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There is a great video on plastic injection molding by 'engineerguy' on YouTube.

[0]: https://www.youtube.com/watch?v=RMjtmsr3CqA

A Lego brick is a remarkably sophisticated piece of technology. Achieving that level of precision involves clever engineering and a very expensive piece of tooling.

https://www.youtube.com/watch?v=RMjtmsr3CqA

⬐ lopmotr

I once built a very simple one in my backyard using a shock absorber from a car as the barrel, which just worked like a syringe with no screw. It was driven by a threaded rod powered by an electric drill. The heater was a spiral stove element or a hot-air paint stripper or both - I forget which. The mold was a stack of aluminium plates that I'd cut with hand tools and bolted together. It was very fiddly to operate but worth the experience!

Driving a car without shock absorbers is also a real experience! With alternating braking and accelerating, you can build up an oscillation that's big enough to bounce the wheels off the ground with almost no forward speed.

⬐ gnicholas

Perfect for curious toddlers. My daughter is always asking to watch videos of how things are made, and this video has a great mix of very simple takeaways (chairs and legos are made out of plastic) and much more complicated concepts that she can be exposed to and grow to understand (the way screws work, how the runners attach).

And now she can run around the house finding the ejector pin witness marks on everything.

⬐ trumped

watch How It's Made[1], this one is probably not my favorite: https://www.youtube.com/watch?v=2NzUm7UEEIY

1. https://www.youtube.com/channel/UCWBkudOTaVbvkCBc0pyZFMA

⬐ viggity

I would have How It's Made on constantly in the background if I could stream more than the 3 most recent seasons on hulu. I love that show, but 3 seasons isn't near enough.

⬐ sdrothrock

I'm not sure how difficult it would be to find them, but the old Reading Rainbow used to have a lot of visits of this kind, and so did Mr. Rogers' Neighborhood (though I watched less of that and can't remember how frequently it happened).

If you can find them somewhere, hopefully she'd get a kick out of them. :)

⬐ nojvek

My dad took me to visit a Kenpoly plant in Nairobi. Had so much respect for machines. They were just ejecting ready made products from this little pellets.

The worker let us cut one or two of those ejector thingis that are attached at the end. He even let us keep one, we called it “the cup with a tail”.

Fun times, so easy to be amused as a kid!

⬐ Exuma

Lol, I guess I am a curious toddler then.

⬐ Judgmentality

This is by far my favorite video of his:

https://www.youtube.com/watch?v=hUhisi2FBuw

⬐ jstimpfle

Also check out the "drinking bird".

⬐ jcims

Here's the How It's Made version - https://www.youtube.com/watch?v=V7Y0zAzoggY

Aluminum baseball bats have a similar manufacturing method - https://www.youtube.com/watch?v=didmRLz4vfU

⬐ beautifulfreak

The book, Serendipity: Accidental Discoveries in Science, claims that some early plastic billiard balls were made of nitrocellulose and sometimes exploded. I suppose Hyatt's celluloid billiard balls were the nonexplosive kind. https://www.amazon.com/Serendipity-Accidental-Discoveries-Ro...

⬐ evgen

Fun history there and if you ever get a chance to watch it, there is a nice episode of Connections ('Countdown', https://archive.org/details/james-burke-connections_s01e09) that uses this as a key point for one of Burke's nice random walks through the history of technology. Nitrocellulose was initially a failure as an explosive, but when mixed with a few other things it was used to replace the ivory in billiard balls as hunters were decimating the elephant populations. Nitrocellulose ended up being the base for smokeless gunpowder that had a huge impact on guns and cannon later in history, but the other big thing it was used for was early film stock. One source of so many fires in theaters (and film storage vaults at studios) in the early 20th century was due to this particular type of film stock.

⬐ giarc

Those are incredibly well done videos. Without realizing it, I just spent 30 minutes watching engineering videos. They are done in a way that anyone could understand.

⬐ jcims

I wish he would Patreon up or something so this could be a full time job. He does an amazing job of making a variety of engineering disciplines accessible to the layman.

⬐ Judgmentality

Admittedly I don't know for sure, but I suspect he enjoys his profession as a university professor.

⬐ Noumenon72

They compare quite favorably to the Paulson training videos we watch in the actual industry, though those were more in depth, many hours longer, and came with interspersed quizzes that really helped my understanding. Both are infinitely superior to almost any classroom.

Topics this video didn't cover include friction/slippage along the barrel wall, circulation in the melt between each screw flight, the thrust bearing at the back end of the screw that takes the load from pushing the plastic forward, two-stage screws that drop the pressure in the middle to let gases be removed from the melt, how the plastic cools differently at the edges and center if it is crystalline/amorphous, and more.

