by Vince D’Alessio
Why kinematic measurement is important for five axis machining
Use of five axis machining has been steadily rising because of its ability to accurately machine tight tolerance, complex parts in fewer set-ups.
An inherent problem during machining is the kinematic errors that occur as a result of the motion of machine parts. This in turn leads to geometric errors on certain features of workpieces during the cutting process. The problem becomes amplified due to linear and rotary axes stacked over each other, resulting in positioning errors of the tool relative to the workpiece.
These kinematic errors also fluctuate and this occurs because of thermal expansion, machine misalignment and levelling, or poor machine tool foundation.
To ensure accurate five axis machining, you need to quantify these kinematic errors or values and compensate the machine positioning. However, measuring machine kinematic misaglinment and applying the necessary compensation values can be tricky and time consuming. Using the
right tools makes this process easy and efficient; such tools include a calibration sphere, a touch probe, an NC option (additional macro valuables) and a macro program (automated cycle).
For more precise measurement, the graph at right provides one suggestion: extend the measurement area. It illustrates the three points: mount the calibration sphere at a 45° angle; extend the area where the calibration sphere moves; and extend the area where the calibration sphere moves from the 4th axis rotation centre to the sphere.
Five axis machining processes will continue to grow, particularly among manufacturers focused on precision machining applications where tight tolerance specifications are a given. To remain competitive in these markets, manufacturers will have to ensure they are equipped with the right machining technologies and the right measurement technologies to provide their customers with high quality products. SMT
Vince D’Alessio is executive vice president of Elliott-Matsuura Canada, Oakville, ON.