Designing Products With Injection Molding in Mind

3D printing is a technique we’ve all been using for ages at home, or via Shapeways, but if you are designing a product, 3D printing will only get you so far. It’s crude, slow, expensive, and has lots of limitations. While it’s great for the prototyping stage, ultimately products manufactured in volume will be manufactured using another method, and most likely it will be injection molding. Knowing how to design a part for injection molding means you can start prototyping with 3D printing, confident that you’ll be able to move to a mold without major changes to the design.

The 2017 Hackaday Prize includes a $30,000 prize for Best Product as we seek products that not only show a great idea, but are designed for manufacturing and have thought through what it takes to get them into the hands of the users. Some of the entries seem to be keenly aware of the challenges associated with moving from prototyping to production. Here are some examples of best practices when prototyping with future injection molding in mind.

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Hackaday Links: March 19, 2017

This is from the Daily Fail, but a working Apple I is going up on the auction block. It’s expected to bring in $317,693 USD. In other news, we’re going to be at the Vintage Computer Festival East at the end of the month. There is usually an Apple I there.

The most popular crowdfunding campaign of the month is Lego tape. It’s an adhesive-backed tape with studs on the top, allowing you to clip Lego pieces into place. How easy would this be to create at home? It’s really just a silicon mold and some 3M stickytape. Anyone up for a home casting challenge?

You guys know the Hackaday Overlords have a Design Lab, right? What’s a Design Lab? It’s a place filled with tools where we allow residents to come in for free, build stuff, give them training, and let them keep all their IP. It’s like a hardware accelerator, but focused on Open Source hardware. It is our gift to the community and we ask nothing in return. But that’s not important right now. We’re doing shots.

2017 will be the first year Maker Faire will have three flagship faires. New York is a given, as is the Bay Area. and A few weeks ago, Chicago grabbed the third flagship faire. If you’ve already bought tickets and scheduled your trip, terrible news: the Chicago Maker Faire has been postponed until late fall.

Flip clocks are cool. What’s a flip clock? The clock in Groundhog Day, or a bunch of flaps, gears, and a synchronous motor that displays the time. You know what’s not cool about flip clocks? They’re usually stuffed in horrible 70s plastic enclosures painted Harvest Gold or Avacado. [bentanme] found a flip clock and stuffed it in a glass jar. It’s kept in place by a few 3D printed parts that ingeniously keep the clock from moving around while still allowing you to see the gears. Neat.

Tools of the Trade — Injection Molding

Having finished the Tools of the Trade series on circuit board assembly, let’s look at some of the common methods for doing enclosures. First, and possibly the most common, is injection molding. This is the process of taking hot plastic, squirting it through a small hole and into a cavity, letting it cool, and then removing the hardened plastic formed in the shape of the cavity.

The machine itself has three major parts; the hopper, the screw, and the mold. The hopper is where the plastic pellets are dumped in. These pellets are tiny flecks of plastic, and if the product is to be colored there will be colorant pellets added at some ratio. The hopper will also usually have a dehumidifier attached to it to remove as much water from the pellets as possible. Water screws up the process because it vaporizes and creates little air bubbles.

Next the plastic flecks go into one end of the screw. The screw’s job is to turn slowly, forcing the plastic into ever smaller channels as it goes through a heating element, mixing the melted plastic with the colorant and getting consistent coloring, temperature, and ever increasing pressure. By the time the plastic is coming out the other end of the screw, and with the assistance of a hydraulic jack, it can be at hundreds of tons of pressure.

Finally, the plastic enters the mold, where it flows through channels into the empty cavity, and allowed to sit briefly to cool.  The mold then separates and ejector pins push the part out of the cavity.

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Hackaday Retro Edition: A New Commodore 64 Case

Some time in the 80s, the plastic injection molds for the Commodore 64C, the Commodore 128, and the Plus/4 were shipped from somewhere in Asia to the great Commodore Mother Brain in West Chester, Pennsylvania. These molds had already produced a million or two cases, but there were some issues with production – too much waste, or something like that. A mechanical engineer took a look at the molds, sent out some recommendations, and moved the 2500 pound molds to a corner of the building.

For some time after a gray day in April, 1994 these molds sat in a West Chester, Pennsylvania warehouse until they were sold off. They made their way to a plastics manufacturer around Dallas, Texas where they sat for twenty years. All things must pass, sometimes several times, and this plastics manufacturer closed down, contacted an auctioneer, and began to sell off some of their equipment.

The hero of our story, [Dallas Moore], owns a small business, buying and selling everything from Barbie dolls to antiques. He found an ad for an auction at a plastics manufacturing plant in the newspaper, and figuring he could find something interesting, headed out to the auction preview.

The auctioneer at this liquidation sale asked [Dallas] what he did, and mentioned there was something pretty cool tucked away in a warehouse full of hardened steel molds. Something about molds for old computers. These were the molds for the Commodore 64C, Commodore 128, and the Commodore Plus/4. A literal crucible of computing history, stacked on a pallet and up for sale.

