
Plastic Injection Molding (2015) [video] - jstimpfle
https://www.youtube.com/watch?v=RMjtmsr3CqA
======
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.

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

~~~
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.

~~~
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.

------
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](https://www.youtube.com/watch?v=2NzUm7UEEIY)

1\.
[https://www.youtube.com/channel/UCWBkudOTaVbvkCBc0pyZFMA](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.

------
Judgmentality
This is by far my favorite video of his:

[https://www.youtube.com/watch?v=hUhisi2FBuw](https://www.youtube.com/watch?v=hUhisi2FBuw)

~~~
jcims
Here's the How It's Made version -
[https://www.youtube.com/watch?v=V7Y0zAzoggY](https://www.youtube.com/watch?v=V7Y0zAzoggY)

Aluminum baseball bats have a similar manufacturing method -
[https://www.youtube.com/watch?v=didmRLz4vfU](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...](https://www.amazon.com/Serendipity-Accidental-Discoveries-Royston-
Roberts/dp/0471602035)

~~~
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](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.

------
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?

~~~
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.

------
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](https://preciousplastic.com)

