In today’s competitive moldmaking marketplace, some mold builders believe the industry’s required tolerances and surface finishes can no longer be achieved with electrodes. Instead, they rely on high-speed cutting of 3D surfaces, which not only meets the necessary tolerance and finish requirements, but can also streamline the manufacturing process and positively impact a shop’s bottom line. This includes the use of five-axis machining, for which the mechanical accuracy and dynamics of the machine are critical, along with the appropriate CAD/CAM, cutting tools, toolholders and workholding systems.

The fast machine motions of five-axis machining, which are true to the contour (meaning the cutting tool/axis motion follows the contour described in the CAD/CAM model as close as possible) require precise control of both acceleration and deceleration along a programmed contour. All of this while keeping machining time, surface quality and geometric accuracy in mind . This can be achieved with a CNC control that uses an approach that is optimized for the milling machine and the manufacturing process. That is, the CNC control has features to either automatically smooth the axis movements or allow the operator to manually set tolerance limits.

At the same time, machine operators must be able to influence the milling results with simple parameter changes. Depending on accuracy and surface quality requirements, the path control of the CNC (which ensures that the machine axes movements follow the programmed path within a predefined tolerance window) directly impacts machining time optimization. That means that, based on the operator or final part priorities, the CNC path can influence the cutting time accuracy or surface finish.

Depending on the application, a shop can get away with using an inexpensive, mainstream CNC solution. However, what many engineers or shop owners do not realize is that when it comes to machining the complex mold surfaces of core and cavity inserts with parting lines and other matching surfaces, shop owners need a sophisticated five-axis CNC motion system. A motion system contains a CNC with a servo-controlled drive system connected to the axis motors and a position measuring system for feedback. Without this, the machine will not be able to reproduce the surface described in the CAD/CAM model.

The recommended system is a closed-loop measuring system, which can master these applications and guarantee a “first time fit” of often previously-hardened mold components (56 HRC or more). A closed-loop measuring system uses a rotation encoder to measure the ball screw rotation, which is then compared to the actual axis position measured by a linear encoder (also known as a glass scale), closing the loop and feeding this information back to the CNC.