⬐ KamiCrit

I still can't believe some tool & die maker machined a die large enough to house an entire plastic lawn chair.

⬐ Noumenon72

At my job, we extruded plastic sheets, so we had dies which were 84 inches wide with an opening of 0.020 inches. It's quite a challenge to get the plastic to spread evenly from the barrel opening all across that width like a river delta. There are two flexible lips inside, you can supply more heat to individual die zones to make it meltier, and at the very edges you stretch the plastic out a little so that several inches of the die end up contributing to one inch of the finished sheet.

⬐ countzeroasl

The other option that is commonly used is using a mold with an internal manifold to heat the plastic, which is injected through heated tips or pneumatic/hydraulic valve gates. This shortens the space on the part such that the flow length of the plastic will be sufficient to fill the part, where with a single gate, it may not due to the part thickness and thermodynamic freeze.

⬐ ggambetta

This looks super fun! What's the viability of doing this at an artisanal scale in the kitchen? E.g carving a mold out of something, melting plastic in the hob, and pouring it into the mold?

I remember as a kid my dad once got some sort of plastic that you made by mixing two liquids (they were very liquid, so not epoxy), and I made molds of things out of putty (or clay?) and then "copied" them with the plastic. Any idea of what this room-temperature binary-plastic could be?

⬐ Doxin

Casting epoxy is a thing that exists, but the chemicals involved should most definitely be kept away from the skin until after they have cured.

⬐ ggambetta

So it's "casting epoxy", thank you :)

⬐ le-mark

I've had a project in mind for several years now that would be ideal for injection molding plastic parts, the only problem is a $10-20k in mold creation would take a long time to pay off and become profitable for a niche product (lego related for example). Does anyone have experience doing this?

⬐ starky

How complicated/large is the part? $10-$20k is a pretty expensive mold these days even for production tools (from China).

If you only need 2000 or so for a simple part to start, and are willing to pay 2-3X the part price, Protolabs is a good option.

Another low tooling cost, low volume option that might be worth looking into is cast urethane.

⬐ klausnrooster

I was told just last week a production mold for an automotive bumper costs about a million $. Mind you, that is a big mold with hot runners, multiple gates, and I think some moving parts. I can't confirm that figure but I do know a small mold for a 4x12 inch rectangular plaque, 3 mm thick, costs $10k. Uh, but that is not from China.

⬐ starky

Depending on how large and complex the mold is, the price does go up a lot.

However, for a 2-up mold for something the size of a game controller, with a 0.5mil shot life, with maybe a slider or two, you are looking at $8-10k at many of the molders I've worked with.

⬐ Gibbon1

You can I think get simple short run molds made for under $5k. Molds made out of CNC milled aluminum instead of hard steel.

⬐ countzeroasl

Possible, depending on how simple the molds are. Typically, this is easier if you have a MUD unit (Master Unit Die) where you can just mill inserts, rather than the whole injection mold (ejection, injection, clamp plates, etc...)

⬐ sporkologist

Make sure you take care of patent issues first—if you're making something that someone else has patented, they can make you stop producing them and/or sue for legal fees. Consult with a patent atty. first if you haven't done so yet. Having said that, epoxy tooling is another lower-cost option besides aluminum.

⬐ wtracy

You might want to test the market first with 3d printed parts. There's a little cottage industry making 3d printed accessories for Lego.

⬐ gonzo

Yes, based on an idea my son had in 2010 (when he was 12), we built a “LEGO compatible” iPhone case.

https://www.smallworks.com/

⬐ catherd

I run a contract manufacturing service in China. We mostly work with US companies bringing new products to market. I'm a little uncertain what you're asking, but my email is in my profile. In general, I can say that individuals trying to start anything hardware related almost universally run into funding problems before they finish (or their idea was just not what the market wanted).

My usual recommendation to people trying to start something hardware related is to do as much as you can in the beginning to make "sales", with sales being defined as whatever you can get that proves someone would actually pay you money for your widget. Prove you have a market before you pay for expensive tooling. That process can vary, but crowdfunding is one example.

Some rough rules of thumb if all you are interested in is cash outlay:

need 2 parts: 3D print or CNC

need 10 parts: silicone mold or CNC

need 200+ parts: injection mold

If lead time to first part, part uniformity, or uncertainty about design changes are factors that might also swing you toward or away from injection molding.

