what u are talking about is actually called pressure casting, not forging. forging is exactly that, pressing and forging solid billet alloy. The alloy is often heated up to soften it, and even in some instances to almost a molten form (Semi-Solid Forging patented by SSR) to make it easier to forge. Casting under high pressure can create good results, but it still isnt forging, low pressure casting is used in most cases, especially OE, so id imagine it is what is used for the GTS-t wheels. Obviously then there is gravity casting, u really want to stay away from this at all costs lol. Generally forging is only used for the disk, the rim is usually "flow formed" or "rolled" which is where they heat up the barrel(rim), spin and press the shape. and yeh, then obviously there is the CNC machining to finish it off.