GunLab has some excellent photos of the steps involved in making AR-18 upper and lower receivers. The first article shows the stages of stamping the lower, while the second shows the same for the upper.
The AR-18 is a design intended to be mass produced by countries lacking the more advanced aluminum-working techniques then state-of-the-art. Its basic operating mechanism, which is essentially the short-stroke piston of an SVT-40 mated to the bolt of an AR-15, has been adapted by several more recent designs, including the G36 and Magpul Masada.
GunLab is an excellent blog, run out of the same shop that hosts ForgottenWeapons. Anyone interested in the production of firearms should find a place in their browser bookmarks for it!