20 years doing this sort of stuff.
Sounds like a simple tool, hopefully its been designed with flat parting lines in a way that makes mismatch easier to deal with.

We need more info.
Is it a set going into a mud base, or whole tool.

All kinds of tips and tricks, depending on what youre building.

Cheers
 
For best results X Y datums should always be from the centerline of the blocks / mold base. This will minimize parting line mismatch between the core and cavity.

"The tightest tolerance is a +/-.002" counter-bore on what I believe is the watercooling port so that should be cake. Two of these counter-bores per half of the mold, UNC hole concentric to counter-bore and 3x holes on the periphery of the UNC hole"

If in fact this a water line tolerance it shows the designer is wasting your time with tolerances that are irrelevant. Always check the tap depth with a water plug if the blocks are to be hardened. Tapping to deep can also be a problem if the plugs can interfere with each other on the corners.

Part tolerances usually are not the problem in mold making. If it's a flat parting line no big deal. If the PL is stepped or a 3d surface it must locate closer than +.0000 to - .0015 to -.0003 depending on the plastic being injected. Correct draft on passcores for proper shut offs are critical. Minimum of 2 degrees preferred.

If the cores and cavity are inserts the mold base work also needs to be precision. Pockets must be on location and to size for proper parting line alignment.

Modern cnc and cad has simplified mold construction. I'm sure with a good design and proper machining techniques you will be fine.

Good luck,
Brian

Sent from my SM-G960U using Tapatalk
 
If possible you want to insert the cavities. It is more work up front but makes repairs or changes easier. If you don't insert up front at least make sure you can do it later if need be. If it is a simple cavity then I say WTF, go for it. One of the biggest issues will be grinding the pins to length, you really need a surface grinder for this. I always would cut them as close as I safely could and then would set up a toolmaker vise and spin them in the V section of the jaw. It was the companies vise so I didn't worry about wear on it. I also migrated to using through-hardened ejector pins vs nitrided so I didn't have to worry about chipping the hard surface with my hack way of grinding them to length. The more info you give us the more help we can be, keep in mind no detail is too small. Nothing wrong with aluminum, in my experience it is the best material to make molds from, both as a mold maker and running the mold.

On top of the part to mold and the current mold design:
How many shots expected from the tool.
What resin and filler.
How will the ejector plate be retracted? Positive pull back or springs?

Since we don't want/ will not write a book on mold design here if you don't pose the questions we can't answer them, and there are far more than you know about, of that I am sure.

By the way, a book on mold design would be a good idea but it is only for ideas, it sure as hell won't teach you how to do it. Like feeds and speeds for machining, good for ideas but only trial and error will teach you what to do.

My biggest fear as a mold maker, cutting into a water line! It is a real "oh shit" moment.
 
Very important to NOT break any corners on the parting line. They must be dead sharp to avoid any flash. Even something tiny like a .005" edge break makes the part look like shit. I worked in a mold shop a long time ago and I learned the hard way to not break any edges.

You will need to add venting to the mold cavity and in the correct places to remove the trapped air when the plastic is injected at very high pressure.

If you are serious about getting into injection molding, I would suggest buying a book on the subject vs trial and error. Something like this would be a good start:

https://www.amazon.com/Handbook-Shr...t+Shrinkage+and+Warpage&qid=1571530614&sr=8-1

This is all good stuff thank you. Toolpaths are good at the parting lines but it's good to be aware of the potential for flashing- Makes total sense. While I do find it incredibly interesting, I wouldn't say I'm serious about getting into injection molding, outside of a few parts I've mused about getting made for some other projects. This seems like a good chance ease into it, learn, make a good contact, and gain a little more street cred.
 
That is only one of many factors in mold design. Gating, ejectors, methods of sticking part to one side, venting, cooling or heating, parting line. Type of molding compound, filled or unfilled, mold filling and flow. Controlling dieseling in deep pockets or ribs. Type A finish or textured.

Just some of the problems I have seen over the years. Lots of others I haven't

Tom

Luckily none of that is really anything I have to worry about on this job but I appreciate the context as to some of the things that has to be considered at a higher level
 
What I'd suggest is don't touch the customer's materials until you've proofed out some real programs on scrap steel or Al blocks. You might even quote to include this "Pre" work, especially if the customer has designed the mold but themselves aren't experts. This way you could both learn as you go, figure out what aspects need changing, then when you've got a true design commit to the mold blanks.

That's never bad advice for sure. Being more high mix low volume, I usually don't proof my programs out past the simulation for sake of time. But that's also usually when it's with materials that I've worked with before, which PX5 (or it's P20 equivalent) are not. So that being said, if my simulation looks good, my concern would then be finish. If I'm proofing it in a different material, I would probably be using different tooling and S&F. Would that not defeat the point then?

I do really like the idea of quoting in the proofing time though. Good way to communicate that I wouldn't be willing to take it on unless I could justify my time spent building a little confidence in the program, in a way that puts the ball in their court. Not sure if that's normal practice or not but I like it- Thanks
 
Are you bound by an NDA or can you post freely online.

Good question. This would actually be my first job where I didn't design the part myself, which is weird now that I think about it. I haven't signed anything nor has it been brought up. I'll ask if he's ok with it. That would mean a lot to me to have one of you vets look over it.

I'd also need to know if the designer of the mold knows his stuff or not; it's pretty easy to make some judgments from what the mold design looks like but it would also be useful to know something of his background.

All I can provide as far as that goes is that I've seen his machine on youtube pumping out parts and he himself has told me that he uses it mostly for hobby projects and occasionally production jobs. So...at least some experience? :) He provided the tool paths in F360 and they look like toolpaths and workflow of someone that knows a thing or two. How much of that I will actually keep or modify for use? TBD.

Not to scare you into abandoning your ambition to learn some of this stuff, but just to advise you of the potential unforseen consequences of a misstep.

Nope, that is all valid feedback. That's why I'm here, those are the kinds of things I want to learn. I know there is much more to mold making than I'm even generally aware of.

I'll get back to y'all when I hear back from him. Hopefully he is cool with it because I would love to get some expert opinion on here about it.
 
If possible you want to insert the cavities. It is more work up front but makes repairs or changes easier. If you don't insert up front at least make sure you can do it later if need be. If it is a simple cavity then I say WTF, go for it.

Can you clarify what you mean by this? And yeah I really think this is a simpler part than it seems people are thinking, which is on me. Probably because small-fish me hears 'mold' and sees things much differently than all you guys that have been doing this since before I was born lol.

One of the biggest issues will be grinding the pins to length, you really need a surface grinder for this.

No talk of pins yet so I'm not really sure if/when/how that will come into play as far as this job is concerned.
 








 
Back
Top