Infill Injection Experiment Makes Stronger Parts

February 25, 2025 by Donald Papp 28 Comments

[JanTec Engineering] was fascinated by the idea of using a 3D printer’s hot end to inject voids and channels in the infill with molten plastic, leading to stronger prints without the need to insert hardware or anything else. Inspiration came from two similar ideas: z-pinning which creates hollow vertical channels that act as reinforcements when filled with molten plastic by the hot end, and VoxelFill (patented by AIM3D) which does the same, but with cavities that are not uniform for better strength in different directions. Craving details? You can read the paper on z-pinning, and watch VoxelFill in (simulated) action or browse the VoxelFill patent.

With a prominent disclaimer that his independent experiments are not a copy of VoxelFill nor are they performing or implying patent infringement, [JanTec] goes on to use a lot of custom G-code (and suffers many messy failures) to perform some experiments and share what he learned.

Using an airbrush nozzle as a nozzle extension gains about 4 mm of extra reach.

One big finding is that one can’t simply have an empty cylinder inside the print and expect to fill it all up in one go. Molten plastic begins to cool immediately after leaving a 3D printer’s nozzle, and won’t make it very far down a deep hole before it cools and hardens. One needs to fill a cavity periodically rather than all in one go. And it’s better to fill it from the bottom-up rather than from the top-down.

He got better performance by modifying his 3D printer’s hot end with an airbrush nozzle, which gave about 4 mm of extra length to work with. This extra long nozzle could reach down further into cavities, and fill them from the bottom-up for better results. Performing the infill injection at higher temperatures helped fill the cavities more fully, as well.

Another thing learned is that dumping a lot of molten plastic into a 3D print risks deforming the print because the injected infill brings a lot of heat with it. This can be mitigated by printing the object with more perimeters and a denser infill so that there’s more mass to deal with the added heat, but it’s still a bit of a trouble point.

[JanTec] put his testing hardware to use and found that parts with infill injection were noticeably more impact resistant than without. But when it came to stiffness, an infill injected part resisted bending only a little better than a part without, probably because the test part is very short and the filled cavities can’t really shine in that configuration.

These are just preliminary results, but got him thinking there are maybe there are possibilities with injecting materials other than the one being used to print the object itself. Would a part resist bending more if it were infill injected with carbon-fibre filament? We hope he does some follow-up experiments; we’d love to see the results.

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Calculating The True Per Part Cost For Injection Molding Vs 3D Printing

October 14, 2024 by Maya Posch 45 Comments

At what point does it make sense to 3D print a part compared to opting for injection molding? The short answer is “it depends.” The medium-sized answer is, “it depends on some back-of-the-envelope calculations specific to your project.” That is what [Slant 3D} proposes in a recent video that you can view below. The executive summary is that injection molding is great for when you want to churn out lots of the same parts, but you have to amortize the mold(s), cover shipping and storage, and find a way to deal with unsold inventory. In a hypothetical scenario in the video, a simple plastic widget may appear to cost just 10 cents vs 70 cents for the 3D printed part, but with all intermediate steps added in, the injection molded widget is suddenly over twice as expensive.

In the even longer answer to the question, you would have to account for the flexibility of the 3D printing pipeline, as it can be used on-demand and in print farms across the globe, which opens up the possibility of reducing shipping and storage costs to almost nothing. On the other hand, once you have enough demand for an item (e.g., millions of copies), it becomes potentially significantly cheaper than 3D printing again. Ultimately, it really depends on what the customer’s needs are, what kind of volumes they are looking at, the type of product, and a thousand other questions.

For low-volume prototyping and production, 3D printing is generally the winner, but at what point in ramping up production does switching to an injection molded plastic part start making sense? This does obviously not even account for the physical differences between IM and FDM (or SLA) printed parts, which may also have repercussions when switching. Clearly, this is not a question you want to flunk when it concerns a business that you are running. And of course, you should bear in mind that these numbers are put forth by a 3D printing company, so at the scale where molding becomes a reasonabe option, you’ll also want to do your own research.

