forging is make something in the forge, in a template. Most commonly used for work done with metal, such as forging a sword.
In the figurative sense, forging is understood as to invent. It's creating false evidence, modeling something that isn't true. As for example in the use of the expression "forge character", which means to appear to be something that is not.
Between the synonyms for the word forge, there is adulterating, forging, manipulating, fabricating, idealizing, creating, plotting, inventing and scheming.
forge one's own death it is when the person pretends to have died, and the reasons and ways to do this are many. There are those who simulate suicide at sea, or in other areas where the disappearance can be hinted at. Depending on the circumstances and motivations, such as for social security or insurance fraud, it is a crime. In Brazil, forging one's own death, except in very specific cases, can be framed as a crime against the heritage, public faith, family, among others, and all the people who contribute to the act also respond criminally.
forge the engine is an expression used among motorsport aficionados and means to replace certain parts of factory by forged elements in order to change the power and noise of the engine, changing the performance of the car.