When your build platform isn’t large enough to print a part in one piece or when you’re working on assemblies, it’s necessary to bond multiple components together. There are a variety of different products and techniques for doing so and in this post, you’ll find a direct comparison for 4 of the most popular methods.
We’ll go over the most popular adhesives and also introduce both chemical and thermal welding techniques that don’t require any additional materials. At the end, there will be a direct comparison of the strength for the different bonding techniques so that you can confidently decide which is best suited for your project.
Techniques in this post work especially well with interlocking components like puzzle piece mechanisms that increase the surface area for adhesives and provide a physical bond. You can learn how to add interlocking components to any of your models using the free software, Blender.
Each of the adhesives listed below were tested using tensile bars. Full bars were printed as controls and compared to bars that were split in half and joined using various techniques. Tensile testers work by increasingly applying force to a bar and an extensometer mounted to the part itself measures elongation. For the purpose of testing various adhesive techniques, we’re most interested in the maximum tensile strength which measures the force at which components break.
Cyanoacrylate Based Superglues
Among the most popular and easiest to use 3D printing adhesives is superglue containing Cyanoacrylate. These glues have low viscosity and dry incredibly quickly (in seconds to minutes) which makes them especially well suited for quickly bonding components together.
The short drying time of Cyanoacrylate based glues can be a disadvantage for some as it makes it challenging to precisely align parts. Special solvents are required to dissolve cured cyanoacrylate glues so it can be important to get this right on the first try. Cyanoacrylate is especially well suited for gluing your fingers together and gloves are a must.
Suitable with: PLA, ABS, SLA Resin
Unsuitable with: Nylon, PETG, TPU
Tensile Strength (complete part): 3903 PSI
Tensile Strength (halved part w/ Cyanoacrylate): 783 PSI
Gorilla Glue is a polyurethane based epoxy that has a much slower drying time and greater elasticity compared to super glue. This is well suited for applications where a highly rigid bond is undesirable or greater drying time is needed to precisely align parts.
Gorilla Glue expands while drying so it’s important not to overuse it. Excess material can be sanded or cut away after drying though does have an opaque off-white finish that can be difficult to hide.
Especially suitable for: TPU (Gorilla Glue’s elasticity and urethane base provide an exceptional bond)
Suitable for: PLA, ABS, SLA Resin, PETG
Tensile Strength (complete part): 9218 PSI
Tensile Strength (halved part w/ Gorilla Glue): 2076 PSI
Resin welding is among the most exciting techniques as it allows for exceptionally high bond strength similar to that of a complete part when done correctly. Resin welding involves using uncured SLA resin at the bond of your part and hardening it with a UV laser. Afterwards, using a UV cure chamber is good practice to ensure that the resin has solidified entirely. This technique has the advantage of allowing for a seamless surface finish as excess resin can be sanded away.
Safety glasses are a must as UV light can be highly damaging to the eyes. It’s important to note that UV light is invisible and the violet color seen when using a UV laser is from just a small portion of light in the visible spectrum.
Suitable for: SLA Resin
Unsuitable for: FDM plastics (technically, this will work but other adhesives are superior)
Tensile Strength (complete part): 8436 PSI
Tensile Strength (halved part w/ Resin Weld): 4193 PSI
Filament welding is another exciting technique that uses pre-processed FDM filament to bond multiple components of a part. A small strand of FDM filament is bound in a rotary tool and used to create a friction weld at the boundary of a part.
If possible, it’s best practice to sandwich the ends of your part between the rotating filament such that molten filament fully forms between the two parts. Otherwise, bond the parts with a cyanoacrylate based glue first and then use Filament Welding to improve strength at the seam. This also has the advantage of allowing for clean and near seamless surface finishes.
Unlike the Resin Welding technique which forms both a chemical and mechanical bond, parts that are bonded using filament welding will be significantly weaker than a single complete part. Filament Welding creates a purely mechanical bond that doesn’t doesn’t benefit from the strength of long and continuous strands of material.
Suitable For: All FDM Materials
Unsuitable For: SLA Resins
Tensile Strength (complete part): 3903 PSI
Tensile Strength (halved part w/ Filament Weld): 376 PSI
Parts printed as a single component will always be significantly stronger than those bonded with epoxies or other welding techniques. Much of the strength of 3D printing comes from long and continuous strands of material and these are broken when a part is split. The exception to this is chemical welding with SLA resins where the resin at the bond can chemically cross-link with adjacent parts. Still, the bond strength is only half that of the original part.
To see these techniques in action, check out Formlabs’ post on creating parts larger than your printer’s build volume where one of their engineers adhered multiple components to make a full-size R2D2.