While people make entire careers out of injection molding, you can do it yourself in small batches. You can even use your 3D printer in the process. If you try injection molding on your own, or with a professional service, be sure to do your homework and learn what you can to avoid making costly mistakes.

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Multi-Material Printing Enables Low Cost Silicone Prototypes

September 4, 2024 by Tom Nardi 10 Comments

While it’s the ideal choice for mass production, injection molding is simply no good for prototyping. The molds are expensive and time-consuming make, so unless you’ve got the funding to burn tens of thousands of dollars on producing new ones each time you make a tweak to your design, they’re the kind of thing you don’t want to have made until you’re absolutely sure everything is dialed in and ready. So how do you get to that point without breaking the bank?

That’s not always an easy question, but if you’re working with silicone parts, the team at OpenAeros thinks they might have a solution for you. As demonstrated through their OpenRespirator project, the team has developed a method of 3D printing single-use molds suitable for large silicone parts that they’re calling Digital-to-Silicone (D2S).

In the video below, [Aaron] and [Jon] explain that they started off by simply printing injection molds in the traditional style. This worked, but the molds can get quite complex, and the time and effort necessary to design and print them wasn’t a great fit for their iterative development cycle. They wanted to be able to do from design to prototype in a day, not a week.

Eventually they realized that if they printed the mold out of a water-soluble filament, they could simplify its design greatly. They’ve documented the design process in detail, but the short version is that you essentially subtract the 3D model of the design you want to produce from a solid shape in your CAD package, and add a few holes for injecting the silicone. Once the silicone has cured, the mold can be dissolved away in warm water to reveal the finished part.

They then took this concept a step further. Thanks to the multi-material capabilities offered by some of the latest 3D printers, it’s possible to print structures within the mold. Once the silicone is injected, these structures can become part of the finished part. For the OpenRespirator, this lets them add PETG stiffening rings around where the filters to snap into the silicone mask body.

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Injection Molding Using A 3D Printer

June 25, 2024 by Maya Posch 16 Comments

Recently [Stefan] of CNC Kitchen took a gander at using his gaggle of 3D printers to try injection molding (IM). Although the IM process generally requires metal molds and specialized machinery, 3D printers can be used for low-volume IM runs which is enough for limited production runs and prototyping before committing to producing expensive IM molds. In the case of [Stefan], he followed Form Labs’ guidance to produce molds from glass-infused Rigid 10K resin (heat deflection temperature of 218 °C). These molds are very rigid, as the ceramic-like noise when [Stefan] taps two together attests to.

Injection molded bolt, with imperfections on the head. (Credit: Stefan, CNC Kitchen)

The actual injection process is where things get more hairy for [Stefan], as he attempts to push the clamped-shut mold against the nozzle of the FDM printer to inject the molten plastic, rather than using an IM press. With PLA at standard extrusion temperature the plastic barely gets into the mold before solidifying, however. Following this, higher temperatures, different materials (PETG, TPU) and high flow-rate extruders are attempted, with varying results.

Many of the struggles would seem to be due to poor mold design, rather than fundamental issues with using an FDM. The Form Labs document details some of the basics, such as opening up the injection gate (to decrease pressure inside the mold), adding air vents to improve flow and so on. Commentators to the video with professional experience point out many of these issues as well, along with the benefits of preheating the mold.

With the caveat that most of the challenge is in making a good mold, we’ve even injection molding done with nothing more exotic than a hot glue gun. If you’ve got a friend, or a long enough lever, you can even inject the plastic by hand.

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These Keycaps Are 100% Recycled Plastic

March 20, 2024 by Kristina Panos 4 Comments

Artisan keycaps are generally meant to replace your Escape key, though they can be used anywhere you like (as long as they fit, of course). Keycap maker [tellybelly] of jankycaps has been experimenting with making keycaps out of 100% recycled plastic, and offers an interesting post detailing their development and production process.

