Another really important part of Raid Mode. The workbench is used to customize your weapons. You can equip your weapons with parts that help you reload faster, hold more ammo per clip, add element attributes to your shots like fire and lightning, etc. It works similar to the main campaign but it also has some other features such as:

• Destroy Parts : since you can’t unequip parts once attached to the weapon, this is the only way to get rid of the parts.
• Destroy weapon : if what you want is to recover your parts instead and don’t care about your weapon, you can always destroy it to retrieve your parts. Really useful if you messed up, but more expensive than destroying a single part.
• Upgrading Beyond Limits : when you finally get yourself ahold of Lv.100 weapons (which can only be found inside Treasure Chests in missions), you can upgrade its Firepower / Capacity / Fire Rate for ~200,000 Gold each time, with ~5,000 Gold increase per upgrade. There’s a maxuimum of 30 upgrades so think carefully.
  These are the things you can do with the workbench. Not much but what you CAN do is really useful.