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3D Printed Soft Plastic Injection Molds Part 1 – The Basics

3D Printed Soft Plastic Injection Molds Part 1 - The Basics 1

I made this awesome 3d printed injection mold, and I've shot hundreds of baits through it in the past few weeks. I'll show you how you can take your lure designs and turn them into injection mold in this multi-part series. Let's get rolling! 

Let's go

In part one of this series, we're going to cover the 3d printers, the resins, and we're going to touch briefly on how you print these molds. In part 2, we're going to go much deeper into the mold design to show you some of the tips and tricks I've learned during this process. I've spent the past few months printing tons and tons of injection molds. I have made tons and tons of mistakes while doing that. The pile of errors I have is much more extensive than the accumulation of successes over the past few weeks. I've hit a stride of good repeatable results in 3d printed injection molds, and we're here to cover the first part of that, which is what you need to get started.  

3d Mold

Resin 3D Printer

First, of course, you're going to need a resin 3d printer. People have made injection molds from FDM printers, but none of the materials are designed to withstand hot plastisol heat. It concerns me when I see people injecting PLA, PetG or ABS molds because their heat deflection temperature and melting temperature are below the standard temperatures. You inject plastisol at around 320 degrees. They all have a heat deflection temperature of approximately 230. Heat deflection temperature is just a fancy way of saying when the material gets this hot, and there's some pressure against it; it starts to deform or deflect. That's why I strongly recommend 3d resin printers instead. Not only are you going to get way better detail and way better quality, but you can also use a resin that has a heat deflection temperature of 385 degrees which is well above the standard temperatures you're going to inject plastisol. 

3d Printer

So what printer to get? I have an Elegoo Saturn, which you've seen in some of my other videos. It is considered a mid-sized consumer resin 3d printer. A couple of things to keep in mind when you're looking at resin 3d printers; some of the main differences generally revolve around the size of the print volume and the type of screen. My Saturn is considered mid-size. It has a print volume of 192X120X200mm/7.55inX4.72inX7.87in. I can fit just about any mold I want. A few customers come to me with giant molds that I can't print, but it covers most of the basics, six-inch and below molds.

3d Printer

I also have a Creality LD-002H. You can certainly print molds with that. You're going to be somewhat limited in width, but if you want to do single cavity molds or you have small crappie-sized lures, it will work for you. The Saturn retails for $499 on amazon. If you see any higher prices, that's people just trying to scalp them right now because the demand is high and the supply is low. So hold out for that $495 – $499 price range before you buy one. The Creality printer I have, I want to say, is right around $200. It's a superb starter printer too, and again they're both mono screens, which will get you faster print time. The resin we'll be talking about requires longer exposure. You'll want to make sure you're getting a mono screen to prolong the life of your 3d printer. The other thing you can look at on the 3d printer is the large size 3d printers like the Peopoly Phenom and The Phenom XL. I wouldn't strongly suggest if it's your first 3d printer, you avoid those printers. I think the Saturn and the Epax X10 are the sizes that make a lot of sense, even for your first printer. If you go too small, you're going to be disappointed. If you go too big, I think you're going to run into many printing problems that come with the printer's size. The Saturn and the Epax are both in that sweet spot where it's going to be big enough to do just about everything you want to do, and it's not going to cause you too many headaches. The longer that screen is on exposing your resin, the shorter its life will be, so you want to get a mono 3d printer. 


The Resin

Next, let's talk about the resin. The only resin I can recommend is Siraya Tech Sculpt Resin. Again, its heat deflection temperature is roughly 380-ish degrees which should be well above what you need to shoot your plastisol. It is a tricky resin to print with. It took me a long time to dial in the settings on my printer, so know that you're going to have to spend a little more time with your printer in getting it dialed correctly.

Heat Enclosure

The major downside with the sculpt resin is it does require a heated enclosure or some way to heat the resin to get it up to about 30 degrees celsius before it prints consistently. I had all kinds of problems before putting it into my enclosure to keep that temperature both high and stable. I'll have a link in the description to my enclosure video. It's going to add about $150 to your cost. I'll have another video and blog coming up shortly where I look at a different method of keeping the resin heated. I'm waiting for a part to come in for that build, and we're going to put that on my Creality printer and see if I can get that going with sculpt.

Cleaning Molds

Also, a sculpt is a kind of a bear to clean. I use acetone sculpt to clean it. You don't want to have it immersed in alcohol or acetone or anything for longer than about 30 seconds when you're going through the cleaning process. It tends to break down and get extra gloopy. With acetone, I can dip it in there. It's pretty intense, and it evaporates quickly. I can drop it in there, shake it in there for 30 seconds, pull it out, and it's going to start drying and evaporating immediately. At this point, you might be like saying, “dude, that's way too complicated.” It's not that difficult if you have been pouring soft plastic lures. If you've been doing hard plastic lures with resins, this is all kind of in the same ballpark. It's just a lot of different terminology, so don't let it scare you away.  


Printing Molds

Let's talk about the actual process of printing these molds. One of the things that tripped me up when I got into 3d resin printing is that most people who use them use them to print miniatures and models and little sculptures. They have most of the tips and tricks you'll find are around those types of prints, and one of the things you'll see almost right off the bat is don't print on the build plate and hollow out your prints. Yes, you can print a mold hollow, but you're significantly weakening the structure. Remember, when we inject mold these, we're going to smash these together in a vise with some nuts and bolts to get them to close properly.

3d Mold with Bolts

If you make it hollow, you're adding a ton of flex in there. Not to mention, it makes the actual printing process a lot more complicated. You have to add holes throughout the mold to drain all of the resin that will get trapped inside. If you don't, it's just way way too complicated. It's a little bit more resin to print it solid, but you're going to get a much more structurally sound and far better mold if you do print it solid. We're talking like two or three dollars worth of resin extra. 

Build Plate

Build Plates

Next up, you'll hear people say never print directly on the build plates, and you know, if I have a miniature with many delicate parts, absolutely don't print on the build plate, but I have a large solid chunk of resin. If I try to position that off the build plate and put support structure all around it, I'm asking for a print failure. That mold will be very heavy, and those support structures from your slicing software are not really made to hold that large heavy of a chunk. What you want to do is, you want to put it flat on the build plate but not flat on its back on the widest portion. You want to print it flat either on the side edge or the best way to do it, vertically. Now, printing it vertically is the longest way to do it in terms of print time. It produces the absolute best results with the fewest failures. Once I started printing vertically, I could get away with some crazy stuff like this print I pulled off, which I think has five molds on it on my Saturn. The benefit of doing it that way is that time-wise, it is the same amount of time to print that big giant batch of molds to print one of the tallest molds on that plate. The downside to printing is that your vat cannot hold that much resin, so I got up every three hours to top off the resin vat while printing, which was a little annoying. Don't go that far, but you can print three, four, or five smaller molds at a time in the same amount of time it takes you to print one mold, and that is awesome.

Plate Scrape

One final tip on printing directly to the build plate when you're designing your mold, you'll want to make a chamfer angled edge around all of the sides of the mold. In whatever 3d modeling program you're using, that will help you get it off the build plate later.  

When part two is done, you'll see it in my next blog. In the meantime, check out my other blogs. Take care and tight lines.