Here are some of the CNC features fundamental to many mold machining processes today:

NURBS Interpolation. This technology for interpolating along curves instead of dividing curves into short, straight line segments is still gaining in popularity. Most of the CAM packages for die/mold applications today now have an option for outputting NURBS-formatted part programs. At the same time, more powerful CNCs have allowed CNC manufacturers to add five-axis NURBS capability, as well as NURBS-related features that deliver improved surface finish, smoother motor performance, faster cutting rates and smaller part program size.

Finer command unit. Most CNC systems issue motion and positioning commands to machine axes using a command unit of 1 micron or coarser. Taking advantage of the increase in processing power, some CNCs today offer a command unit of 1 nanometer (0.000001 mm). This control increment is 1,000 times finer, providing for improved accuracy. It also provides for smoother motor performance, which can allow some machines to accelerate faster without increasing the shock to the machine.

Bell-shaped acc/dec. Also called “jerk control” or “S-curve acc/dec,” bell-shaped acc/dec allows a machine tool to accelerate faster than linear acc/dec. It also provides less position error than various acc/dec types including linear and exponential.

Look-ahead. This is a widely used term, with many performance differences separating the way the feature works on low-end versus high-end controls. In general, look-ahead lets the CNC pre-process the program to ensure superior acc/dec control. The number of look-ahead blocks can range from two blocks to hundreds of blocks depending on the CNC. The number of blocks required depends on factors such as the minimum part program execution time and the acc/dec time constant, but 15 blocks of look ahead is probably the minimum acceptable value.

Digital servo control. Digital servo technology has improved significantly, and most CNC manufacturers can now offer a digital servo solution. Advances include faster communications, serial connections between the drive and CNC, and faster and more numerous digital signal processors. These advances have combined to allow CNCs to control the servo loops more tightly and thus control the machine better.