The auctioneer said one of his friends was interested in the molds, and thought they would make a neat coffee table. Something about this struck [Dallas] the wrong way and for the entire drive home he thought about someone taking history and turning it in to a piece of furniture. He decided to buy these molds and lugged the three 2500 pound pieces of hardened steel to his shop. Not wanting to let a good piece of history go to waste, he contacted another plastics manufacturer, planned a run of a thousand or so Commodore 64C cases in red, white, and blue. [Dallas] is funding the whole production run through Kickstarter.

To me, this is one of the greatest retrocomputing successes in recent memory. There will always be someone putting SD cards in old computers, getting them on the Internet (and especially pointed towards our retro edition), and cloning complete systems in FPGAs. This, though, is a clear example of someone recognizing the historical importance of several thousand pounds of steel, realizing there’s a market out there, and doing the leg work to remanufacture these pieces of history.

I put in my $45 for a red one, and I tipped off [Bil Herd], designer of the C128 and Plus/4, to this Kickstarter. He’s been talking with [Dallas], there I’m sure he’ll chime in on the comments with some retellings of Commodore battle stories.

If it arrives in time, I’ll be bringing my limited-edition red 64C case to the Vintage Computer Festival in Wall, NJ April 17-19. That’s a plug for the event. If you’re in the area, you should come.

EDIT: [Dallas] has a different story of where the molds came from.

Turning a 3D Printer into an Injection Molding Machine

Injection molding machines are able to form very detailed plastic parts, simply by squirting plastic into a mold. 3D printers squirt plastic. Why no one thought of using a 3D printer extruder to push plastic into a mold until now is something we’ll never know.

[bfk] has been working on a way to produce very small, very detailed parts for a while now, and realized the extruder of a 3D printer serves most of the functions of an injection molding machine. It takes plastic, melts it, and forces it through an orifice. Whether that plastic goes to a build platform or into a mold is beside the point; but with a simple silicone mold, anyone can replicate extremely small parts with a tool every hackerspace already has.

The tools required are RTV rubber, which is the most popular mold material around. Aside from that, it’s just silicone lubricant, dowels and LEGO to make sprues, and of course something to make a mold from. Once the mold is made, it’s a simple matter of holding the mold up to the nozzle of a printer and extruding a bit of plastic.

The resulting ‘print’ is as detailed as the best prints that will ever come off a resin printer. It’s great for making parts for very small models like [bfk]’s current project, but this technique could be expanded to anything that needs a lot of small plastic parts with tight tolerances.

Video of the process below.

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DIY Newton’s Cradle Uses Parts Designed on a Smart Phone

Injection Molded Parts

As far as physics demonstrations go, the Newton’s Cradle is probably one of the most recognizable. Named after Sir Isaac Newton, the Newton’s Cradle demonstrates the law of conservation of momentum using swinging ball bearings.

[Scorchworks] decided he wanted to build his own Newton’s Cradle. The frame appears to be cut from MDF or particle board and then screwed together. That material is really easy to obtain and also to work with using inexpensive tools. The tricky part was the ball bearings. Most of the time when you see a Newton’s Cradle, the ball bearings have a small hole drilled in the top with an eye hook attached. The string is then attached to the eye hook.

[Scorchworks] decided to do something different. His plan was to make custom injection molded plastic rings that would fit perfectly around the ball bearings. The most interesting thing is that he designed the injection molding plates entirely on his smart phone while at his child’s baseball practice. To do this, [Scorchworks] used his own Android app, ScorchCAD. ScorchCAD is a free clone of OpenSCAD that is designed to run on Android devices. Most of the functionality of OpenSCAD has been implemented in ScorchCAD, though not all functions work yet. You can find a list of all the supported functions on the project’s website or in the Google Play store.

Once the plates were designed within ScorchCAD, [Scorchworks] exported the STL file and then used Meshcam to generate the gcode for his CNC milling machine. Once he had the plates machined, he just placed the ball bearing into the mold and injected the molten plastic around it. The plastic formed a perfectly shaped ring around the bearing with small loops for the string. [Scorchworks] repeated the process several times to get all of the ball bearings finished.

Finally, the bearings were strung up using some fishing line. A Newton’s Cradle is very sensitive to the positioning of the ball bearings. To account for this, [Scorchworks] tied each end of the fishing line to two different screws on top of the cradle. This way, each screw can be tightened or loosened to adjust the position of each ball bearing.

Mini-Molder: Blow Molder Scratch-Built by Single Hacker

 

We caught up with [James Durand] at Maker Faire. He was one of the rare Makers (no mention of selling or future crowd funding) that had a booth at Maker Faire — he was exhibiting a blow molding machine that he built from scratch.

The fabrication process is 100% [James]. Every custom part was designed and milled by him. All of the assembly techniques were his to learn along the way. And we didn’t see anything that isn’t production ready. We’re both impressed and envious.

About three years ago he got the itch to build the mini-molder after learning about the Mold-A-Rama machine — a blow-molding vending machine that was popular a half century ago. A bit of his journey is documented as a molding category on his blog. For the most part it sounds like 1.5 years spent on the CAD design really paid off. He did share one element that required redesign. The initial prototype had a problem with the molds being pushed up when they came together. He tweaked the mechanism to close with a downward motion by flipping the hinge design. This seems to hold everything in place while the drinking fountain chiller and water pump cool the mold and the plastic model within.