Easy CNC Heat Sealer

Create complicated film structures using your 3D printer and a piece of sand paper. A fun, useful, one-day project.

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Heat seals are everywhere - they do everything from hold a bag of chips closed to strengthening tents used for arctic missions. Chances are you've ripped one apart in the last 24 hours. Historically, the typical hobbyist has been limited to straight-line, manual heat seals. I modified an old 3D printer to create strong and highly customized heat seal profiles for projects such as food packaging, soft robotics, and art pieces.

This was a fun and easy project that you can do right now if you have a 3D printer.

1) Sand the tip of an old nozzle so that it is flat and parallel to the XY motion plane
2) Install the modified nozzle and put a piece of rubber sheet on your print bed
3) Level the print bed, generate the G-code, and start sealing!

Note: If there is interest from the community I would be happy to document the creation process in more detail.

A consulting project needed a way to play around with different heat seal patterns for a soft, fluid heat exchanger made of a polyolefin film.

The conventional way to do this would be to machine a heat seal tool out of steel, heat it, and then adjust stamping pressure, temperature, and time to achieve the desired seal. Whether done as a DIY project, or sent to impulse heat sealing tool manufacturer, the iterative cycle time would be far too long.

It would probably work fine in this case to simply waterjet a stamp from steel. In theory, one could even 3D-print a stamp from a temperature-tolerant material and coat it with a conductive material for resistive heating. Either of those options are well-suited for creating a large number of duplicate heat seals, but are still far too slow if you want to try, say, 10 different patterns in a single afternoon.

A CNC heat sealer makes sense here. A fine, heated tip on the end of a motion gantry would allow for arbitrary patterns to be drawn as heat seals.

Since the requirements of this heat seal project were simple (3mm wide seal, in a forgiving material) I had the idea to repurpose an old filament-based 3D printer into a CNC heat sealer.

The basic premise is as follows: We already have a positioning system capable of moving at different speeds (the printer gantry) and a closed-loop heating device (the printer hot-end). Therefore we only need to do three things:

1 - Replace the heated nozzle with a heated indenter

2 - Add a mechanically compliant material to the print bed so that we are not crashing the gantry in the Z axis when applying heat-seal force

3 - Create a G-code program to turn the desired heat seal pattern into reality

I machined a few different indenters to replace the nozzle before realizing that the nozzle could be modified by sanding the end with sandpaper until the flat sanded region was a circle with a diameter of 3 millimeters. This is very hacky, but it worked well. In theory, this means that the only strictly required hardware change to turn any FFF 3d printer into a CNC heat sealer is to sand down an old nozzle that you have laying around! If you were extremely time pressed, a short, M6 screw with a good head profile would probably work as well.

Next, I added a a sheet of 2mm heat resistant silicone rubber to the print bed. This allows the nozzle to overdrive into the plane of the heat seal without stalling the Z motor. This works fine, but has a notable downside: the material being heat sealed will concave down into the rubber, resulting in trapped stresses and dimensional inaccuracy. The correct way to do this is to add compliance in the Z axis to the nozzle, and rigidly hold the film to be sealed against a stiff surface (e.g. the bare print bed. That said, this improper approach worked fine for a proof of concept, and the sticky rubber had the added benefit of helping the film to lay flat during the process. Since I shortened the nozzle by about 1 mm by sanding it, the existing Z-calibration of the printer would give 1mm of interference into the 2mm thick silicone. This worked well - but if it hadn’t, I could have used the four bed-leveling screws on the printer to lower or raise the bed. It is very forgiving!

The last step is the programming. If the heat seal tool had been some kind of metal wheel on a swivel (like the cutting tool on a vinyl cutter), then the gantry could trace continuous curves without moving in the Z axis. That is not what we have here however, so the movement process will be closer to what is known as “plunge milling” in the world of machining.

In plunge milling, a profile is machined by moving the cutting tool (drill bit, end mill, etc.) such that it is only ever drilling holes of various depths. Imagine cutting a square out of a piece of wood by following the marked lines with a hundred or so individually drilled holes. We can heat seal in the same way, creating the pattern through a sequence of plunge...

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  • 1 × FDM 3D Printer
  • 1 × 300mm x 300 mm Silicone Sheet (1 - 3 mm thick)
  • 1 × Abrasive Tool (sand paper, file, etc.)
  • 1 × Heat Seal Plastic (HDPE, LDPE, Polypro, PET, Nylon, etc.)

  • 1
    Find an old FFF/FDM 3D printer

    The one must-have for this project is some kind of 3 axis gantry. In my case, I used a first-gen Wanhau Duplicator i3 printer from roughly 2015. It was a great little machine, but I have plenty of newer printers now. There are a few different controller types but they all use pretty much the same G-code, with a few well-documented parameters set differently. Between Slic3r, Cura, and Repetier, there is almost always a way to make a gantry trace a path with less than an hour of fiddling. Things are very easy these days.  If your gantry is some other less common system (closed loop actuators, etc.) you are on your own. Turn on the printer and make sure that you can home all the axes successfully. Anything broken must be fixed before you can proceed (with the exception of the heated bed or extruder drive since we won't be using them). If after your test, you can move in all three axes and heat up the nozzle, congratulations, you can make a CNC heat sealer.

    Note: You can also use a nice, functional printer for this project.  Since we are simply replacing the nozzle and adding some rubber to the bed, it should be simple to restore your printer back to printing condition. I happened to have an extra old printer, but that is not the case for everyone. Do what makes most sense for your situation, but remember that a 3D printer is, on average, more useful than a heat sealer. Do not do anything to it that you cannot UNDO!

  • 2
    Remove the old nozzle from the printer's hot end

    Chances are, there is a gunky old nozzle still attached to your printer. Remove it. There are plenty of videos on Youtube that show you exactly how to do this on your specific 3D printer. Do not strip the nozzle's hex profile, and do not twist the nozzle with a wrench without using another tool to support the hot end. You can easily bend your linear guide rods doing this and severely damage your printer/gantry.  Watch the video below, it is probably applicable to most 3D printers. 

  • 3
    Sand a nozzle down to turn it into a heat sealing indenter

    If you wish to use the nozzle you just removed for printing in the future, put it somewhere safe. To continue, you will need a nozzle that you are okay with not being usable for printing again. I had about 10 extra nozzles laying around, but don't worry if you don't have a spare. They are very cheap. In your situation, I would simply use my "good" hot end for this project and order a new one on Amazon. In my experience, most people need to replace their nozzles anyway. If you only have ONE nozzle and cannot get a spare, a screw with an M6 thread and a flat head should work fine as a heat seal indenter (I did not try this but I don't see why it wouldn't work). With a sacrificial nozzle in hand, the modification takes less than a minute: carefully sand down the tip of the nozzle with a piece of sand paper, file, or a rotary tool such that the resulting surface is 2 - 4 mm in diameter. Make effort to not end up with an angled flat on the nozzle...when mounted on the printer, the flat should be parallel to the XY axis motion. Otherwise, one edge of the flattened nozzle will always dig too deep into the film during the sealing process.  The pictures included here show how my nozzle looked after modification.

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