How to Weld and Repair Plastic Parts Using a 3D Print Pen

This instructable aims to show how a 3D print pen can be used to weld and repair broken plastic parts in consumer products. We will show you the required materials, steps, technique and the extra finishing steps to mend small holes and cracks in (compatible) plastic parts in everyday appliances.

• Broken plastic part to weld/repair
• 3D Pen: for this specific instruction a "Intelligent 3D Pen III" was used, but most 'non-toy' 3D print pen should work.
• Printing filament: any type of plastic supported by the used pen, try to find matching or comparable/compatible materials to the broken part for best results.
• Scissors or wire cutter (Optional)
• Acetone (Optional)
• Sand paper (Optional)



WARNING

Using a 3D pen will release potentially toxic fumes that can be unpleasant and dangerous, even with plastics considered 'safe' such as PLA. Make sure to attempt this method in a well ventilated area, outside or with a fume extractor. A filtering mask (N95 or similar) can be useful as well.

It's important to know exactly where to weld the plastic parts together. Having a clear line to follow with your pen is useful and will make the procedure easier and less prone to error. To do this, place the parts in the desired position and think of a line that touches both parts and in which extruded materials could be placed to keep them together.

For repairs where you have to build up layers (e.g. repairing a chip at the edge of a part), orient the part so that you can build up layers easily. Using gravity to hold a layer down as you are laying down another on top (like in a standard 3D printer) can help smooth out the repair process.

It’s important to choose which type to plastic to use. If the broken part in question is made from a thermoplastic that is supported by your pen (and can be easily obtained), that would be your best option. Otherwise, choose a material that is easy available, but the same results are not guaranteed.

Each pen is different, but a general set of instructions can be outlined:

• Set the recommended temperature as said by the manufacturer
• Set the slowest extrusion rate, this will help make more precise lines and allow the plastics extruded from the pen and the part itself to weld together
• Load the filament as explained by your product instructions and make sure that the filament is extruding correctly*
• Practice handling and making lines and shapes with your pen in preparation for the repair itself

*: The extruded filament straight from the tip of the pen should be consistent and unbroken, have the consistency similar to honey, and should not be bubbling

• Start extruding plastic at the end of the line that needs to be soldered
• Push the tip of the pen into the part such that the plastic starts to melt from the tip and new material is placed in the newly formed gap
• Slowly move towards the other side of the line, going in the direction of your wrist
• Once the end of the line is reached, move slowly in the opposite direction placing material in possible empty spots
• When the starting point is again reached stop extruding material, but do not move the pen immediately from the part and let the remaining hot plastic ooze out and cool down for a few seconds before pulling away from the part
• Wait for the repaired section to cool down completely -- this should not take more than a couple of minutes for small pieces.

For repairing larger gaps where the extruded filament would not be supported by the part, much like how a 'regular' 3D printer builds layers, you should be building up layers of filament between the gap, with slow movement to allow the hot extruded plastic to cool and retain its shape. As was previously mentioned, try to position the part so that you can use gravity to hold the extruded filament in place as it cools down, and don't be afraid to extrude more than necessary as it will be removed in the next steps.

On the end of the soldered line there will probably be some strings of material that did not adhere correctly to the part, using a pair of scissors or a wire cutter carefully cut these protrusions off.

The procedure is not super simple and could require a bit to get used to. It is the important to test the strength of the just soldered part.

• Try to scrape off the newly extruded material, if it comes off then it needs to be redone and the pen tip needs to go deeper into the plastic.
• Try pulling apart the joined parts, if they come off the soldering needs to be redone and more material needs to be extruded, while also making sure the pen was deep enough to melt the plastics together.

Useful information:

• ABS was found to be stronger and also slightly easier to use then PLA, but it requires greater attention for toxic fumes and slower movements.
• A general rule of thumb is to use more material and go deeper than you think you need to.
• If two ABS parts are being soldered together using ABS filament, some acetone can be used to smooth and blend everything together. Refer to other tutorials on how to use acetone for this kind of uses.

To obtain extra strength and have a more aesthetically pleasing part more steps can be performed. For these new equipment is needed, in particular:

• Soldering iron with flat surface tip, chisel or bezel
• Sandpaper, any grit between 100 and 400 is fine
• Acetone (optional), will only work for some plastics such as ABS

Using the soldering iron excess material can be melted, either removing it completely or using it to fill smaller holes by flattening down to follow the original surface.

After this, using sandpaper the surface can be smoothed to obtain a finish as close as possible to the original.

Optionally, a small amount of acetone can be placed on a paper towel and by slowly rubbing it on thew surface a more polished finish can be obtained. A more detailed explanation of this process can be found in this Instructible.

These steps can increase the strength of the welding dramatically and are so very recommended.

Enjoy your newly repaired part!