For injection mold tools, assuming the part has a normal level of complexity:

2cm cube: ~$3k, 5 weeks to first shot

15cm x 5cm x 2cm: ~$4k, 5 weeks to first shot

25cm x 15cm x 5cm: ~$8k 8 weeks to first shot

First shot means the first time the tool is tested to make samples. Generally there is a sample approval and testing process you have to go through before any remaining tweaks are made + the final mold texture or polish is added. I find the total time has more to do with how organized and diligent the client is in responding, but assuming nobody drags their feet we generally can be production ready in another 2 weeks or so.

We only work with production tooling (hard steel, lasts a long time). From checking around, if you use aluminum tooling or other "cheap" fast turn prototyping stuff the price doesn't seem to be any less, and in many cases is more. Tooling made in America is usually significantly more... maybe 1.3 - 3x more.

⬐ countzeroasl

As an engineering manager that does these types of projects for a living, I would be happy to chat with anyone who is interested in the actual process, design/manufacturing issues, or rough costs/timeline of this type of project.

⬐ countzeroasl

I am an engineering manager for a plant that does contract manufacturing and specializes in injection molding. I'm happy to answer any questions someone might have about this process, plants that utilize it, or design/manufacturing limitations of it.

⬐ saagarjha

> Likely the device you're watching this on has injection molded parts; you should be able to find ejector pin witness marks and parting lines.

I'm not seeing these on my MacBook. Is that because the parts are not injection molded, or is it because these features have been sanded off or done in a clever way so that it's not easily visible?

⬐ NickNameNick

The body of your MacBook is cnc machined, and bead-blast finished. There may be some markings from the original casting, but they'll be on the inside. All the ejector pin marks on the keyboard keys should be on the inside.

⬐ xyzzy_plugh

On top of that, Apple has some of _the_ most advanced manufacturing technology on the planet. They're continuously a couple years ahead of everyone else for anything similar to their product line, especially around molding processes. If a new, better process hits the market, Apple often snaps them up.

The original unibody aluminum Apple TV remote is a masterpiece.

A lifetime ago, we were working with Foxconn and a colleague managed to sneak onto an Apple floor and take a look at some of their tools -- he was gobsmacked at what they were capable of. The stuff of industrial design engineers' dreams.

⬐ Animats

That's a great talk and animation.

Amusingly, the cheap plastic resin chair shown prominently in the video probably isn't injection-molded. Those are usually formed from a flat sheet.

⬐ naikrovek

He literally shows tooling marks from the injection molding process on the chair...

⬐ Animats

Yes, that one's not from a sheet; it just looks similar to the cheaper ones that are.

⬐ rdiddly

The visuals are good enough to watch this without sound... Always a high benchmark for visual aids.

⬐ trumped

didnt injection molding startup the industrial revolution?

⬐ onesun

No, the steam engine started the industrial revolution.

⬐ None

None

⬐ None

None

⬐ kennywinker

It’s 2018 - ceeating a product from new plastic is probably morally indefensible.

This guy has open source plans for garage-scale plastic recycling machines. If you’re interested in alternatives to new plastic from china https://preciousplastic.com

⬐ Noumenon72

I operated a line like this for seven years before becoming a programmer, except that we extruded continuous paper-thin sheets of plastic for people to print signs on. That was a more skilled process, I guess; injection molders I talked to often had one person monitoring multiple machines.

My plant was in Wisconsin but wasn't heated during the winter when the lines were running. Melting plastic takes so much heat that we were the main electricity consumer in my town.

Because there isn't a check ring in place while the screw is turning, plastic is always trying to slip backwards over the flights of the screw. You have not just heater bands around the barrel, but also cooling water, which makes the plastic less melty so the flights can push it forward without slipping back. The more recycled material you use, generally the cooler you need the barrel because those little flakes melt faster and slip more than virgin pellets.

The many challenges of fighting reality to get your plastic to come out correctly mixed and without bubbles build a lot more character than similar paying jobs like driving a forklift. Facing the same problems repeatedly helped me develop the quick-access note system I still use for debugging and syntax. I wouldn't be half the programmer I am without the life skills from manufacturing. The only problem with being a line operator was that most permanently solvable problems have been engineered out already, so being clever and organized about solving things didn't produce nearly as much value for the plastic factory as it does now that I'm a programmer.

⬐ aidos

My uncle was one of the main mechanics on the big machines NZ’s largest plastic moulding plant.

Even though he’s never done software before, we’ve had lots of interesting discussions about debugging because the process is the same. It’s just that my machines of choice are abstract and his are large, physical and dangerous.

⬐ nameisu

how did you become a programmer? school?

⬐ klausnrooster

I'd like to hear more about your quick-access note system.

⬐ anitil

I'll second that!

⬐ Noumenon72

Just posted. https://news.ycombinator.com/item?id=17389157

Glad at least two people will see it.

