Unlike injection molding where materials are melted and pressed into form, hard milling is the process of shaping objects while in their hardened form. Hard milling is most often used in the tool and die industry for cutting materials such as H13, P20, and S7.
What makes hard milling possible is the hard milling machine's ability to make small cuts very rapidly. Various cutting tools are fitted onto the hard milling machine to produce the product through a computer controlled machining process.
The hard milling process is considered to be a more efficient process than EDM and jig grinding. Shops can achieve much higher rates of productivity by using hard milling. Sipco Molding Technologies for example has cut their manufacturing time in half by eliminating the roughing, grinding, and polishing process through hard milling. Faster manufacturing time means quicker turnaround time and lower production costs.
Before advances in hard milling machinery, hard milling was much less practical than EDM. However, since the 1990's hard milling is much more practical for most jobs with the exception of those with difficult to mill features like internal corners and deep grooves. Additional benefits of the hard milling process are that it yields parts with improved finishes and tighter tolerance.
In short, hard milling is considered to be the new and improved form of milling technology because it removes steel faster, eliminates polishing time while producing a smoother surface finish, eliminates the cost of electrode material, and drastically reduces set up time while improving repeatability.