What do you do when normal injection molding tooling is out of your budget, and silicone molds simply won’t do? You turn to 3D printing if you can. In this case, [tellybelly] and company found a resin designed to withstand high temperatures.

[tellybelly] was able to design the mold using a plethora of online resources, and even verified the flow using a special program. Although the first two versions worked, they had some flaws. Third time’s the charm, though, and then it was time to sort plastic and fire up the shredder.

After heating up the shreds to 200 °C or so, it was time to start the injecting. This part isn’t exactly a cakewalk — mixing different plastics together can vary the workable temperature range that doesn’t degrade the plastic. Although it sounds like the end, [tellybelly] reports that they spent just as much time here as they did at the drawing board, experimenting with pressure on the mold, various cool-down methods, and how long to wait before opening the mold.

Via reddit

Recreating The Pop Ball

February 24, 2024 by Kristina Panos 14 Comments

Those who were kids in the 80s may remember a sweet little toy called the Pop Ball. A simple rubber hemisphere, this rubber cup could be turned inside out and thrown on the ground, where it would hit and bounce sky high whilst knocking itself right side out. The black ones worked particularly well, and were the first to be banned from [electrosync]’s school along with yo-yos, slap bracelets, and any number of toys that eventually became weaponized by enterprising children.

An industrial Vegemite injection-molded version that only kind of worked.

You can still find Pop Balls today, but they don’t work nearly as well as they did originally because of a lower Shore hardness in the rubber. Naturally, as an adult with futuristic toys at hand, [electrosync] just had to try re-creating the ’80s version. But it wasn’t easy.

They started by studying the patents and anything else they could find. They even managed to get a hold of Peter Fish, the original creator of the Pop Ball, to get some questions answered about the things. According to Peter, the black Pop Ball was made from recycled rubber and worked almost too well. Peter sent [electrosync] an old-stock Pop Ball, which they used to modify their CAD design.

It’s easy to root for [electrosync] throughout this journey, which consists of many failed prints and injection molding attempts. At last, they are able to at least recreate the snap of the modern Pop Ball once they finally found the right filament — the extremely elastic Recreus Filaflex 60A TPU. Of course, it wasn’t all lollipops and rainbows from there, because the filament is notoriously difficult to print with, but [electrosync] made it work. Check it out after the break.

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Lessons Learned: Plastic Injection Molding For Products

October 14, 2023 by Donald Papp 21 Comments

Injection molding is one of the technologies that makes the world go round. But what does it actually look like to go through the whole process to get a part made? [Achim Haug] wrote up a blog post that does a fantastic job of explaining what to expect when getting plastic enclosures injection molded in China.

These air quality monitors required a two-part enclosure.

Injection molding a part requires making a custom mold, which is then used by an injection molding machine in a shop to crank out parts. These are two separate jobs, but in China the typical business model is for a supplier to quote a price for both the mold as well as the part production. [Achim] describes not only what navigating that whole process was like, but also goes into detail on what important lessons were learned and shares important tips.

One of the biggest takeaways is to design the part with injection molding in mind right from the start. That means things like avoiding undercuts and changes in part thickness, as well as thinking about where the inevitable mold line will end up.

[Achim] found that hiring a been-there-done-that mold expert as a consultant to review things was a huge help, and well worth the money. As with any serious engineering undertaking, apparently small features or changes can have an outsized impact on costs, and an expert can recognize and navigate those.

In the end, [Achim] says that getting their air quality monitor enclosures injection molded was a great experience and they are very happy with the results, so long as one is willing to put the work in up front. Once the mold has been made, downstream changes can be very costly to make.

[Achim]’s beginning-to-end overview is bound to be useful to anyone looking to actually navigate the process, and we have a few other resources to point you to if you’re curious to learn more. There are basic design concerns to keep in mind when designing parts to make moving to injection molding easier. Some injection molding techniques have even proven useful for 3D printing, such as using crush ribs to accommodate inserted hardware like bearings. Finally, shadow lines can help give an enclosure a consistent look, while helping to conceal mold lines.