We are trying to bake burger buns and we usually play the rounded individual dough on the baking tray and use another baking tray to press it down to flatten it.
Now our hands are so sore after months of doing it. The only reason why we did that in the first place is because our the dough (imagine just a circular ball dough) will expand upwards more than going sideways, making it not wide enough to be a burger bun.
How else can we fix this? Temperature? The way we roll our buns?
Your buns are likely sticking to the bottom of the tray. If they stick, they will expand vertically because they can't expand horizontally. They're stuck.
Dust the trays with semolina flour, rice flour, and/or fine corn meal. You can even lightly dust them with white or rye flour, but the aforementioned flours are preferable.
If you're retarding the buns, consider placing parchment paper on the tray, lightly dusting the parchment with the aforementioned flours, and then panning the buns.
You could also use non-stick Silpats or silicone mats, but that's expensive if you have to buy a lot of them.
I don't know the composition of your dough, how you are shaping them, how much you are working the dough, etc. These could contribute the problem as well. Buns are usually enriched dough (they have butter, milk, etc.) made with low-protein AP flour. They don't need a lot of gluten development or shaping. If you develop the dough too much, it'll hold something close to the original shape (in this case, of a ball of dough instead of a disc).
Flatten the individual balls of dough for each bun into a disk prior to letting them do their final proof on the baking sheet. Usually you would just do this with your hand, a rolling pin, or with the bottom of a floured flat bottomed glass or something similar.
Joe Pastry has a nice blog entry with photos showing the process for hamburger and hot dog buns, using a rolling pin.
Here is a link to a fairly ubiquitous video that shows the process in detail for hand shaping mini-buns (as for sliders) rather than full sized buns. The idea is the same.
