One disadvantage of FDM parts are that they are usually weaker than injection molded ones because of how the extruded lines have to fuse together rather than just being moulded in one piece.

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3D prints are great for those one off things. In the past I’ve printed replacement parts for a swimming pool, a g-clamp I needed for a one off task, I’ve fixed a rotary clothes line…

My most recent print was an AirTag holder for my wallet. Aviator who make the wallet wanted €35 for their one. Mine cost me probably 5p in plastic 😂

Advantages of FDM vs injection moulding :

• Cheap equipment costs
• No need to make moulds/adjust the machine for different parts
• Very complex structures possible
• In some case material usage can be optimized
• Comparatively small machinery

Disadvantages of FDM vs injection moulding :

• Super slow (a 1x1x1cm dice might take in the order of 1h to print, while the injection moulding machine can spit out a whole lot of them in a minute or so)
• Print times scale with the cube of the size. A 20x20x20cm print will take in the order of one week to complete.
• Small details are not so pretty
• Rough surface
• Parts might need some post-processing (e.g. removing supports)
• Filament (e.g. PLA, ~€20/kg) is much more expensive than pellets (e.g. PLA, ~€1-5/kg) used for injection molding
• Many materials that are available for inejction moulding are not available for FDM
• Only very limited foam materials available
• FDM parts are much less robust than injection moulded ones, especially along the layer lines
• FDM has more issues with exact dimensional accuracy. It’s much easier to e.g. make a perfect ABS part with injection moulding than with FDM. In injection moulding you don’t have to worry about warping and stuff like that.

TLDR:

FDM is great when you want to make very few pieces, the part is neither too small (<1cm) or too large (>15cm), you don’t need perfect mechanical properties and it’s fine that the finished part looks kinda rough.

Or if you can only have one device because you have limited space. Then it defaults to the 3D printer due to its versatility.

Wow, there are some really in depth and great replies thank you everyone.

Right now for my use cases some of the advantages I see are:

1. Rapid Prototyping
2. Using FDM where injection molding would struggle, examples include articulating toys.
3. Low volume production runs

Does anyone have a multi-filament printer? I am not quite sure how this would compare with injection molding, but I am able to get relatively fine color changes on a single part. See picture of an earring that I am prototyping.

Advantage of 3D printing is that you can virtually print anything you want and have it available to use within minutes to a few hours without leaving your place or order something to be delivered. The down sides are that it usually needs to be designed with 3D printing in mind. It’s also a bit weaker due to the layer adhesion, it’s surface finish is not as precise (resin is another story though) Also with a decentralized manufacture there is no QC possible so if you design something and put it up online the quality will vary depending on who prints it and on what. Finally, there’s a problem with IP, when you manufacture a mold and inject then sell, you can charge per item, with 3 D print you may pay for the STL but the. There are no restrictions on how many copies you can make. So it’s a challenge to adapt pricing of designs if you’re looking to make a profit from it.

When it comes to mass manufacturing, inject molding is the undisputed king. 3D print times are measured in hours per part, injection molding is measured in seconds or even milliseconds per part. Injection molded parts also have a smoother surface finish and are generally stronger than 3D prints.

Setting up an injection molding run is expensive and time consuming. You have to design molds (requires specialized design skills) and have them machined (costly in time and materials). Setting up a 3D print just requires slicing a model and sending to the printer, which can be as little as a few minutes.

3D printing can also create geometries that are impossible in injection molded parts. With injection molding, there are quite a few specific design requirements to allow the plastic to flow into the mold, cool, and be ejected. With 3D printing, there fewer restrictions on the design.

So, if you want a huge number of something it’s definitely worth it to spend the up front time and money to do injection molding. If you are doing smaller quantities, need to get started fast, or require geometries that are impossible with injection molds, then 3D printing may be a better option.

Sure its good for “rapid” prototyping but the cost and time advantage dont scale. If I need exactly 1 of something FDM will almost always cost less and take less time. If I need 100-1000-10,000 of something FDM will cost far more upfront for printers than the cost of molds and doing a large injection run.

So it really comes down to what you need and want. For testing, and developing something FDM is fantastic, but once you need to scale, traditional manufacturing will win every single time by a mile!

Weaker, not smooth without postprocessing, not food friendly, and of course much slower.