conjunctions - Differences between "in order to", "so that" and "so as to"?

Are there any differences (general or regional differences) between "in order to", "so that" and "so as to"?

I've seen that they may be interchangeable, but I'm not so sure.

Answer

Those are largely similar; however, from here and here:

• in order to and so as to are more formal and used before verbs like know, seem, understand: ... I asked in order to know....


• so that is less formal - and often reduced to so in informal use. It also is used with modal verbs like can: ... so that I can ...


• so that and in order to need a subject/verb: ... I did this so that I could...

Google Ngrams gives, for American English (red = so that, blue = in order to, orange = so as to):

and for British English:

Doesn't look like there is much of a difference between American and British English in that matter.