The difference is in the reference point of time where the speaker perceives him/herself to be.
I will do my homework by 6 p.m.
The time is sometime before 6pm, and the speaker is simply asserting an intention to do the homework before the stated time.
I will have done my homework by 6 p.m.
The time when this sentence is spoken is the same as before, but the speaker is moving the reference point to some time in the future after 6pm. Effectively s/he is saying that "When we next speak (at sometime after 6pm) to see what my homework status is, I will be able to say that I have done my homework".
The future perfect tense is useful when discussing something else that is to happen. For example
"Let's go to the cinema tonight. The movie starts at 7pm and it takes
half an hour to get there. Can you come?"
"I think so. I will have done my homework by 6pm, which gives us half
an hour to eat something before we need to leave. So yes, let's go."
Native English speakers use going to and will interchangeably in many sentences, even sometimes when the events are (or are not) planned in advance. For example, both "the fireworks will start at 7pm tomorrow" and "the fireworks are going to start at 7pm tomorrow" are perfectly fine, even though it's clear they've been planned well in advance.
So it's tough figuring out these differences in meaning.
I have found a context that makes some of these differences in meaning clear to me. I can't say which other contexts these differences carry over to.
I can't watch the movie with you; I'm going to eat out this evening.
Here, it sounds to me like the dinner was planned in advance.
I can't watch the movie with you; I will eat out this evening.
This sounds rather rude to me, because it doesn't sound like the dinner was planned in advance.
I can't watch the movie with you; I eat out this evening.
Here, the simple present sounds to me like habitual action: the speaker eats out every Monday evening.
I can't watch the movie with you; I'm eating out this evening.
Again, the dinner sounds like it was probably planned in advance.
However, simple present continuous doesn't necessarily mean an event has been planned in advance. Both of the following are perfectly fine, and mean the same thing.
It sounds to me like you really need help; I'll come over right after work.
It sounds to me like you really need help; I'm coming over right after work.
The negative of these constructions behaves more or less like the positive. You don't have to have other plans to use "I'm not going to eat out this evening." You can use it if you just aren't planning to eat out. For example, you could say:
I'll be at home at 8:00 if you want to telephone me then; I'm not going to eat out this evening."
Best Answer
For your example both work because you included the prepositional phrase "In June". Without that phrase, the second sentence gives you no information about the timing of the event, while the first still tells you with certainty that it will happen at some point in the future:
"We will bring out two new models"
vs.
"We are bringing out two new models"
In general future fact sounds very certain, and implies something about the timing without any prepositions. Consider the differences between:
"I will survive" versus "I am surviving". The first sounds reassured, while the second sounds like you're barely surviving.
"I will go on vacation" versus "I am going on vacation". The first is clear that this is something that will happen in the future. The second is unclear, it could mean you are leaving right now.