With this build, your basic goal is to run around punching stuff with your Thunder Pulse attack, giving opponents disadvantage when attacking anyone other than you. By level 6 you'll have an AC of 23, with the ability to boost it to 28 via the Shield spell when needed.

Level 1

• Class: Artificer
• Species: Warforged (Alt: Shifter or Human for Tough Feat)
• Background: Old/Custom or Sage
• Origin Feat: Magic Initiate Wizard (Shield, Booming Blade, True Strike)
• Ability Scores: 15 Con (+2), 15 Int (+1), 14 Dex
• Equipment: Scale Mail (for now, Heavy Armor later), Shield, Mace/Spear etc.
• Tinker’s Magic
• Spells: Thorn Whip, Guidance, Absorb Elements, Cure Wounds, Sanctuary, Jump, Faerie Fire

Level 2

• Replicate Magic Item: Shield +1, Weapon +1

Level 3

• Subclass: Armorer
• Tools of the Trade
• Arcane Armor (Swap to Heavy Armor)
• Armor Model (Guardian)
• Armorer Spells: Magic Missile, Thunderwave

Level 4

• Feat: Heavy Armor Master (18 Con)

Level 5

• Extra Attack
• 2nd level spells: (Mirror Image, Shatter for free), Aid, Enlarge/Reduce, Lesser Restoration, Invisibility, Vortex Warp, Web, Homunculus Servant

Level 6

• Magic Item Tinkerer
• 3rd Magic Item: Armor +1, Swap +1 Shield for Repulsion Shield or Sentinel Shield

This is really when the build comes "online." At this point you should have an AC of 23, with the ability to boost it to 28 using Shield as a Reaction when needed.

Level 7

• Flash of Genius -- This is great for party support, and also to increase your own survivability.

Level 8

• Feat: War Caster (17 Int)

Level 9

• Improved Armorer (4th Magic Item: Mind Sharpener)
• 3rd level spells: (Hypnotic Pattern and Lightning Bolt for free), Catnap, dispel Magic, Fly, Revivify, Haste

And at level 9, it’s time for our next damage report! Ooo this is fun. Ok. Since last check, we’ve got the potential to upcast Aid for 15 more hit points, bringing our total max HP to 99, which is nice, but again, pretty low for a tank. I’m really missing that Tough feat. However, we’ve raised our potential AC to 30, assuming we have Haste Active, and that’s WAY better than any other tank I’ve done so far for 5.5 at this level. In addition, we’ve picked up some nice support and defensive and utility options, added a little damage and even a third attack per round for more taunting ability, putting us in a very pretty place at the moment. Our fights at this level? An Adult White Dragon in their lair, 4 Wyverns, and a DC 15 lvl 5 Fireball.

Damage Report! Vs Boss: 15 DtPR, 49 HPR, Typical: 12 and 53, Fireball: 11 and 55

Level 10

• Magic Item Adept
• 5th Magic Item: Shield +2, Cloak of Protection, (Swap Weapon +1 for Weapon +2 when you can, Headband of Intellect? Spellwrought Tattoo? Luckstone? Winged Boots?)

Level 11

• Spell-Storing Item: Cure Wounds (Alt: Lightning Bolt, Hypnotic Pattern)

Level 12

Feat: Telekinetic or Fey Touched (18 Int)

Level 13

• (Fighter 1) Fighting Style: Defense or Interception/Protection
• Weapon Masteries
• Second Wind

At this point you should have an AC of 26, 3 higher than at level 6 (1 more for the +2 shield, 1 for the Cloak of Protection, and one for fighting style). If you have Haste active, and cast Shield, that's a potential AC of 33.

With your Homonculus and spell storing item from level 11, you've also got some healing power you can pull out when needed.

Level 14 (Artificer 13)

4th level spells: (Fire Shield, Greater Invisibility for free), PYF

Level 15 (Artificer 14)

• Advanced Artifice
• 6th magic item: Armor +2, Ring of Protection, Ioun Stone of Protection

Level 16 (Artificer 15)

• Perfected Armor

Level 17 (Artificer 16)

• Feat: +Int (20)

At this point you should be AC 29 -- that's 3 higher than level 13. You get an additional 1 from the +2 armor, 1 from the Ring of Protection, and 1 from the Ioun Stone of Protection.

With Haste that's AC 31, which you can bump to 36 via Shield.

Using Aid, your HP should be 186 at this point.