In the hard milling process there are a number of concerns. For example, a build-up of heat during the cutting process can cause premature tool wear, trapped/welded chips,

spindle growth, spindle/cutter vibration and part piece rigidity.
Limiting the length of tool being used is a high priority, so your CAM software must have a method of verifying holder and tool shank safety relative to the geometry at the stage that it is being machined. Some CAM software monitors the tool and holder relative to the finished model, but it needs to be monitored relative to the in-process model.

In order to keep this tool length to a minimum, more mold and die companies are investing in 4- and 5-axis machining centers. This brings in a new set of variables to deal with relative to the rigidity of the setup of the piece, as well as the rigidity of the rotating part of the machine. The ability to shorten the tool as much as physically possible is the main gain in this strategy.

The toolpaths themselves need to have certain capabilities designed into them. Trochoidal motion during roughing passes is of great value in certain circumstances because it keeps a clearance between the tool and side walls during any type of slotting and allows the chips to be evacuated while maintaining a constant load on the cutter. All roughing toolpaths also must be designed to keep a constant chip load during the course of machining.
Roughing and finishing toolpaths should include the ability to output a radial motion in corners to eliminate dual contact of the cutter as it changes directions. Re-machining toolpaths that go back in to finish the corners should be able to analyze any excess stock areas and remove the excess stock, eliminating cutter overload.

The way that the toolpath approaches the workpiece also is a crucial part of the equation of a high quality toolpath. An approach and escape that are normal to the surface being machined allows for a transitional entry from not cutting to entering the full cut.

CAM systems must have the ability to create and edit standard tool databases. This allows for recordkeeping that often gets lost. The tradition of having the data in your head and calling it experience really benefits no one, as that information and the investment is lost if the person moves on or retires. Setting standards as a company and maintaining that information for all to use shortens the learning curve for new employees and eliminates the secrets that go missing when the employee leaves. CNC machining is an exact science and much more manageable than perceived in the past, if we find a way to document our successes.
Templating—or the ability to recreate an existing process to be applied to the next job and the next job after that—has been recognized as an important feature in CAM software whether hard milling or high-speed machining. Even though products don’t always have similar geometries, there is a very similar base level process that is used from the start of cutting to the end.

The need to re-invent that process at the start of each new job is a waste of time and effort. In the mold manufacturing there is more of a standard process than people realize.
The toolpaths created by many of the off-the-shelf, general-purpose CAM systems are not smooth enough or accurate enough to be used for hard milling effectively. The requirements for hard milling cannot be accomplished with toolpath algorithms created 10 to 20 years ago, as their quality is at a lower level. The older algorithms are created on an approximation of the geometry, commonly referred to as triangulation mesh.

That method was designed and implemented in the early nineties to expedite toolpath calculation with less concern about accuracy and purity. The more effective modern algorithm uses the information from the original CAD surfaces/solids to create the toolpaths with no approximation.

Today’s CNC machines require more information to process more effectively whether it’s hard milling or high-speed machining. The output of these points must be mathematically correct, not just randomly added. You must ask that the results be demonstrated for you—not just something on a computer screen.