Learn German: Man muss schnell hämmern, ehe das Material hart wird. - One must hammer quickly before the material becomes hard.

Both words mean the same thing and act as temporal subordinating conjunctions. In this sentence, ehe and bevor are completely interchangeable. Ehe is slightly more formal or literary, though it is still commonly used in everyday speech, especially in short, common phrases.

Does ehe always force the verb to the end of the clause?

Yes. Just like bevor, ehe is a subordinating conjunction. This means it introduces a dependent clause, so the conjugated verb (wird) must be pushed to the very end of that clause.

Is it possible to say ... ehe das Material hart ist instead?

Yes, but the nuance shifts. Using wird (from werden, to become) emphasizes the physical process of the material changing from soft to hard. Using ist (from sein, to be) focuses merely on the final static state. Since this sentence is about a time-sensitive physical process, wird sounds much more natural.

Why use man muss instead of giving a direct command?

Using the impersonal pronoun man makes this sound like a general principle, a universal rule of thumb, or a guideline from an instruction manual. A direct command or using du musst would apply only to a specific person in a specific moment.