At Ferrotall we want to talk about one of the toughest challenges in machining on 5-axis machining centres: maintaining accuracy throughout the working area, and how GROB has the solution to guarantee maximum machine accuracy.
The idea is to maintain the same accuracy across the entire working area and at every possible angle offered by a 5-axis machining centre.
On 3-axis machining centres, maintaining accuracy is relatively straightforward: the machine is calibrated with a laser interferometer to compensate the positioning accuracy of each individual axis, and for maintenance a calibration system is used to improve the squareness between axes.
The problem arises when two rotary axes are added (the 4th and 5th axes). When machining on 5-axis centres, the positioning of the machine axes can be distorted by the movement and inertia of the workpiece.
To check and compensate for any distortions that may occur, GROB, as a manufacturer of 5-axis universal machining centres, has developed its own method to improve the accuracy of its machines.
Kinematic measuring system on 5-axis machining centres
The most widely standardised system is GSC, which works as follows: a spindle probe is used together with a precision sphere mounted on the pallet. A kinematic cycle touches the sphere with the probe and then rotates to reposition the rotary axis. This action is then repeated. By “chasing” the sphere around the machine's five axes, the true centre of rotation is identified.
However, GROB's own system (kinematic measuring system) has a distinguishing feature: the manufacturer takes it beyond the centre of rotation by using two spheres.
A probe “chases” the spheres to map positioning accuracy across the entire working area. As the pallet tilts and rotates, the probe identifies any rotational or translational deviation – from top to bottom of the Y-axis stroke, from maximum X to maximum Z, and everything in between. The measured deviations are sent to the compensation software, which then refines positioning accuracy.
With this system we compensate not only the rotary axes but, at the same time, the squareness of the linear axes.
With its method, GROB improves the accuracy of five-axis machines, especially those intended to produce complex parts and components for critical applications, guaranteeing maximum accuracy.
Here is a video of our Ferromaster service department (the only one in Spain officially certified by the manufacturer), showing the calibration system with the two spheres mapping every point of the working area of the GROB G550 machining centre.
https://youtu.be/QBhPqLiEJ64If you would like to find out more about GROB machining centres, click here.
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