Like all artisans in Dwarf Fortress, skilled armorsmiths make armor more quickly, and of a higher quality, than unskilled dwarves. The higher the quality of armor, the more damage it can block, which helps to minimize sparring injuries and casualties in combat. A legendary+5 armorsmith is potentially the most valuable dwarf any fortress could hope to have. This makes armorsmith skill a very popular choice in starting builds.
 Training armorsmiths
To train an armorsmith to legendary (or legendary+5, better still), you must have him or her make hundreds of pieces of armor. Use copper for this (or bronze, if you have ample cassiterite): save your precious steel or iron for after the training is done (though you may opt to make a few steel suits early on for your soldiers to wear).
These hundreds of pieces of armor will rapidly clutter the forge, greatly slowing down the smithy's progress. To keep up with a high-skill armorsmith, you must employ several full-time haulers to clear out the shop: either item haulers, to drag the pieces to nearby armor stockpiles, or refuse haulers, to drag the items to a nearby dump. (Dumping, however, requires periodically redesignating the area over the forge ( - - ) in order to mark its contents for dumping.) Setting up several forges and having the smithy move from one to the next when they get cluttered works well in concert with multiple haulers. You can also employ a spare metalsmith of any sort to keep destroying and rebuilding the forges to clear them out.
Making one piece of armor grants 30 experience points, regardless of how many metal bars it takes to create. Therefore, you should train your armorsmiths on pieces of armor that take only one bar to create (helms, caps, shields, bucklers, gauntlets, boots, and leggings). If you wish to recover the metal used to make these items (via melting), you should make chain leggings, which have a 50% recovery rate, higher than that of other armor items. Care should be taken not to melt masterpiece leggings your smith might create during training, as this can cause him or her a VERY bad thought. Consider making a separate stockpile for such high quality items.
 Trading off armor
You may also opt to trade the armor to merchants. In order to determine what type of armor would be best for export, take the "Value / (Weight x Bars Used)" value in the below table, and multiply it by the percentage offered in any trade agreements you have active. Produce the type of armor with the highest result. The reasoning behind this is the weight limit of goods traders can carry when they leave (plus hauling to depot will be a little faster).
|Armor||Value / (Weight x Bars Used)|
In addition to training an armorsmith the hard way, you can try to boost your chances of getting a legendary armorsmith via a strange mood by having your peasants and other dwarves without "moodable" skills construct a single item of armor. This will give them dabbling skill in armorsmithing, and will cause them to become legendary+1 armorsmiths should they have a fey or secretive mood (but not a possession). A moody armorsmith will always create some form of artifact armor, often of incredible value. (It is unclear what the armor multiplier is for "artifact quality" armor, but it is at least masterpiece, x2.0.