By combining prints with screws, nuts, brass fasteners, and pins, They get a rich ecosystem for creating mechanisms with capabilities beyond what we can print ourselves.
Today I want to share some tips on one of my favorite 3D printing techniques: adding heat-set brass inserts. As someone who install this by hand on plastic parts for years, I think many guides overlook some process details that are important for consistent results. brass nipple manufacturers
In our case of 3D printing, we use threaded inserts to add strong filaments to 3D prints. The plastics we usually press on are not very durable, so plastic threads do not last very long. This is especially the case for parts that are frequently assembled and disassembled. Threaded inserts provide a solution to this problem. The most commonly used material for threaded inserts copper, but you can also find it in other materials such as aluminum and stainless steel. Aluminum liners are useful due to their light weight, while stainless steel liners have better corrosion resistance. Copper is the cheapest option and has good properties for most applications.
Softening the surrounding material
Heat adjustable liners work by softening the surrounding material during installation. Once installed, removing the heat source causes this molten plastic to resolidify around the knurled elements and hold it in place. Let’s think about this process in terms of heat transfer. The installation holes are smaller than the Inserts themselves (they are very small), so we cannot install the Inserts by hand. Instead, we first heat the insert and then transfer that heat to the surrounding material, which causes the hole to deform to accommodate the larger shape of the insert.
Over time, heat transfer from the inserted tool, through the insert to contact the surface, and finally out of our 3D printed part, where it disappears. The longer the time spent embedding the part, the more time the heat has to travel into the part where it can deform the surrounding areas of the part. In mass production, this process is done by machine. However, in our case, install manually, so have to consider our time. Finally, don’t forget that when installing the liner, will move the melted plastic to make room for the thermal liner. That extruded plastic has to go somewhere and usually ends up at the bottom of the container.
Of course, copper inserts also have disadvantages: Increased component costs (for inserts) compared to tapping or printing screw holes directly into the plastic.
You need to be able to 3D print the exact holes for the insert to fit well. An alternative is to print a small hole and drill after printing. This will always give you the correct hole diameter, but it is an extra step.
I strongly advise against using a vanilla soldering iron tip for the following reason. Most of these tips are tapered. If use the conical tip of the soldering iron, there is a risk that the tip of the soldering iron will get stuck inside. Remember: metal expands when heated and contracts when cooled.
When install a metal insert into a printed part, conduct heat from the insert into the part, which cools the heated insert a bit and also shrinks the tip of the iron. As a result, when try to pull the iron end, the stakes are raised! I imagine this scenario is similar to the Chinese finger trap. All that said, I don’t have this problem often when I’ve used a vanilla soldering iron tip for this process, but 1 in 5 broken copies is enough to make me find the extra $10 to get a proper tip.
Holes for the inserts
When it comes to measuring the holes for the inserts, I recommend that you follow the dimension information that comes with the insert data sheets. For your quick reference, here is a quick overview of links to some of my favorite inserts and their hole size recommendations.
To accommodate the extruded material, I suggest increasing the hole depth by approximately 50% of the entry length. This change ensures that the extruded plastic has somewhere to go and doesn’t fill the hole where the contents should . Some guides recommend adding a slight taper to the opening portion. This is a nice feature that allows the liners to seat themselves in the hole before installing them using heat. Some brass inserts are tapered, which has the same effect as sitting in an untapered opening. Adding this tapered feature (or purchasing slightly more expensive tapered inserts) isn’t necessary, but it makes the installation process easier.
With the design ready, I recommend using the Slicer 3D printer settings first, specifically the perimeter layer. Slic3r defaults to two perimeter layers for cavity elements. I would recommend increasing this value to at least 4 circuits for two reasons.
First, we want to make sure that our installed liner still “grips” the material after installation. The installed liner will push the material out during installation, so adding layers will improve the chances of not melting during installation.
Second, adding more peripheral layers also reduces the size of the external depressions that form on the part when the brass inserts are close to the outside of the part. These depressions are called zinc marks and are actually a common problem that also occurs with injection molded parts. Sink marks occur because the part shrinks as it cools. I have found that adding circuits reduces this effect. I can’t say for sure why this is, but my best guess is that adding more solid material reduces the free space inside the part, making it harder to mesh the internal geometry. -o in shape.
What are the advantages of using threaded inserts?
The use of copper thread inserts has several advantages compared to other threading methods:
Wires are stronger and last longer than wires glued to plastic.
Stronger threads provide higher clamping forces than threaded plastic threads. They allow us to work on small threads without any problems.
Their design and printing is easier than embedded matrices. The latter requires nut-shaped pockets that create overhangs. Threaded inserts take up less space than a regular nut in a nut trap/pocket.
Make sure your soldering iron has reached its full set temperature before using it to install the pads. If we try to install the liner while the iron is still rising to its set point, the process will take longer and all the heat from the iron will spend more time on our side causing it to crack.
Next, when inserting the brass insert into the hole, apply heat to the insert. Let the weight of the soldering iron tool alone exert the gentle force needed to push the brass insert into place. Gravity has to do most of the work here. This process takes about 10-15 seconds. Continue heating until your liner is about 90% into your part.
Okay, here’s where we deviated from convention. After about 90% of the part is inserted, take the iron and quickly flip the part onto a flat, non-hot surface and gently press the part until it is flush with the material. It used a small piece of sheet metal for this step. Wait about 6-10 more seconds for the part to cool and you’re done! I will call this maneuver the plate pressing technique.
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