Robotic Assembly Lines

"I wonder where the pins come from..."

—The Simpsons

In fiction, robotic factory montages are sometimes added to showcase Special Effects or to establish Infinite Supplies so that the viewers can stop wondering, "Where did all that X come from?" Note: These are assembly lines made of robots, not necessarily assembly lines making robots. Also, these are usually done as a fleeting scene to indicate that it is not that important for the plot.

No real life examples, please; Real Life does not have montages.

Examples of Robotic Assembly Lines include:

Anime and Manga

Ghost in the Shell movie begins with a sequence of Mokoto's (technically a cyborg, but since the only part of her which isn't artificial is her brain) robotic body being assembled.

The first Atomic Robo Free Comic Book Day issue has Robo fighting a seemingly endless supply of Mecha-Mooks, and asking if there's a factory or something to no one in particular. Cue Trope with an editor's note that simply says "Yes!"

I Robot: right before the Needle in a Stack of Needles scene in the warehouse - see that page for details.
Surrogates: while we are visiting the morally ambiguous company
Bicentennial Man: The opening credits has this
Terminator uses this several times.
Shows up in Star Wars: Attack of the Clones with the droid army.
- We also get treated to a clone factory, although we don't quite see the Clone Troopers being "built" we do see the various stages of development, followed by their eventually arming. At the end, we see them being gathered for war.
The opening titles of Willy Wonka and The Chocolate Factory show various forms of candy being created on automated assembly lines. Despite the fact that Willy Wonka doesn't use assembly lines.
Small Soldiers begins with a production line of the titular toys being manufactured (including Terminator-style skeletons and Uncanny Valley-ish rubber "skins").
In X-Men: The Last Stand, this is used for the making of the serum.

GURPS: Ultra-tech has rules for setting these up; specifically focusing on the product being made so that you can get along with the game.

Makes a good level for Super Mario Bros..
Xenogears had that famous scene where you walk into a huge, fully-automated save-point factory, revealing where all those floating symbols came from.
The intro movie to the old computer game Hoyle Word Games.
Portal 2 has a few levels set in the automated production lines making the turrets.
- Some of which happen to devolve into sentient talkative AIs.
Some of the games in the Rhythm Heaven franchise have games that involve building robots on a assembly line, like "Fillbots" from the second game and "Screwbot Factory" from the third game.