What's the difference between:
- ロボット を つくって いる かいしゃ に はいりました。 and
- ロボット を つくる かいしゃ に はいりました。
What's the difference between:
I assume you already know the basics of the progressive form (-ている form).
If you joined an existing company that was already actively manufacturing or developing robots, you can use both sentences. Sentence 1 sounds slightly more conversational and Sentence 2 sounds slightly more bookish, but the difference is small.
However, if you entered a (new) company that will develop robots in the future, the progressive form is inappropriate, so you must use Sentence 2.
ロボットを作る会社に入りました would be the more natural of the two. 作る会社 means "a company that makes...", whereas 作っている会社 means "a company that is making...", which sounds a bit less natural. It implies that the company is making a robot right now at this very instant, rather than it generally producing robots currently.
A verb like 開発する(かいはつする) "To cause development" would sound more natural in the ~ている form here. 開発している会社 "a company that is developing robots". This would indicate that they haven't made robots yet, but are, in this instant, developing them.
作っている会社 means "a company that is making...", which sounds a bit less natural. It implies that the company is making a robot right now at this very instant
-- でも「〇〇はXXを作っている会社です。」ってフツーに言いますし、ググってもいっぱいヒットしますよね。また、この質問でも、 japanese.stackexchange.com/q/105054/9831 「ワンさんが働いている病院」で、不自然ではないですよね。