Feb. 17, 2015 | By Alec

While 3D printing technology is great for producing plastic toys and accessories, the typical desktop FDM 3D printer isn’t great for creating very small and detailed objects. But if you happen to want to replicate something that is small and detailed, your 3D printer does offer another option. By following this handy but extensive tutorial by tinkerer and inventor Bruce Kinsey (also known by his screenname of bfk), you can relatively easily turn your 3D printer into an injection molding machine.

You might know injection molding technology as the previous generation’s plastic manufacturer, the technology that 3D printers are replacing. Typically, these are gigantic machines capable of producing lots of products at once using metal molds and high-pressure extruders. While your 3D printer is not capable of producing the same force as a typical injection molding machine, it does function on the same principle of extruding molten plastic.

Bruce has been working on a method for using that function to produce small and detailed components by holding a mold against his 3D printer’s extrusion head, and has been quite successful. Now this doesn't revolve around STL files or print beds, it can be a surprisingly effective way of making small parts – below you can see Bruce’s method in action to produce a Civil War-era replica of a cannon carriage. The resulting products (not exactly prints, are they?) is just as detailed as anything you can make with high-quality 3D printers, depending on the quality of the mold you use.

Bruce himself using a MakerBot 3D printer as an injection molding machine.

In a nutshell, all you need is a 3D printer that can extrude PLA (ABS might work, but it requires a higher melting temperature) and a few parts to make a mold out of RTV Rubber (Room temerpature Vulcanizing Rubber). This is one of the most popular mold making materials currently available, and inexpensive and easy to use.

Bruce made his mold in an Ikea candlestick holder.

There’s just one downside, and that’s that making a mold to begin with can be a bit complicated at first. For a full list of necessary equipment to make one, as well as a tutorial to actually do it, go to Bruce’s Instructables page here. But beware: making a mold takes quite a lot of time, and there’s also a high level of what Bruce calls ‘iffy results’ or unpredictable mistakes that can’t quite be explained. But if you pull through, you’ve got yourself an excellent manufacturing tool. In Bruce’s words, "Excellent results are possible, but patience is an absolute requirement."

Should you be successful, you’ve now got your hands on a two-part injection molding die. "We're going to use that same process to make a plastic part on your 3D printer, using the mold you just made and your printer's extruder," Bruce explains. "I don't know if this can be called "injection molding", so I'll just call it "injection printing" instead. Maybe he term will stick."

In a nutshell, the process is this: heat up the PLA to whatever temperature you typically use (225 degrees Celsius is common), and place the mold under the extruder, aligning the printer's nozzle up to the hole on the top of the mold. Press it against each other as good as you can, as this somehow seems to determine the quality of the ‘print’.

The finished gun carriage.

Filling the mold obviously depends on the size of the cavity, so this can take a few attempts to time properly. And Bruce argues that it's usually better to overfill the mold than underfill it, so try it out. Then it's a matter of being patient to let the plastic set (you can hold it under running cold water to speed up that process). "When it's cool, pull the part out of your mold and rejoice, knowing you have exponentially improved the capability of your printer from this moment on," Bruce explains.

That is basically all there is to it; it seems deceptively simple, and it is. You’ll probably ruin a few molds before you get it right, but once you do you’ve opened up a whole new avenue of creative options. Have fun with it!



Posted in 3D Printing Applications


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