Every fighter develops a favorite weapon that they stick with through every skirmish. Not many though choose to hone their combat potency with the armor they donned for protection. Just like any good weapon, you recognize your tough steely armor can be a lethal tool. One that cannot be disarmed, and can be swung in any number of ways. Using normal armor as a weapon unfortunately quickly accrues heavy damage to it. To combat this degradation, you have also developed a knack for smithing in order to make your armor sturdier and fix it if damaged.

Juggernaut

Starting at 3rd level, heavy armor that is being worn, for you, is considered a martial weapon. When making what would normally be unarmed attacks, while wearing heavy armor, your strikes deal 1d6 bludgeoning damage. Heavy armor as a weapon, is considered a light weapon. Additionally, any special properties of the armor also affect your melee strikes for the purpose of overcoming damage resistance (adamantine, magic enchantment, etc.).

At 13th level, the damage of your armor attacks is increased to 1d8. 

Bonus Proficiency

When you choose this archetype at 3rd level, you gain proficiency with smithing tools. If you already have proficiency, the bonus is doubled

Customized Armor

Beginning at 7th level, you have developed ways to modifier your armor in unique ways.  By spending 1 day with proper tools, you can add one of the following modification to a set of heavy armor. You can only have one modification on a set of armor, and you can spend another week to change which modification it has. This armor is far too personalized after receiving a modification, making it so no other creature can be proficient with it.

Starting at 10 level, you can add 2 modifications per set of armor. Additionally, at 18th level, the modifications on your armor become more potent.  

Dangerous Edges- You add menacing armaments to your armor. You can add half your proficiency bonus rounded down to attack rolls made with the armor. When you make this modification, you can also change the damage type of your armor to piercing, slashing, or bludgeoning. At 18th level, you can also apply half your proficiency bonus rounded down to damage rolls made with your the armor.

Extra Plating- Thickening up the most important portions of your armor, you bolster its defenses. You can increase the armor's AC by +1. At 18th level, this bonus AC is increased to +3.

Trimmed weight- By removing unnecessary or and excessive portions of the armor, you make it lighter and easier to move in. While wearing the armor, your movement speed is increased by 5 ft. At 18th level, the bonus speed is increased to 15 ft.

Barbed- Coating your armor in sharp barbs causing it to hurt assailants. Any creature that makes melee contact with your armor takes equal to your proficiency modifier. At 18th level, your armor with this modification gives you resistance to natural weapons and unarmored attacks.

Barbed

Coating your armor in sharp barbs causing it to hurt assailants. Any creature that makes melee contact with your armor takes equal to your proficiency modifier. At 18th level, your armor with this modification gives you resistance to natural weapons and unarmored attacks.

Dangerous Edges

You add menacing armaments to your armor. You can add half your proficiency bonus rounded down to attack rolls made with the armor. When you make this modification, you can also change the damage type of your armor to piercing, slashing, or bludgeoning. At 18th level, you can also apply half your proficiency bonus rounded down to damage rolls made with your the armor.

Extra Plating

Thickening up the most important portions of your armor, you bolster its defenses. You can increase the armor's AC by +1. At 18th level, this bonus AC is increased to +3.

Trimmed weight

By removing unnecessary or and excessive portions of the armor, you make it lighter and easier to move in. While wearing the armor, your movement speed is increased by 5 ft. At 18th level, the bonus speed is increased to 15 ft.

Armored Expertise

At 10th level, your armor is like a part of you now. You can don and doff it in half the normal time and receive no penalties while swimming or sleeping in your armor. While wearing heavy armor, you no longer have disadvantage on dexterity (stealth) checks while wearing heavy armor.

Walking Armory

Starting at 15th level, you can now integrate a single one-handed weapon or shield into each arm of your heavy armor. To do so, you must spend a day working and succeed on a smithing check with a DC of 10. Regardless of whether you pass or fail, the weapon or shield is irrevocably changed and can never be turned back into original form. The armor and new gear become one, causing any beneficial features of the armor to also apply to weapon attacks made with the integrated weapons, and the shield's AC is permanently added to the armor's, though you can only add one shield. One of the weapons or shield can be magical in nature, but the DC of the smithing check is increased based on the item's rarity. For uncommon the DC is 12, for rare it's 15, for very rare it's 20, and for legendary items, the DC is 25. Just as with mundane items, the magic item will be destroyed if the check fails. Your hands remain free even with the additional gear.

Superior Modifications

At 18th level, expert craftsmanship and potency with armor have made the modifications of your armor even more powerful. The armor modifications from Customized Armor all become more potent. You can also now integrate a magic weapon or shield into both arm slots of your heavy armor.