Idea for warlock/artificer build

Lv3 Artificer | Battlesmith | Adamadite weapon +1

Lv17 Warlock | Any subclass | Pact weapon to the adamantine and +1 weapon

Also the slasher, bludgeoner, piercer for improved critical.

So possible with the eldritch spite 10d8

What is your Stat spread going to be?  Seems like INT and CHA would compete with each other. 

I don't believe Mystic Arcanum allows for upcasting as it says specifically to pick of a spell of a certain level, but I'll let others rule on that. 

Seems like you're giving up a lot of Warlock power by not choosing a level 6, 7, 8, and 9th level spell that you can cast, there's a lot of options there and probably most are better than a high level smite (like locking down an entire battlefield). 

With just taking battlesmith to lvl 11 you'll get 10 cast of a 5d8(~11/22.5 dmg per target depending on save) 60' Cone that ignores friendly fire(AS a bonus action from your Steel Defender or as a free action from your Homunculus, versus at level 20 you getting 4 6d8 (27 dmg) smites per short rest.  You'll also have better gear, and minions using pipes of haunting, wands of web, etc, all while not even counting your 2 attacks:

Bonus Actions: 

You can add Steel defender attacks (1d8 +6) or Shining Smites (3d6 x3, 2d6x4)

Free actions:

Homunculus providing crowd control(Pipes of Haunting, wand of magic missile, or conjure barrage)

Base attacks (can add 2d6 once per round)

All of this is at Battlesmith 11.... 

I'm also confused as to why you need Artificer, as you're not indicating anything about the build that uses it.  And why all 3 feats instead of just a favored damage type?

If you go with Armorer, you can dump strength and dex, wear plate and shield, and then go all warlock for the rest. Youd have an ac of 20 and throw in mirror image and youre nigh impossible to hit with an attack roll. Youd also have a choice of 3 built in weapons for your armor. A lightning gun, brass knuckles that stun, or a wrecking ball on a chain. Good fun.

Dumping str and dex means you could max int and cha and con and be a good artificer and a good warlock.