⬐ anitil

Oh thank you - everything I was hoping for and more.

⬐ Noumenon72

In the plastic factory, which had zero wireless access because it had metal walls and was basically a Faraday cage, I kept paper notes in my shirt pocket. At first I just wrote down stuff as I learned it: "when the plastic pellets won't feed do this. Here are tips for feeding the trim grinder. Here's what this alarm code means."

The amount of helpful stuff grew fast and I had to keep erasing my notebook and reorganizing it to find things. Settings were organized by machine number, defects by symptom, job changes as a checklist, alarm responses as a flowchart. (You only had 3 minutes before your line would shut down when the 'out-of-pellets' alarm went off, so you had to consider only solutions that might work).

The machine produces a half-ton of plastic every hour so my lookups had to get more and more efficient. Every second you spend looking stuff up means more plastic you have to pick up and throw in the scrap box. I switched to a Word document I could print out and bring with me. I used Word's four levels of headings and the "Generate Table of Contents" feature so I could find the exact page with my issue in seconds. I kept the most important six pages folded up in my front pocket for immediate access. Things like the stacking table ceasing to lower so that the plastic would jam up within minutes.

Every day when you make plastic you fail and waste money, it's very challenging. The consequences are much more tangible than in programming -- orders don't get on trucks, people have to roll up hundreds of pounds of plastic off the floor, the line goes down and you have to spend an hour sweating to get it back up again. So every day I fixed my notebook so that day's timewasters would have been solved faster. Write down how to fix things without calling maintenance, record the solution that worked and not the five that didn't, add a step to a checklist.

So what this did that carries over to programming is it makes you start using your notes as an extension of your memory. There were fixes I wouldn't use for months but could instantly access by the situation (even though I didn't have Ctrl+F). Because of the speed of the lookup, I wouldn't even bother remembering these things at all, which gave me more working memory.

Now I have 280,000 words of notes about programming, but it's not like college note-taking where you'd have to skim pages and pages to find what you need. There's a Python.docx, Concurrency.docx, Testing.docx. It's all organized by headers like "Design patterns", "refactoring conditionals", "String.format expression syntax". That way if I can't remember exactly what I wrote to Ctrl+F, I can still get there very fast -- and see all the other related notes beside it.

They're all on AutoHotKeys so that I can just Ctrl+Alt+D to open "debugging.docx" and search "ConcurrentModificationException" and see exactly what the typical errors I make are that cause this exception and how I solved them last time.

In the end, just like I was able to move to any line in the factory and run it as familiarly as if I had been there for months, I can move from writing a context manager in Python to doing conditional inserts in SQL and recover all the expertise I ever had in under a minute. It's great at my job which is full stack from Bash to Javascript.

The same approach helped me revitalize our support wiki. Walls of text became "if this, click to expand. If that, go to page X". Related issues got stored together so you can go up the hierarchy a level if one approach fails and try others. Information got moved to right when you need it instead of buried on some other page.

I feel like people who use Confluence and text notes to expand their quick-access memory like this are kind of "digital-ready" -- it's like our brain is expandable with an SD card slot that others don't have. Good notes let you crystallize a bit of knowledge every day so you have more room to learn something new the next day.

⬐ anitil

I've tried and tried to do something like this, but it always ends up as a poorly maintained wiki or similar. Maybe the key is that they are living documents for you rather than a write-only sink.

Great stuff

⬐ Noumenon72

Yes, every time I go to it I'm like "Did that section help me find the answer right away, or could it be better?" Then summarize more. Or reorganize, pull out a subtopic that's gotten too big, move things together that are related.

⬐ klausnrooster

Thanks for that great exposition. I tried a similar approach in a TiddlyWiki but when it got larger it was slow and required more and more fiddling. Then as an exercise in how to implement tagging using SQLite and TCL (then Python 2.7, then REBOL, then Python 3.5), a made a command-line thing that I've relied on for about 8 years now (REBOL FTW). I carry it around on a USB stick. Thought of porting it in a way I could use it from my phone but I'll never get around to it - I'm not a developer in the sense you guys are so it would take me months. As a further exercise I cloned that tool in an MS-Access form. I use that version at work. I put everything in it and it has been a huge help - I agree with your SD card slot analogy. Coincidentally I work at a compounder of plastic pellets for automotive use. We mold for testing tensile, etc, so I can appreciate what you were up against. I may steal from you and partition my tools topically (separate tables).

⬐ Noumenon72

Android uses SQLite so you're partway there. The USB stick is a good idea because sometimes I read an article about Python at home and have been emailing it to work.

This video https://www.youtube.com/watch?v=RMjtmsr3CqA was a series of revelations as to how injection molding works.