What do they do with bodies that are facing backwards? Is there a little side channel that flips them around? Nope, they just get tossed back into the hopper to try again. It's effectively random which way they'll be facing when they get picked up, so they'll eventually get through.
I thought that was a nice illustration of keeping things simple and taking advantage of processes you already have, and seems similar in spirit to this.
Just a remark from a Lego nerd: it's attaching arms to bodies, not heads. The neck has a stripe on the front, so that is where the camera looks at to determine which side is facing up.
Maybe there's some defective minifig body with a mechanical flaw that causes it to always get picked up facing backwards, that's spent years being picked up and rejected over and over.
Adapt as needed :)
There's clearly not any air-tight seal. Most of the nubs on the top of pieces only have 3 or 4 points of contact with the piece they're connected to.
I made a mould out of Lego (to make Lego-shaped gummy candies) and with a thin coating of vaseline on the outside, it was indeed water-tight (and silicone-goop-tight too).
They're astonishingly well made for a children's toy.
That said, they've been cutting quality, moving production to China, using cheaper formulation plastic. That's a bad move imnsho. The brand image is quality and people pay for that, if they ever seriously let that go it's going to be game over for them.
Of course, chances are they'll reduce their production costs but maintain the high prices.
Do you have any specific set in mind?
He already has 31052 and 31051 which I think are excellent 3-in-1 sets. Would love to see more like those. They are about AU$80-120 which is a workable birthday/xmas pricepoint.
That's really not that much (1-999 μm). Keep in mind that sub-1mm is micrometer, and 1mm is a huge distance. I'm sure that LEGO bricks have tolerances of single or low double digits of micrometers...
The moulds are permitted a tolerance of up to two micrometres, to ensure the bricks remain connected.
For odd shapes -- clamping both ends then vibrating the grippers (just a little) could split bits.
It's an interesting problem. What percentage is still connected? May be better to pay a slightly higher price for bits are that not connected (distribute the job out to the sellers)