Mold makers are increasingly using high-speed cutting. CNC machines can meet the necessary tolerance and finish requirements and streamline processes instead of EDM machines. A good control system is a key to all this.
The machine’s mechanics determine the feed rate, not the CNC. Combining the right plastic injection molding machinery and control with 5-axis simultaneous machining is no longer a pipe dream.
Moldmaking CNC control requirements
Therefore, what do you need to make the most of machining capabilities and deliver precise, well-finished molds? Controls for milling machines and manufacturing processes should first follow an approach that is optimized for each machine. Essentially, the CNC control can automatically smooth axis movements or allow the operator to set tolerances manually.
It is not only necessary to precisely control acceleration and deceleration along a contour but also compensation. The control should adjust the cutter vector in X, Y dynamically, and Z, for example, to compensate for the rotation of a ball-nose end mill. A constant contact point is essential for achieving demanding finishes. Below are six critical areas.
Mold cores or bases are often machined in five-sided configurations without excessive coordination. The CNC must have a spatial plane function that helps the machinist to select the part it will be machined.
The machinist can then lay out each side of the parts in an X-Y-Z plane without changing the CAM program, improving the tolerances between features on each side.
Monitoring of contour deviations
The control directs axis movements according to the 3D surfaces inside each tolerance band consisting of simple line segments. Automatic smoothing of the block transitions should be possible while the tool moves continuously across the surface of the workpiece.
An internal function monitors the contour deviations to control the automatic smoothing. Users can define a maximum contour deviation with this function. Machine parameter values are typically between 0.01 and 0.02 millimeters.
On circular motions, the tolerance also affects the traverse path. An interpolation milling or mill-turn function is especially useful when the core or cavity has cylindrical details.
When moving from X-plus to X-minus and then from X-minus to X-plus after a step over, the CNC control should be capable of ensuring that all machine axes follow the exact path. After reversing the direction of cutting, there must be an exact reproduction of adjacent paths.
Mitigation of vibrations
A machine axis that moves very fast or changes direction on a point, or a cutting tool with a higher rate of feed than allowed, can generate vibration, damage parts.
Suppose there are any tool vibrations from high dynamic movements or from higher feed rates than permitted. In that case, the CNC control should detect them and adjust feeds and speeds accordingly to prevent chatter marks from appearing on the final part.
A CNC interface should be able to optimize the machine dynamics based on the priority of each feature. On-the-fly optimization and verification should be possible with the control. Consider making several different components with different accuracy, surface finishing, and lead-time requirements on the same machine.
Automatic adjustment of feed and speed
Another machining challenge is milling through mold cores or cavities with varying workpiece thicknesses. It is possible to automatically adjust feeds and speeds without operator intervention with a CNC solution that detects the amount of material currently being cut.
With sensors attached to the CNC, the spindle load and vibration can be measured, and speeds and feeds can be adjusted within milliseconds., the chip removal rate is maximized based on workpiece engagement, cutter, and spindle life by using this technology.